{"paper_id":"70962572-ff23-4776-a6ca-a8cb3fe41fb5","body_text":"http://dx.doi.org/10.14336/AD.2014.0500160  \n*Correspondence should be addressed to:  Sumathi Sanka ran-Walters, Dept. of Medical Microbiology and \nImmunology, University of CA, Davis, One Shields Ave, Davis, CA 95616, USA. Email: ssankara@ucdavis.edu \nISSN: 2152-5250                                                                                                                                                                                       160 \n                  \n \n  \nReview Article \n \nGender Differences, Aging and Hormonal Status in \nMucosal Injury and Repair \n \nIrina Grishina, Anne Fenton, Sumathi Sankaran-Walters* \n \nDepartment of Medical Microbiology and Immunology, University of CA, Davis, One Shields Ave,  \nDavis, CA 95616, USA \n \n  [Received January 12, 2014; Revised February 6, 2014; Accepted February 10, 2014] \n \nABSTRACT: As the “baby boomers” age, the percentage of the population over sixty -five years of age is \nincreasing rapidly. Chronic disease management is an important component in the care of the elderly. The \neffects of aging on different organ systems are also pertinent; such as the weakening homeostatic response to \ninjury in the older individuals. Mucosal surfaces have the largest combined surface area in the body and are \nthe site of important host microbe interactions, especially in the gut which is prone to injury, both from local \nand systemic insult. This susceptibility has been known to increase with age. Therefore it is important to \nunderstand the interplay between aging, injury and recovery at the mucosal surface. Sex hormones play an \nimportant role in the maintenance of the mucosal barrier function as well as the mucosa associated immune \nfunction in both genders. Menopause in women is a defined time period in which major hormonal changes \noccur such as a decline in systemic estradiol levels. The differential leve ls of sex hormones contribute to the \nsexual dimorphism seen in response to injury at the mucosal surface, prior to and following menopause. Thus \nthe effect of sex hormone and aging on mucosal mechanisms in response to injury is an important area of \ninvestigation. \nKey words: aging, mucosal injury, gut mucosa, epithelial barrier function, microbial translocation, estradiol, \nhormones, menopause \n \n \n \n \nBy 2050, the total US population ages 65 and older is \nestimated to reach 89  million [1]. The prevalence of \nchronic diseases is very high in this age group, the likely \nconsequence of which will include increased health care \ncosts [2, 3]. Among the most prevalent chronic conditions \nare cardiovascular disorders, cancer, respiratory dise ase, \narthritis and gastrointestinal disease [4-7]. All these \ndiseases have an underlying immune dysregulation \nrelated etiology, which may cause persistent tissue \ndamage. The increased propensity to tissue damage and \nreduced rate of tissue repair in the elderly contribute to \ndisease progression [7, 8]. Thus, the study of injury and \nrepair in the aging population is significant.  \nMucosal surfaces, particularly those of the urogenital, \nrepiratory and oro-gastro-intestinal (OGI) tracts, are often \naffected by chronic diseases and challenged by \npathologies, due to factors such as infection and chemical \ninsult. For example, sepsis associated with pneumonia \nand urinary tract infections (UTIs) is predominant ly a \ndisease of the aged, with increased incidence and \nmortality occurring in older individuals [9, 10]. \nAdditionally, disorders like dysphagia and gastro -\nesophageal reflux disease, present special management \nchallenges and often led to complications such as \nimpairment of nutritional status and a reduction in the \nquality of life [11, 12]. There is substantial evidence that \nthe aging mucosal surfaces suffer both struct ural and \nfunctional defense defects, thus changing the homeostatic \nbaseline and contributing to compounded pathology when \nchallenged with disease [13, 14]. To be able to facilitate, \nvia pharmaceutical intervention, enhancement of the \nbody’s mucosal compartments and their repair following \n      Volume 5,  Number 2; 160-169, April 2014                       \n\n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     161 \n \ninjury in an aging population, a better understanding of \nage-related changes is required. This review intends to \naddress the current knowledge of the influence of age and \ngender on mucosal injury and repair; and specifically the \ncontribution of sex hormones to these processes.  \nRole of sex hormones in immune modulation \nIn the aging female population increased susceptibility to \nmucosal injury comes on the heels of menopause-induced \nhormonal alterations. During the reproductive years, \nfemales exhibit a more robust humoral and cellular \nimmune response as compared to age mat ched males or \npost-menopausal counterparts [15]. Immun osenescence \nin the aging population is thought, in part, to be a result of \naltered hormonal status and decreased production of \nestrogen (17β-estradiol; E2) [16]. The major effects of E2 \nare mediated through two receptors, ERα and ERβ, both \nof which are expressed on a variety of cell types including, \nbut not limited to, immune cells, epithelial cells and \nmuscle cells [17-19]. Some data also suggest a spatial \ndifference in immune-regulation by the two receptors with \nrespect to tissue type [20]. Estrogen has been shown to \nregulate many facets of the immune response such as \nimmune cell differentiation, cytokine p roduction and \nregulation of Ca 2+ mobilization and release of inducible \nnitric oxide synthase within leukocytes [18, 21]. Thus, it \nis likely that decreased E2 produ ction with aging \nsubstantially impacts mucosal health and recovery via \nloss of its immune-modulatory effects [22-24]. \nLike females, aging males also experience a profound \nreduction in the levels of sex hormones, specifically \nandrogens. Though androgen decline in males is \nassociated with similar defects in mucosal healing and \nrepair, it should be stressed that “male menopause” \nfollows a very different progression pattern as compared \nto female menopause. It has been documented that from \nthe ages of 25 -75 years a healthy male experiences \napproximately 30% loss of circulating testosterone, with \nover 50% of males over the age of 65 years meeting \nendocrine criteria for hypogonadism [25, 26]. In addition \nto testosterone’s direct immune -modulatory function, it \nalso acts as a pro -hormone, converted to both 5α -\nhihydrotestosterone (DHT) and E2 [27]. Because E2 also \ncontributes greatly to sex hormone regulation of immune \nresponse in males, the effects of androgen loss with age is \ncompounded. Independently, androgens con tribute to \nboth pro - and anti -inflammatory states, modulating \ncytokines such as IL-1, IL-2, IL-6 and TNFα in a variety \nof cell types including macrophages, Kupffer cells, \nfibroblasts and splenocytes [28-30]. Thus, in males, it is \nproposed that the major actions of testosterone are \nmediated though both aromatization to E2 and E2 -\nindependent mechanisms; however, it is also the balance \nbetween testosterone a nd E2 which may be responsible \nfor the immune regulation in mucosal healing following \ninjury.    \n \n \n \nFigure 1.  H&E staining of the jejunum . Goblet cells, \nEnterocytes and Paneth cells contribute to innate \nimmunity. Lymphocytes present in the lamina propria and \nintra-epithelial areas provide acquired immunity. Image \nwas obtained at 60X magnification.  \nGut mucosal function and aging \nThe oro-gastro-intestinal (OGI) tract  carries out the \nfunctions of food processing and digestion, nutrient \nabsorption, and expulsion of waste. Along with its role in \ndigestion, the gut also harbors about 90% of the body’s \nlymphocytes within the gut associated lymphoid tissue \n(GALT) [31]. The intestinal structure is comprised of \nsimple columnar epithelium, mucosa, submucosa, smooth \nmuscle and serosa. The absorptive surface area of the \nintestine is increased by plicae circulares , villi, and \nmicrovilli. Glandular epithelium is present along the \nwhole length of the gut in the form of goblet cells, which \nsecrete mucous that lubricates the passage of food and \nprotects the tissue from digestive enzymes (Figure 1). \nChanges in the microenvironment of the small intestine \nare associated with alterations in the composition, pH, and \nthickness of the mucous layer [32, 33]. Villi are in \nvaginations of the mucosa and increase the overall surface \narea of the intestine. The next layer is the muscularis \nmucosa, a layer of smooth muscle that aids  in the action \nof continued peristalsis along the gut. The submucosa \ncontains nerves, blood vessels, and elastic fiber with \ncollagen that stretches with increased capacity but \nmaintains the shape of the intestine. Surrounding this is \nthe muscularis externa  comprised of longitudinal and \nsmooth muscle that helps with continued peristalsis and \n\n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     162 \n \nthe movement of digested material out of and along the \ngut. Lastly there is the serosa, which is made up of loose \nconnective tissue and is coated in mucus so as to prevent \nfriction damage from the intestine rubbing against other \ntissue. \n \n \nFigure 2.  Fluorescent immunohistochemical staining of jejunum tight junction proteins . (A). \nGoblet cell diameter is marked in yellow. Nucleus: Blue Dapi, Cell Membrane: Orange mask. Image \nwas obtained at 100X oil immersion confocal microscope. (B and C) IHC demonstrating the expression \nof Tight junction proteins, occluding (red) and ZO1 (Green) in small intestinal tissue (60X).  \n \nOne of the key characteristics of the GI tract \nepithelium is the rapid proliferation of cells that \ndifferentiate from immature stem cells, within the crypt, \nto terminally maturated cells, which move up the villus.  \nIn the murine model it has been observed that a state of \nhyperproliferation, not hypoproliferation, occurs in the \ngut mucosal epithelial cells of older (aged) rats compared \nto younger rats fed the same diet and with the same living \nconditions [34].  This increased turnover of epithelial cells \nwas hypothesized to be due to increased loss of epithelial \ncells at the tips of the intestinal villi. Fur thermore, \nabnormalities of the  proliferative and differentiation \nresponses became more evident when gastrointestinal \ntissues were stimulated by systemic injury.   \nMucosal barrier function is essential to prevent \npotentially harmful pathogens within the gastrointestinal \nlumen, respiratory tract, and urogenital tract from gaining \naccess to the body [35]. Increased microbial translocation \ninto mucosal tissue and the blood stream results in \nincreased systemic inflammatory cytokine prod uction \n[36-39]. Cellular tight junctions (TJs) are dynamic \nstructures located in the most apical region of cell -cell \ncontact points and play a critical role in maintenance of \nepithelial barrier function, cell polarity, and intercellular \nadhesion [40, 41].  Tight junction proteins include zona \noccludens, occludin (OLCN), claudins (CLDNs) and \nothers (Figure 2). \nDisorders of the gastrointestinal tract, including \nincreased incidence of diarrhea and constipatio n, are \ncommon in elderly people; however, the molecular \nmechanisms of aging that contribute to the vulnerability \nof the gastrointestinal tract have not been fully elucidated. \nStudies suggest that patients with gastrointestinal \ndisorders have increased intestinal permeability. A study \nutilizing the baboon model has shown that gastrointestinal \npermeability was higher in colonic biopsies in aging \nmonkeys [42]. Tight junction protein expression was \ndecreased including zona occluden 1 (ZO-1), OCLN, and \njunctional adhesion molecule -A (JAM -A). Claudin 2 \n(CLDN2), a pore forming tight junction protein, \nexpression was increased. Inflammatory cytokines \ninterferon gamma (IFN -γ), interleukin 6 (IL -6), and \ninterleukin 1 beta (IL-1β) were also found to be increased \nin colonic biopsies from old baboons compared to young \nbaboons, and have previously been shown to directly \nhinder tight junction complex formation [14, 42, 43]. IL-\n1β also contributes to a disruption of tight junction \nintegrity [44]. IL-1β levels are consistently higher in older \nindividuals as well as during the course of systemic \ninflammation and injuries like severe burns. IL-1 receptor \n(IL1R) also plays an important role in the maintenance of \nepithelial integrity in aging [43]. These studies indicate \nthat increased colonic  permeability via age -associated \nremodeling of intestinal epithelial tight junction proteins \nmay be an important component of gastrointestinal \ndysfunction.  \n\n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     163 \n \n \n \n \nFigure 3. Collagen scaffold in small intestinal villus. Collagen is an important \ncomponent of the connective tissue scaffold in the mucosa. Collagen I and III \nare demonstrated using histochemical staining in the jejunum (Collagen: red)  \n \n \nCollagen provides the connective tissue backbone to \nthe OGI mucosa (Figure 3). The effect of aging on \nconnective tissue structure, as it pertains to mucosal tissue \ninjury and repair, has been extensively investigated in the \nrodent model.  Connective tissue and collagen deposition \nin the rat gastric mucosa increases with aging [46]. \nStudies have shown that age -induced changes in gastric \nconnective tissue structure lead to a decreased capacity for \ntissue repair in response to gastric acid [45].  Furthermore, \naccumulation of oxidative produc ts, observed in the \nstomach of older rats, is hypothesized to contribute to \nthickening of connective tissue deposition and \nreplacement of mucosal tissue in the lower part of the \ngastric mucosa [46]. It is known that the intestinal milieu \nof inflammatory cytokines and systemic circulation of sex \nhormones play a significant role in both fibroblast and \nkeratinocyte migration and proliferation. These cell types \nare critical in the deposition and restructuring of collagen \nthroughout the body. Changes in collagen deposition, \ncomposition, and restructuring in aging may impact not \nonly function of the OGI mucosa but also response to \ninjury. \n  \nSex hormones and mucosal barrier function \n \nMucosal surfaces are un ique anatomical niches, as they \nare an interface between a sterile internal environment and \na contaminated external environment [47, 48]. Mucosal \nsites require contact with t he external environment to \nperform nutrient absorption in the small intestine, gas \nexchange in the lungs, water reabsorption in the colon etc. \nFor this reason, one of the key functions of the epithelial \ncells which coat mucosal surfaces is to maintain barr ier \nfunctions from the antigens of the external environment. \nThe epithelial layer possesses polarity and requires close \ncontact between the cells to function as an anatomical \nbarrier. Maintenance of the barrier is critical for mucosal \nand systemic health, and is first to be damaged during \nexternal injury. Rapid healing of the epithelium and \nrevival of barrier function is important in preventing \nongoing immune activation and further infection at \nmucosal sites [49, 50]. With age, this process is slowed \nand results in some of the co -morbidities such as \nendometriosis, increased incidence of UTIs, diarrhea , as \nwell as increased prevalence of pulmonary hypertension \nand protracted recovery from lung disease, associated \nwith mucosal injuries in the aging population. \nDisruption of TJ complexes is associated with a \nvariety of human d iseases including genital and gastric \ncancers, inflammatory bowel disease, and HIV infection \n[51-53]. Interestingly, sex hormones such as E2 play an \nimportant role in the maintenance of tight junctions. E2 \nlevels decrease dramatically during the course of the \nmenopausal transition [54-57]. E2 affects TJ formation, \nwhich can alter the level of bacterial translocation from \nany mucosal surface [58, 59]. A recent study showed that \nincreased E2 in rats induced the expression of TJ protein \nOCLN via binding of ERβ [59]. This resulted in decreased \nintestinal epithelial permeability [59] and microbial \ntranslocation. Conversely, reduced levels of E2, as occurs \nwith aging, particularly during female menopause, can \npotentially increase epithelial permeability and microbial \ntranslocation (Figure 4). No significant disparities are \nobserved between the genders with regards to homeostatic \nepithelial barrier permeability [27]. Therefore, an E2 -\ndependent mechanism for maintenance of the epithelial \nbarrier may contribute equally in both males and females \nto mucosal integrity. \n\n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     164 \n \n \n \n \n \n \n \nFigure 4.  Schematic of the proposed effects of aging and hormonal changes .  Proposed \nmechanism of the loss of mucosal epithelial integrity and microbial translocation and the effects \nof hormonal changes associated with aging. \n \nGender differences in OGI mucosal injury \nRecently, several large -scale, cross -sectional \nepidemiological studies have been performed to \ndetermine whether there is gender -based skewing in \npopulations of individuals with gastro -esophageal reflux \ndiseases (GERD) [60-62]. The three conditions that \ncomprise the majority of this spectrum include Barrett's \nesophagus (BE), erosive reflux disease (ERD), and \nnonerosive reflux disease (non -ERD). Both Barrett’s \nesophagus and ERD are associated with erosive \nesophagitis and mucosal injury [61, 63]. Furthermore, it is \ngenerally accepted that there is a sequential progression \nfrom reflux erosive esophagitis, to Barrett's esophagus, \nand finally to esophageal adenocarcinoma. Reflux erosive \nesophagitis results from exposure of the esophageal \nepithelium to the refluxed  gastroduodenal contents. A \nmale-predominant gender bias exists across the spectrum, \nalthough the ratios become higher with the progression \ntowards esophageal adenocarcinoma. Meanwhile, non -\nerosive reflux diseases generally affect women more than \nmen [60, 62]. These data allude to the gender differences \nin the vulnerability or resistance of the es ophageal \nepithelium to caustic compounds of the gastroduodenal \ncontents in males and females.  \nThere have been reports that females are less affected \nthan males by gastric or intestinal inflammation in \nresponse to chemical insult or bacterial infection [64-66].  \n \nIn these studies E2 was demonstrated to have anti -\ninflammatory activity and thus contributes to tissue \nresistance in females. A recent study by Masaka et al. \nexplored the potential role of E2 in controlling esophageal \ntissue damage [63]. Employing a chronic rat reflux \nesophagitis model, a significant male -predominant, \ngender-related difference in esophageal tissue damage in \nthe presence of exogenous nitric oxide (NO) as an \nexacerbating factor, was found [67]. While in the baseline \nmodel of reflux esophagitis macroscopic esophageal \nulcers and microscopic inflammatory cell infiltrates were \nonly mildly obse rved in both genders, in males, \nexogenous NO exacerbation induced deep esophageal \nulcers and intense inflammation with polymophonuclear \ncell and lymphocyte infiltrates.  In contrast, in female \nreflux esophasitis models, treatment with NO rarely \nexacerbated the mild tissue damage observed at baseline. \nFurther, exogenous 17β -estradiol binding and signaling \nthrough E2 receptors attenuated esophageal tissue damage \nin males and ovariectomised rats via a reduction of mast \ncell-mediated cytotoxity and cytokine, specifically tumor \nnecrosis factor alpha (TNFα), driven inflammation [63, \n68]. Treatment with 17α -estradiol, which binds but does \nnot induce downstream signaling, had no effect on tissue \ndamage. This was the first study showing the prominent \ngender difference in the severity of esophageal tissue \ndamage in a GERD -related animal model. Additional \nunderstanding of the causative luminal or genetic factors \n\n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     165 \n \nin yielding the gender -related difference would b e \nclinically relevant to predict the etiological factors \ninvolved in the pathogenesis of reflux esophagitis in \nhumans [69, 70]. \nSex hormones in tissue repair \nGender variation in wound healing has been observed at \nvarious mucosal sites throughout the body. Specifically, \nvariations in healing rates have been attributed to levels of \ncirculating sex hormones and their effect on modulation \nof inflammation as well as  fibroblast and keratinocytes \ncellular proliferation, differentiation and growth [71-73]. \nIt has been established that both dermal and mucosal \nwound healing is significantly altered by the effects of E2 \nsignaling [74-76]. Kumral et al. recently showed that \ngastric and colonic tissue damage is alleviated by E2, via \nboth ERα and ERβ mediation as well as direct antioxidant \neffects [76]. In addition to its role in inflammatory \nregulation and re -epithelialization, an epidemiological \nstudy by Tuo et al. linked higher circulating E2 levels in \nwomen to the elevated production of duo denal mucosa \nbicarbonate secretion (DBS), a compound central in \nduodenal mucosal protection against acid -induced injury \n[77]. Duodenal ulcers are less prevalent in  pre-\nmenopausal women, compared to age matched men or \npost-menopausal women [78, 79]. In their findings, e x \nvivo stimulation of duodenal tissues with 17β -estradiol \ndid not result in a difference in the levels of DBS \nsecretion. The authors hypothesized that this stemmed \nfrom the result t hat males and females express similar \nlevels of ERα and ERβ on duodenal epithelial cell surface \n[77]. This highlights that the observed sex differences of \nDBS were likely due to the gender differences in \ncirculating E2 levels  rather than a dimorphism in \nexpression levels of E2 receptors between different sexes, \nand can possibly be extrapolated to the other effects of E2.  \nLikewise, metabolites of testosterone, as well as other \nandrogens [5α -dihydrotestosterone (DHT) and \nDehydroepiandrosterone (DHEA)], have been shown to \naffect dermal wound closure by impairing re -\nepithelialization and inducing immunosuppressive effects \n[80]. As in dermal wounds, a study by Engeland et al. \nreported that in oral mucosal damage testosterone levels \nwere inversely correlated with wound healing rates in pre-\nmenopausal women and age matched males.  Conversely, \nin post -menopausal women a positive correlation of \ntestosterone levels and wound healing rates was observed \n[81]. It was hypothesized that the immunomodulatory role \nof testosterone in reducing IL -6, which is mitogenic to \nkeratinocytes, contributes to the effect observed in pre -\nmenopausal women and men. The effect observed in post-\nmenopausal women was not linked to age specifically, but \nhormonal status. Authors put forth the idea that with the \nincreased immune activation observed in post -\nmenopausal women at baseline, higher levels of anti -\ninflammatory testosterone decreased this activation thus \nbeing beneficial to tissue healing [82, 83].  \n \nEstrogen and Urinary Tract Infections \n \nWhile UTIs are most prevalent in females aged 18 -24, a \nsignificant number of women over 50 still contract UTIs \n[84]. Recurrent infections in healthy , aging women ages \n50-70 have been linked to decreased levels of estradiol \n[85]. After menopause, decreased levels of E2 cause \nvulvovaginal atrophy in 25 -50% of women [13]. \nSymptoms such as vaginal dryness, itching, increase in \nvaginal pH, urinary frequency and incontinence, \ncontribute to the impairment of defenses against incoming \npathogens at the urogenital mucosa [86]. Thus estradiol \nsupplementation has been considered as a way to decrease \nthe risk of recurrent infections in the postmenopau sal \npopulation and has demonstrated moderate success [87].  \nOne of the mechanisms by which estradiol therapy in \npost-menopausal women has proven successful may be \nrelated to tight junction formati on enhancement by E2. \nNumerous studies have shown that estrogen treatment, in \nvitro, increases tight junction protein expression including \nZO1 and CLDN in the vaginal epithelium [88]. In both, a \nurothelial cell line and exfoliat ed bladder cells from \npostmenopausal women, estradiol treatment increased \ntranscripts of ZO1 and OCLN as well as e -cadherin \nprotein [86]. This demonstrates that estrogen’s beneficial \neffects on tight junc tion proteins may occur on mucosal \nsurfaces outside of the vagina [86]. Estrogen -mediated \nrestoration of a diminished antimicrobial response in post-\nmenopausal women could also contribute to the decreases \nseen in UTIs following treatment. When post-menopausal \nwomen were given estradiol supplementation for two \nweeks, 75% showed increases in at least three \nantimicrobial peptides in urinary tract cells. The most \nhighly increased peptides were beta -defensin 3 (hBD3), \nbeta-defensin 1 (hBD1), and RNase 7 [86].  \nAn alternate mechanism by which estradiol \nsupplementation can contribute to urogential mucosal \nhealth in post-menopausal women is via its role in vaginal \npH regulation. A number of theories have been proposed \nfor the contribution of E2 toward vaginal pH control, \nincluding direct effects on the epithelium and altering \nvaginal microflora populations [89, 90]. In healthy, \nyoung, menstruating women vaginal microflora is \ndominated by Lactobacilli which produce lactic acid, \nhydrogen peroxide, and various bacterial proteins which \ntogether inhibit overgrowth of any pathogenic bacterial \nspecies [91]. Thu s, the vaginal microflora confers \n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     166 \n \nprotection against pathogens which are associated with \nUTIs. Estrogen has been shown to promote lactobacilli \ncolonization and growth by increasing storage of \nglycogen, the substrate for acid production by bacteria, in \nvaginal epithelial cells [90]. With a decline in E2 levels \nduring menopause, along with decreased glycogen stores \nand quantity of lactobacilli, acid production decreases \nleading to an elevation in vagi nal pH , which facilitates \ngrowth of potential UTI-causing pathogens.    \n \nSex Hormones in Lung Disease \n \nWhile the prevalence of chronic obstructive pulmonary \ndisease (COPD) is greater in men, women appear to be \nmore sensitive to the effects of cigarette smoke in \ndeveloping COPD, often developing COPD after smoking \nless than men [92]. This may be related to an E2-mediated \ndifference in metabolism of cigarette smoke toxins at the \nlung mucosa. Estradiol increases the activity of \ncytochrome P450 (CPY) enzymes, which break down \ntoxins but create harmful metabolites which can be more \ntoxic than their precursors [93]. Because complete \nmetabolism of these toxins requires a rate limiting process \nwhich is not increased by E2, harmful intermediate \nmetabolites may remain in the lungs of women smokers \nlonger than their male counterparts, increasing lung \ndamage and resulting in poorer clinical outcomes.  \nA gender discrepancy in outcomes of cystic fibrosis \n(CF) patients has been seen clinically , with females \nhaving much higher early mortality rates than males [94]. \nThis may be due to an E2 -mediated increase in mucus \nproduction, a principal determinant of mortality in CF \npatients. Estradiol has been shown to increase mucin gene \nexpression in lung epithelium , which may result in \nincreased mucus overall [95]. Additionally, female CF \npatients show lowest lung function just before ovulation, \nsuggesting that this surge of E2 may be enhancing mucus \nproduction and thereby decreasing lung function [96]. \nTaken together, these studies demonstrate the wide \nvariety of ways E2 modulates lung function and affects \ndisease morbidity. In some ins tances, modulation of sex \nhormones may be a viable clinical intervention worthy of \nfurther investigation.  \nSummary \nAging and sex differences play an important role in the \ndevelopment of mucosal injury as well as its repair. The \nrole of sex hormones is controversial at best. The part that \nis clear is that aging mucosal surfaces are extremely \nsusceptible to injury. New studies indicate that the \nmicrobiome may also play an important role in mucosal \nhealth. This too is a rapidly developing area of research \nthat is poorly is understood and likely plays a role in \nhealthy aging. The molecular mechanisms that regulate \naging are poorly understood. Taken together \ncomprehensive studies using relevant animal models are \nneeded to better understand the interplay between \nmucosal injury, gender, sex hormones and aging.  \nAcknowledgements \nWe would like to thank the Department of Medical \nMicrobiology and Immunology, Professor and Chair, Dr. \nSatya Dandekar for her support. Dr. Sankaran is supported \nby a Building Interdisciplinar y Research Careers in \nWomen’s Health award (K12 HD051958) funded by the \nNICHD, ORWH, and the NIA. Irinia Grishina is \nsupported by California HIV Research Program: D10-D-\n303. \nReferences \n[1]  Vincent GK, Velkoff VA (May 2010) THE NEXT \nFOUR DECADES. The Older Population in the United \nStates: 2010 to 2050. Population Estimates and \nProjections.  p. 14, US Census Bureau \n[2]  Hussain A, Rivers PA (2009). Confronting the \nchallenges of long -term health care crisis in the United \nStates. J Health Care Finance, 36: 71-82 \n[3]  Waite LJ (1996). The demographic face of America's \nelderly. Inquiry, 33: 220-224 \n[4]  Ultori C, Cimetti L, Stefanoni P, Pellegrini R, Rapazzini \nP, Capella C  (2013). Merkel cell carcinoma in elderly: \ncase report and review of the l iterature. Aging Clin Exp \nRes, 25: 211-214 \n[5]  Taffet GE, Donohue JF, Altman PR  (2014). \nConsiderations for managing chronic obstructive \npulmonary disease in the elderly. Clin Interv Aging, 9: \n23-30 \n[6]  Kwak HB (2013). Effects of aging and exercise training \non apoptosis in the heart. J Exerc Rehabil, 9: 212-219 \n[7]  Britton E, McLaughlin JT (2013). Ageing and the gut. \nProc Nutr Soc, 72: 173-177 \n[8]  Nair S, Ren J (2012). Autophagy and cardiovascular \naging: lesson learned from rapamycin. Cell Cycle, 11: \n2092-2099 \n[9]  Taniguchi T, Tsuha S, Takayama Y, Shiiki S (2013). \nShaking chills and high body temperature predict \nbacteremia especially among elderly patients. \nSpringerplus, 2: 624 \n[10]  Heppner HJ, Cornel S, Peter W, Philipp B, Katrin S \n(2013). Infections in the elderly. Crit Care Clin, 29: 757-\n774 \n[11]  Becher A, Dent J (2011). Systematic review: ageing and \ngastro-oesophageal reflux disease symptoms, \noesophageal function and reflux oesophagitis. Aliment \nPharmacol Ther, 33: 442-454 \n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     167 \n \n[12]  Poh CH, Navarro-Rodriguez T, Fass R (2010). Review: \ntreatment of gastroesophageal reflux disease in the \nelderly. Am J Med, 123: 496-501 \n[13]  Sturdee DW, Panay N (2010). Recommendations for the \nmanagement of postmenopausal vaginal atrophy. \nClimacteric, 13: 509-522 \n[14]  Tran L, Greenwood -Van Meerveld B  (2013). Age-\nassociated remodeling of the intestinal epithelial barrier. \nJ Gerontol A Biol Sci Med Sci, 68: 1045-1056 \n[15]  Grossman C (1989). Possible underlying mechanisms of \nsexual dimorphism in the immune response, fact and \nhypothesis. J Steroid Biochem, 34: 241-251 \n[16]  Olsen NJ, Kovacs WJ (1996). Gonadal steroids and \nimmunity. Endocr Rev, 17: 369-384 \n[17]  Velders M, Schleipen B, Fritzemeier KH, Zierau O, Diel \nP (2012). Selective estrogen receptor -beta activation \nstimulates skeletal muscle growth and regeneration. \nFASEB J, 26: 1909-1920 \n[18]  Bird MD, Karavitis J, Kovacs EJ (2008). Sex differences \nand estrogen modulation of the cellular immune response \nafter injury. Cell Immunol, 252: 57-67 \n[19]  Buchanan DL, Kurita T, Taylor JA, Lubahn DB, Cunha \nGR, Cooke PS (1998). Role of stromal and epithelial \nestrogen receptors in vaginal epithelial proliferation, \nstratification, and cornification. Endocrinology, 139: \n4345-4352 \n[20]  Hildebrand F, Hubbard WJ, Choudhry MA, Thobe BM, \nPape HC, Chaudry IH (2006). Are the protective effects \nof 17beta -estradiol on splenic macrophages and \nsplenocytes after trauma -hemorrhage mediated via \nestrogen-receptor (ER)-alpha or ER-beta? J Leukoc Biol, \n79: 1173-1180 \n[21]  Kovats S, Carreras E (2008). Regulation of dendritic cell \ndifferentiation and function by estrogen receptor ligands. \nCell Immunol, 252: 81-90 \n[22]  Seko K, Kagami H, Senga K, Ozeki K, Mizutani H, Ueda \nM (2005). Effects of ovariectomy and estrogen \nreplacement on rat oral mucosa. Maturitas, 50: 44-51 \n[23]  Degano B (1998). [The effect of estrogens on the \npermeability of the bronchial mucosa]. Annales de \ndermatologie et de venereologie, 125 Suppl 2: S21-22 \n[24]  Diebel ME, Diebel LN, Liberati DM (2011). Gender \ndimorphism in the gut: mucosal protection by estrogen \nstimulation of IgA transcytosis. J Trauma, 71: 474-479 \n[25]  Harman SM, Metter EJ, Tobin JD, Pearson J, Blackman \nMR (2001). Longitudinal effects of aging on serum total \nand free testosterone levels in healthy men. Baltimore \nLongitudinal Study of Aging. J Clin Endocrinol Metab, \n86: 724-731 \n[26]  Morley JE, Kaiser FE, Perry HM, 3rd, Patrick P, Morley \nPM, Stauber PM, et al. (1997). Longitudinal changes in \ntestosterone, luteinizing hormone, and follicle -\nstimulating hormone in healthy olde r men. Metabolism, \n46: 410-413 \n[27]  Fimmel S, Zouboulis CC (2005). Influence of \nphysiological androgen levels on wound healing and \nimmune status in men. Aging Male, 8: 166-174 \n[28]  Schroder J, Kahlke V, Staubach KH, Zabel P, Stuber F \n(1998). Gender differences in human sepsis. Arch Surg, \n133: 1200-1205 \n[29]  Gornstein RA, Lapp CA, Bustos-Valdes SM, Zamorano \nP (1999). Androgens modulate interleukin -6 production \nby gingival fibroblasts in vitro. J Periodontol, 70: 604 -\n609 \n[30]  Messingham KA, Shirazi M, Duf fner LA, Emanuele \nMA, Kovacs EJ (2001). Testosterone receptor blockade \nrestores cellular immunity in male mice after burn injury. \nJ Endocrinol, 169: 299-308 \n[31]  Macal M, Sankaran S, Chun TW, Reay E, Flamm J, \nPrindiville TJ, et al. (2008). Effective CD4+ T-cell \nrestoration in gut -associated lymphoid tissue of HIV -\ninfected patients is associated with enhanced Th17 cells \nand polyfunctional HIV -specific T -cell responses. \nMucosal Immunol, 1: 475-488 \n[32]  Ikuma M, Hanai H, Kaneko E, Hayashi H, Hoshi T \n(1996). Effects of aging on the microclimate pH of the \nrat jejunum. Biochimica et biophysica acta, 1280: 19-26 \n[33]  Choi SH, Kornegay ET, Eigel WN (1991). \nCharacterization of small intestinal mucus glycoproteins \nfrom pigs of various ages. Comparative biochemistry  \nand physiology. A, Comparative physiology, 99: 677 -\n680 \n[34]  Holt PR, Yeh KY (1989). Small intestinal crypt cell \nproliferation rates are increased in senescent rats. J \nGerontol, 44: B9-14 \n[35]  Viswanathan VK, Hecht G (2000). Innate immunity and \nthe gut. Curr Opin Gastroenterol, 16: 546-551 \n[36]  Balzan S, de Almeida Quadros C, de Cleva R, Zilberstein \nB, Cecconello I (2007). Bacterial translocation: \noverview of mechanisms and clinical impact. J \nGastroenterol Hepatol, 22: 464-471 \n[37]  Aloi M, Cucchiara S ( 2009). Extradigestive \nmanifestations of IBD in pediatrics. Eur Rev Med \nPharmacol Sci, 13 Suppl 1: 23-32 \n[38]  Inagaki-Ohara K, Sasaki A, Matsuzaki G, Ikeda T, \nHotokezaka M, Chijiiwa K, et al. (2006). Suppressor of \ncytokine signalling 1 in lymphocytes regul ates the \ndevelopment of intestinal inflammation in mice. Gut, 55: \n212-219 \n[39]  McGuckin MA, Eri R, Simms LA, Florin TH, Radford -\nSmith G (2009). Intestinal barrier dysfunction in \ninflammatory bowel diseases. Inflamm Bowel Dis, 15: \n100-113 \n[40]  Marchiando AM, Graham WV, Turner JR  (2010). \nEpithelial barriers in homeostasis and disease. Annu Rev \nPathol, 5: 119-144 \n[41]  Turner JR (2009). Intestinal mucosal barrier function in \nhealth and disease. Nat Rev Immunol, 9: 799-809 \n[42]  Tran L, Greenwood -Van Meerveld  B (2013). Age -\nassociated remodeling of the intestinal epithelial barrier. \nJ Gerontol A Biol Sci Med Sci, 68: 1045-1056 \n[43]  Song J, Wolf SE, Wu XW, Finnerty CC, Herndon DN, \nJeschke MG (2011). Proximal gut mucosal epithelial \nhomeostasis in aged IL-1 type I receptor knockout mice \nafter starvation. The Journal of surgical research, 169: \n209-213 \n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     168 \n \n[44]  Al-Sadi R, Ye D, Said HM, Ma TY (2011). Cellular and \nmolecular mechanism of interleukin-1beta modulation of \nCaco-2 intestinal epithelial tight junction barrier.  J Cell \nMol Med, 15: 970-982 \n[45]  Newton JL (2004). Changes in upper gastrointestinal \nphysiology with age. Mech Ageing Dev, 125: 867-870 \n[46]  Kang JM, Kim N, Kim JH, Oh E, Lee BY, Lee BH, et al. \n(2010). Effect of aging on gastric mucosal defense \nmechanisms: ROS, apoptosis, angiogenesis, and sensory \nneurons. Am J Physiol Gastrointest Liver Physiol, 299: \nG1147-1153 \n[47]  Bengmark S (1999). Gut microenvironment and immune \nfunction. Curr Opin Clin Nutr Metab Care, 2: 83-85 \n[48]  Westermann J, Engelhardt B, Ho ffmann JC (2001). \nMigration of T cells in vivo: molecular mechanisms and \nclinical implications. Ann Intern Med, 135: 279-295 \n[49]  Frank JA (2012).  Claudins and alveolar epithelial barrier \nfunction in the lung. Ann N Y Acad Sci, 1257: 175-183 \n[50]  Iizuka M, Konno S Wound healing of intestinal epithelial \ncells. World J Gastroenterol, 17: 2161-2171 \n[51]  Zhang JB, Du XG, Zhang H, Li ML, Xiao G, Wu J, et al. \n(2010). Breakdown of the gut barrier in patients with \nmultiple organ dysfunction syndrome is attenuat ed by \ncontinuous blood purification: effects on tight junction \nstructural proteins. Int J Artif Organs, 33: 5-14 \n[52]  Shen L, Su L, Turner JR (2009). Mechanisms and \nfunctional implications of intestinal barrier defects. Dig \nDis, 27: 443-449 \n[53]  Edelblum KL, Turner JR (2009). The tight junction in \ninflammatory disease: communication breakdown. Curr \nOpin Pharmacol, 9: 715-720 \n[54]  Burger HG, Hale GE, Robertson DM, Dennerstein L \n(2007). A review of hormonal changes during the \nmenopausal transition: focus o n findings from the \nMelbourne Women's Midlife Health Project. Hum \nReprod Update, 13: 559-565 \n[55]  Arnal JF, Laurell H, Fontaine C, Billon A, Calippe B, \nLenfant F, et al. (2009). Estrogen receptor actions on \nvascular biology and inflammation: implications in \nvascular pathophysiology. Climacteric, 12 Suppl 1: 12 -\n17 \n[56]  Al-Azzawi F, Palacios S (2009). Hormonal changes \nduring menopause. Maturitas, 63: 135-137 \n[57]  Wierman ME, Kohrt WM (2007). Vascular and \nmetabolic effects of sex steroids: new insights into  \nclinical trials. Reprod Sci, 14: 300-314 \n[58]  Braniste V, Jouault A, Gaultier E, Polizzi A, Buisson -\nBrenac C, Leveque M, et al. (2010). Impact of oral \nbisphenol A at reference doses on intestinal barrier \nfunction and sex differences after perinatal expos ure in \nrats. Proc Natl Acad Sci U S A, 107: 448-453 \n[59]  Braniste V, Leveque M, Buisson -Brenac C, Bueno L, \nFioramonti J, Houdeau E (2009). Oestradiol decreases \ncolonic permeability through oestrogen receptor beta -\nmediated up -regulation of occludin and jun ctional \nadhesion molecule-A in epithelial cells. The Journal of \nphysiology, 587: 3317-3328 \n[60]  Cook MB, Wild CP, Forman D (2005). A systematic \nreview and meta -analysis of the sex ratio for Barrett's \nesophagus, erosive reflux disease, and nonerosive reflux \ndisease. Am J Epidemiol, 162: 1050-1061 \n[61]  Ford AC, Forman D, Reynolds PD, Cooper BT, \nMoayyedi P (2005). Ethnicity, gender, and \nsocioeconomic status as risk factors for esophagitis and \nBarrett's esophagus. Am J Epidemiol, 162: 454-460 \n[62]  Lin M, Gerson LB, Lascar R, Davila M, Triadafilopoulos \nG (2004). Features of gastroesophageal reflux disease in \nwomen. Am J Gastroenterol, 99: 1442-1447 \n[63]  Masaka T, Iijima K, Endo H, Asanuma K, Ara N, \nIshiyama F, et al  (2013). Gender differences in \noesophageal mucosal injury in a reflux oesophagitis \nmodel of rats. Gut, 62: 6-14 \n[64]  Fox JG, Rogers AB, Ihrig M,  Taylor NS, Whary MT, \nDockray G et al. (2003). Helicobacter pylori -associated \ngastric cancer in INS -GAS mice is gender specific. \nCancer research, 63: 942-950 \n[65]  Houdeau E, Moriez R, Leveque M, Salv ador-Cartier C, \nWaget A, Leng L et al. (2007). Sex steroid regulation of \nmacrophage migration inhibitory factor in normal and \ninflamed colon in the female rat. Gastroenterology, 132: \n982-993 \n[66]  Kruidenier L, van Meeteren ME, Kuiper I, Ja arsma D, \nLamers CB, Zijlstra FJ  et al. (2003). Attenuated mild \ncolonic inflammation and improved survival from severe \nDSS-colitis of transgenic Cu/Zn -SOD mice. Free Radic \nBiol Med, 34: 753-765 \n[67]  Ishiyama F, Iijima K, Asa numa K, Ara N, Yoshitake J, \nAbe Y  et al. (2009). Exogenous luminal nitric oxide \nexacerbates esophagus tissue damage in a reflux \nesophagitis model of rats. Scand J Gastroenterol, 44: \n527-537 \n[68]  Verdu EF, Deng Y, Bercik P, Collins SM (2002). \nModulatory effects of estrogen in two murine models of \nexperimental colitis. Am J Physiol Gastrointest Liver \nPhysiol, 283: G27-36 \n[69]  Shenderov BA (2012). Gut indigenous microbiota and \nepigenetics. Microb Ecol Health Dis, 23 \n[70]  Kang GH, Lee HJ, Hwang KS, Lee S, Kim JH, Kim JS \n(2003). Aberrant CpG island hypermethylation of \nchronic gastritis, in relation to aging, gender, intestinal \nmetaplasia, and chronic inflammation. Am J Pathol, 163: \n1551-1556 \n[71]  Mealey BL, Moritz AJ (2003). Hormonal influences: \neffects of diabetes mellitus and endogenous female sex \nsteroid hormones on the periodontium. Periodontol \n2000, 32: 59-81 \n[72]  Bhardwaj A, Bhardwaj SV (2012). Effect of menopause \non women's periodontium. J Midlife Health, 3: 5-9 \n[73]  Gilliver SC, Ruckshanthi JP, Hardman MJ, Nakayama T, \nAshcroft GS (2008). Sex dimorphism in wound healing: \nthe roles of sex steroids and macrophage migration \ninhibitory factor. Endocrinology, 149: 5747-5757 \n[74]  Campbell L, Emmerson E, Davies F, Gilliver SC, Krust \nA, Chambon P, et al  (2010). Estrogen promotes \ncutaneous wound healing via estrogen receptor beta \nindependent of its antiinflammatory activities. J Exp \nMed, 207: 1825-1833 \n\n I. Grishina et al                                                                                                   Aging and sex hormones in mucosal injury \nAging and Disease • Volume 5, Number 2, April 2014                                                                                     169 \n \n[75]  Gilliver SC, Emmerson E, Campbell L, Chambon P, \nHardman MJ, Ashcroft GS  (2010). 17beta-estradiol \ninhibits wound healing in male mice via estrogen \nreceptor-alpha. Am J Pathol, 176: 2707-2721 \n[76]  Kumral ZN, Memi G, Ercan F, Yegen BC (2013). \nEstrogen Alleviates Acetic Acid -Induced Gastric or \nColonic Damage via Both ERalpha - and ERbeta -\nMediated and Direct An tioxidant Mechanisms in Rats. \nInflammation, in press.  \n[77]  Tuo B, Wen G, Wei J, Liu X, Wang X, Zhang Y, et al  \n(2011). Estrogen regulation of duodenal bicarbonate \nsecretion and sex -specific protection of human \nduodenum. Gastroenterology, 141: 854-863 \n[78]  Kurata JH, Honda GD, Frankl H (1985). The incidence \nof duodenal and gastric ulcers in a large health \nmaintenance organization. Am J Public Health, 75: 625-\n629 \n[79]  Rosenstock SJ, Jorgensen T (1995). Prevalence and \nincidence of peptic ulcer disease in a Danish County--a \nprospective cohort study. Gut, 36: 819-824 \n[80]  Gilliver SC, Ruckshanthi JP, Hardman MJ, Zeef LA, \nAshcroft GS (2009). 5alpha -dihydrotestosterone (DHT) \nretards wound closure by inhibiting re -epithelialization. \nJ Pathol, 217: 73-82 \n[81]  Engeland CG, Sabzehei B, Marucha PT (2009). Sex \nhormones and mucosal wound healing. Brain Behav \nImmun, 23: 629-635 \n[82]  Bouman A, Heineman MJ, Faas MM (2005). Sex \nhormones and the immune response in humans. Hum \nReprod Update, 11: 411-423 \n[83]  Kovacs EJ (2005). Aging, traumatic injury, and estrogen \ntreatment. Exp Gerontol, 40: 549-555 \n[84]  Foxman B, Somsel P, Tallman P, Gilles pie B, Raz R, \nColodner R, et al  (2001). Urinary tract infection among \nwomen aged 40 to 65: behavioral and sexual risk factors. \nJ Clin Epidemiol, 54: 710-718 \n[85]  Stamm WE, Raz R (1999). Factors contributing to \nsusceptibility of postmenopausal women to recurrent \nurinary tract infections. Clin Infect Dis, 28: 723-725 \n[86]  Luthje P, Linden Hirschberg A, Brauner A (2014). \nEstrogenic action on innate defense mechanisms in the \nurinary tract. Maturitas, 77: 32-36 \n[87]  Perrotta C, Aznar M, Mejia R, Albert X, Ng CW (2008). \nOestrogens for preventing recurrent urinary tract \ninfection in postmenopausal women. Obstet Gynecol, \n112: 689-690 \n[88]  Gorodeski GI (2005). Aging and estrogen effects on \ntranscervical-transvaginal epithelial permeability. J Clin \nEndocrinol Metab, 90: 345-351 \n[89]  Aroutcheva A, Gariti D, Simon M, Shott S, Faro J, \nSimoes JA, et al. (2001). Defense factors of vaginal \nlactobacilli. Am J Obstet Gynecol, 185: 375-379 \n[90]  Baldassarre M, Giannone FA, Foschini MP, Battaglia C, \nBusacchi P, Venturoli S, et al  (2013). Effects of long -\nterm high dose testosterone administration on vaginal \nepithelium structure and estrogen receptor -alpha and -\nbeta expression of young women. Int J Impot Res, 25: \n172-177 \n[91]  Gupta K, Stapleton AE, Hooton TM, Roberts PL, \nFennell CL, Stamm WE (1998). Inverse association of \nH2O2-producing lactobacilli and vaginal Escherichia \ncoli colonization in women w ith recurrent urinary tract \ninfections. J Infect Dis, 178: 446-450 \n[92]  Gillum RF (2005). Frequency of attendance at religious \nservices and cigarette smoking in American women and \nmen: the Third National Health and Nutrition \nExamination Survey. Prev Med, 41: 607-613 \n[93]  Tam TW, Akhtar H, Arnason JT, Cvijovic K, Boon H, \nCameron DW, et al  (2011). Inhibition of human \ncytochrome p450 metabolism by blended herbal \nproducts and vitamins. J Pharm Pharm Sci, 14: 1-16 \n[94]  Kerem E, Reisman J, Corey M, Canny GJ, L evison H \n(1992). Prediction of mortality in patients with cystic \nfibrosis. N Engl J Med, 326: 1187-1191 \n[95]  Choi SM, Seo MJ, Lee YG, Lee MJ, Jeon HJ, Kang KK, \net al. (2009). Effects of DA-6034, a flavonoid derivative, \non mucin-like glycoprotein and ocula r surface integrity \nin a rabbit model. Arzneimittelforschung, 59: 498-503 \n[96]  Johannesson M, Ludviksdottir D, Janson C (2000). Lung \nfunction changes in relation to menstrual cycle in \nfemales with cystic fibrosis. Respir Med, 94: 1043-1046","source_license":"CC-BY-4.0","license_restricted":false}