Intermittent Hypoxia Alters Cerebrovascular Recovery After Stroke

Abstract Stroke is a prevalent chronic disease, significantly contributing to mortality and long-term disability. The cerebrovascular recovery process after stroke can be complicated by certain comorbidities, including obstructive sleep apnea syndrome (OSA). However, the mechanisms underlying this deleterious impact of OSA on post-stroke recovery remain elusive. We conducted a preclinical study in rats submitted to stroke and intermittent hypoxia (IH), the main characteristic of OSA, to investigate the effects of IH on stroke lesion and to decipher the pathophysiological mechanisms of this stroke-OSA interaction. Using a malonate model of ischemic stroke on Sprague Dawley rats exposed to either normoxia or intermittent hypoxia for over 56 days, we monitored brain lesion size, microvascular plasticity and blood brain barrier (BBB) permeability using in vivo 4.7T-MRI. Finally, we assessed oxidative stress, inflammation, and angiogenesis-related gene expression by qPCR, and NeuN, GFAP, Collagen IV and ZO-1 expression by immunohistological staining. Our findings indicate that while IH does not significantly affect lesion volume reduction over time, it exacerbates ischemic injury-induced necrosis and neuronal loss. Additionally, IH amplifies post-stroke inflammation, as evidenced by increased IL-6 and TGF-β expression, and induces oxidative stress by increasing DHE staining and decreasing Superoxide Dismutase (SOD1) level. Vascular assessment revealed IH-induced modifications in vessel radius and angiogenic factors expression (VEGF, Ang2), alongside increased BBB permeability and altered expression of aquaporin 1 and claudin 1, particularly in the acute phase post-stroke. These results suggest that IH alters cerebrovascular integrity and exacerbates inflammatory response following ischemic stroke, potentially contributing to poorer long-term functional outcomes. Understanding the mechanisms through which IH exacerbates post-stroke injury may guide the development of targeted neuroprotective strategies to improve stroke recovery in patients with OSA. Competing Interest Statement The authors have declared no competing interest. Abbreviations and acronyms - ADC - apparent diffusion coefficient - Ang1 - angiopoietin 1 - Ang2 - angiopoietin 2 - BBB - blood-brain barrier - BVF - blood volume fraction - ColI-IV - collagen type IV - DAPI - 4′,6-diamidino-2-phenylindole - DHE - dihydroethidium - FOV - field of view - FSL - FMRIB Software Library - GFAP - glial fibrillary acidic protein - HIF-1 - hypoxia inducible factor 1 - IH - Intermittent hypoxia - IL-6 - interleukin 6 - IV - intravenous injection - MRI - magnetic resonance imaging - MRP1 - multidrug resistance-associated protein 1 - NeuN - neuronal nuclear antigen - Nf-kB - nuclear factor kappa light chain enhancer of activated B cells - Nrf1 - nuclear respiratory factor 1 - OSA - Obstructive Sleep Apnea - PBS - phosphate-buffered saline - P-GP - p-glycoprotein - R - vessels radius - ROI - region of interest - RT-qPCR - reverse transcription-quantitative polymerase chain reaction - SE - signal enhancement - SOD1 - superoxide dismutase 1 - StO2 - oxygen saturation - T1W - T1 weighted - T2W - T2 weighted - TGF-B - transforming growth factor beta - tMCAO - transient middle cerebral artery occlusion - TNF-alpha - tumor necrosis factor alpha - VEGF - vascular endothelial growth factor - VEGFR1 - vascular endothelial growth factor receptor 1 - VEGFR2 - vascular endothelial growth factor receptor 2 - ZO-1 - Zona occludens 1