Recovery of forearm and fine digit function after chronic spinal cord injury by simultaneous blockade of inhibitory matrix CSPG production and the receptor PTPσ

Spinal cord injuries, for which there are limited effective clinical treatments, result in enduring paralysis and hypoesthesia due, in part, to the inhibitory microenvironment that develops and limits regeneration/sprouting, especially during chronic stages. Recently, we discovered that targeted enzymatic modulation of the potently inhibitory chondroitin sulfate proteoglycan (CSPG) component of the extracellular and perineuronal net (PNN) matrix via Chondroitinase ABC (ChABC) can rapidly restore robust respiratory function to the previously paralyzed hemi-diaphragm after remarkably long times post-injury (up to 1.5 years) following a cervical level 2 lateral hemi-transection. Importantly, ChABC treatment at cervical level 4 in this chronic model also elicited rapid, albeit modest, improvements in upper arm function. In the present study, we sought to further optimize and elucidate the capacity for nerve sprouting and/or regeneration to restore gross as well as fine motor control of the forearm and digits at lengthy chronic stages post injury. However, instead of using ChABC, we utilized a novel and more clinically relevant systemic, non-invasive combinatorial treatment strategy designed to both reduce and overcome inhibitory CSPGs simultaneously and spatially extensively. Following a three-month upper cervical spinal hemi-lesion using adult female Sprague Dawley rats, we show that the combined treatment has a profound effect on functional recovery of the chronically paralyzed forelimb and paw, specifically during walking as well as precision movements of the digits. Our exciting pre-clinical findings will begin to enhance our understanding of the basic mechanisms underlying functionally beneficial regenerative events occurring at chronic injury stages for clinically relevant translational benefits. Significance statement Overcoming the persistent axon inhibitory environment following a functionally debilitating incomplete spinal cord lesion has long proven to be an elusive dilemma, especially months to years after the initial spinal injury. Current therapeutic and rehabilitative techniques for patients suffering from chronic cervical spinal insults minimally, if at all, address this structural hindrance and support limited return of crucial behaviors such as voluntary use of the arms and hands. Our investigation into the behavioral and anatomical consequences of systemically perturbing the high-affinity binding interaction between the receptor PTPσ and the extracellular chondroitin sulfate proteoglycans highlight an underlying barrier to the restoration of forelimb/paw walking and eating behavior 12-weeks after a cervical spinal hemi-transection.