Abstract
Purpose: :
The ability of the adult mammalian central nervous system (CNS), including the retina, to regenerate is extremely limited and generally restricted to aberrant local sprouting. This can be attributed to several factors, including enhanced expression of inhibitory extracellular matrix (ECM) and cell adhesion molecules, many of which are found in areas of glial hypertrophy and scar formation. For instance, following injury or photoreceptor degeneration, a dense inhibitory ECM barrier, rich in neurocan and CD44, is formed at the level of the outer limiting membrane. These molecules function as chemical inhibitors to cellular migration, thereby impeding host-transplant integration. The matrix metalloproteinases are a family of molecules known to digest these inhibitory ECM proteins, and these include MMP2. The purpose of this study was to investigate whether active MMP2 could be delivered via a biodegradable polymer directly to the site of retinal injury, thereby inducing barrier removal and enhanced donor cell integration.
Methods: :
All experiments, including retinal explantation or subretinal transplantation of retinal progenitor cells, were performed using rd1 (retinal degeneration) mice. Western blotting, immunocytochemistry and gel zymography were used to assess the level of expression, localization and activity of MMP-2, respectively. Western blot and immunocytochemical analyses were used to determine the level and location of basement membrane molecule expression and degree of donor stem cell integration.
Results: :
Pre-activated MMP2 loaded into biodegradable PLGA polymers maintained its activity throughout polymer fabrication and degradation. Although a significant amount of CD44 and neurocan degradation was observed, this polymer did not have any evident negative effects on the progenitor cells or retinal tissue. As a result, a significantly greater number of retinal progenitor cells migrated beyond the glial barrier into the degenerating retina. These cells took up residence in all layers of the retina and began to express the appropriate cellular markers.
Conclusions: :
Controlled delivery of active MMP2 via a biodegradable polymer resulted in inhibitory ECM barrier removal and enhanced progenitor cell migration while preserving retinal architecture.
Keywords: regeneration • retina • transplantation