Extracellular matrix alterations in müller glial cells in a retinal degeneration mouse model

Abstract

Müller glial cells (MGC) are retinal stem cells, although their re- generative capacity is very low in mammals. We recently demon- strated that these cells in the rd1 retinal degeneration mouse have decreased regenerative potential, an excessive number of neurons interacting with MGC, and a notable reduction in their lamellipodia, respective to their wild type (wt) counterparts. This suggests that ex- tracellular matrix (ECM) protein synthesis and/or secretion could be altered in rd1, interfering with the substrate adhesion and lamellipo- dia extension, and thus affecting rd1 MGC morphology and functionality. The aim of this work was to study rd1 ECM protein expression and localization, and determine whether ECM pretreatment could restore the rd1 MGC morphology and functionality. Using mixed neuron-glial cultures obtained from postnatal day two rd1 and wt mice retinas, we analyzed by immunocytochemistry, osteonectin and fibronectin (FN) expression at 6 days in vitro, and we quantified focal adhesions with paxillin. On the other hand, rd1 mixed cultures were seeded on culture dishes previously treated or not with ECM enriched conditioned medium (CM). We analyzed rd1 MGC mor- phology, proliferation and photoreceptor survival (using BrdU and DAPI respectively). Our preliminary results showed a decrease in osteonectin expression, an alteration in FN expression, and a de- crease in number and length of focal adhesions in rd1 MGC when compared to the wt condition. Instead, the pretreatment with CM promoted rd1 MGC cytoplasmatic extension, increased glial cell proliferation, decreased the number of neurons with pyknotic and fragmented nuclei, and decreased the Neuron/MGC ratio by 26.9%. These results indicate that rd1 MGC display alterations in EMC pro- tein synthesis and/or secretion, and that EMC supplementation im- proves MGC morphology and functionality.