Abstract
Purpose: :
Retinal detachment leads to pathobiological responses from Müller cells (MCs), leading to disruption in retinal integrity and function. Here, we assess the role of β2 and γ3 laminin chains in maintaining structural and functional integrity of MCs and inner retinal neurons.
Methods: :
Laminin β2-/-γ3-/- animals were used for this study. The structural integrity of retinal cells was analyzed by immunohistochemistry using various cell specific markers. Real time PCR and immunoblots were used to analyze gene expression.
Results: :
We showed previously that laminin β2 and γ3 chains are expressed in the ILM, Bruch’s membrane and vascular basement membranes. Genetic deletion of β2 and γ3 chains results in the disruption of the ILM, leading to retinal dysplasia. We posit that loss of attachment of MCs leads to defects in organization and development of MCs subsequently disrupting retinal structure. In β2-/-γ3-/- retina, MCs extend aberrant processes into the sub-retinal space and vitreous body and adherens junctions at the apical surface of the MC are disrupted, suggesting disruptions in MC polarity. Subretinal ectopic cells are present at these junctional defects. Basal processes from MCs appear to contribute to the formation of an epiretinal membrane coinciding with the loss of the laminin receptors, dystroglycan and beta-1 integrin. Moreover, MCs undergo gliosis, up-regulate GFAP, in the regions of ILM disruption. Most importantly, MCs re-enter the cell cycle, as judged by markers including phosH3. These data suggest that adhesion to the ILM is laminin-dependent and critical for the developmental stability of MCs. Other remodeling events, perhaps secondary to MC disruptions, occur in β2-/-γ3-/- retinae. Ganglion cells (GCs) sprout and seemingly contribute to epiretinal membranes while horizontal cells sprout into the subretinal space. As laminin deletion also leads to GC death, we analyzed GC death by dual labeling with Brn3a and activated caspase3. There is an increase in apoptotic GCs in β2-/-γ3-/- retinae during the first two postnatal weeks. In addition to GC death, dendritogenesis in GCs is disrupted: using genetically labeled GCs, we show that there is a dramatic decrease in the number and branching of β2-/-γ3-/- GCs.
Conclusions: :
These data suggest that adhesion to the ILM inhibits MC proliferation and maintains normal cellular architecture, promoting neuronal survival and development. Loss of adhesion results in pathobiologic responses in laminin mutants that mimic many of the events in human disease.
Keywords: Muller cells • extracellular matrix • retinal detachment