The role of non-caveolar caveolin-1 in Müller glia

Abstract

Purpose : Caveolin1 (Cav1) is associated with glaucoma risk and has established roles in the blood-retinal barrier function and retinal inflammatory modulation. The function of Cav1 is generally attributed to its ability to form flask-shaped caveolae membranes along with its accessory protein, PTRF/Cavin1. However, its function(s) outside caveolae (i.e., “non-caveolar Cav1”) have received less attention. In this study, we provide compelling evidence that Müller glial Cav1 protein is stably expressed outside of caveolae and without PTRF/Cavin1 and it promotes interleukin-6 (IL-6) secretion.

Methods : Eyes from PTRF/Cavin1 null mice and controls were evaluated for Cav1 expression by immunohistochemistry along with vascular (CD31) and Müller glial markers (gluthamine synthetase). Expression of Cav1 and PTRF/Cavin1 in immortalized Müller glia (MIO-M1) cells was compared to retinal microvascular endothelial and PC3 prostate cancer cell lines by SDS-PAGE and Western blotting. Transgenic expression of PTRF/Cavin1 in MIO-M1 cells was accomplished by adenoviral gene delivery. The effect of PTRF/Cavin1 expression on production of IL-6 was by ELISA.

Results : Ablation of PTRF/Cavin1, in vivo, resulted in dramatic loss of Cav1 protein expression in retinal and choroidal vasculature but had no effect on Cav1 expression in Müller glia. Consistently, deletion of Cav1 from the neuroretina did not affect PTRF/Cavin1 expression, while endothelial Cav1 deletion significantly downregulated retinal PTRF/Cavin1 expression. In cultured MIO-M1 Müller cells, Cav1 was stably expressed without PTRF/Cavin1 in a temperature-resistant high molecular weight aggregate. Ad5-PTRF/Cavin1 delivery to MIO-M1 cells resulted in significant suppression of both basal and lipopolysaccharide (LPS)-induced IL-6 secretion.

Conclusions : Our results suggest that Cav1 in Muller glia is stably-expressed without PTRF/Cavin1 resides predominantly outside of caveolae where it acts to modulate retinal innate immunity. The mechanism by which the non-caveolar localization of Cav1 modulated innate signaling remains to be elucidated.

This is a 2020 ARVO Annual Meeting abstract.