Abstract
Purpose :
Astrocytes play an important role in the pathogenesis of glaucoma. A unique feature of astrocytes is that they are extensively coupled by gap junctions (GJ) composed of connexin 43 (Cx43). However, the role of this astrocytic connectivity on retinal ganglion cell (RGC) loss seen in glaucomatous injury is not fully understood. Previously, we reported that astrocyte-specific deletion of Cx43 markedly reduced RGC death aasociated with chronic elevation of intraocular pressure (IOP). Here, we examine the effect of sustained IOP elevation on expression and function of astrocytic Cx43, and determined whether conditional ablation of Cx43 improves visual function in glaucoma.
Methods :
Experimental glaucoma in wild-type (WT) mice and in astrocyte-specific Cx43 knockout (Cx43KO) mice was induced by intracameral injection of polystyrene microbeads. Cx43 expression and RGC survival (using Brn3a labeling) after 4- and 8-weeks of IOP elevation was assessed by immunohistochemistry. GJ coupling was evaluated by measuring the spread of a GJ permeable tracer neurobiotin (NB;5mg/mL) loaded into single astrocytes to adjacent astrocytes. RGC function was examined by recording positive scotopic threshold response (pSTR) at light intensities ranging between -4.5 and -3.9 log.cd.s/m2. All comparisons were made between bead-injected eyes and both contralateral and naïve eyes. Student’s t-test and ANOVA, followed by Tukey’s test were used for statistical analysis.
Results :
Eight weeks of IOP elevation increased astrocytic Cx43 expression by ~40% (n=5, p<0.05) compared to controls eyes. GJ connectivity was markedly enhanced with IOP elevation, with the number of NB labeled astrocytes increasing by 2-fold compared to controls (n=4, p=0.005). Deletion of Cx43 in astrocytes was neuroprotective, with RGC survival increasing by ~90% (n=5-8, p<0.001) and by ~93% after 4- and 8-weeks (n=10, p<0.001) of IOP elevation, respectively, compared to WT eyes. The pSTR amplitude was significantly reduced in WT mice by 43% (at -4.3 log.cd.s/m2; n=9, p<0.001) after 8 weeks of IOP elevation, but this decrease was not observed in Cx43KO mice.
Conclusions :
Glaucomatous injury markedly increases Cx43 expression and coupling between astrocytes. Our results indicate that astrocytic Cx43 GJ channels play a deleterious role in RGC survival, and that ablation of astrocytic connectivity preserves visual function in glaucoma.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.