Ocular hypertension vascular phenotypes occur independently of HIF1a signaling in amacrine cells

Abstract

Purpose : The relationship between eye pressure and retinal vascular changes in glaucoma is not understood. We recently found that mild eye pressure increases in mice cause plexus specific degradation of the intermediate retinal capillary plexus (IRCP) that precedes retinal ganglion cell (RGC) loss. We also saw upregulation of hypoxia inducible factor 1 alpha (HIF1a) and most of its targets in amacrine cells (ACs), but not RGCs. We explore the requirement of HIF1a in ACs for phenotypes caused by ocular hypertension (OHT).

Methods : Control animals were C57BL6J (WT, n=7, 12 wk) and experimental animals were Ptf1a-Cre^+/-; HIF1a^CKO/CKO (AC-HIF1a-KO, n=3, 12 wk). Polystyrene microbeads were used to induce OHT and the fellow eye served as the IOP control. Photopic contrast sensitivity was assessed with optokinetic response (OKR) testing. After 6 weeks, both retinas were stained with antibodies to RBPMS (RGCs) and CD31 (endothelium). We performed confocal microscopy to image the vascular structure. We used a published workflow to access vessel complexity (Sholl analysis) and capillary architecture (junction density, total vessel density, percent vessel area, vessel diameter; ImageJ and AngioTool).

Results : Intraocular pressure of WT and AC-HIF1a-KO mice was increased by 4.21 mmHg and 5.18 mmHg, respectively. As expected, neither group showed significant RGC loss at this level of IOP. Fellow eyes of WT and AC-HIF1a-KO animals differed in several ways: 1) retinal complexity was reduced in AC-HIF1a-KO eyes; 2) all metrics of capillary architecture were reduced in the IRCP of AC-HIF1a-KO eyes; 3) junction density and total vessel density were increased in the superficial retinal capillary plexus of AC-HIF1a-KO eyes; 4) the deep retinal capillary plexus was unaffected. As expected, the effect of OHT in WT eyes showed reduced values of all four metrics of capillary architecture. The effect of OHT in AC-HIF1a-KO eyes, despite the abnormal context, was similar. In both cases there were no effects of OHT on the superficial or deep retinal capillary plexi. Photopic contrast sensitivity was dramatically reduced in the OHT eye of AC-HIF1a-KO mice.

Conclusions : The absence of HIF1a in ACs results in grossly abnormal retinal vasculature. Nevertheless, the effects of OHT remain specific to the IRCP and occur independently of HIF1a in ACs. Additional studies will be needed to determine the mechanisms of OHT specificity.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.