Abstract
Purpose :
Intraocular pressure is dynamically regulated by homeostatic pressure sensing mechanisms within the conventional outflow pathway. Mechanoactivated Piezo1 and TRPV4 channels mediate nonselective cation currents in human and rodent trabecular meshwork (TM) cells in response to moderate (5 – 25 mm Hg) pressure stimuli, but their contribution to ocular hypertension (OHT) and neurodegeneration remains poorly understood.
Methods :
We generated a mouse line with a floxed Trpv4 gene in exon 6 and mated it with Mgp:Cre mice to selectively ablate TRPV4 channels from the TM; a similar approach was used to conditionally knock out (cKO) the Piezo1 channel. IOP in wild-type and cKO mice was elevated through iridocorneal occlusion by magnetic microbeads (MBs). RGC density was determined by counting RBPMS-ir cells, and TRPV4 protein expression was assessed using a validated antibody (Ryskamp et al., J. Neurosci., 2011).
Results :
MB microinjection induced sustained OHT that was decreased in TRPV4 cKO (MgpCre:Trpv4fl/fl) but not Piezo1 cKO (MgpCre:Piezo1fl/fl) eyes. MB injection was associated with increased TRPV4-ir in peripheral RGCs in wild-type retinas, but this effect was not observed in TRPV4 cKO mice. TRPV4 cKO retinas showed a significant (P < 0.05) reduction in the fraction of aRGCs vs. the pan RGC cohort. The overall peripheral RGC density was significantly reduced in hypertensive Piezo1 cKO (P < 0.01) and WT (P < 0.05) but not in TRPV4 cKO eyes.
Conclusions :
This study provides evidence that regulation of conventional outflow by pressure-sensing cation channels has a profound functional impact on the long-term viability of retinal projection neurons. We found that selective ablation of TRPV4 and Piezo1 channels had opposing effects on OHT; TRPV4 cKO eyes decreased, and Piezo1 cKO eyes increased in IOP, respectively. Mechanochannel-dependent IOP regulation was associated with RGC survival, with RGC subtypes showing differential sensitivity to mechanical loads.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.