Pericyte dysfunction promotes neurovascular deficits in glaucoma

Abstract

Purpose : Major vascular defects are observed in glaucoma patients, but the mechanisms underlying these alterations are poorly understood. Pericytes, the contractile cells that wrap along capillaries, regulate blood flow in response to metabolic demand. We recently identified inter-pericyte tunneling nanotubes (IP-TNTs), fine tubular processes that connect two distally-located pericytes and are essential for neurovascular coupling. Here, we asked whether pericytes/IP-TNTs contribute to neurovascular dysfunction in glaucoma.

Methods : Ocular hypertension (OHT) was induced by injecting magnetic microbeads into the anterior chamber of mice. Two-photon laser scanning microscopy was used for live imaging of retinal pericytes, IP-TNTs, calcium (Ca²⁺) signals, light-evoked capillary dynamics and blood flow changes. Ca²⁺influx induces pericyte contraction, thus we generated micecarrying a pericyte-specific Ca²⁺indicator (NG2-GCaMP6), and mice with a pericyte-specific conditional deletion of the voltage-dependent Ca²⁺channel alpha 1C subunit (Cav1.2) (CACNA1Cnull) for analysis of microvascular responses.

Results : Our data show early and sustained reduction of capillary diameter and blood flow at pericyte locations in eyes subjected to OHT relative to sham-operated controls (blood flow - sham: 15 ± 0.6 red blood cell (RBC)/s, OHT-2 weeks: 11.6 ± 0.8 RBC/s, n=58-86 capillaries, N=5-6 mice/group, Student’s t-test p<0.01). Vascular deficits correlated with a substantial increase in the number of pericytes with elevated Ca²⁺, visualized in NG2-GCaMP6 mice (sham: 11.9 ± 2.1 pericytes, OHT-2 weeks: 41.6 ± 2.4 pericytes, n=167-235 pericytes, N=5-13 mice/group, Student’s t-test p<0.001). OHT led to IP-TNT rupture with consequent deficits in light-evoked neurovascular coupling (blood flow change - sham: 16.2 ± 3.6 %, OHT-2 weeks: 4.7 ± 1.0 %, n=29-32 capillaries, N=5-6 mice/group, Student’s t-test p<0.01). Remarkably, selective blockage of Ca²⁺influx to pericytes (CACNA1Cnull mice) restored capillary dynamics, blood flow, and light-evoked neurovascular coupling in glaucomatous retinas.

Conclusions : Early calcium-induced pericyte contraction in glaucoma leads to reduced capillary diameter/blood flow and IP-TNT rupture leading to neurovascular impairment. Our data reveal a critical role for pericytes in OHT-related vascular deficits, and suggest that restoration of Ca²⁺homeostasis in pericytes is effective to rescue neurovascular function in glaucoma.

This is a 2021 ARVO Annual Meeting abstract.