Glia-derived S100ß promotes pericyte-mediated capillary constriction and reduced blood flow in glaucomatous and ischemic retinas

Abstract

Purpose : Pericytes are crucial for microvascular dynamics regulation and blood flow. Capillary constriction has been linked to calcium (Ca²⁺) increase in pericytes; however, the mechanism of Ca²⁺ influx and its role on vascular deficits is currently unknown. The S100 calcium-binding protein B (S100ß), an important regulator of Ca²⁺ dynamics, is produced by astrocytes. Here, we asked: i) does retinal glia-derived S100ß contribute to Ca²⁺ increase in pericytes, and ii) does S100ß regulate pericyte-mediated capillary dysfunction after injury?

Methods : Two-photon laser scanning microscopy (TPLSM) was used to visualize pericytes in living mice expressing red fluorescence or the Ca²⁺ indicator GCaMP6 in pericytes (NG2-DsRed, NG2-GCaMP6). Capillary blood flow was quantified by TPLSM as red blood cells crossing a pre-fixed location per unit time. Ocular hypertension was induced by magnetic microbeads occlusion, and transient ischemia by ligation of the central retinal artery. S100ß expression was examined by immunostaining, western blots, and qPCR, and its function was modulated by intraocular injection of recombinant S100ß (gain-of-function) or a function-blocking antibody (FBA) (loss-of-function)

Results : S100ß levels increased in astrocytes and Müller glia in glaucomatous and ischemic retinas, which correlated with reduced capillary diameter and blood flow at pericyte locations, along with intrapericyte Ca²⁺ increase (12.6± 2a.u.) relative to controls (5.3± 2 a.u.) (T-test, p<0.001, n=6 mice/group). Intraocular administration of recombinant S100ß further increased Ca²⁺ influx to pericytes and exacerbated blood flow impairment (T-test, p<0.001, n=6 mice/group). In contrast, selective inhibition of S100ß with a FBA decreased intrapericyte Ca²⁺, reduced the number of capillary constrictions at pericyte locations, restored capillary diameter (FBA:4.9± 0.2 µm, control:5.17± 0.2 µm), and improved single-capillary blood flow (FBA:0 red blood cell (RBC)/sec, control:16 RBC/sec) (T-test, p<0.001, n=6 mice/group)

Conclusions : Our data support that: i) intrapericyte Ca²⁺ plays a critical role in the regulation of capillary diameter and blood flow in glaucomatous and ischemic optic neuropathies, and ii) retinal glia-derived S100ß is an important regulator of Ca²⁺ influx into pericytes, thus exerting a crucial regulation on microvascular dynamics in physiological and pathological conditions

This is a 2021 ARVO Annual Meeting abstract.