Abstract
Purpose :
Pericytes play crucial roles in the regulation of microvascular dynamics. Capillary constriction has been linked to calcium increase in pericytes, however, the mechanism of calcium influx and its role on vascular deficits is unknown. The S100 calcium-binding protein ß (S100ß), a regulator of calcium-dependent processes, is produced by astrocytes. Here, we asked: i) does glia-derived S100ß contribute to calcium increase in pericytes? and ii) does S100ß regulate pericyte-mediated capillary dysfunction after glaucomatous or ischemic injury?
Methods :
Two-photon laser scanning microscopy (TPLSM) was used to visualize pericytes in living mice expressing red fluorescence or the calcium indicator GCaMP6 in pericytes (NG2-DsRed, NG2-GCaMP6). Capillary blood flow was quantified by TPLSM as red blood cells (RBC) crossing a pre-fixed location per second. Ocular hypertension was induced by magnetic microbead occlusion, and transient ischemia by ligation of the central retinal artery. S100ß function was modulated by intraocular injection of recombinant S100ß (increase) or a function blocking antibody (decrease).
Results :
S100ß expression was upregulated in astrocytes and Müller glia in glaucomatous and ischemic retinas, which correlated with intrapericyte calcium increase (injury: 12.6 ± 2 a.u., sham: 5.3 ± 2 a.u.), reduced capillary diameter, and compromised blood supply (Student’s t-test, p<0.001, n=6 mice/group). Intraocular administration of recombinant S100ß further increased calcium load in pericytes and exacerbated blood flow impairment (Student’s t-test, p<0.001, n=6 mice/group). In contrast, inhibition of S100ß decreased intrapericyte calcium, reduced the number of constrictions (treated: 1268 ± 153, control: 1374 ± 98), restored capillary diameter (treated: 4.9 ± 0.2 µm, control: 5.17 ± 0.2 µm), and improved blood flow (treated: 0 RGB/sec, control: 16 RBC/sec) (Student’s t-test, p<0.001, n=6 mice/group).
Conclusions :
Our data indicate that: i) intrapericyte calcium plays a critical role in the regulation of capillary diameter and blood flow in glaucomatous and ischemic damage, and ii) retinal glia-derived S100ß is an important regulator of calcium influx into pericytes, thus exerting a crucial regulation on microvascular dynamics in physiological and pathological conditions.
This is a 2020 ARVO Annual Meeting abstract.