Abstract
Purpose :
Pericytes have a fundamental role in maintaining vascular homeostasis and their malfunction is thought to be an early event in diabetic retinopathy (DR). Cross-sectional studies have reported increased levels of leucine-rich α-2 glycoprotein 1 (LRG1) in the plasma and vitreous humor of diabetic patients but failed to establish whether LRG1 plays an active role in disease pathogenesis. Our study aimed to elucidate the role of LRG1 in the early microvascular events taking place in the diabetic retina using experimental models of DR.
Methods :
We took advantage of two murine models of type I diabetes (STZ and Akita) to correlate Lrg1 expression to the retinal vascular changes happening over 6 months of hyperglycaemia. We also compared global Lrg1-deficient mice to wild-type littermates to identify the contribution of LRG1 to the vascular abnormalities in diabetic retinas (N=10/group, males, C57Bl/6). We then designed in vitro culture models incorporating human primary retinal pericytes (HRP) to assess the effects of LRG1 on the morphology, signalling and function of pericytes (N=3).
Results :
We found increased LRG1 expression in diabetic retinas early after hyperglycaemia onset (4-8 wks). In both models, diabetic retinas were characterised by an increased number of semi-detached pericytes (or ‘pericyte bridges’), stretching their processes between adjacent capillaries of the deep plexus (50% increase at 16 wks). This increase did not occur in the diabetic retinas of Lrg1-deficient mice. Morphometric analyses revealed that these hyper-activated pericytes, and their processes, were almost-exclusively associated with bent capillaries (Fig.), suggesting that these structures can exert tractional forces on endothelial cells (ECs). Based on these observations, we subjected cultured HRPs to increasing doses of recombinant LRG1 and revealed a phenotypic switch towards a more star-shaped morphology coupled to an enhanced ability to contract collagen type I. This contractile phenotype was associated with increased expression of typical myofibroblast proteins (αSMA, vimentin, fibronectin).
Conclusions :
We have shown that LRG1 is up-regulated early on after hyperglycaemia onset in the retina and triggers a myofibroblastic-like phenotype in pericytes. We believe that targeting LRG1 could prevent or revert EC-pericyte decoupling and normalise the vasculature, paving the way to more timely and effective treatments in DR.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.