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Anastasios Sepetis, Marie O'Connor, Alexandra Hoeh, Morgane Gourlaouen, Stephen E Moss, John Greenwood; LRG1 as a modulator of pericyte-coverage in oxygen-induced retinopathy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4531.
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© ARVO (1962-2015); The Authors (2016-present)
In diseases characterized by abnormal neovascularization such as diabetic retinopathy, the new vessels lack pericyte coverage and exhibit tortuosity, leakage and haemorrhage. TGFβ is involved in the recruitment of pericytes to nascent vessels through ALK1-Smad1/5/8 and ALK5-Smad2/3 signalling. In mesenchymal cells, ALK1-Smad1/5/8 signalling leads to cell proliferation and inhibits differentiation into mural cells while the ALK5-Smad2/3 pathway promotes mitosis, migration and differentiation into mural cells. Leucine-rich α-2-glycoprotein 1 (LRG1) is a modulator of TGFβ signalling. By binding to endoglin LRG1 promotes the ALK1-Smad1/5/8 signalling pathway, thus we hypothesized that LRG1 may have an important role in pericyte recruitment.
Retinae from 6 weeks old Lrg1-/- (n=8) and WT mice (n=6) were digested with trypsin, stained with PA-Schiff and haematoxylin, imaged using a light microscope and the endothelial cell (EC)/pericyte ratio was calculated. Student’s t-Test was performed to determine statistical significance. The oxygen-induced retinopathy mouse model was used to assess pericyte coverage in the neovascular tufts and the leading edge of the retinal revascularization in P17 Lrg1-/- and WT mice (n=8/group). The retinae were stained for the pericyte markers NG2 and αSMA and the endothelial cell marker CD31. Images were acquired using confocal microscopy under identical conditions and settings. NG2/CD31 and αSMA/CD31 ratios were quantified in the above areas and two-way ANOVA and Bonferroni post test were used for statistical analysis.
Quantification of EC/pericyte ratio revealed no difference between the control genotypes. Quantification of pericyte/EC ratio for NG2 and αSMA in the neovascular tufts showed that Lrg1 deletion leads to a higher ratio of NG2+ pericytes (17.1% increase, p<0.05), with no affect on the αSMA+ pericyte population. In the leading edge Lrg1 deletion does not affect pericyte coverage. In the tufts, pericyte coverage was increased in both WT and Lrg1-/- compared to the leading edge area.
We demonstrate that under physiological conditions, deficiency of Lrg1 does not alter perivascular coverage. However, during abnormal neovascularization, as the one observed in the OIR mouse model, Lrg1 deficiency seems to lead to increased pericyte recruitment. These data suggest that LRG1 decreases pericyte coverage and may be a therapeutic target for vessel normalization.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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