Presence of tubulointerstitial
fibrosis is predictive of progressive decline in kidney function, independent of its underlying cause. Injury to the renal microvasculature is a major factor in the progression of
fibrosis and identification of factors that regulate endothelium in
fibrosis is desirable as they might be candidate targets for treatment of
kidney diseases. The current study investigates how loss of Angipoietin-1 (Angpt1), a
ligand for endothelial
tyrosine-kinase receptor Tek (also called Tie2), affects tubulointerstitial
fibrosis and renal microvasculature. Inducible Angpt1 knockout mice were subjected to unilateral
ureteral obstruction (UUO) to induce
fibrosis, and kidneys were collected at different time points up to 10 days after obstruction. Staining for
aSMA showed that Angpt1 deficient kidneys had significantly more
fibrosis compared to wildtype mice 3, 6, and 10 days after UUO. Further investigation 3 days after UUO showed a significant increase of Col1a1 and
vimentin in Angpt1 deficient mice, as well as increased gene expression of Tgfb1, Col1a1, Fn1, and CD44. Kidney injury molecule 1 (Kim1/Havcr1) was significantly more increased in Angpt1 deficient mice 1 and 3 days after UUO, suggesting a more severe injury early in the fibrotic process in Angpt1 deficient mice. Staining for
endomucin showed that
capillary rarefaction was evident 3 days after UUO and Angpt1 deficient mice had significantly less capillaries 6 and 10 days after UUO compared to UUO kidneys in wildtype mice.
RNA sequencing revealed downregulation of several markers for endothelial cells 3 days after UUO, and that Angpt1 deficient mice had a further downregulation of Emcn, Plvap, Pecam1, Erg, and Tek. Our results suggest that loss of Angpt1 is central in
capillary rarefaction and fibrogenesis and propose that manipulations to maintain Angpt1 levels may slow down
fibrosis progression.