L-Endoglin Overexpression Increases Renal Fibrosis after Unilateral Ureteral Obstruction

Abstract

Transforming growth factor-β (TGF-β) plays a pivotal role in renal fibrosis. Endoglin, a 180 KDa membrane glycoprotein, is a TGF-β co-receptor overexpressed in several models of chronic kidney disease, but its function in renal fibrosis remains uncertain. Two membrane isoforms generated by alternative splicing have been described, L-Endoglin (long) and S-Endoglin (short) that differ from each other in their cytoplasmic tails, being L-Endoglin the most abundant isoform. The aim of this study was to assess the effect of L-Endoglin overexpression in renal tubulo-interstitial fibrosis. For this purpose, a transgenic mouse which ubiquitously overexpresses human L-Endoglin (L-ENG+) was generated and unilateral ureteral obstruction (UUO) was performed in L-ENG+ mice and their wild type (WT) littermates. Obstructed kidneys from L-ENG+ mice showed higher amounts of type I collagen and fibronectin but similar levels of α-smooth muscle actin (α-SMA) than obstructed kidneys from WT mice. Smad1 and Smad3 phosphorylation were significantly higher in obstructed kidneys from L-ENG+ than in WT mice. Our results suggest that the higher increase of renal fibrosis observed in L-ENG+ mice is not due to a major abundance of myofibroblasts, as similar levels of α-SMA were observed in both L-ENG+ and WT mice, but to the higher collagen and fibronectin synthesis by these fibroblasts. Furthermore, in vivo L-Endoglin overexpression potentiates Smad1 and Smad3 pathways and this effect is associated with higher renal fibrosis development.

Overexpression of the short endoglin isoform reduces renal fibrosis and inflammation after unilateral ureteral obstruction

“…In agreement with these reports, our present data in the UUO model of tubulo-interstitial fibrosis shows the increase in both Eng mRNA and protein expression in the O kidney ( Figure 1). Several authors demonstrated that Eng promotes fibrosis in different kidney experimental models [15,16,[33][34][35][36][37] and other experimental models of tissue fibrosis in organs such as heart [13,38], liver [39] or skin [40]. Two different Eng isoforms that differs exclusively in the intracellular tail have been reported in both humans [18] and mice [19].…”

“…It has been described that L-and S-Eng differentially modulate the TGF-β1 signaling pathway [20,21]. A previous study from our group demonstrated that L-Eng overexpression increases renal fibrosis after unilateral ureteral obstruction (UUO) [16].…”

“…To generate a transgenic mice expressing human S-Eng (S-ENG + ), HA-tagged L-Eng-pCAGGS [16] and S-Eng cDNA [18] in pCDH (System Biosciences) were used to derive the S-Eng-pCAGGS construct. The pCDH-S-Eng was digested with NotI and the obtained Eng fragment was inserted into the L-Eng-pCAGGS plasmid previously digested with NotI.…”

“…The S-Eng-pCAGGS plasmid is under the control of a ubiquitous actin promoter [16]. The pCAGGS plasmid contains, from 5′ to 3′, a CMV enhancer, a chicken enhancer and promoter, a β-globin intron, an EcoRI site, and a β-globin polyadenylation motif.…”

“…Eng is a TGF-β1 co-receptor that participates in TGF-β1 signaling, and many studies have addressed the involvement of Eng in several fibrotic processes [11][12][13][14][15][16]. Eng is overexpressed in kidneys of patients with chronic kidney disease [17] and in kidneys of animals with several experimental models of renal fibrosis [15].…”