Abstract
To investigate the levels of (Pro) renin receptor [(P) RR], α-smooth muscle actin (α-SMA), fibronectin (FN), and vacuolar H+-ATPase (V-ATPase) subunits (B2, E, and c) in rat unilateral ureteral obstruction (UUO) models and rat proximal tubular epithelial cells (NRK-52E) treated with prorenin to elucidate the role of V-ATPase in these processes by activating the (P) RR. UUO significantly upregulated (P) RR, V-ATPase subunits, α-SMA and FN expression in tubulointerstitium or tubular epithelial cells. A marked colocalization of (P) RR and the B2 subunit was also observed. Prorenin treatment upregulated α-SMA, FN, (P) RR, and V-ATPase subunits and activity in NRK52E cell in a dose- and time-dependent manner. The V-ATPase inhibitor bafilomycin A1 partially blocked prorenin-induced (P) RR, FN, and α-SMA expression. Co-immunoprecipitate and immunofluorescence results demonstrated that the V-ATPase B2 subunit bound to the (P) RR, which was upregulated after prorenin stimulation. Either siRNA-mediated (P) RR or B2 subunit knockdown partially reduced V-ATPase activity and attenuated prorenin-induced FN and α-SMA expression. From the data we can assume that activation of (P) RR and V-ATPase may play an important role in tubulointerstitial fibrosis with possible involvement of interaction of V-ATPase B2 subunit and (P)RR.
Highlights
The (P) RR is composed of 350 amino acids in four different domains: a short cytosolic domain, a single transmembrane domain, an extracellular domain, and an N-terminal signal peptide[11]
Immunofluorescence demonstrated increased α -SMA and FN accumulation in the interstitial or tubular epithelial cells, and the V-ATPase B2 subunit and (P) RR dramatically accumulated in the apical regions of tubular epithelial cells 7 days after ureteral obstruction (UUO) (Fig. 1D)
Dual-immunofluorescence staining using confocal microscopy revealed that (P) RR colocalized with V-ATPase B2, and it was markedly increased in the apical regions of tubular epithelial cells on day 7 after UUO (Fig. 1D)
Summary
The (P) RR is composed of 350 amino acids in four different domains: a short cytosolic domain, a single transmembrane domain, an extracellular domain, and an N-terminal signal peptide[11]. V-ATPase is responsible for the acidification of intracellular compartments and cellular pH homeostasis in all cell types. Vacuole acidification along these pathways is essential for many cellular functions including the processing of hormones such as insulin, receptor endocytosis and recycling, and membrane fusion events[13]. We evaluated V-ATPase subunit and (P) RR expression and colocalization in an established animal model of kidney fibrosis, unilateral ureteral obstruction (UUO), and examined the roles and interactions of these proteins in prorenin-induced FN and SMA expression in NEK52E cells
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