Figure 8

OSTN increased intracellular cGMP via GC-A/NPR1 and consequently decreased phosphorylation of p38MAPK. (a) MPC5 (mouse podocyte cells) were stimulated by ADR at various concentrations to assess mRNA expression of Ccl2 and Des. (b) ADR-stimulated MPC5 were treated by OSTN and ANP to evaluate mRNA expression of Ccl2 and Des. (c) Phosphorylation of p38 MAPK at 2 h and mRNA expression of Des and Ccl2 at 24 h in MPC5 stimulated with ADR and TNF-α and simultaneously with FR167653 or vehicle. The grouping of gels cropped from the same lines of the same gel. Full-length blots/gels are presented in Supplementary Fig. S13c. (d) Expression of Npr1 mRNA in MPC5 transfected with Npr1 siRNAs or control siRNAs. Intracellular cGMP in MPC5 transfected with Npr1 siRNAs or control siRNAs and subsequently treated with OSTN or vehicle. (e) Proposed mechanisms of OSTN-protective roles in ADR-stimulated podocytes. NPR-C has no intrinsic enzymatic activity and decreases local concentrations of natriuretic peptides through receptor-mediated homeostatic internalization and degradation. OSTN binds to NPR-C with high affinity and enhances guanylyl cyclase A (GC-A)/NPR1 signaling in podocytes by inhibiting natriuretic peptide degradation. Activation of GC-A leads to the synthesis of cGMP, and the physiological effects of natriuretic peptides are mediated by three cGMP-binding proteins: cGMP-dependent protein kinase, cGMP-regulated phosphodiesterase, and cyclic nucleotide-dependent ion channel. The physiological effects of natriuretic peptides in podocytes inhibit phosphorylation of p38 MAPK, which was an important mediator of ADR-induced podocyte injury, and downregulate Ccl2 mRNA. As a result, it ameliorates podocyte injury such as albuminuria, upregulation of desmin, and loss of foot projections. V, vehicle; A, 10^–6 M ANP; OA, 10^–6 M OSTN and 10^–6 M ANP; FR, FR167653. Data are mean ± SD. *P < 0.05, **P < 0.01, ***P < 0.001 by one-way ANOVA analysis.