Angiotensin II Contributes to Podocyte Injury by Increasing TRPC6 Expression via an NFAT-Mediated Positive Feedback Signaling Pathway

Abstract

The transient receptor potential channel C6 (TRPC6) is a slit diaphragm-associated protein in podocytes involved in regulating glomerular filter function. Gain-of-function mutations in TRPC6 cause hereditary focal segmental glomerulosclerosis (FSGS), and several human acquired proteinuric diseases show increased glomerular TRPC6 expression. Angiotensin II (AngII) is a key contributor to glomerular disease and may regulate TRPC6 expression in nonrenal cells. We demonstrate that AngII regulates TRPC6 mRNA and protein levels in cultured podocytes and that AngII infusion enhances glomerular TRPC6 expression in vivo. In animal models for human FSGS (doxorubicin nephropathy) and increased renin-angiotensin system activity (Ren2 transgenic rats), glomerular TRPC6 expression was increased in an AngII-dependent manner. TRPC6 expression correlated with glomerular damage markers and glomerulosclerosis. We show that the regulation of TRPC6 expression by AngII and doxorubicin requires TRPC6-mediated Ca(2+) influx and the activation of the Ca(2+)-dependent protein phosphatase calcineurin and its substrate nuclear factor of activated T cells (NFAT). Accordingly, calcineurin inhibition by cyclosporine decreased TRPC6 expression and reduced proteinuria in doxorubicin nephropathy, whereas podocyte-specific inducible expression of a constitutively active NFAT mutant increased TRPC6 expression and induced severe proteinuria. Our findings demonstrate that the deleterious effects of AngII on podocytes and its pathogenic role in glomerular disease involve enhanced TRPC6 expression via a calcineurin/NFAT positive feedback signaling pathway.

Gain-of-function Mutations in Transient Receptor Potential C6 (TRPC6) Activate Extracellular Signal-regulated Kinases 1/2 (ERK1/2)

“…Such a loop could potentially parallel or augment the well established positive feedback loop involving the TRPC6-calcineurin-NFAT pathway (25,26,103), especially because ERK activation in our system was inhibited by cyclosporine A.…”

Regulation of TRPC6 ion channels in podocytes — Implications for focal segmental glomerulosclerosis and acquired forms of proteinuric diseases

“…Accordingly, calcineurin inhibition by cyclosporine decreased TRPC6 expression and reduced proteinuria, whereas podocyte-specific inducible expression of a constitutively active NFAT mutant increased TRPC6 expression and induced severe proteinuria. These important findings demonstrated that the deleterious effects of Ang II on podocytes and its pathogenic role in glomerular diseases most probably involve an enhanced TRPC6 expression via a calcineurin/NFAT positive feedback signaling pathway (51).…”

“…Moreover, TRPC6 expression correlated with glomerular damage markers and glomerulosclerosis. The regulation of TRPC6 expression by Ang II required TRPC6-mediated Ca 2+ influx and the activation of calcineurin and its substrate NFAT (51). Accordingly, calcineurin inhibition by cyclosporine decreased TRPC6 expression and reduced proteinuria, whereas podocyte-specific inducible expression of a constitutively active NFAT mutant increased TRPC6 expression and induced severe proteinuria.…”

“…It has been shown that TRPC6 protein is functionally connected to the podocyte actin cytoskeleton, which is rearranged upon overexpression of TRPC6 (20,48). Previous studies suggested the involvement of TRPC6 in the pathology of nongenetic forms of proteinuric disease (16,35,48,51). Under pathological conditions, activation of TRPC6 may cause an increase in intracellular calcium and affect critical interactions with podocyte structural proteins, leading to abnormalities in the slit diaphragm and/or podocyte foot processes.…”

“…Likewise, TRPC6 may also amplify injurious signals mediated by Ang II resulting in apoptosis of podocytes. As detailed below, functional link between TRPC6 action and expression and Ang II pathway activation has been proposed (51).…”