The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of cyclosporine A

Abstract

The immunosuppressive action of the calcineurin inhibitor cyclosporine A (CsA) stems from the inhibition of nuclear factor of activated T cells (NFAT) signaling in T cells. CsA is also used for the treatment of proteinuric kidney diseases. As it stands, the antiproteinuric effect of CsA is attributed to its immunosuppressive action. Here we show that the beneficial effect of CsA on proteinuria is not dependent on NFAT inhibition in T cells, but rather results from the stabilization of the actin cytoskeleton in kidney podocytes. CsA blocks the calcineurin-mediated dephosphorylation of synaptopodin, a regulator of Rho GTPases in podocytes, thereby preserving the phosphorylation-dependent synaptopodin–14-3-3β interaction. Preservation of this interaction, in turn, protects synaptopodin from cathepsin L–mediated degradation. These results represent a new view of calcineurin signaling and shed further light on the treatment of proteinuric kidney diseases. Novel calcineurin substrates such as synaptopodin may provide promising starting points for antiproteinuric drugs that avoid the serious side effects of long-term CsA treatment.

Impairment of podocyte function by diphtheria toxin—a new reversible proteinuria model in mice

“…Thus, together with 1.6 mg of DTx per mouse 114 pg LPS were administred i.p., which is B10 6 -fold below the dosages used in LPS-proteinuria experiments. 13 To further exclude undesired LPS effects, we tested heat-treated DTx (951C for 10 min) and treated LPS-resistant C3H/HeJ mice with DTx.…”

“…Therefore, LPS application was extensively studied as a model for sepsis where proteinuria is an early feature. Reiser et al 12,13 described a reversible LPS-induced model of proteinuria where intraperitoneal (i.p.) injection of 200 mg LPS induced a transient proteinuria within hours returning to baseline after 2 days.…”

CD2AP, Dendrin, and Cathepsin L in the Kidney

“…2 Furthermore, we and others have shown that appearance of cytoplasmic CatL leads to the loss of dynamin 3 and synaptopodin 4 due to proteolysis, which in turn results in reorganization of the actin cytoskeleton in podocytes.…”

“…Furthermore, although our original study used podocytes as the model system, CD2AP 4 and possibly dendrin 5 may be expressed in diverse cells of the kidney, including tubules. The data from Weins et al 1 suggest that dendrineCD2AP-dependent regulation of CatL expression, originally identified in podocytes, is also present in other cells of the kidney including proximal tubules.…”

Out-of-frame start codons prevent translation of truncated nucleo-cytosolic cathepsin L in vivo

“…In the cytosol, cleavage of dynamin, synaptopodin and CD2AP by cathepsin L in renal podocytes leads to cytoskeletal reorganization and triggers the breakdown of the glomerular filtration barrier in a mouse model of proteinuric kidney disease [22][23][24] . Furthermore, the presence of endogenous cathepsin L inhibitors in the nucleus suggests some degree of regulation of cathepsin L activity in this compartment 25,26 .…”