Cytoskeleton Rearrangements Modulate TRPC6 Channel Activity in Podocytes

Abstract

The actin cytoskeleton of podocytes plays a central role in the functioning of the filtration barrier in the kidney. Calcium entry into podocytes via TRPC6 (Transient Receptor Potential Canonical 6) channels leads to actin cytoskeleton rearrangement, thereby affecting the filtration barrier. We hypothesized that there is feedback from the cytoskeleton that modulates the activity of TRPC6 channels. Experiments using scanning ion-conductance microscopy demonstrated a change in migration properties in podocyte cell cultures treated with cytochalasin D, a pharmacological agent that disrupts the actin cytoskeleton. Cell-attached patch-clamp experiments revealed that cytochalasin D increases the activity of TRPC6 channels in CHO (Chinese Hamster Ovary) cells overexpressing the channel and in podocytes from freshly isolated glomeruli. Furthermore, it was previously reported that mutation in ACTN4, which encodes α-actinin-4, causes focal segmental glomerulosclerosis and solidifies the actin network in podocytes. Therefore, we tested whether α-actinin-4 regulates the activity of TRPC6 channels. We found that co-expression of mutant α-actinin-4 K255E with TRPC6 in CHO cells decreases TRPC6 channel activity. Therefore, our data demonstrate a direct interaction between the structure of the actin cytoskeleton and TRPC6 activity.

Reorganization and Suppression of Store-Operated Calcium Entry in Podocytes of Type 2 Diabetic Rats

“…Previously, in CHO cells overexpressing human TRPC6 channels, we recorded single channels with an estimated conductance of 20 ± 1 pS in cell-attached mode [ 9 ]. Ilatovskaya et al also revealed channels with similar characteristics and conductance of 22 pS in freshly isolated glomerular mouse podocytes, which were absent in TRPC6KO mice [ 16 ].…”

“…In addition, we observed Tg-induced activation of the channels with conductance of about 6.5 ± 0.4 pS, which we did not analyze further because of rare observation and complication in analysis upon activation together with TRPC6 channels. We, as well as another group, have already registered and described these channels in rat podocytes earlier [ 9 , 51 ].…”

“…Disturbances in Ca 2+ signaling play a central role in podocyte pathophysiology [ 8 ]. One of the key regulators of intracellular Ca 2+ in glomerular podocytes is considered to be TRPC6 (Transient Receptor Potential Canonical 6) channels [ 9 , 10 , 11 , 12 , 13 ]. TRPC6 channels form a relatively non-selective cation channel with single channel conductance of 15–45 pS and could be activated by diacylglycerol (DAG) upon stimulation of G q/11 -coupled receptors linked to phospholipase Cβ (PLCβ), particularly angiotensin receptors [ 14 , 15 , 16 , 17 ].…”

A critical role of the podocyte cytoskeleton in the pathogenesis of glomerular proteinuria and autoimmune podocytopathies

“…Overexpression of TRPC6 in podocytes leads to an increase in cytosolic calcium, the downregulation of nephrin and synaptopodin, and the activation of RhoA, which leads to the derangement of F-actin and the reduction of foot processes. 41,42 Increased calcium flux through TRPC6 is one of the main determinants of podocyte injury in nephropathy, including FSGS, diabetic nephropathy, and nephrotic syndrome. [43][44][45][46][47] Ang II can increase the expression of TRPC6 in cultured podocytes.…”

Role of ion channels in the mechanism of proteinuria (Review)

“…3) (73). Another study showed that TRPC6, an important ion channel in podocytes, can interact with other SD proteins, as well as with signal transduction molecules such as vascular endothelial growth factor to regulate the actin cytoskeleton rearrangement of podocytes, thus affecting pathological proteinuria (74). It has been also reported that TRPC6 is upregulated in renal diseases, commonly accompanied by proteinuria, including membranous nephropathy, focal glomerulopathy and minor pathological nephropathy (75)(76)(77).…”