Podocyte Purinergic P2X4 Channels Are Mechanotransducers That Mediate Cytoskeletal Disorganization

Abstract

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X 4 ) blocker 5-BDBD. Moreover, mechanical P2X 4 channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X 4 channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X 4 channels as mechanotransducers in podocytes.

Renoprotection: focus on TRPV1, TRPV4, TRPC6 and TRPM2

“…However, Forst and colleagues found that upon mechanical stimulation podocytes release ATP, which stimulates the P2X purinoceptor 4 (P2X4) and eventually results in Ca 2+ influx without the contribution of TRPC6 (Forst et al . ). These findings demonstrate that a mechano‐gated TRPC6‐independent Ca 2+ entry pathway exists in podocytes.…”

Mechanosensitive Gq/11 Protein–Coupled Receptors Mediate Myogenic Vasoconstriction

“…In addition, TRPC channels did not play an important role. Instead ATP‐gated P 2 X 4 cation channels were identified as pivotal mechanotransducers in podocytes while mechanosensors in these cells have not been identified yet . Since vascular autoregulation is of paramount importance in physiology, one may speculate that several yet to identify backup‐strategies have evolved which cooperate to constantly maintain blood flow, perfusion pressure and vascular tone.…”

The renal and blood pressure response to low sodium diet in P2X4 receptor knockout mice

“…Such endothelial dysfunction would impair BP regulation through the pressure natriuresis response (Ivy and Bailey ), but P2X4 is also expressed in glomerular podocytes(Forst et al. ) and throughout the renal tubule (Turner et al. ).…”

“…P2X4 À/À mice are hypertensive and have an impaired endothelial production of nitric oxide in response to increased vascular flow (Yamamoto et al 2006). Such endothelial dysfunction would impair BP regulation through the pressure natriuresis response (Ivy and Bailey 2014), but P2X4 is also expressed in glomerular podocytes (Forst et al 2016) and throughout the renal tubule (Turner et al 2003). Whether loss of renal tubular P2X4 contributes to hypertension in P2X4 À/À mice is not known.…”