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Abstract: TH-PO750

Downregulation of TRPM4 and Consequent Increase in TRPC6 Activity Are Critical Initiation Events Leading to Podocyte Injury

Session Information

Category: Glomerular Diseases

  • 1403 Podocyte Biology

Authors

  • Zhang, Ying, Department of Cell Biology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Fukusumi, Yoshiyasu, Department of Cell Biology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Yasuda, Hidenori, Department of Cell Biology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Kayaba, Mutsumi, Department of Cell Biology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Kawachi, Hiroshi, Department of Cell Biology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
Background

TRPM4 was identified as a molecule downregulated in PAN nephropathy, a mimic of MCNS, by RNA-seq analysis. TRPM4, a member of TRP channels, is a monovalent cation channel, which facilitates Na+ influx, and consequently suppresses Ca2+ influx. We have reported that TRPM4 is restrictedly expressed at podocytes in glomeruli, and is mainly localized at the surface of the foot process just above the slit diaphragm. However, the function of TRPM4 in podocyte is not elucidated yet. TRPC6, a Ca2+ channel localized at the slit diaphragm, is also a member of TRP channels. It is accepted that increase in TRPC6 activity plays a critical role in several types of podocyte injury. However, no studies on the association of TRPM4 with TRPC6 have been reported.

Methods

Variants expression of TRPM4 was analyzed with RNA materials of human cultured podocyte. To analyze the relation between TRPM4 and TRPC6, gene silencing studies with siRNA were performed with cultured podocytes. The effect of 9-phenanthrol, a specific TRPM4 inhibitor on the expression of TRPC6 was analyzed. The kinetics of the expressions of TRPM4, TRPC6, and podocyte functional molecules were analyzed in cultured podocytes treated with adriamycin, a reagent that is capable of inducing FSGS-like podocyte injury by injection into rats.

Results

A unique TRPM4 variant, lacking exon 17, was expressed in podocytes. The expression of TRPC6 was altered in TRPM4-knockdowned podocytes, but TRPM4 expression was not altered in TRPC6-knockdowned podocytes. The 9-phenanthrol treatment clearly promoted the expression of TRPC6 (139.76% ± 5.49%, P < 0.05). TRPM4 was clearly downregulated (62.25% ± 7.74%, P < 0.01) and the expression of TRPC6 was increased (120.27 % ± 31.23%) at 14 hours after adriamycin treatment. At this time point, neither any morphological alterations nor altered expressions of podocyte functional molecules were detected yet.

Conclusion

The depletion assays with siRNAs suggested that TRPM4 is an upstream regulator of TRPC6. The study with 9-phenanthrol clearly showed that functional loss of TRPM4 promoted TRPC6 expression. It is conceivable that downregulation of TRPM4 and consequent increase in TRPC6 activity are critical initiation events leading to podocyte injury. TRPM4 is available as an early marker to detect podocyte injury.