Downregulation of TRPC6 protein expression by high glucose, a possible mechanism for the impaired Ca²⁺signaling in glomerular mesangial cells in diabetes

Abstract

The present study was performed to investigate whether transient receptor potential (TRPC)6 participated in Ca 2ϩ signaling of glomerular mesangial cells (MCs) and expression of this protein was altered in diabetes. Western blots and real-time PCR were used to evaluate the expression level of TRPC6 protein and mRNA, respectively. Cell-attached patch-clamp and fura-2 fluorescence measurements were utilized to assess angiotensin II (ANG II)-stimulated membrane currents and Ca 2ϩ responses in MCs. In cultured human MCs, high glucose significantly reduced expression of TRPC6 protein, but there was no effect on either TRPC1 or TRPC3. The high glucose-induced effect on TRPC6 was time and dose dependent with the maximum effect observed on day 7 and at 30 mM glucose, respectively. In glomeruli isolated from streptozotocin-induced diabetic rats, TRPC6, but not TRPC1, was markedly reduced compared with the glomeruli of control rats. Furthermore, TRPC6 mRNA in MCs was also significantly decreased by high glucose as early as 1 day after treatment with maximal reduction on day 4. Patch-clamp experiments showed that ANG II-stimulated membrane currents in MCs were significantly attenuated or enhanced by knockdown or overexpression of TRPC6, respectively. Fura-2 fluorescence measurements revealed that the ANG II-induced Ca 2ϩ influxes were markedly inhibited in MCs with TRPC6 knockdown, reminiscent of the impaired Ca 2ϩ entry in response to ANG II in high glucose-treated MCs. These results suggest that the TRPC6 protein expression in MCs was downregulated by high glucose and the deficiency of TRPC6 protein might contribute to the impaired Ca 2ϩ signaling of MCs seen in diabetes.

Impairment of hepatic nuclear factor-4α binding to theStim1promoter contributes to high glucose-induced upregulation of STIM1 expression in glomerular mesangial cells

“…Kidneys and liver were removed after rats were anesthetized. Glomeruli were isolated as described in our previous publication (17). The isolated glomeruli and a piece of homogenized liver tissue (ϳ100 mg) were solubilized in lysis buffer.…”

The Role of Transient Receptor Potential Cation Channels in Ca2+ Signaling

“…Furthermore, Trpc6 KO mice showed an elevated blood pressure and increased vascular smooth muscle contractility that was only partly recovered by the constitutively-active TRPC3-type channels, which are up-regulated in the smooth muscle cells of Trpc6 KO mice (Dietrich et al 2005). Lastly, TRPC6 channel activity at the slit diaphragm is shown to be essential for proper regulation of podocyte structure and function (Reiser et al 2005;Graham et al 2007). The functional role of TRPC7 is still unclear, but it is suggested that TRPC7 conducts Ca 2þ in AT1-induced myocardial apoptosis via a calcineurin-dependent pathway and can thereby contribute to the process of heart failure (Satoh et al 2007).…”

Epoxyeicosatrienoic Acids, TRP Channels, and Intracellular Ca 2+ in the Vasculature

“…22 In addition, TRPC6 expression is downregulated by high glucose; thus, modulation of TRPC6 may play a role in the cardiovascular complications of diabetes. 23 The present study expands our understanding of the roles of TRPC6 in endothelial biology to include a role as an EET effector, and suggests that a loss of EET signaling may partially explain the detrimental effects of TRPC6 dysregulation. Furthermore, this study suggests that targeted pharmacological intervention to enhance TRPC6 or EET function may be useful for improving endothelial function.…”