Effect of HIF1α on the TRPC6 channel of glomerular podocytes under chronic hypoxia

Chronic hypoxia plays an important role in the initiation and progression of chronic renal disease. The pathogenic role of chronic hypoxia in tubulointerstitial injury has been investigated widely, but little is known about acute hypoxia implications in glomerular damage. In this study, we investigated the effect of chronic hypoxia on transient receptor potential cation channel 6 (TRPC6) and the underlying mechanism in cultured human podocytes.

Fluo-3 was used as a calcium indicator of the OAG-induced receptor operated calcium entry (ROCE) and basal [Ca²⁺]i levels were monitored using laser scanning confocal microscope after exposure of cells to chronic hypoxia. 2-aminoethoxydiphenylborane (2-APB), a pharmacological blocker of TRPCs channels, was used to determine the role of TRPC6 in podocytes under chronic hypoxia. The mRNA expression and protein levels of TRPC6 were determined using Real-time RT-PCR and Western Blotting under normoxic and chronic hypoxic conditions. Actin arrangement was analyzed by confocal microscopy using phalloidin staining of F-actin in podocytes.

Cytosolic free Ca²⁺ was increased by hypoxia or the treatment of TRPC6 agonist OAG under normoxic conditions. The increase of intracellular Ca²⁺ induced by hypoxia was time- and dose-dependent, which can be inhibited by 2-APB, demonstrating that the changes of intracellular Ca²⁺ induced by OAG depend on the activation of TRPC6. Further study showed that the TRPC6 expression levels were significantly increased by hypoxia, which were inhibited by the HIF1α inhibitor in podocytes. Similarly, the increase of intracellular Ca²⁺ induced by hypoxia was decreased when the podocytes were incubated with HIF1α inhibitor. We also found that F-actin was ruptured by hypoxia in podocytes, showing cytoskeleton reorganization.

TRPC6 mRNA and protein expression levels were significantly increased in podocytes under hypoxia, which may result in the increase of intracellular Ca²⁺. This alternation of TRPC6 may be relevant to the modulation of HIF1α. Hypoxia in podocytes can result in cytoskeleton reorganization, which further leads to podocytes injury and disfunction.