Palmitate induces human glomerular mesangial cells fibrosis through CD3-6mediated transient receptor potential canonical channel 6/nuclear factor of activated T cell 2 activation

Background: Our previous study suggested that palmitate (PA) induces human glomerular mesangial cells (HMCs) fibrosis. However, the mechanism is not fully understood. Recent studies suggested that transient receptor potential canonical channel 6 (TRPC6)/nuclear factor of activated T cell 2 (NFAT2) played an important role in renal fibrosis. Moreover, cluster of differentiation 36 (CD36) regulated the synthesis of TPRC6 agonist diglyceride. In the present study, we investigated whether PA induced HMCs fibrosis via TRPC6/NFAT2 mediated by CD36. Methods: A type 2 diabetic nephropathy (DN) model was established in Sprague Dawley rats, and HMCs were stimulated with PA. Lipid accumulation and free fatty acid (FFA) uptake were measured. The expression levels of TGF-beta 1, p-Smad2/3, FN, TRPC6, NFAT2 and CD36 were evaluated. The intracellular calcium concentration ([Ca2+]i) was assessed. Results: FFA were elevated in type 2 DN rats with kidney fibrosis in addition to NFAT2 and CD36 expression. In vitro, PA induced HMCs fibrosis, [Ca2+](i) elevation and NFAT2 activation. SKF96365 or TRPC6-siRNA could attenuate PA-induced HMCs damage. By contrast, the TRPC6 activator showed the opposite effect. Moreover, NFAT2-siRNA also suppressed PA-induced HMCs fibrosis. CD36 knockdown inhibited the PA-induced [Ca2+](i) elevation and NFAT2 expression. In addition, long-term treatment with PA decreased TRPC6 expression in HMCs. Conclusion: The results of this study demonstrated that PA could induce the activation of the [Ca2+](i)/NFAT2 signaling pathway through TRPC6, which led to HMCs fibrosis. Although activation of TRPC6 attributed to CD36-mediated lipid deposition, long-term stimulation of PA may lead to negative feedback on the expression of TPRC6.