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Published September 2017 | Accepted Version
Journal Article Open

Store Operated Calcium Entry Suppressed TGF-β1/SMAD3 Signaling Pathway in Glomerular Mesangial Cells

Abstract

Our previous study demonstrated that the abundance of extracellular matrix proteins was suppressed by store-operated Ca^(2+) entry (SOCE) in mesangial cells (MCs). The present study was conducted to investigate the underlying mechanism focused on the transforming growth factor-β1 (TGF-β1)/Smad3 pathway, a critical pathway for ECM expansion in diabetic kidneys. We hypothesized that SOCE suppressed ECM protein expression by inhibiting this pathway in MCs. In cultured human MCs, we observed that TGF-β1 (5 ng/ml for 15 h) significantly increased Smad3 phosphorylation, as evaluated by immunoblot. However, this response was markedly inhibited by thapsigargin (1 µM), a classical activator of store-operated Ca^(2+) channels. Consistently, both immunocytochemistry and immunoblot showed that TGF-β1 significantly increased nuclear translocation of Smad3, which was prevented by pretreatment with thapsigargin. Importantly, the thapsigargin effect was reversed by lanthanum (La^(3+); 5 µM) and GSK-7975A (10 µM), both of which are selective blockers of store-operated Ca^(2+) channels. Furthermore, knockdown of Orai1, the pore-forming subunit of the store-operated Ca^(2+) channels, significantly augmented TGF-β1-induced Smad3 phosphorylation. Overexpression of Orai1 augmented the inhibitory effect of thapsigargin on TGF-β1-induced phosphorylation of Smad3. In agreement with the data from cultured MCs, in vivo knockdown of Orai1 specific to MCs using a targeted nanoparticle small interfering RNA delivery system resulted in a marked increase in abundance of phosphorylated Smad3 and in nuclear translocation of Smad3 in the glomerulus of mice. Taken together, our results indicate that SOCE in MCs negatively regulates the TGF-β1/Smad3 signaling pathway.

Additional Information

© 2016 American Journal of Physiology-Renal Physiology. Submitted 1 September 2016; accepted in final form 15 June 2017. We thank GlaxoSmithKline (Brentford, UK) for providing the GSK-7975A compound and Dr. Joseph Yuan at the University of North Texas Health Science Center at Fort Worth for providing the expression plasmid for human Orai1 (mCherry-Red-Orai1/p3X FLAG-CMV 7.1). The work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant RO1-DK-079968 (Y. Ma), an American Heart Association Southwest Affiliate Grant-in-Aid (16GRNT27780043; R. Ma), an award from the Harry S. Moss Heart Trust (Y. Ma), and a Grant-in-Aid Research Grant for doctoral students from Sigma Xi (S. Chaudhari). No conflicts of interest, financial or otherwise, are declared by the authors. Author Contributions: S.C., W.L., Y.W., and H.J. performed experiments; S.C., W.L., Y.M., and R.M. analyzed data; S.C., W.L., M.E.D., J.E.Z., and R.M. interpreted results of experiments; S.C., W.L., and Y.M. prepared figures; S.C. drafted manuscript; S.C., W.L., Y.W., H.J., Y.M., and R.M. approved final version of manuscript; M.E.D., J.E.Z., and R.M. edited and revised manuscript.

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