THE MTOR INHIBITOR RAPAMYCIN INDUCES CTGF AND TIMP-1 EXPRESSION IN RAT KIDNEY: IMPLICATION OF TGF-?/SMAD SIGNALING CASCADE
Dr. Amany Balah* and Omnia Ezzate
The mTOR-inhibitor rapamycin is a potent drug used as immunosuppressive agent. It is usually used either alone or in combination with calcineurin inhibitors. Despite its beneficial role in organ transplantation rapamycin in some cases can promote fibrosis in the kidney. In cultured mesangial cells, rapamycin has been shown to activate TGF-/Smad signaling pathway in reactive oxygen species (ROS)-dependent manner. The present work was designed to test whether rapamycin-induced TGF-/Smad signaling pathway and subsequent profibrotic gene expression observed in cultured mesangial cells would also occur in vivo. The present work demonstrates that treatment of animals with rapamycin causes an increase in the expression of the profibrotic genes connective tissue growth factor (CTGF) and tissue inhibitor of metalloproteinase-1 (TIMP-1) on mRNA and protein levels in dose-dependent manner. Furthermore, it was found that rapamycin has the ability to activate TGF-/Smad signaling pathway in rat kidney as demonstrated by an increase in plasma TGF- level and subsequent Smad phosphorylation. Moreover, it was found that administration of the antioxidant N-acetyl cysteine (NAC) along with rapamycin significantly reduced plasma TGF-level and Smad-2 phosphorylation. Most interestingly, the expression of CTGF and TIMP-1 induced by rapamycin was highly reduced in the presence of either NAC or a neutralizing TGF- antibody on mRNA and protein levels indicating that ROS and subsequent TGF- activation are involved in CTGF and TIMP-1 expression induced by rapamycin. Finally, the present study demonstrates that rapamycin has the ability to induce CTGF and TIMP-1 expression in ROS and TGF--dependent manner in rat kidney (in vivo).
Keywords: Rapamycin, CTGF, TIMP-1, TGF-?, rat kidney.
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