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Angiotensin II (Ang II) promotes the development and progression of podocytopathy. CD2-associated protein (CD2AP) in podocytes, anchoring slit diaphragm proteins to actin filaments of podocyte cytoskeleton, facilitates the nephrin-induced PI3-K/AKT signaling, which protects podocytes from apoptosis. AMP-activated protein kinase (AMPK), as a sensor of cellular energy status, has been known to play an important role in the pathophysiology of metabolic diseases, including diabetes, and its renal complications. We investigated the role of AMPK on the changes of CD2AP and podocyte apoptosis induced by Ang II.
Mouse podocytes were incubated in media containing various concentrations of Ang II and AMPK-related agents. The changes of CD2AP and podocyte apoptosis were observed by confocal imaging, western blotting, and FACS assay according to the presence of Ang II.
CD2AP and AMPKa were located diffusely but predominantly in peripheral cytoplasm and co-localized with nephrin. Ang II reduced AMPKa in time and dose-sensitive manners and also decreased CD2AP stainings diffusely and induced spatial separation from concentrated nephrin, similar to those of compound C-treated condition. AICAR and metformin, AMPK activators, ameliorated the abnormal distributional changes of AMPKa and CD2AP. Ang II also reduced (Thr172) phosphorylation of AMPKa and CD2AP in time- and concentration-dependent manners, which were significantly recovered by metformin and AICAR. Ang II type 1 receptor antagonist, losartan also recovered CD2AP suppressed by Ang II. LY294002, a PI3-K inhibitor, reduced CD2AP suppressed by Ang II. Ang II increased apoptosis in time- and concentration-dependent manners, which were ameliorated by AMPK activators, however, aggravated by siCD2AP.
Our findings suggest that Ang II induces the relocation and suppression of podocyte CD2AP and AMPKa via Ang II type 1 receptor and through the inhibition of PI3-K signaling, which trigger podocyte apoptosis induced by Ang II.