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Abstract
A role for the cytoplasmic protein synphilin-1 in regulating energy balance has been demonstrated recently. Expression of synphilin-1 increases ATP levels in cultured cells. However, the mechanism by which synphilin-1 alters cellular energy status is unknown. Here, we used cell models and biochemical approaches to investigate the cellular functions of synphilin-1 on the AMP-activated protein kinase (AMPK) signaling pathway, which may affect energy balance. Overexpression of synphilin-1 increased AMPK phosphorylation (activation). Moreover, synphilin-1 interacted with AMPK by co-immunoprecipitation and GST (glutathione S-transferase) pull-down assays. Knockdown of synphilin-1 reduced AMPK phosphorylation. Overexpression of synphilin-1 also altered AMPK downstream signaling, i.e., a decrease in acetyl CoA carboxylase (ACC) phosphorylation, and an increase in p70S6K phosphorylation. Treatment of compound C (an AMPK inhibitor) reduced synphilin-1 binding with AMPK. In addition, compound C diminished synphilin-1-induced AMPK phosphorylation, and the increase in cellular ATP (adenosine triphosphate) levels. Our results demonstrated that synphilin-1 couples with AMPK, and they exert mutual effects on each other to regulate cellular energy status. These findings not only identify novel cellular actions of synphilin-1, but also provide new insights into the roles of synphilin-1 in regulating energy currency, ATP.
Highlights
Recent studies in transgenic animal models suggest that synphilin-1 is involved in regulating energy homeostasis [1,2]
To assess whether synphilin-1 alters AMPK phosphorylation, HEK 293 cells were transiently transfected with human synphilin-1, followed by a Western blot analysis using anti-phospho-AMPKα antibodies
There were no significant differences detected in total AMPKα, acetyl CoA carboxylase (ACC) and p70 ribosomal S6 kinase (p70S6K) levels between cells expressing synphilin-1 and just the vector (Figure 1A,C)
Summary
Recent studies in transgenic animal models suggest that synphilin-1 is involved in regulating energy homeostasis [1,2]. Expression of synphilin-1 increased cellular ATP levels [2]. It is not clear how synphilin-1 alters the energy balance. A decrease in hypothalamic AMPK activity is associated with suppression of feeding behavior, while activation of AMPK leads to increased food intake. Insulin and leptin suppress hypothalamic AMPK activity [29] Orexigenic peptides such as the gut-derived hormone ghrelin and the neuropeptide agouti-related peptide [29] stimulate hypothalamic AMPK activity to increase food intake [30,31]. We conclude that synphilin-1 interacts with AMPK and modulates energy homeostasis in cells
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