A conserved MADS-box phosphorylation motif regulates differentiation and mitochondrial function in skeletal, cardiac, and smooth muscle cells

Abstract

Exposure to metabolic disease during fetal development alters cellular differentiation and perturbs metabolic homeostasis, but the underlying molecular regulators of this phenomenon in muscle cells are not completely understood. To address this, we undertook a computational approach to identify cooperating partners of the myocyte enhancer factor-2 (MEF2) family of transcription factors, known regulators of muscle differentiation and metabolic function. We demonstrate that MEF2 and the serum response factor (SRF) collaboratively regulate the expression of numerous muscle-specific genes, including microRNA-133a (miR-133a). Using tandem mass spectrometry techniques, we identify a conserved phosphorylation motif within the MEF2 and SRF Mcm1 Agamous Deficiens SRF (MADS)-box that regulates miR-133a expression and mitochondrial function in response to a lipotoxic signal. Furthermore, reconstitution of MEF2 function by expression of a neutralizing mutation in this identified phosphorylation motif restores miR-133a expression and mitochondrial membrane potential during lipotoxicity. Mechanistically, we demonstrate that miR-133a regulates mitochondrial function through translational inhibition of a mitophagy and cell death modulating protein, called Nix. Finally, we show that rodents exposed to gestational diabetes during fetal development display muscle diacylglycerol accumulation, concurrent with insulin resistance, reduced miR-133a, and elevated Nix expression, as young adult rats. Given the diverse roles of miR-133a and Nix in regulating mitochondrial function, and proliferation in certain cancers, dysregulation of this genetic pathway may have broad implications involving insulin resistance, cardiovascular disease, and cancer biology.

Mevalonate Cascade Inhibition by Simvastatin Induces the Intrinsic Apoptosis Pathway via Depletion of Isoprenoids in Tumor Cells

“…After washing, the cells they were imaged using florescence microscope and the fluorescence was quantified on ImageJ software in at least 50 individual cells in different views (NIH, Bethesda, MD, USA)88.…”

A MADS‐box transcription factor regulates a central step in sporulation of the oomycete Phytophthora infestans

“…Prior studies identified several transcription factors that are induced during sporulation in P. infestans, including the MADS‐box transcription factor PiMADS (Ah‐Fong et al ., ) . MADS‐box proteins occur in nearly all eukaryotes, where they regulate a broad spectrum of cellular processes, such as flower development (Smaczniak et al ., ), muscle formation (Mughal et al ., ), and fungal cell wall biosynthesis (Rocha et al ., ). The MADS‐box domain participates in DNA‐binding and dimerization, and differences in the C‐terminal of region of the domain have been used to classify such proteins as either type I (SRF, human serum response factor) or type II (MEF2, myocyte enhancer factor 2).…”

Nix induced mitochondrial fission, mitophagy, and myocyte insulin resistance are abrogated by PKA phosphorylation

“…Previously, we described a lipotoxicity-activated signaling pathway leading to increased expression of the mitophagy receptor Nix 35 . This conserved pathway responds to elevated diacylglycerols by activating PKC which inhibits the expression of microRNA-133a, a negative regulator of Nix expression.…”

“…This conserved pathway responds to elevated diacylglycerols by activating PKC which inhibits the expression of microRNA-133a, a negative regulator of Nix expression. Furthermore, we established that this pathway is activated in rodents fed a high fat diet (HF), and further exacerbated in animals exposed to gestational diabetes mellitus during fetal development 35 .…”

“…Given our previous findings that Nix is induced in this rodent model 35 , and that phospholipids have been implicated in both mitochondrial dynamics and mTOR signaling, we investigated the role of Nix in regulating aspects of mitochondrial quality control following exposure to lipotoxicity. To begin, we expressed Nix in C2C12 myoblasts and monitored mitochondrial morphology using a mitochondrial-targeted Emerald fluorophore (mito-emerald).…”