Type 2 diabetes-induced overactivation of P300 contributes to skeletal muscle atrophy by inhibiting autophagic flux.

AIMS:Although autophagy impairment is a well-established cause of muscle atrophy and P300 has recently been identified as an important regulator of autophagy, the effects of P300 on autophagy and muscle atrophy in type 2 diabetes (T2D) remain unexplored. We aimed at characterizing the role of P300 in diabetic muscle and its underlying mechanism. MAIN METHODS:Protein levels of phosphorylated P300, total P300, acetylated histone H3, LC3, p62 and myosin heavy chain, and mRNA levels of Atrogin-1 and MuRF1 were analyzed in palmitic acid (PA)-treated myotubes and db/db mice. Autophagic flux was assessed using transmission electron microscopy, immunofluorescence and mRFP-GFP-LC3 lentivirus transfection in cells. Muscle weight, blood glucose and grip strength were measured in mice. Hematoxylin and eosin (H&E) staining was performed to determine changes in muscle fiber size. To investigate the effects of P300 on autophagy and myofiber remodeling, a P300 specific inhibitor, c646, was utilized. 3-Methyladenine (3-MA) was utilized to inhibit autophagosomes formation, and chloroquine (CQ) was used to block autophagic flux. KEY FINDINGS:Phosphorylation of P300 in response to PA enhanced its activity and subsequently suppressed autophagic flux, leading to atrophy-related morphological and molecular changes in myotubes. Inhibition of P300 reestablished autophagic flux and ameliorated PA-induced myotubes atrophy. However, this effect was largely abolished by co-treatment with the autophagy inhibitor CQ. In vivo results demonstrated that inhibition of P300 partially rescued muscle wasting in db/db mice, accompanied with autophagy reactivation. SIGNIFICANCE:The findings revealed that T2D-induced overactivation of P300 contributes to muscle atrophy by blocking autophagic flux.

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