Abstract Rationale Skeletal muscle atrophy is a critical systemic manifestation of COPD, strongly associated with cigarette smoke exposure. Impaired mitochondrial quality control (MQC) and resultant oxidative stress (OS) are key drivers of this muscle wasting, but the specific upstream signaling events initiated by smoke exposure remain unknown. Objectives To identify the upstream regulator linking CSE to muscle atrophy and to elucidate the molecular mechanism by which it dismantles MQC and triggers OS. We specifically investigated the role of HDAC6 and its regulation of mitochondrial protein stability via post-translational modification (PTM) crosstalk. Methods We utilized in vitro models (C2C12, HSkMC myotubes) exposed to CSE, and in vivo mouse models (muscle-specific AAV9-sgRNA knockout, genetic/pharmacological inhibition) of CSE-induced atrophy. Mechanisms were dissected using protein-protein interaction (Co-IP), PTM assays (acetylation/ubiquitination IP), CHX pulse-chase, and site-directed mutagenesis. Functional outcomes were measured by TEM, Seahorse (respiratory capacity), JC-1 (membrane potential), and redox assays (MitoSOX, GSH/GSSG, MDA). Atrophy was quantified by muscle grip strength, fiber CSA, and atrogene (MuRF1, Atrogin-1) expression. Measurements and Main Results We found HDAC6 is robustly upregulated by CSE in all models. HDAC6 inhibition or knockout provided profound protection against atrophy, rescuing muscle function, fiber CSA, and atrogene expression. Mechanistically, HDAC6 inhibition reversed CSE-induced mitophagy failure (restored TEM morphology) and mitochondrial dysfunction (normalized JC-1 and Seahorse metrics), thereby mitigating OS (normalized MitoSOX, GSH/GSSG, and MDA). We identified the essential mitophagy regulator Prohibitin 2 (PHB2) as a novel HDAC6-interacting protein. HDAC6 promotes PHB2 degradation by facilitating its ubiquitination. We identified NEDD4 as the cognate E3 ligase and demonstrated that HDAC6 knockout prevents NEDD4-mediated PHB2 degradation. This PTM crosstalk is precise: HDAC6 utilizes its DD2 domain to specifically deacetylate PHB2 at Lysine 216 (K216). Mutation of this site (PHB2-K216R) rendered PHB2 resistant to both HDAC6-mediated deacetylation and subsequent degradation. Critically, overexpression of PHB2 (or the K216R mutant) was sufficient to rescue muscle atrophy induced by either CSE or HDAC6 overexpression. Conclusions We have identified a novel pathogenic axis: CSE upregulates HDAC6, which deacetylates PHB2 at K216, triggering its NEDD4-mediated degradation. This dismantles MQC, causes severe oxidative stress, and drives muscle atrophy. HDAC6 is a specific and targetable upstream driver of smoking-related myopathy. (Abbreviations)COPD: Chronic Obstructive Pulmonary DiseaseCSE: Cigarette Smoke ExtractHDAC6: Histone Deacetylase 6PHB2: Prohibitin 2NEDD4: Neural Precursor Cell Expressed, Developmentally Downregulated 4PTM: Post-Translational ModificationMQC: Mitochondrial Quality ControlOS: Oxidative StressCSA: Cross-Sectional Area This abstract is funded by: No
Wang et al. (Fri,) studied this question.