MDH2 lactylation promotes pulmonary vascular remodelling through PHB2-Associated mitochondrial dysfunction in pulmonary hypertension

Background Pulmonary hypertension (PH) is characterized by pulmonary vascular remodelling (PVR) driven by pathological proliferation of pulmonary artery smooth muscle cells (PASMCs). Malate dehydrogenase 2 (MDH2) is a mitochondrial enzyme essential for maintaining cellular redox balance and metabolic flux1. While histone lactylation regulates transcription, the role of non-histone mitochondrial protein lactylation in PVR remains unclear2,3. Purpose To determine the role of MDH2 lactylation in regulating mitochondrial homeostasis and PVR in hypoxic PH. Methods Sugen5416/hypoxia (SuHx) rats and platelet-derived growth factor (PDGF)-stimulated human PASMCs were utilised. Lactylomic profiling identified MDH2 as a target, and its stability was analysed via molecular assays (CHX, MG132, ubiquitination). Proliferation and migration were assessed through functional assays and MDH2 loss/gain-of-function. Protein interactions and mitochondrial function were examined using co-immunoprecipitation (Co-IP), mass spectrometry, and electron microscopy. In vivo, oxamate and adeno-associated virus (AAV)-mediated MDH2 modulation were employed to evaluate haemodynamics and PVR. Results Lactylomic profiling revealed a marked increase in MDH2 lactylation in SuHx rat lungs, which was further validated in pulmonary vascular tissues and lactate-treated human PASMCs. Although Mdh2 mRNA was stable, lactate stabilised MDH2 protein by limiting proteasomal degradation. Functionally, lactate promoted PASMC proliferation and migration, effects that were attenuated by MDH2 knockdown, enhanced by AAV-mediated MDH2 overexpression, and reversed by oxamate. Mechanistically, mass spectrometry and Co-IP identified prohibitin 2 (PHB2) as an interacting partner of MDH2, with mitochondrial colocalisation observed in PASMCs. MDH2 accumulation enhanced its interaction with PHB2, which in turn increased PHB2-LC3 association, suggesting activation of PHB2-dependent mitophagy. MDH2 accumulation was associated with mitochondrial structural damage, decreased mitochondrial membrane potential, and excessive ROS production. Silencing MDH2 or disrupting the MDH2-PHB2 interaction alleviated mitochondrial dysfunction and suppressed PASMC proliferative responses. In vivo, oxamate reduced PVR and right ventricular systolic pressure in SuHx rats, whereas AAV-mediated MDH2 overexpression aggravated haemodynamic impairment and partially blunted the protective effects of lactate inhibition. Conclusion MDH2 lactylation drives mitochondrial dysfunction and PVR in PH. Suppressing pathological MDH2 lactylation may provide a therapeutic strategy.Mechanism diagram