ERK/Drp1‐dependent mitochondrial fission contributes to HMGB1‐induced autophagy in pulmonary arterial hypertension

OBJECTIVES: High‐mobility group box‐1 (HMGB1) and aberrant mitochondrial fission mediated by excessive activation of GTPase dynamin‐related protein 1 (Drp1) have been found to be elevated in patients with pulmonary arterial hypertension (PAH) and critically implicated in PAH pathogenesis. However, it remains unknown whether Drp1‐mediated mitochondrial fission and which downstream targets of mitochondrial fission mediate HMGB1‐induced pulmonary arterial smooth muscle cells (PASMCs) proliferation and migration leading to vascular remodelling in PAH. This study aims to address these issues. METHODS: Primary cultured PASMCs were obtained from male Sprague‐Dawley (SD) rats. We detected RNA levels by qRT‐PCR, protein levels by Western blotting, cell proliferation by Cell Counting Kit‐8 (CCK‐8) and EdU incorporation assays, migration by wound healing and transwell assays. SD rats were injected with monocrotaline (MCT) to establish PAH. Hemodynamic parameters were measured by closed‐chest right heart catheterization. RESULTS: HMGB1 increased Drp1 phosphorylation and Drp1‐dependent mitochondrial fragmentation through extracellular signal‐regulated kinases 1/2 (ERK1/2) signalling activation, and subsequently triggered autophagy activation, which further led to bone morphogenetic protein receptor 2 (BMPR2) lysosomal degradation and inhibitor of DNA binding 1 (Id1) downregulation, and eventually promoted PASMCs proliferation/migration. Inhibition of ERK1/2 cascade, knockdown of Drp1 or suppression of autophagy restored HMGB1‐induced reductions of BMPR2 and Id1, and diminished HMGB1‐induced PASMCs proliferation/migration. In addition, pharmacological inhibition of HMGB1 by glycyrrhizin, suppression of mitochondrial fission by Mdivi‐1 or blockage of autophagy by chloroquine prevented PAH development in MCT‐induced rats PAH model. CONCLUSIONS: HMGB1 promotes PASMCs proliferation/migration and pulmonary vascular remodelling by activating ERK1/2/Drp1/Autophagy/BMPR2/Id1 axis, suggesting that this cascade might be a potential novel target for management of PAH.