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.