PACS2-SERCA2 complex destabilization drives mitochondria-associated membrane remodeling in hypoxic pulmonary hypertension

Background

Mitochondria-associated membranes (MAMs) are critical structures that coordinate endoplasmic reticulum (ER)-mitochondria Ca2+ transfer and metabolic homeostasis. Disruption of MAM homeostasis contributes to abnormal proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs) in hypoxic pulmonary hypertension (HPH). However, its upstream molecular mechanisms remain unclear.

Purpose

To determine whether hypoxia-induced disruption of the PACS2-sarco/endoplasmic reticulum Ca2+-ATPase 2 (SERCA2) complex drives MAM remodeling and Ca2+ dyshomeostasis, thereby promoting pathological PASMC proliferation and pulmonary vascular remodeling (PVR).

Methods

Proteomic data from lung tissues of patients with pulmonary hypertension and HPH mice were integrated to identify potential MAM regulators. Vascular smooth muscle cell (VSMC)-specific Pacs2 knockout and knockin mouse models, together with hypoxia-treated human PASMCs, were established to comprehensively evaluate pulmonary hemodynamics, PVR, MAM ultrastructure, ER-mitochondrial Ca2+ transfer, and mitochondrial energy metabolism. Co-immunoprecipitation and domain-mapping mutagenesis were performed to characterize the PACS2-SERCA2 interaction and its regulation under hypoxia.

Results

Chronic hypoxia significantly reduced PACS2 levels in pulmonary arteries and PASMCs, accompanied by decreased MAM contacts and impaired mitochondrial Ca2+ uptake. In addition, overexpression of PACS2 significantly inhibited PASMC proliferation.

VSMC-specific deletion of PACS2 exacerbated PVR and increased right ventricular systolic pressure. In contrast, PACS2 overexpression significantly improved hypoxia-induced abnormalities in pulmonary hemodynamics and vascular wall thickening.

Mechanistically, PACS2 formed a stable complex with SERCA2 to maintain MAM structural integrity and ER-mitochondrial Ca2+ transfer. Hypoxia destabilized the PACS2-SERCA2 complex, promoted PACS2 translocation from MAMs to the cytosol, and induced tripartite motif-containing 67 (TRIM67)-mediated ubiquitination and degradation. This process led to MAM remodeling, disruption of mitochondrial Ca2+ homeostasis, and mitochondrial dysfunction, thereby promoting pathological PASMC proliferation. Overexpression of SERCA2 or stabilization of the PACS2-SERCA2 interaction partially restored MAM structure and Ca2+ homeostasis and attenuated PVR.

Conclusions

Hypoxia disrupts the stability of the PACS2-SERCA2 complex, leading to MAM remodeling and ER-mitochondrial Ca2+ dyshomeostasis, thereby driving abnormal PASMC proliferation and PVR. Enhancing the interaction between PACS2 and SERCA2 to reconstruct MAM Ca2+ homeostasis may represent a potential therapeutic strategy for HPH.Mechanism diagram