Introduction

As a highly prevalent cardiopulmonary disorder, pulmonary arterial hypertension (PAH) is characterized with diffused vascular remodeling and pulmonary artery resistance, resulting in subsequent right ventricular dysfunction [1, 2]. Dysfunctional pulmonary arterial smooth muscle cells were manifested with abnormal proliferation and migration of PASMCs, together driving progressive remodeling of peripheral pulmonary arteries and augmented right ventricular afterload [3, 4]. However, the cellular and molecular mechanism modulating hypoxic PAH remains undefined. In addition, Metabolic reprogramming serves as a crucial driver in PAH, including hyper-glycolytic reprogramming, aberrant iron handling, insulin insensitivity, and defective sphingosine metabolism [5,6,7,8], however, whether and how mitochondrial dynamics regulates hypoxic PAH remain incompletely understood.

The coiled–coil–helix–coiled–coil–helix domain (CHCHD)-containing proteins are identified as a kind of conserved nucleus-encoded small mitochondrial proteins [9], among which have various important pathophysiological roles. Recently, CHCHD2 has been suggested to be associated with motor dysfunction and pathogenesis of Parkinson's disease (PD) [10, 11], particularly in mitochondrial homeostasis [12, 13]. Specifically, hepatocyte CHCHD2 contributed to liver fibrosis in nonalcoholic fatty liver disease (NAFLD) [14], whereas CHCHD3 was found to improve mitochondrial function via increasing mitochondrial ROS and promoting ferroptosis, by which modulated tumorigenesis [15]. In line with CHCHD2, CHCHD10 has been verified to be involved in multiple neurological alterations including Parkinson’s disease (PD), frontotemporal dementia (FTD), as well as Alzheimer's disease (AD) [13, 16]. CHCHD10 also serves as a mitochondrial modulator in adipose browning [42]. It plays a vital role in mitochondrial intermembrane space bridging and biogenesis of respiratory complexes [43]. In addition, SAM50 has been reported to be directly interacted with CHCHD3 and CHCHD6 [35, 44], by which SAM50 signaling enhanced OPA1 and Mfn1/2 expression while downregulating p-Drp1 and Fis1. This results in the formation of tight and parallel cristae, augmented expression of cardiac mitochondrial complex subunits, increased ATP generation, but reduced secretion of cytochrome C from mitochondria and oxidative damage [44]. Disruption of SAM50 and CHCHD3 crosstalk triggered mitochondrial cristae remodeling and resulted in palmitate-induced cardiomyocyte hypertrophy [45]. Herein, we found that CHCHD4 directly bound to SAM50 in PASMCs to regulate mitochondrial oxidative phosphorylation and aberrant proliferation and migration of PASMCs in hypoxic PAH.

Abnormal mitochondrial dynamics, including fission, fusion, and autophagy, are a key pathological feature of PAH. These alterations contribute to unrestricted cell proliferation and apoptosis resistance, leading to the development of PAH. Downregulation of Mfn2 impairs mitochondrial fusion, while excessive activation of Drp1 triggers aberrant mitochondrial fission, both of which are elevated in PAH patients [46,47,48,49,50]. Dysfunctional mitochondrial autophagy has been reported to generate excessive amount of reactive oxygen species (ROS), and it is also involved in modulating PAH by regulating AMPK/mTOR signal pathway [51, 52]. In current study, we found that CHCHD4 overexpression contributed to Mfn1 and Opa1 expression, and suppressed hypoxia induced Drp1 upregulation. We revealed that CHCHD4 modulated mitochondrial dynamics by directly interacting with SAM50, therefore targeting defective mitochondrial dynamics might serve as a potential approach for PAH treatment.

Limitations

Although we uncovered that CHCHD4 significantly restored mitochondrial oxidative phosphorylation in PASMCs, the link between defective mitochondria and proliferation and migration of PASMCs deserved further research. Moreover, we provide a new insight for CHCHD4-mediated protective effects in PAH, however, whether and how other CHCHDs regulates PAH progression is poorly understood. Here, male adult rats are utilized in our exploration, and the deviation attributed to sex difference should not be ignored. Importantly, insufficient evidence of CHCHD4 agonist hinders the clinical and translational value in this research.

Conclusion

We revealed that CHCHD4 was significantly downregulated among CHCHD proteins in rat PASMCs during hypoxia and lung tissues of rats with hypoxia-induced PAH. Interestingly, AAV serotype 1-induced CHCHD4 elevation conspicuously alleviates pulmonary artery resistance and vascular remodeling, and orchestrates mitochondrial oxidative phosphorylation in PASMCs. We also found overexpression of CHCHD4 impeded proliferation and migration of PASMCs. Mechanistically, through lung tissues bulk RNA-sequencing (RNA-seq), we further identified CHCHD4 modulated mitochondrial dynamics by directly interacting with SAM50, a barrel protein on mitochondrial outer membrane surface. Furthermore, knockdown of SAM50 reversed the biological effects of CHCHD4 overexpression in isolated PASMCs. We demonstrated that elevated CHCHD4 orchestrates mitochondrial oxidative phosphorylation and antagonizes aberrant proliferation and migration of PASMCs, thereby disturbing hypoxic PAH.