Upregulation of Dynamin 2 Increases Mitochondrial Fission and Cell Proliferation in Pulmonary Arterial Hypertension

Introduction: The obstructive vasculopathy in pulmonary arterial hypertension (PAH) results in part from acquired mitochondrial changes in pulmonary arterial smooth muscle cells (PASMC), including increased mitotic fission. Mitotic fission, mitochondrial division which is coordinated with mitosis to equitably distribute mitochondria to daughter cells, is mediated by activation of dynamin-related protein 1 (Drp1). To complete mitochondrial fission, Drp1 requires assistance from the GTPase dynamin 2 (DNM2).

Hypothesis: Pathological increase in DNM2 expression drives mitochondrial fission and proliferation of PAH PASMC.

Methods: Immunoblots of human PASMC and immunohistochemistry and immunofluorescence of lung sections from human (n=5/group) and monocrotaline (MCT) rats with PAH (n=4-5/group) were used to assess the expression of DNM2. The effect of manipulating DNM2 on cell proliferation, cell cycle and apoptosis were assessed by flow cytometry. Mitochondrial fission was quantified using confocal imaging.

Results: DNM2 protein expression is increased in human PAH PASMC. DNM2 is also increased in the media of small pulmonary arteries of PAH patients and MCT-PAH rats. Silencing DNM2 inhibited mitochondrial fission and reduced proliferation causing cell cycle arrest in G1/G0 phase. Silencing DNM2 in PAH PASMC also induced apoptosis. Conversely, augmenting DNM2 in normal PASMC induced mitochondrial fission and accelerated cell proliferation. miR-124-3p, a putative negative regulator of DNM2, is decreased in PAH PASMC. Augmenting miR-124-3p decreased DNM2 expression, inhibited proliferation and induced apoptosis in PAH PASMC.

Conclusion: In health, DNM2 regulates mitochondrial fission whilst in disease, epigenetic upregulation of DNM2 increases mitotic fission, which drives pathologic proliferation and apoptosis resistance. The miR-124-3p-DNM2 pathway offers novel PAH therapeutic targets.