Abstract 13283: Mitochondrial DNA Damage and Remodelling of Nucleoid Bodies in Pulmonary Artery Smooth Muscle Cells From Human Patients With Pulmonary Arterial Hypertension

Abstract

Introduction: Pulmonary arterial hypertension (PAH) is an obstructive pulmonary vasculopathy characterized by pulmonary artery smooth muscle cell (PASMC) hyperproliferation. PAH-PASMC have mitochondrial defects, including increased fragmentation, and increased production of reactive oxygen species (ROS). Mitochondrial-derived ROS can cause DNA damage. Mitochondrial DNA (mtDNA) is surrounded by replication proteins which form nucleoid bodies (NB). Hypothesis: We hypothesize that mtDNA damage is increased and NB structure altered in human PAH PASMC. Methods & Results: We profiled mtDNA and NB composition and integrity in control and PAH PASMC (n = 5/group). mtDNA content was assessed via confocal immunofluorescence of discrete extranuclear double-stranded DNA colocalized with mitochondria. Lower mtDNA content was observed in PAH PASMC vs control (1.8±0.2 vs 3.5±0.2 mtDNAs/μm 3 mitochondria, p<0.0001). Reduced mtDNA in PAH vs control was validated by qPCR (0.69±0.07 vs 1.00±0.07 ng mtDNA/μg cellular protein, n=4-5, p=0.0182). siRNA targeting of Mitofusin2 (Mfn2) in normal PASMC to mimic the mitochondrial fragmentation of PAH, reduced total mtDNA compared to control (1.05±0.06 vs 3.5±0.2 mtDNA/μm 3 mitochondria, n=9, p<0.0001), suggesting increased fission reduces mtDNA expression. Amplification of an 8.8kb mtDNA fragment, a measure of mtDNA damage, revealed increased damage in PAH vs control (14.3±3.9 vs 28.7±2.4 pg mtDNA, n=4, p=0.02). PAH PASMC exhibited higher expression of NB proteins vs control (n=5/measurement): TFAM (+96.7±23.3%, p=0.0032), SSBP (+63.4±14.4%, p=0.0023), and POLG (+59.0±24.0%, p=0.0397). These results were confirmed via immunoblotting for TFAM (+161.9±39.3%, n=4-5, p=0.0045) . Immunofluorescence verified increased TFAM in PAH PASMC vs control. Conclusions: We report a paradoxical upregulation of NB proteins despite reduced mtDNA content and elevated mtDNA damage in PAH. We speculate there is an unsuccessful compensatory attempt to restore mtDNA levels by increasing the expression of mtDNA’s replication apparatus in PAH PASMC.