Mitochondrial Dysfunction Dictates Energy Metabolism Reprogramming in Pulmonary Arterial Hypertension
Authors: Niihori Maki , Vasilyev Mikhail , James Joel , McClain Nolan , Rafikov Ruslan , Rafikova Olga 
Published: May 2022

Introduction

Pulmonary arterial hypertension (PAH) is a progressive fatal disease with a complex pathogenic mechanism. Recent studies report that nearly 60% of patients with PAH have metabolic syndrome (MS). Unrecognized glucose intolerance and insulin resistance were also shown to be common in PAH, raising the possibility that metabolic disease predisposes to PAH. Nevertheless, the mechanistic link between the PAH and metabolic disorders remains unexplored. Mitochondrial dysfunction (MD) is one of the primary pathogenic events tightly associated with PAH and MS/ type 2 diabetes pathobiology and could play a causative role in severe metabolic perturbations.

Hypothesis

We hypothesized that dysfunctional mitochondria are sufficient to initiate metabolic rearrangements associated with PAH and classical metabolic disorders.

Methods

In this study, we used the recently established rat model reproducing a human mutation in the NFU1 protein, which is responsible for mitochondrial homeostasis. NFU1G206Crats develop a severe MD and spontaneously develop PAH characterized by increased right ventricle (RV) systolic pressure, RV hypertrophy, and obliterative disease of the small pulmonary arteries. An intraperitoneal glucose tolerance test (IPGTT) was used to assess the ability of NFU1G206Crats to metabolize glucose. Plasma insulin levels were measured to control insulin sensitivity. Pulmonary arterial smooth muscle cells (PASMCs) isolated from WT and NFU1G206C rats were used for measuring fatty acid oxidation (FAO) by Seahorse palmitate‐BSA oxidation assay, mitochondria isolations, and western blot analysis.

Results

After 5 hours of fasting, WT and NFU1G206C rats had the same baseline glucose levels (glucose (mg/dL) is 89.5±2.0 vs. 92.0±6.2; p=0.47 in WT (N=5) vs. NFU1G206C(N=6)). However, 15 min after glucose administration (2 g/kg), NFU1G206Cshowed significantly higher levels of blood glucose, which reached the peak by 30 min (193.4±32.3 vs. 340.8±50.1; p<0.05 in WT vs. NFU1G206C) and remained high even after 120 min, when the glucose level of WT rats reached the baseline (96.1±11.1 vs. 155.9±15.9; p<0.02 in WT vs. NFU1G206C). MD was also sufficient to induce a significantly delayed insulin response in NFU1G206Ccompared to WT, suggesting the reduced insulin sensitivity in rats with MD. We also discovered an upregulated expression of free fatty acid (FFA) transporters, CD36 and CPT1, in NFU1G206C PASMC, which corresponded to the increased levels of basal FAO in the mutant cells. This discovery was confirmed by mitochondrial proteome analysis, revealing a significantly upregulated FA metabolism and dysregulated FA synthesis in NFU1G206C PASMC. NFU1G206C PASMC also had an increased membrane translocation of PKCα, one of the diacylglycerol‐dependent PKCs activated by FFAs and involved in reduced insulin sensitivity.

Conclusion

We conclude that the MD secondary to the NFU1 insufficiency induces significant metabolic derangements, such as increased flux of fatty acids, glucose intolerance, and insulin insensitivity associated with classic metabolic disorders and recently implemented in the pathogenesis of PAH. The severe metabolic reprogramming revealed in PASMC correlates with progressive pulmonary vascular disease in NFU1G206Crats.