BOLA (BolA Family Member 3) Deficiency Controls Endothelial Metabolism and Glycine Homeostasis in Pulmonary Hypertension

Abstract

Background-Deficiencies of iron-sulfur (Fe-S) clusters, metal complexes that control redox state and mitochondrial metabolism, have been linked to pulmonary hypertension (PH), a deadly vascular disease with poorly defined molecular origins. The BolA Family Member 3 (BOLA3) regulates Fe-S biogenesis, and mutations in BOLA3 result in multiple mitochondrial dysfunction syndrome, a fatal disorder associated with PH. The mechanistic role of BOLA3 in PH remains undefined. Methods-In vitro assessment of BOLA3 regulation and gain and loss of function assays were performed in human pulmonary artery endothelial cells (PAECs) using siRNA and lentiviral vectors expressing the mitochondrial isoform of BOLA3. Polymeric nanoparticle 7C1 was utilized for lung endothelial-specific delivery of BOLA3 siRNA oligonucleotides in mice. Overexpression of pulmonary vascular BOLA3 was performed by orotracheal transgene delivery of adenoassociated virus in mouse models of PH. Results-In cultured hypoxic PAECs as well as lung from human Group 1 and 3 PH patients as well as multiple rodent models of PH, endothelial BOLA3 expression was down-regulated, which involved HIF-2α-dependent transcriptional repression via HDAC-mediated histone deacetylation. In vitro gain and loss of function studies demonstrated that BOLA3 regulated Fe-S integrity, thus modulating lipoate-containing 2-oxoacid dehydrogenases with consequent control over glycolysis and mitochondrial respiration. In contexts of siRNA knockdown and naturally occurring human genetic mutation, cellular BOLA3 deficiency down-regulated the glycine cleavage system protein H (GCSH), thus bolstering intracellular glycine content. In the setting of these alterations of oxidative metabolism and glycine levels, BOLA3 deficiency increased endothelial proliferation, survival, and vasoconstriction, while decreasing angiogenic potential. In vivo, pharmacologic knockdown of endothelial BOLA3 and targeted overexpression of BOLA3 in mice demonstrated that BOLA3 deficiency promotes histologic and hemodynamic manifestations of PH. Notably, the therapeutic effects of BOLA3 expression were reversed by exogenous glycine supplementation. Conclusions-BOLA3 acts as a crucial lynchpin connecting Fe-S-dependent oxidative respiration and glycine homeostasis with endothelial metabolic reprogramming critical to PH pathogenesis. These results provide a molecular explanation for the clinical associations linking PH with hyperglycinemic syndromes and mitochondrial disorders. These findings also identify novel metabolic targets, including those involved in epigenetics, iron-sulfur biogenesis, and glycine biology, for diagnostic and therapeutic development. Yu et al.

Schistosomiasis Pulmonary Arterial Hypertension

“…Many studies have started to dissect the immunological events that underlie SchPH pathogenesis (1,61,87,89,92,96,97,(103)(104)(105)(106)(107)(108)(109)(110)(111)(112)(113)(114). The current understanding of the signaling events is summarized in Figure 6.…”

An Hb-mediated circulating macrophage contributing to pulmonary vascular remodeling in sickle cell disease

“…Intense immunoreactivity for ferritin-H ( Figure 5D) suggested that most Fe 3+ was likely bound in an unreactive form, leaving Hb and Fe 2+ as the primary prooxidant iron species with SCD PH lung macrophages. We further explored the localization of iron (as iron-sulfur, Fe-S) in mitochondrial ferredoxin proteins because Fe-S deficiencies have been implicated in PH (23,24). Ferredoxin reductase is shown colocalizing with mitochondria and iron, suggesting that intact Fe-S clusters in SCD PH ( Figure 5E).…”

Bola3 Regulates Beige Adipocyte Thermogenesis via Maintaining Mitochondrial Homeostasis and Lipolysis

“…The potential molecular function of BolA proteins in functional cell types, particularly Bola3, remains to be resolved. Recently, Bola3 was reported to act a connective role between Fe-S-dependent oxidative respiration and glycine homeostasis in the process of endothelial metabolic re-programming, which is critical for pulmonary hypertension pathogenesis ( 21 ). Beige adipocyte is a re-programmed type of white adipocyte upon certain stimuli, and it largely depends on mitochondrial oxidative phosphorylation to drive thermogenesis ( 22 ).…”