Iron-sulfur (Fe–S) clusters are essential cofactors most commonly known for their role mediating electron transfer within the mitochondrial respiratory chain. The Fe–S cluster pathways that function within the respiratory complexes are highly conserved between bacteria and the mitochondria of eukaryotic cells. Within the electron transport chain, Fe–S clusters play a critical role in transporting electrons through Complexes I, II and III to cytochrome c, before subsequent transfer to molecular oxygen. Fe–S clusters are also among the binding sites of classical mitochondrial inhibitors, such as rotenone, and play an important role in the production of mitochondrial reactive oxygen species (ROS). Mitochondrial Fe–S clusters also play a critical role in the pathogenesis of disease. High levels of ROS produced at these sites can cause cell injury or death, however, when produced at low levels can serve as signaling molecules. For example, Ndufs2, a Complex I subunit containing an Fe–S center, N2, has recently been identified as a redox-sensitive oxygen sensor, mediating homeostatic oxygen-sensing in the pulmonary vasculature and carotid body. Fe–S clusters are emerging as transcriptionally-regulated mediators in disease and play a crucial role in normal physiology, offering potential new therapeutic targets for diseases including malaria, diabetes, and cancer.

Rationale: Pulmonary arterial hypertension (PAH) is an obstructive vasculopathy characterized by excessive pulmonary artery smooth muscle cell (PASMC) proliferation, migration, and apoptosis resistance. This cancer-like phenotype is promoted by increased cytosolic calcium ([Ca²⁺]_cyto), aerobic glycolysis, and mitochondrial fission. Objectives: To determine how changes in mitochondrial calcium uniporter (MCU) complex (MCUC) function influence mitochondrial dynamics and contribute to PAH’s cancer-like phenotype. Methods: PASMCs were isolated from patients with PAH and healthy control subjects and assessed for expression of MCUC subunits. Manipulation of the pore-forming subunit, MCU, in PASMCs was achieved through small interfering RNA knockdown or MCU plasmid-mediated up-regulation, as well as through modulation of the upstream microRNAs (miRs) miR-138 and miR-25. In vivo, nebulized anti-miRs were administered to rats with monocrotaline-induced PAH. Measurements and Main Results: Impaired MCUC function, resulting from down-regulation of MCU and up-regulation of an inhibitory subunit, mitochondrial calcium uptake protein 1, is central to PAH’s pathogenesis. MCUC dysfunction decreases intramitochondrial calcium ([Ca²⁺]_mito), inhibiting pyruvate dehydrogenase activity and glucose oxidation, while increasing [Ca²⁺]_cyto, promoting proliferation, migration, and fission. In PAH PASMCs, increasing MCU decreases cell migration, proliferation, and apoptosis resistance by lowering [Ca²⁺]_cyto, raising [Ca²⁺]_mito, and inhibiting fission. In normal PASMCs, MCUC inhibition recapitulates the PAH phenotype. In PAH, elevated miRs (notably miR-138) down-regulate MCU directly and also by decreasing MCU’s transcriptional regulator cAMP response element–binding protein 1. Nebulized anti-miRs against miR-25 and miR-138 restore MCU expression, reduce cell proliferation, and regress established PAH in the monocrotaline model. Conclusions: These results highlight miR-mediated MCUC dysfunction as a unifying mechanism in PAH that can be therapeutically targeted.

Background: Mitotic fission is increased in pulmonary arterial hypertension (PAH), a hyperproliferative, apoptosis-resistant disease. The fission mediator dynamin-related protein 1 (Drp1) must complex with adaptor proteins to cause fission. Drp1-induced fission has been therapeutically targeted in experimental PAH. Here, we examine the role of 2 recently discovered, poorly understood Drp1 adapter proteins, mitochondrial dynamics protein of 49 and 51 kDa (MiD49 and MiD51), in normal vascular cells and explore their dysregulation in PAH. Methods: Immunoblots of pulmonary artery smooth muscle cells (control, n=6; PAH, n=8) and immunohistochemistry of lung sections (control, n=6; PAH, n=6) were used to assess the expression of MiD49 and MiD51. The effects of manipulating MiDs on cell proliferation, cell cycle, and apoptosis were assessed in human and rodent PAH pulmonary artery smooth muscle cells with flow cytometry. Mitochondrial fission was studied by confocal imaging. A microRNA (miR) involved in the regulation of MiD expression was identified using microarray techniques and in silico analyses. The expression of circulatory miR was assessed with quantitative reverse transcription–polymerase chain reaction in healthy volunteers (HVs) versus patients with PAH from Sheffield, UK (plasma: HV, n=29, PAH, n=27; whole blood: HV, n=11, PAH, n=14) and then confirmed in a cohort from Beijing, China (plasma: HV, n=19, PAH, n=36; whole blood: HV, n=20, PAH, n=39). This work was replicated in monocrotaline and Sugen 5416-hypoxia, preclinical PAH models. Small interfering RNAs targeting MiDs or an miR mimic were nebulized to rats with monocrotaline-induced PAH (n=4–10). Results: MiD expression is increased in PAH pulmonary artery smooth muscle cells, which accelerates Drp1-mediated mitotic fission, increases cell proliferation, and decreases apoptosis. Silencing MiDs (but not other Drp1 binding partners, fission 1 or mitochondrial fission factor) promotes mitochondrial fusion and causes G1-phase cell cycle arrest through extracellular signal-regulated kinases 1/2– and cyclin-dependent kinase 4–dependent mechanisms. Augmenting MiDs in normal cells causes fission and recapitulates the PAH phenotype. MiD upregulation results from decreased miR-34a-3p expression. Circulatory miR-34a-3p expression is decreased in both patients with PAH and preclinical models of PAH. Silencing MiDs or augmenting miR-34a-3p regresses experimental PAH. Conclusions: In health, MiDs regulate Drp1-mediated fission, whereas in disease, epigenetic upregulation of MiDs increases mitotic fission, which drives pathological proliferation and apoptosis resistance. The miR-34a-3p-MiD pathway offers new therapeutic targets for PAH.

Introduction: Metabolic Dysfunction‐Associated Steatotic Liver Disease (MASLD) has emerged as the most prevalent chronic liver disease worldwide, affecting ~25%–30% of the adult population, with higher prevalence observed in individuals with obesity and type 2 diabetes. Among reported MASLD cases, prevalence is consistently higher in men than in women, and global incidence has risen by ~50% over the past two decades, mirroring the global rise in obesity and metabolic syndrome. MASLD encompasses a spectrum of hepatic pathologies ranging from simple steatosis to steatohepatitis, fibrosis and cirrhosis. Despite its high prevalence, the heterogeneity in disease progression and relative absence of approved pharmacological therapies pose challenges for effective clinical management. Methods and Results: This review synthesises current literature on MASLD across epidemiology, pathophysiology, clinical presentation and treatment. Key molecular mechanisms, including lipid metabolism dysregulation, insulin resistance and mitochondrial dysfunction, are examined with a focus on understanding the basis for progression to metabolic dysfunction‐associated steatohepatitis (MASH). Clinical manifestations, diagnostic tools and risk stratification systems for MASLD are summarised. Current and emerging therapies such as lifestyle interventions, pharmacological agents and microbiome‐targeted strategies are reviewed. The review also highlights ongoing challenges, including diagnostic limitations, disease heterogeneity and disparities in care. Conclusion: MASLD is a complex, multifactorial liver disease with a growing public health impact, driven by the rising prevalence of metabolic syndrome. Mitochondrial dysfunction is a critical nexus linking genetic susceptibility to metabolic stress and inflammatory responses. Preclinical models that capture these mitochondrial contributions are vital for therapeutic discovery and for advancing personalised medicine approaches in MASLD care.