Biology subjects

Choo, H. J.

Publications and source records attributed to Choo, H. J..

3 recordsLinked to original sources

bioRxiv2025

Neat1 alleviates ischemic injury in skeletal muscles

Peripheral artery disease (PAD) has historically been regarded as an age-related vascular disorder; however, recent attention has shifted toward the myopathic components of the disease. Conventional interventions, such as revascularization, have had limited success in reversing muscle pathology or preventing adverse outcomes like amputation. Hypoxia-inducible factors (HIFs) are key regulators of cellular responses to ischemia, including the promotion of angiogenesis and glycolysis. While pharmacological stabilization of HIF proteins represents a promising therapeutic strategy, its efficacy is diminished in aged muscles due to their intrinsically low basal HIF expression. We hypothesized that long noncoding RNAs (lncRNAs) might enhance the hypoxic response in aged muscle through post-transcriptional regulation of HIF expression. Our study identified a long noncoding RNA Neat1, as a critical mediator of the hypoxia-induced stress response, including upregulation of Hif1. In a murine hindlimb ischemia model, Neat1 knockout mice exhibited extensive necrosis following femoral artery ligation, whereas Neat1 overexpression conferred protection against ischemic injury. Mechanistically, we found that Neat1 regulates the stability of Hif1a mRNA, as Hif1a transcript levels were significantly reduced in Neat1-deficient muscle cells. Importantly, aged muscles displayed a blunted hypoxic response due to diminished Hif1a expression--an effect that was reversed through Neat1 overexpression, resulting in improved resistance to ischemic damage. In summary, our findings highlight Neat1 as a novel regulator of muscle adaptation to hypoxia in aging. Enhancing Neat1 expression may represent a promising therapeutic strategy for improving ischemic outcomes in patients with peripheral artery disease.

cell biology↗

bioRxiv2020

Defective Trafficking of Annexins to the Site of Injury in ANO5-Knockout Muscle Fibers

Mutations in ANO5 (TMEM16E) cause limb-girdle muscular dystrophy R12 (limb-girdle muscular dystrophy type 2L). Recent evidence implicates defective plasma membrane repair as a likely mechanism for the disorder. Here, we probe the ANO5-dependency of the membrane repair pathway using a laser wounding assay in Ano5 knockout mouse muscle fibers. Wounded myofibers from Ano5 knockout mice exhibit delayed membrane resealing relative to wild type fibers as revealed by an increased uptake of the membrane-impermeant FM1-43 dye and a prolonged elevation of intracellular Ca2+. The trafficking of several annexin proteins, which together form a cap at the site of injury, is altered in Ano5 knockout fibers. Annexin A2 accumulates at the wound to nearly twice the level observed in WT fibers, while annexin A6 accumulation is substantially inhibited in the absence of ANO5. Furthermore, trafficking of annexins A1 and A5 to the cap is decreased in the Ano5 knockout. These changes are correlated with an alteration in the fine structure of the annexin repair cap and the shedding of annexin-positive extracellular vesicles. Our results suggest that the meticulous coordination of the annexin repair machinery required to effectively reseal wounded sarcolemma is disrupted in Ano5 knockout mice. ANO5 is a putative phospholipid scramblase, responsible for exposure of intracellular phospholipids to the extracellular leaflet of the plasma membrane. However, because the membrane repair defect is rescued by overexpression of wild type ANO5 or a scramblase-defective mutant, we suggest that ANO5-mediated phospholipid scrambling is not essential for membrane repair. Significance StatementMutations in ANO5/TMEM16E cause myopathies of variable severity, with some patients losing ambulation entirely. Unfortunately, relatively little is known about the function of ANO5 at the protein level, but it has been suggested that ANO5 plays a role in the repair of injured muscle plasma membranes. Here, we investigate the mechanism of ANO5-mediated repair and find that annexin proteins, which in normal muscle form a cap to seal wounds, traffic abnormally to the cap when ANO5 is not expressed. Muscle fibers lacking ANO5 reseal more slowly and thus are exposed to prolonged intracellular calcium elevation that can damage the fibers. Our findings contribute to the growing literature implicating failed repair as a probable pathogenic mechanism in patients with ANO5 mutations.

cell biology↗

bioRxiv2020

Intrinsic and extrinsic factors collaborate to activate pharyngeal satellite cells without muscle injury

Satellite cells (SCs), adult muscle stem cells in craniofacial muscles proliferate and differentiate/fuse without injury, unlike quiescent SCs in uninjured limb muscle. However, whether intrinsic or extrinsic factors driving their increased basal activity are largely unknown. We compared SCs from the pharynx, which contains constrictor muscles critical for swallowing, to SCs from limb muscle. Pharyngeal SCs are intrinsically more proliferative and contain higher mitochondrial content relative to limb SCs. Pharyngeal SCs occupy less quiescent microenvironments containing collagen V and pharyngeal muscles provide a distinctive SC niche enriched with neighboring resident macrophages and fibroadipogenic progenitors. Loss of SCs impacts pharyngeal myofiber cross-sectional area and the number of neighboring cells, suggesting that SCs are required to maintain pharyngeal muscle homeostasis and its unique niche. Taken together, this study gives new insights to explain the distinctive SC activity of craniofacial muscles, which may explain their unique susceptibility to various muscular dystrophies.

cell biology↗