Laboratory of Muscle Pathology, Fragility and Aging, Department of Biological Sciences, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile.
Millennium Institute on Immunology and Immunotherapy, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile.
Biol Res. 2023 Jun 8;56(1):30. doi: 10.1186/s40659-023-00436-3.
Skeletal muscle is sensitive to bile acids (BA) because it expresses the TGR5 receptor for BA. Cholic (CA) and deoxycholic (DCA) acids induce a sarcopenia-like phenotype through TGR5-dependent mechanisms. Besides, a mouse model of cholestasis-induced sarcopenia was characterised by increased levels of serum BA and muscle weakness, alterations that are dependent on TGR5 expression. Mitochondrial alterations, such as decreased mitochondrial potential and oxygen consumption rate (OCR), increased mitochondrial reactive oxygen species (mtROS) and unbalanced biogenesis and mitophagy, have not been studied in BA-induced sarcopenia.
We evaluated the effects of DCA and CA on mitochondrial alterations in CC myotubes and a mouse model of cholestasis-induced sarcopenia. We measured mitochondrial mass by TOM20 levels and mitochondrial DNA; ultrastructural alterations by transmission electronic microscopy; mitochondrial biogenesis by PGC-1α plasmid reporter activity and protein levels by western blot analysis; mitophagy by the co-localisation of the MitoTracker and LysoTracker fluorescent probes; mitochondrial potential by detecting the TMRE probe signal; protein levels of OXPHOS complexes and LC3B by western blot analysis; OCR by Seahorse measures; and mtROS by MitoSOX probe signals.
DCA and CA caused a reduction in mitochondrial mass and decreased mitochondrial biogenesis. Interestingly, DCA and CA increased LC3II/LC3I ratio and decreased autophagic flux concordant with raised mitophagosome-like structures. In addition, DCA and CA decreased mitochondrial potential and reduced protein levels in OXPHOS complexes I and II. The results also demonstrated that DCA and CA decreased basal, ATP-linked, FCCP-induced maximal respiration and spare OCR. DCA and CA also reduced the number of cristae. In addition, DCA and CA increased the mtROS. In mice with cholestasis-induced sarcopenia, TOM20, OXPHOS complexes I, II and III, and OCR were diminished. Interestingly, the OCR and OXPHOS complexes were correlated with muscle strength and bile acid levels.
Our results showed that DCA and CA decreased mitochondrial mass, possibly by reducing mitochondrial biogenesis, which affects mitochondrial function, thereby altering potential OCR and mtROS generation. Some mitochondrial alterations were also observed in a mouse model of cholestasis-induced sarcopenia characterised by increased levels of BA, such as DCA and CA.
骨骼肌肉对胆汁酸（BA）敏感，因为它表达 BA 的 TGR5 受体。鹅脱氧胆酸（CA）和脱氧胆酸（DCA）通过 TGR5 依赖性机制诱导肌少症样表型。此外，胆盐水解诱导的肌少症的小鼠模型的特征是血清 BA 水平升高和肌肉无力，这些改变依赖于 TGR5 的表达。线粒体改变，如线粒体电势和耗氧率（OCR）降低、线粒体活性氧物种（mtROS）增加以及生物发生和自噬失衡，尚未在 BA 诱导的肌少症中进行研究。
我们评估了 DCA 和 CA 对 CC 肌管和胆盐水解诱导的肌少症小鼠模型中线粒体改变的影响。我们通过 TOM20 水平和线粒体 DNA 测量线粒体质量；通过透射电子显微镜测量超微结构改变；通过 PGC-1α 质粒报告基因活性测量线粒体生物发生；通过 Western blot 分析测量蛋白质水平；通过 MitoTracker 和 LysoTracker 荧光探针的共定位测量噬线粒体；通过检测 TMRE 探针信号测量线粒体电势；通过 Western blot 分析测量 OXPHOS 复合物和 LC3B 的蛋白水平；通过 Seahorse 测量 OCR；通过 MitoSOX 探针信号测量 mtROS。
DCA 和 CA 导致线粒体质量减少和线粒体生物发生减少。有趣的是，DCA 和 CA 增加了 LC3II/LC3I 比值，并降低了自噬通量，与升高的噬线粒体样结构一致。此外，DCA 和 CA 降低了线粒体电势，并降低了 OXPHOS 复合物 I 和 II 的蛋白水平。结果还表明，DCA 和 CA 降低了基础、ATP 连接、FCCP 诱导的最大呼吸和备用 OCR。DCA 和 CA 还减少了嵴的数量。此外，DCA 和 CA 增加了 mtROS。在胆盐水解诱导的肌少症小鼠中，TOM20、OXPHOS 复合物 I、II 和 III 以及 OCR 减少。有趣的是，OCR 和 OXPHOS 复合物与肌肉力量和胆汁酸水平相关。
我们的结果表明，DCA 和 CA 减少了线粒体质量，可能是通过减少线粒体生物发生来实现的，这影响了线粒体功能，从而改变了潜在的 OCR 和 mtROS 的产生。在胆盐水解诱导的肌少症小鼠模型中也观察到了一些线粒体改变，其特征是 BA 水平升高，如 DCA 和 CA。
