Fig 2: Summary of the mitochondrial alterations observed in early breast cancer patients undergoing chemotherapy. Through the analysis of vastus lateralis muscle biopsies taken before (pre) and after (post) breast cancer chemotherapy (CT), we identified an increased mitochondrial loss (grey box) that may be explained by a decrease in PGC‐1α1 protein levels, reflecting a reduced mitochondrial biogenesis process (in blue). Mitochondrial dynamics (in red) were also impaired, as evidenced by a dysregulation in the fusion process, mediated by a decrease in the mitochondrial outer membrane fusion marker MFN2, without any change in MFN1 and OPA1. No change was observed in fission markers (Fis1 and DRP1), indicating a dysregulation in the mitochondrial fusion/fission balance. These alterations are likely leading to the accumulation of fragmented and damaged mitochondria (rose‐coloured mitochondria), corroborated by the accumulation of S3‐OPA1 isoform. As a consequence, fragmented and damaged mitochondria accumulate in skeletal muscle and produce excessive amounts of reactive oxygen species such as H2O2 (in orange). As mentioned above, we found no change in mitochondrial fission, a prerequisite step for the activation of mitophagy. Despite the absence of change in the expression of different mitophagy markers (Parkin, PINK1, and Mul1; in green), two contradictory hypotheses arise from these results: defective mitophagy (Hypothesis 1) or a relative increase in mitophagy (increased mitophagic potential reflected by the Parkin/VDAC ratio; Hypothesis 2). Antioxidant enzyme (in orange), lipid peroxidation (in brown), and carbonylated protein levels (in yellow) were unchanged. However, we found a large increase in Bax protein levels, a proapoptotic protein that initiates apoptosis, and no change was observed for Bcl‐2, its antiapoptotic counterpart (in black). While several pre‐clinical studies found increased levels in the active (cleaved)‐caspase 3/pro‐caspase 3 ratio, the slight increase observed in our study did not reach significance (in black dotted line).

Fig 3: SIAH1 played an essential role in PINK1-mediated mitophagy.a PRKN protein levels in different HCC cells were analyzed by Western blotting. SH-SY5Y cells were used as the positive controls for PRKN expression. b–d Huh7 cells were transfected with siRNA targeting SIAH1 (b), MUL1 (c), or STUB1 (d) before treatment with sorafenib (5 μM) for 24 h. ###P < 0.001. e SIAH1-silenced Huh7 cells were treated with sorafenib (5 μM) for 20 h, and then, the protein levels were measured by western blotting. f After treatment with sorafenib for the indicated times, mtDNA was measured, and the results are shown in Fig. 4f, and the fluorescence intensities were analyzed, and the results are summarized in the lower panel, #P < 0.05.