The mitochondrial-targeted antioxidant SkQ1 prevents mitochondrial-linked apoptosis but not necroptosis or skeletal muscle atrophy in ovarian cancer
The degree to which mitochondrial-linked cell death pathways contribute to skeletal muscle atrophy during cancer remain unknown. Here, we combined a novel and robust mouse model of metastatic ovarian cancer with chronic administration of the mitochondrial-targeted antioxidant SkQ1 to determine the time-dependent and muscle-specific relationships of mitochondrial-linked apoptosis and necroptosis to the development of muscle atrophy in the type II B-rich gastrocnemius. Early-stage ovarian cancer reduced type II B fibre cross-sectional area in the gastrocnemius but did not alter mitochondrial H2O2 emission despite increased activities of mitochondrial-linked caspase-9 and-3 regulators of apoptosis. During late-stage ovarian cancer, sustained atrophy was associated with increased mitochondrial H2O2 emission potential in vitro, a greater probability of calcium-triggered mitochondrial permeability transition and increases in downstream caspase-9 and -3 activity. SkQ1 attenuated mitochondrial H2O2 emission and caspase-9 and -3 activity in late-stage ovarian cancer but did not prevent atrophy. Necroptosis markers were heterogeneous across time with total RIPK1 increasing during early-stage cancer which reverted to normal levels by late-stages while phosphorylated RIPK3 decreased below control levels. These discoveries indicate that preventing increases in mitochondrial-linked apoptotic caspase-9 and -3 activity during late-stage ovarian cancer with SkQ1 does not prevent atrophy of type II B fibres. Furthermore, necroptotic markers are inconclusive during cancer in this muscle type but are not modified by SkQ1. These results do not support a causal relationship between mitochondrial H2O2-linked apoptosis or necroptosis and atrophy in type II B fibres during ovarian cancer but do not rule out potential relationships in other muscle types. Key PointsO_LICancer increases mitochondrial reactive oxygen species (ROS) in skeletal muscle during atrophy, but the role of ROS in regulating cell death remains unknown. C_LIO_LIWe show that attenuating gastrocnemius mitochondrial ROS with the mitochondrial-targeted antioxidant SkQ1 prevented mitochondrial-linked pro-apoptotic caspase 9- and 3-activities but did not affect markers of necroptosis in a mouse model of ovarian cancer. C_LIO_LIReductions in gastrocnemius muscle fibre cross-sectional areas and the wet weights of several muscles were not prevented by SkQ1. C_LIO_LIThese findings demonstrate that mitochondrial ROS regulate apoptotic caspases but not necroptosis, and neither pathway is linked to gastrocnemius atrophy in mice with ovarian cancer. C_LIO_LIThe degree to which mitochondrial ROS-linked cell death pathways regulate muscle mass in other muscle types and cancer models requires further investigation. C_LI