Global mitophagy inhibition via BNIP3 ablation is not sufficient to alleviate skeletal muscle impairments in male and female tumor-bearing mice.

Abstract

Cancer cachexia (CC) is marked by severe skeletal muscle loss and dysfunction, associated with mitochondrial degeneration. Our previous studies showed induction of the mitophagy marker BNIP3 3-wk post-Lewis lung carcinoma (LLC) induction. We hypothesize that excessive mitophagy contributes to muscle wasting in CC. To test this, we used a Bnip3 knockout (KO) mouse model with LLC-induced CC to assess its impact on muscle outcomes. Eight-wk-old male and female mice were injected with 1 × 10⁶ LLC cells or PBS (sham controls). After 4 wk, we assessed muscle function through dorsiflexor electrophysiology, muscle protein synthesis via deuterium oxide labeling, and mitochondrial respiration. Plantaris and white gastrocnemius muscles were analyzed for mitochondrial respiratory function, tibialis anterior (TA) for muscle cross-sectional area, and mixed gastrocnemius for protein and mRNA analysis. Bnip3 KO showed some benefits in males, including attenuated fat loss and splenomegaly and near-significant attenuation of extensor digitorum longus (EDL) mass loss. In females, Bnip3 KO did not prevent relative muscle atrophy or functional impairments. In males, KO lowered protein synthesis independent of cancer. Despite KO reducing mitophagy markers, it did not improve muscle mitochondrial respiration or functional outcomes. In both sexes, KO mice exhibited unbalanced mitochondrial dynamics with increased fission and reduced fusion, processes also impaired by LLC. Overall, global Bnip3 ablation may not offer significant benefits for CC by itself. These findings suggest that targeting aberrant mitophagy via complete Bnip3 deletion is insufficient to alleviate cancer-induced muscle detriments in both biological sexes, whereas BNIP3-mediated mitophagy may be needed to maintain protein anabolism.NEW & NOTEWORTHY Global Bnip3 KO alleviates loss of fat mass and splenomegaly in LLC-bearing male and female mice. Bnip3 deletion is insufficient to attenuate relative muscle loss. BNIP3 appears essential for normal muscle protein anabolism and contractile function in males but not females, regardless of the tumor-bearing state.