Role of mitophagy in pancreatic cancer cachexia-induced muscle atrophy

To explore the role of mitophagy in pancreatic cancer cachexia-induced muscle atrophy and its underlying mechanism.

Six male C57BL/6J mice (8 weeks old, weighing 20~30 g) were equally and randomly divided into a control group (intrapancreatic injection of normal saline) and a cachexia group (orthotopic pancreatic injection of KPC1199 cells). After successful model establishment, gastrocnemius muscles were harvested for transmission electron microscopy (TEM) to assess mitochondrial ultrastructure. Western blotting was performed to quantify mitochondrial respiratory chain complexes (Ⅰ ~ Ⅳ) and autophagy-related proteins, while immunofluorescence staining was conducted to evaluate mitochondrial-lysosomal colocalization. In in vitro experiments, C2C12 myoblasts were differentiated into myotubes, and then divided into a control group (standard culture) and a cachexia group (co-cultured with KPC1199 cells for 48 h using transwell chambers). Mitochondrial-lysosomal colocalization and autophagy-related protein expression were analyzed with immunofluorescence assay and Western blotting. The mitochondrial division inhibitor Mdivi-1 (20 μmol/L) was added to the co-culture system to assess its myotube diameter.

Compared to the control mice, the cachectic mice exhibited mitochondrial swelling, reduced cristae density, and significantly increased mitochondrial-lysosomal colocalization in gastrocnemius muscle (P<0.05). Western blotting revealed the expression levels of mitochondrial respiratory chain proteins complex Ⅰ (1.00±0.04 vs 0.51±0.04, P<0.05), complex Ⅱ (1.00±0.13 vs 0.73±0.15, P<0.05), complex Ⅲ (1.00±0.20 vs 0.64±0.01, P<0.05), complex Ⅳ (1.00±0.06 vs 0.65±0.02, P<0.05) and PGC1α (1.00±0.03 vs 0.62±0.06, P<0.05) were decreased, and the levels of mitophagy markers, LC3-Ⅰ/Ⅱ (1.00±0.14 vs 1.65±0.25, P<0.05), PINK1 (1.00±0.11 vs 1.51±0.05, P<0.05), and BNIP3 (1.00±0.22 vs 2.02±0.10, P<0.05) were elevated when compared to the control. In the C2C12 myotube model, tumor cell co-culture increased mitochondrial-lysosomal colocalization and upregulated mitophagy-related protein expression (P<0.05), consistent with the in vivo findings. Mdivi-1 treatment increased myotube diameter from 220.6±35.5 μm to 315.0±39.1 μm (R²=0.6665, P<0.05).

Mitophagy is activated in pancreatic cancer cachexia-induced muscle atrophy. Inhibiting mitophagy can effectively alleviate muscle atrophy induced by pancreatic cancer cachexia.