Cancer-induced Changes In Endoplasmic Stress And Autophagy Responses After Mechanical Overload In ApcMin/+ Mice

Abstract

Cancer cachexia is characterized by the severe weight and muscle loss. The endoplasmic reticulum (ER) stress and autophagy perpetuate skeletal muscle homeostasis. Tumor cells elicit ER stress and unfolded protein response (UPR) in skeletal muscle. The inhibition of ER stress also activates protein degradation and autophagy, which magnifies muscle mass declination. While UPR moderates mechanical stress, the adaptations in UPR and autophagy in cancer cachexia are unknown. PURPOSE: To determine whether tumor burden alters UPR and autophagy responses to mechanical overload in mice. METHODS: Age-matched male wild-type (WT, n = 5) and ApcMin/+ (Min, n = 5) mice were utilized. Synergist ablation (SA) was performed on the left leg, while the right leg served as an internal control. Seven days after mechanical overload, the plantaris muscles were removed. After tissue homogenization, routine Western blotting was conducted using 80 ~ 120 μg of the total protein. Independent t-test (WT vs. Min) and two-way ANOVA (genotype x treatment) were used for statistical analysis. The coefficient of determination (r^2) was used to examine a significant correlation. RESULTS: Min mice showed a decrease of BW by 9.8% compared to their peak BW. Similarly, sham control plantaris weight in Min mice was smaller than that of WT mice (18.7 ± 0.6 mg vs. 15.1 ± 0.3 mg for WT and Min, respectively). In both mice, mechanical overload increased the plantaris weights, but the response was small in Min mice (43.3 ± 5.8% vs. 21.3 ± 4.6%, p ≤ 0.05). Western blot analysis resulted in Min mice having a reduced phospho-p70S6K after mechanical overload than WT mice (4.2-fold vs. 1.9-fold, p ≤ 0.05). Phosphorylated eukaryotic translation initiation factor 2α (p-eIF2α, 4.2-fold vs. 3.0-fold, p ≤ 0.05) and beclin (4.3-fold vs. 1.8-fold, p ≤ 0.05) levels were reduced in response to the stimulus in Min mice. A significant correlation was observed between p70S6K and eIF2α and between p70S6K and Beclin regardless of mouse genotype. The slopes of the regression curve in Min mice were smaller than WT mice (p ≤ 0.05). CONCLUSIONS: Reduced ER stress and autophagy responses to mechanical overload were associated with decreased mTORC1 signaling in cachectic mice. Supported by Louisiana BORSF (LEQSF(2017-20)-RD-A-22).