Eccentric contraction-induced myofiber growth in tumor-bearing mice

Abstract

Cancer cachexia is characterized by the progressive loss of skeletal muscle mass. While mouse skeletal muscle's response to an acute bout of stimulated low-frequency concentric muscle contractions is disrupted by cachexia, gaps remain in our understanding of cachexia's effects on eccentric contraction-induced muscle growth. The purpose of this study was to determine whether repeated bouts of stimulated high-frequency eccentric muscle contractions [high-frequency electrical muscle stimulation (HFES)] could stimulate myofiber growth during cancer cachexia progression, and whether this training disrupted muscle signaling associated with wasting. Male Apc(Min/+) mice initiating cachexia (N = 9) performed seven bouts of HFES-induced eccentric contractions of the left tibialis anterior muscle over 2 wk. The right tibialis anterior served as the control, and mice were killed 48 h after the last stimulation. Age-matched C57BL/6 mice (N = 9) served as wild-type controls. Apc(Min/+) mice lost body weight, muscle mass, and type IIA, IIX, and IIB myofiber cross-sectional area. HFES increased myofiber cross-sectional area of all fiber types, regardless of cachexia. Cachexia increased muscle noncontractile tissue, which was attenuated by HFES. Cachexia decreased the percentage of high succinate dehydrogenase activity myofibers, which was increased by HFES, regardless of cachexia. While cachexia activated AMP kinase, STAT3, and ERK1/2 signaling, HFES decreased AMP kinase phosphorylation, independent of the suppression of STAT3. These results demonstrate that cachectic skeletal muscle can initiate a growth response to repeated eccentric muscle contractions, despite the presence of a systemic cachectic environment.

Keywords: cancer cachexia; eccentric contractions; high-frequency electrical stimulation; muscle inflammation; myofiber growth.

Fig. 1.

Effects of multiple bouts of high-frequency electrical stimulation (HFES) on circulating interleukin (IL)-6 in C57BL/6 and Apc^Min/+ mice. A: experimental design. At 16 wk of age, male C57BL/6 and Apc^Min/+ mice performed multiple bouts of HFES. Each stimulation procedure was separated by 48 h, and mice were killed 48 h after the last stimulation. Mice were fasted 5 h before death. B: plasma IL-6 levels pre- and posttraining. Values are means ± SE. Statistical significance was set at P < 0.05: difference between *C57BL/6 and Apc^Min/+ mice, and ‡pre- and posttraining. ND, not detectable.

Fig. 2.

Effects of HFES on tibialis anterior (TA) myosin heavy chain type IIB (A), IIX (B), and IIA (C) myofiber cross-sectional area (CSA) in C57BL/6 and Apc^Min/+ mice. All analysis was performed in the TA muscle. CSA values are means ± SE. Statistical significance was set at P < 0.05: main effect of &HFES and #Apc^Min/+ mice.

Fig. 3.

Effects of HFES on TA muscle extracellular matrix remodeling, regeneration, and myofiber oxidative capacity in C57BL/6 and Apc^Min/+ mice. A: representative images of hematoxylin- and eosin-stained TA muscle cross sections. Scale bar, 50 μm. The percentage of noncontractile tissue (B), centralized nuclei (C), and high succinate dehydrogenase (SDH) enzyme activity myofibers (D) in C57BL/6 and Apc^Min/+ mice is shown. All analysis was performed in the TA muscle. Values are means ± SE. Statistical significance was set at P < 0.05: †difference between all groups; ‡difference between all groups; &main effect of HFES; and #main effect of Apc^Min/+ mice.

Fig. 4.

Effects of HFES on TA muscle cachectic signaling in Apc^Min/+ mice. A: representative Western blot (right) and quantification of the ratio (left) of phosphorylated (p) and total forms of NF-κB, signal transducer and activator of transcription 3 (STAT3), 5′-adenosine monophosphate-activated protein kinase (AMPK), and extracellular signal-regulated kinase-1/2 (ERK1/2), and total atrogin-1 protein expression in the nonstimulated control leg of C57BL/6 and Apc^Min/+ mice. Samples from the nonstimulated control leg of C57BL/6 and Apc^Min/+ mice were run on the same gel. Data are normalized to the nonstimulated control leg of C57BL/6 mice. Values are means ± SE. Statistical significance was set at P < 0.05. *difference between C57BL/6 and Apc^Min/+ mice. B: representative Western blot (right) and quantification of the ratio (left) of phosphorylated and total forms of NF-κB, STAT3, AMPK and ERK1/2, and total atrogin-1 protein expression in the nonstimulated control leg and HFES leg of Apc^Min/+ mice. Samples from the nonstimulated control leg and HFES leg of Apc^Min/+ mice were run on the same gel. Data are normalized to the nonstimulated control leg of Apc^Min/+ mice. All analysis was performed in the TA muscle. Values are means ± SE. Statistical significance was set at P < 0.05: *difference between nonstimulated control leg and HFES leg. IOD, integrated optical density.