Cancer cachexia decreases specific force and accelerates fatigue in limb muscle

Abstract

Cancer cachexia is a complex metabolic syndrome that is characterized by the loss of skeletal muscle mass and weakness, which compromises physical function, reduces quality of life, and ultimately can lead to mortality. Experimental models of cancer cachexia have recapitulated this skeletal muscle atrophy and consequent decline in muscle force generating capacity. However, more recently, we provided evidence that during severe cancer cachexia muscle weakness in the diaphragm muscle cannot be entirely accounted for by the muscle atrophy. This indicates that muscle weakness is not just a consequence of muscle atrophy but that there is also significant contractile dysfunction. The current study aimed to determine whether contractile dysfunction is also present in limb muscles during severe Colon-26 (C26) carcinoma cachexia by studying the glycolytic extensor digitorum longus (EDL) muscle and the oxidative soleus muscle, which has an activity pattern that more closely resembles the diaphragm. Severe C-26 cancer cachexia caused significant muscle fiber atrophy and a reduction in maximum absolute force in both the EDL and soleus muscles. However, normalization to muscle cross sectional area further demonstrated a 13% decrease in maximum isometric specific force in the EDL and an even greater decrease (17%) in maximum isometric specific force in the soleus. Time to peak tension and half relaxation time were also significantly slowed in both the EDL and the solei from C-26 mice compared to controls. Since, in addition to postural control, the oxidative soleus is also important for normal locomotion, we further performed a fatigue trial in the soleus and found that the decrease in relative force was greater and more rapid in solei from C-26 mice compared to controls. These data demonstrate that severe cancer cachexia causes profound muscle weakness that is not entirely explained by the muscle atrophy. In addition, cancer cachexia decreases the fatigue resistance of the soleus muscle, a postural muscle typically resistant to fatigue. Thus, specifically targeting contractile dysfunction represents an additional means to counter muscle weakness in cancer cachexia, in addition to targeting the prevention of muscle atrophy.

Figure 1. Soleus contractile properties and fiber size in control and C-26

A) The absolute force-frequency relationship, B) maximal tetanic force, C) specific force-frequency relationship, D) maximum specific force, E) time to peak twitch tension , F) one half twitch relaxation time, G) relative force (in percent of initial force) during fatigue protocol, and H) percent of initial force at select time-points. I) Representative images taken from cross sections of the soleus in control and C-26 mice. Sections were incubated with an anti-laminin antibody to allow for visualization of muscle fibers (red), and anti-myosin heavy chain (MHC) Type I (blue) and anti-MHC Type IIa (green) antibodies. Black fibers represent Type IIb/x fibers. The cross sectional area (CSA) of each muscle fiber type was measured and the mean CSA of each fiber type shown in (J). K) Percentage of each soleus muscle fiber type in control and C-26 mice. Each bar represents the mean ± SE for 6 muscles per group. *Significantly different from control (P<0.05).

Figure 2. Extensor Digitorum Longus contractile properties and fiber size in control and C-26 tumor bearing mice

A) The absolute force-frequency relationship, B) maximal tetanic force, C) specific force-frequency relationship, D) maximum specific force, E) time to peak twitch tension and, F) one half twitch relaxation time of the EDL from control and ∼26 day C-26 tumor bearing mice. G) Representative cross sections taken from the EDL of control and C-26 mice. Sections were incubated with an anti-laminin antibody to allow for visualization of muscle fibers (red), and anti-myosin heavy chain (MHC) Type I (blue, but no Type I fibers were detected) and anti-MHC Type IIa (green) antibodies. Black fibers represent Type IIb/x fibers. The cross sectional area (CSA) of each muscle fiber type was measured and the mean CSA of each fiber type shown in (H). I) Percentage of each EDL muscle fiber type in control and C-26 mice. Each bar represents the mean ± SE for 6 muscles per group. *Significantly different from control (P<0.05).