Muscle-specific activation of calpain system in hindlimb unloading rats and hibernating Daurian ground squirrels: a comparison between artificial and natural disuse

Abstract

To determine whether the regulation of calpain system is involved in non-hibernators and hibernators in disused condition, the soleus (SOL) and extensor digitorum longus (EDL) muscles were used for investigating the muscle mass, the ratio of muscle wet weight/body weight (MWW/BW), fiber-type distribution, fiber cross-sectional area (CSA), and the protein expression of MuRF1, calpain-1, calpain-2, calpastatin, desmin, troponin T, and troponin C in hindlimb unloading rats and hibernating Daurian ground squirrels. The muscle mass, MWW/BW, and fiber CSA were found significantly decreased in SOL and EDL of hindlimb unloading rats, but unchanged in hibernating ground squirrels. The MuRF1 expression was increased in both SOL and EDL of unloading rats, while it was only increased in SOL, but maintained in EDL of hibernating ground squirrels. The expression levels of calpain-1 and calpain-2 were increased in different degrees in unloaded SOL and EDL in rats, while they were maintained in EDL and even reduced in SOL of hibernating ground squirrels. Besides, the expression of calpastatin was decreased in unloaded rats, but increased in hibernating ground squirrels. The desmin expression was decreased in unloaded rats, but maintained in hibernating squirrels. Interestingly, the levels of troponin T and troponin C were decreased in both SOL and EDL of unloaded rats, but increased in hibernating ground squirrels with muscle-type specificity. In conclusion, differential calpain activation and substrate-selective degradation in slow and fast muscles are involved in the mechanisms of muscle atrophy of unloaded rats and remarkable ability of muscle maintenance of hibernating ground squirrels.

Partial Weight-Bearing in Female Rats: Proof of Concept in a Martian-Gravity Analog

“…While PWB led to a transient body weight loss in male rats (Mortreux et al, 2018(Mortreux et al, , 2019a,c), we did not observe any significant fluctuations of the females' body weight, either compared to the control group or to their pre-suspension baseline. This sex-based difference has been reported previously after exposure to 14 and 30 days of hindlimb unloading (Il'ina-Kakueva, 2002;David et al, 2006;Chang et al, 2018;Deschenes et al, 2018), and in our study, was further associated with a similar food intake, which was eventually greater at the end of the experiment in the PWB40 group when normalized to animals' body weight, compared to the PWB100 controls.…”

“…In our pilot study, females exposed to 14 days of PWB40 did not exhibit a decreased soleus mass; however, we were able to detect a significant atrophy of the type I myofibers, which was not associated with a myofiber type switch throughout the muscle (Figure 3D). The absence of fiber-type switch has previously been described in female rats (Il'ina-Kakueva, 2002;Deschenes et al, 2018), though others have not identified this (Chang et al, 2018). Taken together, our analysis of the soleus muscle allows us to hypothesize that in females, preferential myofiber atrophy occurs prior to myofiber-type switch and gross muscle atrophy, however, it remains to be confirmed in longer experiments.…”

Differential protein metabolism and regeneration in hypertrophic diaphragm and atrophic gastrocnemius muscles in hibernating Daurian ground squirrels

“…The muscle fiber cross-sectional area (CSA) and fiber type composition were measured by 191 immunofluorescent analysis as described by our laboratory previously (Chang et al 2018b). Briefly, 192 5 mm of the mid-belly of lateral gastrocnemius muscle was cut into 10-μm thick frozen muscle 193 cross-sections at -20℃ with a cryostat (Leica, Wetzlar, CM1850, Germany).…”

“…Daurian ground squirrels during hibernation, whereas the expression of calpastatin, an endogenous 121 inhibitor of calpains, is increased in both (Chang et al 2018b). Calpain can degrade substrates such 122 as desmin, troponin T, troponin I, titin, alpha-fodrin and alpha-actinin, (Barta et al 2005).…”

Predominant synthesis of giant myofibrillar proteins in striated muscles of the long-tailed ground squirrel Urocitellus undulatus during interbout arousal

“…Molecular mechanisms lying at the core of muscle mass retention in hibernators have been broadly discussed recently 23,[28][29][30][31][32][33][34][35][36][37][38] . Various mechanisms are suggested to be responsible both for the decrease of atrophy development during torpor and for the activation of protein synthesis and muscle mass retention during arousals.…”