Unexpected regulation pattern of the IKKβ/NF-κB/MuRF1 pathway with remarkable muscle plasticity in the Daurian ground squirrel (Spermophilus dauricus).

As a typical hibernator, the Daurian ground squirrel (Spermophilus dauricus) spends considerable time in a state of reduced activity with prolonged fasting. Despite this, they experience little muscle atrophy and have thus become an interesting anti-disuse muscle atrophy model. The IKKβ/NF-κB signaling pathway is significant to muscle atrophy due to the protein degradation resulting from the upregulation of the E3 ubiquitin ligase MuRF1. The current study showed that the IKKβ/NF-κB signaling pathway and MuRF1 maintained relatively steady mRNA and protein expression levels, with little muscle atrophy observed in the soleus (slow-twitch, SOL) or extensor digitorum longus (fast-twitch, EDL) during hibernation (HIB); however, mRNA expression significantly increased in the SOL and EDL muscle during interbout arousal (IBA), as did the MuRF1 mRNA level in the SOL and MuRF1 protein level in the EDL. Interestingly, the expressions of p50 and MuRF1 significantly increased during HIB in the gastrocnemius (mixed muscle, GAS) and showed moderate atrophy, but dramatically decreased during IBA. Elevated IKKβ and p50 mRNA and protein expression in the cardiac muscle (CM) during HIB did not accompany increased MuRF1 expression or muscle wasting. Importantly, almost all increased or decreased indicators in the tested tissues recovered to pre-hibernation levels after HIB. This is the first study to report on the unexpected regulation of the IKKβ/NF-κB/MuRF1 pathway with remarkable muscle plasticity in Daurian ground squirrels during hibernation. Furthermore, we found that different types of muscles exhibited different strategies to cope with prolonged hibernation-induced disuse muscle atrophy.