Key result
Hibernation in bears was associated with a 2.1-3.4-fold decrease in T2 fragments of titin in skeletal muscles and an increase in the stiffer N2B titin isoform in the left ventricle.
Hibernation in bears induces specific adaptations in striated muscle protein isoforms, including an increase in the stiffer N2B titin isoform in the left ventricle.
Suggests protein preservation mechanisms during atrophy in hibernators; leaves open applications to preventing cardiac or skeletal muscle loss in humans.
Seasonal changes in the isoform composition of thick and thin filament proteins (titin, myosin heavy chains (MyHCs), nebulin), as well as in the phosphorylation level of titin in striated muscles of brown bear (Ursus arctos) and hibernating Himalayan black bear (Ursus thibetanus ussuricus) were studied. We found that the changes that lead to skeletal muscle atrophy in bears during hibernation are not accompanied by a decrease in the content of nebulin and intact titin-1 (T1) isoforms. However, a decrease (2.1-3.4-fold) in the content of T2 fragments of titin was observed in bear skeletal muscles (m. gastrocnemius, m. longissimus dorsi, m. biceps) during hibernation. The content of the stiffer N2B titin isoform was observed to increase relative to the content of its more compliant N2BA isoform in the left ventricles of hibernating bears. At the same time, in spite of the absence of decrease in the total content of T1 in the myocardium of hibernating brown bear, the content of T2 fragments decreased ~1.6-fold. The level of titin phosphorylation only slightly increased in the cardiac muscle of hibernating brown bear. In the skeletal muscles of brown bear, the level of titin phosphorylation did not vary between seasons. However, changes in the composition of MyHCs aimed at increasing the content of slow (I) and decreasing the content of fast (IIa) isoforms of this protein during hibernation of brown bear were detected. Content of MyHCs I and IIa in the skeletal muscles of hibernating Himalayan black bear corresponded to that in the skeletal muscles of hibernating brown bear.
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Salmov et al. (2015) studied Hibernation in bears. Hibernation vs. Non-hibernating season was evaluated on Isoform composition of giant proteins and titin phosphorylation. Hibernation in bears was associated with a 2.1-3.4-fold decrease in T2 fragments of titin in skeletal muscles and an increase in the stiffer N2B titin isoform in the left ventricle.
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