Abstract
Hibernating brown bears, Ursus arctos, undergo extended periods of inactivity and yet these large hibernators are resilient to muscle disuse atrophy. Physiological characteristics associated with atrophy resistance in bear muscle have been examined (e.g., muscle mechanics, neural activity) but roles for molecular signaling/regulatory mechanisms in the resistance to muscle wasting in bears still require investigation. Using quantitative reverse transcription PCR (RT-qPCR), the present study characterized the responses of 36 microRNAs linked with development, metabolism, and regeneration of skeletal muscle, in the vastus lateralis of brown bears comparing winter hibernating and summer active animals. Relative levels of mRNA of selected genes (mef2a, pax7, id2, prkaa1, and mstn) implicated upstream and downstream of the microRNAs were examined. Results indicated that hibernation elicited a myogenic microRNA, or "myomiR", response via MEF2A-mediated signaling. Upregulation of MEF2A-controlled miR-1 and miR-206 and respective downregulation of pax7 and id2 mRNA are suggestive of responses that promote skeletal muscle maintenance. Increased levels of metabolic microRNAs, such as miR-27, miR-29, and miR-33, may facilitate metabolic suppression during hibernation via mechanisms that decrease glucose uptake and fatty acid oxidation. This study identified myomiR-mediated mechanisms for the promotion of muscle regeneration, suppression of ubiquitin ligases, and resistance to muscle atrophy during hibernation mediated by observed increases in miR-206, miR-221, miR-31, miR-23a, and miR-29b. This was further supported by the downregulation of myomiRs associated with a muscle injury and inflammation (miR-199a and miR-223) during hibernation. The present study provides evidence of myomiR-mediated signaling pathways that are activated during hibernation to maintain skeletal muscle functionality in brown bears.
Highlights
MethodsSix free-ranging brown bears (Ursus arctos; females; 2-3 years old), fitted with GPS collars, have been followed by the Scandinavian Brown Bear Research Project (SBBRP) in the Dalarna and Gävleborg counties, Sweden
A group of 36 myomiRs known to be crucial for skeletal muscle development, metabolism, and regeneration (Diniz & Wang, 2016; Horak et al, 2016; Lima et al, 2017) and 5 key upstream and downstream mRNA transcripts were investigated in vastus lateralis muscle from winter hibernating versus summer-active bears
The present study sought to assess the role of microRNAs as regulatory factors in limiting atrophy of U. arctos skeletal muscle during winter hibernation
Summary
Six free-ranging brown bears (Ursus arctos; females; 2-3 years old), fitted with GPS collars, have been followed by the Scandinavian Brown Bear Research Project (SBBRP) in the Dalarna and Gävleborg counties, Sweden. Their immobilization was performed as previously reported (Evans et al, 2012), to allow sampling during hibernation in late February 2015 or 2016 and again during the active summer period in early June of the same years. After darting in their den (winter) or from a helicopter (summer), immobilized individuals were moved onto an insulated blanket prior to tissue sampling.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
