title: Suppressed bone remodeling in black bears conserves energy and bone mass during hibernation.
abstract: Decreased physical activity in mammals increases bone turnover and uncouples bone formation from bone resorption, leading to hypercalcemia, hypercalcuria, bone loss and increased fracture risk. Black bears, however, are physically inactive for up to 6 months annually during hibernation without losing cortical or trabecular bone mass. Bears have been shown to preserve trabecular bone volume and architectural parameters and cortical bone strength, porosity and geometrical properties during hibernation. The mechanisms that prevent disuse osteoporosis in bears are unclear as previous studies using histological and serum markers of bone remodeling show conflicting results. However, previous studies used serum markers of bone remodeling that are known to accumulate with decreased renal function, which bears have during hibernation. Therefore, we measured serum bone remodeling markers (BSALP and TRACP) that do not accumulate with decreased renal function, in addition to the concentrations of serum calcium and hormones involved in regulating bone remodeling in hibernating and active bears. Bone resorption and formation markers were decreased during hibernation compared with when bears were physically active, and these findings were supported by histomorphometric analyses of bone biopsies. The serum concentration of cocaine and amphetamine regulated transcript (CART), a hormone known to reduce bone resorption, was 15-fold higher during hibernation. Serum calcium concentration was unchanged between hibernation and non-hibernation seasons. Suppressed and balanced bone resorption and formation in hibernating bears contributes to energy conservation, eucalcemia and the preservation of bone mass and strength, allowing bears to survive prolonged periods of extreme environmental conditions, nutritional deprivation and anuria.
authors.affiliation: Department of Cellular Biology and Anatomy, Georgia Regents University, Augusta, GA 30912, USA.
authors.forename: Meghan
authors.initials: M
authors.lastname: McGee-Lawrence
authors.affiliation: Center for Alcohol Studies, Rutgers University, New Brunswick, NJ 08901, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: Buckendahl
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University, New Haven, CT 06520, USA.
authors.forename: Caren
authors.initials: C
authors.lastname: Carpenter
authors.affiliation: Nordic Bioscience Biomarkers and Research, Herlev, Denmark.
authors.forename: Kim
authors.initials: K
authors.lastname: Henriksen
authors.affiliation: Department of Fish and Wildlife Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Vaughan
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523, USA seth.donahue@colostate.edu.
authors.forename: Seth
authors.initials: S
authors.lastname: Donahue
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D015415:Biomarkers / Q000097:blood; D016723:Bone Remodeling / Q000502:physiology*; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000097:blood; D005260:Female; D006605:Hibernation / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000097:blood; D011247:Pregnancy; D012621:Seasons; D001503:Ursidae / Q000097:blood / Q000502:physiology*; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein
chemical_list: D015415:Biomarkers; D009419:Nerve Tissue Proteins; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein; D000469:Alkaline Phosphatase; D002118:Calcium
keywords: CART; Calcium metabolism; Disuse; Skeletal adaptation; Ursus americanus