Undercarboxylated osteocalcin and ibandronate combination ameliorates hindlimb immobilization‐induced muscle wasting

• Published in: The Journal of physiology Vol. 601; no. 10; pp. 1851 - 1867
• Main Authors: Lin, Xuzhu, Smith, Cassandra, Moreno‐Asso, Alba, Zarekookandeh, Navabeh, Brennan‐Speranza, Tara C., Duque, Gustavo, Hayes, Alan, Levinger, Itamar
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.05.2023
• Subjects: Aged; Aging; AKT protein; Animals; Biopsy; Bisphosphonates; Body weight; Extracellular signal-regulated kinase; Glucose; Glucose - metabolism; Glucose tolerance; hindlimb immobilization; Hindlimb Suspension; Humans; Ibandronic acid; Ibandronic Acid - metabolism; Immobilization; Insulin - metabolism; Insulin Resistance; Limbs; Metabolism; Mice; Mice, Inbred C57BL; muscle wasting; Muscle, Skeletal - metabolism; Muscles; Muscular Atrophy - drug therapy; Muscular Atrophy - etiology; Muscular Atrophy - prevention & control; Myotubes; Osteocalcin; Osteocalcin - metabolism; Osteocalcin - pharmacology; Osteoporosis; Phosphorylation; Proteins; Proto-Oncogene Proteins c-akt - metabolism; Quadriceps muscle; Signal transduction; Skeletal muscle; TOR protein; undercarboxylated osteocalcin; undercarboxylated osteocalcin; bisphosphonates; hindlimb immobilization; glucose metabolism; muscle wasting
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP283990

Immobilization leads to muscle wasting and insulin resistance, particularly during ageing. It has been suggested that undercarboxylated osteocalcin (ucOC) improves muscle mass and glucose metabolism. Bisphosphonates, an anti‐osteoporosis treatment, might protect muscle wasting independent of ucOC. We hypothesize that the combination of ucOC and ibandronate (IBN) treatments has superior protective effects against immobilization‐induced muscle wasting and insulin resistance than either treatment alone. C57BL/6J mice were hindlimb‐immobilized for two weeks, with injections of vehicle, ucOC (90 ng/g daily) and/or IBN (2 μg/g weekly). Insulin/oral glucose tolerance tests (ITT/OGTT) were performed. Immediately after immobilization, muscles (extensor digitorum longus (EDL), soleus, tibialis anterior, gastrocnemius and quadriceps) were isolated and measured for muscle mass. Insulin‐stimulated glucose uptake (EDL and soleus) was examined. Phosphorylation/expression of proteins in anabolic/catabolic pathways were examined in quadriceps. Primary human myotubes derived from older adult muscle biopsies were treated with ucOC and/or IBN, then signalling proteins were analysed. Combined treatment, but not individual treatments, significantly increased the muscle weight/body weight ratio in immobilized soleus (31.7%; P = 0.013) and quadriceps (20.0%; P = 0.0008) muscles, concomitant with elevated p‐Akt (S473)/Akt ratio (P = 0.0047). Combined treatment also enhanced whole‐body glucose tolerance (16.6%; P = 0.0011). In human myotubes, combined treatment stimulated greater activation of ERK1/2 (P = 0.0067 and 0.0072) and mTOR (P = 0.036), and led to a lesser expression of Fbx32 (P = 0.049) and MuRF1 (P = 0.048) than individual treatments. These findings suggest a potential therapeutic role for the ucOC and bisphosphonates combination in protecting against muscle wasting induced by immobilization and ageing. Key points It has been suggested that undercarboxylated osteocalcin (ucOC) improves muscle mass and glucose metabolism. Bisphosphonates, an anti‐osteoporosis treatment, might protect against muscle wasting independent of ucOC. The combination treatment of ucOC and ibandronate was shown to exert a greater therapeutic effect against immobilization‐induced muscle wasting, and led to greater activation of anabolic pathway and less expression of catabolic signalling proteins in myotubes derived from older adults, compared with individual treatments. The combination treatment was found to improve whole‐body glucose tolerance. Our findings suggest a potential therapeutic role for the ucOC and bisphosphonates combination in protecting against muscle wasting induced by immobilization and ageing. figure legend Undercarboxylated osteocalcin (ucOC) and ibandronate (IBN) in combination improve muscle mass and glucose disposal. Two weeks of hindlimb immobilization in mice led to leg muscle atrophy as well as muscle insulin resistance. Injections of both undercarboxylated osteocalcin (intraperitoneal (ip)) and ibandronate (subcutaneous (sc)) alleviated muscle wasting in a muscle type‐specific manner. In addition, this combination treatment improved glucose disposal in mice. In both immobilized mouse muscle and human primary myotubes derived from older adults, the combination treatment with ucOC and IBN resulted in greater activation of the proteins involved in the anabolic signalling pathway, including Akt and mTORC1. In primary myotubes, this treatment reduced the expression of proteins involved in catabolic signalling pathway, such as Fbx32 and MuRF1. These findings suggest that the ucOC and bisphosphonates combination has potential in treating muscle wasting and insulin resistance induced by immobilization and ageing.