Bone's responses to mechanical loading are impaired in type 1 diabetes

• Published in: Bone (New York, N.Y.) Vol. 81; pp. 152 - 160
• Main Authors: Parajuli, Ashutosh, Liu, Chao, Li, Wen, Gu, Xiaoyu, Lai, Xiaohan, Pei, Shaopeng, Price, Christopher, You, Lidan, Lu, X. Lucas, Wang, Liyun
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2015
• Subjects: Akita diabetic mouse; Animals; Bone formation; Cells, Cultured; Diabetes Mellitus, Type 1 - metabolism; Diabetes Mellitus, Type 1 - pathology; Female; Fluid flow; Male; Mice; Mice, Inbred C57BL; Orthopedics; Osteocyte mechanosensitivity; Osteogenesis - physiology; Rats; Ulna - metabolism; Ulna - pathology; Ulnar mechanical loading; Weight-Bearing - physiology; Osteocyte mechanosensitivity; Akita diabetic mouse; Bone formation; Ulnar mechanical loading; Fluid flow
• ISSN: 8756-3282; 1873-2763; 1873-2763
• DOI: 10.1016/j.bone.2015.07.012

Diabetes adversely impacts many organ systems including the skeleton. Clinical trials have revealed a startling elevation in fracture risk in diabetic patients. Bone fractures can be life threatening: nearly 1 in 6 hip fracture patients die within one year. Because physical exercise is proven to improve bone properties and reduce fracture risk in non-diabetic subjects, we tested its efficacy in type 1 diabetes. We hypothesized that diabetic bone's response to anabolic mechanical loading would be attenuated, partially due to impaired mechanosensing of osteocytes under hyperglycemia. Heterozygous C57BL/6-Ins2Akita/J (Akita) male and female diabetic mice and their age- and gender-matched wild-type (WT) C57BL/6J controls (7-month-old, N=5–7 mice/group) were subjected to unilateral axial ulnar loading with a peak strain of 3500με at 2Hz and 3min/day for 5days. The Akita female mice, which exhibited a relatively normal body weight and a mild 40% elevation of blood glucose level, responded with increased bone formation (+6.5% in Ct.B.Ar, and 4 to 36-fold increase in Ec.BFR/BS and Ps.BFR/BS), and the loading effects, in terms of changes of static and dynamic indices, did not differ between Akita and WT females (p≥0.1). However, loading-induced anabolic effects were greatly diminished in Akita males, which exhibited reduced body weight, severe hyperglycemia (+230%), diminished bone formation (ΔCt.B.Ar: 0.003 vs. 0.030mm2, p=0.005), and suppressed periosteal bone appositions (ΔPs.BFR/BS, p=0.02). Hyperglycemia (25mM glucose) was further found to impair the flow-induced intracellular calcium signaling in MLO-Y4 osteocytes, and significantly inhibited the flow-induced downstream responses including reduction in apoptosis and sRANKL secretion and PGE2 release. These results, along with previous findings showing adverse effects of hyperglycemia on osteoblasts and mesenchymal stem cells, suggest that failure to maintain normal glucose levels may impair bone's responses to mechanical loading in diabetics. •We aimed to test whether mechanical loading, a potent anabolic factor, can rescue the weak bone phenotype in diabetics•Mildly diabetic mice responded to anabolic loading, while mice with severe hyperglycemia showed diminished responses•Hyperglycemia impaired osteocyte's responses to fluid flow stimulation in vitro•Failure to maintain normal glucose levels may impair bone's responses to mechanical loading in diabetics