Glucose metabolism influences the adaptive response of osteocytes to mechanical stimuli via CCN1

Bone loss is a diabetic-related complication. Chronic hyperglycemia affects bone quality, quantity and function1. Recently, reduced bone response to mechanical loading in diabetic mice have been reported2. However, it remains unclear whether hyperglycemic condition affects mechanosensing of osteocytes known as mechanical sensor cells through the changes of molecular mechanism. In this study, we addressed the identification of mechano-sensitive and glucose-dependent molecular mechanisms in osteocytes. First, we isolated osteocyte related mechanosensitive genes by examining bone tissues and osteocytic cells derived from in vivo and in vitro mechanical loading model. RNA sequencing analysis of a murine bone tissues exposed to 6 weeks of voluntary wheel running showed 146 genes were respond to mechanical loading. Of these genes, 4 genes were also reacted to ultrasound stimulation in murine osteocytic cell line. Only one gene of 4 genes, Ccn1 (cysteine-rich 61, Cyr61), was upregulated by both wheel running exercise in vivo and ultra sound stimulation in vitro. Thus, Ccn1 was considered specific candidate gene for mechanosensing in osteocytes. Next, we examined the effect of glucose level on CCN1 expression induced by mechanical stimuli by using obese mice model and high-glucose-exposed osteocytic cells. The mechanical stress-induced elevation of CCN1 expression was totally abolished by high glucose condition both in mice bone and osteocytic cells. Our findings support a new role of CCN1 as a glucose dependent mechanosensing molecules in osteocytes contributing to diabetic bone abnormality. Overall design: Male mice at 6 weeks of age were divided into two groups: normal chow diet/sedentary (ND/SED) and normal chow diet/wheel cage running (ND/WCR). Mice in ND/SED groups were individually housed in a normal cage without a running wheel, and mice in ND/WCR group were individually housed in wheel cages with free access to a running wheel (140-mm diameter, 60-mm wide; MELQUEST, Toyama, Japan). After 6 weeks, mice were removed from the wheel cages or static cages, euthanized under anesthesia and femoral bones were isolated. RNA samples derived from ND/SED mice (n=3) and ND/WCR mice (n=3) were compared.