Cell. 2010 Jul 23;142(2):309-19. doi: 10.1016/j.cell.2010.06.002.

Insulin receptor signaling in osteoblasts regulates postnatal bone acquisition and body composition.

Fulzele K, Riddle RC, DiGirolamo DJ, Cao X, Wan C, Chen D, Faugere MC, Aja S, Hussain MA, Brüning JC, Clemens TL.

Source

Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.

Abstract

Global energy balance in mammals is controlled by the actions of circulating hormones that coordinate fuel production and utilization in metabolically active tissues. Bone-derived osteocalcin, in its undercarboxylated, hormonal form, regulates fat deposition and is a potent insulin secretagogue. Here, we show that insulin receptor (IR) signaling in osteoblasts controls osteoblast development and osteocalcin expression by suppressing the Runx2 inhibitor Twist2. Mice lacking IR in osteoblasts have low circulating undercarboxylated osteocalcin and reduced bone acquisition due to decreased bone formation and deficient numbers of osteoblasts. With age, these mice develop marked peripheral adiposity and hyperglycemia accompanied by severe glucose intolerance and insulin resistance. The metabolic abnormalities in these mice are improved by infusion of undercarboxylated osteocalcin. These results indicate the existence of a bone-pancreas endocrine loop through which insulin signaling in the osteoblast ensures osteoblast differentiation and stimulates osteocalcin production, which in turn regulates insulin sensitivity and pancreatic insulin secretion.

Comment in

No bones about it: insulin modulates skeletal remodeling. [Cell. 2010]
No bones about it: insulin modulates skeletal remodeling.Rosen CJ, Motyl KJ. Cell. 2010 Jul 23; 142(2):198-200.

PMID:: 20655471; [PubMed - indexed for MEDLINE]
PMCID:: PMC2925155

Free PMC Article

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Figure 1

Insulin receptor signaling promotes osteoblast differentiation

(A) Immunohistochemical staining for insulin receptor (a) and an isotype control (b) in trabecular bone of the distal metaphysis. Filled arrows denote osteoblasts, open arrows denote osteocytes. Muscle was used as positive control (c). (B) Western Blot analysis of the insulin receptor expression in primary osteoblasts isolated from IR^flox/flox mice after infection with adenovirus expressing Cre or GFP as a control. (C) Quantification of osteoblast proliferation by BrdU uptake in control and ΔIR osteoblasts. (D) Quantification of osteoblast apoptosis via Annexin V staining in control and ΔIR osteoblasts treated with 8ng/ml staurosporine. (E–G) Examination of osteoblast differentiation following the deletion of IR. (E) Alkaline phosphatase (ALP) and Alizarin Red (ARS) staining after 7 and 14 days of differentiation, respectively. (F) RT-PCR analysis of IR, Runx2, ATF4, and Osteocalcin (OCN) expression after 7 days of differentiation. (G) ALP and ARS staining after culture in the presence or absence of 13nM IGF-1. (H) Osteocalcin promoter activity assessed in Mc3t3-E1 cells transfected with OC1050-Luc and treated with insulin for 6 hours. (I) ChIP analysis of Runx2 binding to the osteocalcin promoter after 6 hours of 10nM insulin treatment. (J) ChIP analysis of Runx2 binding to the osteocalcin promoter in control and ΔIR osteoblasts. (K) RT-PCR analysis of Osteocalcin (OCN) and Runx2 expression in primary osteoblasts treated with 10nM insulin for 6 hours. (L) Microarray analysis of insulin-regulated genes 4-fold over- or under-expressed and related to bone remodeling in ΔIGF-1R osteoblasts as identified by gene ontology analysis (see also Table S1). (M) Twist1 and Twist2 expression in ΔIGF-1R osteoblasts 24 hours after 10nM insulin treatment. (N) Expression of regulators of Runx2 activity in control and ΔIR osteoblasts after 7 days of differentiation. (O) Co-immunoprecipitation of Runx2 and Twist2 in control and ΔIR osteoblasts.

Insulin receptor signaling in osteoblasts regulates postnatal bone acquisition and body composition

Cell. 2010 July 23;142(2):309-319.