Osteocalcin Effect on Human β-Cells Mass and Function

Abstract

The osteoblast-specific hormone osteocalcin (OC) was found to regulate glucose metabolism, fat mass, and β-cell proliferation in mice. Here, we investigate the effect of decarboxylated OC (D-OC) on human β-cell function and mass in culture and in vivo using a Nonobese diabetic-severe combined immunodeficiency mouse model. We found that D-OC at dose ranges from 1.0 to 15 ng/mL significantly augmented insulin content and enhanced human β-cell proliferation of cultured human islets. This was paralleled by increased expression of sulfonylurea receptor protein; a marker of β-cell differentiation and a component of the insulin-secretory apparatus. Moreover, in a Nonobese diabetic-severe combined immunodeficiency mouse model, systemic administration of D-OC at 4.5-ng/h significantly augmented production of human insulin and C-peptide from the grafted human islets. Finally, histological staining of the human islet grafts showed that the improvement in the β-cell function was attributable to an increase in β-cell mass as a result of β-cell proliferation indicated by MKI67 staining together with the increased β-cell number and decreased α-cell number data obtained using laser scanning cytometry. Our data for the first time show D-OC-enhanced β-cell function in human islets and support future exploitation of D-OC-mediated β-cell regulation for developing useful clinical treatments for patients with diabetes.

Proprotein convertase furin regulates osteocalcin and bone endocrine function

“…Hence, the vast majority of OCN secreted by osteoblasts is trapped in bone ECM, in which it constitutes the most abundant noncollagenous polypeptide. Although both γ-carboxylated (Gla) and undercarboxylated (ucOCN) forms of OCN are detected in serum, most in vitro and in vivo studies concur to indicate that the endocrine function of OCN is fulfilled by ucOCN in mice and humans (3,4,11). This has been recently confirmed genetically through the inactivation of Ggcx specifically in osteoblasts, which resulted in increased circulating levels of ucOCN and improved glucose tolerance in mice (12).…”

“…Accordingly, when fed a normal diet, Ocn-deficient mice (Ocn -/-) exhibit reduced glucose tolerance, insulin sensitivity, and circulating insulin levels, as well as decreased energy expenditure and increased fat mass (2). Mechanistic studies conducted in cell cultures and mice showed that OCN improves glucose handling by promoting insulin secretion from β cells (3,4), by favoring glucose uptake in myofibers (5), and by increasing energy expenditure (6). Studies in mice demonstrated that OCN function in β cells and myofibers is mediated through its binding to the G protein-coupled receptor family C group 6 member A (GPRC6A) (3,5).…”

Osteocalcin in the brain: from embryonic development to age-related decline in cognition

“…Although energy metabolism is certainly a critical aspect of osteocalcin biology, whereby it affects 2 in mice, rats and humans 3-12 , functions of β-cells 13 , myoblasts and likely other cell types, it by no means tells the entire story of osteocalcin. If anything, a hallmark of this hormone is that it regulates a large and continually growing number of physiological functions and developmental processes 14 (Figure 1).…”

Bone and Muscle Endocrine Functions: Unexpected Paradigms of Inter-organ Communication

“…Explaining in part their changes in fat mass, energy expenditure is significantly decreased in Osteocalcin deficient and increased in Esp osb −/− mice (Lee et al, 2007). These observations have ben recently extended to human pancreatic islets, in which the addition of uncarboxylated osteocalcin increases the expression of the Insulin and of Cyclind2 and Cdk4 genes, two genes needed for β-cell proliferation (Sabek et al, 2015). Moreover, circulating osteocalcin levels are inversely correlated in adults with fasting glucose circulating insulin levels, body mass index and body fat (Fernandez-Real et al, 2009).…”