Effects of leptin on the expression of alpha1 (I) collagen gene in human osteoblast-like MG63 cells

Adiponectin is a candidate biomarker of lower extremity bone density in men with chronic spinal cord injury

Adipose tissue is a major regulator of bone metabolism and in the general population obesity is associated with greater bone mineral density (BMD). However, bone-fat interactions are multifactorial, and may involve pathways that influence both bone formation and resorption with competing effects on the skeleton. One such pathway involves adipocyte production of adipokines that regulate bone metabolism. In this study we determined the association between BMD, walking status, and circulating adipokines (adiponectin and leptin) in 149 men with chronic spinal cord injury (SCI). Although adipokine levels did not vary significantly based on walking status, there was a significant inverse association between adiponectin and BMD in wheelchair users independent of body composition. We found no association between adiponectin and BMD in the walkers and no association between leptin and BMD in either group. These findings suggest that for subjects with chronic SCI, walking may mitigate the effect of adiponectin mediated bone loss. For wheelchair users, adipose-derived adiponectin may contribute to SCI-induced osteoporosis because the osteoprotective benefits of obesity appear to require mechanical loading during ambulation.

Leptin promotes ossification through multiple ways of bone metabolism in osteoblast: a pilot study

Leptin may be a potential option in preventing osteoporosis for menopausal women. The objective of this study is to explore the molecular mechanism of leptin on bone metabolism in osteoblast. Primary osteoblasts were isolated from parietal bone of adult female rats. mRNA level of OB-Rb in osteoblasts was inhibited by siRNA to block leptin signal transmission. The whole genome expression was tested by using gene chip to preliminarily explore the molecular mechanism of leptin in regulating osteoblast activity. The optimal concentration of siRNA was 25 nM, resulting in a maximal inhibition of OB-Rb mRNA. Ossification (p < 0.05) and bone mineralization (p = 0.0001) were downregulated by inhibiting leptin signal transmission, while bone resorption (p = 0.007), osteoblast differentiation (p = 0.026) and negative regulation of bone remodeling (p = 0.004) were upregulated. The expressions of some genes were regulated by OB-Rb siRNA. The expressions of alkaline phosphatase (p = 0.014) and osteocalcin (p = 0.002) were reduced, while that of vascular endothelial growth factor A (p = 0.0076) and IL-6 (p = 0.021) were increased. In a model of osteoblast, leptin positively promotes ossification through multiple ways including bone mineralization, remodeling, resorption and osteoblast differentiation, but which way plays the most critical role is not discussed in this study and needs to be clarified in future.

Biphasic effects of TGFβ1 on BMP9-induced osteogenic differentiation of mesenchymal stem cells

We have found that the previously uncharacterized bone morphogenetic protein-9 (BMP9) is one of the most osteogenic factors. However, it is unclear if BMP9 cross-talks with TGFβ1 during osteogenic differentiation. Using the recombinant BMP9 adenovirus, we find that low concentration of rhTGFβ1 synergistically induces alkaline phosphatase activity in BMP9-transduced C3H10T1/2 cells and produces more pronounced matrix mineralization. However, higher concentrations of TGFβ1 inhibit BMP9-induced osteogenic activity. Real-time PCR and Western blotting indicate that BMP9 in combination with low dose of TGFβ1 potentiates the expression of later osteogenic markers osteopontin, osteocalcin and collagen type 1 (COL1a2), while higher concentrations of TGFβ1 decrease the expression of osteopontin and osteocalcin but not COL1a2. Cell cycle analysis reveals that TGFβ1 inhibits C3H10T1/2 proliferation in BMP9-induced osteogenesis and restricts the cells in G(0)/G(1) phase. Our findings strongly suggest that TGFβ1 may exert a biphasic effect on BMP9-induced osteogenic differentiation of mesenchymal stem cells.