Adipocyte-secreted factors and higher bone mass in obese people

Several studies have reported controversial results about the positive correlation between the body fat mass and bone mineral density. It remains unclear whether some adipocyte-secreted factors can act on bone metabolism, directly on osteoblasts, to favor bone formation or osteoclasts, which control bone resorption. The authors of this study [1] investigated the effect of fat cell secreted molecules on proliferation and differentiation of preosteoblasts.

They showed that fat cell secretion factors increased proliferation of murine preosteoblast cells by almost 3-fold. This proliferation was reduced by inhibiting FGFR1, the receptor of FGF. Accordingly, the authors evidenced that human adipocytes secreted bFGF. This molecule alone is sufficient to induce preosteoblast proliferation. When preosteoblasts were stimulated to proliferate by adipocyte-secreted factors, the OPG/RANKL ratio increased 9-fold in a PI3K-dependant manner. OPG (osteoprotegerin) is a well-known inhibitor of osteoclast differentiation and bone resorption. On the other hand, RANKL promotes osteoclast differentiation. Moreover, stimulated pre-osteoblasts inhibited the formation of mature osteoclasts.

In conclusion, human adipocytes secrete factors that directly act on preosteoblasts and alter their crosstalk with osteoclasts. This study highlights the effects of adipocytes on bone metabolism and argues in favor of the positive relationship between body fat mass and bone mineral density. It could explain the higher bone mass in obese people.

1. Kühn MC et al. Mol Cell Endocrinol. 2011; Doi :10.1016/j.mce.2011.10.018.

Optimal monitoring time interval between DXA measures in children

The monitoring time interval (MTI) is the expected time in years necessary to detect a significant change between two measures that exceeds the measurement error. The aim of this paper [1] was to determine MTI values for dual X-ray absorptiometry (DXA) scans in normal children according to age, sex, and skeletal sites.

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Inpp4b as a regulator of bone mass

Osteoclasts are the major cell type involved in bone resorption. Unbalanced increase of osteoclasts activity decreases bone mass and favors osteoporosis. The authors of this study [1] identified a regulator of osteoclastogenesis, inositol polyphosphate 4-phosphatase type 2 α (Inpp4bα), a member of the PI3 kinase signaling pathway.

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Gfi1: a new therapeutic target for multiple myeloma bone disease

Inhibition of osteoblast differentiation characterizes multiple myeloma (MM) bone disease and persists even when patients are in long-term remission. The authors of this study [1] developed a murine multiple myeloma model in which the bone marrow stromal cells remained unresponsive to osteoblast differentiation, inhibiting signals after removal of MM cells.

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Sympathetic control of bone mass is regulated by osteopontin

Activation of the sympathetic nervous system is known to reduce bone mass through mechanisms that remain unclear. Using cell-based studies and murine genetics, the authors [1] showed that osteopontin (OPN) is required for the sympathetic activity on bone metabolism.

Osteopontin is a cytokine and one of the major members of noncollagenous extracellular matrix proteins of bone.
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