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The proteins of the hedgehog (Hh) family regulate various aspects of development. Recently, members of this family have been shown to regulate skeletal formation in vertebrates and to control both chondrocyte and osteoblast differentiation. In the present study, we analyzed the effect of Sonic hedgehog (Shh) on the osteoblastic and adipocytic commitment/differentiation. Recombinant N-terminal Shh (N-Shh) significantly increased the percentage of both the pluripotent mesenchymal cell lines C3H10T1/2 and ST2 and calvaria cells responding to bone morphogenetic protein 2 (BMP-2), in terms of osteoblast commitment as assessed by measuring alkaline phosphatase (ALP) activity. This synergistic effect was mediated, at least partly, through the positive modulation of the transcriptional output of BMPs via Smad signaling. Furthermore, N-Shh was found to abolish adipocytic differentiation of C3H10T1/2 cells both in the presence or absence of BMP-2. A short treatment with N-Shh was sufficient to dramatically reduce the levels of the adipocytic-related transcription factors C/EBPalpha and PPARgamma in both C3H10T1/2 and calvaria cell cultures. Given the inverse relationship between marrow adipocytes and osteoblasts with aging, agonists of the Hh signaling pathway might constitute potential drugs for preventing and/or treating osteopenic disorders.

Protein A (PA), a cell wall component of SAC, activates human B cells by cross-linking the Fabs of membrane immunoglobulins. Recent data indicate that PA binds only to Fabs that use VH3 heavy chains, and thus it has been designated as a B-cell superantigen. We previously reported thatStaphylococcus aureus Cowan I (SAC) -induced IgM rheumatoid factor (RF) by human PBMC was mediated by PA. Therefore, we sought to determine if SAC-induced IgMRF production was confined to PA-binding B cells and if these B cells were enriched for the expression of VH3 heavy chains. We observed that the elicitation of IgMRF in response to SAC was limited to a subset of B cells that bind PA and that this subset was enriched for VH3 mRNA expression. Taken together, these results suggest that IgMRFs produced in response to SAC are enriched for usage of VH3 heavy chains. Thus, this SAC-induced autoantibody response appears to represent a new B-cell superantigenic property of PA.