Cell-cell fusion is a dynamic phenomenon promoting cytoskeletal reorganization and phenotypic changes. To characterize factors essential for fusion of macrophage lineage cells, we identified the multitransmembrane protein, osteoclast stimulatory transmembrane protein (OC-STAMP), and analyzed its function. OC-STAMP-deficient mice exhibited a complete lack of cell-cell fusion of osteoclasts and foreign body giant cells (FBGCs), both of which are macrophage-lineage multinuclear cells, although expression of dendritic cell specific transmembrane protein (DC-STAMP), which is also essential for osteoclast/FBGC fusion, was normal. Crossing OC-STAMP-overexpressing transgenic mice with OC-STAMP-deficient mice restored inhibited osteoclast and FBGC cell-cell fusion seen in OC-STAMP-deficient mice. Thus, fusogenic mechanisms in macrophage-lineage cells are regulated via OC-STAMP and DC-STAMP. ß

Controlling osteoclastogenesis is critical to maintain physiological bone homeostasis and prevent skeletal disorders. Although signaling activating nuclear factor of activated T cells 1 (NFATc1), a transcription factor essential for osteoclastogenesis, has been intensively investigated, factors antagonistic to NFATc1 in osteoclasts have not been characterized. Here, we describe a novel pathway that maintains bone homeostasis via two transcriptional repressors, B cell lymphoma 6 (Bcl6) and B lymphocyte–induced maturation protein-1 (Blimp1). We show that Bcl6 directly targets ‘osteoclastic’ molecules such as NFATc1, cathepsin K, and dendritic cell-specific transmembrane protein (DC-STAMP), all of which are targets of NFATc1. Bcl6-overexpression inhibited osteoclastogenesis in vitro, whereas Bcl6-deficient mice showed accelerated osteoclast differentiation and severe osteoporosis. We report that Bcl6 is a direct target of Blimp1 and that mice lacking Blimp1 in osteoclasts exhibit osteopetrosis caused by impaired osteoclastogenesis resulting from Bcl6 up-regulation. Indeed, mice doubly mutant in Blimp1 and Bcl6 in osteoclasts exhibited decreased bone mass with increased osteoclastogenesis relative to osteoclast-specific Blimp1-deficient mice. These results reveal a Blimp1–Bcl6–osteoclastic molecule axis, which critically regulates bone homeostasis by controlling osteoclastogenesis and may provide a molecular basis for novel therapeutic strategies.

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The authors regret that the dosage of RANKL and control antibodies used in the HSC mobilization experiments shown in Figure 6 were incorrectly reported in micrograms. The correct dosages were 5 mg/kg anti-RANKL and 2.5 mg/kg control antibody. The html and pdf versions of the article have been corrected.

The mobilization of hematopoietic stem cells does not require osteoclasts, which may even have an inhibitory effect.

Osteoporosis is a complex disease with various causes, such as estrogen loss, genetics, and aging. Here we show that a dominantnegative form of aldehyde dehydrogenase 2 (ALDH2) protein, ALDH2Ã 2, which is produced by a single nucleotide polymorphism (rs671), promotes osteoporosis due to impaired osteoblastogenesis. Aldh2 plays a role in alcohol-detoxification by acetaldehyde-detoxification; however, transgenic mice expressing Aldh2 Ã 2 (Aldh2 Ã 2 Tg) exhibited severe osteoporosis with increased levels of blood acetaldehyde without alcohol consumption, indicating that Aldh2 regulates physiological bone homeostasis. Wild-type osteoblast differentiation was severely inhibited by exogenous acetaldehyde, and osteoblastic markers such as osteocalcin, runx2, and osterix expression, or phosphorylation of Smad1,5,8 induced by bone morphogenetic protein 2 (BMP2) was strongly altered by acetaldehyde. Acetaldehyde treatment also inhibits proliferation and induces apoptosis in osteoblasts. The Aldh2 Ã 2 transgene or acetaldehyde treatment induced accumulation of the lipid-oxidant 4-hydroxy-2-nonenal (4HNE) and expression of peroxisome proliferator-activated receptor gamma (PPARg), a transcription factor that promotes adipogenesis and inhibits osteoblastogenesis. Antioxidant treatment inhibited acetaldehyde-induced proliferation-loss, apoptosis, and PPARg expression and restored osteoblastogenesis inhibited by acetaldehyde. Treatment with a PPARg inhibitor also restored acetaldehyde-mediated osteoblastogenesis inhibition. These results provide new insight into regulation of osteoporosis in a subset of individuals with ALDH2 Ã 2 and in alcoholic patients and suggest a novel strategy to promote bone formation in such osteopenic diseases. ß

The recent trend of product diversification in the Indonesian banking industry underscores the importance of non-interest income activities. This study examines the relationship between product diversification and bank risk over the period of 2002-2008. Our analysis shows clear evidence that the effect of product diversification on bank risk depends highly on the bank's asset size. Specifically, the degree of product diversification is negatively associated with bank risk for small-sized banks. Conversely, the degree of product diversification is positively related to bank risk for large-sized banks. This finding suggests that deregulation encouraging banks to become more involved in non-traditional activities may have an adverse effect on the overall banking system where large-sized banks are playing a significant role in Indonesia.