破骨細胞演化自骨髓白血球系細胞，過程中受到許多因素與細胞激素的調空，當中 包含巨噬細胞集落刺激因子（Macrophage colony-stimulating factor, M-CSF) 以及受 體活化核因子配位蛋白（Receptor activator of NF-κB lignad , RANKL). 當細胞表面 核因子受體（Receptor activator of NF-κB, RANK）受到配位蛋白刺激之後，下由的 T 細胞活化核因子(Nuclear factor of activated T cells cytoplasmic 1, NFATc1) 傳遞訊 息誘導細胞表面表現DC-STAMP( dendritic cell-specific transmembrane protein). DC-STAMP 已經被證實在破骨細胞、肌肉細胞、巨大細胞等多核細胞的細胞融合 過程中扮演不可或缺的角色。近期的研究結果指出，DC-STAMP 是細胞融合的必 備要素，但在融合的過程中，DC-STAMP 的內化、修飾並潛進細胞質內，為破骨 細胞融合的必經過程。本研究室101 年度國科會計畫成果卻發現，補充HMB 不僅具 有促進骨質增生，亦有減少骨質分解的作用。後續實驗並發現，補充HMB 確實明 顯的抑制血液中破骨前趨細胞表面DC-STAMP 的表現，然而RANK 的下游訊息傳 遞因子NFATc1 的表現量並未受到影響，反而是上游的RANK 表現量的大幅下 降。基於此一證據，本研究室懷疑HMB 對於破骨細胞新生成作用的抑制效應，可 能不只是在前趨細胞融合成為多核細胞的階段，反倒是在單核球細胞準備分化為破 骨前趨細胞的階段，就已經出現抑制作用。有鑒於此，本次研究計畫將著重於補充 HMB 對於骨髓幹細胞分化為破骨前趨細胞的階段所產生的急性影響。 本研究計畫自「國立台灣體育運動大學」招募年齡20-22 歲的非專長訓練自願受 試者，受試者進行短期服用HMB 後，進行分析單核球細胞被誘導成為破骨前趨細 胞所產生的影響。
Osteoclasts, a kind of multinuclear cell which are derived from myeloid lineage, require complicate modulation by several cytokines. Macrophage colony-stimulating factor (M-CSF) induces myeloid precursors to differentiate to osteoclast precursors that express RANK (Receptor activator of NF-κB) and TREM2 (Triggering receptor expressed by myeloid cells-2) receptors. Upon RANK ligand (RANKL) stimulation and ITAM (Immunoreceptor tyrosine-based activation motif ) activation, osteoclast precursors undergo further differentiation to mononuclear osteoclasts with NFATc1 (Nuclear factor of activated T cells, cytoplasmic 1) induction and express osteoclast-related genes such as encoding TNF-receptor associated protein (TRAP), cathepsin K (CtsK) and dendritic cell-specific transmembrane protein(DC-STAMP). Mononuclear osteoclasts then fusion into multinuclear osteoclasts and function as polarized bone resorbing cells. Previous studies indicated that cell to cell fusion media through DC-STAMP is essential for osteoclastogenesis. Expression of DC-STAMP on cell surface had been identified as a reliable marker of osteoclast progenitors (OCPs). Researchers indicated that DC-STAMP expression is required to initiate the regulation of cell fusion but removal of the inhibitory signal mediated through DC-STAMP is also required for the OCP differentiation program to fully progress. Dietary supplement of β-hydroxy-β-methylbutyrate (HMB) had been proven not only increase muscle mass but also increase the mass, density and Architectures of skeleton tissues in animal studies. According to the result of 2012 NSC project, we discovered that HMB supplement not only increase bone formation but also inhibited bone resorption through inhibition of NF-kb pathway. In the following study, we discovered that HMB supplement inhibit osteoclastogenesis through suppress DC-STAMP expression. Result of our previous study indicated that HMB dramatically reduced DC-STAMP expression on PBMC as well as RANK expression on cell surface as we predicted. However, mRNA expression the RANK downstream signal transducer NFATc1 remain unaffected. Such result indicate that inhibition effect of HMB supplement might happened before RANK expression and consequently lead to reduced DC-STAMP expression. Therefore, we design present study to investigate the effects of HMB supplement on signal transduction pathway of myeloid lineage deviriation to OCP on peripheral blood monocyte cells.