巨噬細胞的移走作用是寄主對抗病原菌感染及修復受傷組織的必要免疫反應。已知cAMP專一性phosphodiesterase 4 (PDE4)是免疫細胞內主要水解cAMP的酵素，且在活化的巨噬細胞中，抑制PDE4以提升細胞內cAMP濃度，可抑制多種免疫發炎反應，進而減緩相關的發炎疾病。目前PDE4抑制劑的抗發炎作用已有較廣泛的報導，然而PDE4對巨噬細胞移走作用的調控仍知之甚少。為此，本研究使用格蘭氏陰性細菌外膜的lipopolysaccharide (LPS)刺激小鼠Raw 264.7巨噬細胞，並以傷口癒合試驗檢測PDE4抑制劑或cAMP對細胞移走的影響。結果顯示LPS會輕微地，但顯著地，誘導巨噬細胞移走，而PDE4抑制劑rolipram會大幅提升此作用，此外，巨噬細胞移走也會隨著rolipram濃度上升而逐漸增加。我們發現rolipram提升的移走作用需要血清的參與，因為在無血清培養下此提升作用不會產生。進一步以不同濃度的牛胎血清(0、2、10% FBS)處理細胞，結果顯示，rolipram與血清能協同促進LPS所誘導的巨噬細胞移走。此外，小鼠與馬血清也具有相同的協同作用，這表示在哺乳動物的血清中，可能有共同的因子會與rolipram協同促進LPS誘導巨噬細胞的移走。實驗進一步證實此rolipram作用是經由活化exchange proteins directly activated by cAMP (Epac)，而非protein kinase A的訊息傳導路徑所致，我們推測這是在血清因子的影響下，由cAMP/Epac訊息傳導與LPS/TLR4訊息傳導的交互作用所引起的移走作用。這些結果表明，隨同血清因子的參與，PDE4抑制劑能促使巨噬細胞被招募至發炎部位，以致更有效的清除病原體及修復傷口。;Macrophage migration is an essential step in host defense against infection and wound healing. Elevation of cAMP by inhibiting phosphodiesterase 4 (PDE4), enzymes that specifically degrade cAMP, is known to suppress various inflammatory responses in activated macrophages, but the role of PDE4 in macrophage migration is poorly understood. Here we show that the migration of Raw 264.7 macrophages stimulated with LPS was markedly and dose-dependently induced by the PDE4 inhibitor rolipram as assessed by scratch wound healing assay. Additionally, this response required the involvement of serum in the culture medium as serum starvation abrogated the effect. Further analysis revealed that rolipram and serum exhibited synergistic effect on the migration. Moreover, the enhanced migration by rolipram was mediated by activating cAMP/exchange proteins directly activated by cAMP (Epac) signaling, presumably via interaction with LPS/TLR4 signaling with the participation of unknown serum components. These results suggest that PDE4 inhibitors, together with serum components, may serve as positive regulators of macrophage recruitment for more efficient pathogen clearance and wound repair.
