紅血球生成素透過減少生物體內巨噬細胞活化以抑制腎臟纖維化

Abstract

紅血球生成素 (Erythropoietin，EPO) 是種多功能細胞因子，除了紅血球生成，紅血球生成素也表現組織保護的效果。近期證據指出紅血球生成素的多樣性功能是透過其與不同的受器結合而來，當紅血球生成素與EPO receptor (EPOR) 同型二聚體接合，執行紅血球生成；而當與EPOR及β common receptor (βcR 又稱作CD131) 所形成的異型二聚體接合，則執行組織修護。然而，許多獨立研究發現腎臟中並沒有EPOR，也無其訊息傳遞路徑的存在。 在腎臟纖維化的進程中，巨噬細胞扮演不可或缺的角色之一。Lin等人先前研究定義出小鼠體內巨噬細胞不同的亞群，其在腎臟的受損及修復扮演不同角色。又，Nariz等人研究指出紅血球生成素可透過抑制nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) 而將巨噬細胞去活化。我們對EPO防護慢性腎臟病 (chronic kidney disease，CKD) 的病程進展是否是透過巨噬細胞感到有興趣。利用小鼠單側輸尿管阻塞 (unilateral ureteral obstruction，UUO)作為模型，我們發現紅血球生成素於慢性腎臟病確實有抑制纖維化的效果。雖然單側輸尿管阻塞的腎臟之巨噬細胞數量並不受影響，但其呈現被紅血球生成素去活化的情形，inducible nitric oxide synthase (iNOS), macrophage inflammatory protein-1α (Mip-1α、CCL3)、macrophage inflammatory protein 2 (Mip-2、CXCL2)、interleukin-1β (IL1-β)、tumor necrosis factor-α (TNF-α) 等表示促傷害型的巨噬細胞 (pro-injurious macrophages，M1) 的基因皆被調降；Arginase-1(Arg-1)、chemokine (C-C motif) ligand 17 (CCL-17)、chemokine (C-C motif) ligand 22 (CCL22)、transforming growth factor-β1 (TGF-β1)、insulin-like growth factor-1 (IGF-1) 等表示促纖維化型的巨噬細胞 (pro-fibrotic，M2) 的基因也皆被調降。骨髓衍生巨噬細胞(bone-marrow derived macrophages，BMDM)呈現相同結果。因此，我們認為同時去活化促傷害型(M1)及促纖維化型(M2)的巨噬細胞可能是EPO抑制腎臟纖維化的其中一種機制。未來的研究必須鑑定何種受器及訊息傳遞鏈參與EPO對腎臟中巨噬細胞的影響。長期的目標希望可以透過瞭解EPO與位於腎臟內標的物的交互作用，發展EPO的衍生物或類似物應用於防止慢性腎病惡化。

Erythropoietin (EPO) is a multi-functional cytokine. In addition to erythropoiesis, EPO has been shown its tissue protective effect. Current evidence suggests that the pleiotropic effects of EPO are mediated by homodimer EPO receptor (EPOR) and heterocomplex composed of EPOR and β common receptor (βcR also known as CD131) for erythropoiesis and tissue protection respectively. However many independent studies found no expression and functional signaling of EPOR in the kidney. Macrophages are one of the key players in the progression of renal fibrosis. Previous studies by Lin et al. have defined macrophage subpopulations who play distinctive roles in renal injury and repair in mice. Evidence from Nariz et al. suggests macrophages can be deactivated by EPO through nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inhibition. We are intrigued by whether EPO protected chronic kidney disease (CKD) from progression through targeting macrophages. Using mouse models of unilateral ureteral obstruction (UUO), we have confirmed the antifibrotic effect of EPO in CKD. Although the cell numbers were not affected, UUO kidney macrophages were deactivated by EPO in vivo, as demonstrated by the downregulation of inducible nitric oxide synthase (iNOS), macrophage inflammatory protein-1α (Mip-1α, CCL3), macrophage inflammatory protein 2 (Mip-2, CXCL2), interleukin-1β (IL1-β), tumor necrosis factor-α (TNF-α) genes, which represent as pro-injurious (M1) macrophages; and Arginase-1 (Arg-1), chemokine (C-C motif) ligand 17 (CCL-17), chemokine (C-C motif) ligand 22 (CCL22), transforming growth factor-β1 (TGF-β1), insulin-like growth factor-1 (IGF-1) genes, which represent as pro-fibrotic (M2) macrophages. And the same result was detected by using bone marrow-derived macrophages (BMDM) in vitro. Therefore, we demonstrated that one of the mechanisms underlying the antifibrotic effect of EPO might be deactivating both pro-injurious and pro-fibrotic macrophages. Further studies need to identify the receptors and intracellular signaling mediating the effect of EPO on kidney macrophages. Long-term aim is to develop a novel EPO derivative or mimetic for renoprotection through understanding the interaction between EPO and its targets in the kidney.