類澱粉神經病變之神經退化機制

Abstract

家族性類澱粉多發性神經病變(Familial amyloidotic polyneuropathy, FAP)是一種有甲狀腺素運送蛋白(transthyretin, TTR)沉澱形成類澱粉纖維堆積的疾病，主要又以周邊神經系統受影響。其症狀一開始和發炎性神經病變極為相似且組織切片上也有巨噬細胞浸潤，但是使用免疫抑制治療卻效果不彰，目前其神經退化之機制仍尚未明朗。本研究除了利用型態學的方法分析正常人(n=4)、糖尿病截肢(Diabetic amputation, DM)(n=13)、慢性脫髓鞘多發性神經炎(Chronic inflammatory demyelinating polyneuropathy, CIDP)(n=3)以及家族性類澱粉多發性神經病變患者(n=13)的有髓鞘神經纖維密度以及微血管病變因子，也利用免疫組織化學染色的方法觀察家族性類澱粉多發性神經病變之巨噬細胞浸潤和分型、纖維蛋白沉積及其相關因子。實驗發現雖然家族性類澱粉多發性神經病變的Iba1免疫反應和慢性脫髓鞘多發性神經炎一樣偏高(正常人：0.08±0.03 O.D., DM：1.46±1.09 O.D., CIDP：5.35±1.38 O.D., FAP：3.01±1.05 O.D.)，但有髓鞘神經纖維密度卻喪失嚴重，並且和可能是血管引起的糖尿病病變的退化程度相似(正常人：7595±1718 fibers/mm2, DM：2599±1601 fibers/mm2, CIDP：5046±2462 fibers/mm2, FAP：1086±686.1 fibers/mm2)。此外，家族性類澱粉多發性神經病變和糖尿病病人皆可觀察到微血管管壁厚度增厚(正常人：2.8±0.4μm, DM：4.46±0.83μm , CIDP：2.77±0.32, FAP：4.4±0.8μm)且管腔面積較狹窄(正常人：15.2±5.1%, DM：4.4±1.4%, CIDP：13.2±4.5%, FAP：9.1±4.4%)，並和有髓鞘神經密度和皆有顯著相關(p < 0.05)。在此疾病的血管中也有不等的纖維蛋白沉積於神經內膜微血管(37.24±29.50%)和神經外膜的血管中(37.42±16.92%)，並且和有髓鞘神經纖維密度以及Iba1免疫反應呈正相關(p < 0.05)，雖然凝血酶調節素表現量沒有差異但其中組織因子有上調並和纖維蛋白有正相關(p < 0.05)，也觀察到組織型纖維蛋白溶酶原激活物也有下調的現象。進一步我們發現替代性活化巨噬細胞的標定CD206有免疫反應於神經內膜中。綜合以上結果，我們提供了家族性類澱粉多發性神經病變的神經內膜微血管病變與神經退化嚴重程度相關聯的型態學證據，了解纖維蛋白有被上調造成不正常堆積於管腔內，並且連結纖維蛋白和巨噬細胞彼此的關係，此外，也提供巨噬細胞作用於此疾病的新思維，希望有助於運用在臨床治療上。

Familial amyloid polyneuropathy (FAP) is characterized by the extracellular deposition of transthyretin (TTR) aggregates which form amyloid fibrils, particularly in the peripheral nervous system. The mechanisms of nerve degeneration in FAP remain unclear. In the present study, we performed morphological and immunohistochemical analysis of sural nerve biopsies from 13 patients with FAP, 3 patients with chronic inflammatory demyelinating polyneuropathy (CIDP), 13 diabetic amputee and 4 control subjects. Although the infiltration pattern of Iba1(+) macrophages resembled that of CIDP, the density of myelinated fibers was markedly reduced in FAP. Narrowing of lumen area (p < 0.05) and thickened wall thickness (p < 0.05) were observed in FAP. In FAP patients, the severity of neuropathy was correlated with capillary wall thickness (p < 0.05) and percentage of lumen area (%) (p < 0.05)。The proportion of fibrin accumulated endoneurial vessels was positively correlated with myelinated fiber density (p < 0.05) and Iba1 expression (p < 0.05). We also examined the expression of tissue factor, thrombomodulin and tissue plasminogen activator (tPA) to investigate the activation of coagulation and fibrinolysis. The immunoreactivity of tissue factor was upregulated in the vessels and associated with fibrin deposition (p < 0.05). But there was no alternation in the thrombomodulin expression. The expression of tPA was almost absent in FAP nerves (p < 0.05). To identify the phenotype of the macrophage present in the endoneurium, immunohistochemistry of CD206 was performed, and it was up-regulated in FAP compared with control group. In conclusion, we provided structural and pathological evidence that vascular changes were related to the severity of nerve degeneration in FAP. Upregulation of coagulation cascade in FAP leading to fibrin deposition in the epineurial and endoneurial vessels was also observed. Moreover, we determined that the macrophage phenotype in the endoneurium which was classified as alternatively activated macrophage, which may offer new insight into the function of macrophages in FAP.