TGF-β调控VEGF介导血管新生平衡紊乱在慢性放射性肠炎纤维化中的作用及其分子机制

Chronic radiation enteritis (CRE) is a common late complication of radiotherapy to the pelvic malignancies, and is characterized by microangiopathy and progressive fibrosis, but the relation between them and the underlying mechanism is largely unclear and needs further research. Our previous studies showed obvious microangiopathy including a reduced capillary density and the irregular architectural chaos of the microvasuclar wall in CRE patients. Angiostatic factors such as angiostasis, urokinase type plasminogen activator (uPA), thrombospodin-1 (TSP-1) were overexpressed in CRE, while unexpectedly angiogenic factors such as transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), matrix metalloproteinases-9 (MMP-9) were also over-expressed in CRE patients. Based on those abnormal phenomenons, We proposed the scientific hypothesis that “TGF-β regulates VEGF expression, and then mediated the dysregulation of angiogenic balance, which leads to microangiopathy and promotes the fibrosis in CRE”. In order to verify this hypothesis, this project intends to explore the correlation of TGF-β/VEGF polymorphisms, expression and CRE risk and prognosis; Then to clarify the mechanism of TGF-β activation that promotes fibrosis in CRE and to reveal TGF-β via Smad 2/3 pathway to elevate the level of VEGF expression; Finally, to verify these above mechanisms in vivo by constructing conditional gene-knockout rats. This study wil help to clarify the molecular mechanism of microangiopathy and fibrosis in CRE, and to provide scientific evidences for preventing and treating CRE fibrosis.

慢性放射性肠炎（CRE）是盆腔恶性肿瘤放疗后的常见晚期并发症，微血管损害和进行性纤维化是主要病理特征，但两者的关系、调控机制尚不清楚。我们前期研究发现，在CRE组织中微血管损害（包括血管新生减少和微血管形态结构异常），抑血管信号如血管抑素（AS）、uPA等均高表达，而促血管信号如TGF-β、VEGF等也异常高表达。基于上述血管新生的异常现象，本课题提出TGF-β调控VEGF表达，使血管新生平衡发生紊乱导致微血管损害，从而刺激纤维化形成的科学假设。拟在CRE中深入研究TGF-β、VEGF基因多态性、表达水平与CRE的临床相关性；阐明TGF-β-Smad2/3-VEGF信号通路参与纤维化进程的分子调控机制，并建立基因敲除大鼠模型验证。本研究有助于揭示微血管损害的内在机制及与纤维化发生发展的联系，为临床防治CRE纤维化提供科学依据。

慢性放射性肠炎（CRE）是盆腔恶性肿瘤放疗后的常见晚期并发症，出现在放疗结束后数月甚至数年，发生率高达20%，严重影响患者的生活质量。肠壁粘膜下层纤维化和血管病变是CRE最主要的病理特征，但其分子机制远未阐明。前期我们通过对CRE临床标本进行抗体芯片检测发现，血管抑素angiostatin和趋化因子CXCL16在CRE中高表达；进一步研究发现angiostatin在发生CRE的病变肠管粘膜层和粘膜下层均异常广泛高表达，其表达分布特征主要弥漫性聚集在血管外，而在正常肠管其主要局限在血管内，且在CRE中伴随着肠粘膜下层微血管密度的显著降低，表明angiostatin的异常分布和高表达可能是CRE微血管生成减少的主要原因，此研究结果已发表在Dig Dis Sci (2018) 杂志。同时，我们发现CXCL16在CRE中表达升高后，能进一步通过激活TGF-β/Smad2/3活化肠成纤维细胞，使其分泌纤维蛋白collagen等增多，进而促进纤维化的发生；更重要的是，在我们构建的CRE动物模型中，利用CXCL16单克隆中和性抗体阻断CXCL16的作用能有效地抑制CRE纤维化的发生和发展。这些研究结果不仅为CRE血管损伤和纤维化发生的机制增添了新的内容，同时为CRE的临床诊断和治疗提供了潜在的生物标记物和分子靶点。