云芝多糖通过TLR2/Akt途径防治小肠辐射损伤的机制研究

Gastrointestinal radiation injury is the most important limiting factor during radiotherapy of the abdomen cancer or heavily radiation-exposed injury in the nuclear accident. Our data showed the toll-like receptor 2 pathway agonist-Peptidoglycan （PGN） was intestine specific radioprotector and mitigator, AKT1/AKT2/AKT3 genes'regulation was different between the intestine and colon cancer from the same mice received PGN and irradiation. Polysaccharide Krestin（PSK）, another TLR2 agonist,is promising as a radiation mitigator. Here,the abdomen of C57BL/6J & intestine stem cell marker gene Lgr5/Bmil knockin mice were exposed to irradition. Constrasting endothelial /epithelial/stem cell apoptosis from the intestine will reveal PSK's target cell. TLR2/AKT1's role in PSK's radioprotector/mitigator would be revealed by TLR2 knockout & AKT1 mutant mice. Furthermore, series of studies such as overexpression/RNA interfere/inhibitor of AKT1/2/3 gene will answer PSK's target gene. These preclinical studies are expected to lead to clinical trials to prove the potential of PSK for treating abdominal cancer patients and intestine damaged patients in the nuclear explosion.

小肠的高放射敏感性极大限制了肠型放射病救治和腹部肿瘤放疗。课题组前期工作表明：Toll样受体2（TLR2）激动剂- - 细菌肽聚糖照前或照后给予均能明显延长10Gy全身照射小鼠的生存期；减轻荷瘤鼠15Gy腹部放疗引起的肠损伤，且不影响放射对结肠癌的治疗；对比结肠癌和小肠，AKT1/2/3基因表达变化相反。课题组还试验了一种应用安全的抗肿瘤TLR2激动剂- - 蘑菇云芝多糖（PSK），发现PSK也能显著延长10Gy X射线照射小鼠的生存期。本课题将用C57BL/6J、肠道干细胞标志物基因敲入小鼠建立腹部照射模型，照前或照后给予PSK,比较小肠的上皮、内皮、干细胞存活，得出PSK作用的靶细胞；应用TLR2基因敲除小鼠、AKT1基因无功能突变小鼠得出PSK作用与TLR2和AKT1的关系；在细胞水平上，阐明PSK通过TLR2/AKT途径减轻肠辐射损伤的调控机制。研究结果将为PSK应用于临床提供理论依据。

小肠的高放射敏感性极大限制了肠型放射病救治和腹部肿瘤放疗。本项目主要研究了Toll样受体2（TLR2）激动剂之一云芝多糖PSK发挥肠道辐射保护作用的靶细胞：肠道的上皮细胞、内皮细胞还是干细胞和关键信号通路：Akt1、Akt2、Akt3激酶，还是其它调控途径发挥作用。结果表明：PSK于10Gy全身照射前0.5小时给药减少小肠内皮细胞凋亡，PSK照后24小时给药促进小肠隐窝干细胞增殖。PSK促进肠道隐窝Lgr5+干细胞的增殖与抑制BMP通路有关。PSK通过TLR2/Akt1通路对小肠起到辐射防护作用。因此，PSK既可以作为辐射防护药，又可以用作辐射救治药物，而且这种药物是来自于云芝，药食同源，没有毒副作用。而另一个TLR2激动剂肽聚糖PGN通过TLR2-IL13-Akt3-mTOR通路起作用，在照射后的小肠中PGN激活这条信号通路促进隐窝增殖，而在照射后的结直肠肿瘤中，PGN抑制了这条信号通路从而抑制肿瘤生长。因而对荷瘤小鼠来说，照射后24小时给予PGN，既促进损伤的肠道修复，又辅助放疗更持久地抑制肿瘤生长。PGN有很大希望解决临床肿瘤放疗中放射治疗是一面双刃剑，杀肿瘤也杀正常组织，绝大多数放疗辅助药物杀肿瘤也杀正常组织、保护正常组织也保护肿瘤的两难问题。这些研究结果为PSK和PGN应用于核事故中病人救治、战士防护、腹部肿瘤病人放疗提供了实验依据。