LAMP-2调控MRP2在原发性胆汁性肝硬化中的作用及机制

Primary biliary cirrhosis (PBC) is characterized by the chronic intrahepatic cholestasis, which is related to the abnormality of hepatocyte canalicular surfaces. We have previously reported that increased immunoreactivity of lysosome-associated membrane protein-2 (LAMP-2) was evident in the livers of PBC patients. Further data demonstrated that the basal serum LAMP-2 level was also increased in PBC, and a decline of serum LAMP-2 may help to predict ursodeoxycholic acid response in PBC. To address the specific functions of LAMP-2 in PBC, we generated rats deficient in this protein. Unexpectedly, LAMP-2 deficiency causes a phenotype of early intrahepatic cholestasis with morphological changes of the bile canaliculi. Further studies showed that redistribution of multidrug resistance-associated protein-2 (MRP2) was found in the livers of LAMP-2y/- rats by histochemistry. Kojima et al. reported that redistribution of MRP2 into intracellular structures was found in PBC, but the mechanism still needs to be further clarified. In this study, we hypothesized that LAMP-2 was involved in regulating the localization and/or function of MRP2 in hepatocytes, which might be responsible for the cholestasis in PBC patients. Therefore, the present study aims to further clarify the potential roles and mechanisms of LAMP-2 in regulating MRP2, which may help illuminate the mechanisms of intrahepatic cholestasis and find the novel therapeutic targets in PBC patients.

PBC是一种肝内胆汁淤积性肝病，发病机制至今不清。本课题组在国际上率先发现肝脏LAMP-2表达及分布变化与PBC疾病进展正相关，且PBC外周血LAMP-2下降程度有助于评判患者对熊去氧胆酸治疗的应答。为进一步探讨LAMP-2在PBC中的作用，我们构建了LAMP-2基因敲除大鼠，发现该模型鼠呈现有肝内胆汁淤积的表型，免疫组化提示肝脏MRP2定位异常。既往研究报道：PBC肝脏MRP2表达分布异常，提示其参与了患者的胆汁淤积，但机制不清。我们的科学假设是：LAMP-2可能通过调控肝细胞胆管膜转运体MRP2的定位和/或功能，参与了PBC的发生、发展。本课题拟在前期工作基础上，进一步探讨LAMP-2对MRP2定位和/或功能的调控作用及可能的调控机制；验证LAMP-2调控MRP2在PBC发病及诊治中的作用。该项目是本课题组既往对LAMP-2与PBC研究的深入，对于理解 PBC 发生发展具有重要意义。

原发性胆汁性胆管炎（PBC）是一种自身免疫介导的慢性肝内胆汁淤积性肝病。本课题组在国际上率先发现肝脏溶酶体相关膜蛋白2（LAMP-2）表达及分布变化与PBC疾病进展正相关，且PBC外周血LAMP-2下降程度有助于评判患者对熊去氧胆酸治疗的应答。本项目借助LAMP-2基因敲除大鼠模型，评估了LAMP-2分子对肝脏功能的影响。研究发现：LAMP-2基因敲除大鼠呈现有肝内胆汁淤积的表型，表现为血清中反应早期胆汁淤积的指标碱性磷酸酶（ALP）升高，胆汁排泄功能降低，电镜检测发现毛细胆管发育障碍和早期肝内胆汁淤积现象；LAMP-2敲除大鼠对胆汁淤积的耐受性降低，更易发生胆汁排泄障碍，表现为借助经典的胆汁淤积模型（胆总管结扎模型）人为诱导胆汁淤积时， 血清中直接反应胆汁淤积的指标胆红素在 LAMP-2 基因缺陷鼠中的升高更明显。进一步研究发现，LAMP-2敲除大鼠肝细胞胆管侧膜上重要的胆汁排泄分子多药耐药相关蛋白2（MRP2）的定位和功能异常，LAMP-2可能通过影响F-actin和Radixin实现对MRP2的调控，从而影响胆汁排泄。