Role of microRNA_21 in acetaminophen-induced acute liver failure

急性肝衰竭（ALF）的特征是肝细胞功能严重和突然丧失， 先前肝功能正常，可能导致多器官系统衰竭和死亡。在美国，毒品- 诱导性肝损伤是ALF的主要原因，对乙酰氨基酚（APAP）中毒约占50%， ALF病例。APAP诱导的ALF会影响儿童、青少年和年轻人。N-乙醯基 半胱氨酸是APAP诱导的ALF目前唯一可用的治疗方法;然而，它不是完全有效的 死亡率为30%，另外10%需要肝脏移植。因此，替代或补充- 对于患有以下疾病的个体，特别是儿童，迫切需要有效的药理学治疗： APAP诱导的ALF。MicroRNA（miRNAs）与肝脏炎症、纤维化和病毒性肝炎有关。 感染miRNAs在进入临床的过程中是非常有吸引力的治疗靶点，但miRNAs的作用 作为APAP诱导的ALF的治疗剂仍然没有探索。microRNA-21（miR-21）是一种有吸引力的癌症。 因为它是最高表达的肝脏miRNAs之一，并受到APAP的动态调节 服药过量此外，在ALF自发恢复的患者中， 肝脏活检，强烈表明降低肝脏miR-21水平可能是一种有效的治疗方法 关于APAP-ALF miR-21减少对APAP-ALF具有保护作用的一种机制可能是由于 肝脏分区的变化。肝脏分区对于氨解毒、葡萄糖/能量代谢和 异生物代谢特异性肝脏miRNAs的药理学操作可能导致短暂的肝脏 分区破坏，可以防止APAP诱导的ALF。我们有初步数据表明，miR-21基因 小鼠中的消融可防止APAP诱导的ALF，并减弱APAP介导的血清中ALF的增加 肝酶和减少肝坏死。此外，转基因小鼠中miR-21的过表达 加重APAP诱导的肝损伤。我们也有初步的数据表明miR-21优先被 在门静脉周围肝细胞中表达。此外，miR-21消融破坏了肝细胞癌的表达模式。 谷氨酰胺合成酶，这表明缺乏miR-21导致门静脉周围样肝脏表型， 也有助于APAP诱导的ALF中miR-21下调的保护作用。基于这些 令人兴奋的初步数据，我们建议测试中心假设，即“miR-21调节肝脏分区， miR-21的下调导致门脉周样肝脏表型，其保护免于APAP诱导的肝细胞凋亡。 肝毒性。”这一假设将在以下具体目标进行检验：1）检验假设， miR-21消融可防止APAP诱导的肝毒性，而miR-21过表达则会加剧APAP诱导的肝毒性; 2） 为了验证miR-21的急性药理学下调可以保护APAP诱导的细胞凋亡的假设， 急性肝衰竭; 3）验证miR-21优先在门静脉周围肝细胞中表达的假设 并调节肝分区从而调节APAP诱导的肝毒性。

Acute liver failure (ALF) is characterized by severe and sudden loss of hepatocellular function in patients with previously normal liver function which may lead to multiorgan system failure and death. In the US, drug- induced liver injury is the main cause of ALF, and acetaminophen (APAP) intoxication accounts for ~50% of ALF cases. APAP-induced ALF disproportionally affects children, adolescents and young adults. N-acetyl- cysteine is the only currently available therapy for APAP-induced ALF; however, it is not completely effective with a mortality rate of 30% and another 10% requiring liver transplant. Therefore, alternative or complemen- tary pharmacological therapies are desperately needed for individuals, especially children, suffering from APAP-induced ALF. MicroRNAs (miRNAs) have been implicated in liver inflammation, fibrosis, and viral infection. MiRNAs are highly attractive therapeutic targets on their way into the clinic, but the role of miRNAs as therapeutic agents in APAP-induced ALF remains unexplored. MicroRNA-21 (miR-21) is an attractive candi- date because it is one of the most highly expressed hepatic miRNAs and is dynamically regulated by APAP overdose. Furthermore, in patients with spontaneous recovery from ALF, miR-21 expression is decreased in liver biopsies, strongly suggesting that reduction of hepatic miR-21 levels may be a valid therapeutic approach for APAP-ALF. One mechanism by which miR-21 reduction is protective against APAP-ALF may be due to changes in liver zonation. Liver zonation is critical for ammonia detoxification, glucose/ energy metabolism, and xenobiotic metabolism. Pharmacological manipulation of specific hepatic miRNAs could lead to transient liver zonation disruption that may protect against APAP-induced ALF. We have preliminary data that miR-21 genetic ablation in mice protects against APAP-induced ALF, with attenuation of APAP-mediated increases in serum hepatic enzymes and reduced liver necrosis. Furthermore, miR-21 over-expression in transgenic mice exacerbates the APAP-induced liver injury. We also have preliminary data that miR-21 is preferentially expressed in periportal hepatocytes. In addition, miR-21 ablation disrupts the expression pattern of hepatic glutamine synthetase, suggesting that the lack of miR-21 leads to a periportal-like liver phenotype that may also contribute to the protective effect of miR-21 downregulation in APAP-induced ALF. Based on these exciting preliminary data, we propose to test the central hypothesis that “miR-21 regulates liver zonation, and downregulation of miR-21 leads to a periportal-like liver phenotype that protects against APAP-induced hepatotoxicity.” This hypothesis will be tested in the following specific aims: 1) To test the hypothesis that miR-21 ablation protects against, while miR-21 over-expression exacerbates, APAP-induced hepatotoxicity; 2) To test the hypothesis that acute pharmacological downregulation of miR-21 protects against APAP-induced acute liver failure; 3) To test the hypothesis that miR-21 is preferentially expressed in periportal hepatocytes and regulates liver zonation thereby modulating APAP-induced hepatotoxicity.