Tomita Kyoko, Kabashima Ayano, Freeman Brittany L, Bronk Steven F, Hirsova Petra, Ibrahim Samar H
Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota.
Division of Pediatric Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota.
J Cell Biochem. 2017 Oct;118(10):3249-3259. doi: 10.1002/jcb.25973. Epub 2017 May 15.
Saturated fatty acids (SFA) and their toxic metabolites contribute to hepatocyte lipotoxicity in nonalcoholic steatohepatitis (NASH). We previously reported that hepatocytes, under lipotoxic stress, express the potent macrophage chemotactic ligand C-X-C motif chemokine 10 (CXCL10), and release CXCL10-enriched extracellular vesicles (EV) by a mixed lineage kinase (MLK) 3-dependent mechanism. In the current study, we sought to examine the signaling pathway responsible for CXCL10 induction during hepatocyte lipotoxicity. Here, we demonstrate a role for signal transducer and activator of transcription (STAT) 1 in regulating CXCL10 expression. Huh7 and HepG2 cells were treated with lysophosphatidylcholine (LPC), the toxic metabolite of the SFA palmitate. In LPC-treated hepatocytes, CXCL10 induction is mediated by a mitogen activated protein kinase (MAPK) signaling cascade consisting of a relay kinase module of MLK3, MKK3/6, and p38. P38 in turn induces STAT1 Ser727 phosphorylation and CXCL10 upregulation in hepatocytes, which is reduced by genetic or pharmacological inhibition of this MAPK signaling cascade. The binding and activity of STAT1 at the CXCL10 gene promoter were identified by chromatin immunoprecipitation and luciferase gene expression assays. Promoter activation was attenuated by MLK3/STAT1 inhibition or by deletion of the consensus STAT1 binding sites within the CXCL10 promoter. In lipotoxic hepatocytes, MLK3 activates a MAPK signaling cascade, resulting in the activating phosphorylation of STAT1, and CXCL10 transcriptional upregulation. Hence, this kinase relay module and/or STAT1 inhibition may serve as a therapeutic target to reduce CXCL10 release, thereby attenuating NASH pathogenesis. J. Cell. Biochem. 118: 3249-3259, 2017. © 2017 Wiley Periodicals, Inc.
饱和脂肪酸（SFA）及其毒性代谢产物在非酒精性脂肪性肝炎（NASH）中导致肝细胞脂肪毒性。我们之前报道过，在脂肪毒性应激下，肝细胞会表达强效巨噬细胞趋化配体C-X-C基序趋化因子10（CXCL10），并通过混合谱系激酶（MLK）3依赖性机制释放富含CXCL10的细胞外囊泡（EV）。在当前研究中，我们试图研究肝细胞脂肪毒性期间负责CXCL10诱导的信号通路。在此，我们证明了信号转导和转录激活因子（STAT）1在调节CXCL10表达中的作用。用溶血磷脂酰胆碱（LPC）（SFA棕榈酸酯的毒性代谢产物）处理Huh7和HepG2细胞。在LPC处理的肝细胞中，CXCL10的诱导由丝裂原活化蛋白激酶（MAPK）信号级联介导，该信号级联由MLK3、MKK3/6和p38的中继激酶模块组成。P38进而诱导肝细胞中STAT1 Ser727磷酸化和CXCL10上调，而这种MAPK信号级联的基因或药理学抑制会使其降低。通过染色质免疫沉淀和荧光素酶基因表达测定法确定了STAT1在CXCL10基因启动子处的结合和活性。MLK3/STAT1抑制或CXCL10启动子内共有STAT1结合位点的缺失会减弱启动子激活。在脂肪毒性肝细胞中，MLK3激活MAPK信号级联，导致STAT1的激活磷酸化和CXCL10转录上调。因此，这种激酶中继模块和/或STAT1抑制可作为减少CXCL10释放的治疗靶点，从而减轻NASH发病机制。《细胞生物化学杂志》118: 3249 - 3259, 2017。© 2017威利期刊公司
