Division of Liver Diseases, Mount Sinai School of Medicine, New York, New York 10029, USA.
J Cell Physiol. 2010 Jun;223(3):648-57. doi: 10.1002/jcp.22063.
Hepatic stellate cells (HSCs) store retinoids and triacylglycerols in cytoplasmic lipid droplets. Two prominent features of HSC activation in liver fibrosis are loss of lipid droplets along with increase of alpha-smooth muscle actin (alpha-SMA), but the link between these responses and HSC activation remains elusive. In non-adipose cells, adipose differentiation-related protein (ADRP) coats lipid droplets and regulates their formation and lipolysis; however its function in HSCs is unknown. Here, we observed, in human liver sections or primary HSC culture, ADRP localization to lipid droplets of HSCs, and reduced staining coincident with loss of lipid droplets in liver fibrosis and in culture-activated HSCs, consistent with HSC activation. In the LX-2 human immortalized HSCs, with scant lipid droplets and features of activated HSCs, we found that the upregulation of ADRP mRNA by palmitate is potentiated by retinol, accompanied by increased ADRP protein, generation of retinyl palmitate, and lipid droplet formation. ADRP induction also led to decreased expression of alpha-SMA mRNA and its protein, while ADRP knockdown with small interfering RNA (siRNA) normalized alpha-SMA expression. Furthermore, ADRP induction by retinol and palmitate resulted in decreased expression of collagen I and matrix metalloproteinase-2 mRNA, fibrogenic genes associated with activated HSCs, while increasing matrix metalloproteinase-1 mRNA; ADRP knockdown with siRNA reversed these changes. Tissue inhibitor of metalloproteinase-1 was not affected. Thus, ADRP upregulation mediated by retinol and palmitate promotes downregulation of HSC activation and is functionally linked to the expression of fibrogenic genes.
肝星状细胞（HSCs）在细胞质脂滴中储存类视黄醇和三酰基甘油。肝纤维化中 HSC 活化的两个显著特征是脂滴的丢失以及α-平滑肌肌动蛋白（α-SMA）的增加，但这些反应与 HSC 活化之间的联系仍不清楚。在非脂肪细胞中，脂肪分化相关蛋白（ADRP）覆盖脂滴并调节其形成和脂解；然而，其在 HSCs 中的功能尚不清楚。在这里，我们在人肝切片或原代 HSC 培养物中观察到 ADRP 定位于 HSCs 的脂滴，并且在肝纤维化和培养活化的 HSCs 中脂滴丢失时染色减少，与 HSC 活化一致。在 LX-2 人永生化 HSCs 中，脂滴稀少且具有活化的 HSCs 特征，我们发现棕榈酸通过视黄醇上调 ADRP mRNA 的表达，伴随着 ADRP 蛋白增加、视黄醇棕榈酸的生成和脂滴形成。ADRP 诱导也导致α-SMA mRNA 及其蛋白表达减少，而用小干扰 RNA（siRNA）敲低 ADRP 则使α-SMA 表达正常化。此外，视黄醇和棕榈酸诱导的 ADRP 诱导导致与活化的 HSCs 相关的纤维化基因胶原 I 和基质金属蛋白酶-2 mRNA 的表达减少，而基质金属蛋白酶-1 mRNA 的增加；用 siRNA 敲低 ADRP 逆转了这些变化。金属蛋白酶组织抑制剂-1不受影响。因此，视黄醇和棕榈酸介导的 ADRP 上调促进了 HSC 活化的下调，并与纤维化基因的表达在功能上相关。
