Regenerative medicine for liver diseases : Analysis of the development and differentiation of hepatic oval cells

我们首先检查了在2-乙酰氨基芴/部分肝切除术（AAF/PH）模型中经历再生的肝中的制瘤素M（OSM）和OSM特异性受体（OSM-R）的表达。OSM在卵圆细胞和枯否细胞中均有表达，但OSM-R仅在卵圆细胞中表达。当大鼠卵圆细胞（OC 15 -5）在表达大鼠OSM cDNA的293 T细胞的条件培养基中孵育时，这导致生长抑制，形态改变为具有微绒毛和具有发达细胞器的大细胞质，并且在OC 15 -5细胞中表达肝细胞标志物，如酪氨酸氨基转移酶和色氨酸加氧酶。这些结果表明OSM是诱导OC 15 -5细胞向肝细胞分化的关键介质，并表明OSM/OSM-R系统在卵圆细胞向肝细胞分化中起关键作用，从而促进肝再生。接下来，我们检测了Dlk在AAF/PH模型中的表达。免疫荧光染色显示Dlk+细胞表达卵圆细胞标志物细胞角蛋白19（CK 19）和甲胎蛋白，表明Dlk在卵圆细胞中表达。但Dl 1 k+细胞仅占CK 19+卵圆细胞总数的20%左右。Dlk+细胞比Dlk-细胞更远离门静脉定位，并且与成熟肝细胞相邻。此外，在PH后第12天，仅3%的Dlk+卵圆细胞表达Ki 67，而约13%的总卵圆细胞表达Ki 67，表明Dlk+卵圆细胞比Dlk-卵圆细胞增殖性低。综上所述，这些结果证明Dlk在卵圆细胞亚群中表达，并且Dlk+细胞代表Dlk-卵圆细胞和成熟肝细胞之间的中间细胞。

We first examined the expression of Oncostatin M(OSM) and OSM-specific receptor(OSM-R) in the liver undergoing regeneration in the 2-acetylaminofluorene/partial hepatectomy(AAF/PH) model. OSM was expressed in both oval cells and Kupffer cells, but OSM-R was exclusively expressed in oval cells. When rat oval cells (OC15-5) were incubated in the conditioned medium of 293T cells expressing rat OSM cDNA, this resulted in suppression of growth, changes in morphology to possess microvilli and large cytoplasm with developed organells, and expression of hepatocyte markers, such as tyrosine amino transferase and tryptophan oxygenase, in OC15-5 cells. These results indicate that OSM is a key mediator for induction of the differentiation of OC15-5 cells into hepatocytes, and suggest that the OSM/OSM-R system plays a pivotal role in the differentiation of oval cells into hepatocytes, thereby promoting liver regeneration.Next, we examined the expression of Dlk in the AAF/PH model. Immunofluoresence staining analysis revealed that Dlk+ cells expressed oval cell markers, cytokeratin 19(CK19) and α-fetoprotein, indicating that Dlk is expressed in oval cells. However, Dl1k+ cells accounted for only about 20% of total CK19+ oval cells. Dlk+ cells were localized more distantly from the portal vein than Dlk- cells, and were adjacent to mature hepatocytes. Furthermore, at day 12 after PH, only 3% of Dlk+ oval cells expressed Ki67, whereas about 13% of total oval cells expressed Ki67, indicating that Dlk+ oval cells are less proliferative than Dlk- oval cells. Taken together, these results demonstrate that Dlk is expressed in a subpopulation of oval cells and that Dlk+ cells represent intermediate cells between Dlk- oval cells and mature hepatocytes.