Schwall R H, Robbins K, Jardieu P, Chang L, Lai C, Terrell T G
Department of Endocrine Research, Genentech, Inc., South San Francisco, California 94080.
Hepatology. 1993 Aug;18(2):347-56. doi: 10.1016/0270-9139(93)90018-i.
While studying endocrine responses to activin in female rats, we discovered that activin caused a marked reduction in liver mass. The regressed livers exhibited no gross signs of necrosis or infarction, but histopathological evaluation revealed extensive cell death in the centrilobular regions. The dying cells appeared to fragment into structures resembling apoptotic bodies. Liver mass and histological appearance were restored after cessation of activin infusion, indicating that on an organ level, this effect was reversible. To determine whether the effects observed in vivo were caused by direct actions on the liver, we then tested activin on isolated hepatocytes in serum-free medium. Under these conditions, activin caused many hepatocytes to undergo fragmentation, which was accompanied by a loss of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-reducing activity, an index of viability. We compared the effects of activin with those of transforming growth factor-beta because activin is structurally related to transforming growth factor-beta and because transforming growth factor-beta has been shown previously to induce cell death in hepatocytes. Both proteins caused cell death of comparable magnitude, as defined by the extent of loss of MTT-reducing activity, but transforming growth factor-beta was active at one tenth of the effective activin concentrations. A neutralizing monoclonal antibody to transforming growth factor-beta blocked the response to transforming growth factor-beta but had no effect on the response to activin. Conversely, follistatin, an activin-binding protein, blocked the response to activin but not to transforming growth factor-beta. Inhibin, which antagonizes the effects of activin in many systems, had little effect on the response to activin. Activin and transforming growth factor-beta differed in their onset of action; exposure to transforming growth factor-beta for only 1 hr induced a maximal response, whereas maximal response to activin required its continuous presence for 24 hr. These results show a novel effect of activin on cell death in hepatocytes in vivo and in vitro, suggesting that activin may have a previously unrecognized role in regulating hepatic function.
在研究雌性大鼠对激活素的内分泌反应时，我们发现激活素可导致肝脏重量显著减轻。萎缩的肝脏未出现坏死或梗死的明显迹象，但组织病理学评估显示小叶中央区域存在广泛的细胞死亡。垂死的细胞似乎破碎成类似凋亡小体的结构。停止注入激活素后，肝脏重量和组织学外观得以恢复，这表明在器官水平上，这种效应是可逆的。为了确定体内观察到的效应是否由对肝脏的直接作用引起，我们随后在无血清培养基中对分离的肝细胞进行了激活素测试。在这些条件下，激活素导致许多肝细胞发生破碎，同时伴随着作为活力指标的3-（4,5-二甲基噻唑-2-基）-2,5-二苯基四氮唑溴盐（MTT）还原活性丧失。我们将激活素的作用与转化生长因子-β的作用进行了比较，因为激活素在结构上与转化生长因子-β相关，且先前已表明转化生长因子-β可诱导肝细胞死亡。两种蛋白质导致的细胞死亡程度相当，以MTT还原活性丧失的程度来定义，但转化生长因子-β在有效激活素浓度的十分之一时就具有活性。一种针对转化生长因子-β的中和单克隆抗体可阻断对转化生长因子-β的反应，但对激活素的反应无影响。相反，卵泡抑素，一种激活素结合蛋白，可阻断对激活素的反应，但对转化生长因子-β的反应无影响。抑制素在许多系统中拮抗激活素的作用，对激活素的反应影响很小。激活素和转化生长因子-β在作用起效时间上有所不同；仅暴露于转化生长因子-β1小时即可诱导最大反应，而对激活素的最大反应需要其持续存在24小时。这些结果显示了激活素在体内和体外对肝细胞细胞死亡的新作用，表明激活素可能在调节肝功能方面具有先前未被认识到的作用。
