Leifeld L, Kothe S, Söhl G, Hesse M, Sauerbruch T, Magin T M, Spengler U
Evangelisches Krankenhaus Kalk, Cologne, Germany.
Eur J Clin Invest. 2009 Jun;39(6):481-8. doi: 10.1111/j.1365-2362.2009.02133.x. Epub 2009 Apr 9.
Keratins are intermediate filament proteins of epithelial cells with pivotal functions for cell integrity. They comprise keratins 18 [K18] and 8 [K8] in hepatocytes. Keratins are of major importance for an intact cellular microarchitecture and have protective functions in human liver diseases. In mice, K8 has been demonstrated to protect against Fas-antibody-induced liver failure by direct interaction with apoptotic regulators, while the role of K18 remains unresolved.
We analysed effects of K18 deficiency on Fas-induced liver failure in mice. We determined survival and analysed induction of apoptosis after injection of the agonistic Fas antibody Jo2 into K18(-/-) and wild-type control mice by TUNEL assay and fluorometrically analysed caspase-3, -8 and -9 activities 1, 2 and 3 h after Jo2 injection.
In K18(-/-) mice, survival of Fas-antibody treated mice was significantly shorter than that of wild-type controls (P = 0.02). However, shortened survival of K18(-/-) mice was caused by increased hepatic damage but was not correlated to enhanced induction of apoptotic pathways, as neither numbers of TUNEL positive apoptotic cells nor activities of caspases-3, -8 and -9 differed between K18(-/-) and K18(+/+) mice at any point of time.
K18(-/-) mice are significantly more susceptible to Fas-antibody-induced liver failure. The cytoprotective effect of K18 is not explained by a differential activation of caspases-3, -8 and -9, suggesting that K18 does not directly interfere with apoptotic regulators. Importantly, however, K18 exerts significant protective functions by other mechanisms.
角蛋白是上皮细胞的中间丝蛋白，对细胞完整性具有关键作用。在肝细胞中，它们由角蛋白18（K18）和角蛋白8（K8）组成。角蛋白对于完整的细胞微结构至关重要，并且在人类肝脏疾病中具有保护作用。在小鼠中，已证明K8通过与凋亡调节因子直接相互作用来预防Fas抗体诱导的肝衰竭，而K18的作用仍未明确。
我们分析了K18基因缺失对小鼠Fas诱导的肝衰竭的影响。我们测定了生存率，并通过TUNEL法分析了向K18基因敲除（K18(-/-)）小鼠和野生型对照小鼠注射激动性Fas抗体Jo2后凋亡的诱导情况，并在Jo2注射后1、2和3小时通过荧光法分析了半胱天冬酶-3、-8和-9的活性。
在K18(-/-)小鼠中，Fas抗体处理小鼠的生存率明显短于野生型对照（P = 0.02）。然而，K18(-/-)小鼠生存率缩短是由肝损伤增加引起的，但与凋亡途径的增强诱导无关，因为在任何时间点，K18(-/-)和K18(+/+)小鼠之间TUNEL阳性凋亡细胞数量以及半胱天冬酶-3、-8和-9的活性均无差异。
K18(-/-)小鼠对Fas抗体诱导的肝衰竭明显更易感。K18的细胞保护作用不能通过半胱天冬酶-3、-8和-9的差异激活来解释，这表明K18不会直接干扰凋亡调节因子。然而，重要的是，K18通过其他机制发挥显著的保护作用。
