探討TNF在由對乙醯氨基酚引起的急性肝損傷中扮演的角色

Abstract

細胞壞死後會釋出的許多物質會引起無菌發炎反應，所引起的發炎反應其目的為移除細胞殘骸，以避免造成周圍組織持續性的傷害。本實驗中分別給予WT和TNF受體缺陷（TNFR1-/-）小鼠過量的acetaminophen （APAP），觀察到TNFR1-/-小鼠在血清中肝功能指數（ALT activity）、促發炎激素（proinflammatory cytokines）的釋放有降低的情形；而且，提前給予小鼠阻斷TNF訊息傳遞的藥物”Enbrel”，發現可有效降低APAP引起的肝損傷及其引起的發炎反應，顯示TNFR1在APAP誘導的肝損傷模式中扮演重要角色。接著，藉由產生骨髓置換小鼠（bone marrow chimeras），我們想探討在APAP引起肝損傷的模式中，TNF是作用於由從骨髓分化而來的細胞（bone marrow derived cells），抑或於非從骨髓分化而來的細胞（non-bone marrow derived cells）。實驗結果顯示將WT小鼠的骨髓置換至TNFR1-/-小鼠中，ALT及proinflammatory cytokines有上升的情形，顯示表現在從骨髓分化而來的細胞上的TNFR1受到TNF刺激後引起之反應對於APAP引起肝損傷是重要的。接著，分離小鼠的肝臟細胞並進行體外培養，發現TNF並未加強APAP引起的肝細胞毒性。在腹腔注射脂多醣引起小鼠體內TNF的產生也無法加劇APAP引起的肝毒性，反而可以顯著的保護小鼠免於嚴重的肝損傷。由本研究結果顯示，在APAP引起的無菌發炎反應中，TNF的訊號作用在從骨髓分化而來的細胞上的TNFR1，且此訊號對於APAP引起的無菌發炎反應及肝損傷是相當重要的，但若要釐清負責接收TNF訊號的細胞種類，則需要更進一步的研究。另外，本研究也給予IL-1受體缺陷（IL-1R -/-）小鼠過量APAP，發現IL-1R -/-小鼠的肝損傷及發炎反應都有較WT小鼠顯著降低的情形。綜合以上結果，我們確認了TNF作用在骨髓細胞分化而來的TNFR1，在APAP引起的肝細胞受損中的角色，並了解TNF和IL-1β可能透過協同作用（synergistic effect）在APAP引起的肝細胞壞死中扮演重要角色。

Cell death in vivo could induce an acute inflammatory response via the release of various intracellular components. This type of inflammatory response is called sterile inflammatory response. The function of sterile inflammatory response is to clear up cell debris and promote tissue repair. However, uncontrolled leukocytes recruitement and activation could result in severe tissue damage, thus causing various inflammatory diseases. Here we used acetaminophen-induced liver injury and inflammation as a model to study the role of TNF in sterile inflammation. The results showed that both liver injury and the production of proinflammatory cytokines were attenuated in TNFR1-/- mice. Furthermore, mice which were pretreated with EnbrelR were also protected from APAP-induced hepatotoxicity. Next, we generated bone marrow chimeras to study whether bone marrow-derived cells or non-bone marrow derived cells are responsible for receiving the TNF signal. The results showed that TNFR1-/- mice reconstituted with WT bone marrow had increased levels of ALT and proinflammatory cytokines, which indicated that TNFR1 expression on bone marrow-derived cells may played a critical role in APAP-induced liver hepatotoxicity. Consistently, TNF treatment did not sensitize hepatocytes to APAP toxicity in vitro. Interestingly, using LPS to stimulate TNF production in vivo did not sensitize mice to APAP-induced liver injury. Instead, LPS and APAP cotreatment showed significantly protective effect on liver injury. Our results demonstrateded that TNF stimulation on bone marrow-derived cells may play an important role in mediating APAP-induced liver injury and inflammation; however, more research needs to be done to understand which cell type is responsible for receiving the TNF signal. Apart from TNF, the role of IL-1/IL-1R in APAP-induced liver injury was examined as well. The results showed that IL-1R-deficient mice were protected from APAP-induced liver injury.