Kupffer cells protect liver sinusoidal endothelial cells from Fas-dependent apoptosis in sepsis by down-regulating gp130.

Endothelial cell (EC) dysfunction is a key feature of multiple organ injury, the primary cause of fatality seen in critically ill patients. Although the development of EC dysfunction in the heart and lung is well studied in sepsis, it remains unclear in the liver. Herein, we report that liver sinusoidal ECs (LSECs; defined as CD146(+)CD45(-)) exhibit increased intercellular adhesion molecule-1 (CD54) and Fas in response to sepsis induced by cecal ligation and puncture (CLP). By using magnetically enriched LSEC (CD146(+)) populations, we show evidence of marked apoptosis, with a twofold decline in viable LSECs in CLP animals compared with sham controls. These changes and increased serum alanine aminotransferase levels were all mitigated in septic Fas(-/-) and Fas ligand(-/-) animals. Although we previously reported increased numbers of Fas ligand expressing CD8(+) T lymphocytes in the septic liver, CD8(+) T-cell deficiency did not reverse the onset of LSEC apoptosis/damage. However, Kupffer cell depletion with clodronate liposomes resulted in greater apoptosis and Fas expression after CLP and a decrease in glycoprotein 130 expression on LSECs, suggesting that STAT3 activation may protect these cells from injury. Our results document a critical role for death receptor-mediated LSEC injury and show the first evidence that Kupffer cells are essential to the viability of LSECs, which appears to be mediated through glycoprotein 130 expression in sepsis.

Structural Correlates of PPAR Agonist Rescue of Experimental Chronic Alcohol-Induced Steatohepatitis.

Chronic alcoholic liver disease is associated with hepatic insulin resistance, inflammation, oxidative and ER stress, mitochondrial dysfunction, and DNA damage. Peroxisome-proliferator activated receptor (PPAR) agonists are insulin sensitizers that have anti-inflammatory/anti-oxidant effects. We previously showed that PPAR agonists can restore hepatic insulin responsiveness in chronic ethanol-fed rats with steatohepatitis. Herein, we furthered our investigations by characterizing the histological and ultrastructural changes mediated by PPAR agonist rescue of alcohol-induced steatohepatitis. Adult male Long Evans rats were pair fed with isocaloric liquid diets containing 0% or 37% ethanol (caloric) for 8 weeks. After 3 weeks on the diets, rats were treated with vehicle, or a PPAR-α, PPAR-δ, or PPAR-γ agonist twice weekly by i.p. injection. Ethanol-fed rats developed steatohepatitis with disordered hepatic chord architecture, mega-mitochondria, disruption of the RER, increased apoptosis, and increased 4-hydroxynonenal (HNE) and 3-nitrotyrosine (NTyr) immunoreactivity. PPAR-δ and PPAR-γ agonists reduced the severity of steatohepatitis, and restored the hepatic chord-like architectural, mitochondrial morphology, and RER organization, and the PPAR-δ agonist significantly reduced hepatic HNE. On the other hand, prominent RER tubule dilation, which could reflect ER stress, persisted in ethanol-exposed, PPAR-γ treated but not PPAR-δ treated livers. The PPAR-α agonist exacerbated both steatohepatitis and formation of mega-mitochondria, and it failed to restore RER architecture or lower biochemical indices of oxidative stress. In conclusion, improved hepatic insulin responsiveness and decreased inflammation resulting from PPAR-δ or PPAR-γ agonist treatments of alcohol-induced steatohepatitis are likely mediated by enhanced signaling through metabolic pathways with attendant reductions in ER stress, oxidative stress, and mitochondrial dysfunction.

Deficiency of Bid protein reduces sepsis-induced apoptosis and inflammation, while improving septic survival.

Increased apoptotic cell death is believed to play a pathological role in patients with sepsis and experimental animals. Apoptosis can be induced by either a cell death receptor (extrinsic) or a mitochondrial (intrinsic) pathway. Bid, a proapoptotic member of the Bcl-2 family, is thought to mediate the cross talk between the extrinsic and intrinsic pathways of apoptosis; however, little is known about the action of Bid in the development of apoptosis and organ-specific tissue damage/cell death as seen in polymicrobial sepsis. Our results show that after the onset of sepsis, tBid (the active form of Bid) is significantly increased in mitochondrial fractions of the thymus, spleen, Peyer patches, and liver, and that Fas or FasL deficiency blocks Bid activation in various tissues after septic challenge. Increased Bid activation is correlated with increased active caspase-3, caspase-9, and apoptosis during sepsis. Bid-deficient mice exhibit significantly reduced apoptosis in the thymus, spleen, and Peyer patches compared with background mice after sepsis. Furthermore, Bid-deficient mice had significantly reduced systemic and local inflammatory cytokine levels and improved survival after sepsis. These data support not only the contribution of Bid to sepsis-induced apoptosis and the onset of septic morbidity/mortality, but also the existence of a bridge between extrinsic apoptotic signals, e.g., FasL:Fas, TNF:TNFR, and so on, and the intrinsic mitochondrial pathway via Bid-tBid activation during sepsis.

CD8+ T cells promote inflammation and apoptosis in the liver after sepsis: role of Fas-FasL.

Although studies blocking the Fas pathway indicate it can decrease organ damage while improving septic (cecal ligation and puncture, CLP) mouse survival, little is known about how Fas-Fas ligand (FasL) interactions mediate this protection at the tissue level. Here, we report that although Fas expression on splenocytes and hepatocytes is up-regulated by CLP and is inhibited by in vivo short interfering RNA, FasL as well as the frequency of CD8(+) T cells are differentially altered by sepsis in the spleen (no change in FasL, decreased percentage of CD8(+) and CD4(+) T cells) versus the liver (increased FasL expression on CD8(+) T cells and increase in percentage/number). Adoptive transfer of CLP FasL(+/+) versus FasL(-/-) mouse liver CD8(+) T cells to severe combined immunodeficient or RAG1(-/-) recipient mice indicated that these cells could induce inflammation. The FasL-mediated cytotoxic capacity of these septic mouse liver CD8(+) T cells was shown by their ability to damage directly cultured hepatocytes. Finally, although CD8(-/-) mice exhibited a reduction in both CLP-induced liver active caspase-3 staining and blood interleukin-6 levels, only FasL(-/-) (but not CD8(-/-)) protected the septic mouse spleen from increasing apoptosis. Thus, although truncating Fas-FasL signaling ameliorates many untoward effects of sepsis, the pathological mode of action is distinct at the tissue level.