Damage-associated molecular patterns (DAMPs) initiate inflammatory pathways that are common to both sterile and infectious processes. The DAMP, high-mobility group box 1 (HMGB1), and the transcription factor, interferon regulatory factor 1 (IRF-1), have been independently associated as key players in ischemia-reperfusion (I/R) injury. Our study demonstrates that IRF-1 contributes to hepatocellular release of HMGB1 and further that IRF-1 is a necessary component of HMGB1 release in response to hypoxia or after liver I/R. We also link the nuclear upregulation of IRF-1 to the presence of functional Toll-like receptor 4 (TLR4), a pattern recognition receptor also important in sterile and infectious processes. Using IRF-1 chimeric mice, we show that IRF-1 upregulation in hepatic parenchymal cells, and not in the bone marrow-derived immune cells, is responsible for HMGB1 release during ischemic liver injury. Finally, our study also demonstrates a role for IRF-1 in modulating the acetylation status and subsequent release of HMGB1 through histone acetyltransferases. We found that serum HMGB1 is acetylated after liver I/R and that this process was dependent on IRF-1. Additionally, liver I/R induced a direct association of IRF-1 and the nuclear histone acetyltransferase enzyme p300. Together, these findings suggest that I/R-induced release of acetylated HMGB1 is a process that is dependent on TLR4-mediated upregulation of IRF-1.
Dendritic cells (DCs) induce and regulate both innate and adaptive immune responses; however, their in vivo functional importance in hepatic ischemia/reperfusion (IR) injury is perplexing. We hypothesized that liver-resident DC and locally recruited blood-borne DC might have distinctive roles in hepatic IR injury. We tested this hypothesis by using DC-deficient, fms-like tyrosine kinase 3 ligand (Flt3L) knockout (KO) mice in hepatic warm (70% partial clamping for 60 minutes) and cold IR injury (liver transplant [LTx] with 24-hour cold storage). Flt3L KO liver and lymphoid organs contained virtually no CD11c 1 F4/80 2 DC. Hepatic warm IR injury was significantly lower in Flt3L KO than in wildtype (WT) mice with lower alanine aminotransferase (ALT) levels, reduced hepatic necrosis, and lower neutrophil infiltration. Hepatic messenger RNA (mRNA) and protein levels for inflammatory cytokines (tumor necrosis factor alpha [TNFa], interleukin [IL]-6) and chemokines (CCL2, CXCL2) were also significantly lower in Flt3L KO than in WT mice, indicating that lack of both liver-resident and blood-borne DC ameliorated hepatic warm IR injury. Adoptive transfer of splenic or hepatic WT DC into Flt3L KO or WT mice increased hepatic warm IR injury, suggesting injurious roles of DC infusion. When Flt3L KO liver was transplanted into WT mice, ALT levels were significantly higher than in WT to WT LTx, with enhanced hepatic necrosis and neutrophil infiltration, indicating a protective role of liver-resident DC. Conclusion: Using both warm and cold hepatic IR models, this study suggests differential roles of liver-resident versus blood-borne DC, and points to the importance of the local microenvironment in determining DC function during hepatic IR injury. (HEPATOLOGY 2013;57:1585-1596
Classically, the continuous-time Langevin diffusion converges exponentially fast to its stationary distribution π under the sole assumption that π satisfies a Poincaré inequality. Using this fact to provide guarantees for the discrete-time Langevin Monte Carlo (LMC) algorithm, however, is considerably more challenging due to the need for working with chi-squared or Rényi divergences, and prior works have largely focused on strongly log-concave targets. In this work, we provide the first convergence guarantees for LMC assuming that π satisfies either a Lata la-Oleszkiewicz or modified log-Sobolev inequality, which interpolates between the Poincaré and log-Sobolev settings. Unlike prior works, our results allow for weak smoothness and do not require convexity or dissipativity conditions.
Ischemia/reperfusion (I/R) injury remains a key risk factor significantly affecting morbidity and mortality after liver transplantation (LTx). B7-H1, recently identified member of the B7 family, is known to play important roles in regulating local immune responses. We hypothesized that B7-H1 plays crucial roles during innate immune responses induced by hepatic I/R injury and tested this hypothesis in the mouse LTx model using B7-H1 KO liver grafts with 24 hr cold storage. Cold I/R injury in WT to WT LTx enhanced constitutive B7-H1 expression on dendritic cells and sinusoidal endothelial cells, and promptly induced B7-H1 on hepatocytes. When B7-H1 KO liver grafts were transplanted into WT recipients, serum ALT levels and graft necrosis were significantly higher than WT to WT LTx. Augmented tissue injury in B7-H1 KO grafts was associated with increased frequencies and absolute numbers of graft CD3+ T cells, in particular CD8+ T cells. B7-H1 KO grafts had significantly lower incidences of Annexin V+ CD8+ T cells, indicating the failure to delete infiltrating CD8+ T cells. To evaluate the relative contribution of parenchymal and bone marrow-derived cell (BMDC) B7-H1 expression, chimeric liver grafts lacking B7-H1 on parenchymal cells or BMDC were generated and transplanted into WT recipients. Selective B7-H1 deficiency on parenchymal cells or BMDC resulted in similar levels of ALT and liver injury, suggesting that both parenchymal and BMDC B7-H1expression is involved in the control of liver damage. Human livers upregulated B7-H1 expression after LTx. Conclusion: The study demonstrates that graft tissue expression of B7-H1 plays critical roles in regulating inflammatory responses during LTx-induced hepatic I/R injury, and suggests that negative coregulatory signals may have an important function in hepatic innate immune responses.
Ischemia/reperfusion (I/R) injury in liver grafts, initiated by cold preservation and augmented by reperfusion, is a major problem complicating graft quality, post-transplant patient care, and outcomes of liver transplantation (LTx). Kupffer cells (KC) play important roles in I/R injury; however, little is known about their changes during cold preservation. We examined whether pretreatment with carbon monoxide (CO), a cytoprotective product of heme degradation, would influence KC activity during cold storage and protect the liver graft against LTx-induced I/R injury. In vitro, primary rat KC were stimulated for 24 hrs with hypothermia (4°C, 20% O2), LPS, or hypoxia (37°C, 5% O2) with and without CO pretreatment. When exposed to hypothermia, rat KC produced ROS, but not TNF-α or NO. Preincubation of KC with CO upregulated HSP70 and inhibited ROS generation. When liver grafts obtained from donor rats exposed to CO (250 ppm) for 24 hrs were transplanted after 18 hrs cold preservation in UW solution, HSP70 expression in the grafts increased, and serum AST/ALT levels as well as necrotic area and inflammatory infiltrates were significantly reduced after LTx, when compared to control grafts. CO-pretreated liver grafts showed less TNF-α, ICAM-1 and iNOS mRNA upregulation, as well as reduced pro-apoptotic Bax mRNA, cleaved caspase-3 and PARP expressions. Thus, donor pretreatment with CO ameliorates I/R injury associated with LTx, with an increased hepatic HSP70 expression, particularly in KC population.
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