Audrey H. Lau

Inhibition of Neuronal Apoptosis by Docosahexaenoic Acid (22:6n-3) ROLE OF PHOSPHATIDYLSERINE IN ANTIAPOPTOTIC EFFECT

Enrichment of Neuro 2A cells with docosahexaenoic acid (22:6n-3) decreased apoptotic cell death induced by serum starvation as evidenced by the reduced DNA fragmentation and caspase-3 activity. The protective effect of 22:6n-3 became evident only after at least 24 h of enrichment before serum starvation and was potentiated as a function of the enrichment period. During enrichment 22:6n-3 incorporated into phosphatidylserine (PS) steadily, resulting in a significant increase in the total PS content. Similar treatment with oleic acid (18:1n-9) neither altered PS content nor resulted in protective effect. Hindering PS accumulation by enriching cells in a serine-free medium diminished the protective effect of 22:6n-3. Membrane translocation of Raf-1 was significantly enhanced by 22:6n-3 enrichment in Neuro 2A cells. Consistently, in vitrobiomolecular interaction between PS/phosphatidylethanolamine /phosphatidylcholine liposomes, and Raf-1 increased in a PS concentration-dependent manner. Collectively, enrichment of neuronal cells with 22:6n-3 increases the PS content and Raf-1 translocation, down-regulates caspase-3 activity, and prevents apoptotic cell death. Both the antiapoptotic effect of 22:6n-3 and Raf-1 translocation are sensitive to 22:6n-3 enrichment-induced PS accumulation, strongly suggesting that the protective effect of 22:6n-3 may be mediated at least in part through the promoted accumulation of PS in neuronal membranes.

Dendritic cells and immune regulation in the liver

Hepatic dendritic cells (DC) unquestionably play important roles in the induction and regulation of immune responses. Due to their paucity, functional characterisation of these important antigen presenting cells has been slow but use of DC growth factors (in particular GM-CSF and Flt3L) that markedly enhance their numbers has proved helpful in furnishing adequate study material. While there is growing evidence that DC function is affected in the pathogenesis of liver disease, most work to date has been performed on non-hepatic DC. Increasing knowledge of hepatic DC biology is likely to improve our understanding of disease pathogenesis and resistance to and therapy of liver disease.

Low TLR4 Expression by Liver Dendritic Cells Correlates with Reduced Capacity to Activate Allogeneic T Cells in Response to Endotoxin

Signaling via TLRs results in dendritic cell (DC) activation/maturation and plays a critical role in the outcome of primary immune responses. So far, no data exist concerning TLR expression by liver DC, generally regarded as less immunostimulatory than secondary lymphoid tissue DC. Because the liver lies directly downstream from the gut, it is constantly exposed to bacterial LPS, a TLR4 ligand. We examined TLR4 expression by freshly isolated, flow-sorted C57BL/10 mouse liver DC compared with spleen DC. Real-time PCR revealed that liver CD11c+CD8α− (myeloid) and CD11c+CD8α+ (“lymphoid-related”) DC expressed lower TLR4 mRNA compared with their splenic counterparts. Lower TLR4 expression correlated with reduced capacity of LPS (10 ng/ml) but not anti-CD40-stimulated liver DC to induce naive allogeneic (C3H/HeJ) T cell proliferation. By contrast to LPS-stimulated splenic DC, these LPS-activated hepatic DC induced alloantigen-specific T cell hyporesponsiveness in vitro, correlated with deficient Th1 (IFN-γ) and Th2 (IL-4) responses. When higher LPS concentrations (≥100 ng/ml) were tested, the capacity of liver DC to induce proliferation of T cells and Th1-type responses was enhanced, but remained inferior to that of splenic DC. Hepatic DC activated by LPS in vivo were inferior allogeneic T cell stimulators compared with splenic DC, whereas adoptive transfer of LPS-stimulated (10 ng/ml) liver DC induced skewing toward Th2 responses. These data suggest that comparatively low expression of TLR4 by liver DC may limit their response to specific ligands, resulting in reduced or altered activation of hepatic adaptive immune responses.

Chronic high Epstein–Barr viral load carriage in pediatric small bowel transplant recipients

Lau AH, Soltys K, Sindhi RK, Bond G, Mazariegos GV, Green M. Chronic high Epstein–Barr viral load carriage in pediatric small bowel transplant recipients.
Pediatr Transplantation 2010: 14:549–553.

Ethanol affects the generation, cosignaling molecule expression, and function of plasmacytoid and myeloid dendritic cell subsets in vitro and in vivo

The influence of ethanol (EtOH) on multiple dendritic cell (DC) subsets, in the steady state or following their mobilization in vivo, has not been characterized. Herein, generation of mouse bone marrow‐derived DC (BMDC) in response to fms‐like tyrosine kinase 3 ligand was inhibited by physiologically relevant concentrations of EtOH with selective suppression of plasmacytoid (p)DC. EtOH reduced surface expression of costimulatory molecules (CD40, CD80, CD86) but not that of coinhibitory CD274 (B7‐H1) on resting or CpG‐stimulated DC subsets. Interleukin (IL)‐12p70 production by activated DC was impaired. Consistent with these findings, EtOH‐exposed BMDC exhibited a reduced capacity to induce naïve, allogeneic T cell proliferation and impaired ability to prime T cells in vivo. DC subsets freshly isolated from EtOH‐fed mice were also examined. Liver DC, inherently immature and resistant to maturation, exhibited little change in their low surface cosignaling molecule expression, whereas splenic DC showed reduced expression of surface costimulatory molecules in response to CpG stimulation in vivo. These splenic DC elicited reduced naïve, allogeneic T cell proliferation in vitro, and the stimulatory capacity of resting but not CpG‐activated liver DC was reduced by chronic EtOH administration. T cells from animals primed with EtOH‐exposed DC produced elevated levels of IL‐10 following ex vivo challenge with donor alloantigen. Thus, EtOH impairs cytokine‐driven differentiation and function of myeloid DC and pDC in vitro. Hepatic DC from chronic EtOH‐fed mice are less affected than splenic DC, which exhibit impaired functional maturation following CpG stimulation. These results indicate a potential mechanism by which alcohol consumption is associated with immunosuppression.

Antigen-presenting cells under the influence of alcohol

The negative influence of alcohol (ethanol) and its metabolites on innate and adaptive immunity is well-recognized. Much attention has recently been focused on the impact of acute and chronic alcohol exposure on antigen-presenting cells (APC). In particular, insights have been gained into how the properties of human blood monocytes and rodent macrophages are influenced by alcohol in vitro and in vivo. Here, we review the impact of alcohol on various aspects of APC function and the underlying mechanisms, including its effects on intracellular signaling events. We also discuss new information regarding the influence of alcohol on various APC populations in the liver, a primary site of alcohol metabolism.

Effects of docosapentaenoic acid on neuronal apoptosis.

We previously established that n−3 FA status in membrane phospholipids influences the biosynthesis and accumulation of PS in neuronal tissues. We also demonstrated that neuronal apoptosis under adverse conditions is prevented by DHA enrichment in a PS-dependent manner. In this study, we examined the effect of a structural analog of DHA, docosapentaenoic acid (22∶5n−6, DPA), which accumulates in neuronal membranes during n−3 FA deficiency. We observed that enrichment of neuronal cells with DPA increased the total PS content in comparison to nonenriched control. However, the increase was significantly less than that observed in DHA-enriched cells, primarily due to the fact that the 18∶0,22∶5n−6 species was not accumulated as effectively as 18∶0,22∶6n−3 in PS. As was the case with DHA, DPA enrichment also protected against cell death induced by staurosporine treatment in Neuro 2A cells, but to a lesser extent. These data indicate that provision of DPA in place of DHA is sufficient neither for fully supporting PS accumulation nor for cell survival. The in vitro interaction between Raf-1 and membrane was affected not only by the PS content but also by the fatty acyl composition in PS. The reduction of PS concentration as well as the substitution of 18∶0,22∶6 with 16∶0,18∶1 in the liposome considerably reduced the interaction with Raf-1. These data suggest that depletion of DHA from neuronal tissues may have a compounding effect on Raf-1 translocation in growth factor signaling. The fact that DPA cannot fully support the protective role played by DHA may provide a basis for the adverse effect of n−3 FA deficiency on neuronal development and function.

Liver tolerance mediated by antigen presenting cells: fact or fiction?

Possible mechanisms by which liver antigen presenting cells (APC) may facilitate tolerance induction are discussed. Tolerance may be facilitated by a distinctive combination of factors, linked to the unique anatomical and microenvironmental features of the liver.

Posttransplant metabolic syndrome in children and adolescents after liver transplantation: A systematic review†

During long‐term follow‐up, 18% to 67% of pediatric liver transplant recipients are overweight or obese, with rates varying by age and pretransplant weight status. A similar prevalence of posttransplant obesity has been seen in adults. Adults also develop posttransplant metabolic syndrome and, consequently, cardiovascular disease at rates that exceed the rates in age‐ and sex‐matched populations. Posttransplant metabolic syndrome has never been studied in pediatric liver transplant recipients, and this population is growing as transplant outcomes continue to improve. Here we systematically review the literature for each component of metabolic syndrome—obesity, hypertension, dyslipidemia, and glucose intolerance—in pediatric liver transplant recipients. Their rates of obesity are similar to the rates in children in the general US population. However, hypertension, dyslipidemia, and diabetes are more common than would be expected in transplant recipients according to age, sex, and obesity severity. Immunosuppressive medications are major contributors. The limitations of previous studies, including heterogeneous methods of diagnosis, follow‐up times, and immunosuppressive regimens, hinder the analysis of risk factors. Importantly, no studies have reported graft or patient outcomes associated with components of metabolic syndrome after pediatric liver transplantation. However, if the trends in children are similar to the trends seen in adults, these conditions may lead to significant long‐term morbidity. Further research on the prevalence, causes, and consequences of posttransplant metabolic syndrome in pediatric liver transplant recipients is needed and will ultimately help to improve long‐term outcomes. Liver Transpl, 2012.

Comparative evaluation of CC chemokine-induced migration of murine CD8α+ and CD8α- dendritic cells and their in vivo trafficking

Murine CD11c+CD8α− and CD11c+CD8α+ dendritic cells (DCs) differentially regulate T cell responses. Although specific chemokines that recruit immature (i) or mature (m) CD8α− DCs have been identified, little is known about the influence of chemokines on CD8α+ DCs. iDCs and mDCs isolated from spleens of fms‐like tyrosine kinase 3 ligand‐treated B10 mice were compared directly for migratory responses to a panel of CC chemokines or following local or systemic administration. In vitro assays were performed using Transwell® chambers. iDCs did not respond to any CC chemokines tested. Both subsets of mDCs migrated to CCL19 and CCL21, with consistently lower percentages of CD8α+ DCs migrating. Chemokine receptor mRNA and protein expression were analyzed, but no correlation between expression and function was demonstrated. In vivo trafficking of fluorochrome‐labeled DCs (B10; H2b) was assessed by immunohistochemistry and by rare‐event flow cytometric analysis of allogeneic recipient (BALB/c; H2d) draining lymph node (DLN) and spleen cells. Twenty‐four hours after intravenous injection, chloromethylfluorescein diacetate‐positive CD8α+ and CD8α− mDCs were detected by immunohistochemistry in spleens in similar numbers (that decreased over time). Following subcutaneous injection, both DC subsets were detected in DLN at 24 h, but only CD8α− DCs were evident by flow analysis at 48 h. Although CD8α+ DCs migrate from peripheral tissues to T cell areas of (allogeneic) secondary lymphoid organs, they appear to mobilize as mDCs and less efficiently than CD8α− mDCs.