Interactions between CD8+ T cells and endothelial cells are important in both protective and pathologic immune responses. Endothelial cells regulate the recruitment of CD8 + T cells into tissues, and the activation of CD8 + T cells by antigen presentation and costimulatory signals. PD-L1 and PD-L2 are recently described B7-family molecules which bind to PD-1 on activated lymphocytes and down-regulate T cell activation. We found that PD-L1 is expressed on interferon-+ stimulated cultured human and mouse endothelial cells, while PD-L2 was found on stimulated human but not mouse endothelial cells. Expression was further upregulated by TNF- § . Antibody blockade of endothelial cell PD-L1 and PD-L2 enhanced endothelial cell costimulation of PHA-activated human CD8 + T cells. Antibody blockade of mouse endothelial cell PD-L1 enhanced both IFN-+ secretion and cytolytic activity of CD8 + T cells in response to endothelial cell antigen presentation. These results show that IFN-+ activated endothelial cells can inhibit T cell activation via expression of the immunoinhibitory PD-L1 and PD-L2 molecules. Endothelial expression of PD-ligands would allow activation and extravasation of T cells without excessive vessel damage. Our findings highlight a potentially important pathway by which endothelial cells down-regulate CD8 + T cellmediated immune responses.

Functional ␥-secretase inhibitors (FGSIs) can block the cleavage of several transmembrane proteins including amyloid precursor protein (APP), and the cell fate regulator Notch-1. FGSIs, by inhibiting APP processing, block the generation of amyloid ␤ (A␤) peptides and may slow the development of Alzheimer's disease. FGSIs used to inhibit APP processing may disrupt Notch processing, thus interfering with cell fate determination. Described herein is a FGSI-mediated gastrointestinal toxicity characterized by cell population changes in the ileum of rats, which are indicative of Notch signaling disruption. Microarray analysis of ileum from FGSItreated rats revealed differential expression responses in a number of genes indicative of Notch signaling perturbation, including the serine protease adipsin. We were able to show that FGSI-treated rats had elevated levels of adipsin protein in gastrointestinal contents and feces, and by immunohistochemistry demonstrated that adipsin containing ileum crypt cells were increased in FGSI-treated rats. The mouse Adipsin proximal promoter contains a putative binding site for the Notchinduced transcriptional regulator Hes-1, which we demonstrate is able to bind Hes-1. Additional studies in 3T3-L1 preadipocytes demonstrate that this FGSI inhibits Hes-1 expression while up-regulating adipsin expression. Overexpression of Hes-1 was able to down-regulate adipsin expression and block pre-adipocyte differentiation. We propose that adipsin is a Hes-1-regulated gene that is de-repressed during FGSI-mediated disruption of Notch/Hes-1 signaling. Additionally, the aberrant expression of adipsin, and its presence in feces may serve as a noninvasive biomarker of gastrointestinal toxicity associated with perturbed Notch signaling.The small intestine can be a site of injury associated with drug treatment (1-3). Tissue organization within the small intestine relies upon a small number of stem cells in the intestinal crypts to continuously produce several types of differentiated cells that together comprise the villous epithelium (enterocytes, goblet cells, paneth cells, and enteroendocrine cells) (4). This rapid maturation, transport, and cell loss make the small intestine particularly susceptible to toxicants that affect cell differentiation and proliferation (5, 6). The process by which dividing intestinal epithelial stem cells in the crypt produce differentiated progeny requires the transcriptional regulation of genes necessary for cell fate determination. The control of this cell fate determination pathway is dependent on a number of positive and negative transcription factors that operate in undifferentiated precursor cells of the crypt (6 -8). For example, the bHLH transcriptional repressor protein Hairy and Enhancer of split homologue-1 (Hes-1) 1 has been shown to be important in determining whether differentiating intestinal epithelial stem cells adopt an exocrine/secretory (goblet cell, enteroendocrine cell, paneth cell) fate or an absorptive (enterocyte) fate (9). Expression of Hes-1 is kn...

The oxysterol receptors LXR (liver X receptor)-␣ and LXR␤ are nuclear receptors that play a key role in regulation of cholesterol and fatty acid metabolism. We found that LXRs also play a significant role in glucose metabolism. Treatment of diabetic rodents with the LXR agonist, T0901317, resulted in dramatic reduction of plasma glucose. In insulin-resistant Zucker (fa/fa) rats, T0901317 significantly improved insulin sensitivity. Activation of LXR did not induce robust adipogenesis but rather inhibited the expression of several genes involved in hepatic gluconeogenesis, including phosphoenolpyruvate carboxykinase (PEPCK). Hepatic glucose output was dramatically reduced as a result of this regulation. Nuclear run-on studies indicated that transcriptional repression was primarily responsible for the inhibition of PEPCK by the LXR agonist. In addition, we show that the regulation of the liver gluconeogenic pathway by LXR agonists was a direct effect on hepatocytes. These data not only suggest that LXRs are novel targets for diabetes but also reveal an unanticipated role for these receptors, further linking lipid and glucose metabolism.Type II diabetes mellitus is a prevalent metabolic disease in developed countries, with insufficient therapies for treatment and prevention (1, 2). Studies in recent years have suggested that nuclear receptors are intimately linked to the pathophysiology of diabetes. The antidiabetic thiazolidinediones have been identified as ligands of proxisome proliferator-activated receptor ␥ (PPAR␥) 1 (3, 4). Retinoid X receptor (RXR) ligands have also been shown to lower plasma glucose levels in rodent diabetic models (3-5).Originally identified as orphan members of the nuclear receptor superfamily, liver X receptors exist as two isoforms, LXR␣ and LXR␤. The two isoforms display distinct patterns of expression with LXR␣ being primarily expressed in liver, intestine, and kidney, whereas LXR␤ is expressed ubiquitously (6). Oxysterols were identified as the putative physiological ligands for the LXRs (7), and additional studies have demonstrated that these receptors act as sensors for these cholesterol metabolites and are essential components of a physiological feedback loop regulating cholesterol metabolism and transport (8). Consistent with their role in regulation of these metabolic pathways, several LXR-regulated genes involved in lipid metabolism and cholesterol transport have been identified including ABCA1, ABCG1, ABCG5, ABCG8, ApoE, CETP, Cyp7a, LPL, SREBP1c, and FAS (8 -14).As a result of the close relationship between lipid and carbohydrate metabolism, we examined the potential role LXRs may play in glucose homeostasis by using a specific LXR agonist, T0901317, (11) in rodent models of diabetes. Our findings indicated that T0901317 dose-dependently lowered plasma glucose level in both db/db and Zucker diabetic fatty (ZDF) rat models. In the fa/fa insulin-resistant rat model, T0901317 significantly improved insulin sensitivity. Examination of the liver gluconeogenesis pathway revealed dra...

Liver X receptors (LXR) belong to the nuclear receptor superfamily that can regulate important lipid metabolic pathways. The plasma phospholipid transfer protein (PLTP) is known to mediate transfer of phospholipids from triglyceride-rich lipoproteins to high density lipoprotein (HDL) and plays a critical role in HDL metabolism. We report here that a specific LXR agonist, T0901317, elevated HDL cholesterol and phospholipid in C57/BL6 mice and generated enlarged HDL particles that were enriched in cholesterol, ApoAI, ApoE, and phospholipid. The appearance of these HDL particles upon oral dosing of T0901317 in C57/BL6 mice was closely correlated with the increased plasma PLTP activity and liver PLTP mRNA levels. Nuclear run-on assay indicated that the effect of LXR agonist on PLTP expression was at the transcriptional level. In mouse peritoneal macrophage cells, PLTP expression was also up-regulated by the LXR/RXR (retinoid X receptor) heterodimer. However, cholesterol efflux in mouse peritoneal macrophage cells from PLTP-deficient mice (PLTP0) was not significantly different from wild type animals. Although in PLTP-deficient mice, the induction of HDL cholesterol as well as HDL particle size increase persisted, the extent of the induction was greatly attenuated. We conclude that PLTP is a direct target gene of LXRs in vivo and plays an important role in LXR agonistmediated HDL cholesterol and size increase in mice.Epidemiological studies have revealed that plasma HDL 1 cholesterol is inversely correlated to coronary artery disease in humans. Several hypotheses have been proposed to explain the benefits of HDL. Among these, reverse cholesterol transport concept has been widely accepted. This notion, proposed more than 30 years ago by Glomset (1), is defined as the process through which nascent HDL particles remove excessive free cholesterol from peripheral tissues and carry it back to the liver for catabolism. The studies on cellular cholesterol efflux pathway were highlighted by the recent breakthrough defining the genetic defects associated with Tangier disease and hypoalphalipoproteinemia (2-5). The mutations of ATP-binding cassette transport protein 1 (ABCA1) were identified as the underlining cause of the rare genetic disorder that leads to almost total absence of plasma ApoAI and HDL cholesterol and to massive accumulation of cholesterol esters in macrophage cells.Plasma phospholipid transfer protein (PLTP) activity is also closely related to HDL levels. PLTP transfers phospholipids from triglyceride-rich lipoproteins to HDL during lipolysis. Moreover, it also participates the phospholipid exchanges between HDL particles (21). Disruption of PLTP in mice dramatically reduces plasma HDL cholesterol and phospholipid levels (6). Although its role in the circulation has been studied extensively, its potential function in the reverse cholesterol transport pathway and HDL biogenesis awaits further elucidation.Liver X receptors (LXRs) belong to the orphan nuclear receptor superfamily and exist in two isoforms, LXR␣ a...