T cell cholesterol transport is a metabolic checkpoint that links intestinal immune responses to dietary lipid absorption.

The intrinsic pathways that control membrane organization in immune cells and the impact of such pathways on cellular function are not well defined. Here we report that the non-vesicular cholesterol transporter Aster-A links plasma membrane (PM) cholesterol availability in T cells to immune signaling and systemic metabolism. Aster-A is recruited to the PM during T-cell receptor (TCR) activation, where it facilitates the removal of newly generated "accessible" membrane cholesterol. Loss of Aster-A leads to excess PM cholesterol accumulation, resulting in enhanced TCR nano-clustering and signaling, and Th17 cytokine production. Finally, we show that the mucosal Th17 response is restrained by PM cholesterol remodeling. Ablation of Aster-A in T cells leads to enhanced IL-22 production, reduced intestinal fatty acid absorption, and resistance to diet-induced obesity. These findings delineate a multi-tiered regulatory scheme linking immune cell lipid flux to nutrient absorption and systemic physiology.

Hepatic lipopolysaccharide binding protein partially uncouples inflammation from fibrosis in MAFLD.

Non-alcoholic fatty liver disease (NAFLD), recently renamed metabolic-associated fatty liver disease (MAFLD), is the most common liver disease worldwide. The progression to fibrosis, occurring against a backdrop of hepatic steatosis and inflammation, critically determines liver-related morbidity and mortality. Inflammatory processes contribute to various stages of MAFLD and thought to instigate hepatic fibrosis. For this reason, targeting inflammation has been heavily nominated as a strategy to mitigate liver fibrosis. Lipopolysaccharide binding protein (LBP) is a secreted protein that plays an established role in innate immune responses. Here, using adoptive transfer studies and tissue-specific deletion models we show that hepatocytes are the dominant contributors to circulating LBP. In a murine model of MAFLD, hepatocyte-specific deletion of LBP restrained hepatic inflammation and improved liver function abnormalities, but not measures of fibrosis. Human studies, including genetic evidence, corroborate an important role for LBP in hepatic inflammation with minimal impact on fibrosis. Collectively, our data argues against the idea that targeting hepatic inflammation is a viable approach to reducing fibrosis.

Hepatic nonvesicular cholesterol transport is critical for systemic lipid homeostasis.

In cell models, changes in the 'accessible' pool of plasma membrane (PM) cholesterol are linked with the regulation of endoplasmic reticulum sterol synthesis and metabolism by the Aster family of nonvesicular transporters; however, the relevance of such nonvesicular transport mechanisms for lipid homeostasis in vivo has not been defined. Here we reveal two physiological contexts that generate accessible PM cholesterol and engage the Aster pathway in the liver: fasting and reverse cholesterol transport. During fasting, adipose-tissue-derived fatty acids activate hepatocyte sphingomyelinase to liberate sequestered PM cholesterol. Aster-dependent cholesterol transport during fasting facilitates cholesteryl ester formation, cholesterol movement into bile and very low-density lipoprotein production. During reverse cholesterol transport, high-density lipoprotein delivers excess cholesterol to the hepatocyte PM through scavenger receptor class B member 1. Loss of hepatic Asters impairs cholesterol movement into feces, raises plasma cholesterol levels and causes cholesterol accumulation in peripheral tissues. These results reveal fundamental mechanisms by which Aster cholesterol flux contributes to hepatic and systemic lipid homeostasis.

Aster-dependent nonvesicular transport facilitates dietary cholesterol uptake.

Intestinal absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1) assists in the initial step of dietary cholesterol uptake, but how cholesterol moves downstream of NPC1L1 is unknown. We show that Aster-B and Aster-C are critical for nonvesicular cholesterol movement in enterocytes. Loss of NPC1L1 diminishes accessible plasma membrane (PM) cholesterol and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate PM cholesterol and show endoplasmic reticulum cholesterol depletion. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, the Aster pathway can be targeted with a small-molecule inhibitor to manipulate cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption.

Aster-dependent non-vesicular transport facilitates dietary cholesterol uptake.

Intestinal cholesterol absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1), the target of the drug ezetimibe (EZ), assists in the initial step of dietary cholesterol uptake. However, how cholesterol moves downstream of NPC1L1 is unknown. Here we show that Aster-B and Aster-C are critical for non-vesicular cholesterol movement in enterocytes, bridging NPC1L1 at the plasma membrane (PM) and ACAT2 in the endoplasmic reticulum (ER). Loss of NPC1L1 diminishes accessible PM cholesterol in enterocytes and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate cholesterol at the PM and display evidence of ER cholesterol depletion, including decreased cholesterol ester stores and activation of the SREBP-2 transcriptional pathway. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, we show that the Aster pathway can be targeted with a small molecule inhibitor to manipulate dietary cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption. One-Sentence Summary: Identification of a targetable pathway for regulation of dietary cholesterol absorption.

Vertical Sleeve Gastrectomy Attenuates the Progression of Non-Alcoholic Steatohepatitis in Mice on a High-Fat High-Cholesterol Diet.

OBJECTIVE: To determine whether vertical sleeve gastrectomy (VSG) attenuates fibrosis in mice on a high-fat high-cholesterol (HFHC) diet. BACKGROUND: Bariatric surgery mitigates non-alcoholic steatohepatitis in 85-90% of obese patients. While animal models demonstrate similar results on a high-fat diet, none have observed the effects of bariatric surgery on a combined HFHC diet. METHODS: Mice on a HFHC diet were used to confirm the development of hepatic fibrosis at 8 (n = 15) and 24 (n = 15) weeks. A separate cohort of mice on a HFHC diet for 12 weeks was subjected to either VSG (n = 18) or sham (n = 12) operations and remained on a HFHC diet for an additional 20 weeks. Changes in weight, dyslipidemia, and the development of steatosis and fibrosis were documented. Serum was obtained for bile acid analysis by liquid chromatography and mass spectrometry, while hepatic gene expression by RT-PCR was performed to evaluate intrahepatic lipid metabolism. RESULTS: Hepatic steatosis and fibrosis developed after 8 weeks on the HFHC diet. After VSG, mice demonstrated a sustained decrease in weight with a significant decrease in fibrosis compared to sham mice. Serum total cholesterol, HDL, and LDL were significantly reduced following surgery, while serum bile acids were significantly elevated. Intra-hepatic cholesterol excretion was not upregulated based on hepatic gene expression of CYP7A1 and ABCG5/8. CONCLUSIONS: VSG attenuates the development of hepatic fibrosis in diet-induced obese mice, presumably through enhancement of cholesterol elimination at the intestinal level.

Characterization of T cell immunophenotypes in intestinal transplantation: A pilot study.

Immunophenotyping of peripheral blood mononuclear cells has been shown to be a useful, non-invasive method of predicting acute cellular rejection (ACR) following intestinal transplantation (ITx). Our objectives were to characterize differences in the T cell immunophenotype of ITx recipients in peripheral blood samples (1) collected late versus early after ITx and (1) associated with episodes of ACR and infectious enteritis. An IRB-approved, cross-sectional study of ITx recipients was performed. Peripheral blood samples were collected during normal visits and episodes of allograft dysfunction. A total of 38 patients were included in the analysis: 31 ITx recipients (87% liver-inclusive allografts) and 7 intestinal failure control patients. Of the ITx patients, 26 patients were pediatric patients (<21 years). A total of 70 samples were analyzed from ITx recipients, including 51 during normal visits and 19 during episodes of allograft dysfunction (median of 2 samples per patient; range of 1-6 samples per patient). In the late (n = 32) versus early post-ITx (n = 19) normal samples, there was a significantly higher percentage of central memory CD4 T cells (p = .001). In the ACR (n = 5) versus infectious enteritis (n = 14) samples, there was a higher percentage of CD8 T cells expressing HLA-DR (p = .002), CD57 (p < .001), and KLRG1 (p < .001) and a higher percentage of CD4 T cells expressing CD57 (p = .03). Additional studies are needed with larger cohorts to validate these changes in the T cell immunophenotype. Further elucidating T cell immunophenotypes in ITx will lead to a better understanding of immune mechanisms of allograft dysfunction, identification of potential biomarkers in ITx, and optimized selection of immunosuppressive therapies.

Risk factors for arthralgias or myalgias associated with quinupristin-dalfopristin therapy.

STUDY OBJECTIVE: To evaluate risk factors for the development of arthralgias or myalgias associated with quinupristin-dalfopristin. DESIGN: Retrospective chart review and case-control analysis. SETTING: An 850-bed tertiary care medical center. PATIENTS: All adult and pediatric patients who had received quinupristin-dalfopristin through either a compassionate-use protocol (February 1996-October 1999) or in the year after quinupristin-dalfopristin was added to the hospital formulary (November 1999-October 2000) were included in this study. Case patients were those who developed arthralgias or myalgias while receiving quinupristin-dalfopristin therapy; control patients were those who received quinupristin-dalfopristin but did not develop arthralgias or myalgias. INTERVENTION: Medical records, pharmacy dispensing information, and microbiology data were reviewed by a physician and a pharmacist, both of whom specialized in infectious diseases. Presence or absence of arthralgias or myalgias was the primary outcome assessed. MEASUREMENTS AND MAIN RESULTS: Quinupristin-dalfopristin was administered to 68 patients during the period defined by the study. Arthralgias and myalgias could not be assessed in 18 of the 68 patients because they were sedated and paralyzed, or they were young children who could not communicate the presence of pain. Univariate analysis demonstrated that significant risk factors for arthralgias or myalgias associated with quinupristin-dalfopristin were female sex, chronic liver disease, receipt of liver transplant, elevated bilirubin level at baseline, major surgery, and receipt of either mycophenolate or cyclosporine. Multivariate analysis demonstrated a strong association with chronic liver disease, receipt of liver transplant, elevated bilirubin level at baseline, and receipt of either cyclosporine or mycophenolate. Of 50 evaluable patients receiving quinupristin-dalfopristin, 25 had pain that may have been associated with this antimicrobial agent. CONCLUSION: The mechanism for development of arthralgias or myalgias associated with quinupristin-dalfopristin remains unknown, but these adverse events are more likely to occur in patients with chronic liver disease and those who have received a liver transplant or are receiving cyclosporine or mycophenolate.