High-fat diet reveals the impact of Sar1b defects on lipid and lipoprotein profile and cholesterol metabolism.

Biallelic pathogenic variants of the Sar1b gene cause chylomicron retention disease (CRD) whose central phenotype is the inability to secrete chylomicrons. Patients with CRD experience numerous clinical symptoms such as gastrointestinal, hepatic, neuromuscular, ophthalmic, and cardiological abnormalities. Recently, the production of mice expressing either a targeted deletion or mutation of Sar1b recapitulated biochemical and gastrointestinal defects associated with CRD. The present study was conducted to better understand little-known aspects of Sar1b mutations, including mouse embryonic development, lipid profile, and lipoprotein composition in response to high-fat diet, gut and liver cholesterol metabolism, sex-specific effects, and genotype-phenotype differences. Sar1b deletion and mutation produce a lethal phenotype in homozygous mice, which display intestinal lipid accumulation without any gross morphological abnormalities. On high-fat diet, mutant mice exhibit more marked abnormalities in body composition, adipose tissue and liver weight, plasma cholesterol, non-HDL cholesterol and polyunsaturated fatty acids than those on the regular Chow diet. Divergences were also noted in lipoprotein lipid composition, lipid ratios (serving as indices of particle size) and lipoprotein-apolipoprotein distribution. Sar1b defects significantly reduce gut cholesterol accumulation while altering key players in cholesterol metabolism. Noteworthy, variations were observed between males and females, and between Sar1b deletion and mutation phenotypes. Overall, mutant animal findings reveal the importance of Sar1b in several biochemical, metabolic and developmental processes.

Sar1b mutant mice recapitulate gastrointestinal abnormalities associated with chylomicron retention disease.

Chylomicron retention disease (CRD) is an autosomal recessive disorder associated with biallelic Sar1b mutations leading to defects in intracellular chylomicron (CM) trafficking and secretion. To date, a direct cause-effect relationship between CRD and Sar1b mutation has not been established, but genetically modified animal models provide an opportunity to elucidate unrecognized aspects of these mutations. To examine the physiological role and molecular mechanisms of Sar1b function, we generated mice expressing either a targeted deletion or mutation of human Sar1b using the CRISPR-Cas9 system. We found that deletion or mutation of Sar1b in mice resulted in late-gestation lethality of homozygous embryos. Moreover, compared with WT mice, heterozygotes carrying a single disrupted Sar1b allele displayed lower plasma levels of triglycerides, total cholesterol, and HDL-cholesterol, along with reduced CM secretion following gastric lipid gavage. Similarly, decreased expression of apolipoprotein B and microsomal triglyceride transfer protein was observed in correlation with the accumulation of mucosal lipids. Inefficient fat absorption in heterozygotes was confirmed via an increase in fecal lipid excretion. Furthermore, genetically modified Sar1b affected intestinal lipid homeostasis as demonstrated by enhanced fatty acid ß-oxidation and diminished lipogenesis through the modulation of transcription factors. This is the first reported mammalian animal model with human Sar1b genetic defects, which reproduces some of the characteristic CRD features and provides a direct cause-effect demonstration.

Extracellular vesicles derived from injured vascular tissue promote the formation of tertiary lymphoid structures in vascular allografts.

Tertiary lymphoid structures (TLS) accumulate at sites of chronic injury where they function as an ectopic germinal center, fostering local autoimmune responses. Vascular injury leads to the release of endothelial-derived apoptotic exosome-like vesicles (ApoExo) that contribute to rejection in transplanted organs. The purpose of the study was to evaluate the impact of ApoExo on TLS formation in a model of vascular allograft rejection. Mice transplanted with an allogeneic aortic transplant were injected with ApoExo. The formation of TLS was significantly increased by ApoExo injection along with vascular remodeling and increased levels of antinuclear antibodies and anti-perlecan/LG3 autoantibodies. ApoExo also enhanced allograft infiltration by γδT17 cells. Recipients deficient in γδT cells showed reduced TLS formation and lower autoantibodies levels following ApoExo injection. ApoExo are characterized by proteasome activity, which can be blocked by bortezomib. Bortezomib treated ApoExo reduced the recruitment of γδT17 cells to the allograft, lowered TLS formation, and reduced autoantibody production. This study identifies vascular injury-derived extracellular vesicles (ApoExo), as initiators of TLS formation and demonstrates the pivotal role of γδT17 in coordinating TLS formation and autoantibody production. Finally, our results suggest proteasome inhibition with bortezomib as a potential option for controlling TLS formation in rejected allografts.

Torque Teno virus in children who underwent orthotopic liver transplantation: new insights about a common pathogen.

BACKGROUND: Torque Teno virus (TTV) is a ubiquitous infectious agent. Transplant recipients are at risk of hepatitis E virus (HEV) infection and could be vulnerable to TTV-associated adverse effects. The aim of this study was to evaluate the influence of immunosuppression and HEV infection on TTV replication and liver injury in pediatric patients after orthotopic liver transplantation (OLT). METHODS: Pediatric recipients of liver transplants were classified into the following 2 groups: (1) those with normal serum aminotransferases levels and (2) those with persistently increased serum aminotransferases levels and histological features of chronic hepatitis of unknown etiology. The TTV load was assessed in 342 serum samples by use of TaqMan real-time polymerase chain reaction, along with TTV genogroups and coinfection with HEV. RESULTS: TTV DNA was detected in 96% of tested serum samples. Viral load was significantly lower in patients with features of chronic hepatitis, of whom 78% had liver fibrosis scores of ≥2. Viral load decreased during posttransplantation follow-up. Viral load and genogroups were influenced by immunosuppression. Lower viral load was observed in patients coinfected with HEV. CONCLUSIONS: TTV infection is widespread, and its replication is closely related to immune status and viral coinfection. High TTV viremia is not associated with hepatitis after OLT, but, conversely, liver inflammatory activity impairs TTV replication.

Phenotype and outcomes of very early onset and early onset inflammatory bowel diseases in a Montreal pediatric cohort.

Objectives: The incidence of very-early-onset inflammatory bowel disease (VEO-IBD) and early-onset IBD (EO-IBD) is increasing. Here, we report their phenotype and outcomes in a Montreal pediatric cohort. Methods: We analyzed data from patients diagnosed with IBD between January 2014 and December 2018 from the CHU Sainte-Justine. The primary endpoint was to compare the phenotypes of VEO-IBD and EO-IBD. The secondary endpoints involved comparing outcomes and rates of steroid-free clinical remission (SFCR) at 12 (±2) months (m) post-diagnosis and at last follow-up. Results: 28 (14 males) and 67 (34 males) patients were diagnosed with VEO-IBD and EO-IBD, respectively. Crohn's disease (CD) was more prevalent in EO-IBD (64.2% vs. 39.3%), whereas unclassified colitis (IBD-U) was diagnosed in 28.6% of VEO-IBD vs. 10.4% of EO-IBD (p < 0.03). Ulcerative colitis (UC) and IBD-U predominantly presented as pancolitis in both groups (VEO-IBD: 76.5% vs. EO-IBD: 70.8%). Combining all disease subtypes, histological upper GI lesions were found in 57.2% of VEO-IBD vs. 83.6% of EO-IBD (p < 0.009). In each subtype, no differential histological signature (activity, eosinophils, apoptotic bodies, granulomas) was observed between both groups. At 12 m post-diagnosis, 60.8% of VEO-IBD and 62.7% of EO-IBD patients were in SFCR. At a median follow-up of 56 m, SFCR was observed in 85.7% of VEO-IBD vs. 85.0% of EO-IBD patients. Conclusion: The rate of patients in SFCR at 1-year post-diagnosis and at the end of follow-up did not significantly differ between both groups.

Glycomacropeptide for Management of Insulin Resistance and Liver Metabolic Perturbations.

BACKGROUND AND AIMS: The increasing prevalence and absence of effective global treatment for metabolic syndrome (MetS) are alarming given the potential progression to severe non-communicable disorders such as type 2 diabetes and nonalcoholic fatty liver disease. The purpose of this study was to investigate the regulatory role of glycomacropeptide (GMP), a powerful milk peptide, in insulin resistance and liver dysmetabolism, two central MetS conditions. MATERIALS AND METHODS: C57BL/6 male mice were fed a chow (Ctrl), high-fat, high-sucrose (HFHS) diet or HFHS diet along with GMP (200 mg/kg/day) administered by gavage for 12 weeks. RESULTS: GMP lowered plasma insulin levels (in response to oral glucose tolerance test) and HOMA-IR index, indicating a more elevated systemic insulin sensitivity. GMP was also able to decrease oxidative stress and inflammation in the circulation as reflected by the decline of malondialdehyde, F2 isoprostanes and lipopolysaccharide. In the liver, GMP raised the protein expression of the endogenous anti-oxidative enzyme GPx involving the NRF2 signaling pathway. Moreover, the administration of GMP reduced the gene expression of hepatic pro-inflammatory COX-2, TNF-α and IL-6 via inactivation of the TLR4/NF-κB signaling pathway. Finally, GMP improved hepatic insulin sensitization given the modulation of AKT, p38 MAPK and SAPK/JNK activities, thereby restoring liver homeostasis as revealed by enhanced fatty acid ß-oxidation, reduced lipogenesis and gluconeogenesis. CONCLUSIONS: Our study provides evidence that GMP represents a promising dietary nutraceutical in view of its beneficial regulation of systemic insulin resistance and hepatic insulin signaling pathway, likely via its powerful antioxidant and anti-inflammatory properties.