QTL-mapping in the obese Berlin Fat Mouse identifies additional candidate genes for obesity and fatty liver disease

Identification of additional body weight QTLs in the Berlin Fat Mouse BFMI861 lines using time series data

The Berlin Fat Mouse Inbred line (BFMI) is a model for obesity and metabolic syndrome. The sublines BFMI861-S1 and BFMI861-S2 differ in weight despite high genetic similarity and a shared obesity-related locus. This study focused on identifying additional body weight quantitative trait loci (QTLs) by analyzing weekly weight measurements in a male population of the advanced intercross line BFMI861-S1 x BFMI861-S2. QTL analysis, utilizing 200 selectively genotyped mice (GigaMUGA) and 197 males genotyped for top SNPs, revealed a genome-wide significant QTL on Chr 15 (68.46 to 81.40 Mb) for body weight between weeks 9 to 20. Notably, this QTL disappeared (weeks 21 to 23) and reappeared (weeks 24 and 25) coinciding with a diet change. Additionally, a significant body weight QTL on Chr 16 (3.89 to 22.79 Mb) was identified from weeks 6 to 25. Candidate genes, including Gpt, Cbx6, Apol6, Apol8, Sun2 (Chr 15) and Trap1, Rrn3, Mapk1 (Chr 16), were prioritized. This study unveiled two additional body weight QTLs, one of which is novel and responsive to diet changes. These findings illuminate genomic regions influencing weight in BFMI and emphasize the utility of time series data in uncovering novel genetic factors.

MTARC1 and HSD17B13 Variants Have Protective Effects on Non-Alcoholic Fatty Liver Disease in Patients Undergoing Bariatric Surgery

The severity of hepatic steatosis is modulated by genetic variants, such as patatin-like phospholipase domain containing 3 (PNPLA3) rs738409, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, and membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738. Recently, mitochondrial amidoxime reducing component 1 (MTARC1) rs2642438 and hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) rs72613567 polymorphisms were shown to have protective effects on liver diseases. Here, we evaluate these variants in patients undergoing bariatric surgery. A total of 165 patients who underwent laparoscopic sleeve gastrectomy and intraoperative liver biopsies and 314 controls were prospectively recruited. Genotyping was performed using TaqMan assays. Overall, 70.3% of operated patients presented with hepatic steatosis. NASH (non-alcoholic steatohepatitis) was detected in 28.5% of patients; none had cirrhosis. The increment of liver fibrosis stage was associated with decreasing frequency of the MTARC1 minor allele (p = 0.03). In multivariate analysis MTARC1 was an independent protective factor against fibrosis ≥ 1b (OR = 0.52, p = 0.03) and ≥ 1c (OR = 0.51, p = 0.04). The PNPLA3 risk allele was associated with increased hepatic steatosis, fibrosis, and NASH (OR = 2.22, p = 0.04). The HSD17B13 polymorphism was protective against liver injury as reflected by lower AST (p = 0.04) and ALT (p = 0.03) activities. The TM6SF2 polymorphism was associated with increased ALT (p = 0.04). In conclusion, hepatic steatosis is common among patients scheduled for bariatric surgery, but the MTARC1 and HSD17B13 polymorphisms lower liver injury in these individuals.