Niemann-Pick C1-like 1 (NPC1L1) mediates intestinal uptake of dietary and biliary cholesterol and is the target of ezetimibe, a cholesterol absorption inhibitor used to treat hypercholesterolemia. Genetic deletion of NPC1L1 or ezetimibe treatment protects mice from high-fat diet (HFD)-induced obesity; however, the molecular mechanisms responsible for this therapeutic benefit remain unknown. A major metabolic fate of cholesterol is its conversion to bile acids. We found that NPC1L1 knockout (L1-KO) mice fed an HFD had increased energy expenditure, bile acid pool size, and fecal bile acid excretion rates. The elevated bile acid pool in the HFD-fed L1-KO mice was enriched with tauro-β-muricholic acid. These changes in the L1-KO mice were associated with reduced ileal mRNA expression of fibroblast growth factor 15 (FGF15) and increased hepatic mRNA expression of cholesterol 7α-hydroxylase (Cyp7A1) and mitochondrial sterol 27-hydroxylase (Cyp27A1). In addition, mRNA expression of the membrane bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) and type 2 iodothyronine deiodinase (Dio2) were elevated in brown adipose tissue of L1-KO mice, which is known to promote energy expenditure. Thus, altered bile acid homeostasis and signaling may play a role in protecting L1-KO mice against HFD-induced obesity.

Disorders in cholesterol and bile acid metabolism have been acknowledged as critical in pathogenesis of hypercholesterolemia. Coiled-coil domain containing 80 (CCDC80) has been closely linked to lipid homeostasis in mice, with its role in cholesterol metabolism yet to be fully elucidated. This study aims to uncover the regulatory mechanisms of CCDC80 in diet-induced hypercholesterolemia. We generated a CCDC80 knockout (CCDC80-/-) model in C57BL/6 mouse. The initial transcriptional and metabolic consequences of removing CCDC80 were accessed at baseline by gene expression microarrays and gas chromatography-mass spectrometry / ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, respectively. The hepatic cholesterol was investigated in both CCDC80+/+ and CCDC80-/- male mice at baseline and after feeding a high-cholesterol diet for 12 weeks. The regulatory effects of CCDC80 on gene expressions and protein masses were measured by RT-qPCR and western blot, respectively. At baseline, the KEGG pathway enrichment analysis combining metabolomics, lipidomics and transcriptomics, revealed a down-regulation of hepatic bile acid biosynthesis by CCDC80-knockout, especially for primary bile acids. In the hypercholesterolemic models, our results showed that deficiency of CCDC80 increased plasma and liver cholesterol levels, but decreased fecal neutral and acidic sterols excretion in mice. Mechanistically, we found that such effects were partly mediated by attenuating the alternative pathway of bile acid synthesis catalyzed by oxysterol 7-alpha-hydroxylase (CYP7B1). In conclusion, our results suggest CCDC80 as a novel modulator of cholesterol homeostasis in male mice. Deficiency of CCDC80 could further impair fecal sterols excretion in diet-induced hypercholesterolemia.

Hypericum perforatum L. (HP), a well-known natural medicine, has a potential effect on menopausal hypercholesterolemia. However, the effect of HP extract on gut microbiota and related metabolites, which play vital roles in metabolic disease occurrence, in the context of estrogen deficiency have not yet been reported. The aims of the present study were to investigate the effects of HP extract on gut microbial composition and related metabolite profiles in ovariectomized (OVX) rats and reveal the relationships between pathological indicators and alterations in both gut microbial composition at the genus level and metabolites. Body weight, serum parameters, liver lipids and histomorphology were determined. Microbial composition was analyzed using 16S rRNA sequencing. Fecal short-chain fatty acids (SCFAs) and serum bile acids were quantitatively measured. Correlations between pathological indicators and alteration in gut microbiota and metabolites were investigated using Spearman's rank correlation test. Gene expression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7α-hydroxylase (CYP7A1) and cholesterol 27-hydroxylase (CYP27A1) in the liver and G protein-coupled receptors (GPCRs; GPR43 and GPR41), ZO-1 and occludin in the cecum were determined by PCR. Microbial composition and metabolite profiles were significantly changed in OVX rats compared with sham rats. Twelve bacterial genera, 5 SCFAs and 12 bile acids were identified as differential biomarkers. Differential genera, SCFAs and bile acids were closely associated with weight, total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C). In OVX rats, HP administration can significantly reverse the pathological symptoms of body weight gain, serum lipid disorders and hepatic steatosis, at the meanwhile, reestablish gut microbial composition and metabolite profiles. Moreover, HP administration significantly upregulated the levels of CYP7A1, GPR43 and GPR41. In conclusion, HP can ameliorate estrogen deficiency-induced hypercholesterolemia. The underlying mechanism may be associated with improvements in gut microbiota composition and the profile of related metabolites as well as increases in bile acid secretion.

To review the formation, catabolism, and the possible atherogenic properties of Lp-X. The conversion of cholesterol to bile acids is regulated by several mechanisms including cholesterol 7 alpha hydroxylase, fibroblast growth factor 19, and farnesoid X receptors. During cholestasis these mechanisms are altered and there is an accumulation of bile acids and cholesterol in plasma. The hypercholesterolemia observed in cholestasis is due to the presence of an anomalous lipoprotein called lipoprotein-X (Lp-X). Lp-X is a lipoprotein rich in phospholipid and free cholesterol present in plasma of patients with cholestasis and, with some variations, in patients with lecithin-cholesterol-acyl-transferase deficiency (LCAT), and after lipid infusion. Lp-X is formed from a bile lipoprotein moving to the blood vessels where it incorporates small quantities of triglycerides, apo-C and esterified cholesterol and becomes a "mature" Lp-X. The activity of the phosphatidilcholine canalicular transporter Mdr2 P-glycoprotein (homologous to the human ABCB4) is essential for LpX appearance, since its suppression abolishes Lp-X formation. However, the concentration of Lp-X in plasma is determined also by the degree of the cholestasis, the residual liver function, and the LCAT deficiency. The Lp-X catabolism seems to be mediated by the reticuloendothelial system and possibly the kidney. Lp-X might be considered a defense mechanism against the toxic effect of free cholesterol in cholestasis. The frequency of cardiovascular events in patients affected by primary biliary cholangitis, in whom the Lp-X is present in high concentration, are not increased. Further studies could now clarify the remaining open questions on the role of Lp-X in the dyslipidemia of cholestasis.

Prostaglandin E receptor subtype 4 (EP4) knockout mice develops spontaneous hypercholesterolemia but the detailed mechanisms by which EP4 affects cholesterol homeostasis remains unexplored. We sought to determine the cause of hypercholesterolemia in EP4 knockout mice, focusing on the role of EP4 in regulating the synthesis and elimination of cholesterol. Deficiency of EP4 significantly decreased total bile acid levels in the liver by 26.2% and the fecal bile acid content by 27.6% as compared to wild type littermates, indicating that the absence of EP4 decreased hepatic bile acid synthesis and their subsequent excretion in stools. EP4 deficiency negatively regulate bile acid synthesis through repression of phosphorylated extracellular signal-regulated kinase 1/2 (ERK)-mediated cholesterol 7α-hydroxylase (CYP7A1) expression and that the hypercholesterolemia in EP4 knockout mice is due to a defect in cholesterol conversion into bile acids. Deficiency of EP4 also increased de novo cholesterol synthesis and altered cholesterol fluxes in and out of the liver. Treating high fat diet-challenged mice with the pharmacological EP4 agonist, CAY10580 (200 μg/kg body weight/day i.p) for three weeks effectively prevented diet-induced hypercholesterolemia, enhanced endogenous bile acid synthesis and their fecal excretion. In summary, EP4 plays a critical role in maintaining cholesterol homeostasis by regulating the synthesis and elimination of bile acids. Activation of EP4 serves as an effective novel strategy to promote cholesterol disposal in the forms of bile acids in order to lower plasma cholesterol levels.