MiRNA-223 Inhibits MouseGallstone Formation by Targeting Key Transporters in Hepatobiliary Cholesterol Secretion Pathway

BackgroudMiRNA-223 has previously been reported to play an essential role in hepatic cholesterol homeostasis by suppressing cholesterol synthesis, attenuating cholesterol uptake by hepatocyte from and promoting cholesterol efflux into the blood. However, its role in regulation of biliary cholesterol secretion and gallstone formation remains unknown.MethodsMice with conventional knockout (KO), hepatocyte-specific knockout (ΔHepa) / knockdown (KD) or gain expression of miRNA-223 were included in the study and were subjected to lithogenic diet (LD) for various weeks. The gallbladders were harvested and subjected to cholesterol crystal imaging and gallstone mass measurement. Liver tissues were collected for western blotting, RT-qPCR, and immunohistochemistry staining. Levels of cholesterol, bile salt, phospholipids, and triglyceride were determined in serum, liver tissues, and bile by enzyme color reactive assays. 3’ UTR reporter gene assays were used to verify the direct target genes for miRNA-223.ResultsLD-induced gallstone formation was remarkably accelerated in miRNA-223 KO, ΔHepa, and KD mice with concurrent enhancement in total cholesterol levels in liver tissue and bile. Key biliary cholesterol transporters ABCG5 and ABCG8 were identified as direct targets of miRNA-223. Reversely, AAV-mediated hepatocyte-specific miRNA-223 overexpression prevented gallstone progression with reduced targets protein expression.ConclusionThe present study demonstrates a novel role of miRNA-223 in the regulation of hepatic bile cholesterol secretion pathway and gallstone formation by targeting ABCG5 and ABCG8 expression. Therefore, elevating miRNA-223 would be a potentially novel approach to overcome the sternness of cholesterol gallstone disease.Graphical Abstract

Simultaneous Determination of Biliary and Intestinal Cholesterol Secretion Reveals That CETP (Cholesteryl Ester Transfer Protein) Alters Elimination Route in Mice

Objective: Determine the impact of CETP (cholesteryl ester transfer protein) on the route of cholesterol elimination in mice. Approach and Results: We adapted our protocol for biliary cholesterol secretion with published methods for measuring transintestinal cholesterol elimination. Bile was diverted and biliary lipid secretion maintained by infusion of bile acid. The proximal small bowel was perfused with bile acid micelles. In high-fat, high-cholesterol–fed mice, the presence of a CETP transgene increased biliary cholesterol secretion at the expense of transintestinal cholesterol elimination. The increase in biliary cholesterol secretion was not associated with increases in hepatic SR-BI (scavenger receptor BI) or ABCG5 (ATP-binding cassette G5) ABCG8. The decline in intestinal cholesterol secretion was associated with an increase in intestinal Niemann-Pick disease, type C1, gene-like 1 mRNA. Finally, we followed the delivery of HDL (high-density lipoprotein) or LDL (low-density lipoprotein) cholesteryl esters (CE) from plasma to bile and intestinal perfusates. HDL-CE favored the biliary pathway. Following high-fat feeding, the presence of CETP directed HDL-CE away from the bile and towards the intestine. The presence of CETP increased LDL-CE delivery to bile, whereas the appearance of LDL-CE in intestinal perfusate was near the lower limit of detection. Conclusions: Biliary and intestinal cholesterol secretion can be simultaneously measured in mice and used as a model to examine factors that alter cholesterol elimination. Plasma factors, such as CETP, alter the route of cholesterol elimination from the body. Intestinal and biliary cholesterol secretion rates are independent of transhepatic or transintestinal delivery of HDL-CE, whereas LDL-CE was eliminated almost exclusively in the hepatobiliary pathway.

Abstract 390: The Absence of Abcg5 Abcg8 Reveals a Sexually Dimorphic Adaption to Impaired Biliary Cholesterol Secretion

Objective: The ABCG5 ABCG8 (G5G8) sterol transporter is the primary mechanism for biliary cholesterol secretion, but mice maintain fecal sterol excretion in its absence. The mechanism by which mice maintain sterol excretion in the absence of this pathway is not known. Transintestinal cholesterol excretion (TICE) is an alternative pathway to hepatobiliary secretion. We investigated the impact of G5G8 deficiency on TICE in the absence of Sitosterolemia. Methods and Results: We compared both hepatobiliary and transintestinal cholesterol excretion rates in wild-type (WT) and G5G8 deficient mice of both sexes. WT and G5G8 were maintained on a plant-sterol free diet from the time of weaning to prevent the development of secondary phenotypes associated with Sitosterolemia. Biliary and intestinal cholesterol secretion rates were determined by biliary diversion with simultaneous perfusion of the proximal 10 cm of the small bowel. Among WT mice, biliary cholesterol secretion was greater in female mice compared to males. Conversely, male mice exhibited greater rates of TICE than females. As expected, WT mice had higher biliary cholesterol secretion rates than their G5G8 deficient littermates. However, the decline in biliary cholesterol secretion was far less in male mice compared to females in the absence of G5G8. In female mice, the absence of G5G8 resulted in a two-fold increase in TICE, whereas males were unaffected. Conclusion: Female mice are more dependent upon the biliary pathway for cholesterol excretion, whereas males are more dependent upon TICE. G5G8 independent pathways are present for both biliary and intestinal cholesterol secretion. Female and male mice differ in their adaptation to G5G8 deficiency in order to maintain fecal sterol excretion.