Cellular imbalances of cholesterol and fatty acid metabolism result in pathological processes, including atherosclerosis and metabolic syndrome. Recent work from our group and others has shown that the intronic microRNAs hsa-miR-33a and hsa-miR-33b are located within the sterol regulatory element-binding protein-2 and -1 genes, respectively, and regulate cholesterol homeostasis in concert with their host genes. Here, we show that miR-33a and -b also regulate genes involved in fatty acid metabolism and insulin signaling. miR-33a and -b target key enzymes involved in the regulation of fatty acid oxidation, including carnitine O-octaniltransferase, carnitine palmitoyltransferase 1A, hydroxyacyl-CoAdehydrogenase, Sirtuin 6 (SIRT6), and AMP kinase subunit-α. Moreover, miR-33a and -b also target the insulin receptor substrate 2, an essential component of the insulin-signaling pathway in the liver. Overexpression of miR-33a and -b reduces both fatty acid oxidation and insulin signaling in hepatic cell lines, whereas inhibition of endogenous miR-33a and -b increases these two metabolic pathways. Together, these data establish that miR-33a and -b regulate pathways controlling three of the risk factors of metabolic syndrome, namely levels of HDL, triglycerides, and insulin signaling, and suggest that inhibitors of miR-33a and -b may be useful in the treatment of this growing health concern.lipid homeostasis | posttranscriptional regulation | cardiovascular disease

The possible role of candidate receptors in the cellular penetration of HCV from serum of infected patients remains unclear. SR-BI/Cla1 interacts with plasma HDL, native and modified LDL, and VLDL, and facilitates cellular cholesterol efflux to lipoprotein acceptors. SR-BI/Cla1 binds HCV E2 protein and interacts with HCV pseudotypes via the HVR1 of the E2 envelope glycoprotein. Our data reveal that functional SR-BI/Cla1 expressed on the surface of CHO cells mediates the binding and uptake of HCV from the sera of infected patients. Interaction between HCV and SR-BI/Cla1 is not sensitive to either anti-E2 or anti-HVR1 antibodies but is effectively inhibited by anti-betalipoprotein antibodies and competed out by apoB-containing lipoproteins and notably by VLDL. We interpret our data to indicate that VLDL associated with or incorporated into HCV plays a critical role in the primary interaction of HCV with SR-BI/Cla1, whereas the HCV E2 protein does not. In addition, our findings in hepatoma cell lines suggest that the interaction of HCV with human hepatocytes is equally mediated, at least in a part, by VLDL, and as such may represent an alternative pathway for infection. The association of HCV with ApoB-containing lipoproteins may promote cellular uptake of this virus in the presence of neutralizing antibodies.

SARS-CoV-2, the etiological agent of COVID-19, has so far resulted in >6.1 million deaths worldwide. The spike protein (S) of the virus directs infection of the lungs and other tissues by binding the angiotensin-converting enzyme 2 (ACE2) receptor.

Hepatic secretion of apolipoprotein-B (apoB), the major protein of atherogenic lipoproteins, is regulated through posttranslational degradation. We reported a degradation pathway, post-ER presecretory proteolysis (PERPP), that is increased by reactive oxygen species (ROS) generated within hepatocytes from dietary polyunsaturated fatty acids (PUFA). We now report the molecular processes by which PUFA-derived ROS regulate PERPP of apoB. ApoB exits the ER; undergoes limited oxidant-dependent aggregation; and then, upon exit from the Golgi, becomes extensively oxidized and converted into large aggregates. The aggregates slowly degrade by an autophagic process. None of the oxidized, aggregated material leaves cells, thereby preventing export of apoBlipoproteins containing potentially toxic lipid peroxides. In summary, apoB secretory control via PERPP/autophagosomes is likely a key component of normal and pathologic regulation of plasma apoB levels, as well as a means for remarkably late-stage quality control of a secreted protein.

This article is available online at http://www.jlr.org teins (VLDL) from liver. From a clinical perspective, plasma apoB100 levels and the apoB100/apoA1 ratio are superior to any other lipoprotein-related indices used to estimate risk of acute myocardial infarction ( 1 ). This illustrates the need for a deep understanding of the cellular mechanisms that regulate apoB100 production and secretion. Although rat hepatoma McA-RH7777 cells secrete much of their apoB100 as buoyant VLDL, it would be desirable to have a similar cell line of human origin. Many studies of human apoB100 metabolism have used the hepatoma HepG2 cell line. Despite their general use, however, HepG2 cells secrete relatively dense, lipid-poor apoB100-containing particles, unlike the buoyant VLDL particles secreted in vivo by mammalian liver. An alternative human cell model with a more native level of VLDL secretion would strongly benefi t the lipoprotein fi eld and might advance novel insights into apoB100 metabolism.Recently, Huh-7 cells were proposed as a superior human hepatic cell model for the study of apoB100 metabolism and VLDL secretion [see references 2, 3)] and are becoming more widely used for these purposes [see references ( 4, 5 )]. To our knowledge, however, there have been no published studies of the basic characteristics of Huh-7 cells with regard to apoB100 and VLDL metabolism. In the present report, we have fi lled this gap in knowledge and also have compared the results to those with HepG2 cells. Based on the available evidence, Huh-7 cells resemble HepG2 cells in many respects, with neither cell Apolipoprotein-B100 (apoB100) is the essential protein for the assembly and secretion of very low density lipopro- Abbreviations: apoB100, apolipoprotein-B100; MEK-ERK, mitogenactivated protein kinase kinase-extracellular signal regulated kinase; MTP, microsomal triglyceride transfer protein; OA, oleic acid.