Running Title: Lipid transfer proteins and lipoprotein assemblyAbbreviations used: ARF1, ADP ribosylation factor 1; AUP1, ancient ubiquitous protein 1; Blps, apoB-containing lipoproteins; CIDEB, cell death-inducing DFF45-like effector B; COPII, coat protein complex II; cLDs, cytoplasmic lipid droplets; ER, endoplasmic reticulum; MTTP, microsomal triglyceride transfer protein; PLTP, phospholipid transfer protein AbstractA better understanding of intracellular lipoprotein assembly may help identify proteins with important roles in lipid disorders. ApoB-containing lipoproteins are macromolecular lipid and protein micelles that act as specialized transport vehicles for hydrophobic lipids. They are assembled predominantly in enterocytes and hepatocytes to transport dietary and endogenous fat, respectively, to different tissues. Assembly occurs in the endoplasmic reticulum and is dependent on lipid re-synthesis in the endoplasmic reticulum and on a chaperone, namely microsomal triglyceride transfer protein. Precursors for lipid synthesis are obtained from extracellular sources and from cytoplasmic lipid droplets. Microsomal triglyceride transfer protein is the major and essential lipid transfer protein that transfers phospholipids and triacylglycerols to nascent apoB for the assembly of lipoproteins. Assembly is aided by cell death-inducing DFF45-like effector B and by phospholipid transfer protein, which may facilitate additional deposition of triacylglycerols and phospholipids, respectively, to apoB. Here, we summarize the current understanding of the different steps in the assembly of apoB-containing lipoproteins and discuss the role of lipid transfer proteins in these steps to help identify new clinical targets for lipid-associated disorders, such as heart disease. IntroductionHydrophobic lipids serve as a source of energy, structural components for membranes, and precursors of hormones. Owing to their hydrophobicity, lipids require special means of transport in the aqueous milieu of the human body. Three different modes of lipid transport are known. First, micellar solubilization of lipids in the intestinal lumen facilitates hydrolysis of dietary lipids in the lumen and uptake by enterocytes. Second, transport of lipids bound to proteins, e.g., albumin, occurs in the circulation. Third, the most efficient process of transporting lipids in bulk through an aqueous milieu of the blood circulation is via special protein-lipid macromolecular micelles called lipoproteins, which consist of a hydrophilic surface and a hydrophobic core. The hydrophilic surface is a monolayer of phospholipids that also contains free cholesterol and other exchangeable proteins called apolipoproteins. The lipoprotein core is devoid of proteins and consists of hydrophobic lipids, such as triacylglycerols, cholesteryl esters, vitamin E, and vitamin A. A major protein constituent of these lipoproteins is apoB, which is a very hydrophobic scaffolding protein. The apoB-containing lipoproteins (B-lps) are large spherical particles and are classif...

Lipid accumulation is a pathological feature of every type of kidney injury. Despite this striking histological feature, physiological accumulation of lipids in the kidney is poorly understood. We studied whether the accumulation of lipids in the fasted kidney are derived from lipoproteins or NEFAs. With overnight fasting, kidneys accumulated triglyceride, but had reduced levels of ceramide and glycosphingolipid species. Fasting led to a nearly 5-fold increase in kidney uptake of plasma [C]oleic acid. Increasing circulating NEFAs using a β adrenergic receptor agonist caused a 15-fold greater accumulation of lipid in the kidney, while mice with reduced NEFAs due to adipose tissue deficiency of adipose triglyceride lipase had reduced triglycerides. Cluster of differentiation () mRNA increased 2-fold, and angiopoietin-like 4 (), an LPL inhibitor, increased 10-fold. Fasting-induced kidney lipid accumulation was not affected by inhibition of LPL with poloxamer 407 or by use of mice with induced genetic LPL deletion. Despite the increase in CD36 expression with fasting, genetic loss of CD36 did not alter fatty acid uptake or triglyceride accumulation. Our data demonstrate that fasting-induced triglyceride accumulation in the kidney correlates with the plasma concentrations of NEFAs, but is not due to uptake of lipoprotein lipids and does not involve the fatty acid transporter, CD36.

The emergence of the SARS-CoV-2 pandemic has prompted scientists to search for an efficient antiviral medicine to overcome the rapid spread and the marked increase in the number of patients worldwide. In this regard natural products could be a potential source of substances active against coronavirus infections. A systematic computer-aided virtual screening approach was carried out using commercially available natural products found on the Zinc Database in addition to an in-house compound library to identify potential natural product inhibitors of SARS-CoV-2 main protease (MPRO). The top eighteen hits from the screening were selected for in vitro evaluation on the viral protease (SARS-CoV-2 MPRO). Five compounds (naringenin, 2,3′,4,5′,6-pentahydroxybenzophenone, apigenin-7-O-glucoside, sennoside B, and acetoside) displayed high activity against the viral protein. Acteoside showed similar activity to the positive control GC376. The most potent compounds were tested in vitro on SARS-CoV-2 Egyptian strain where only naringenin showed moderate anti-SARS-CoV-2 activity at non-cytotoxic micromolar concentrations in vitro with a significant selectivity index (CC50/IC50 = 178.748/28.347 = 6.3). Moreover; a common feature pharmacophore model was generated to explain the requirements for enzyme inhibition by this diverse group of active ligands. These results pave a path for future repurposing and development of natural products to aid in the battle against COVID-19.