Biology subjects

Chorba, J. S.

Publications and source records attributed to Chorba, J. S..

4 recordsLinked to original sources

bioRxiv2024

TOMM40 regulates hepatocellular and plasma lipid metabolism via an LXR-dependent pathway

The gene encoding TOMM40 (Transporter of Outer Mitochondrial Membrane 40) is adjacent to that encoding APOE, which has a central role in lipid and lipoprotein metabolism. Human genetic variants near APOE and TOMM40 are strongly associated with plasma lipid levels, but a specific role for TOMM40 in lipid metabolism has not been established. Investigating this, we show that suppression of TOMM40 in human hepatoma cells upregulates expression of APOE and LDLR in part via activation of LXRB (NR1H2) by oxysterols, with consequent increased uptake of VLDL and LDL. This is in part due to disruption of mitochondria-endoplasmic reticulum contact sites, with resulting accrual of reactive oxygen species and non-enzymatically derived oxysterols. With TOMM40 knockdown, cellular triglyceride and lipid droplet content are increased, effects attributable in part to receptor-mediated VLDL uptake, since lipid staining is significantly reduced by concomitant suppression of either LDLR or APOE. In contrast, cellular cholesterol content is reduced due to LXRB-mediated upregulation of the ABCA1 transporter as well as increased production and secretion of oxysterol-derived cholic acid. Consistent with the findings in hepatoma cells, in vivo knockdown of TOMM40 in mice results in significant reductions of plasma triglyceride and cholesterol concentrations, reduced hepatic cholesterol and increased triglyceride content, and accumulation of lipid droplets leading to development of steatosis. These findings demonstrate a role for TOMM40 in regulating hepatic lipid and plasma lipoprotein levels and identify mechanisms linking mitochondrial function with lipid metabolism. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=132 SRC="FIGDIR/small/600910v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@17b0c8forg.highwire.dtl.DTLVardef@17599aaorg.highwire.dtl.DTLVardef@1bb6ab2org.highwire.dtl.DTLVardef@15a035f_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

Genome-Wide Screening Reveals CSDE1 as a Novel Regulator of the LDL Receptor

The low-density lipoprotein receptor (LDLR) controls cellular delivery of cholesterol and clears LDL from the bloodstream, protecting against atherosclerotic heart disease, the leading cause of death in the United States. We therefore sought to identify regulators of the LDLR beyond the targets of current clinical therapies and known causes of familial hypercholesterolemia. We show that Cold Shock Domain-Containing Protein E1 (CSDE1) enhances hepatic LDLR mRNA decay via its 3 untranslated region to regulate atherogenic lipoproteins in vivo. Using parallel phenotypic genome-wide CRISPR interference screens, we found 40 specific regulators of the LDLR left unidentified by observational human genetics. Among these, we show that CSDE1 regulates the LDLR at least as strongly as the mechanistically distinct pathways exploited by the best available clinical therapies: statins and PCSK9 inhibitors. Additionally, we show that hepatic gene silencing of Csde1 treats diet-induced dyslipidemia in mice better than that of Pcsk9. Our results reveal the therapeutic potential of manipulating a newly identified key factor in the post-transcriptional regulation of the LDLR mRNA for the prevention of cardiovascular disease. We anticipate that our approach of modelling a clinically relevant phenotype in a forward genetic screen, followed by mechanistic pharmacologic dissection and in vivo validation, will serve as a generalizable template for the identification of therapeutic targets in other human disease states. One Sentence SummaryA genome-wide CRISPR screen identifies CSDE1 as a key regulator of hepatic LDLR mRNA decay in vivo, making it a promising target for heart disease. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=137 HEIGHT=200 SRC="FIGDIR/small/235028v2_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@d53b79org.highwire.dtl.DTLVardef@133b48corg.highwire.dtl.DTLVardef@1926d97org.highwire.dtl.DTLVardef@58d863_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2020

A SARS-CoV-2-Human Protein-Protein Interaction Map Reveals Drug Targets and Potential Drug-Repurposing

An outbreak of the novel coronavirus SARS-CoV-2, the causative agent of COVID-19 respiratory disease, has infected over 290,000 people since the end of 2019, killed over 12,000, and caused worldwide social and economic disruption1,2. There are currently no antiviral drugs with proven efficacy nor are there vaccines for its prevention. Unfortunately, the scientific community has little knowledge of the molecular details of SARS-CoV-2 infection. To illuminate this, we cloned, tagged and expressed 26 of the 29 viral proteins in human cells and identified the human proteins physically associated with each using affinity-purification mass spectrometry (AP-MS), which identified 332 high confidence SARS-CoV-2-human protein-protein interactions (PPIs). Among these, we identify 66 druggable human proteins or host factors targeted by 69 existing FDA-approved drugs, drugs in clinical trials and/or preclinical compounds, that we are currently evaluating for efficacy in live SARS-CoV-2 infection assays. The identification of host dependency factors mediating virus infection may provide key insights into effective molecular targets for developing broadly acting antiviral therapeutics against SARS-CoV-2 and other deadly coronavirus strains.

systems biology↗

bioRxiv2018

Cell-associated, Heparin-like Molecules Modulate the Ability of LDL to Regulate PCSK9 Uptake

Proprotein convertase subtilisin/kexin type 9 (PCSK9) targets the LDL receptor (LDLR) for degradation, increasing plasma LDL and, consequently, cardiovascular risk. Uptake of secreted PCSK9 is required for its predominant effect on the LDLR. LDL itself inhibits this uptake, though the mechanism by which it does so remains unclear. In this study, we investigated the relationship between LDL, the PCSK9:LDLR interaction, and PCSK9 uptake. We show that LDL inhibits binding of PCSK9 to the epidermal growth factor precursor homology domain A (EGF-A) domain of the LDLR in vitro more impressively than it inhibits PCSK9 uptake in cells. Furthermore, a cell-based factor responsive to heparin-targeting treatments can explain this difference, consistent with its identity as a cell surface heparan sulfate proteoglycan (HSPG), a known co-receptor for PCSK9. Furthermore, we show that the entire PCSK9 prodomain, but not truncated variants, rescues PCSK9 uptake in the presence of LDL, suggesting that PCSK9:LDL binding requires the entire prodomain. Additionally, we show that the gain-of-function (GOF) PCSK9 variant S127R has increased affinity for heparin-like molecules such as HSPGs, potentially explaining the biochemical basis for its phenotype. Overall, our findings suggest a model where PCSK9, LDL, and HSPGs all interact to regulate PCSK9 uptake into the hepatocyte.

biochemistry↗