Molecular Metabolism最新文献

{"title":"Thyroid hormone receptor beta (THRβ1) is the major regulator of T3 action in human iPSC-derived hepatocytes.","authors":"Lorraine Soares De Oliveira, Joseph E Kaserman, Anne H Van Der Spek, Nora J Lee, Hendrik J Undeutsch, Rhiannon B Werder, Andrew A Wilson, Anthony N Hollenberg","doi":"10.1016/j.molmet.2024.102057","DOIUrl":"10.1016/j.molmet.2024.102057","url":null,"abstract":"<p><strong>Objective: </strong>Thyroid hormone (TH) action is mediated by thyroid hormone receptor (THR) isoforms. While THRβ1 is likely the main isoform expressed in liver, its role in human hepatocytes is not fully understood.</p><p><strong>Methods: </strong>To elucidate the role of THRβ1 action in human hepatocytes we used CRISPR/Cas9 editing to knock out THRβ1 in induced pluripotent stem cells (iPSC). Following directed differentiation to the hepatic lineage, iPSC-derived hepatocytes were then interrogated to determine the role of THRβ1 in ligand-independent and -dependent functions.</p><p><strong>Results: </strong>We found that the loss of THRβ1 promoted alterations in proliferation rate and metabolic pathways regulated by T3, including gluconeogenesis, lipid oxidation, fatty acid synthesis, and fatty acid uptake. We observed that key genes involved in liver metabolism are regulated through both T3 ligand-dependent and -independent THRβ1 signaling mechanisms. Finally, we demonstrate that following THRβ1 knockout, several key metabolic genes remain T3 responsive suggesting they are THRα targets.</p><p><strong>Conclusions: </strong>These results highlight that iPSC-derived hepatocytes are an effective platform to study mechanisms regulating TH signaling in human hepatocytes.</p>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":" ","pages":"102057"},"PeriodicalIF":7.0,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142558272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"RNA-binding protein YBX3 promotes PPARγ-SLC3A2 mediated BCAA metabolism fueling brown adipogenesis and thermogenesis","authors":"Lin-Yun Chen ,&nbsp;Li-Wen Wang ,&nbsp;Jie Wen ,&nbsp;Jing-Dong Cao ,&nbsp;Rui Zhou ,&nbsp;Jin-Lin Yang ,&nbsp;Ye Xiao ,&nbsp;Tian Su ,&nbsp;Yan Huang ,&nbsp;Qi Guo ,&nbsp;Hai-Yan Zhou ,&nbsp;Xiang-Hang Luo ,&nbsp;Xu Feng","doi":"10.1016/j.molmet.2024.102053","DOIUrl":"10.1016/j.molmet.2024.102053","url":null,"abstract":"<div><h3>Objective</h3><div>Activating brown adipose tissue (BAT) thermogenesis is a promising approach to combat obesity and metabolic disorders. The post-transcriptional regulation of BAT thermogenesis mediated by RNA-binding proteins (RBPs) is still not fully understood. This study explores the physiological role of novel RBPs in BAT differentiation and thermogenesis.</div></div><div><h3>Methods</h3><div>We used multiple public datasets to screen out novel RBPs responsible for BAT differentiation and thermogenesis. In vitro loss- and gain-of-function experiments were performed in both C3H10T1/2 preadipocytes and mature brown adipocytes to determine the role of Y-box binding protein 3 (YBX3) in brown adipocyte differentiation and thermogenesis. Adeno-associated virus (AAV)-mediated BAT-specific knockdown or overexpression of <em>Ybx3</em> was applied to investigate the function of YBX3 <em>in vivo</em>.</div></div><div><h3>Results</h3><div>YBX3 is a brown adipocyte-enriched RBP induced by cold stimulation and β-adrenergic signaling. Both <em>in vitro</em> loss- and gain-of-function experiments demonstrate that YBX3 is essential for brown adipocyte differentiation and thermogenesis. BAT-specific loss of <em>Ybx3</em> dampens thermogenesis and exacerbates diet-induced obesity in mice, while overexpression of <em>Ybx3</em> promotes thermogenesis and confers protection against diet-induced metabolic dysfunction. Transcriptome analysis and mitochondrial stress test indicate that <em>Ybx3</em> deficiency compromises the mitochondrial oxidative phosphorylation, leading to thermogenic failure. Mechanistically, YBX3 stabilizes the mRNA of <em>Slc3a2</em> and <em>Pparg</em>, which facilitates branched-chain amino acid (BCAA) influx and catabolism and fuels brown adipocyte differentiation and thermogenesis.</div></div><div><h3>Conclusions</h3><div>YBX3 facilitates BAT fueling BCAA to boost thermogenesis and energy expenditure, which protects against obesity and metabolic dysfunction. Thus, YBX3 could be a promising therapeutic target for obesity.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102053"},"PeriodicalIF":7.0,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142558271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Macrophages on the run: Exercise balances macrophage polarization for improved health","authors":"Yotam Voskoboynik ,&nbsp;Andrew D. McCulloch ,&nbsp;Debashis Sahoo","doi":"10.1016/j.molmet.2024.102058","DOIUrl":"10.1016/j.molmet.2024.102058","url":null,"abstract":"<div><h3>Objective</h3><div>Exercise plays a crucial role in maintaining and improving human health. However, the precise molecular mechanisms that govern the body’s response to exercise or/compared to periods of inactivity remain elusive. Current evidence appears to suggest that exercise exerts a seemingly dual influence on macrophage polarization states, inducing both pro-immune response M1 activation and cell-repair-focused M2 activation. To reconcile this apparent paradox, we leveraged a comprehensive meta-analysis of 75 diverse exercise and immobilization published datasets (7000+ samples), encompassing various exercise modalities, sampling techniques, and species.</div></div><div><h3>Methods</h3><div>75 exercise and immobilization expression datasets were identified and processed for analysis. The data was analyzed using boolean relationships which uses binary gene expression relationships in order to increase the signal to noise achieved from the data, allowing for the use of comparison across such a diverse set of datasets. We utilized a boolean relationship-aided macrophage gene model [1], to model the macrophage polarization state in pre and post exercise samples in both immediate exercise and long term training.</div></div><div><h3>Results</h3><div>Our modeling uncovered a key temporal dynamic: exercise triggers an immediate M1 surge, while long term training transitions to sustained M2 activation. These patterns were consistent across different species (human vs mouse), sampling methods (blood vs muscle biopsy), and exercise type (resistance vs endurance), and routinely showed statistically significant results. Immobilization was shown to have the opposite effect of exercise by triggering an immediate M2 activation. Individual characteristics like gender, exercise intensity and age were found to impact the degree of polarization without changing the overall patterns. To model macrophages within the specific context of muscle tissue, we identified a focused gene set signature of muscle resident macrophage polarization, allowing for the precise measurement of macrophage activity in response to exercise within the muscle.</div></div><div><h3>Conclusions</h3><div>These consistent patterns across all 75 examined studies suggest that the long term health benefits of exercise stem from its ability to orchestrate a balanced and temporally-regulated interplay between pro-immune response (M1) and reparative macrophage activity (M2). Similarly, it suggests that an imbalance between pro-immune and cell repair responses could facilitate disease development. Our findings shed light on the intricate molecular choreography behind exercise-induced health benefits with a particular insight on its effect on the macrophages within the muscle.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102058"},"PeriodicalIF":7.0,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142546428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"TGF-β antagonism synergizes with PPARγ agonism to reduce fibrosis and enhance beige adipogenesis","authors":"Young Jae Bahn ,&nbsp;Yanling Wang ,&nbsp;Pradeep Dagur ,&nbsp;Nicholas Scott ,&nbsp;Cheryl Cero ,&nbsp;Kelly T. Long ,&nbsp;Nhuquynh Nguyen ,&nbsp;Aaron M. Cypess ,&nbsp;Sushil G. Rane","doi":"10.1016/j.molmet.2024.102054","DOIUrl":"10.1016/j.molmet.2024.102054","url":null,"abstract":"<div><h3>Objectives</h3><div>Adipose tissue depots vary markedly in their ability to store and metabolize triglycerides, undergo beige adipogenesis and susceptibility to metabolic disease. The molecular mechanisms that underlie such heterogeneity are not entirely clear. Previously, we showed that TGF-β signaling suppresses beige adipogenesis via repressing the recruitment of dedicated beige progenitors. Here, we find that TGF-β signals dynamically regulate the balance between adipose tissue fibrosis and beige adipogenesis.</div></div><div><h3>Methods</h3><div>We investigated adipose tissue depot-specific differences in activation of TGF-β signaling in response to dietary challenge. RNA-seq and fluorescence activated cell sorting was performed to identify and characterize cells responding to changes in TGF-β signaling status. Mouse models, pharmacological strategies and human adipose tissue analyses were performed to further define the influence of TGF-β signaling on fibrosis and functional beige adipogenesis.</div></div><div><h3>Results</h3><div>Elevated basal and high-fat diet inducible activation of TGF-β/Smad3 signaling was observed in the visceral adipose tissue depot. Activation of TGF-β/Smad3 signaling was associated with increased adipose tissue fibrosis. RNA-seq combined with fluorescence-activated cell sorting of stromal vascular fraction of epididymal white adipose tissue depot resulted in identification of TGF-β/Smad3 regulated ITGA5+ fibrogenic progenitors. TGF-β/Smad3 signal inhibition, genetically or pharmacologically, reduced fibrosis and increased functional beige adipogenesis. TGF-β/Smad3 antagonized the beneficial effects of PPARγ whereas TGF-β receptor 1 inhibition synergized with actions of rosiglitazone, a PPARγ agonist, to dampen fibrosis and promote beige adipogenesis. Positive correlation between TGF-β activation and ITGA5 was observed in human adipose tissue, with visceral adipose tissue depots exhibiting higher fibrosis potential than subcutaneous or brown adipose tissue depots.</div></div><div><h3>Conclusions</h3><div>Basal and high-fat diet inducible activation of TGF-β underlies the heterogeneity of adipose tissue depots. TGF-β/Smad3 activation promotes adipose tissue fibrosis and suppresses beige progenitors. Together, these dual mechanisms preclude functional beige adipogenesis. Controlled inhibition of TβRI signaling and concomitant PPARγ stimulation can suppress adipose tissue fibrosis and promote beige adipogenesis to improve metabolism.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102054"},"PeriodicalIF":7.0,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142504366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PET imaging of sodium-glucose cotransporters (SGLTs): Unveiling metabolic dynamics in diabetes and oncology","authors":"Konrad Klimek ,&nbsp;Xinyu Chen ,&nbsp;Takanori Sasaki ,&nbsp;Daniel Groener ,&nbsp;Rudolf A. Werner ,&nbsp;Takahiro Higuchi","doi":"10.1016/j.molmet.2024.102055","DOIUrl":"10.1016/j.molmet.2024.102055","url":null,"abstract":"<div><h3>Background</h3><div>Sodium-glucose cotransporters (SGLTs) play a crucial role in glucose regulation and are essential therapeutic targets for diabetes management. Recent advancements have leveraged SGLT-targeted PET imaging to examine these transporters' roles in both health and disease.</div></div><div><h3>Scope of Review</h3><div>This review highlights recent innovations in PET imaging targeting SGLTs, with a particular focus on SGLT-specific radiotracers, such as alpha-methyl-4-deoxy-4-¹⁸F-fluoro-<span>d</span>-glucopyranoside (Me-4FDG). It emphasizes the advantages of these radiotracers over conventional ¹⁸F-2-fluoro-2-deoxy-<span>d</span>-glucose (2-FDG) imaging, especially in assessing SGLT activity. Additionally, the review addresses their potential in evaluating the pharmacodynamics of SGLT inhibitors, investigating metabolic changes in diabetes, and staging cancers.</div></div><div><h3>Major Conclusions</h3><div>SGLT-targeted PET imaging offers promising improvements in diagnostic accuracy and therapeutic planning. The findings underscore the physiological and pathological significance of SGLTs, indicating that this imaging approach could shape future diagnostic and therapeutic strategies in metabolic and oncologic fields.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102055"},"PeriodicalIF":7.0,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142504365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"cAMP driven UCP1 induction in human adipocytes requires ATGL-catalyzed lipolysis","authors":"Anand Desai ,&nbsp;Zinger Yang Loureiro ,&nbsp;Tiffany DeSouza ,&nbsp;Qin Yang ,&nbsp;Javier Solivan-Rivera ,&nbsp;Silvia Corvera","doi":"10.1016/j.molmet.2024.102051","DOIUrl":"10.1016/j.molmet.2024.102051","url":null,"abstract":"<div><h3>Objective</h3><div>The uncoupling protein 1 (UCP1) is induced in brown or “beige” adipocytes through catecholamine-induced cAMP signaling, which activates diverse transcription factors. UCP1 expression can also be enhanced by PPARγ agonists such as rosiglitazone (Rsg). However, it is unclear whether this upregulation results from de-novo differentiation of beige adipocytes from progenitor cells, or from the induction of UCP1 in pre-existing adipocytes. To explore this, we employed human adipocytes differentiated from progenitor cells and examined their acute response to Rsg, to the adenylate-cyclase activator forskolin (Fsk), or to both simultaneously.</div></div><div><h3>Methods</h3><div>Adipocytes generated from primary human progenitor cells were differentiated without exposure to PPARγ agonists, and treated for 3, 6 or 78 h to Fsk, to Rsg, or to both simultaneously. Bulk RNASeq, RNAScope, RT-PCR, CRISPR-Cas9 mediated knockout, oxygen consumption and western blotting were used to assess cellular responses.</div></div><div><h3>Results</h3><div><em>UCP1</em> mRNA expression was induced within 3 h of exposure to either Rsg or Fsk, indicating that Rsg’s effect is independent on additional adipocyte differentiation. Although Rsg and Fsk induced distinct overall transcriptional responses, both induced genes associated with calcium metabolism, lipid droplet assembly, and mitochondrial remodeling, denoting core features of human adipocyte beiging. Unexpectedly, we found that Fsk-induced <em>UCP1</em> expression was reduced by approximately 80% following CRISPR-Cas9-mediated knockout of <em>PNPLA2</em>, the gene encoding the triglyceride lipase ATGL. As anticipated, ATGL knockout suppressed lipolysis; however, the associated suppression of UCP1 induction indicates that maximal cAMP-mediated <em>UCP1</em> induction requires products of ATGL-catalyzed lipolysis. Supporting this, we observed that the reduction in Fsk-stimulated UCP1 induction caused by ATGL knockout was reversed by Rsg, implying that the role of lipolysis in this process is to generate natural PPARγ agonists.</div></div><div><h3>Conclusions</h3><div><em>UCP1</em> transcription is known to be stimulated by transcription factors activated downstream of cAMP-dependent protein kinases. Here we demonstrate that <em>UCP1</em> transcription can also be acutely induced through PPARγ-activation. Moreover, both pathways are activated in human adipocytes in response to cAMP, synergistically inducing UCP1 expression. The stimulation of PPARγ in response to cAMP may result from the production of natural PPARγ activating ligands through ATGL-mediated lipolysis.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102051"},"PeriodicalIF":7.0,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142504364","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interruption of glucagon signaling augments islet non-alpha cell proliferation in SLC7A2- and mTOR-dependent manners","authors":"Katie C. Coate ,&nbsp;Chunhua Dai ,&nbsp;Ajay Singh ,&nbsp;Jade Stanley ,&nbsp;Brittney A. Covington ,&nbsp;Amber Bradley ,&nbsp;Favour Oladipupo ,&nbsp;Yulong Gong ,&nbsp;Scott Wisniewski ,&nbsp;Katelyn Sellick ,&nbsp;Erick Spears ,&nbsp;Greg Poffenberger ,&nbsp;Anna Marie R. Schornack ,&nbsp;Alexandria Bustabad ,&nbsp;Tyler Rodgers ,&nbsp;Nandita Dey ,&nbsp;Leonard D. Shultz ,&nbsp;Dale L. Greiner ,&nbsp;Hai Yan ,&nbsp;Alvin C. Powers ,&nbsp;E. Danielle Dean","doi":"10.1016/j.molmet.2024.102050","DOIUrl":"10.1016/j.molmet.2024.102050","url":null,"abstract":"<div><h3>Objective</h3><div>Dysregulated glucagon secretion and inadequate functional beta cell mass are hallmark features of diabetes. While glucagon receptor (GCGR) antagonism ameliorates hyperglycemia and elicits beta cell regeneration in pre-clinical models of diabetes, it also promotes alpha and delta cell hyperplasia. We sought to investigate the mechanism by which loss of glucagon action impacts pancreatic islet non-alpha cells, and the relevance of these observations in a human islet context.</div></div><div><h3>Methods</h3><div>We used zebrafish, rodents, and transplanted human islets comprising six different models of interrupted glucagon signaling to examine their impact on delta and beta cell proliferation and mass. We also used models with global deficiency of the cationic amino acid transporter, SLC7A2, and mTORC1 inhibition via rapamycin, to determine whether amino acid-dependent nutrient sensing was required for islet non-alpha cell growth.</div></div><div><h3>Results</h3><div>Inhibition of glucagon signaling stimulated delta cell proliferation in mouse and transplanted human islets, and in mouse islets. This was rapamycin-sensitive and required SLC7A2. Likewise, <em>gcgr</em> deficiency augmented beta cell proliferation via SLC7A2- and mTORC1-dependent mechanisms in zebrafish and promoted cell cycle engagement in rodent beta cells but was insufficient to drive a significant increase in beta cell mass in mice.</div></div><div><h3>Conclusions</h3><div>Our findings demonstrate that interruption of glucagon signaling augments islet non-alpha cell proliferation in zebrafish, rodents, and transplanted human islets in a manner requiring SLC7A2 and mTORC1 activation. An increase in delta cell mass may be leveraged for future beta cell regeneration therapies relying upon delta cell reprogramming.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102050"},"PeriodicalIF":7.0,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142470188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"FITM2 deficiency results in ER lipid accumulation, ER stress, and reduced apolipoprotein B lipidation and VLDL triglyceride secretion in vitro and in mouse liver","authors":"Haizhen Wang ,&nbsp;Cyrus Nikain ,&nbsp;Konstantinos I. Fortounas ,&nbsp;Jaume Amengual ,&nbsp;Ozlem Tufanli ,&nbsp;Maxwell La Forest ,&nbsp;Yong Yu ,&nbsp;Meng C. Wang ,&nbsp;Russell Watts ,&nbsp;Richard Lehner ,&nbsp;Yunping Qiu ,&nbsp;Min Cai ,&nbsp;Irwin J. Kurland ,&nbsp;Ira J. Goldberg ,&nbsp;Sujith Rajan ,&nbsp;M. Mahmood Hussain ,&nbsp;Jeffrey L. Brodsky ,&nbsp;Edward A. Fisher","doi":"10.1016/j.molmet.2024.102048","DOIUrl":"10.1016/j.molmet.2024.102048","url":null,"abstract":"<div><h3>Objective</h3><div>Triglycerides (TGs) associate with apolipoprotein B100 (apoB100) to form very low density lipoproteins (VLDLs) in the liver. The repertoire of factors that facilitate this association is incompletely understood. FITM2, an integral endoplasmic reticulum (ER) protein, was originally discovered as a factor participating in cytosolic lipid droplet (LD) biogenesis in tissues that do not form VLDL. We hypothesized that in the liver, in addition to promoting cytosolic LD formation, FITM2 would also transfer TG from its site of synthesis in the ER membrane to nascent VLDL particles within the ER lumen.</div></div><div><h3>Methods</h3><div>Experiments were conducted using a rat hepatic cell line (McArdle-RH7777, or McA cells), an established model of mammalian lipoprotein metabolism, and mice. FITM2 expression was reduced using siRNA in cells and by liver specific cre-recombinase mediated deletion of the <em>Fitm2</em> gene in mice. Effects of FITM2 deficiency on VLDL assembly and secretion <em>in vitro</em> and <em>in vivo</em> were measured by multiple methods, including density gradient ultracentrifugation, chromatography, mass spectrometry, stimulated Raman scattering (SRS) microscopy, sub-cellular fractionation, immunoprecipitation, immunofluorescence, and electron microscopy.</div></div><div><h3>Main findings</h3><div>1) FITM2-deficient hepatic cells <em>in vitro</em> and <em>in vivo</em> secrete TG-depleted VLDL particles, but the number of particles is unchanged compared to controls; 2) FITM2 deficiency in mice on a high fat diet (HFD) results in decreased plasma TG levels. The number of apoB100-containing lipoproteins remains similar, but shift from VLDL to low density lipoprotein (LDL) density; 3) Both <em>in vitro</em> and <em>in vivo</em>, when TG synthesis is stimulated and FITM2 is deficient, TG accumulates in the ER, and despite its availability this pool is unable to fully lipidate apoB100 particles; 4) FITM2 deficiency disrupts ER morphology and results in ER stress.</div></div><div><h3>Conclusion</h3><div>The results suggest that FITM2 contributes to VLDL lipidation, especially when newly synthesized hepatic TG is in abundance. In addition to its fundamental importance in VLDL assembly, the results also suggest that under dysmetabolic conditions, FITM2 may be an important factor in the partitioning of TG between cytosolic LDs and VLDL particles.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102048"},"PeriodicalIF":7.0,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142470174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distinct genetic signals at the FGF21 locus complicate studies of FGF21's role in diet regulation using human cohort data","authors":"Stina Ramne ,&nbsp;Mario García-Ureña ,&nbsp;Matthew P. Gillum ,&nbsp;Lars Ängquist ,&nbsp;Torben Hansen ,&nbsp;Jordi Merino ,&nbsp;Niels Grarup","doi":"10.1016/j.molmet.2024.102049","DOIUrl":"10.1016/j.molmet.2024.102049","url":null,"abstract":"<div><h3>Objectives</h3><div>Experimental and genetic studies suggest that fibroblast growth factor 21 (FGF21) modulates macronutrient and alcohol preferences, but evidence of such regulation in humans remains scarce. To address this gap in translation, we aimed to map the relationships between plasma FGF21 levels, <em>FGF21</em> genetic variation and habitual macronutrient intake in a large human population.</div></div><div><h3>Methods</h3><div>We fine-mapped and performed colocalization of the <em>FGF21</em> genetic region in GWAS summary statistics of plasma FGF21 levels and macronutrient intake. UK Biobank data were used to investigate the associations between <em>FGF21</em> genetic variants, plasma FGF21 protein levels, and macronutrient intake (including alcohol) assessed with repeated 24-hour recalls. One- and two-sample mendelian randomization were performed to estimate the effects of plasma FGF21 on macronutrient intake.</div></div><div><h3>Results</h3><div>We show that the main macronutrient-associated variant rs838133 and the FGF21 cis-pQTL rs838131, both in the <em>FGF21</em> gene, are distinct genetic signals. Effect directions also suggest that the influence of <em>FGF21</em> variation on macronutrient intake appear more complex than by direct mediation through plasma FGF21. Only when considering this complexity at <em>FGF21,</em> is plasma FGF21 estimated to reduce alcohol and increase protein and fat intake using mendelian randomization. Importantly, plasma FGF21 levels also appear markedly elevated by primarily high alcohol and low protein intake.</div></div><div><h3>Conclusions</h3><div>These findings support the feedback diet-regulatory mechanism of FGF21 in humans, but highlights the need for mechanistic characterization of the complex <em>FGF21</em> genetic region.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102049"},"PeriodicalIF":7.0,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142470172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distinct roles for the domains of the mitochondrial aspartate/glutamate carrier citrin in organellar localization and substrate transport","authors":"Sotiria Tavoulari ,&nbsp;Denis Lacabanne ,&nbsp;Gonçalo C. Pereira ,&nbsp;Chancievan Thangaratnarajah,&nbsp;Martin S. King,&nbsp;Jiuya He,&nbsp;Suvagata R. Chowdhury,&nbsp;Lisa Tilokani,&nbsp;Shane M. Palmer,&nbsp;Julien Prudent,&nbsp;John E. Walker,&nbsp;Edmund R.S. Kunji","doi":"10.1016/j.molmet.2024.102047","DOIUrl":"10.1016/j.molmet.2024.102047","url":null,"abstract":"<div><h3>Objective</h3><div>Citrin, the mitochondrial aspartate/glutamate carrier isoform 2 (AGC2), is structurally and mechanistically the most complex SLC25 family member, because it consists of three domains and forms a homo-dimer. Each protomer has an N-terminal calcium-binding domain with EF-hands, followed by a substrate-transporting carrier domain and a C-terminal domain with an amphipathic helix. The absence or dysfunction of citrin leads to citrin deficiency, a highly prevalent pan-ethnic mitochondrial disease. Here, we aim to understand the role of different citrin domains and how they contribute to pathogenic mechanisms in citrin deficiency.</div></div><div><h3>Methods</h3><div>We have employed structural modeling and functional reconstitution of purified proteins in proteoliposomes to assess the transport activity and calcium regulation of wild-type citrin and pathogenic variants associated with citrin deficiency. We have also developed a double knockout of citrin and aralar (AGC1), the two paralogs of the mitochondrial aspartate/glutamate carrier, in HAP1 cells to perform mitochondrial imaging and to investigate mitochondrial localisation.</div></div><div><h3>Results</h3><div>Using 33 pathogenic variants of citrin we clarify determinants of subcellular localization and transport mechanism. We identify crucial elements of the carrier domain that are required for transport, including those involved in substrate binding, network formation and dynamics. We show that the N-terminal domain is not involved in calcium regulation of transport, as previously thought, but when mutated causes a mitochondrial import defect.</div></div><div><h3>Conclusions</h3><div>Our work introduces a new role for the N-terminal domain of citrin and demonstrates that dysfunction of the different domains contributes to distinct pathogenic mechanisms in citrin deficiency.</div></div>","PeriodicalId":18765,"journal":{"name":"Molecular Metabolism","volume":"90 ","pages":"Article 102047"},"PeriodicalIF":7.0,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142470173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}