Promoted Lipid Accumulation Research Articles

ASC Regulates Subcutaneous Adipose Tissue Lipogenesis and Lipolysis via p53/AMPKα Axis.

Obesity has become an extensive threat to human health due to associated chronic inflammation and metabolic diseases. Apoptosis-associated speck-like protein (ASC) is a critical link between inflammasome and apoptosis-inducing proteins. In this study, we aimed to clarify the role of ASC in lipid metabolism. With high-fat diet (HFD) and knockout leptin gene mice (ob/ob), we found that ASC expression in subcutaneous adipose tissue (SAT) correlated with obesity. It could also positively regulate the reprogramming of cellular energy metabolism. Stromal vascular fractions (SVF) cells derived from the SAT of Asc−/− mice or SVF from wild-type (WT) mice transfected with ASC siRNA were used to further investigate the underlying molecular mechanisms. We found ASC deficiency could lead to lipogenesis and inhibit lipolysis in SAT, aggravating lipid accumulation and impairing metabolic balance. In addition, our results showed that p53 and AMPKα expression were inhibited in SAT when ASC level was low. p53 and AMP-activated protein kinase α (AMPKα) were then assessed to elucidate whether they were downstream of ASC in regulating lipid metabolism. Our results revealed that ASC deficiency could promote lipid accumulation by increasing lipogenesis and decreasing lipolysis through p53/AMPKα axis. Regulation of ASC on lipid metabolism might be a novel therapeutic target for obesity.

Silencing 1,3-β-glucan synthase gene promotes total lipid production and changes fatty acids composition by affecting carbon flow distribution in Phaeodactylum tricornutum

To clarify the effect of 1,3-β-glucan (known as chrysolaminarin) synthase ( Pt BGS) on carbon flow distribution, expression of 1,3-β-glucan synthase gene ( Ptbgs ) was silenced by RNA interference in Phaeodactylum tricornutum . The results showed that the chrysolaminarin content in all transgenic strains was significantly lower than that in the wild-type (WT), while the total lipid content increased to varying degrees. Importantly, the decrease in chrysolaminarin content was significantly correlated with the increase in total lipid content. There was no significant difference in the protein content between all the transgenic strains and WT. Thus, Pt BGS mainly affected the distribution of carbon flow in total lipids and polysaccharides , mainly chrysolaminarin. Silencing Ptbgs changed the fatty acids composition , and specifically promoted polyunsaturated fatty acids production and reduced monounsaturated fatty acids content, but had only a little effect on saturated fatty acids content. Interestingly, the growth of transgenic strains was not influenced while the lipid content increased, indicating that Ptbgs silencing may be an effective strategy to improve lipid production in diatoms. • Distribution of carbon flow can be affected by 1,3-β-glucan synthase ( Pt BGS). • Inhibiting the expression of Ptbgs promoted lipid accumulation. • Silencing Ptbgs changed the fatty acids composition. • Interfering with Ptbgs exerted little effect on growth in Phaeodactylum tricornutum . • Ptbgs silencing may be an effective strategy to improve lipid production in diatoms.

A long non-coding RNA lnc210 promotes adipogenic differentiation of buffalo intramuscular adipocytes

Intramuscular fat (IMF) content is one of the most significant factors influencing beef quality in terms of tenderness, flavor, and juiciness. Thus, internal factors affecting IMF deposition have received considerable attention for decades. In this study, we demonstrated a long non-coding RNA, lnc210, promoted adipogenic differentiation of buffalo intramuscular adipocytes. lnc210 was rich in adipose tissue and showed increased expression with the adipogenic differentiation of buffalo intramuscular adipocytes. lnc210 was mainly expressed in the nucleus of adipocytes. Full-length lnc210 was obtained by rapid amplification of cDNA ends technology. lnc210 overexpression promoted lipid accumulation by upregulating the mRNA expression of peroxisome proliferator-activated receptor gamma (PPARG) and CCAAT enhancer binding protein alpha (C/EBPα) in buffalo intramuscular adipocytes. These results provide a basis for an in-depth analysis of the role of lnc210 in accelerating IMF deposition in buffaloes.

Angiotensin II induces podocyte metabolic reprogramming from glycolysis to glycerol-3-phosphate biosynthesis

Recent studies have reported that Angiotensin II (Ang II) contributes to podocyte injury by interfering with metabolism. Glycolysis is essential for podocytes and glycolysis abnormality is associated with glomerular injury in chronic kidney disease (CKD). Glycerol-3-phosphate (G-3-P) biosynthesis is a shunt pathway of glycolysis, in which cytosolic glycerol-3-phosphate dehydrogenase 1 (GPD1) catalyzes dihydroxyacetone phosphate (DHAP) to generate G-3-P in the presence of the NADH. G-3-P is not only a substrate in glycerophospholipids and glyceride synthesis but also can be oxidated by mitochondrial glycerol-3-phosphate dehydrogenase (GPD2) to regenerate DHAP in mitochondria. Since G-3-P biosynthesis links to glycolysis, mitochondrial metabolism and lipid synthesis, we speculate G-3-P biosynthesis abnormality is probably involved in podocyte injury. In this study, we demonstrated that Ang II upregulated GPD1 expression and increased G-3-P and glycerophospholipid syntheses in podocytes. GPD1 knockdown protected podocytes from Ang II-induced lipid accumulation and mitochondrial dysfunction. GPD1 overexpression exacerbated Ang II-induced podocyte injury. In addition, we proved that lipid accumulation and mitochondrial dysfunction were correlated with G-3-P content in podocytes. These results suggest that Ang II upregulates GPD1 and promotes G-3-P biosynthesis in podocytes, which promote lipid accumulation and mitochondrial dysfunction in podocytes.

SEMA7AR148W mutation promotes lipid accumulation and NAFLD progression via increased localization on the hepatocyte surface.

Genetic polymorphisms are associated with the development of nonalcoholic fatty liver disease (NAFLD). Semaphorin7a (Sema7a) deficiency in mouse peritoneal macrophages reduces fatty acid (FA) oxidation. Here, we identified 17 individuals with SEMA7A heterozygous mutations in 470 patients with biopsy-proven NAFLD. SEMA7A heterozygous mutations increased susceptibility to NAFLD, steatosis severity, and NAFLD activity scores in humans and mice. The Sema7aR145W mutation (equivalent to human SEMA7AR148W) significantly induced small lipid droplet accumulation in mouse livers compared with WT mouse livers. Mechanistically, the Sema7aR145W mutation increased N-glycosylated Sema7a and its receptor integrin β1 proteins in the cell membranes of hepatocytes. Furthermore, Sema7aR145W mutation enhanced its protein interaction with integrin β1 and PKC-α and increased PKC-α phosphorylation, which were both abrogated by integrin β1 silencing. Induction of PKCα_WT, but not PKCα_dominant negative, overexpression induced transcriptional factors Srebp1, Chrebp, and Lxr expression and their downstream Acc1, Fasn, and Cd36 expression in primary mouse hepatocytes. Collectively, our findings demonstrate that the SEMA7AR148W mutation is a potentially new strong genetic determinant of NAFLD and promotes intrahepatic lipid accumulation and NAFLD in mice by enhancing PKC-α–stimulated FA and triglyceride synthesis and FA uptake. The inhibition of hepatic PKC-α signaling may lead to novel NAFLD therapies.

The effect of salinity stress on the growth and lipid accumulation of Scenedesmus quadricauda FACHB-1297 under xylose mixotrophic cultivation

In the commercial production of microalgae biodiesel, high culture cost and low lipid production yields are two major limitations. Finding cheap carbon sources and ways to promote lipid accumulation can achieve low-cost cultivation and efficient lipid production. The impact of NaCl on the growth and lipid accumulation in Scenedesmus quadricauda FACHB-1297 under xylose mixotrophic cultivation was explored in this study. The results showed that when NaCl concentration were 0.88–5.85 g/L, the biomass concentration and lipid content were 2.15–2.68 and 1.19–1.80 times higher than those in BG11 medium, respectively. Under the optimal NaCl concentration of 2.63 g/L, the highest lipid content (39.33%) was achieved, with the biomass concentration of 0.72 g/L, the total nitrogen removal efficiency of 39.00%, and the total phosphorus removal efficiency of nearly 100.00%, except for a higher total sugar content of 19.26% and total protein content of 5.38%. In short, these results indicated that 2.63 g/L NaCl treatment was an efficient way to promote the lipid accumulation of S. quadricauda FACHB-1297 using xylose in papermaking waste liquid to produce biofuel.

Manganese-Induced Oxidative Stress Contributes to Intestinal Lipid Deposition via the Deacetylation of PPARγ at K339 by SIRT1.

Aims: Excessive manganese (Mn) exposure is toxic, and induces lipid deposition, but the underlying mechanisms remain elusive. Herein, we explored how dietary Mn supplementation affects lipid deposition and metabolism in the intestine of vertebrates using the yellow catfish Pelteobagrus fulvidraco as the model. Results: High-Mn (H-Mn) diet increased intestinal Mn content, promoted lipid accumulation and lipogenesis, and inhibited lipolysis. In addition, it induced oxidative stress, upregulated metal-response element-binding transcription factor-1 (MTF-1), and peroxisome proliferator-activated receptor gamma (PPARγ) protein expression in the nucleus, induced PPARγ acetylation, and the interaction between PPARγ and retinoid X receptor alpha (RXRα), while it downregulated sirtuin 1 (SIRT1) expression and activity. Mechanistically, Mn activated the MTF-1/divalent metal transporter 1 (DMT1) pathway, increased Mn accumulation in the mitochondria, and induced oxidative stress. This in turn promoted lipid deposition via deacetylation of PPARγ at K339 by SIRT1. Subsequently, PPARγ mediated Mn-induced lipid accumulation through transcriptionally activating fatty acid translocase, stearoyl-CoA desaturase 1, and perilipin 2 promoters. Innovation: These studies uncover a previously unknown mechanism by which Mn induces lipid deposition in the intestine via the oxidative stress-SIRT1-PPARγ pathway. Conclusion: High dietary Mn intake activates MTF-1/DMT1 and oxidative stress pathways. Oxidative stress-mediated PPARγ deacetylation at K339 site contributes to increased lipid accumulation. Our results provided a direct link between Mn and lipid metabolism via the oxidative stress-SIRT1-PPARγ axis. Antioxid. Redox Signal. 37, 417-436.

Highly efficient harvesting and lipid extraction of limnetic Chlorella sorokiniana SDEC-18 grown in seawater for microalgal biofuel production

The low efficiency and high costs involved in harvesting microalgae and extracting lipids have been major barriers toward large scale algae-based biofuel production. Here we demonstrate the feasibility of employing seawater as a substitute for freshwater in cultivating Chlorella sorokiniana SDEC-18. Strikingly, compared to freshwater, seawater was found to 1) enhance Chlorella autoflocculation, reaching 90 % settling efficiency within 2 h; 2) promote lipid accumulation, reaching about 60 % (0.19–0.28 g/L of lipid concentration) due to salinity stress; and 3) improve lipid-extraction efficiency, with full extraction achieved after only the second extraction step. The mechanisms for enhanced Chlorella harvest were revealed through the observation of extracellular polymeric substances using transmission electron microscopy after lanthanum fixation. Moreover, new insights into cell fragility under salinity stress have been obtained through our pioneering proposal of the involvement of Chlorella microtubules. The advances we have achieved in Chlorella harvesting and lipid extraction lay the foundation for a new generation of biofuel production.

Lipid characteristics of fatty liver induced by high expression of Golgi protein 73

Fatty liver disease is a common chronic liver disease which is mainly induced by abnormal lipid metabolism. To find out the effect of GP73 on lipid metabolism in the liver, we constructed a high GP73 expression liver model through a tail vein injection of AAV-GP73 into eight-week-old C57BL/6J mice. Liver lipid metabolomics analysis showed that lipids in the liver of mice, especially the triglycerides, were significantly increased. In addition, kyoto encyclopedia of genes and genomes enrichment analysis showed that GP73 altered lipid metabolites profile that may further disturb many signaling pathways related to cellular metabolism. The diseases linked to type II diabetes, non-alcoholic fatty liver disease (NAFLD) and choline metabolism in cancer cells were more likely to be dysregulated. Thus, GP73 may induce fatty liver by regulating lipid metabolism and promoting lipid accumulation in the liver.

Adipose cells and tissues soften with lipid accumulation while in diabetes adipose tissue stiffens

Adipose tissue expansion involves both differentiation of new precursors and size increase of mature adipocytes. While the two processes are well balanced in healthy tissues, obesity and diabetes type II are associated with abnormally enlarged adipocytes and excess lipid accumulation. Previous studies suggested a link between cell stiffness, volume and stem cell differentiation, although in the context of preadipocytes, there have been contradictory results regarding stiffness changes with differentiation. Thus, we set out to quantitatively monitor adipocyte shape and size changes with differentiation and lipid accumulation. We quantified by optical diffraction tomography that differentiating preadipocytes increased their volumes drastically. Atomic force microscopy (AFM)-indentation and -microrheology revealed that during the early phase of differentiation, human preadipocytes became more compliant and more fluid-like, concomitant with ROCK-mediated F-actin remodelling. Adipocytes that had accumulated large lipid droplets were more compliant, and further promoting lipid accumulation led to an even more compliant phenotype. In line with that, high fat diet-induced obesity was associated with more compliant adipose tissue compared to lean animals, both for drosophila fat bodies and murine gonadal adipose tissue. In contrast, adipose tissue of diabetic mice became significantly stiffer as shown not only by AFM but also magnetic resonance elastography. Altogether, we dissect relative contributions of the cytoskeleton and lipid droplets to cell and tissue mechanical changes across different functional states, such as differentiation, nutritional state and disease. Our work therefore sets the basis for future explorations on how tissue mechanical changes influence the behaviour of mechanosensitive tissue-resident cells in metabolic disorders.

Tuftelin 1 Facilitates Hepatocellular Carcinoma Progression through Regulation of Lipogenesis and Focal Adhesion Maturation.

Hepatocellular carcinoma (HCC) is the most common type of primary liver malignancy with poor prognosis worldwide. Emerging evidences demonstrated critical roles of lipid de novo synthesis in HCC progression, yet its regulatory mechanisms are not fully understood. Herein, we found that tuftelin 1 (TUFT1), an acidic phosphorylated glycoprotein with secretory capacity, was significantly upregulated in HCC and had an excellent correlation with patient survival and malignancy features. Through database mining and experimental validation, we found that TUFT1 was associated with fatty acid metabolism and promoted lipid accumulation in HCC cells. Further, we found that TUFT1 can interact with CREB1, a transcription factor for hepatic lipid metabolism, and regulate its activity and the transcriptions of key enzymes for lipogenesis. TUFT1 promoted HCC cell proliferation significantly, which was partially reversed by treatment of an inhibitor of CREB1, KG-501. Moreover, TUFT1 promoted the capacity of HCC cell invasion in vitro, which was likely mediated by its association with zyxin, a zinc-binding phosphoprotein responsible for the formation of fully mature focal adhesions on extracellular matrix. We found that TUFT1 can interact with ZYX and inhibit its expression and recruitments to focal complexes in HCC cells. Collectively, our study uncovered new regulatory mechanisms of TUFT1-mediated lipogenesis, cell proliferation, and invasion.

Overexpression of SCAP inhibits autophagy and promotes lipid accumulation in vascular smooth muscle cells

Overexpression of SCAP inhibits autophagy and promotes lipid accumulation in vascular smooth muscle cells

The Chlamydomonas transcription factor MYB1 mediates lipid accumulation under nitrogen depletion.

Microalgae accumulate high levels of oil under stress, but the underlying biosynthetic pathways are not fully understood. We sought to identify key regulators of lipid metabolism under stress conditions. We found that the Chlamydomonas reinhardtii gene encoding the MYB-type transcription factor MYB1 is highly induced under stress conditions. Two myb1 mutants accumulated less total fatty acids and storage lipids than their parental strain upon nitrogen (N) depletion. Transcriptome analysis revealed that genes involved in lipid metabolism are highly enriched in the wild-type but not in the myb1-1 mutant after 4 h of N depletion. Among these genes were several involved in the transport of fatty acids from the chloroplast to the endoplasmic reticulum (ER): acyl-ACP thioesterase (FAT1), Fatty Acid EXporters (FAX1, FAX2), and long-chain acyl-CoA synthetase1 (LACS1). Furthermore, overexpression of FAT1 in the chloroplast increased lipid production. These results suggest that, upon N depletion, MYB1 promotes lipid accumulation by facilitating fatty acid transport from the chloroplast to the ER. This study identifies MYB1 as an important positive regulator of lipid accumulation in C. reinhardtii upon N depletion, adding another player to the established regulators of this process, including NITROGEN RESPONSE REGULATOR 1 (NRR1) and TRIACYLGLYCEROL ACCUMULATION REGULATOR 1 (TAR1).

Metformin Ameliorates Hepatic Steatosis induced by olanzapine through inhibiting LXR\u03b1/PCSK9 pathway

Studies have confirmed that olanzapine, the mainstay treatment for schizophrenia, triggers metabolic diseases, including non-alcoholic fatty liver disease (NAFLD). However, the etiology of olanzapine-induced NAFLD is poorly understood. Proprotein convertase subtilisin kexin type 9 (PCSK9) is involved in NAFLD pathogenesis, and metformin can significantly decrease circulating PCSK9. The purpose of this study was to investigate the role of PCSK9 and explore the therapeutic effect of metformin for olanzapine-associated NAFLD. Olanzapine significantly upregulated PCSK9 and promoted lipid accumulation in mouse livers and HepG2 and AML12 cells. Metformin ameliorated these pathological alterations. PCSK9 upstream regulator liver X receptor α (LXRα) was significantly upregulated in olanzapine-induced NAFLD. LXRα antagonist treatment and LXRα overexpression resulted in a decrease and increase of PCSK9, respectively. Hepatic lipogenesis-associated genes FAS and SCD1 were significantly upregulated in olanzapine-induced NAFLD mice and HepG2 cells overexpressing PCSK9, and genes related to lipid β-oxidation (SCAD and PPARα) were downregulated, while metformin reversed these changes. In addition, we found that LXRα overexpression compromised the effect of metformin on PCSK9 levels and intracellular lipid droplet formation. Taken together, our findings suggest that olanzapine enhances hepatic PCSK9 expression by upregulating LXRα, thereby increasing FAS and SCD1 expression as well as decreasing SCAD and PPARα, and promoting lipid accumulation, and, subsequently, NAFLD, which is ameliorated by metformin.

Hepatitis C Virus Alters Macrophage Cholesterol Metabolism Through Interaction with Scavenger Receptors.

Lipid accumulation and inflammation act together to induce, sustain, and further development of chronic liver disease. Hepatitis C virus (HCV) infection induces metabolic and immune changes in liver macrophages, promoting lipid accumulation and inflammation that synergize and culminate in the development of steatohepatitis and fibrogenesis. Chronic HCV patients have increased liver macrophages with disruptions in cholesterol metabolism and alterations in inflammatory mediators. While HCV-induced changes in inflammatory mediators are well documented, how HCV triggers metabolic change in macrophages is unknown. In this report, we examined the mechanism of macrophage sensing of HCV to cause metabolic impairment and subsequent immune dysfunction. We demonstrate that HCV protein and RNA kinetics in macrophages are distinct from hepatocytes. In macrophages, HCV RNAs and protein accumulate rapidly after exposure but internalized RNAs quickly decline to a low-level set point. Notably, exposure of macrophages to HCV resulted in increased lipids and cholesterol and activation of cholesterol-sensing, immunomodulatory liver X receptors (LXRs). Furthermore, we provide evidence that HCV RNA accumulation in macrophages occurs through scavenging receptors. These results suggest that HCV released from infected hepatocytes stimulates accumulation of lipids and activation of LXR in macrophages contributing to metabolic changes involved in HCV-induced chronic liver disease. Our results provide novel insight into mechanisms through which impaired lipid metabolism in macrophages associated with HCV infection promotes development of liver steatohepatitis and fibrosis.

Small-Molecule Inhibitors Targeting Lipolysis in Human Adipocytes.

Chronically elevated circulating fatty acid levels promote lipid accumulation in nonadipose tissues and cause lipotoxicity. Adipose triglyceride lipase (ATGL) critically determines the release of fatty acids from white adipose tissue, and accumulating evidence suggests that inactivation of ATGL has beneficial effects on lipotoxicity-driven disorders including insulin resistance, steatohepatitis, and heart disease, classifying ATGL as a promising drug target. Here, we report on the development and biological characterization of the first small-molecule inhibitor of human ATGL. This inhibitor, designated NG-497, selectively inactivates human and nonhuman primate ATGL but not structurally and functionally related lipid hydrolases. We demonstrate that NG-497 abolishes lipolysis in human adipocytes in a dose-dependent and reversible manner. The combined analysis of mouse- and human-selective inhibitors, chimeric ATGL proteins, and homology models revealed detailed insights into enzyme–inhibitor interactions. NG-497 binds ATGL within a hydrophobic cavity near the active site. Therein, three amino acid residues determine inhibitor efficacy and species selectivity and thus provide the molecular scaffold for selective inhibition.

Obesity promotes lipid accumulation in mouse cartilage-A potential role of acetyl-CoA carboxylase (ACC) mediated chondrocyte de novo lipogenesis.

Obesity promotes the development of osteoarthritis (OA). It is also well-established that obesity leads to excessive lipid deposition in nonadipose tissues, which often induces lipotoxicity. The objective of this study was to investigate changes in the levels of various lipids in mouse cartilage in the context of obesity and determine if chondrocyte de novo lipogenesis is altered.We used Oil Red O to determine the accumulation of lipid droplets in cartilage from mice fed high-fat diet (HFD) or low-fat diet (LFD). We further used mass spectrometry-based lipidomic analyses to quantify levels of different lipid species. Expression of genes involving in fatty acid (FA) uptake, synthesis, elongation, and desaturation were examined using quantitative polymerase chain reaction. To further study the potential mechanisms, we cultured primary mouse chondrocytes under high-glucose and high-insulin conditions to mimic the local microenvironment associated with obesity and subsequently examined the abundance of cellular lipid droplets. The acetyl-CoA carboxylase (ACC) inhibitor, ND-630, was added to the culture medium to examine the effect of inhibiting de novo lipogenesis on lipid accumulation in chondrocytes.When compared to the mice receiving LFD, the HFD group displayed more chondrocytes with visible intracellular lipid droplets. Significantly higher amounts of total FAs were also detected in the HFD group. Five out of six significantly upregulated FAs were ω-6 FAs, while the two significantly downregulated FAs were ω-3 FAs. Consequently, the HFD group displayed a significantly higher ω-6/ω-3 FA ratio. Ether linked phosphatidylcholine was also found to be higher in the HFD group. Fatty acid desaturase (Fad1-3), fatty acid-binding protein 4 (Fabp4), and fatty acid synthase (Fasn) transcripts were not found to be different between the treatment groups and fatty acid elongase (Elovl1-7) transcripts were undetectable in cartilage. Ceramide synthase 2 (Cers-2), the only transcript found to be changed in these studies, was significantly upregulated in the HFD group. In vitro, chondrocytes upregulated de novo lipogenesis when cultured under high-glucose, high-insulin conditions, and this observation was associated with the activation of ACC, which was attenuated by the addition of ND-630.This study provides the first evidence that lipid deposition is increased in cartilage with obesity and that this is associated with the upregulation of ACC-mediated de novo lipogenesis. This was supported by our observation that ACC inhibition ameliorated lipid accumulation in chondrocytes, thereby suggesting that ACC could potentially be targeted to treat obesity-associated OA.

Dysfunction of lipid storage droplet-2 suppresses endoreplication and induces JNK pathway-mediated apoptotic cell death in Drosophila salivary glands

The lipid storage droplet-2 (LSD-2) protein of Drosophila is a homolog of mammalian perilipin 2, which is essential for promoting lipid accumulation and lipid droplet formation. The function of LSD-2 as a regulator of lipolysis has also been demonstrated. However, other LSD-2 functions remain unclear. To investigate the role of LSD-2, we performed tissue-specific depletion in the salivary glands of Drosophila using a combination of the Gal4-upstream activating sequence system and RNA interference. LSD-2 depletion inhibited the entry of salivary gland cells into the endoreplication cycle and delayed this process by enhancing CycE expression, disrupting the development of this organ. The deficiency of LSD-2 expression enhanced reactive oxygen species production in the salivary gland and promoted JNK-dependent apoptosis by suppressing dMyc expression. This phenomenon did not result from lipolysis. Therefore, LSD-2 is vital for endoreplication cell cycle and cell death programs.

α-ketoisocaproic acid promotes ER stress through impairment of autophagy, thereby provoking lipid accumulation and insulin resistance in murine preadipocytes

α-ketoisocaproic acid (AKA), a metabolite of l-leucine, is one of the branched-chain amino acids (BCAAs) involved in energy metabolism. However, the effects of AKA on lipid metabolism, insulin signaling, and related mechanisms in preadipocytes have not been reported. Herein, we investigated the impacts of AKA on lipid accumulation in 3T3-L1 murine preadipocytes. Treatment with AKA for 4 days enhanced lipid accumulation and expression of lipogenic proteins, such as cleaved sterol-regulatory element-binding proteins (SREBP1) and stearoyl-CoA desaturase-1 (SCD1) in 3T3-L1 cells. Increased endoplasmic reticulum (ER) stress markers, such as phosphorylation of eukaryotic initiation factor 2 (eIF2) and CHOP, were observed in the presence of AKA. AKA treatment increased mTOR phosphorylation and reducing autophagy markers, such as LC3 conversion and degradation of p62. Treatment with rapamycin, an mTOR inhibitor, reduced the effects of AKA on ER stress and lipogenesis in 3T3-L1 preadipocytes. The present study demonstrates that AKA increases ER stress by impairing mTOR/autophagy signaling, thus promoting lipid accumulation and insulin resistance in preadipocytes. In particular, if AKA is taken together with substances that can suppress ER stress, more effective skeletal muscle gain will be possible.

High-Fat-Diet-Induced Extracellular Matrix Deposition Regulates Integrin-FAK Signals in Adipose Tissue to Promote Obesity.

High-fat-diet (HFD) is an important factor in obesity. Extracellular matrix (ECM) regulates white adipose tissue (WAT), but its mechanism is unknown. This study uses three models-HFD-fed mice, human with obesity, and 3T3-L1 adipocytes with oleic acid (OA)/macromolecular crowders (MMC) treatment. Glucose and lipids metabolic disorders, increased collagen I/IV and laminin α2/4 (LAMA2/4), and upregulated integrins (ITGA1/ITGA7) - focal adhesion kinase (FAK) - c-Jun N-terminal kinase (JNK)/extracellular regulated protein kinase 1/2 (ERK1/2) signals in obese WAT from mice and human are observed. The upregulation of ECM - integrin - FAK signals is stronger in subcutaneous WAT than that in visceral WAT of mice, but these results are reversed in human. In vitro, oleic acid (OA) promotes lipid accumulation and upregulates collagen IV, LAMA4, and p-JNK. MMC is used to induce ECM deposition in adipocytes. MMC promotes adipocyte differentiation and integrins - FAK - JNK/ERK1/2 signals. When FAK phosphorylation is inhibited, downstream p-JNK is decreased. Inhibition of FAK phosphorylation reduces adipocyte differentiation, but MMC partially reverses this effect. HFD-induced ECM deposition, whose signals are transmitted into adipocytes through upregulating ITGA1/ITGA7, activates the phosphorylation of intracellular FAK - JNK/ERK1/2 signals, and promotes adipogenesis in WAT. This mechanism provides novel therapeutic targets to treat obesity.