Adipose tissue plays a major role in retinoic acid-mediated metabolic homoeostasis

Identification of Genetic Polymorphisms Associated with Interindividual Variability of Vitamin A Concentration in Adipose Tissue of Healthy Male Adults

BACKGROUND

Adipose tissue vitamin A (VA), that is, mainly retinol (RET) and its esters, comes from preformed VA and proVA carotenoids present in our food. Adipose tissue VA acts as hormonal cue maintaining essential aspects of adipocyte biology, which includes fat mobilization and catabolism, energy balance, and glucose homeostasis, and it is thus of particular interest to study its determinants, including genetic ones.

OBJECTIVES

This study aimed to identify genetic variations associated with adipose tissue VA concentration.

METHODS

Forty-two healthy male adults received, in a randomized crossover design, 3 test meals. Periumbilical adipose tissue samples were collected on 6 occasions, that is, at fast and 8 h after consumption of each meal. RET concentration was measured in both plasma and the adipose tissue following saponification. Participants were genotyped using whole-genome microarrays. A total of 1305 single nucleotide polymorphism (SNPs) in or near 27 candidate genes were included for univariate analysis. Partial least squares (PLS) regression was carried out to find the best combination of SNPs associated with the interindividual variability in adipose tissue RET concentration.

RESULTS

Adipose tissue RET concentration was not associated with plasma RET concentrations (r = -0.184, P = 0.28). Interindividual variability of adipose tissue RET concentration was high (coefficient of variation = 62%). Twenty-nine SNPs were significantly (P < 0.05) associated with adipose tissue RET concentration and a PLS regression model identified 16 SNPs as explanatory variables of this concentration. The SNPs were in or near peroxisome proliferator activated receptor gamma, retinoid X receptor alpha, signaling receptor and transporter of retinol, cluster of differentiation 36, free fatty acid receptor 4, aldehyde dehydrogenase 1 family member A1, monoglyceride lipase, diacylglycerol O-acyltransferase 2, and polycystic kidney disease 1-like 2.

CONCLUSIONS

A combination of 16 SNPs has been associated with the interindividual of adipose tissue VA concentration in humans. This trial was registered at clinicaltrials.gov as NCT02100774.

ACSL1 positively regulates adipogenic differentiation

Aberrant adipogenic differentiation is strongly associated with obesity and related metabolic diseases. Elucidating the key factors driving adipogenesis is an effective strategy for identifying novel therapeutic targets for treating metabolic diseases represented by obesity. In this study, transcriptomic techniques were employed to investigate the functional genes that regulate adipogenic differentiation in OP9 cells and 3T3-L1 cells. The findings indicated a notable upregulation of Acsl1 expression throughout the adipogenic differentiation process. Knocking down Acsl1 led to a decrease in the expression of genes associated with adipogenesis and a reduction in triglyceride accumulation. Additionally, Acsl1 overexpression promoted adipocyte differentiation and adipose-specific overexpression of Acsl1 markedly aggravated steatosis induced by a high-fat diet. Mechanistically, Cyp2f2, Dusp23 and Gstm2 are the crucial genes implicated in Acsl1-induced adipogenic differentiation. The findings of this study indicate that Acsl1 promotes adipogenesis and could serve as a potential therapeutic target for treating obesity and related metabolic disorders.

Associations of dietary sources of antioxidant intake and NAFLD: NHANES 2017-2020 and Mendelian randomization

Purpose

To determine the association between dietary antioxidant sources and non-alcoholic fatty liver disease (NAFLD).

Methods

In this observational study, we utilized NHANES 2017-2020 data to identify the factors associated with NAFLD in dietary antioxidant sources via weighted multivariate logistic regression models. Then, Mendelian randomization (MR) was applied to investigate the effect of dietary antioxidant sources on NAFLD at the genetic level.

Results

Of the six dietary sources of antioxidants, only vitamin E (Vit E) was significantly associated with NAFLD (OR = 0.98; 95% CI: 0.97-0.99; p = 0.001). Upon adjusting for all covariates, it was determined that the highest quartile of dietary Vit E intake was associated with a decreased NAFLD occurrence compared with the lowest quartile of dietary Vit E intake (p < 0.001). The results of IVW-MR analysis revealed an association between Vit E and NAFLD (OR = 0.028; p = 0.039).

Conclusion

Our research indicates a negative and linear relationship between daily vitamin E intake and NAFLD.

The Interplay between Liver and Adipose Tissue in the Onset of Liver Diseases: Exploring the Role of Vitamin Deficiency

The deficiency of vitamins, a condition known as "hidden hunger", causes comprehensive pathological states. Research over the years has identified a relationship between liver diseases and hypovitaminosis or defects in vitamin metabolism. The exact mechanisms remain elusive; however, the crucial involvement of specific vitamins in metabolic functions, alongside the reclassification of liver disease as metabolic dysfunction-associated steatotic liver disease (MASLD), has prompted researchers to investigate the potential cause-effect dynamics between vitamin deficiency and liver disease. Moreover, scientists are increasingly investigating how the deficiency of vitamins might disrupt specific organ crosstalk, potentially contributing to liver disease. Although the concept of a dysmetabolic circuit linking adipose tissue and the liver, leading to liver disease, has been discussed, the possible involvement of vitamin deficiency in this axis is a relatively recent area of study, with numerous critical aspects yet to be fully understood. In this review, we examine research from 2019 to July 2024 focusing on the possible link between liver-adipose tissue crosstalk and vitamin deficiency involved in the onset and progression of non-alcoholic fatty liver disease (NAFLD). Studies report that vitamin deficiency can affect the liver-adipose tissue axis, mainly affecting the regulation of systemic energy balance and inflammation.

Gehua Jiejiu Dizhi decoction ameliorates alcoholic fatty liver in mice by regulating lipid and bile acid metabolism and with exertion of antioxidant stress based on 4DLabel-free quantitative proteomic study

OBJECTIVE

To analyze the effect and molecular mechanism of Gehua Jiejiu Dizhi decoction (, GJDD) on alcoholic fatty live disease (AFLD) by using proteomic methods.

METHODS

The male C57BL/6J mouse were randomly divided into four groups: control group, model group, GJDD group and resveratrol group. After the AFLD model was successfully prepared by intragastric administration of alcohol once on the basis of the Lieber-DeCarli classical method, the GJDD group and resveratrol group were intragastrically administered with GJDD (4900 mg/kg) and resveratrol (400 mg/kg) respectively, once a day for 9 d. The fat deposition of liver tissue was observed and evaluated by oil red O (ORO) staining. 4DLabel-free quantitative proteome method was used to determine and quantify the protein expression in liver tissue of each experimental group. The differentially expressed proteins were screened according to protein expression differential multiples, and then analyzed by Gene ontology classification and Kyoto Encyclopedia of Genes and Genomes pathway enrichment. Finally, expression validation of the differentially co-expressed proteins from control group, model group and GJDD group were verified by targeted proteomics quantification techniques.

RESULTS

In semiquantitative analyses of ORO, all kinds of steatosis (ToS, MaS, and MiS) were evaluated higher in AFLD mice compared to those in GJDD or resveratrol-treated mice. 4DLabel-free proteomics analysis results showed that a total of 4513 proteins were identified, of which 3763 proteins were quantified and 946 differentially expressed proteins were screened. Compared with the control group, 145 proteins were up-regulated and 148 proteins were down-regulated in the liver tissue of model group. In addition, compared with the model group, 92 proteins were up-regulated and 135 proteins were down-regulated in the liver tissue of the GJDD group. 15 differentially co-expressed proteins were found between every two groups (model group vs control group, GJDD group vs model group and GJDD group vs control group), which were involved in many biological processes. Among them, 11 differentially co-expressed key proteins (Aox3, H1-5, Fabp5, Ces3a, Nudt7, Serpinb1a, Fkbp11, Rpl22l1, Keg1, Acss2 and Slco1a1) were further identified by targeted proteomic quantitative technology and their expression patterns were consistent with the results of 4D label-free proteomic analysis.

CONCLUSIONS

Our study provided proteomics-based evidence that GJDD alleviated AFLD by modulating liver protein expression, likely through the modulation of lipid metabolism, bile acid metabolism and with exertion of antioxidant stress.

Reactive nitrogen species-mediated cell proliferation during tail regeneration and retinoic acid as a putative modulator of tissue regeneration in the geckos

Reactive nitrogen species (RNS), a mediator of nitrosative stress, plays a vital role during wound healing but its role during tissue regeneration is poorly understood. In the present study, the role of RNS was investigated post-tail autotomy and limb amputation in a gecko species, Hemidactylus murrayi Gleadow, 1887. Tail autotomy led to an increased expression of iNOS and nitrosative stress leading to protein S-nitrosylation that probably restricted the acute inflammatory response caused by wounding. Increased nitrosative stress was also associated with proliferation of the wound epithelium and the tail blastema. Nitric oxide synthase inhibitor (L-NAME) caused retarded growth and structural abnormalities in the regenerating tail while peroxynitrite inhibitor (FeTmPyp) arrested tail regeneration. Spermine NONOate and retinoic acid, used as NO donors generated small outgrowths post-amputation of limbs with an increased number of proliferating cells and s-nitrosylation indicating the role of nitric oxide signalling in cell proliferation during regeneration. Additionally, retinoic acid treatment caused regeneration of nerve, muscle and adipose tissue in the regenerated limb structure 105 days post-amputation suggesting it to be a putative modulator of tissue regeneration in the non-regenerating limbs.

Transcriptomic (DNA Microarray) and Metabolome (LC-TOF-MS) Analyses of the Liver in High-Fat Diet Mice after Intranasal Administration of GALP (Galanin-like Peptide)

The aim of this research was to test the efficacy and potential clinical application of intranasal administration of galanin-like peptide (GALP) as an anti-obesity treatment under the hypothesis that GALP prevents obesity in mice fed a high-fat diet (HFD). Focusing on the mechanism of regulation of lipid metabolism in peripheral tissues via the autonomic nervous system, we confirmed that, compared with a control (saline), intranasally administered GALP prevented further body weight gain in diet-induced obesity (DIO) mice with continued access to an HFD. Using an omics-based approach, we identified several genes and metabolites in the liver tissue of DIO mice that were altered by the administration of intranasal GALP. We used whole-genome DNA microarray and metabolomics analyses to determine the anti-obesity effects of intranasal GALP in DIO mice fed an HFD. Transcriptomic profiling revealed the upregulation of flavin-containing dimethylaniline monooxygenase 3 (Fmo3), metallothionein 1 and 2 (Mt1 and Mt2, respectively), and the Aldh1a3, Defa3, and Defa20 genes. Analysis using the DAVID tool showed that intranasal GALP enhanced gene expression related to fatty acid elongation and unsaturated fatty acid synthesis and downregulated gene expression related to lipid and cholesterol synthesis, fat absorption, bile uptake, and excretion. Metabolite analysis revealed increased levels of coenzyme Q10 and oleoylethanolamide in the liver tissue, increased levels of deoxycholic acid (DCA) and taurocholic acid (TCA) in the bile acids, increased levels of taurochenodeoxycholic acid (TCDCA), and decreased levels of ursodeoxycholic acid (UDCA). In conclusion, intranasal GALP administration alleviated weight gain in obese mice fed an HFD via mechanisms involving antioxidant, anti-inflammatory, and fatty acid metabolism effects and genetic alterations. The gene expression data are publicly available at NCBI GSE243376.

Identification of novel SCD1 inhibitor alleviates nonalcoholic fatty liver disease: critical role of liver-adipose axis

Due to the complexity and incomplete understanding of the crosstalk between liver and adipose tissue, especially the processes of hepatic lipogenesis and adipogenic differentiation, there are currently no effective drugs for the treatment of nonalcoholic fatty liver disease (NAFLD). Stearoyl-coenzyme A desaturase 1 (SCD1), which is abundantly expressed in liver and adipose tissue, may mediate the cross-talk between liver and adipose tissue. Thus, it is essential to develop specific SCD1 inhibitors that target the liver-adipose axis. Herein, we identified a novel SCD1 inhibitor, E6446, through a high-throughput virtual screen. E6646 significantly inhibited adipogenic differentiation and hepatic lipogenesis via SCD1-ATF3 signaling. The SPR results showed that E6446 had a strong interaction ability with SCD1 (KD:4.61 μM). Additionally, E6646 significantly decreased hepatic steatosis, hepatic lipid droplet accumulation and insulin resistance in high-fat diet (HFD)-fed mice. Taken together, our findings not only suggest that E6446 can serve as a new, safe and highly effective anti-NAFLD agent for future clinical use but also provide a molecular basis for the future development of SCD1 inhibitors that inhibit both adipogenic differentiation and hepatic lipogenesis. Video Abstract.

Retinoic Acid Signaling in Fatty Liver Disease

Retinoic acid (RA) is a metabolite of vitamin A and is essential for development and growth as well as cellular metabolism. Through genomic and nongenomic actions, RA regulates a variety of physiological functions. Dysregulation of RA signaling is associated with many diseases. Targeting RA signaling has been proven valuable to human health. All-trans retinoic acid (AtRA) and anthracycline-based chemotherapy are the standard treatment of acute promyelocytic leukemia (APL). Both human and animal studies have shown a significant relationship between RA signaling and the development and progression of nonalcoholic fatty liver disease (NAFLD). In this review article, we will first summarize vitamin A metabolism and then focus on the role of RA signaling in NAFLD. AtRA inhibits the development and progression of NAFLD via regulating lipid metabolism, inflammation, thermogenesis, etc.

Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis : Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease with an increasing global prevalence associated with tremendous clinical, economic, and health-related quality-of-life burden. Currently, no effective pharmacological therapy is available for NAFLD. Adipogenesis process is accompanied by fat synthesis which may participate in the occurrence and development of NAFLD. Despite intensive investigations, numerous mechanistic aspects of adipogenesis remain unclear and many potential therapeutic targets are yet to be discovered.In this study, the transcriptomics and lipidomics approaches were used to explore the functional genes regulating adipogenesis and the potential mechanism in OP9 cells and adipose-derived stem cells.We find that NADH:ubiquinone oxidoreductase subunit b9 (Ndufb9) is up-regulated in adipogenesis (p < 0.001), and silencing Ndufb9 (83% silencing efficiency) inhibits adipogenesis. The effect of Ndufb9 is mediated through stearoyl-CoA desaturase 1 (Scd1). Aramchol, a SCD1 inhibitor, significantly blocks adipogenesis (markedly TG decrease, p < 0.001).Our study broadens the understanding of the role of Ndufb9 in adipogenesis and provides a new target for the treatment of NAFLD.

Slc25a5 regulates adipogenesis by modulating ERK signaling in OP9 cells

Background

A comprehensive understanding of the molecular mechanisms of adipogenesis is a critically important strategy for identifying new targets for obesity intervention.

Methods

Transcriptomic and lipidomic approaches were used to explore the functional genes regulating adipogenic differentiation and their potential mechanism of action in OP9 cells and adipose-derived stem cells. Oil Red O staining was used to detect oil droplets in adipocytes.

Results

RNA sequencing (RNA-seq) showed that Slc25a5 expression was significantly upregulated in adipogenic differentiation. Depletion of Slc25a5 led to the suppressed expression of adipogenesis-related genes, reduced the accumulation of triglycerides, and inhibited PPARγ protein expression. Moreover, the knockdown of Slc25a5 resulted in significant reduction of oxidative phosphorylation (OXPHOS) protein expression (ATP5A1, CQCRC2, and MTCO1) and ATP production. The RNA-seq and real-time quantitative polymerase chain reaction (RT–qPCR) results suggested that adipogenic differentiation is possibly mediated by ERK1/2 phosphorylation, and this hypothesis was confirmed by intervention with PD98059 (an ERK 1/2 inhibitor).

Conclusions

This study indicates that Slc25a5 inhibits adipogenesis and might be a new therapeutic target for the treatment of obesity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00314-y.