Effects of 1,25(OH)2 D3 on lipid droplet growth in adipocytes

Vitamin D3 supplementation shapes the composition of gut microbiota and improves some obesity parameters induced by high-fat diet in mice

PURPOSE

Individuals with vitamin D (VD) insufficiency have a greater tendency to develop obesity and have increased systemic inflammation. Gut microbiota are involved in the regulation of host inflammation and energy metabolism, which plays a role in the pathogenesis of obesity. Thus, we aimed to evaluate the effects of different doses of VD3 on body weight, serum lipids, inflammatory factors, and intestinal barrier function in obese mice and to explore the regulatory effect of VD3 on gut microbiota in obese mice.

METHODS

Male C57BL/6 J mice received a normal chow diet (NCD, 10% fat) or high-fat diet (HFD, 60% fat) to induce obesity within 10 weeks. Then, HFD mice were supplemented with 5650, 8475, or 11,300 IU VD3/kg diet for 8 weeks. Finally, 16 s rRNA analysis was performed to analyze gut microbiota composition in cecal contents. In addition, body weight, serum lipids, inflammatory factors, and intestinal barrier function were analyzed.

RESULTS

VD3 supplementation reduced body weight and the levels of TG, TC, HDL-C, TNF-α, IL-1β and LPS, and increased ZO-1 in HFD-fed mice. Moreover, it increased α-diversity, reduced F/B ratio and altered microbiota composition by increasing relative abundance of Bacteroidetes, Proteobacteria, Desulfovibrio, Dehalobacterium, Odoribacter, and Parabacteroides and reducing relative abundance of Firmicutes and Ruminococcus. There were significant differences between HFD and NCD groups in several metabolic pathways, including endotoxin biosynthesis, tricarboxylic acid cycle, lipid synthesis and metabolism, and glycolysis.

CONCLUSIONS

Low, medium, and high doses of VD3 inhibited weight gain, reduced levels of blood lipids and inflammatory factors, and improved endotoxemia and gut barrier function in obese mice. It also increased the α-diversity of gut microbiota in obese mice and reduced the relative abundance of some intestinal pathogenic bacteria, increased the relative abundance of some beneficial bacteria, and corrected the intestinal flora disorder of obese mice, with the low- and high-dose groups showing better effects than the medium-dose group.

SUMO-specific protease 2 regulates lipid droplet size through ERRα-mediated CIDEA expression in adipocytes

Lipid droplets are not only lipid storage sites but also are closely related to lipid metabolism. Lipid droplet growth increases lipid storage capacity and suppresses lipolysis via lipase associated with the lipid droplet surface. The cell death-inducing DFF45-like effector (CIDE) family of proteins mediates lipid droplet fusion, which mainly contributes to lipid droplet growth. We previously demonstrated small ubiquitin-like modifier (SUMO)-specific protease 2 (SENP2) plays important roles in lipid metabolism and induction/maintenance of adipogenesis. In this study, we determined whether SENP2 regulates lipid droplet size in adipocytes. Overexpression of SENP2 increased lipid droplet size in differentiated 3T3-L1 adipocytes and facilitated CIDEA transcription. We found SENP2 increased CIDEA expression mainly through desumoylation of estrogen-related receptor α (ERRα), which acted in coordination with peroxisome proliferator-activated receptor γ-coactivator α. In addition, palmitate treatment increased SENP2 and CIDEA mRNA levels. Specific small interfering RNA-mediated knockdown of SENP2, as well as ERRα knockdown, eliminated palmitate-induced CIDEA expression. These results suggest SENP2 enhances CIDEA expression by modulating ERRα when SENP2 is upregulated, such as after palmitate treatment, to increase lipid droplet size in adipocytes.

Effect of vitamin D3 on lipid droplet growth in adipocytes of mice with HFD-induced obesity

Vitamin D-regulating action of PPARγ on obesity has been confirmed on adipocyte differentiation. However, it is not clear whether vitamin D affects the morphological size of mature adipocytes by influencing the expression of PPARγ in vivo. Our hypothesis was that Vitamin D3 (VitD3) inhibits the growth of adipocyte size by suppressing PPARγ expression in white adipocytes of obese mice. Five-week-old male C57BL/6J mice were randomly divided into normal diet and high-fat diet groups. After 10 weeks, the body weight between the two groups differed by 26.91%. The obese mice were randomly divided into a high-fat diet, solvent control, low-dose VitD3 (5000 IU/kg·food), medium-dose VitD3 (7500 IU/kg·food), high-dose VitD3 (10,000 IU/kg·food), and PPAR γ antagonist group, and the intervention lasted for 8 weeks. Diet-induced obesity (DIO) mice fed high-dose VitD3 exacerbated markers of adiposity (body weight, fat mass, fat mass rate, size of white and brown adipocytes, mRNA, and protein levels of ATGL and Fsp27), and the protein level of ATGL and Fsp27 decreased in the low-dose group. In conclusion, high-dose VitD3 possibly via inhibiting the ATGL expression, thereby inhibiting lipolysis, increasing the volume of adipocytes, and decreasing their fat-storing ability resulted in decreased Fsp27 expression. Therefore, long-term high-dose oral VitD3 may not necessarily improve obesity, and we need more clinical trials to explore the intervention dose and duration of VitD3 in the treatment of VitD3 deficiency in obese patients.

UCP1 activation: Hottest target in the thermogenesis pathway to treat obesity using molecules of synthetic and natural origin

Uncoupling protein 1 (UCP1) has been discovered as a possible target for obesity treatment because of its widespread distribution in the inner mitochondrial membrane of brown adipose tissue (BAT) and high energy expenditure capabilities to burn calories as heat. UCP1 is dormant and does not produce heat without activation as it is inhibited by purine nucleotides. However, activation of UCP1 via either direct interaction with the UCP1 protein, an increase in the expression of UCP1 genes or the physiological production of fatty acids can lead to a rise in the thermogenesis phenomenon. Hence, activation of UCP1 through small molecules of synthetic and natural origin can be considered as a promising strategy to mitigate obesity.

Vitamin D improves hepatic steatosis in NAFLD via regulation of fatty acid uptake and β-oxidation

INTRODUCTION

The study aimed to explore the association of serum 25(OH)D₃ and hepatic steatosis in non-alcoholic fatty liver disease (NAFLD) patients and to determine whether the effect of vitamin D (VD) is mediated by activation of the peroxisome proliferator-activated receptor α (PPARα) pathway.

METHODS

The study contained a case-control study, in vivo and in vitro experiments. A case-control study was conducted to compare serum parameters between NAFLD patients and controls and to evaluate the association of 25(OH)D₃ and NAFLD. In vivo study, male Wistar rats were randomly divided into control and model groups, fed a standard chow diet and a high-fat diet (HFD), respectively, for 7 weeks to generate an NAFLD model. Then, the rats were treated with VD and a PPARα antagonist (MK886) for 7 weeks. Tissue and serum were collected and assessed by biochemical assays, morphological analysis, histological analysis, and western blot analysis. In vitro, HepG2 cells were incubated with oleic acid (OA) to induce steatosis, which was evaluated by staining. HepG2 cells were pretreated with MK886 followed by calcitriol treatment, and differences in lipid metabolism-related proteins were detected by western blot.

RESULTS

NAFLD patients were characterized by impaired liver function, dyslipidemia, and insulin resistance. Serum 25(OH)D₃ was negatively associated with alanine aminotransferase (ALT) in NAFLD. VD deficiency was a risk factor for patients with no advanced fibrosis. Adequate VD status (25(OH)D₃ >20 ng/mL) had a protective effect in patients after adjustment for confounding variables. NAFLD rats showed hyperlipidemia with severe hepatic steatosis, systematic inflammation, and lower serum 25(OH)D₃. VD treatment ameliorated hepatic steatosis both in NAFLD rats and OA-induced HepG2 cells. Further, MK886 inhibited the anti-steatosis effect of VD.

CONCLUSION

The study revealed that an adequate VD level may act as a protective factor in NAFLD and that VD may alleviate hepatic steatosis via the PPARα signaling pathway.

Amelioration of lipid accumulations and metabolism disorders in differentiation and development of 3T3-L1 adipocytes through mulberry leaf water extract

BACKGROUND

Obesity is a worldwide problem that resulted from the excessive fat accumulation in adipose tissue, leading to the impairment of individual health. Mulberry leaf is an important traditional Chinese medicine and has been used to alleviate obesity for a long term. However, its underlying molecular mechanisms have not been fully elucidated yet.

PURPOSE

In this study, we aimed to investigate the inhibition effects of mulberry leaf water extract (MLWE) on lipid accumulation during the process of differentiation of 3T3-L1 preadipocytes and development of mature adipocytes through the combination of molecular biology assays and metabolomic analysis.

METHODS

The quality consistency and main chemical ingredients of MLWE were analyzed by high performance liquid chromatography and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), respectively. Oil red O staining was used to mirror lipid accumulation. Lipogenesis-, lipolysis- and inflammation-related genes were evaluated by real-time PCR and western blot, respectively. Untargeted metabolomics were performed by LC-MS/MS.

RESULTS

Prepared method and quality of MLWE were stable and reliable. A total of 34 compounds were identified and 14 of them were undoubtedly confirmed. MLWE supplementation could dose-dependently inhibit the aggregation of lipid droplets, and the expressions of sterol regulatory element-binding protein (SREBP)-1c, peroxisome proliferator-activated receptor (PPAR) γ, acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), tumor necrosis factor (TNF)-α and interleukin (IL)-6, and increase the expressions of adenosine monophosphate-activated protein kinase (AMPK), hormone-sensitive lipase (HSL) and IL-10 in the differentiation of preadipocytes. Furthermore, MLWE treatment could dose-dependently decrease the level of triglycerides and the expressions of ACC, FAS, TNF-α, and IL-6, and up-regulate the level of glycerol and the expressions of PPARα, adiponectin (ADPN), adiponectin receptor (AdipoR) 1, AdipoR2, AMPK, HSL, and IL-10 in the development of mature adipocytes. Untargeted metabolomics showed that a total of 5 and 18 differential metabolites were reversed by MLWE intervention in the differentiation of preadipocytes and the development of mature adipocytes, respectively, which involved in the biosynthesis of unsaturated fatty acids, arachidonic acid metabolism and glycerophospholipids metabolism.

CONCLUSION

Taken together, this study firstly verified that MLWE could effectively alleviate lipid accumulation and inflammation by regulating ADPN/AMPK-mediated signaling pathways and relevant metabolic disturbances including biosynthesis of unsaturated fatty acids, arachidonic acid metabolism and glycerophospholipids metabolism.

The Action of Vitamin D in Adipose Tissue: Is There the Link between Vitamin D Deficiency and Adipose Tissue-Related Metabolic Disorders?

Adipose tissue plays an important role in systemic metabolism via the secretion of adipocytokines and storing and releasing energy. In obesity, adipose tissue becomes dysfunctional and characterized by hypertrophied adipocytes, increased inflammation, hypoxia, and decreased angiogenesis. Although adipose tissue is one of the major stores of vitamin D, its deficiency is detective in obese subjects. In the presented review, we show how vitamin D regulates numerous processes in adipose tissue and how their dysregulation leads to metabolic disorders. The molecular response to vitamin D in adipose tissue affects not only energy metabolism and adipokine and anti-inflammatory cytokine production via the regulation of gene expression but also genes participating in antioxidant defense, adipocytes differentiation, and apoptosis. Thus, its deficiency disturbs adipocytokines secretion, metabolism, lipid storage, adipogenesis, thermogenesis, the regulation of inflammation, and oxidative stress balance. Restoring the proper functionality of adipose tissue in overweight or obese subjects is of particular importance in order to reduce the risk of developing obesity-related complications, such as cardiovascular diseases and diabetes. Taking into account the results of experimental studies, it seemed that vitamin D may be a remedy for adipose tissue dysfunction, but the results of the clinical trials are not consistent, as some of them show improvement and others no effect of this vitamin on metabolic and insulin resistance parameters. Therefore, further studies are required to evaluate the beneficial effects of vitamin D, especially in overweight and obese subjects, due to the presence of a volumetric dilution of this vitamin among them.

An integrative multiomics approach to characterize anti-adipogenic and anti-lipogenic effects of Akkermansia muciniphila in adipocytes

The cellular components of Akkermansia muciniphila are considered potential biotherapeutics for the improvement of obesity, diabetes, and metabolic diseases. However, the molecular-based mechanism of A. muciniphila for treatment of obesity, which can provide important evidence for human research, has rarely been explored. Here, we applied integrative multiomics approaches to investigate the underlying molecular mechanism involved in obesity treatment by A. muciniphila. First, the treatment with a cell lysate of A. muciniphila reduced lipid accumulation in 3T3-L1 cells and downregulated the mRNA expression of proteins involved in adipogenesis and lipogenesis. Our proteomic results revealed that A. muciniphila decreased the expression of proteins involved in fat cell differentiation, fatty acid metabolism, and energy metabolism in adipocytes. Moreover, A. muciniphila significantly reduced the level of metabolites related to glycolysis, the TCA cycle, and ATP in adipocytes. Interestingly, serine protease inhibitor A3 (SERPINA3) homologs were overexpressed in the 3T3-L1 cells treated with A. muciniphila. Small interfering RNA (siRNA) transfection demonstrated that A. muciniphila upregulates SERPINA3G expression and inhibits lipogenesis in adipocytes. Taken together, our multiomics-based approaches enabled to uncover the molecular mechanism of A. muciniphila for treatment of obesity and provide potent anti-lipogenic agents.

Network pharmacology-based research uncovers cold resistance and thermogenesis mechanism of Cinnamomum cassia

BACKGROUND

Cinnamomum cassia (L.) J.Presl (Cinnamon) was known as a kind of hot herb, improved circulation and warmed the body. However, the active components and mechanisms of dispelling cold remain unknown.

METHODS

The effects of several Chinses herbs on thermogenesis were evaluated on body temperature and activation of brown adipose tissue. After confirming the effect, the components of cinnamon were identified using HPLC-Q-TOF/MS and screened with databases. The targets of components were obtained with TCMSP, SymMap, Swiss and STITCH databases. Thermogenesis genes were predicted with DisGeNET and GeneCards databases. The protein-protein interaction network was constructed with Cytoscape 3.7.1 software. GO enrichment analysis was accomplished with STRING databases. KEGG pathway analysis was established with Omicshare tools. The top 20 targets for four compounds were obtained according to the number of edges of PPI network. In addition, the network results were verified with experimental research for the effects of extracts and major compounds.

RESULTS

Cinnamon extract significantly upregulated the body temperature during cold exposure.121 components were identified in HPLC-Q-TOF/MS. Among them, 60 compounds were included in the databases. 116 targets were obtained for the compounds, and 41 genes were related to thermogenesis. The network results revealed that 27 active ingredients and 39 target genes. Through the KEGG analysis, the top 3 pathways were PPAR signaling pathway, AMPK signaling pathway, thermogenesis pathway. The thermogenic protein PPARγ, UCP1 and PGC1-α was included in the critical targets of four major compounds. The three major compounds increased the lipid consumption and activated the brown adipocyte. They also upregulated the expression of UCP1, PGC1-α and pHSL, especially 2-methoxycinnamaldehyde was confirmed the effect for the first time. Furthermore, cinnamaldehyde and cinnamon extract activated the expression of TRPA1 on DRG cells.

CONCLUSION

The mechanisms of cinnamon on cold resistance were investigated with network pharmacology and experiment validation. This work provided research direction to support the traditional applications of thermogenesis.