Adipocyte differentiation is regulated by mitochondrial trifunctional protein α-subunit via sirtuin 1

Serum vitamin D status and metabolic syndrome: a systematic review and dose-response meta-analysis

BACKGROUD/OBJECTIVES

Evidence has suggested an association between serum vitamin D and metabolic syndrome (MetS), but prospective studies are very limited. The objective was to assess the dose-response association between serum vitamin D concentration and MetS risk using a systematic review and meta-analysis of updated observational studies.

MATERIALS/METHODS

Using MEDLINE, PubMed, and Embase, a systematic literature search was conducted through February 2020 and the references of relevant articles were reviewed. A random-effects model was used to estimate the summary odds ratio/relative risk and 95% confidence interval (CI). Heterogeneity among studies was evaluated with I² statistic. In total, 23 observational studies (19 cross-sectional studies, and four cohort studies) were included in the meta-analysis.

RESULTS

The pooled estimates (95% CI) for MetS per 25-nmol/L increment in serum vitamin D concentration were 0.80 (95% CI, 0.76–0.84; I² = 53.5) in cross-sectional studies, and 0.85 (95% CI, 0.72–0.98; I² = 85.8) in cohort studies. Similar results were observed, irrespectively of age of study population, study location, MetS criteria, and adjustment factors. There was no publication bias for the dose-response meta-analysis of serum vitamin D concentrations and MetS.

CONCLUSIONS

Dose-response meta-analysis demonstrated that a 25-nmol/L increment in the serum vitamin D concentration was associated with 20% and 15% lower risks of MetS in cross-sectional studies and cohort studies, respectively.

SIRT1 deacetylates mitochondrial trifunctional enzyme α subunit to inhibit ubiquitylation and decrease insulin resistance

Dysregulation of free acid metabolism is a major contributor to the development of insulin resistance and diabetes. Mitochondrial trifunctional enzyme subunit (MTPα) has a critical role in fatty acid β-oxidation. However, the association between MTPα and insulin resistance is not definitively known. Here, we aimed to determine how MTPα affects insulin resistance. We tested how MTPα affected glucose uptake in insulin-resistant 3T3-L1 adipocytes and white adipose tissue (WAT) of db/db diabetic mice. We also measured how acetylation and ubiquitylation modifications regulated MTPα activation and stability, using quantitative real-time polymerase chain reactions, immunoblotting, and immunoprecipitation. We found that MTPα overexpression promoted glucose uptake via Glut4 translocation to the plasma membrane in 3T3-L1 adipocytes. Moreover, MTPα upregulation decreased glycemia in db/db mice. Deacetylation increased MTPα protein stability and its ability to reduce insulin resistance. The activation of SIRT1, a major deacetylase, prevented MTPα degradation by decreasing its acetylation in adipocytes. Our study demonstrates a new role for MTPα in reducing insulin resistance. Acetylation and ubiquitylation modifications of MTPα were crucial to regulating its function in glucose metabolism.

Effect of vitamin D supplementation in combination with weight loss diet on lipid profile and sirtuin 1 in obese subjects with vitamin D deficiency: a double blind randomized clinical trial

Background: Due to inconsistent evidence regarding the potential role of vitamin D on lipid profile and sirtuin 1 (SIRT-1), this study was designed to investigate the effect of vitamin D supplementation in combination with weight loss diet on lipid profile and SIRT-1 in obese subjects with vitamin D deficiency.

Methods: Forty-four obese subjects with vitamin D deficiency were randomly assigned in a randomized clinical trial to receive either a weight reduction diet supplemented with 50000IU vitamin D3 pearl (n = 22) or placebo (n = 22) once weekly for 12 weeks. Changes in total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG) and low high density lipoprotein cholesterol (HDL-C) and SIRT-1 were the primary outcomes. Secondary outcomes were changes in body mass index (BMI), 25(OH) D and parathyroid hormone (PTH). Physical activity and dietary intakes were also assessed.

Results: During the intervention, PTH (mean difference, -33.36; 95% CI: -49.15 to -17.57;P<0.001) and LDL-C (mean difference, -15.91; 95% CI: -21.76 to -10.07; P<0.001) decreased and 25(OH) D (mean difference, 36.44; 95% CI: 29.05 to 43.83; P<0.001) increased significantly in the vitamin D group. BMI (mean differences: -2.40; 95% CI: [-2.92 to-1.88] in vitamin D group and mean differences: -1.90; 95% CI [-6.58 to -3.01] in placebo group, P<0.05 for both groups), TC (mean difference,-21.31; 95% CI: -27.24 to -15.38; P<0.001 in vitamin D group and mean difference, -12.54; 95% CI: -19.02 to -6.06; P<0.001 in placebo group) and TG (mean difference,-21.31; 95% CI: -27.24 to -15.38; P<0.001in vitamin D group and mean difference, -12.54; 95% CI: -19.02 to -6.06; P<0.001 in placebo group) decreased and SIRT-1(mean difference, 3.95; 95% CI: 1.18 to 6.73; P=0.007in vitamin D group and mean difference,1.91; 95% CI: 0.31 to 3.63 in placebo group, P=0.022) increase significantly in both group. At end of the study, 25(OH) D and PTH showed significant differences in between-group analyses(P<0.05). No significant difference was detected for HDL-C in within and between groups.

Conclusion: This study gives no support for any beneficial effect of vitamin D supplementation on lipid profile and SIRT-1 in obese subjects with vitamin D deficiency.