No abstract

The improvement of both proinflammatory status and glucose uptake in adipocytes under 1,25-(OH)(2) D(3) effect suggests that low-grade inflammation could be linked to vitamin D deficiency. This observation offers new perspectives in the context of obesity and associated physiopathological disorders.

Metabolic syndrome (MetS) is defined as a constellation of many metabolic disorders such as hypertension, impaired glucose tolerance, dyslipidemia and obesity, being this last disorder a key factor in the etiology of the syndrome. The widespread of MetS in actual society, mainly in developed countries, is becoming an important health problem and is increasing the need to develop new treatments against this pathology is increasing fast. The main objective of the present study was to evaluate the MetS-associated alterations developed in a new glucose diet-induced-obesity (DIO) rodent model. These alterations were also compared to those alterations developed in a fructose-DIO rodent model. Wistar rats were divided into four groups: Control (C), High-fat (HF), High-fat/high-fructose (HFF) and High-fat/high-glucose (HFG). The animals were fed ad libitum for 20 weeks. At the end of the study, HFG animals showed lower expression of energy expenditure genes when compared to the other DIO groups. Oxidative stress biomarkers such as MDA and mitochondrial RT-qPCR analyses showed an increase of oxidative damage together with mitochondrial dysfunction in HFG group. This group also showed increased insulin and glucose plasma levels, though HFF animals showed the greatest increase on these parameters. All DIO groups showed increased plasma levels of triglycerides. Altogether, our results indicated a better impact of glucose than fructose, when combined with a high-fat diet, to induce most of the alterations associated with MetS in rats. In addition, our research facilitates a new animal model to evaluate future treatments for MetS.

No abstract

Altogether, these data are evidence of a proinflammatory loop mediated by NF-κB and miR-155 that could participate in the amplification of inflammatory status in adipocytes.

Immune cell infiltration of expanding adipose tissue during obesity and its role in insulin resistance has been described and involves chemokines. However, studies so far have focused on a single chemokine or its receptor (especially CCL2 and CCL5) whereas redundant functions of chemokines have been described. The objective of this work was to explore the expression of chemokines in inflamed adipose tissue in obesity. Human and mouse adipocytes were analyzed for expression of chemokines in response to inflammatory signal (TNF-α) using microarrays and gene set enrichment analysis. Gene expression was verified by qRT-PCR. Chemokine protein was determined in culture medium with ELISA. Chemokine expression was investigated in human subcutaneous adipose tissue biopsies and mechanism of chemokine expression was investigated using chemical inhibitors and cellular and animal transgenic models. Chemokine encoding genes were the most responsive genes in TNF-α treated human and mouse adipocytes. mRNA and protein of 34 chemokine genes were induced in a dose-dependent manner in the culture system. Furthermore, expression of those chemokines was elevated in human obese adipose tissue. Finally, chemokine expression was reduced by NF-κB inactivation and elevated by NF-κB activation. Our data indicate that besides CCL2 and CCL5, numerous other chemokines such as CCL19 are expressed by adipocytes under obesity-associated chronic inflammation. Their expression is regulated predominantly by NF-κB. Those chemokines could be involved in the initiation of infiltration of leukocytes into obese adipose tissue.

Inflammation of adipose tissue is believed to be a contributing factor to many chronic diseases associated with obesity. Vitamin D (VD) is now known to limit this metabolic inflammation by decreasing inflammatory marker expression and leukocyte infiltration in adipose tissue. In this study, we investigated the impact of VD on microRNA (miR) expression in inflammatory conditions in human and mouse adipocytes, using high-throughput methodology (miRNA PCR arrays). Firstly, we identified three miRs (miR-146a, miR-150, and miR-155) positively regulated by TNFα in human adipocytes. Interestingly, the expression of these miRs was strongly prevented by 1,25(OH)D preincubation. These results were partly confirmed in 3T3-L1 adipocytes (for miR-146a and miR-150). The ability of VD to control the expression of these miRs was confirmed in diet-induced obese mice: the levels of the three miRs were increased following high fat (HF) diet in epididymal white adipose tissue and reduced in HF diet fed mice supplemented with VD. The involvement of NF-κB signaling in the induction of these miRs was confirmed in vitro and in vivo using aP2-p65 transgenic mice. Finally, the ability of VD to deactivate NF-κB signaling, via p65 and IκB phosphorylation inhibition in murine adipocyte, was observed and could constitute a driving molecular mechanism. This study demonstrated for the first time that VD modulates the expression of miRs in adipocytes in vitro and in adipose tissue in vivo through its impact on NF-κB signaling pathway, which could represent a new mechanism of regulation of inflammation by VD.

Vitamin D (VD) displays immunoregulatory effects and reduces adipocyte inflammation, which may participate to a reduction of adipose tissue macrophage infiltration in the context of obesity-associated low-grade inflammation. These observations have been described mainly in vitro, through the evaluation of a limited number of inflammatory markers. Here, we studied the effects of 1,25 dihydroxy-VD on chemokine network expression in adipocytes (by transcriptomic approach), and we confirm the physiological relevance of these data in vivo, by demonstrating the effect of VD on cytokine and chemokine gene expression as well as on macrophage infiltration in adipose tissue. 1,25 dihydroxy-VD down-regulated (-1.3- to -10.8-fold) the mRNA expression of 29 chemokines and limited macrophage migration in TNFα-conditioned adipocyte medium (1.5-fold; P < .05). This effect was associated with a reduction in p65 and IκB (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha) phosphorylation (2-fold compared with TNFα; P < .05). The effects of VD were confirmed in mice injected ip with lipopolysaccharide (acute inflammation) and diet-induced obese mice (metabolic inflammation), where the levels of mRNA encoding proinflammatory cytokines and chemokines (∼2-fold) were reduced in adipocytes (acute and metabolic inflammation) and adipose tissue and that macrophage infiltration was also inhibited in the adipose tissue of obese mice (metabolic inflammation). Altogether, these results showed that VD displayed a global immunoregulatory impact on adipocytes, notably via the inhibition of chemokine expression and macrophage infiltration in inflamed adipose tissue.