AICAR Attenuates TNFα-Induced Inappropriate Secretion of Monocyte Chemoattractant Protein-1 and Adiponectin in 3T3-L1 Adipocytes

Salicylate Sodium Suppresses Monocyte Chemoattractant Protein-1 Production by Directly Inhibiting Phosphodiesterase 3B in TNF-α-Stimulated Adipocytes

As a worldwide health issue, obesity is associated with the infiltration of monocytes/macrophages into the adipose tissue causing unresolved inflammation. Monocyte chemoattractant protein-1 (MCP-1) exerts a crucial effect on obesity-related monocytes/macrophages infiltration. Clinically, aspirin and salsalate are beneficial for the treatment of metabolic diseases in which adipose tissue inflammation plays an essential role. Herein, we investigated the effect and precise mechanism of their active metabolite salicylate on TNF-α-elevated MCP-1 in adipocytes. The results indicated that salicylate sodium (SAS) could lower the level of MCP-1 in TNF-α-stimulated adipocytes, which resulted from a previously unrecognized target phosphodiesterase (PDE), 3B (PDE3B), rather than its known targets IKKβ and AMPK. The SAS directly bound to the PDE3B to inactivate it, thus elevating the intracellular cAMP level and activating PKA. Subsequently, the expression of MKP-1 was increased, which led to the decrease in p-EKR and p-p38. Both PDE3B silencing and the pharmacological inhibition of cAMP/PKA compromised the suppressive effect of SAS on MCP-1. In addition to PDE3B, the PDE3A and PDE4B activity was also inhibited by SAS. Our findings identify a previously unrecognized pathway through which SAS is capable of attenuating the inflammation of adipocytes.

Mesenchymal Stem Cell Differentiation into Adipocytes Is Equally Induced by Insulin and Proinsulin In Vitro

Background and Objectives

In advanced β-cell dysfunction, proinsulin is increasingly replacing insulin as major component of the secretion product. It has been speculated that proinsulin has at least the same adipogenic potency than insulin, leading to an increased tendency of lipid tissue formation in patients with late stage β-cell dysfunction.

Methods and Results

Mesenchymal stem cells obtained from liposuction material were grown in differentiation media containing insulin (0.01 μmol), proinsulin (0.01 μmol) or insulin+proinsulin (each 0.005 μmol). Cell culture supernatants were taken from these experiments and an untreated control at weeks 1, 2, and 3, and were stored at −80°C until analysis. Cell differentiation was microscopically supervised and adiponectin concentrations were measured as marker for differentiation into mature lipid cells. This experiment was repeated three times. No growth of lipid cells and no change in adiponectin values was observed in the negative control group (after 7/14/12 days: 3.2±0.5/3.3±0.1/4.4±0.5 ng/ml/12 h). A continuous differentiation into mature adipocytes (also confirmed by Red-Oil-staining) and a corresponding increase in adiponectin values was observed in the experiments with insulin (3.6±1.9/5.1±1.4/13.3±1.5 ng/ml/12 h; p<0.05 week 1 vs. week 3) and proinsulin (3.3±1.2/3.5±0.3/12.2±1.2 ng/ml/12 h; p<0.05). Comparable effects were seen with the insulin/proinsulin combination.

Conclusions

Proinsulin has the same adipogenic potential than insulin in vitro. Proinsulin has only 10~20% of the glucose-lowering effect of insulin. It can be speculated that the adipogenic potential of proinsulin may be a large contributor to the increased body weight problems in patients with type 2 diabetes and advanced β-cell dysfunction.

Astragalus polysaccharides attenuates TNF-α-induced insulin resistance via suppression of miR-721 and activation of PPAR-γ and PI3K/AKT in 3T3-L1 adipocytes

Insulin resistance is associated with obesity and type 2 diabetes. The aim of this study was to explore the mechanism of how Astragalus Polysaccharides (APS) improves insulin resistance in 3T3-L1 adipocytes. A cell culture model of insulin resistance was established in mature 3T3-L1 adipocytes by treating them with TNF-α, high glucose and insulin. Glucose uptake levels were detected in each group. To determine the mechanism by which APS improves insulin resistance in 3T3-L1 adipocytes, qRT-PCR was used to detect the expression of miR-721, and Western blots were used to detect the expression or activity of PPAR-γ, PAKT, PI3K, AKT, and GLUT4. Immunostaining was used to detect the expression of GLUT4. We successfully madea model of insulin resistance in mature 3T3-L1 adipocytes. APS increased glucose uptake levels in insulin-resistant adipocytes in a dose- and time-dependent manner, and also increased insulin sensitivity. APS suppressed miR-721 with its target gene PPAR-γ in a dose-dependent manner. miR-721 or PPAR inhibitor T0070907 inhibited the expressions of PPAR-γ, pAKT, and GLUT4 and also reduced glucose accumulation. APS attenuated these miR-721- and PPAR-γ-induced changes. APS increased insulin sensitivity by attenuating the effects of miR-721. The PI3K inhibitor wortmannin reduced the APS-increased pAKT, glucose uptake, and GLUT4 levels, and also reduced those levels in the presence of insulin with or without APS. Taken together, our findings suggest that APS promotes glucose uptake and increases insulin sensitivity in 3T3-L1 adipocytes and may involve the miR-721-PPAR-γ-PI3K/AKT-GLUT4 signaling pathway. These might be new therapeutic targets for treating insulin resistance in obesity and diabetes.