Abstract
Background/objectivesPentraxin 3 (PTX3) has been characterized as a soluble and multifunctional pattern recognition protein in the regulation of innate immune response. However, little is known about its role in adipose tissue inflammation and obesity. Herein, we investigated the role of PTX3 in the regulation of lipopolysaccharide (LPS)-induced inflammation in adipocytes and adipose tissue, as well as high-fat diet (HFD)-induced metabolic inflammation in obesity.MethodsPtx3 knockdown 3T3-L1 Cells were generated using shRNA for Ptx3 gene and treated with different inflammatory stimuli. For the in vivo studies, Ptx3 knockout mice were treated with 0.3 mg/kg of LPS for 6 h. Adipose tissues were collected for gene and protein expression by qPCR and western blotting, respectively. Ptx3 knockout mice were fed with HFD for 12 week since 6 week of age.ResultsWe observed that the expression of PTX3 in adipose tissue and serum PTX3 were markedly increased in response to LPS administration. Knocking down Ptx3 in 3T3-L1 cells reduced adipogenesis and caused a more profound and sustained upregulation of proinflammatory gene expression and signaling pathway activation during LPS-stimulated inflammation in 3T3-L1 adipocytes. In vivo studies showed that PTX3 deficiency significantly exacerbated the LPS-induced upregulation of inflammatory genes and downregulation of adipogeneic genes in visceral and subcutaneous adipose tissue of mice. Accordingly, LPS stimulation elicited increased activation of nuclear factor-κB (NF-κB) and p44/42 MAPK (Erk1/2) signaling pathways in visceral and subcutaneous adipose tissue. The expression of PTX3 in adipose tissue was also induced by HFD, and PTX3 deficiency led to the upregulation of proinflammatory genes in visceral adipose tissue of HFD-induced obese mice.ConclusionsOur results suggest a protective role of PTX3 in LPS- and HFD-induced sustained inflammation in adipose tissue.
Highlights
Low-grade chronic inflammation in adipose tissue is a causal link between obesity and insulin resistance [1]
We investigated the role of Pentraxin 3 (PTX3) in the regulation of inflammation in adipocytes and adipose tissue by LPS stimulation in Ptx3-knockdown adipocytes and Ptx3-/- mice, as well as metabolic inflammation induced by high-fat diet (HFD) feeding in Ptx3-/- mice
Our results suggest that PTX3 plays a protective role against sustained inflammation in adipose tissue via modulating nuclear factor-κB (NF-κB) and p44/42 mitogenactivated protein kinase (MAPK) (Erk1/2) signaling pathway activation
Summary
Total RNA was extracted from cells and frozen tissues with TRIZOL reagent (Invitrogen, Carlsbad, CA). We subsequently examined a time course of the activation of TLR4-mediated inflammatory signaling pathways, including NF-κB p65, Erk1/2, and Stat in Scr and Ptx3-kd adipocytes in response to LPS stimulation. While LPS stimulates a peak level of PTX3 expression at 6 h (Fig. 1d), the peak activation of Erk1/2 and Stat occurs at 3 h This suggests a role of PTX3 in the resolution rather than initiation of inflammation. To prove this hypothesis, we conducted a time course of LPS-induced expression of inflammatory cytokines in Scr and Ptx3-kd adipocytes. Similar to what we have observed in Ptx silencing 3T3-L1 adipocytes, Ptx3-/- mice exhibited elevated phosphorylation of NF-κB and Erk1/2 induced by 6 h treatment of LPS in gonadal and inguinal WATs compared with WT mice (Fig. 6c, d). We found a trend towards a decrease in adiponectin in sera and a significant downregulation of adiponectin gene expression in gonadal
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