title: TLR4 activation and IL-6-mediated cross talk between adipocytes and mononuclear cells synergistically stimulate MMP-1 expression.
abstract: Obesity is associated with increased monocyte infiltration into adipose tissue and hence increased interaction between adipocytes and monocytes. Although it has been shown that matrix metalloproteinases (MMP) play a critical role in adipose tissue development, the effect of adipocyte and monocyte interaction on MMP production remains largely unknown. Furthermore, although it has been shown that Toll-like receptor 4 (TLR4), a receptor mediating innate immune response, plays an important role in the obesity-associated inflammation and insulin resistance, the effect of TLR4 activation in coculture of adipocytes and monocytes on MMP production has not been investigated. In this study, we cocultured adipocytes with U937 mononuclear cells in a Transwell coculture system and activated TLR4 with lipopolysaccharide or palmitic acid. We found that TLR4 activation and the coculture had a synergistic effect on MMP-1 production. In our further investigation on the underlying mechanisms, it was indicated that adipocyte-derived IL-6 and TLR4 activation acted in concert to synergistically stimulate MMP-1 expression by U937 cells. Taken together, this study has uncovered a novel mechanism potentially involved in MMP-1 up-regulation in adipose tissue, which may facilitate adipose tissue development and obesity.
authors.affiliation: Ralph H. Johnson Veterans Affairs Medical Center, and Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, 114 Doughty Street, Charleston, South Carolina 29403, USA.
authors.forename: Devadoss J
authors.initials: DJ
authors.lastname: Samuvel
authors.forename: Junfei
authors.initials: J
authors.lastname: Jin
authors.forename: Kamala P
authors.initials: KP
authors.lastname: Sundararaj
authors.forename: Yanchun
authors.initials: Y
authors.lastname: Li
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Zhang
authors.forename: Maria F
authors.initials: MF
authors.lastname: Lopes-Virella
authors.forename: Yan
authors.initials: Y
authors.lastname: Huang
mesh_terms: D017667:Adipocytes / Q000378:metabolism*; D002460:Cell Line; D018920:Coculture Techniques; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000378:metabolism*; D020781:Matrix Metalloproteinase 1 / Q000096:biosynthesis*; D009765:Obesity / Q000209:etiology / Q000378:metabolism; D019899:Paracrine Communication; D020239:Receptor Cross-Talk; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; D051197:Toll-Like Receptor 4; D020781:Matrix Metalloproteinase 1