Adipocyte-mononuclear cell interaction, Toll-like receptor 4 activation, and high glucose synergistically up-regulate osteopontin expression via an interleukin 6-mediated mechanism.
Although it has been reported that osteopontin, a matrix glycoprotein and proinflammatory cytokine, mediates obesity-induced adipose tissue macrophage infiltration and insulin resistance, it remains unclear how osteopontin is up-regulated in adipose tissue in obese humans and animals. In this study, we incubated U937 mononuclear cells with adipocytes in a transwell system and studied how cell interaction regulated osteopontin expression. Results showed that coculture of U937 cells with adipocytes led to a marked increase in osteopontin production when compared with that released by independent cultures of U937 cells. Moreover, lipopolysaccharide or palmitic acid-induced TLR4 activation and high glucose further augmented the coculture-stimulated osteopontin secretion. Similar observations were made in the coculture of human primary monocytes and adipocytes. Real time PCR studies showed that coculture of U937 cells and adipocytes increased osteopontin mRNA in U937 cells, but not adipocytes, suggesting that adipocyte-derived soluble factor may stimulate osteopontin expression by U937 cells. In our studies to explore the underlying mechanism, we found that the neutralizing antibodies against interleukin (IL)-6 or IL-6 small interfering RNA transfection in adipocytes effectively inhibited coculture-stimulated osteopontin expression, suggesting that IL-6 released by adipocytes plays an essential role in the coculture-stimulated osteopontin expression by U937 cells. In conclusion, this study has demonstrated that cell interaction, TLR4 activation, and high glucose up-regulate osteopontin expression, and adipocyte-derived IL-6 played a major role in the up-regulation.
Samuvel
Devadoss J
DJ
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.
Sundararaj
Kamala P
KP
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.
Li
Yanchun
Y
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.
Lopes-Virella
Maria F
MF
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425; From the Ralph H. Johnson Veterans Affairs Medical Center, Medical University of South Carolina, Charleston, South Carolina 29425.
Huang
Yan
Y
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425; From the Ralph H. Johnson Veterans Affairs Medical Center, Medical University of South Carolina, Charleston, South Carolina 29425. Electronic address: huangyan@musc.edu.
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000906:Antibodies / Q000494:pharmacology; D002450:Cell Communication; D002478:Cells, Cultured; D018920:Coculture Techniques; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D004797:Enzyme-Linked Immunosorbent Assay; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015850:Interleukin-6 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D053495:Osteopontin / Q000235:genetics* / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D020298:U937 Cells; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D000906:Antibodies; D005419:Flavonoids; D007093:Imidazoles; D015850:Interleukin-6; D008070:Lipopolysaccharides; D011725:Pyridines; D011994:Recombinant Proteins; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D018808:Transcription Factor AP-1; D053495:Osteopontin; D048051:p38 Mitogen-Activated Protein Kinases; D005947:Glucose; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one