Research

Signaling pathways involved in LPS induced TNFalpha production in human adipocytes

Laurence Hoareau^1* , Karima Bencharif^1* , Philippe Rondeau¹ , Ravi Murumalla¹ , Palaniyandi Ravanan¹ , Frank Tallet² , Pierre Delarue³ , Maya Cesari¹ , Régis Roche^1* and Franck Festy^1*

¹  LBGM-GEICO, Laboratoire de Biochimie et de Génétique Moléculaire - Groupe d'Etude sur l'Inflammation Chronique et l'Obésité, Université de l'île de la Réunion, 15 avenue René Cassin 97715 Saint Denis Messag Cedex, France

²  Service de biochimie, Centre Hospitalier Félix Guyon, Saint-Denis, Ile de la Réunion, France

³  Cabinet de Chirurgie Plastique, Saint-Denis, Ile de La Réunion, France

author email corresponding author email* Contributed equally

Journal of Inflammation 2010, 7:1doi:10.1186/1476-9255-7-1

Published:	8 January 2010

Abstract

Background

The development of obesity has been linked to an inflammatory process, and the role of adipose tissue in the secretion of pro-inflammatory molecules such as IL-6 or TNFalpha has now been largely confirmed. Although TNFalpha secretion by adipose cells is probably induced, most notably by TLR ligands, the activation and secretion pathways of this cytokine are not yet entirely understood. Moreover, given that macrophagic infiltration is a characteristic of obesity, it is difficult to clearly establish the level of involvement of the different cellular types present within the adipose tissue during inflammation.

Methods

Primary cultures of human adipocytes and human peripheral blood mononuclear cells were used. Cells were treated with a pathogen-associated molecular pattern: LPS, with and without several kinase inhibitors. Western blot for p38 MAP Kinase was performed on cell lysates. TNFalpha mRNA was detected in cells by RT-PCR and TNFalpha protein was detected in supernatants by ELISA assays.

Results

We show for the first time that the production of TNFalpha in mature human adipocytes is mainly dependent upon two pathways: NFkappaB and p38 MAP Kinase. Moreover, we demonstrate that the PI3Kinase pathway is clearly involved in the first step of the LPS-pathway. Lastly, we show that adipocytes are able to secrete a large amount of TNFalpha compared to macrophages.

Conclusion

This study clearly demonstrates that the LPS induced activation pathway is an integral part of the inflammatory process linked to obesity, and that adipocytes are responsible for most of the secreted TNFalpha in inflamed adipose tissue, through TLR4 activation.