Altered signalling and gene expression associated with the immune system and the inflammatory response in obesity

White adipose tissue functions not only as an energy store but also as an important endocrine organ and is involved in the regulation of many pathological processes. The obese state is characterised by a low-grade systemic inflammation, mainly a result of increased adipocyte as well as fat resident- and recruited-macrophage activity. In the past few years, various products of adipose tissue including adipokines and cytokines have been characterised and a number of pathways linking adipose tissue metabolism with the immune system have been identified. In obesity, the pro- and anti-inflammatory effects of adipokines and cytokines through intracellular signalling pathways mainly involve the nuclear factor kappa B (NF-kappaB) and the Jun N-terminal kinase (JNK) systems as well as the I kappa B kinase beta (IKK-beta). Mitogen-activated protein kinase (MAPK) and extracellular-signal-regulated kinase (ERK) pathways, which lead to signal transducer and activator of transcription 3 (STAT3) activation, are also important in the production of pro-inflammatory cytokines. Obesity increases the expression of leptin and other cytokines, as well as some macrophage and inflammatory markers, and decreases adiponectin expression in adipose tissue. A number of cytokines, e.g. tumour necrosis factor alpha (TNF-alpha) and monocyte chemotactic protein 1 (MCP-1), and some pro-inflammatory interleukins, leuckocyte antigens, chemochines, surface adhesion molecules and metalloproteases are up-regulated whereas other factors are down-regulated. The present paper will focus on the molecular mechanisms linking obesity and inflammation with emphasis on the alteration of signalling and gene expression in adipose cell components.