ABSTRACT
Obesity is an important risk factor for heart disease, diabetes, and certain cancers, but the molecular basis for obesity is poorly understood. The transcriptional repressor AEBP1, which functions as a negative regulator of PTEN through a protein-protein interaction, is highly expressed in the stromal compartment of adipose tissues, including proliferative preadipocytes, and its expression is abolished in terminally differentiated, nonproliferative adipocytes. Here we show that transgenic overexpression of AEBP1 during adipogenesis coupled with a high-fat diet (HFD) resulted in massive obesity in female transgenic (AEBP1(TG)) mice via adipocyte hyperplasia. AEBP1 levels dynamically changed with aging, and HFD induced AEBP1 expression in females. Thus, HFD-fed AEBP1(TG) females display hyperinduction of AEBP1 and a marked reduction of PTEN level with concomitant hyperactivation of the survival signal in white adipose tissue. Our results suggest that AEBP1 plays a key functional role in in vivo modulation of adiposity via fat-cell proliferation and is involved in a sex-specific susceptibility to diet-induced obesity by the estrogen signaling pathway.
Subject(s)
Carboxypeptidases/physiology , Dietary Fats/toxicity , Obesity/enzymology , Obesity/physiopathology , Repressor Proteins/physiology , Sex Characteristics , 3T3 Cells , Adipocytes/enzymology , Adipocytes/pathology , Adipogenesis/genetics , Animals , Carboxypeptidases/biosynthesis , Carboxypeptidases/genetics , Cell Proliferation , Female , Gene Expression Regulation, Enzymologic , Genetic Predisposition to Disease , Hyperplasia/genetics , Mice , Mice, Transgenic , Obesity/genetics , PTEN Phosphohydrolase/antagonists & inhibitors , PTEN Phosphohydrolase/physiology , Repressor Proteins/biosynthesis , Repressor Proteins/genetics , Signal Transduction/geneticsABSTRACT
During inflammatory responses in the brain, the expression of cytochrome P450 isoforms in the CNS are modulated and the capacity of the brain to metabolize drugs and to synthesize or degrade certain endogenous chemicals and drugs is diminished. While this response can be attributed in part, to the production and action of cytokines within the brain, it is also likely that other inflammatory mediators play an integral role. This paper investigates a potential role for nitric oxide (NO) in the loss of cytochrome P450 (CYP1A) in the brain during inflammation. Escherichia coli lipopolysaccharide (LPS), a commonly used proinflammatory endotoxin, was incubated with cultured rat astrocytes to provide a model of inflammation in the CNS. CYP1A activity was significantly decreased in cultured astrocytes incubated with LPS for 24 h. This loss in enzyme activity was accompanied by a substantial production of nitric oxide (NO) by these cells. Immunohistochemical examination demonstrated an upregulation of inducible nitric oxide synthase (iNOS) expression following the exposure of astrocytes to LPS. The addition of a selective iNOS blocker (1400W) caused a partial but significant reversal of the LPS-mediated loss in CYP1A. The incubation of astrocytes with the NO-generating compound (DETA NONOate) resulted in a loss of CYP1A. Taken together, these observations suggest that NO plays a pivotal role in the inflammation mediated loss in CYP1A activity in the brain.
Subject(s)
Astrocytes/metabolism , Cytochrome P-450 CYP1A1/metabolism , Lipopolysaccharides/pharmacology , Nitric Oxide/metabolism , Amidines/pharmacology , Animals , Astrocytes/cytology , Astrocytes/drug effects , Benzylamines/pharmacology , Cells, Cultured , Enzyme Inhibitors/pharmacology , Immunohistochemistry , Inflammation/metabolism , Nitric Oxide Donors/pharmacology , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase/metabolism , Nitric Oxide Synthase Type II , Nitroso Compounds/pharmacology , RatsABSTRACT
The interaction and modulation of hepatic cytochrome P450 enzymes by infection and inflammation has been well described both in clinical settings and in animal models. Recent evidence found that inflammation in the central nervous system (CNS) leads to alterations in cytochrome P450 activity in both brain and liver. The bacterial endotoxin lipopolysaccharide (LPS) was used to induce an inflammatory response in cultured astrocytes as a model of CNS inflammation. This inflammatory response involves a range of immune mediators, such as acute phase cytokines, nitric oxide, prostanoid products, and reactive oxygen species. It is hypothesized that cytokines, released during inflammation, act to modulate the expression of specific isoforms of cytochrome P450 resulting in altered activity levels. High levels of the cytokines tumor necrosis factor-alpha and interleukin-1beta were released into culture medium after the addition of LPS to astrocyte cultures. When these same cytokines were added directly to the cultures, they also were able to modulate levels of CYP1A activity. The concurrent addition of dexamethasone to astrocytes blocked both the cytokine release and the alteration of CYP1A activity, thus supporting a role for these cytokines in this response. These results provide evidence suggesting an involvement of acute phase cytokines in mediating the LPS-induced depression of CYP1A activity in cultured astrocytes.
