Glial cell line-derived neurotrophic factor protects against high-fat diet-induced obesity.

Obesity is a growing epidemic with limited effective treatments. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) was recently shown to enhance ß-cell mass and improve glucose control in rodents. Its role in obesity is, however, not well characterized. In this study, we investigated the ability of GDNF to protect against high-fat diet (HFD)-induced obesity. GDNF transgenic (Tg) mice that overexpress GDNF under the control of the glial fibrillary acidic protein promoter and wild-type (WT) littermates were maintained on a HFD or regular rodent diet for 11 wk, and weight gain, energy expenditure, and insulin sensitivity were monitored. Differentiated mouse brown adipocytes and 3T3-L1 white adipocytes were used to study the effects of GDNF in vitro. Tg mice resisted the HFD-induced weight gain, insulin resistance, dyslipidemia, hyperleptinemia, and hepatic steatosis seen in WT mice despite similar food intake and activity levels. They exhibited significantly (P<0.001) higher energy expenditure than WT mice and increased expression in skeletal muscle and brown adipose tissue of peroxisome proliferator activated receptor-α and ß1- and ß3-adrenergic receptor genes, which are associated with increased lipolysis and enhanced lipid ß-oxidation. In vitro, GDNF enhanced ß-adrenergic-mediated cAMP release in brown adipocytes and suppressed lipid accumulation in differentiated 3T3L-1 cells through a p38MAPK signaling pathway. Our studies demonstrate a novel role for GDNF in the regulation of high-fat diet-induced obesity through increased energy expenditure. They show that GDNF and its receptor agonists may be potential targets for the treatment or prevention of obesity.

Bacterial-induced inflammation in germ-free rabbit appendix.

The intestinal ecosystem is defined by a series of interactions between the microbiota, the mucosal epithelium, and the gut-associated lymphoid tissue (GALT). Perturbations in the fine balance of the interactions between these components can result in gastrointestinal diseases such as inflammatory bowel disease (IBD). The pathophysiology of IBD is thought to develop as a result of dysregulated mucosal immune responses to normal luminal microflora. Several animal models for IBD have been developed and underscore the role of the immune system in development of disease. Most of the existing animal models studying IBD are based on the use of chemically induced IBD or of genetically modified and germ-free animals. It is, however, important to study inflammatory responses that can develop from interactions between bacteria, the mucosal epithelium, and GALT in animals that are not genetically modified or immunocompromised. In this report, we document the use of a germ-free ligated rabbit appendix model to induce inflammatory changes in response to specific bacteria. With the introduction of a Bacteroides vulgatus isolate from humans into the germ-free ligated appendix, we found chronic inflammatory changes, including glandular distortion, gland drop-out, decreased goblet cells, and crypt abscess formation. However, with the introduction of other experimental luminal contents, we observed no inflammation. These results show that specific microbial composition can induce inflammation. We suggest that this model may be useful to study the mechanism by which specific bacteria establish inflammatory responses in the gut.

Positive selection of the peripheral B cell repertoire in gut-associated lymphoid tissues.

Gut-associated lymphoid tissues (GALTs) interact with intestinal microflora to drive GALT development and diversify the primary antibody repertoire; however, the molecular mechanisms that link these events remain elusive. Alicia rabbits provide an excellent model to investigate the relationship between GALT, intestinal microflora, and modulation of the antibody repertoire. Most B cells in neonatal Alicia rabbits express V(H)n allotype immunoglobulin (Ig)M. Within weeks, the number of V(H)n B cells decreases, whereas V(H)a allotype B cells increase in number and become predominant. We hypothesized that the repertoire shift from V(H)n to V(H)a B cells results from interactions between GALT and intestinal microflora. To test this hypothesis, we surgically removed organized GALT from newborn Alicia pups and ligated the appendix to sequester it from intestinal microflora. Flow cytometry and nucleotide sequence analyses revealed that the V(H)n to V(H)a repertoire shift did not occur, demonstrating the requirement for interactions between GALT and intestinal microflora in the selective expansion of V(H)a B cells. By comparing amino acid sequences of V(H)n and V(H)a Ig, we identified a putative V(H) ligand binding site for a bacterial or endogenous B cell superantigen. We propose that interaction of such a superantigen with V(H)a B cells results in their selective expansion.