Normal development and function of dendritic cells in mice lacking IDO-1 expression.

Dendritic cells (DCs) have been shown to express the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase (IDO-1), a protein presently thought to exert dual and possibly contrasting effects on the immune response. Depletion of tryptophan and release of tryptophan catabolites have been shown to exert a tolerogenic influence on T cell responses, while the IDO enzymatic activity has been recently suggested to promote DC maturation. In this report, we have explored the putative role of IDO-1 in regulating DC biology by analyzing DC development and function from IDO-1 deficient mice. In keeping with previous observations, lack of IDO-1 expression was found to affect in vitro DC generation from bone mouse precursors cultured in the presence of GM-CSF. However, change in growth factor (Flt3L) and/or culture conditions (low-adherence vessels) abolished the difference observed between wt (wild type) and IDO-1-deficient, in vitro generated DCs. Moreover, IDO-1-deficient mice displayed a normal DC compartment in vivo, suggesting that IDO-1 does not play a significant role in DC development and function in vivo. Collectively, these observations suggest that despite a possible role for IDO-1 expression in regulating DC differentiation in vitro under commonly used culture conditions, IDO-1 is largely dispensable for DC development and function in vivo.

Transgenic Artifacts Caused by Passenger Human Growth Hormone.

The minigene encoding human growth hormone (hGH) has been incorporated into over 300 transgenic mouse lines to improve transgene expression. However, unexpected and functional hGH expression can drastically alter physiology. We list here the mouse lines in which ectopic hGH has been confirmed, and we provide a wiki for lines awaiting analysis.

Metabolic and Behavioural Phenotypes in Nestin-Cre Mice Are Caused by Hypothalamic Expression of Human Growth Hormone.

The Nestin-Cre driver mouse line has mild hypopituitarism, reduced body weight, a metabolic phenotype and reduced anxiety. Although several causes have been suggested, a comprehensive explanation is still lacking. In this study we examined the molecular mechanisms leading to this compound phenotype. Upon generation of the Nestin-Cre mice, the human growth hormone (hGH) minigene was inserted downstream of the Cre recombinase to ensure efficient transgene expression. As a result, hGH is expressed in the hypothalamus. This results in the auto/paracrine activation of the GH receptor as demonstrated by the increased phosphorylation of signal transducer and activator of transcription 5 (STAT5) and reduced expression of growth hormone releasing hormone (Ghrh). Low Ghrh levels cause hypopituitarism consistent with the observed mouse growth hormone (mGH) deficiency. mGH deficiency caused reduced activation of the GH receptor and hence reduced phosphorylation of STAT5 in the liver. This led to decreased levels of hepatic Igf-1 mRNA and consequently postnatal growth retardation. Furthermore, genes involved in lipid uptake and synthesis, such as CD36 and very low-density lipoprotein receptor were upregulated, resulting in liver steatosis. In conclusion, this study demonstrates the unexpected expression of hGH in the hypothalamus of Nestin-Cre mice which is able to activate both the GH receptor and the prolactin receptor. Increased hypothalamic GH receptor signaling explains the observed hypopituitarism, reduced growth and metabolic phenotype of Nestin-Cre mice. Activation of either receptor is consistent with reduced anxiety.

Impaired islet function in commonly used transgenic mouse lines due to human growth hormone minigene expression.

The human growth hormone (hGH) minigene is frequently used in the derivation of transgenic mouse lines to enhance transgene expression. Although this minigene is present in the transgenes as a secondcistron, and thus not thought to be expressed, we found that three commonly used lines, Pdx1-Cre(Late), RIP-Cre, and MIP-GFP, each expressed significant amounts of hGH in pancreatic islets. Locally secreted hGH binds to prolactin receptors on ß cells, activates STAT5 signaling, and induces pregnancy-like changes in gene expression, thereby augmenting pancreatic ß cell mass and insulin content. In addition, islets of Pdx1-Cre(Late) mice have lower GLUT2 expression and reduced glucose-induced insulin release and are protected against the ß cell toxin streptozotocin. These findings may be important when interpreting results obtained when these and other hGH minigene-containing transgenic mice are used.

Mice deficient in the respiratory chain gene Cox6a2 are protected against high-fat diet-induced obesity and insulin resistance.

Oxidative phosphorylation in mitochondria is responsible for 90% of ATP synthesis in most cells. This essential housekeeping function is mediated by nuclear and mitochondrial genes encoding subunits of complex I to V of the respiratory chain. Although complex IV is the best studied of these complexes, the exact function of the striated muscle-specific subunit COX6A2 is still poorly understood. In this study, we show that Cox6a2-deficient mice are protected against high-fat diet-induced obesity, insulin resistance and glucose intolerance. This phenotype results from elevated energy expenditure and a skeletal muscle fiber type switch towards more oxidative fibers. At the molecular level we observe increased formation of reactive oxygen species, constitutive activation of AMP-activated protein kinase, and enhanced expression of uncoupling proteins. Our data indicate that COX6A2 is a regulator of respiratory uncoupling in muscle and we demonstrate that a novel and direct link exists between muscle respiratory chain activity and diet-induced obesity/insulin resistance.