Anti-obesity and metabolic efficacy of the ß3-adrenergic agonist, CL316243, in mice at thermoneutrality compared to 22°C.

OBJECTIVE: Mice are typically housed at environmental temperatures below thermoneutrality, whereas humans live near thermoneutrality. This difference affects energy physiology and, potentially, anti-obesity drug efficacy. Here ß3-adrenergic agonist treatment at thermoneutrality (30°C) versus room temperature (22°C) is compared. METHODS: Male C57BL/6J mice were singly housed at 30°C or 22°C and treated with vehicle or CL316243, a ß3-agonist, for 4 weeks. Food intake, energy expenditure, body and adipose weight, brown adipose activity, white adipose browning, and glucose tolerance were evaluated. CL316243 treatment was studied in both chow- and high-fat diet-fed mice. RESULTS: Mice at 30°C, compared to 22°C, had reduced food intake, metabolic rate, and brown adipose activity, as well as increased adiposity. At both temperatures, CL316243 treatment increased brown adipose activation and energy expenditure and improved glucose tolerance. At 30°C, CL316243 increased energy expenditure disproportionately to changes in food intake, thus reducing adiposity, while at 22°C these changes were matched, yielding unchanged adiposity. CONCLUSIONS: CL316243 treatment can have beneficial metabolic effects in the absence of adiposity changes. In addition, the interaction between environmental temperature and CL316243 treatment is different from the interaction between environmental temperature and 2,4-dinitrophenol treatment reported previously, suggesting that each drug mechanism must be examined to understand the effect of environmental temperature on drug efficacy.

Biphasic effect of melanocortin agonists on metabolic rate and body temperature.

The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.

The chemical uncoupler 2,4-dinitrophenol (DNP) protects against diet-induced obesity and improves energy homeostasis in mice at thermoneutrality.

The chemical uncoupler 2,4-dinitrophenol (DNP) was an effective and widely used weight loss drug in the early 1930s. However, the physiology of DNP has not been studied in detail because toxicity, including hyperthermia and death, reduced interest in the clinical use of chemical uncouplers. To investigate DNP action, mice fed a high fat diet and housed at 30 °C (to minimize facultative thermogenesis) were treated with 800 mg/liter DNP in drinking water. DNP treatment increased energy expenditure by ∼ 17%, but did not change food intake. DNP-treated mice weighed 26% less than controls after 2 months of treatment due to decreased fat mass, without a change in lean mass. DNP improved glucose tolerance and reduced hepatic steatosis without observed toxicity. DNP treatment also reduced circulating T3 and T4 levels, Ucp1 expression, and brown adipose tissue activity, demonstrating that DNP-mediated heat generation substituted for brown adipose tissue thermogenesis. At 22 °C, a typical vivarium temperature that is below thermoneutrality, DNP treatment had no effect on body weight, adiposity, or glucose homeostasis. Thus, environmental temperature should be considered when assessing an anti-obesity drug in mice, particularly agents acting on energy expenditure. Furthermore, the beneficial effects of DNP suggest that chemical uncouplers deserve further investigation for the treatment of obesity and its comorbidities.

Network analysis of the focal adhesion to invadopodia transition identifies a PI3K-PKCα invasive signaling axis.

In cancer, deregulated signaling can produce an invasive cellular phenotype. We modeled the invasive transition as a theoretical switch between two cytoskeletal structures: focal adhesions and extracellular matrix-degrading invadopodia. We constructed molecular interaction networks of each structure and identified upstream regulatory hubs through computational analyses. We compared these regulatory hubs to the status of signaling components from head and neck carcinomas, which led us to analyze phosphatidylinositol 3-kinase (PI3K) and protein kinase C α (PKCα). Consistent with previous studies, PI3K activity promoted both the formation and the activity of invadopodia. We found that PI3K induction of invadopodia was increased by overexpression of SH2 (Src homology 2) domain-containing inositol 5'-phosphatase 2 (SHIP2), which converts the phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] that is produced by PI3K activity to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], which is believed to promote invadopodia formation. Knockdown of PKCα had divergent effects on invadopodia formation, depending on the status of PI3K. Loss of PKCα inhibited invadopodia formation in cells with wild-type PI3K pathway status. Conversely, in cells with constitutively active PI3K (through activating PI3K mutants or lacking the endogenous opposing enzyme PTEN), PKCα knockdown increased invadopodia formation. Mechanistic studies revealed a negative feedback loop from PKCα that dampened PI3K activity and invasive behavior in cells with genetic hyperactivation of the PI3K pathway. These studies demonstrated the potential of network modeling as a discovery tool and identified PI3K and PKCα as interacting regulators of invasive behavior.