Differential transcriptional activation of select metabolic genes in response to variations in exercise intensity and duration.

Cellular adaptations to endurance training are influenced by the intensity and duration of exercise. To examine the impact of exercise intensity and duration on the acute transcriptional regulation of metabolic genes in red (RG) and white (WG) gastrocnemius muscle, rats completed either low-intensity [ approximately 50% maximal O2 uptake (VO2 max)] treadmill exercise (LIE) for 45 min, LIE for 180 min, or high-intensity ( approximately 75% VO2 max) exercise (HIE) for 45 min. LIE for 45 min activated (P < 0.05) transcription of the pyruvate dehydrogenase kinase-4 (PDK4), uncoupling protein-3 (UCP3), heme oxygenase-1 (HO-1), and hexokinase II (HK II) genes in RG within 1 h after exercise. In WG, transcription of PDK4, UCP3, HKII, and lipoprotein lipase (LPL) was also induced, whereas transcription of the HO-1 gene did not change. In RG, extending LIE duration from 45 to 180 min elicited a similar activation of PDK4 and UCP3 ( approximately 15-fold) but a far greater increase in HO-1 (>30-fold) and HKII transcription (>25-fold). In WG, extending LIE for 180 min induced a much greater and prolonged (through 2- to 4-h recovery) activation of PDK4, UCP3 (both >200-fold), and HO-1 (>10-fold). HIE elicited a similar pattern of gene activation to LIE in both RG and WG, with the exception that HIE triggered >10-fold activation of HO-1 in WG. These data provide evidence that both the intensity and the duration of exercise affect the transcriptional regulation of metabolic genes in muscle in a fiber type-specific manner, possibly reflecting the relative stress imposed by the exercise bout.

Severe diabetes, age-dependent loss of adipose tissue, and mild growth deficiency in mice lacking Akt2/PKB beta.

The serine/threonine kinase Akt/PKB plays key roles in the regulation of cell growth, survival, and metabolism. It remains unclear, however, whether the functions of individual Akt/PKB isoforms are distinct. To investigate the function of Akt2/PKBbeta, mice lacking this isoform were generated. Both male and female Akt2/PKBbeta-null mice exhibit mild growth deficiency and an age-dependent loss of adipose tissue or lipoatrophy, with all observed adipose depots dramatically reduced by 22 weeks of age. Akt2/PKBbeta-deficient mice are insulin resistant with elevated plasma triglycerides. In addition, Akt2/PKBbeta-deficient mice exhibit fed and fasting hyperglycemia, hyperinsulinemia, glucose intolerance, and impaired muscle glucose uptake. In males, insulin resistance progresses to a severe form of diabetes accompanied by pancreatic beta cell failure. In contrast, female Akt2/PKBbeta-deficient mice remain mildly hyperglycemic and hyperinsulinemic until at least one year of age. Thus, Akt2/PKBbeta-deficient mice exhibit growth deficiency similar to that reported previously for mice lacking Akt1/PKBalpha, indicating that both Akt2/PKBbeta and Akt1/PKBalpha participate in the regulation of growth. The marked hyperglycemia and loss of pancreatic beta cells and adipose tissue in Akt2/PKBbeta-deficient mice suggest that Akt2/PKBbeta plays critical roles in glucose metabolism and the development or maintenance of proper adipose tissue and islet mass for which other Akt/PKB isoforms are unable to fully compensate.

Antiobesity effects of chronic cannabinoid CB1 receptor antagonist treatment in diet-induced obese mice.

We determined the effect of a cannabinoid CB1 receptor antagonist (AM-251; N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) on food intake, body weight and adipose tissue mass in Western diet-induced obese (DIO) mice using a chronic, interrupted, oral dosing paradigm. The dosing paradigm was 2 weeks on treatment (treatment 1), 2 weeks off-treatment, followed by 2 weeks on treatment (treatment 2). During treatment 1 and treatment 2, food intake and body weight were reduced after a single dose. At 30 mg/kg/day, anorectic efficacy was maintained through 12 days (treatment 1) and 7 days (treatment 2). Body weight of AM-251-treated mice remained less than vehicle-treated mice throughout treatment 1 and treatment 2. Administration of AM-251 reduced inguinal subcutaneous, retroperitoneal and mesenteric adipose tissue mass. Antiobesity effects of AM-251 were lost during the off-treatment period, and hyperphagia was observed in treated animals. With re-initiation of AM-251 treatment, mice again responded to the effects of the compound. These results support the hypothesis that chronic treatment of obese individuals with cannabinoid CB1 receptor antagonists is a viable pharmacologic approach to sustained weight loss.

Validation of a high-resolution X-ray computed tomography system to measure murine adipose tissue depot mass in situ and longitudinally.

INTRODUCTION: Obesity is a significant public health concern with considerable academic and industrial research effort underway to discover novel drugs to treat this disease. The aim of this study was to validate a recently developed high-resolution X-ray computed tomography (micro CT) system capable of measuring murine adipose tissue depot mass in situ. METHODS: The micro CT was used to generate a series of cross-sectional X-ray images from which individual adipose tissue depot mass was quantified. Four individual adipose tissue depots were studied: inguinal subcutaneous, epididymal, retroperitoneal, and mesenteric. The relationship between micro CT-derived adipose tissue mass and adipose mass measured gravimetrically was determined. The effect of strain (C57/Bl6, C3H/HeNCR1BR, and db/db) and age (49 vs. 99 days) on adipose tissue depot mass was studied. RESULTS: Validation studies in which adipose tissue depot mass was determined by micro CT and by gravimetry were conducted in the three strains of mice at 49 and 99 days of age. The correlation of micro CT and gravimetric measures of adipose tissue mass exceeded 90% in all strains at 99 days, and in the C57/Bl6 and C3H/HeNCR1BR strains at 49 days. At 49 days, the correlation in the db/db strain was 82%. Micro CT methodology distinguished both age and strain differences in the adipose tissue depots studied (P<.0001, in all cases). DISCUSSION: Micro CT is a valid method to quantify the mass of individual adipose tissue depots in mice. This method of determining adipose tissue mass is not a terminal procedure; thus, this methodology may be particularly useful for the longitudinal assessment of the effects of drug intervention on adipose tissue depot mass.

AMP-activated protein kinase activates transcription of the UCP3 and HKII genes in rat skeletal muscle.

AMP-activated protein kinase (AMPK) has recently emerged as a key signaling protein in skeletal muscle, coordinating the activation of both glucose and fatty acid metabolism in response to increased cellular energy demand. To determine whether AMPK signaling may also regulate gene transcription in muscle, rats were given a single subcutaneous injection (1 mg/g) of the AMP analog 5-aminoimidazole-4-carboxamide-1-beta-d-ribonucleoside (AICAR). AICAR injection activated (P < 0.05) AMPK-alpha 2 ( approximately 2.5-fold) and transcription of the uncoupling protein-3 (UCP3, approximately 4-fold) and hexokinase II (HKII, approximately 10-fold) genes in both red and white skeletal muscle. However, AICAR injection also elicited (P < 0.05) an acute drop (60%) in blood glucose and a sustained (2-h) increase in blood lactate, prompting concern regarding the specificity of AICAR on transcription. To maximize AMPK activation in muscle while minimizing potential systemic counterregulatory responses, a single-leg arterial infusion technique was employed in fully conscious rats. Relative to saline-infused controls, single-leg arterial infusion of AICAR (0.125, 0.5, and 2.5 micro g. g(-1). min(-1) for 60 min) induced a dose-dependent increase (2- to 4-fold, P < 0.05) in UCP3 and HKII transcription in both red and white skeletal muscle. Importantly, AICAR infusion activated transcription only in muscle from the infused leg and had no effect on blood glucose or lactate levels. These data provide evidence that AMPK signaling is linked to the transcriptional regulation of select metabolic genes in skeletal muscle.