The anorectic and thermogenic effects of pharmacological lactate in male mice are confounded by treatment osmolarity and co-administered counterions.

Lactate is a circulating metabolite and a signalling molecule with pleiotropic physiological effects. Studies suggest that lactate modulates energy balance by lowering food intake, inducing adipose browning and increasing whole-body thermogenesis. Yet, like many other metabolites, lactate is often commercially produced as a counterion-bound salt and typically administered in vivo through hypertonic aqueous solutions of sodium L-lactate. Most studies have not controlled for injection osmolarity and the co-injected sodium ions. Here, we show that the anorectic and thermogenic effects of exogenous sodium L-lactate in male mice are confounded by the hypertonicity of the injected solutions. Our data reveal that this is in contrast to the antiobesity effect of orally administered disodium succinate, which is uncoupled from these confounders. Further, our studies with other counterions indicate that counterions can have confounding effects beyond lactate pharmacology. Together, these findings underscore the importance of controlling for osmotic load and counterions in metabolite research.

ROS-induced ribosome impairment underlies ZAKα-mediated metabolic decline in obesity and aging.

The ribotoxic stress response (RSR) is a signaling pathway in which the p38- and c-Jun N-terminal kinase (JNK)-activating mitogen-activated protein kinase kinase kinase (MAP3K) ZAKα senses stalling and/or collision of ribosomes. Here, we show that reactive oxygen species (ROS)-generating agents trigger ribosomal impairment and ZAKα activation. Conversely, zebrafish larvae deficient for ZAKα are protected from ROS-induced pathology. Livers of mice fed a ROS-generating diet exhibit ZAKα-activating changes in ribosomal elongation dynamics. Highlighting a role for the RSR in metabolic regulation, ZAK-knockout mice are protected from developing high-fat high-sugar (HFHS) diet-induced blood glucose intolerance and liver steatosis. Finally, ZAK ablation slows animals from developing the hallmarks of metabolic aging. Our work highlights ROS-induced ribosomal impairment as a physiological activation signal for ZAKα that underlies metabolic adaptation in obesity and aging.

Atlas of exercise metabolism reveals time-dependent signatures of metabolic homeostasis.

Tissue sensitivity and response to exercise vary according to the time of day and alignment of circadian clocks, but the optimal exercise time to elicit a desired metabolic outcome is not fully defined. To understand how tissues independently and collectively respond to timed exercise, we applied a systems biology approach. We mapped and compared global metabolite responses of seven different mouse tissues and serum after an acute exercise bout performed at different times of the day. Comparative analyses of intra- and inter-tissue metabolite dynamics, including temporal profiling and blood sampling across liver and hindlimb muscles, uncovered an unbiased view of local and systemic metabolic responses to exercise unique to time of day. This comprehensive atlas of exercise metabolism provides clarity and physiological context regarding the production and distribution of canonical and novel time-dependent exerkine metabolites, such as 2-hydroxybutyrate (2-HB), and reveals insight into the health-promoting benefits of exercise on metabolism.

Time of Exercise Specifies the Impact on Muscle Metabolic Pathways and Systemic Energy Homeostasis.

While the timing of food intake is important, it is unclear whether the effects of exercise on energy metabolism are restricted to unique time windows. As circadian regulation is key to controlling metabolism, understanding the impact of exercise performed at different times of the day is relevant for physiology and homeostasis. Using high-throughput transcriptomic and metabolomic approaches, we identify distinct responses of metabolic oscillations that characterize exercise in either the early rest phase or the early active phase in mice. Notably, glycolytic activation is specific to exercise at the active phase. At the molecular level, HIF1α, a central regulator of glycolysis during hypoxia, is selectively activated in a time-dependent manner upon exercise, resulting in carbohydrate exhaustion, usage of alternative energy sources, and adaptation of systemic energy expenditure. Our findings demonstrate that the time of day is a critical factor to amplify the beneficial impact of exercise on both metabolic pathways within skeletal muscle and systemic energy homeostasis.

The protein source determines the potential of high protein diets to attenuate obesity development in C57BL/6J mice.

The notion that the obesogenic potential of high fat diets in rodents is attenuated when the protein:carbohydrate ratio is increased is largely based on studies using casein or whey as the protein source. We fed C57BL/6J mice high fat-high protein diets using casein, soy, cod, beef, chicken or pork as protein sources. Casein stood out as the most efficient in preventing weight gain and accretion of adipose mass. By contrast, mice fed diets based on pork or chicken, and to a lesser extent mice fed cod or beef protein, had increased adipose tissue mass gain relative to casein fed mice. Decreasing the protein:carbohydrate ratio in diets with casein or pork as protein sources led to accentuated fat mass accumulation. Pork fed mice were more obese than casein fed mice, and relative to casein, the pork-based feed induced substantial accumulation of fat in classic interscapular brown adipose tissue accompanied by decreased UCP1 expression. Furthermore, intake of a low fat diet with casein, but not pork, as a protein source reversed diet-induced obesity. Compared to pork, casein seems unique in maintaining the classical brown morphology in interscapular brown adipose tissue with high UCP1 expression. This was accompanied by increased expression of genes involved in a futile cycling of fatty acids. Our results demonstrate that intake of high protein diets based on other protein sources may not have similar effects, and hence, the obesity protective effect of high protein diets is clearly modulated by protein source.