Unlike in humans hepatic expression of FGF

Unlike in humans, hepatic expression of FGF21 increases in mice consuming KD and is a necessary mediator of the physiologic adaptations to the diet. FGF21 knockout (KO) mice gain, rather than lose weight on the diet [6]. FGF21 also activates BAT in part by increasing SNS drive [3,7]. In addition, the ob/ob mouse, a model with a diminished SNS outflow [8], is also partially resistant to the full effects of KD; glucose tolerance is improved, but weight loss is not observed [6]. As it is known that both metabolic rate and the BAT thermogenic program are regulated by the SNS [9], we hypothesized that the SNS may play a role in the AVE 0991 sale to ketogenic diets. To test this hypothesis, we used a mouse model lacking all β-adrenergic receptors (β-less mice) [10] and measured the response to KD. In contrast to weight-loss observed in normal WT mice, β-less mice consuming KD had a distinctly different phenotype gaining rather than losing weight. This weight-gain was observed despite demonstrating a typical pattern of ketotic gene expression in the liver. Interestingly, unlike in the liver, the adipose tissue of β-less mice failed to show the expected adaptation to KD. While increased uncoupling protein 1 (UCP1) protein was observed in WT BAT, this increase was not observed in the β-less mice. Furthermore, we demonstrate that increased UCP1 expression observed in WT mice consuming KD was mediated through increased SNS drive to BAT 24-hours after switching to the KD diet. This SNS outflow profile was absent in the β-less mice. Our findings confirm that SNS activity, mediated through β-adrenergic receptors, is required for the physiologic response and adaptation to the ketogenic diet that ultimately results in weight loss.
Materials and methods
Results
Discussion In humans, ketogenic diets have generated interest as a dietary intervention for both weight loss [4,13,14] and the management of type II diabetes [15]. These low-carbohydrate, high fat diets have also been studied in mouse models to better understand the physiologic mechanisms that mediate weight loss and to define long term consequences of the diets. KD feeding in mice induces a unique metabolic state in mice characterized by weight loss, activation of BAT, and improved insulin sensitivity [1,6,16]. Furthermore, mice consuming this diet demonstrate long term resistance to weight gain with no adverse effects on morbidity or mortality [5]. The data presented here demonstrate for the first time that, sympathetic nerve activity acting through β-adrenergic receptors is critical for the energy expenditure induced weight loss in mice consuming KD, but not for other long term adaptations to the diet. We found that unlike WT mice consuming KD [1], β-less mice gain rather than lose weight due to a failure to increase energy expenditure. This is consistent with previous observations in mouse models with diminished SNS activity, such as the ob/ob mouse, that are unable to increase energy expenditure and also gain weight when consuming the diet [6,17]. BAT is a specialized fat depot, the activation of which can lead to increased energy expenditure, heat production, and a negative energy balance in mice, limiting weight gain [18–20]. KD consumption in WT mice leads to increased EE and activation of BAT as indicated by a remarkable 5-fold increase in UCP1 protein level [1]. In contrast, β-less mice showed no increase in EE and were unable to activate BAT, suggesting that intact sympathetic tone is required for BAT activation and subsequent weight loss on KD. Sympathetic activation of BAT is mediated through β-adrenergic receptors. In rodents, brown adipocytes are characterized by predominant expression of β3 adrenergic receptor, very low levels of the β1 receptor, and likely vascular tissue expression of β 2-receptors [21,22]. The hormone norepinephrine, released from sympathetic nerve terminals and acting primarily through the β3 adrenergic receptor, has long been known to be a key regulator of BAT activation [23,24]. In cold exposed β3 knockout mice, β1 receptors have been shown to be capable of mediating an increase in BAT UCP1 [25]. Therefore in this study, we used the β1, β2, β3 triple receptor knockout (β-less) model to determine the role of beta-receptors in mediating this response.