Very-low-protein diets lead to reduced food intake and weight loss, linked to inhibition of hypothalamic mTOR signaling, in mice.

The protein leverage hypothesis predicts that low dietary protein should increase energy intake and cause adiposity. We designed 10 diets varying from 1% to 20% protein combined with either 60% or 20% fat. Contrasting the expectation, very low protein did not cause increased food intake. Although these mice had activated hunger signaling, they ate less food, resulting in decreased body weight and improved glucose tolerance but not increased frailty, even under 60% fat. Moreover, they did not show hyperphagia when returned to a 20% protein diet, which could be mimicked by treatment with rapamycin. Intracerebroventricular injection of AAV-S6K1 significantly blunted the decrease in both food intake and body weight in mice fed 1% protein, an effect not observed with inhibition of eIF2a, TRPML1, and Fgf21 signaling. Hence, the 1% protein diet induced decreased food intake and body weight via a mechanism partially dependent on hypothalamic mTOR signaling.

Of Mice and Men: Impacts of Calorie Restriction on Metabolomics of the Cerebellum.

The main purpose of research in mice is to explore metabolic changes in animal models and then predict or propose potential translational benefits in humans. Although some researchers in the brain research field have mentioned that the mouse experiments results still lack the complex neuroanatomy of humans, caution is required to interpret the findings. In mice, we observed in article seventeenth of the series of the effects of graded levels of calorie restriction, metabolomic changes in the cerebellum indicated activation of hypothalamocerebellar connections driven by hunger responses. Therefore, the purpose of the current perspective is to set this latest paper into a wider context of the physiological, behavioral, and molecular changes seen in these mice and to compare and contrast them with previous human studies.

The Effects of Graded Levels of Calorie Restriction: XVI. Metabolomic Changes in the Cerebellum Indicate Activation of Hypothalamocerebellar Connections Driven by Hunger Responses.

Calorie restriction (CR) remains the most robust intervention to extend life span and improve healthspan. Though the cerebellum is more commonly associated with motor control, it has strong links with the hypothalamus and is thought to be associated with nutritional regulation and adiposity. Using a global mass spectrometry-based metabolomics approach, we identified 756 metabolites that were significantly differentially expressed in the cerebellar region of the brain of C57BL/6J mice, fed graded levels of CR (10, 20, 30, and 40 CR) compared to mice fed ad libitum for 12 hours a day. Pathway enrichment indicated changes in the pathways of adenosine and guanine (which are precursors of DNA production), aromatic amino acids (tyrosine, phenylalanine, and tryptophan) and the sulfur-containing amino acid methionine. We also saw increases in the tricarboxylic acid cycle (TCA) cycle, electron donor, and dopamine and histamine pathways. In particular, changes in l-histidine and homocarnosine correlated positively with the level of CR and food anticipatory activity and negatively with insulin and body temperature. Several metabolic and pathway changes acted against changes seen in age-associated neurodegenerative disorders, including increases in the TCA cycle and reduced l-proline. Carnitine metabolites contributed to discrimination between CR groups, which corroborates previous work in the liver and plasma. These results indicate the conservation of certain aspects of metabolism across tissues with CR. Moreover, this is the first study to indicate CR alters the cerebellar metabolome, and does so in a graded fashion, after only a short period of restriction.

The effects of graded levels of calorie restriction: VII. Topological rearrangement of hypothalamic aging networks.

Connectivity in a gene-gene network declines with age, typically within gene clusters. We explored the effect of short-term (3 months) graded calorie restriction (CR) (up to 40 %) on network structure of aging-associated genes in the murine hypothalamus by using conditional mutual information. The networks showed a topological rearrangement when exposed to graded CR with a higher relative within cluster connectivity at 40CR. We observed changes in gene centrality concordant with changes in CR level, with Ppargc1a, and Ppt1 having increased centrality and Etfdh, Traf3 and Abcc1 decreased centrality as CR increased. This change in gene centrality in a graded manner with CR, occurred in the absence of parallel changes in gene expression levels. This study emphasizes the importance of augmenting traditional differential gene expression analyses to better understand structural changes in the transcriptome. Overall our results suggested that CR induced changes in centrality of biological relevant genes that play an important role in preventing the age-associated loss of network integrity irrespective of their gene expression levels.

The effects of graded levels of calorie restriction: VI. Impact of short-term graded calorie restriction on transcriptomic responses of the hypothalamic hunger and circadian signaling pathways.

Food intake and circadian rhythms are regulated by hypothalamic neuropeptides and circulating hormones, which could mediate the anti-ageing effect of calorie restriction (CR). We tested whether these two signaling pathways mediate CR by quantifying hypothalamic transcripts of male C57BL/6 mice exposed to graded levels of CR (10 % to 40 %) for 3 months. We found that the graded CR manipulation resulted in upregulation of core circadian rhythm genes, which correlated negatively with circulating levels of leptin, insulin-like growth factor 1 (IGF-1), insulin, and tumor necrosis factor alpha (TNF-α). In addition, key components in the hunger signaling pathway were expressed in a manner reflecting elevated hunger at greater levels of restriction, and which also correlated negatively with circulating levels of insulin, TNF-α, leptin and IGF-1. Lastly, phenotypes, such as food anticipatory activity and body temperature, were associated with expression levels of both hunger genes and core clock genes. Our results suggest modulation of the hunger and circadian signaling pathways in response to altered levels of circulating hormones, that are themselves downstream of morphological changes resulting from CR treatment, may be important elements in the response to CR, driving some of the key phenotypic outcomes.