Sexual dimorphism in hypothalamic inflammation in the offspring of dams exposed to a diet rich in high fat and branched-chain amino acids

Maternal High Fat Diet in Lactation Impacts Hypothalamic Neurogenesis and Neurotrophic Development, Leading to Later Life Susceptibility to Obesity in Male but Not Female Mice

Early life nutrition can reprogram development and exert long-term consequences on body weight regulation. In mice, maternal high-fat diet (HFD) during lactation predisposed male but not female offspring to diet-induced obesity when adult. Molecular and cellular changes in the hypothalamus at important time points are examined in the early postnatal life in relation to maternal diet and demonstrated sex-differential hypothalamic reprogramming. Maternal HFD in lactation decreased the neurotropic development of neurons formed at the embryo stage (e12.5) and impaired early postnatal neurogenesis in the hypothalamic regions of both males and females. Males show a larger increased ratio of Neuropeptide Y (NPY) to Pro-opiomelanocortin (POMC) neurons in early postnatal neurogenesis, in response to maternal HFD, setting an obese tone for male offspring. These data provide insights into the mechanisms by which hypothalamic reprograming by early life overnutrition contributes to the sex-dependent susceptibility to obesity in adult life in mice.

The Potential Effects of Isoleucine Restricted Diet on Cognitive Impairment in High-Fat-Induced Obese Mice via Gut Microbiota-Brain Axis

SCOPE

Obesity induced by high-fat diet (HFD) can cause lipid metabolism disorders and cognitive impairment. Isoleucine restriction can effectively alleviate lipid metabolism disorders caused by HFD but the underlying mechanisms on cognition are unknown.

METHODS AND RESULTS

Thirty 3-month-old C57BL/6J mice are divided equally into the following groups: the control group, HFD group, and HFD Low Ile group (67% reduction in isoleucine in high fat feeds). Feeding for 11 weeks with behavioral testing, which shows that isoleucine restriction attenuates HFD-induced cognitive dysfunction. As observed by staining, isoleucine restriction inhibits HFD-induced neuronal damage and microglia activation. Furthermore, isoleucine restriction significantly increases the relative abundance of gut microbiota, decreases the proportion of Proteobacteria, and reduces the levels of lipopolysaccharide (LPS) in serum and brain. Isoleucine restriction reduces protein expression of TLR4/MyD88/NF-κB signaling pathway and inhibits upregulation of proinflammatory cytokine genes and protein expression in mice brain. In addition, isoleucine restriction significantly improves insulin resistance in the brain as well as synaptic plasticity impairment.

CONCLUSION

Isoleucine restriction may be a potential intervention to reduce HFD-induced cognitive impairment by altering gut microbiota, reducing neuroinflammation, insulin resistance, and improving synaptic plasticity in mice brain.

The contradictory role of branched-chain amino acids in lifespan and insulin resistance

Branched-chain amino acids (BCAAs; a mixture of leucine, valine and isoleucine) have important regulatory effects on glucose and lipid metabolism, protein synthesis and longevity. Many studies have reported that circulating BCAA levels or dietary intake of BCAAs is associated with longevity, sarcopenia, obesity, and diabetes. Among them, the influence of BCAAs on aging and insulin resistance often present different benefits or harmful effects in the elderly and in animals. Considering the nonobvious correlation between circulating BCAA levels and BCAA uptake, as well as the influence of diseases, diet and aging on the body, some of the contradictory conclusions have been drawn. The regulatory mechanism of the remaining contradictory role may be related to endogenous branched-chain amino acid levels, branched-chain amino acid metabolism and mTOR-related autophagy. Furthermore, the recent discovery that insulin resistance may be independent of longevity has expanded the research thinking related to the regulatory mechanism among the three. However, the negative effects of BCAAs on longevity and insulin resistance were mostly observed in high-fat diet-fed subjects or obese individuals, while the effects in other diseases still need to be studied further. In conclusion, there is still no definite conclusion on the specific conditions under which BCAAs and insulin resistance extend life, shorten life, or do not change lifespan, and there is still no credible and comprehensive explanation for the different effects of BCAAs and insulin resistance on lifespan.

Leucine supplementation in maternal high-fat diet alleviated adiposity and glucose intolerance of adult mice offspring fed a postweaning high-fat diet

BACKGROUND

Combined maternal and postnatal high-fat (HF) diet intake predisposes offspring to metabolic dysregulation during adulthood. As the inhibitory effects of leucine consumption on obesity and metabolic disorders have been reported, the effects of maternal leucine supplementation on metabolic dysregulation in adult offspring were investigated.

METHODS

Female mice were exposed to a control (C) or HF diet, with or without leucine (L) supplementation (1.5%, w/v), 3 weeks before mating, during pregnancy, and during lactation (C, CL, HF, and HFL). Male offspring were exposed to an HF diet for 12 weeks after weaning (C/HF, CL/HF, HF/HF, and HFL/HF). Serum biochemical parameters were determined for both the dams and offspring. Oral glucose tolerance test and qRT-PCR analysis were used to investigate metabolic dysregulation in the offspring.

RESULTS

HFL dams exhibited higher relative adipose tissue weights than HF dams. Body weight, relative adipose tissue weight, and serum glucose levels were lower in the HFL/HF offspring than in the HF/HF offspring. Maternal leucine supplementation tended to alleviate glucose intolerance in the offspring of HF diet-fed dams. Additionally, mRNA levels of fibroblast growth factor 21 (FGF21), a hepatokine associated with glucose homeostasis, were higher in HFL/HF offspring than in HF/HF offspring and were negatively correlated with adiposity and serum glucose levels. The mRNA levels of genes encoding a FGF21 receptor complex, Fgf receptor 1 and klotho β, and its downstream targets, proliferator-activated receptor-γ co-activator 1α and sirtuin 1, were higher in adipose tissues of the HFL/HF offspring than in those of the HF/HF offspring. Serum lipid peroxide levels were lower in HFL dams than in HF dams and positively correlated with body and adipose tissue weights of offspring.

CONCLUSIONS

Leucine supplementation in HF diet-fed dams, but not in control diet-fed dams, resulted in an anti-obesity phenotype accompanied by glucose homeostasis in male offspring challenged with postnatal HF feeding. Activation of FGF21 signaling in the adipose tissue of offspring may be responsible for these beneficial effects of leucine.

Short-term exposure to an obesogenic diet causes dynamic dysregulation of proteasome-mediated protein degradation in the hypothalamus of female rats

OBJECTIVES

Previous work has shown that exposure to a high fat diet dysregulates the protein degradation process in the hypothalamus of male rodents. However, whether this occurs in a sex-independent manner is unknown. The objective of this study was to determine the effects of a short-term obesogenic diet on the ubiquitin-proteasome mediated protein degradation process in the hypothalamus of female rats.

METHODS

We fed young adult female rats a high fat diet or standard rat chow for 7 weeks. At the end of the 7th week, animals were euthanized and hypothalamus nuclear and cytoplasmic fractions were collected. Proteasome activity and degradation-specific (K48) ubiquitin signaling were assessed. Additionally, we transfected female rats with CRISPR-dCas9-VP64 plasmids in the hypothalamus prior to exposure to the high fat diet in order to increase proteasome activity and determine the role of reduced proteasome function on weight gain from the obesogenic diet.

RESULTS

We found that across the diet period, females gained weight significantly faster on the high fat diet than controls and showed dynamic downregulation of proteasome activity, decreases in proteasome subunit expression and an accumulation of degradation-specific K48 polyubiquitinated proteins in the hypothalamus. Notably, while our CRISPR-dCas9 manipulation was able to selectively increase some forms of proteasome activity, it was unable to prevent diet-induced proteasome downregulation or abnormal weight gain.

CONCLUSIONS

Collectively, these results reveal that acute exposure to an obesogenic diet causes reductions in the protein degradation process in the hypothalamus of females.

Female and male C57BL/6J offspring exposed to maternal obesogenic diet develop altered hypothalamic energy metabolism in adulthood

Maternal obesity is exceedingly common and strongly linked to offspring obesity and metabolic disease. Hypothalamic function is critical to obesity development. Hypothalamic mechanisms causing obesity following exposure to maternal obesity have not been elucidated. Therefore, we studied a cohort of C57BL/6J dams, treated with a control or high-fat-high-sugar diet, and their adult offspring to explore potential hypothalamic mechanisms to explain the link between maternal and offspring obesity. Dams treated with obesogenic diet were heavier with mild insulin resistance, which is reflective of the most common metabolic disease in pregnancy. Adult offspring exposed to maternal obesogenic diet had no change in body weight but significant increase in fat mass, decreased glucose tolerance, decreased insulin sensitivity, elevated plasma leptin, and elevated plasma thyroid-stimulating hormone. In addition, offspring exposed to maternal obesity had decreased energy intake and activity without change in basal metabolic rate. Hypothalamic neurochemical profile and transcriptome demonstrated decreased neuronal activity and inhibition of oxidative phosphorylation. Collectively, these results indicate that maternal obesity without diabetes is associated with adiposity and decreased hypothalamic energy production in offspring. We hypothesize that altered hypothalamic function significantly contributes to obesity development. Future studies focused on neuroprotective strategies aimed to improve hypothalamic function may decrease obesity development.NEW & NOTEWORTHY Offspring exposed to maternal diet-induced obesity demonstrate a phenotype consistent with energy excess. Contrary to previous studies, the observed energy phenotype was not associated with hyperphagia or decreased basal metabolic rate but rather decreased hypothalamic neuronal activity and energy production. This was supported by neurochemical changes in the hypothalamus as well as inhibition of hypothalamic oxidative phosphorylation pathway. These results highlight the potential for neuroprotective interventions in the prevention of obesity with fetal origins.

ERα-Dependent Regulation of Adropin Predicts Sex Differences in Liver Homeostasis during High-Fat Diet

Non-alcoholic fatty liver disease (NAFLD) represents a public health issue, due to its prevalence and association with other cardiometabolic diseases. Growing evidence suggests that NAFLD alters the production of hepatokines, which, in turn, influence several metabolic processes. Despite accumulating evidence on the major role of estrogen signaling in the sexually dimorphic nature of NAFLD, dependency of hepatokine expression on sex and estrogens has been poorly investigated. Through in vitro and in vivo analysis, we determined the extent to which hepatokines, known to be altered in NAFLD, can be regulated, in a sex-specific fashion, under different hormonal and nutritional conditions. Our study identified four hepatokines that better recapitulate sex and estrogen dependency. Among them, adropin resulted as one that displays a sex-specific and estrogen receptor alpha (ERα)-dependent regulation in the liver of mice under an excess of dietary lipids (high-fat diet, HFD). Under HFD conditions, the hepatic induction of adropin negatively correlates with the expression of lipogenic genes and with fatty liver in female mice, an effect that depends upon hepatic ERα. Our findings support the idea that ERα-mediated induction of adropin might represent a potential approach to limit or prevent NAFLD.

Mechanisms mediating the impact of maternal obesity on offspring hypothalamic development and later function

As obesity rates have risen around the world, so to have pregnancies complicated by maternal obesity. Obesity during pregnancy is not only associated with negative health outcomes for the mother and the baby during pregnancy and birth, there is also strong evidence that exposure to maternal obesity causes an increased risk to develop obesity, diabetes and cardiovascular disease later in life. Animal models have demonstrated that increased weight gain in offspring exposed to maternal obesity is usually preceded by increased food intake, implicating altered neuronal control of food intake as a likely area of change. The hypothalamus is the primary site in the brain for maintaining energy homeostasis, which it coordinates by sensing whole body nutrient status and appropriately adjusting parameters including food intake. The development of the hypothalamus is plastic and regulated by metabolic hormones such as leptin, ghrelin and insulin, making it vulnerable to disruption in an obese in utero environment. This review will summarise how the hypothalamus develops, how maternal obesity impacts on structure and function of the hypothalamus in the offspring, and the factors that are altered in an obese in utero environment that may mediate the permanent changes to hypothalamic function in exposed individuals.

The Role of Elevated Branched-Chain Amino Acids in the Effects of Vertical Sleeve Gastrectomy to Reduce Weight and Improve Glucose Regulation

Elevated levels of branched-chain amino acids (BCAAs) and their metabolites are strongly positively associated with obesity, insulin resistance, and type 2 diabetes. Bariatric surgery is among the best treatments for weight loss and associated morbidities. Clinical studies have reported that bariatric surgery decreases the circulating levels of BCAAs. The objective of this study was to test the hypothesis that reduced BCAA levels contribute to the metabolic improvements of sustained weight loss and improved glucose tolerance after vertical sleeve gastrectomy (VSG). We find that, as in humans, circulating BCAAs are significantly lower in VSG rats and mice. To increase circulating BCAAs, we tested mice with either increased dietary intake of BCAAs or impaired BCAA catabolism by total body deletion of mitochondrial phosphatase 2C (Pp2cm). Our results show that a decrease in circulating BCAAs is not necessary for sustained body weight loss and improved glucose tolerance after VSG.

Increased branched-chain amino acid (BCAA) levels are biomarkers of metabolic disease, and bariatric surgeries reduce BCAA levels. Bozadjieva Kramer et al. show that both dietary and genetic manipulations can block the surgical effect on BCAAs but do not alter potent, beneficial effects on weight loss and glucose tolerance.

Mechanistic insight into high-fat diet-induced metabolic inflammation in the arcuate nucleus of the hypothalamus

A high-fat diet (HFD) is linked with cytokines production by non-neuronal cells within the hypothalamus, which mediates metabolic inflammation. These cytokines then activate different inflammatory mediators in the arcuate nucleus of the hypothalamus (ARC), a primary hypothalamic area accommodating proopiomelanocortin (POMC) and agouti-related peptide (AGRP) neurons, first-order neurons that sense and integrate peripheral metabolic signals and then respond accordingly. These mediators, such as inhibitor of κB kinase-β (IKKβ), suppression of cytokine signaling 3 (SOCS3), c-Jun N-terminal kinases (JNKs), protein kinase C (PKC), etc., cause insulin and leptin resistance in POMC and AGRP neurons and support obesity and related metabolic complications. On the other hand, inhibition of these mediators has been shown to counteract the impaired metabolism. Therefore, it is important to discuss the contribution of neuronal and non-neuronal cells in HFD-induced hypothalamic inflammation. Furthermore, understanding few other questions, such as the diets causing hypothalamic inflammation, the gender disparity in response to HFD feeding, and how hypothalamic inflammation affects ARC neurons to cause impaired metabolism, will be helpful for the development of therapeutic approaches to prevent or treat HFD-induced obesity.

Maternal High-Fat-High-Carbohydrate Diet-Induced Obesity Is Associated with Increased Appetite in Peripubertal Male but Not Female C57Bl/6J Mice

Diet-induced maternal obesity might play a critical role in altering hypothalamic development, predisposing the offspring to obesity and metabolic disease later in life. The objective of this study was to describe both phenotypic and molecular sex differences in peripubertal offspring energy homeostasis, using a mouse model of maternal obesity induced by a high-fat-high-carbohydrate (HFHC) diet. We report that males, not females, exposed to a maternal HFHC diet had increased energy intake. Males exposed to a maternal HFHC diet had a 15% increased meal size and a 46% increased frequency, compared to the control (CON) males, without a change in energy expenditure. CON and HFHC offspring did not differ in body weight, composition, or plasma metabolic profile. HFHC diet caused decreased hypothalamic glucocorticoid expression, which was further decreased in males compared to females. Maternal weight, maternal caloric intake, and male offspring meal frequency were inversely correlated with offspring hypothalamic insulin receptor (IR) expression. There was a significant interaction between maternal-diet exposure and sex in hypothalamic IR. Based on our preclinical data, we suggest that interventions focusing on normalizing maternal nutrition might be considered to attenuate nutritional influences on obesity programming and curb the continuing rise in obesity rates.