Leptin and the Blood-Brain Barrier: Curiosities and Controversies

Maternal high fat diet programs spatial learning and central leptin signaling in mouse offspring in a sex-specific manner

Environmental factors in early life have been demonstrated to increase the risk of neurodevelopmental disorders in offspring, especially the deficiency of the cognitive ability. Leptin has emerged as a key hormone that conveys information on energy stores, but there is growing appreciation that leptin signaling may also play an important role in neurodevelopment. The present study aimed to investigate whether maternal HFD exposure impairs the offspring learning and memory through the programming of central leptin system. We observed that hippocampus-dependent learning and memory were impaired in male but not female offspring from HFD-fed maternal ancestors (C57BL/6 mice), as assessed by novel object recognition and Morris water maze tests. Moreover, the chromatin immunoprecipitation results revealed the maternal HFD consumption led to the increasement in the binding of the histone marker H3K9me3 in male offspring, which mediates gene silencing in the leptin receptor promoter region. Furthermore, there was an increase in the expression of the histone methylase SUV39H1 in male but not female offspring, which regulates H3K9me3. Additionally, it has been observed that IL-6 and IL-1 also could lead to similar alternations when acting on cultured hippocampal neurons in vitro. Taken together, our data suggest that maternal HFD consumption influences male offspring hippocampal cognitive performance in a sex-specific manner, and central leptin signaling may serve as the cross-talk between maternal diet and cognitive impairment in offspring.

AZGP1 in POMC neurons modulates energy homeostasis and metabolism through leptin-mediated STAT3 phosphorylation

Zinc-alpha2-glycoprotein (AZGP1) has been implicated in peripheral metabolism; however, its role in regulating energy metabolism in the brain, particularly in POMC neurons, remains unknown. Here, we show that AZGP1 in POMC neurons plays a crucial role in controlling whole-body metabolism. POMC neuron-specific overexpression of Azgp1 under high-fat diet conditions reduces energy intake, raises energy expenditure, elevates peripheral tissue leptin and insulin sensitivity, alleviates liver steatosis, and promotes adipose tissue browning. Conversely, mice with inducible deletion of Azgp1 in POMC neurons exhibit the opposite metabolic phenotypes, showing increased susceptibility to diet-induced obesity. Notably, an increase in AZGP1 signaling in the hypothalamus elevates STAT3 phosphorylation and increases POMC neuron excitability. Mechanistically, AZGP1 enhances leptin-JAK2-STAT3 signaling by interacting with acylglycerol kinase (AGK) to block its ubiquitination degradation. Collectively, these results suggest that AZGP1 plays a crucial role in regulating energy homeostasis and glucose/lipid metabolism by acting on hypothalamic POMC neurons.

ANMCO (Italian Association of Hospital Cardiologists) scientific statement: obesity in adults-an approach for cardiologists

Obesity is a complex, chronic disease requiring a multidisciplinary approach to its management. In clinical practice, body mass index and waist-related measurements can be used for obesity screening. The estimated prevalence of obesity among adults worldwide is 12%. With the expected further increase in overall obesity prevalence, clinicians will increasingly be managing patients with obesity. Energy balance is regulated by a complex neurohumoral system that involves the central nervous system and circulating mediators, among which leptin is the most studied. The functioning of these systems is influenced by both genetic and environmental factors. Obesity generally occurs when a genetically predisposed individual lives in an obesogenic environment for a long period. Cardiologists are deeply involved in evaluating patients with obesity. Cardiovascular risk profile is one of the most important items to be quantified to understand the health risk due to obesity and the clinical benefit that a single patient can obtain with weight loss. At the individual level, appropriate patient involvement, the detection of potential obesity causes, and a multidisciplinary approach are tools that can improve clinical outcomes. In the near future, we will probably have new pharmacological tools at our disposal that will facilitate achieving and maintaining weight loss. However, pharmacological treatment alone cannot cure such a complex disease. The aim of this paper is to summarize some key points of this field, such as obesity definition and measurement tools, its epidemiology, the main mechanisms underlying energy homeostasis, health consequences of obesity with a focus on cardiovascular diseases and the obesity paradox.Level of evidence V: report of expert committees.

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

A critical update on the leptin-melanocortin system

The discovery of leptin in 1994 was an "eureka moment" in the field of neurometabolism that provided new opportunities to better understand the central control of energy balance and glucose metabolism. Rapidly, a prevalent model in the field emerged that pro-opiomelanocortin (POMC) neurons were key in promoting leptin's anorexigenic effects and that the arcuate nucleus of the hypothalamus (ARC) was a key region for the regulation of energy homeostasis. While this model inspired many important discoveries, a growing body of literature indicates that this model is now outdated. In this review, we re-evaluate the hypothalamic leptin-melanocortin model in light of recent advances that directly tackle previous assumptions, with a particular focus on the ARC. We discuss how segregated and heterogeneous these neurons are, and examine how the development of modern approaches allowing spatiotemporal, intersectional, and chemogenetic manipulations of melanocortin neurons has allowed a better definition of the complexity of the leptin-melanocortin system. We review the importance of leptin in regulating glucose homeostasis, but not food intake, through direct actions on ARC POMC neurons. We further highlight how non-POMC, GABAergic neurons mediate leptin's direct effects on energy balance and influence POMC neurons.

Regional specific effect of saturated vs unsaturated fat on leptin receptor signalling in mice brain areas regulating feeding

Leptin receptors (LepR) are expressed in brain areas controlling food intake homeostasis, such as the hypothalamus, the hippocampus and the prefrontal cortex. In a previous study we reported that long-term intake of saturated and monounsaturated fat alters hypothalamic LepR signalling. The current study aims at investigating the effect of foods high in either saturated (SOLF) or monounsaturated fat (UOLF) on LepR functionality in the hippocampus and the prefrontal cortex. Male mice were placed on SOLF/UOLF (eight weeks), then treated with recombinant murine leptin (1 mg/kg). After 60 min, brain regions were dissected and processed for western blot of phosphorylated STAT3 (pSTAT3), Akt (pAkt) and AMPK (pAMPK). Levels of SOCS3 were also quantified. SOLF itself increased basal levels of pSTAT3, while UOLF impaired leptin-induced phosphorylation of both Akt and AMPK. SOCS3 levels were specifically increased by UOLF within the prefrontal cortex. Our results show that SOLF and UOLF differently affect LepR signalling within the hippocampus and the prefrontal cortex, which points to the complex effect of saturated and unsaturated fat on brain function, particularly in areas regulating food intake.

Gene Polymorphisms of Hormonal Regulators of Metabolism in Patients with Schizophrenia with Metabolic Syndrome

Background: Metabolic syndrome (MetS) is a common complication of long-term treatment of persons with schizophrenia taking (atypical) antipsychotics. In this study, we investigated the existence of an association with polymorphisms of genes for four hormones that regulate energy metabolism. Methods: We recruited 517 clinically admitted white patients (269M/248F) with a verified diagnosis of schizophrenia (ICD-10) and with a stable physical condition. Participants were classified for having or not having MetS and genotyped for 20 single-nucleotide polymorphisms (SNPs) in the genes encoding insulin-induced gene 2 (INSIG2), ghrelin (GHRL), leptin (LEP), and leptin receptor (LEPR). Results: The 139 patients (26.9%) with MetS were significantly more likely to be women, older, and ill longer, and had a larger body mass index (BMI). Four polymorphisms (rs10490624, rs17587100, rs9308762, and rs10490816) did not meet the Hardy–Weinberg equilibrium (HWE) criterion and were excluded. Only genotypes and alleles of the rs3828942 of LEP gene (chi2 = 7.665, p = 0.022; chi2 = 5.136, p = 0.023) and the genotypes of the rs17047718 of INSIG2 gene (chi2 = 7.7, p = 0.021) had a significant association with MetS. Conclusions: The results of our study suggest that the LEP and INSIG2 genes play a certain causal role in the development of MetS in patients with schizophrenia.

Dietary lipids from body to brain

Dietary habits have drastically changed over the last decades in Western societies. The Western diet, rich in saturated fatty acids (SFA), trans fatty acids (TFA), omega-6 polyunsaturated fatty acids (n-6 PUFA) and cholesterol, is accepted as an important factor in the development of metabolic disorders, such as obesity and diabetes type 2. Alongside these diseases, nutrition is associated with the prevalence of brain disorders. Although clinical and epidemiological studies revealed that metabolic diseases and brain disorders might be related, the underlying pathology is multifactorial, making it hard to determine causal links. Neuroinflammation can be a result of unhealthy diets that may cause alterations in peripheral metabolism. Especially, dietary fatty acids are of interest, as they act as signalling molecules responsible for inflammatory processes. Diets rich in n-6 PUFA, SFA and TFA increase neuroinflammation, whereas diets rich in monounsaturated fatty acids (MUFA), omega-3 (n-3) PUFA and sphingolipids (SL) can diminish neuroinflammation. Moreover, these pro- and anti-inflammatory diets might indirectly influence neuroinflammation via the adipose tissue, microbiome, intestine and vasculature. Here, we review the impact of nutrition on brain health. In particular, we will discuss the role of dietary lipids in signalling pathways directly applicable to inflammation and neuronal function.