PI3K signaling: A key pathway in the control of sympathetic traffic and arterial pressure by leptin

Leptin and Associated Neural Pathways Underlying Obesity-Induced Hypertension

Obesity rates have surged to pandemic levels, placing tremendous burden on our society. This chronic and complex disease is related to the development of many life-threatening illnesses including cardiovascular diseases. Hypertension caused by obesity increases the risk for cardiovascular mortality and morbidity by promoting stroke, myocardial infarction, congestive heart failure, and end-stage renal disease. Overwhelming evidence supports neural origins for obesity-induced hypertension and pinpoints the adipose-derived hormone, leptin, and the sympathetic nervous system as major causal factors. Hyperleptinemia in obesity is associated with selective leptin resistance where leptin's renal sympathoexcitatory and pressor effects are preserved while the metabolic actions are impaired. Understanding the mechanisms driving this phenomenon is critical for developing effective therapeutics. This review describes the neural mechanisms of obesity-induced hypertension with a focus on the molecular and neuronal substrates of leptin action.

Rheumatic diseases and metabolism: where centre and periphery meet

Over the past few decades, the connection between metabolism and various inflammatory and rheumatic diseases has been an area of active investigation. Nonetheless, the precise mechanisms underlying these relationships remain a topic of ongoing debate, owing in part to conflicting data. This discrepancy can be attributed to the predominant focus on peripheral mechanisms in research into the metabolic consequences of rheumatic diseases. However, a wealth of evidence supports the notion that the central nervous system, specifically the hypothalamus, has an important influence on metabolic homeostasis. Notably, links have been established between crucial hypothalamic mechanisms responsible for regulating energy balance (including food intake, thermogenesis, and glucose and lipid metabolism), such as AMP-activated protein kinase, and the pathophysiology of rheumatoid arthritis. This Review aims to comprehensively examine the current understanding of central metabolic control in rheumatic diseases and explore potential therapeutic options that target this pathophysiological mechanism.

Unveiling the intricate dance: Obesity and TNBC connection examined

Amid the dynamic field of cancer research, various targeted therapies have proven crucial in combating breast cancer, the most prevalent cancer among women globally. Triple Negative Breast Cancer (TNBC) stands out from other types of breast cancer due to the absence of three key receptors on the cell surface (progesterone, estrogen, and HER2). Researchers are working on finding ways to address TNBC's elusive biomarkers and minimize the damage caused by the disease through treatments like chemotherapies and targeted pathway receptors. One connection that should receive more attention is the link between TNBC and obesity. Obesity is defined as consuming significantly more energy than is expended, resulting in a high BMI. Moreover, obesity fosters a cancer-friendly environment characterized by inflammation, elevated levels of hormones, proteins, and signaling that activate pathways promoting cancer. Non-Hispanic black women have experienced notable disparities in TNBC rates. Various factors have led to the higher incidence and poorer outcomes of TNBC in non-Hispanic black women. This detailed review explores the complex relationship between obesity and TNBC, examining how the two disorders are connected in terms of disparities and offering a glimpse into future research and interventions.

New Insights into Adiponectin and Leptin Roles in Chronic Kidney Disease

Chronic kidney disease (CKD) is commonly associated with a high burden of comorbidities and poor clinical outcomes. Malnutrition–inflammation–atherosclerosis syndrome is common in the more severe stages of CKD, suggesting a close interplay for these three comorbid conditions. Both malnutrition and obesity are associated with a disturbed adipokine profile and inflammation, contributing to a higher risk of cardiovascular disease (CVD) events. Adiponectin and leptin have important roles in carbohydrate and lipid metabolism, and in the inflammatory process. The effects of adiponectin and leptin alterations in CKD, which are usually increased, and their association with the different comorbidities found in CKD, will be focused on to understand their crosstalk with the risk of CVD events. Nonetheless, although adiponectin and leptin contribute to a higher risk of CVD events, further studies are warranted to fully clarify their roles, especially when different comorbidities exist.

Relationship between Leptin and Insulin Resistance among Community-Dwelling Middle-Aged and Elderly Populations in Taiwan

The relationship between leptin and insulin resistance among middle-aged and elderly populations in Asia is seldom reported. Our research included 398 middle-aged and elderly Taiwanese individuals. First, we divided participants into three groups according to the tertiles of the homeostasis model assessment of insulin resistance (HOMA-IR) to analyze the parameters between each group. Pearson’s correlation was then applied to calculate the correlation between HOMA-IR and cardiometabolic risk factors after adjusting for age. A scatter plot indicated a relationship between serum leptin levels and the HOMA-IR index. Finally, the coefficients of the serum leptin level and HOMA-IR were assessed by multivariate linear regression. The participants in the high HOMA-IR index group were more likely to have higher serum leptin levels. Meanwhile, the HOMA-IR index was positively correlated with serum leptin levels, even after adjusting for age. Serum leptin levels were positively correlated with the HOMA-IR index (β = 0.226, p < 0.01) in the multivariate linear regression after adjusting for age, sex, smoking, drinking, BMI, triglycerides, systolic blood pressure, fasting plasma glucose, uric acid, ALT, and creatinine. Furthermore, the leptin−creatinine ratio also showed a significantly positive relationship with HOMA-IR in the same multivariate linear regression model. In conclusion, serum leptin levels showed a positive relationship with insulin resistance in middle-aged and elderly people in Taiwan. Furthermore, serum leptin levels may be an independent risk factor for insulin resistance according to our study.

Prenatal inflammation exposure-programmed hypertension exhibits multi-generational inheritance via disrupting DNA methylome

The multi-generation heredity trait of hypertension in human has been reported, but the molecular mechanisms underlying multi-generational inheritance of hypertension remain obscure. Recent evidence shows that prenatal inflammatory exposure (PIE) results in increased incidence of cardiovascular diseases, including hypertension. In this study we investigated whether and how PIE contributed to multi-generational inheritance of hypertension in rats. PIE was induced in pregnant rats by intraperitoneal injection of LPS or Poly (I:C) either once on gestational day 10.5 (transient stimulation, T) or three times on gestational day 8.5, 10.5, and 12.5 (persistent stimulation, P). Male offspring was chosen to study the paternal inheritance. We showed that PIE, irrespectively induced by LPS or Poly (I:C) stimulation during pregnancy, resulted in multi-generational inheritance of significantly increased blood pressure in rat descendants, and that prenatal LPS exposure led to vascular remodeling and vasoconstrictor dysfunction in both thoracic aorta and superior mesenteric artery of adult F2 offspring. Furthermore, we revealed that PIE resulted in global alteration of DNA methylome in thoracic aorta of F2 offspring. Specifically, PIE led to the DNA hypomethylation of G beta gamma (Gβγ) signaling genes in both the F1 sperm and the F2 thoracic aorta, and activation of PI3K/Akt signaling was implicated in the pathologic changes and dysregulated vascular tone of aortic tissue in F2 LPS-P offspring. Our data demonstrate that PIE reprogrammed DNA methylome of cells from the germline/mature gametes contributes to the development of hypertension in F2 PIE offspring. This study broadens the current knowledge regarding the multi-generation effect of the cumulative early life environmental factors on the development of hypertension.

Leptin and Obesity: Role and Clinical Implication

The peptide hormone leptin regulates food intake, body mass, and reproductive function and plays a role in fetal growth, proinflammatory immune responses, angiogenesis and lipolysis. Leptin is a product of the obese (ob) gene and, following synthesis and secretion from fat cells in white adipose tissue, binds to and activates its cognate receptor, the leptin receptor (LEP-R). LEP-R distribution facilitates leptin's pleiotropic effects, playing a crucial role in regulating body mass via a negative feedback mechanism between adipose tissue and the hypothalamus. Leptin resistance is characterized by reduced satiety, over-consumption of nutrients, and increased total body mass. Often this leads to obesity, which reduces the effectiveness of using exogenous leptin as a therapeutic agent. Thus, combining leptin therapies with leptin sensitizers may help overcome such resistance and, consequently, obesity. This review examines recent data obtained from human and animal studies related to leptin, its role in obesity, and its usefulness in obesity treatment.

Reprint of: Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Factors Responsible for Obesity-Related Hypertension

PURPOSE OF REVIEW

The major health issue of being overweight or obese relates to the development of hypertension, insulin resistance and diabetic complications. One of the major underlying factors influencing the elevated blood pressure in obesity is increased activity of the sympathetic nerves to particular organs such as the kidney.

RECENT FINDINGS

There is now convincing evidence from animal studies that major signals such as leptin and insulin have a sympathoexcitatory action in the hypothalamus to cause hypertension. Recent studies suggest that this may involve 'neural plasticity' within hypothalamic signalling driven by central actions of leptin mediated via activation of melanocortin receptor signalling and activation of brain neurotrophic factors. This review describes the evidence to support the contribution of the SNS to obesity related hypertension and the major metabolic and adipokine signals.

Traveling from the hypothalamus to the adipose tissue: The thermogenic pathway

Brown adipose tissue (BAT) is a specialized tissue critical for non-shivering thermogenesis producing heat through mitochondrial uncoupling; whereas white adipose tissue (WAT) is responsible of energy storage in the form of triglycerides. Another type of fat has been described, the beige adipose tissue; this tissue emerges in existing WAT depots but with thermogenic ability, a phenomenon known as browning. Several peripheral signals relaying information about energy status act in the brain, particularly the hypothalamus, to regulate thermogenesis in BAT and browning of WAT. Different hypothalamic areas have the capacity to regulate the thermogenic process in brown and beige adipocytes through the sympathetic nervous system (SNS). This review discusses important concepts and discoveries about the central control of thermogenesis as a trip that starts in the hypothalamus, and taking the sympathetic roads to reach brown and beige fat to modulate thermogenic functions.

Pathophysiology and Potential Non-Pharmacologic Treatments of Obesity or Kidney Disease Associated Refractory Hypertension

PURPOSE OF REVIEW

The review assesses the role of non-pharmacologic therapy for obesity and chronic kidney disease (CKD) associated refractory hypertension (rf HTN).

RECENT FINDINGS

Hypertensive patients with markedly heightened sympathetic nervous system (SNS) activity are prone to develop refractory hypertension (rfHTN). Patients with obesity and chronic kidney disease (CKD)-associated HTN have particularly heightened SNS activity and are at high risk of rfHTN. The role of bariatric surgery is increasingly recognized in treatment of obesity. Current evidence advocates for a greater role of bariatric surgery in the management of obesity-associated HTN. In contrast, renal denervation does not appear have a role in the management of obesity or CKD-associated HTN. The role of baroreflex activation as adjunctive anti-hypertensive therapy remains to be defined.

Leptin as a Mediator of Obesity-Induced Hypertension

Hypertension and associated cardiovascular diseases represent the most common health complication of obesity and the leading cause of morbidity and mortality in overweight and obese patients. Emerging evidence suggests a critical role for the central nervous system particularly the brain action of the adipocyte-derived hormone leptin in linking obesity and hypertension. The preserved ability of leptin to cause cardiovascular sympathetic nerve activation despite the resistance to the metabolic actions of the hormone appears essential in this pathological process. This review describes the evidence supporting the neurogenic bases for obesity-associated hypertension with a particular focus on the neuronal and molecular signaling pathways underlying leptin's effects on sympathetic nerve activity and blood pressure.

Facilitation of breathing by leptin effects in the central nervous system

With the global epidemic of obesity, breathing disorders associated with excess body weight have markedly increased. Respiratory dysfunctions caused by obesity were originally attributed to mechanical factors; however, recent studies have suggested a pathophysiological component that involves the central nervous system (CNS) and hormones such as leptin produced by adipocytes as well as other cells. Leptin is suggested to stimulate breathing and leptin deficiency causes an impairment of the chemoreflex, which can be reverted by leptin therapy. This facilitation of the chemoreflex may depend on the action of leptin in the hindbrain areas involved in the respiratory control such as the nucleus of the solitary tract (NTS), a site that receives chemosensory afferents, and the ventral surface of the medulla that includes the retrotrapezoid nucleus (RTN), a central chemosensitive area, and the rostral ventrolateral medulla (RVLM). Although the mechanisms and pathways activated by leptin to facilitate breathing are still not completely clear, evidence suggests that the facilitatory effects of leptin on breathing require the brain melanocortin system, including the POMC-MC4R pathway, a mechanism also activated by leptin to modulate blood pressure. The results of all the studies that have investigated the effect of leptin on breathing suggest that disruption of leptin signalling as caused by obesity-induced reduction of central leptin function (leptin resistance) is a relevant mechanism that may contribute to respiratory dysfunctions associated with obesity.

Long-Lived αMUPA Mice Show Attenuation of Cardiac Aging and Leptin-Dependent Cardioprotection

αMUPA transgenic mice spontaneously consume less food compared with their wild type (WT) ancestors due to endogenously increased levels of the satiety hormone leptin. αMUPA mice share many benefits with mice under caloric restriction (CR) including an extended life span. To understand mechanisms linked to cardiac aging, we explored the response of αMUPA hearts to ischemic conditions at the age of 6, 18, or 24 months. Mice were subjected to myocardial infarction (MI) in vivo and to ischemia/reperfusion ex vivo. Compared to WT mice, αMUPA showed functional and histological advantages under all experimental conditions. At 24 months, none of the WT mice survived the first ischemic day while αMUPA mice demonstrated 50% survival after 7 ischemic days. Leptin, an adipokine decreasing under CR, was consistently ~60% higher in αMUPA sera at baseline. Leptin levels gradually increased in both genotypes 24h post MI but were doubled in αMUPA. Pretreatment with leptin neutralizing antibodies or with inhibitors of leptin signaling (AG-490 and Wortmannin) abrogated the αMUPA benefits. The antibodies also reduced phosphorylation of the leptin signaling components STAT3 and AKT specifically in the αMUPA myocardium. αMUPA mice did not show elevation in adiponectin, an adipokine previously implicated in CR-induced cardioprotection. WT mice treated for short-term CR exhibited cardioprotection similar to that of αMUPA, however, along with increased adiponectin at baseline. Collectively, the results demonstrate a life-long increased ischemic tolerance in αMUPA mice, indicating the attenuation of cardiac aging. αMUPA cardioprotection is mediated through endogenous leptin, suggesting a protective pathway distinct from that elicited under CR.

Hypothalamic-autonomic control of energy homeostasis

Regulation of energy homeostasis is tightly controlled by the central nervous system (CNS). Several key areas such as the hypothalamus and brainstem receive and integrate signals conveying energy status from the periphery, such as leptin, thyroid hormones, and insulin, ultimately leading to modulation of food intake, energy expenditure (EE), and peripheral metabolism. The autonomic nervous system (ANS) plays a key role in the response to such signals, innervating peripheral metabolic tissues, including brown and white adipose tissue (BAT and WAT), liver, pancreas, and skeletal muscle. The ANS consists of two parts, the sympathetic and parasympathetic nervous systems (SNS and PSNS). The SNS regulates BAT thermogenesis and EE, controlled by central areas such as the preoptic area (POA) and the ventromedial, dorsomedial, and arcuate hypothalamic nuclei (VMH, DMH, and ARC). The SNS also regulates lipid metabolism in WAT, controlled by the lateral hypothalamic area (LHA), VMH, and ARC. Control of hepatic glucose production and pancreatic insulin secretion also involves the LHA, VMH, and ARC as well as the dorsal vagal complex (DVC), via splanchnic sympathetic and the vagal parasympathetic nerves. Muscle glucose uptake is also controlled by the SNS via hypothalamic nuclei such as the VMH. There is recent evidence of novel pathways connecting the CNS and ANS. These include the hypothalamic AMP-activated protein kinase-SNS-BAT axis which has been demonstrated to be a key modulator of thermogenesis. In this review, we summarize current knowledge of the role of the ANS in the modulation of energy balance.

Dual action of leptin on rest-firing and stimulated catecholamine release via phosphoinositide 3-kinase-driven BK channel up-regulation in mouse chromaffin cells

KEY POINTS

Leptin is an adipokine produced by the adipose tissue regulating body weight through its appetite-suppressing effect and, as such, exerts a relevant action on the adipo-adrenal axis. Leptin has a dual action on adrenal mouse chromaffin cells both at rest and during stimulation. At rest, the adipokine inhibits the spontaneous firing of most cells by enhancing the probability of BK channel opening through the phosphoinositide 3-kinase signalling cascade. This inhibitory effect is absent in db(-) /db(-) mice deprived of Ob receptors. During sustained stimulation, leptin preserves cell excitability by generating well-adapted action potential (AP) trains of lower frequency and broader width and increases catecholamine secretion by increasing the size of the ready-releasable pool and the rate of vesicle release. In conclusion, leptin dampens AP firing at rest but preserves AP firing and enhances catecholamine release during sustained stimulation, highlighting the importance of the adipo-adrenal axis in the leptin-mediated increase of sympathetic tone and catecholamine release.

ABSTRACT

Leptin is an adipokine produced by the adipose tissue regulating body weight through its appetite-suppressing effect. Besides being expressed in the hypothalamus and hippocampus, leptin receptors (ObRs) are also present in chromaffin cells of the adrenal medulla. In the present study, we report the effect of leptin on mouse chromaffin cell (MCC) functionality, focusing on cell excitability and catecholamine secretion. Acute application of leptin (1 nm) on spontaneously firing MCCs caused a slowly developing membrane hyperpolarization followed by complete blockade of action potential (AP) firing. This inhibitory effect at rest was abolished by the BK channel blocker paxilline (1 μm), suggesting the involvement of BK potassium channels. Single-channel recordings in 'perforated microvesicles' confirmed that leptin increased BK channel open probability without altering its unitary conductance. BK channel up-regulation was associated with the phosphoinositide 3-kinase (PI3K) signalling cascade because the PI3K specific inhibitor wortmannin (100 nm) fully prevented BK current increase. We also tested the effect of leptin on evoked AP firing and Ca(2+) -driven exocytosis. Although leptin preserves well-adapted AP trains of lower frequency, APs are broader and depolarization-evoked exocytosis is increased as a result of the larger size of the ready-releasable pool and higher frequency of vesicle release. The kinetics and quantal size of single secretory events remained unaltered. Leptin had no effect on firing and secretion in db(-) /db(-) mice lacking the ObR gene, confirming its specificity. In conclusion, leptin exhibits a dual action on MCC activity. It dampens AP firing at rest but preserves AP firing and increases catecholamine secretion during sustained stimulation, highlighting the importance of the adipo-adrenal axis in the leptin-mediated increase of sympathetic tone and catecholamine release.

Leptin at gender-specific concentrations does not affect glucose transport, expression of glucose transporters and leptin receptors in human lymphocytes

Leptin shows pleiotropic effects in organisms including an important role in the regulation of glucose homeostasis. Elevated serum leptin, particularly in obese individuals, is a warning sign of energy imbalance, hyperinsulinemia, insulin resistance and other metabolic risk factors that are strongly associated with type 2 diabetes. Obesity is also related to a higher rate of infections and immune function deterioration may in part ensue from decreased glucose uptake as the main energy source for lymphocytes. The aim of this study was to investigate the effect of physiologic and low pathophysiologic gender-specific leptin concentration found in lean and obese subjects on glucose transport, the expression of glucose transporters and leptin receptors in human peripheral blood lymphocytes. Isolated lymphocytes were incubated with human leptin at gender-specific concentrations observed in normal weight and obese subjects. Glucose uptake in lymphocytes was determined using nonmetabolizable radiolabeled deoxy-D-glucose. The expression of GLUT1, 3, 4 and leptin receptors was investigated using methods of immunocytochemistry and flow cytometry. Leptin at concentrations used in the study does not change glucose transport into lymphocytes and seems to have no influence on the expression of glucose transporters and leptin receptors. Further studies are necessary to address the relationship between leptin, glucose transport and the lymphocytes' function in obesity.

Selective leptin resistance revisited

In addition to effects on appetite and metabolism, leptin influences many neuroendocrine and physiological systems, including the sympathetic nervous system. Building on my Carl Ludwig Lecture of the American Physiological Society, I review the sympathetic and cardiovascular actions of leptin. The review focuses on a critical analysis of the concept of selective leptin resistance (SLR) and the role of leptin in the pathogenesis of obesity-induced hypertension in both experimental animals and humans. We introduced the concept of SLR in 2002 to explain how leptin might increase blood pressure (BP) in obese states, such as diet-induced obesity (DIO), that are accompanied by partial leptin resistance. This concept, analogous to selective insulin resistance in the metabolic syndrome, holds that in several genetic and acquired models of obesity, there is preservation of the renal sympathetic and pressor actions of leptin despite attenuation of the appetite and weight-reducing actions. Two potential overlapping mechanisms of SLR are reviewed: 1) differential leptin molecular signaling pathways that mediate selective as opposed to universal leptin action and 2) brain site-specific leptin action and resistance. Although the phenomenon of SLR in DIO has so far focused on preservation of sympathetic and BP actions of leptin, consideration should be given to the possibility that this concept may extend to preservation of other actions of leptin. Finally, I review perplexing data on the effects of leptin on sympathetic activity and BP in humans and its role in human obesity-induced hypertension.