Obesity-associated hyperleptinemia alters the gliovascular interface of the hypothalamus to promote hypertension

Hyperleptinemia results in systemic inflammation and the exacerbation of ischemia-reperfusion myocardial injury

Aim

Hyperleptinemia potentiates the effects of many atherogenic factors, such as inflammation, platelet aggregation, migration, hypertrophy, proliferation of vascular smooth muscle cells, and endothelial cell dysfunction. The present study analysed the effects of long-term hyperleptinemia in an in vivo myocardial ischemia-reperfusion model to demonstrate whether the in vivo deleterious effect also affects cardiac structure and function.

Main methods

Rats were subcutaneously administered leptin for 8 days to estimate the involvement of the JAK/STAT pathway. Data from 58 male Wistar rats were included in the final analysis. Myocardial infarction (MI) was modelled by the 30-minute ligation of the main left coronary artery followed by 120-minute reperfusion. Hemodynamic measurements, electrocardiography monitoring, echocardiography, myocardial infarct size and area at risk, blood biochemical parameters, leptin, IL-6, TNF-alpha, FGF-21, and cardiomyocyte morphology were measured. The expression of JAK2, p-JAK2, STAT3, p-STAT3 was assessed by Western Blot analysis. Statistical analyses were performed using IBM SPSS Statistics v.26.

Key findings

Eight-day hyperleptinemia in rats leads to an increase in blood pressure and heart rate, myocardial hypertrophy, impaired LV function, the frequency of ischemic arrhythmias, dyslipidemia, systemic inflammation, and the size of induced myocardial infarction. Significance: The blockade of the JAK/STAT signalling pathway effectively reverses the negative effects of leptin, including increased blood pressure and total cholesterol.

Microvascular Inflammation and Cardiovascular Prevention: The Role of Microcirculation as Earlier Determinant of Cardiovascular Risk

Healthcare systems encumbered by cardiovascular diseases demand adequate cardiovascular prevention. Indeed, even with the most novel therapies, the residual cardiovascular risk still fuels morbidity and mortality. Addressing inflammation as a putative mediator of this risk has brought along promising in vitro results, though large clinical trials have only in part confirmed them. To fully exploit the therapeutic potential between the inflammatory hypothesis, a change of viewpoint is required. Focus on microcirculation, whose dysfunction is the primary driver of cardiometabolic disease, is mandatory. Several factors play a pivotal role in the capacity of microvascular inflammation to promote a health-to-disease transition: the adipose tissue (in particular, perivascular and epicardial), the mitochondria function, the hyperglycemic damage and their epigenetic signature. Indeed, the low-grade inflammatory response, which is now an acknowledged hallmark of cardiometabolic disease, is promoted by these mediators and leaves a permanent epigenetic scar on the microvasculature. Even if a more profound knowledge about the mechanisms of metabolic memory has been brought to light by recent evidence, we still have to fully understand its mechanisms and clinical potential. Addressing the detrimental role of inflammation by targeting the microvascular phenotype and leveraging epigenetics is the road down which we must go to achieve satisfactory cardiovascular prevention, ultimately leading to disease-free ageing.

The Emerging Role of Metabolism in Brain-Heart Axis: New Challenge for the Therapy and Prevention of Alzheimer Disease. May Thioredoxin Interacting Protein (TXNIP) Play a Role?

Alzheimer disease (AD) is the most frequent cause of dementia and up to now there is not an effective therapy to cure AD. In addition, AD onset occurs decades before the diagnosis, affecting the possibility to set up appropriate therapeutic strategies. For this reason, it is necessary to investigate the effects of risk factors, such as cardiovascular diseases, in promoting AD. AD shows not only brain dysfunction, but also alterations in peripheral tissues/organs. Indeed, it exists a reciprocal connection between brain and heart, where cardiovascular alterations participate to AD as well as AD seem to promote cardiovascular dysfunction. In addition, metabolic dysfunction promotes both cardiovascular diseases and AD. In this review, we summarize the pathways involved in the regulation of the brain-heart axis and the effect of metabolism on these pathways. We also present the studies showing the role of the gut microbiota on the brain-heart axis. Herein, we propose recent evidences of the function of Thioredoxin Interacting protein (TXNIP) in mediating the role of metabolism on the brain-heart axis. TXNIP is a key regulator of metabolism at both cellular and body level and it exerts also a pathological function in several cardiovascular diseases as well as in AD.

Astrocyte Gliotransmission in the Regulation of Systemic Metabolism

Normal brain function highly relies on the appropriate functioning of astrocytes. These glial cells are strategically situated between blood vessels and neurons, provide significant substrate support to neuronal demand, and are sensitive to neuronal activity and energy-related molecules. Astrocytes respond to many metabolic conditions and regulate a wide array of physiological processes, including cerebral vascular remodeling, glucose sensing, feeding, and circadian rhythms for the control of systemic metabolism and behavior-related responses. This regulation ultimately elicits counterregulatory mechanisms in order to couple whole-body energy availability with brain function. Therefore, understanding the role of astrocyte crosstalk with neighboring cells via the release of molecules, e.g., gliotransmitters, into the parenchyma in response to metabolic and neuronal cues is of fundamental relevance to elucidate the distinct roles of these glial cells in the neuroendocrine control of metabolism. Here, we review the mechanisms underlying astrocyte-released gliotransmitters that have been reported to be crucial for maintaining homeostatic regulation of systemic metabolism.

Female Sex and Angiotensin-Converting Enzyme (ACE) Insertion/Deletion Polymorphism Amplify the Effects of Adiposity on Blood Pressure

The pathophysiological link between adiposity and blood pressure is not completely understood, and evidence suggests an influence of sex and genetic determinants. We aimed to identify the relationship between adiposity and blood pressure, independent of a robust set of lifestyle and metabolic factors, and to examine the modulating role of sex and Angiotensin-Converting Enzyme (ACE) insertion/deletion (I/D) polymorphisms. In the Relationship Between Insulin Sensitivity and Cardiovascular Disease (RISC) study cohort, 1211 normotensive individuals, aged 30 to 60 years and followed-up after 3.3 years, were characterized for lifestyle and metabolic factors, body composition, and ACE genotype. Body mass index (BMI) and waist circumference (WC) were independently associated with mean arterial pressure, with a stronger relationship in women than men (BMI: r=0.40 versus 0.30; WC: r=0.40 versus 0.30, both P<0.01) and in individuals with the ID and II ACE genotypes in both sexes (P<0.01). The associations of BMI and WC with mean arterial pressure were independent of age, sex, lifestyle, and metabolic variables (standardized regression coefficient=0.17 and 0.18 for BMI and WC, respectively) and showed a significant interaction with the ACE genotype only in women (P=0.03). A 5 cm larger WC at baseline increased the risk of developing hypertension at follow-up only in women (odds ratio, 1.56 [95% CI, 1.15-2.10], P=0.004) and in II genotype carriers (odds ratio, 1.87 [95% CI, 1.09-3.20], P=0.023). The hypertensive effect of adiposity is more pronounced in women and in people carrying the II variant of the ACE genotype, a marker of salt sensitivity.

The Impact of Bariatric Surgery Versus Non-Surgical Treatment on Blood Pressure: Systematic Review and Meta-Analysis

The purpose of this study was to compare bariatric surgery versus non-surgical treatment on blood pressure for patients with obesity. Nineteen RCTs (1353 total patients) were included. In the pooled analyses, bariatric surgery reduces more systolic blood pressure (WMD: - 3.937 mmHg, CI95%: - 6.000 to - 1.875, p < 0.001, I² = 0%), diastolic blood pressure (WMD: - 2.690 mmHg, CI95%: - 3.994 to - 1.385, P < 0.001, I² = 0%) and more antihypertensives. In subgroup analyses, patients after Roux-en-Y gastric bypass, with poor control of hypertension (BP > 130/80 mmHg) and diabetes mellitus (HbA1C > 7.0%, FPG > 7.0 mmol/L), elder patients (> 45 years), non-severe obesity (BMI < 40 kg/cm², body weight < 120 kg), less waist circumference (< 115 cm) tend to decrease more blood pressure. Besides, patients after surgery also lost more weight (p < 0.001), decreased more waist circumference (p < 0.001), fasting plasma glucose (p < 0.001), glycosylated hemoglobin (p < 0.001), triglycerides (p < 0.001), hsCRP (p = 0.001), increased more high-density lipoprotein cholesterol (p < 0.001), and had better remission of metabolic syndrome (p < 0.001). Changes in total cholesterol, low-density lipoprotein cholesterol, renal function, resting heart rate, and 6-min walking test were not significantly different. Therefore, bariatric surgery is more effective than non-surgical treatment in controlling patients' blood pressure.

Tanycytic networks mediate energy balance by feeding lactate to glucose-insensitive POMC neurons

Hypothalamic glucose sensing enables an organism to match energy expenditure and food intake to circulating levels of glucose, the main energy source of the brain. Here, we established that tanycytes of the hypothalamic arcuate nucleus, specialized glia that line the wall of the third ventricle, convert brain glucose supplies into lactate that they transmit through monocarboxylate transporters to arcuate proopiomelanocortin neurons, which integrate this signal to drive their activity and to adapt the metabolic response to meet physiological demands. Furthermore, this transmission required the formation of extensive Connexin-43 gap-junction-mediated metabolic networks by arcuate tanycytes. Selectively suppressing either tanycytic monocarboxylate transporters or gap junctions resulted in altered feeding behavior and energy metabolism. Tanycytic intercellular communication and lactate production are thus integral to the mechanism by which hypothalamic neurons that regulate energy and glucose homeostasis efficiently perceive alterations in systemic glucose levels as a function of the physiological state of the organism.

High-Fat Diet Impairs Mouse Median Eminence: A Study by Transmission and Scanning Electron Microscopy Coupled with Raman Spectroscopy

Hypothalamic dysfunction is an initial event following diet-induced obesity, primarily involving areas regulating energy balance such as arcuate nucleus (Arc) and median eminence (ME). To gain insights into the early hypothalamic diet-induced alterations, adult CD1 mice fed a high-fat diet (HFD) for 6 weeks were studied and compared with normo-fed controls. Transmission and scanning electron microscopy and histological staining were employed for morphological studies of the ME, while Raman spectroscopy was applied for the biochemical analysis of the Arc-ME complex. In HFD mice, ME β2-tanycytes, glial cells dedicated to blood-liquor crosstalk, exhibited remarkable ultrastructural anomalies, including altered alignment, reduced junctions, degenerating organelles, and higher content of lipid droplets, lysosomes, and autophagosomes. Degenerating tanycytes also displayed an electron transparent cytoplasm filled with numerous vesicles, and they were surrounded by dilated extracellular spaces extending up to the subependymal layer. Consistently, Raman spectroscopy analysis of the Arc-ME complex revealed higher glycogen, collagen, and lipid bands in HFD mice compared with controls, and there was also a higher band corresponding to the cyanide group in the former compared to the last. Collectively, these data show that ME β₂-tanycytes exhibit early structural and chemical alterations due to HFD and reveal for the first-time hypothalamic cyanide presence following high dietary lipids consumption, which is a novel aspect with potential implications in the field of obesity.

Leptin Receptor Blockade Attenuates Hypertension, but Does Not Affect Ventilatory Response to Hypoxia in a Model of Polygenic Obesity

Background

Obesity can cause hypertension and exacerbates sleep-disordered breathing (SDB). Leptin is an adipocyte-produced hormone, which increases metabolic rate, suppresses appetite, modulates control of breathing, and increases blood pressure. Obese individuals with high circulating levels of leptin are resistant to metabolic and respiratory effects of leptin, but they appear to be sensitive to hypertensive effects of this hormone. Obesity-induced hypertension has been associated with hyperleptinemia. New Zealand obese (NZO) mice, a model of polygenic obesity, have high levels of circulating leptin and hypertension, and are prone to develop SDB, similarly to human obesity. We hypothesize that systemic leptin receptor blocker Allo-aca will treat hypertension in NZO mice without any effect on body weight, food intake, or breathing.

Methods

Male NZO mice, 12–13 weeks of age, were treated with Allo-aca (n = 6) or a control peptide Gly11 (n = 12) for 8 consecutive days. Doses of 0.2 mg/kg were administered subcutaneously 2×/day, at 10 AM and 6 PM. Blood pressure was measured by telemetry for 48 h before and during peptide infusion. Ventilation was assessed by whole-body barometric plethysmography, control of breathing was examined by assessing the hypoxic ventilatory response (HVR), and polysomnography was performed during light-phase at baseline and during treatment. Heart rate variability analyses were performed to estimate the cardiac autonomic balance.

Results

Systemic leptin receptor blockade with Allo-aca did not affect body weight, body temperature, and food intake in NZO mice. Plasma levels of leptin did not change after the treatment with either Allo-aca or the control peptide Gy11. NZO mice were hypertensive at baseline and leptin receptor blocker Allo-aca significantly reduced the mean arterial pressure from 134.9 ± 3.1 to 124.9 ± 5.7 mmHg during the light phase (P < 0.05), whereas the control peptide had no effect. Leptin receptor blockade did not change the heart rate or cardiac autonomic balance. Allo-aca did not affect minute ventilation under normoxic or hypoxic conditions and HVR. Ventilation, apnea index, and oxygen desaturation during NREM and REM sleep did not change with leptin receptor blockade.

Conclusion

Systemic leptin receptor blockade attenuates hypertension in NZO mice, but does not exacerbate obesity and SDB. Thus, leptin receptor blockade represents a potential pharmacotherapy for obesity-associated hypertension.

Moderate Caloric Restriction Partially Improved Oxidative Stress Markers in Obese Humans

Oxidative stress and inflammation are implicated in obesity. Therefore, we investigated whether moderate and short-term calorie restriction (CR) reflects a real-life situation, mediates weight loss, and improves oxidative stress markers. We analyzed oxidative stress markers in patients with obesity undergoing moderate CR. Serum oxidative stress markers (myeloperoxidase (MPO), superoxide dismutase (SOD), catalase, total antioxidant status (TAS), and reactive oxygen species (ROS) (generation by endothelial cells in vitro)) were measured in 53 subjects (mean BMI 37.8 ± 5.9 kg/m²) who underwent 8 weeks of CR, which included a reduction of 300-500 kcal/day. MPO was the most CR-sensitive parameter. The mean level of serum MPO in patients with obesity was 20% higher than that in post CR intervention (p < 0.001). SOD increased by 12% after CR (p < 0.05), which was largely due to the improvement in glucose tolerance and the reduction in insulin resistance after CR. Other tested parameters were not modified during the treatment. CR resulted in an expected decrease in body weight (by 5.9 ± 4.6 kg, p < 0.0001) and other anthropometric parameters. Additionally, it was accompanied by a significant change in hsCRP, hsTNF alpha, hsIL-6, leptin (all p < 0.0001), and HOMA-IR (p < 0.05). Cardiovascular and metabolic parameters were also partially improved. Short-term, moderate CR partially improves antioxidant capacity but is enough to substantially change anthropometric parameters in obese patients. Our observations indicate that mimicking real-life situations and low-cost dietary intervention can be successfully implemented in obesity treatment with a simultaneous moderate effect on antioxidant status.

Hypothalamic Astrocytes as a Specialized and Responsive Cell Population in Obesity

Astrocytes are a type of glial cell anatomically and functionally integrated into the neuronal regulatory circuits for the neuroendocrine control of metabolism. Being functional integral compounds of synapses, astrocytes are actively involved in the physiological regulatory aspects of metabolic control, but also in the pathological processes that link neuronal dysfunction and obesity. Between brain areas, the hypothalamus harbors specialized functional circuits that seem selectively vulnerable to metabolic damage, undergoing early cellular rearrangements which are thought to be at the core of the pathogenesis of diet-induced obesity. Such changes in the hypothalamic brain region consist of a rise in proinflammatory cytokines, the presence of a reactive phenotype in astrocytes and microglia, alterations in the cytoarchitecture and synaptology of hypothalamic circuits, and angiogenesis, a phenomenon that cannot be found elsewhere in the brain. Increasing evidence points to the direct involvement of hypothalamic astrocytes in such early metabolic disturbances, thus moving the study of these glial cells to the forefront of obesity research. Here we provide a comprehensive review of the most relevant findings of molecular and pathophysiological mechanisms by which hypothalamic astrocytes might be involved in the pathogenesis of obesity.