Fatty acid sensing in the brain: The role of glial-neuronal metabolic crosstalk and horizontal lipid flux

Synergism Between Hypothalamic Astrocytes and Neurons in Metabolic Control

Astrocytes are no longer considered as passive support cells. In the hypothalamus, these glial cells actively participate in the control of appetite, energy expenditure, and the processes leading to obesity and its secondary complications. Here we briefly review studies supporting this conclusion and the advances made in understanding the underlying mechanisms.

Brain lipid sensing and the neural control of energy balance

The central nervous system continuously detects circulating concentrations of lipids such as fatty acids and troglycerides. Once information has been detected, the central nervous system can in turn participate in the control of energy balance and blood sugar levels and in particular regulate the secretion and action of insulin. Neurons capable of detecting circulating lipid variations are located in the hypothalamus and in other regions such as the nucleus accumbens, the striatum or the hippocampus. An excess of lipids will have deleterious effects and may induce central lipotoxicity, in particular following local production of ceramides and the appearance of neuroinflammation which may lead to metabolic diseases such as obesity and type 2 diabetes.

Network pharmacology combined with lipidomics to reveal the regulatory effects and mechanisms of Kangzao granules in the hypothalamus of rats with central precocious puberty

Central precocious puberty (CPP) is a prevalent endocrine disorder that primarily affects children, specifically females, and is associated with various physical and psychological complications. Although Kangzao granules (KZG) are efficacious in managing CPP, the underlying mechanisms remain unclear. Therefore, this study aimed to elucidate the therapeutic mechanisms of KZG using network pharmacology, molecular docking, pharmacodynamics, and pathway validation. A putative compound-target-pathway network was constructed using Cytoscape, before KEGG and Gene Ontology enrichment analyses were conducted. Moreover, molecular docking was performed using AutoDockTools. Quality control of the 10 key components of KZG was carried out using UHPLC-ESI/LTQ-Orbitrap-MS/MS, and hypothalamic lipids were analyzed using UHPLC-Q-Exactive Orbitrap MS/MS. In total, 87 bioactive compounds that targeting 110 core proteins to alleviate CPP were identified in KZG. Lipidomic analysis revealed 18 differential lipids among the CPP, KZG, and control groups, wherein fatty acids were significantly reduced in the model group; however, these changes were effectively counteracted by KZG treatment. Molecular docking analysis revealed a strong binding affinity between flavonoids and RAC-alpha serine/threonine-protein kinase (AKT) when docked into the crystal structure. Moreover, a substantial disruption in lipid metabolism was observed in the model group; however, treatment with KZG efficiently reversed these alterations. Furthermore, the phosphoinositide 3-kinase/AKT signaling pathway was identified as a pivotal regulator of hypothalamic lipid metabolism regulator. Overall, this study highlights the effectiveness of a multidisciplinary approach that combines network pharmacology, lipidomics, molecular docking, and experimental validation in the elucidation of the therapeutic mechanisms of KZG in CPP treatment.

The differential effects of palmitic acid and oleic acid on the metabolic response of hypothalamic astrocytes from male and female mice

Diets rich in saturated fats are more detrimental to health than those containing mono- or unsaturated fats. Fatty acids are an important source of energy, but they also relay information regarding nutritional status to hypothalamic metabolic circuits and when in excess can be detrimental to these circuits. Astrocytes are the main site of central fatty acid β-oxidation, and hypothalamic astrocytes participate in energy homeostasis, in part by modulating hormonal and nutritional signals reaching metabolic neurons, as well as in the inflammatory response to high-fat diets. Thus, we hypothesized that how hypothalamic astrocytes process-specific fatty acids participates in determining the differential metabolic response and that this is sex dependent as males and females respond differently to high-fat diets. Male and female primary hypothalamic astrocyte cultures were treated with oleic acid (OA) or palmitic acid (PA) for 24 h, and an untargeted metabolomics study was performed. A clear predictive model for PA exposure was obtained, while the metabolome after OA exposure was not different from controls. The observed modifications in metabolites, as well as the expression levels of key metabolic enzymes, indicate a reduction in the activity of the Krebs and glutamate/glutamine cycles in response to PA. In addition, there were specific differences between the response of astrocytes from male and female mice, as well as between hypothalamic and cerebral cortical astrocytes. Thus, the response of hypothalamic astrocytes to specific fatty acids could result in differential impacts on surrounding metabolic neurons and resulting in varied systemic metabolic outcomes.

Neuroprotective Effects of Metformin Through AMPK Activation in a Neurotoxin-Based Model of Cerebellar Ataxia

Cerebellar ataxia is a heterogeneous group of neural disorders clinically characterized by cerebellar dysfunction. The diagnosis of patients with progressive cerebellar ataxia is complex due to the direct correlation with other neuron diseases. Although there is still no cure for this pathological condition, some metabolic, hereditary, inflammatory, and immunological factors affecting cerebellar ataxia are being studied and may become therapeutic targets. Advances in studying the neuroanatomy, pathophysiology, and molecular biology of the cerebellum (CE) contribute to a better understanding of the mechanisms behind the development of this disorder. In this study, Wistar rats aged 30 to 35 days were injected intraperitoneally with 3-acetylpyridine (3-AP) and/or metformin (for AMP-activated protein kinase (AMPK) enzyme activation) and euthanized in 24 hours and 4 days after injection. We analyzed the neuromodulatory role of the AMPK on cerebellar ataxia induced by the neurotoxin 3-AP in the brain stem (BS) and CE, after pre-treatment for 7 and 15 days with metformin, a pharmacological indirect activator of AMPK. The results shown here suggest that AMPK activation in the BS and CE leads to a significant reduction in neuroinflammation in these regions. AMPK was able to restore the changes in fatty acid composition and pro-inflammatory cytokines caused by 3-AP, suggesting that the action of AMPK seems to result in a possible neuroprotection on the cerebellar ataxia model.

Profiling and Cellular Analyses of Obesity-Related circRNAs in Neurons and Glia under Obesity-like In Vitro Conditions

Recent evidence indicates that the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease, is associated with metabolic disorders such as diabetes and obesity. Various circular RNAs (circRNAs) have been found in brain tissues and recent studies have suggested that circRNAs are related to neuropathological mechanisms in the brain. However, there is a lack of interest in the involvement of circRNAs in metabolic imbalance-related neuropathological problems until now. Herein we profiled and analyzed diverse circRNAs in mouse brain cell lines (Neuro-2A neurons, BV-2 microglia, and C8-D1a astrocytes) exposed to obesity-related in vitro conditions (high glucose, high insulin, and high levels of tumor necrosis factor-alpha, interleukin 6, palmitic acid, linoleic acid, and cholesterol). We observed that various circRNAs were differentially expressed according to cell types with many of these circRNAs conserved in humans. After suppressing the expression of these circRNAs using siRNAs, we observed that these circRNAs regulate genes related to inflammatory responses, formation of synaptic vesicles, synaptic density, and fatty acid oxidation in neurons; scavenger receptors in microglia; and fatty acid signaling, inflammatory signaling cyto that may play important roles in metabolic disorders associated with neurodegenerative diseases.