Global transcriptome analysis of rat hypothalamic arcuate nucleus demonstrates reversal of hypothalamic gliosis following surgically and diet induced weight loss

Exercise Rescues Obesogenic-Related Genes in the Female Hypothalamic Arcuate Nucleus: A Potential Role of miR-211 Modulation

Obesity is a major public health concern that is associated with negative health outcomes. Exercise and dietary restriction are commonly recommended to prevent or combat obesity. This study investigates how voluntary exercise mitigates abnormal gene expression in the hypothalamic arcuate nucleus (ARC) of diet-induced obese (DIO) rats. Using a transcriptomic approach, novel genes in the ARC affected by voluntary wheel running were assessed alongside physiology, pharmacology, and bioinformatics analysis to evaluate the role of miR-211 in reversing obesity. Exercise curbed weight gain and fat mass, and restored ARC gene expression. High-fat diet (HFD) consumption can dysregulate satiety/hunger mechanisms in the ARC. Transcriptional clusters revealed that running altered gene expression patterns, including inflammation and cellular structure genes. To uncover regulatory mechanisms governing gene expression in DIO attenuation, we explored miR-211, which is implicated in systemic inflammation. Exercise ameliorated DIO overexpression of miR-211, demonstrating its pivotal role in regulating inflammation in the ARC. Further, in vivo central administration of miR-211-mimic affected the expression of immunity and cell cycle-related genes. By cross-referencing exercise-affected and miR-211-regulated genes, potential candidates for obesity reduction through exercise were identified. This research suggests that exercise may rescue obesity through gene expression changes mediated partially through miR-211.

The Significance of Hypothalamic Inflammation and Gliosis for the Pathogenesis of Obesity in Humans

Accumulated preclinical literature demonstrates that hypothalamic inflammation and gliosis are underlying causal components of diet-induced obesity in rodent models. This review summarizes and synthesizes available translational data to better understand the applicability of preclinical findings to human obesity and its comorbidities. The published literature in humans includes histopathologic analyses performed postmortem and in vivo neuroimaging studies measuring indirect markers of hypothalamic tissue microstructure. Both support the presence of hypothalamic inflammation and gliosis in children and adults with obesity. Findings predominantly point to tissue changes in the region of the arcuate nucleus of the hypothalamus, although findings of altered tissue characteristics in whole hypothalamus or other hypothalamic regions also emerged. Moreover, the severity of hypothalamic inflammation and gliosis has been related to comorbid conditions, including glucose intolerance, insulin resistance, type 2 diabetes, and low testosterone levels in men, independent of elevated body adiposity. Cross-sectional findings are augmented by a small number of prospective studies suggesting that a greater degree of hypothalamic inflammation and gliosis may predict adiposity gain and worsening insulin sensitivity in susceptible individuals. In conclusion, existing human studies corroborate a large preclinical literature demonstrating that hypothalamic neuroinflammatory responses play a role in obesity pathogenesis. Extensive or permanent hypothalamic tissue remodeling may negatively affect the function of neuroendocrine regulatory circuits and promote the development and maintenance of elevated body weight in obesity and/or comorbid endocrine disorders.

Trends in Gliosis in Obesity, and the Role of Antioxidants as a Therapeutic Alternative

Obesity remains a global health problem. Chronic low-grade inflammation in this pathology has been related to comorbidities such as cognitive alterations that, in the long term, can lead to neurodegenerative diseases. Neuroinflammation or gliosis in patients with obesity and type 2 diabetes mellitus has been related to the effect of adipokines, high lipid levels and glucose, which increase the production of free radicals. Cerebral gliosis can be a risk factor for developing neurodegenerative diseases, and antioxidants could be an alternative for the prevention and treatment of neural comorbidities in obese patients.

AIM

Identify the immunological and oxidative stress mechanisms that produce gliosis in patients with obesity and propose antioxidants as an alternative to reducing neuroinflammation.

METHOD

Advanced searches were performed in scientific databases: PubMed, ProQuest, EBSCO, and the Science Citation index for research on the physiopathology of gliosis in obese patients and for the possible role of antioxidants in its management.

CONCLUSION

Patients with obesity can develop neuroinflammation, conditioned by various adipokines, excess lipids and glucose, which results in an increase in free radicals that must be neutralized with antioxidants to reduce gliosis and the risk of long-term neurodegeneration.

The timeline of neuronal and glial alterations in experimental obesity

In experimental models, hypothalamic dysfunction is a key component of the pathophysiology of diet-induced obesity. Early after the introduction of a high-fat diet, neurons, microglia, astrocytes and tanycytes of the mediobasal hypothalamus undergo structural and functional changes that impact caloric intake, energy expenditure and systemic glucose tolerance. Inflammation has emerged as a central component of this response, and as in other inflammatory conditions, there is a time course of events that determine the fate of distinct cells involved in the central regulation of whole-body energy homeostasis. Here, we review the work that identified key mechanisms, cellular players and temporal features of diet-induced hypothalamic abnormalities.

Roux-en-Y Gastric Bypass and Caloric Restriction but Not Gut Hormone-Based Treatments Profoundly Impact the Hypothalamic Transcriptome in Obese Rats

BACKGROUND

The hypothalamus is an important brain region for the regulation of energy balance. Roux-en-Y gastric bypass (RYGB) surgery and gut hormone-based treatments are known to reduce body weight, but their effects on hypothalamic gene expression and signaling pathways are poorly studied.

METHODS

Diet-induced obese male Wistar rats were randomized into the following groups: RYGB, sham operation, sham + body weight-matched (BWM) to the RYGB group, osmotic minipump delivering PYY3-36 (0.1 mg/kg/day), liraglutide s.c. (0.4 mg/kg/day), PYY3-36 + liraglutide, and saline. All groups (except BWM) were kept on a free choice of high- and low-fat diets. Four weeks after interventions, hypothalami were collected for RNA sequencing.

RESULTS

While rats in the RYGB, BWM, and PYY3-36 + liraglutide groups had comparable reductions in body weight, only RYGB and BWM treatment had a major impact on hypothalamic gene expression. In these groups, hypothalamic leptin receptor expression as well as the JAK-STAT, PI3K-Akt, and AMPK signaling pathways were upregulated. No significant changes could be detected in PYY3-36 + liraglutide-, liraglutide-, and PYY-treated groups.

CONCLUSIONS

Despite causing similar body weight changes compared to RYGB and BWM, PYY3-36 + liraglutide treatment does not impact hypothalamic gene expression. Whether this striking difference is favorable or unfavorable to metabolic health in the long term requires further investigation.

Proteome Analysis of the Hypothalamic Arcuate Nucleus in Chronic High-Fat Diet-Induced Obesity

The hypothalamus plays a central role in the integrated regulation of feeding and energy homeostasis. The hypothalamic arcuate nucleus (ARC) contains a population of neurons that express orexigenic and anorexigenic factors and is thought to control feeding behavior via several neuronal circuits. In this study, a comparative proteomic analysis of low-fat control diet- (LFD-) and high-fat diet- (HFD-) induced hypothalamic ARC was performed to identify differentially expressed proteins (DEPs) related to changes in body weight. In the ARC in the hypothalamus, 6621 proteins (FDR < 0.01) were detected, and 178 proteins were categorized as DEPs (89 upregulated and 89 downregulated in the HFD group). Among the Gene Ontology molecular function terms associated with the DEPs, protein binding was the most significant. Fibroblast growth factor receptor substrate 2 (Frs2) and SHC adaptor protein 3 (Shc3) were related to protein binding and involved in the neurotrophin signaling pathway according to Kyoto Encyclopedia of Genes and Genomes analysis. Furthermore, high-precision quantitative proteomic analysis revealed that the protein profile of the ARC in mice with HFD-induced obesity differed from that in LFD mice, thereby offering insight into the molecular basis of feeding regulation and suggesting Frs2 and Shc3 as novel treatment targets for central anorexigenic signal induction.

Glymphatic imaging and modulation of the optic nerve

Optic nerve health is essential for proper function of the visual system. However, the pathophysiology of certain neurodegenerative disease processes affecting the optic nerve, such as glaucoma, is not fully understood. Recently, it was hypothesized that a lack of proper clearance of neurotoxins contributes to neurodegenerative diseases. The ability to clear metabolic waste is essential for tissue homeostasis in mammals, including humans. While the brain lacks the traditional lymphatic drainage system identified in other anatomical regions, there is growing evidence of a glymphatic system in the central nervous system, which structurally includes the optic nerve. Named to acknowledge the supportive role of astroglial cells, this perivascular fluid drainage system is essential to remove toxic metabolites from the central nervous system. Herein, we review existing literature describing the physiology and dysfunction of the glymphatic system specifically as it relates to the optic nerve. We summarize key imaging studies demonstrating the existence of a glymphatic system in the optic nerves of wild-type rodents, aquaporin 4-null rodents, and humans; glymphatic imaging studies in diseases where the optic nerve is impaired; and current evidence regarding pharmacological and lifestyle interventions that may help promote glymphatic function to improve optic nerve health. We conclude by highlighting future research directions that could be applied to improve imaging detection and guide therapeutic interventions for diseases affecting the optic nerve.