The interaction of lipocalin-2 and astrocytes in neuroinflammation: mechanisms and therapeutic application

Cholesterol´s role in membrane organization and nicotinic acetylcholine receptor function: Implications for aging and Alzheimer's disease

Biological membranes are complex entities composed of various molecules exhibiting lateral and transbilayer lipid asymmetries, along with a selective spatial distribution of different membrane proteins. This dynamic orchestration is crucial for proper physiological functions, undergoes changes with aging, and is disturbed in several neurological disorders. In this review, we analyze the impact of disruption in this equilibrium on physiological aging and the onset of pathological conditions. Alzheimer´s disease (AD) is a multifactorial neurodegenerative disorder in the elderly, characterized by the increased presence of the Aβ peptide, which supports the amyloid hypothesis of the disease. However, AD also involves a progressive loss of cholinergic innervation, leading to the cholinergic hypothesis of the disease. Nicotinic acetylcholine receptors (nAChRs) are transmembrane proteins, and Aβ peptides, their oligomeric and fibrillar species, which increase in hydrophobicity as they develop, interact with membranes. Therefore, a membrane hypothesis of the disease emerges as a bridge between the other two. Here, we discuss the impact of the membrane environment, through direct or indirect mechanisms, on cholinergic signaling and Aβ formation and subsequent incorporation into the membrane, with a special focus on the crucial role of cholesterol in these processes.

ADAMTS18 deficiency leads to abnormal brain methylation metabolism, dysregulated neuroinflammatory response, and unsound blood-brain barrier structure in mice

ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin motifs) family is a group of secretory proteases involved in the maintenance of central nervous system (CNS) homeostasis and neuronal disease. ADAMTS18 is a member of this family and has been linked to the integrity of the human brain's white matter. However, the cellular and molecular basis of ADAMTS18 in brain metabolism and homeostasis remains unclear. In this study, a total of 47,719 genes were identified in 8 independent wild type (WT) and Adamts18 knockout (KO) mouse brain samples using brain transcriptomic analysis. The abundance of 100 genes in brain was significantly different between WT and KO mice. ADAMTS18 deficiency resulted in decreased S-adenosine homocysteine hydrolase (SAHH) levels, impaired brain methyl cycle metabolism and dysregulation of neuroinflammatory-related factors (e.g., Lrg1, and Lcn2) in mouse brain. The number and branching complexity of microglia in brain tissue of Adamts18 KO mice were significantly reduced. Adamts18 KO mice also showed poor blood-brain barrier (BBB) integrity. Mechanically, ADAMTS18 deficiency resulted in significant downregulation of Il- 34, Csf1r, Cx3cl1, Cx3cr1, Fn, Tgfb1, Tgfbr2, Smad4 and Sall1 genes related to microglia expansion, migration, characteristic development and maintenance. BBB integrity related markers Glut1, Plvap, Zo- 1, Occludin or Aqp- 4 were partially dysregulated in the brain tissue of Adamts18 KO mice and significantly deteriorated after LPS stimulation. Collectively, these results shed light on the significance of ADAMTS18 in brain methyl cycle metabolism, neuroinflammatory regulation and BBB structure maintenance.

Early stage of metabolic dysfunction associated steatotic liver disease disrupts circadian rhythm and induces neuroinflammation in rats

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is a chronic liver disease affecting 25% of the European population, with rising global incidence. Liver damage includes ballooning, steatosis, inflammation and fibrosis. Associated brain disorders include sleep, cognitive issues, anxiety, and depression. While neurological complications in advanced MASLD are well documented, early cerebral manifestations remain largely unexplored. This study aimed at developing an MASLD rat model to assess the onset of early brain damage, focusing on impairments of the circadian cycle rhythm and associated neuroinflammation. Sprague Dawley rats were divided into two groups: one received a high-fat, high-cholesterol (HFHC) diet for 90 days, while the other received a standard diet. Histological analysis showed significant hepatic steatosis, ballooning, and inflammation in the HFHC group (p < 0.01). These lesions correlated with elevated hepatic triglycerides (p < 0.01), increased Alanine Aminotransferase, Aspartate Aminotransferase, total cholesterol, and low-density lipoprotein, alongside decreased plasma high-density lipoprotein. Behavioural analysis using activity wheels revealed that the HFHC rats steadily maintained their activity level during the rest periods when compared with controls (p < 0.05). This behavioural alteration occurred alongside neuroinflammation, demonstrated by changes in the expression of 36 and 17 inflammatory mediators in the cerebellum and frontal cortex respectively. These changes were associated with an increase in the expression of glial cell markers (Aif1 and Gfap genes) and an increase in the number of microglial cells, affecting the frontal cortex and cerebellum differently. This rat model of early MASLD shows circadian rhythm disturbances, which could reflect sleep disorders in humans. These early brain disturbances specific to MASLD, which occur before the symptoms of liver disease become clinically apparent, could therefore be used as an early diagnosis marker for MASLD patients.

Mechanism of LCN2 in cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury (CIRI) is a complex pathophysiological process faced by brain tissues after ischemic stroke treatment, which involves mechanisms of inflammatory response, oxidative stress and apoptosis, and severely affects treatment outcome. Lipocalin-2 (LCN2), an acute-phase protein, is significantly up-regulated after CIRI and promotes neural repair by enhancing astrocyte phagocytosis, but its over-activation may also trigger secondary inflammation and demyelination injury. LCN2 also plays a key role in neuroinflammation regulation by regulating the polarization state of astrocytes and the release of inflammatory factors, and may affect the integrity of the blood-brain barrier and a variety of pathologic injury processes. In view of the important role of LCN2 in CIRI, this article reviews the mechanism of LCN2, aiming to provide new ideas and methods for the treatment of ischemic stroke.

LCN2 blockade mitigating metabolic dysregulation and redefining appetite control in type 2 diabetes

LCN2 has an osteokine important for appetite regulation; in type 2 diabetes (T2D) it is not known whether appetite regulation mediated by LCN2 in the brain is altered. In this work, we focus on exploring the role of blocking LCN2 in metabolic health and appetite regulation within the central nervous system of mice with T2D.

MATERIAL AND METHODS

4-week-old male C57BL/6 mice were used, divided into four experimental groups: intact, T2D, TD2/anti-LCN2, and T2D/IgG as isotype control. T2D was induced by low doses of streptozotocin and a high-carbohydrate diet. LCN2 blockade was performed by intraperitoneal administration of a polyclonal anti-LCN2 antibody. We analyzed metabolic parameters, food intake, feeding patterns, and serum LCN2 and leptin concentrations. In another group of intact or T2D mice, we analyzed the effect of blocking LCN2 and recombinant LCN2 on food consumption in a fasting-refeeding test and, the expression of cFOS and LCN2 in brain sections, specifically in the hypothalamus, piriform cortex, visceral area, arcuate nucleus and caudate-putamen.

RESULTS

T2D caused an increase in serum LCN2, without alterations in Ad libitum feeding, but with changes in the feeding pattern associated with alterations in LCN2-cFOS signalling in hypothalamic and non-hypothalamic brain regions. Blocking LCN2 improved metabolic parameters, increased Ad libitum feeding, and restored the feeding pattern after fasting, which is associated with enhanced LCN2 signalling in the brain.

CONCLUSIONS

Blocking LCN2 restores metabolic health and normalizes the pattern of food consumption by normalizing LCN2 signalling in different brain regions.

Lipocalin-2 as a therapeutic target for diabetes neurological complications

INTRODUCTION

Diabetes mellitus, a chronic disorder with persistent hyperglycemia, severely affects the quality of life through significant neurological impairments, including neuropathy and cognitive dysfunction. Inflammation and oxidative stress are key factors in these complications, and Lipocalin-2 (LCN2), which is involved in inflammation and iron homeostasis, is crucial in these processes.

AREA COVERED

This review explores the potential of LCN2 as a therapeutic target for mitigating diabetes neurological complications. By examining the mechanisms by which LCN2 contributes to neuroinflammation, we discuss the therapeutic strategies that target LCN2 to alleviate diabetic neuropathy and cognitive dysfunction.

EXPERT OPINION

To fully grasp the impact of LCN2 on neurological health, it is essential to understand its multifaceted role in metabolic regulation. Because effective LCN2-targeting drugs must penetrate the blood - brain barrier, various strategies are being developed to meet this requirement. Such therapeutics could treat various neurological complications, including diabetic encephalopathy, retinopathy, and peripheral neuropathy. While animal models offer insights into pathophysiology and potential treatments, their limitations must be acknowledged. Therefore, future research should bridge the gaps between animal findings, human studies, and clinical applications. Moreover, comprehensive personalized approaches, including LCN2-targeting drugs, lifestyle changes, and regularly monitoring individual patients, may be required to manage diabetic complications.

Antidepressant Effects of Ginsenoside Rc on L-Alpha-Aminoadipic Acid-Induced Astrocytic Ablation and Neuroinflammation in Mice

Depression is a prevalent and debilitating mental disorder that affects millions worldwide. Current treatments, such as antidepressants targeting the serotonergic system, have limitations, including delayed onset of action and high rates of treatment resistance, necessitating novel therapeutic strategies. Ginsenoside Rc (G-Rc) has shown potential anti-inflammatory and neuroprotective effects, but its antidepressant properties remain unexplored. This study investigated the antidepressant effects of G-Rc in an L-alpha-aminoadipic acid (L-AAA)-induced mouse model of depression, which mimics the astrocytic pathology and neuroinflammation observed in major depressive disorder. Mice were administered G-Rc, vehicle, or imipramine orally after L-AAA injection into the prefrontal cortex. G-Rc significantly reduced the immobility time in forced swimming and tail suspension tests compared to vehicle treatment, with more pronounced effects than imipramine. It also attenuated the expression of pro-inflammatory cytokines (TNF-α, IL-6, TGF-β, lipocalin-2) and alleviated astrocytic degeneration, as indicated by increased GFAP and decreased IBA-1 levels. Additionally, G-Rc modulated apoptosis-related proteins, decreasing caspase-3 and increasing Bcl-2 levels compared to the L-AAA-treated group. These findings suggest that G-Rc exerts antidepressant effects by regulating neuroinflammation, astrocyte-microglia crosstalk, and apoptotic pathways in the prefrontal cortex, highlighting its potential as a novel therapeutic agent for depression.

Antidepressant Effect of Heracleum moellendorffii Extract on Behavioral Changes in Astrocyte Ablation Mouse Model of Depression by Modulating Neuroinflammation through the Inhibition of Lipocalin-2

Astrocyte dysfunction and inflammation play a pivotal role in depression. In this study, we evaluated the antidepressant properties of Heracleum moellendorffii root extract (HME), which is traditionally used for inflammation-related diseases, in a mouse model with astrocyte depletion that resembles the prefrontal cortex pathology of depressive patients. Mice were divided into four groups, with 10 mice per group. To induce astrocyte ablation in the mice's prefrontal cortex (PFC), we used astrocytic toxin L-alpha-aminoadipic acid (L-AAA) and administered HME orally at 200 and 500 mg/kg for 22 days. We utilized the tail suspension test (TST) to assess depression-like behaviors and the open field test (OFT) to evaluate anxiety-like activities. Additionally, astrocytic and inflammatory markers in the PFC were evaluated using immunohistochemistry and ELISA. The results showed that infusion of L-AAA significantly decreased the expression of astrocytic glial fibrillary acidic protein (GFAP), which was accompanied by increased depression and anxiety-like behaviors. However, HME significantly reversed these effects by dose-dependently enhancing GFAP expression and modulating inflammatory markers, such as TNF-α, IL-6, and particularly lipocalin-2, a master proinflammatory mediator. These results imply that HME contributes to the alleviation of depression and anxiety-like behaviors by promoting astrocyte recovery and reducing neuroinflammation, especially through lipocalin-2 inhibition.