Lipocalin-2 promotes adipose-macrophage interactions to shape peripheral and central inflammatory responses in experimental autoimmune encephalomyelitis

ITE-mediated AhR activation attenuates atherosclerosis by promoting macrophage M2-like polarization through NF-κB/LCN2 pathway suppression

AIMS

Atherosclerosis (AS) is a chronic inflammatory disease characterized by lipid accumulation and inflammation. Macrophage phenotypic transformation plays a critical role in AS progression. Aryl hydrocarbon receptor (AhR) has been proved to regulate the phenotype of macrophages. This study investigates the role and molecular mechanism of AhR activation by its endogenous ligand, 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) attenuates AS.

MATERIALS AND METHODS

We employed Western blotting to analyze the expression of AhR, NF-κB, and lipocalin-2 (LCN2). Flow cytometry and immunofluorescence staining were used to assess the phenotype of macrophages. Plaque progression was evaluated using pathological staining. Transcriptome sequencing was utilized to explore the potential mechanism by which AhR promotes macrophage phenotypic transformation. CUT&Tag-qPCR and lentivirus infection confirmed that the AhR/NF-κB/LCN2 pathway regulates macrophage polarization.

KEY FINDINGS

Activation of AhR by ITE reduced plaque area and inhibited lipid deposition. ITE significantly increased the number of M2-like macrophages both in vivo and in vitro. Transcriptome sequencing identified LCN2 as a key target for AhR-mediated macrophage M2-like polarization. Furthermore, AhR activation suppressed the NF-κB/LCN2 pathway.

SIGNIFICANCE

Our findings reveal that AhR promotes the macrophages to exhibit M2-like characteristics to attenuate AS by inhibiting the NF-κB/LCN2 pathway. These results suggest that AhR may serve as a novel therapeutic target for AS.

Complexin 2 contributes to the protective effect of NAD+ on neuronal survival following neonatal hypoxia-ischemia

Nicotinamide adenine dinucleotide (NAD) is a key coenzyme involved in cell metabolism associated with aging, cancer, neurodegenerative diseases and metabolic disorders. We recently showed that NAD+ therapy significantly improved neurobehavioral outcomes in neonatal mice after hypoxia-ischemia (HI), and bioinformatics analysis revealed that the expression of complexin 2 (CPLX2) in the injured cerebral cortex was significantly decreased 24 h after HI injury but could be reversed by NAD+ intervention. In this study we explored the role of CPLX2 in the survival and function of neonatal hypoxic-ischemic cortical neurons. HI models were established by permanent ligation of the left common carotid artery in mice. CPLX2-knockdown lentiviral vector was injected intraventricularly on postnatal day 1 (P1); CPLX2 knockout mice were also used. NAD+ (5 mg·kg-1·d-1, i.p.) was administered before HI surgery, thereafter once a day until sampling. We showed that NAD+ administration significantly ameliorated the morphological damages and neurobehavioral defects, and elevated the seizure thresholds in HI mice. All the beneficial effects of NAD+ were abolished by CPLX2 knockdown or knockout. In HT22 neuronal cells subjected to OGD/R, pretreated with NAD+ (100 μM) for 12 h significantly increased the cell viability, decreased the LDH levels, and inhibited the ferroptosis evidenced by the changes in redox-related parameters including concentrations of Fe2+, GSH, MDA, H2O2 as well as the expression of GPX4 and SLC7A11. CPLX2 knockdown in HT22 neuronal cells blocked the protective effects of NAD+ as in HI mice, whereas CPLX2 overexpression enhanced the inhibitory effects of NAD+ on ferroptosis in HT22 neuronal cells.

Lipocalin-2 and intestinal diseases

Dysfunction of the intestinal barrier is a prevalent phenomenon observed across a spectrum of diseases, encompassing conditions such as mesenteric artery dissection, inflammatory bowel disease, cirrhosis, and sepsis. In these pathological states, the integrity of the intestinal barrier, which normally serves to regulate the selective passage of substances between the gut lumen and the bloodstream, becomes compromised. This compromised barrier function can lead to a range of adverse consequences, including increased permeability to harmful substances, the translocation of bacteria and their products into systemic circulation, and heightened inflammatory responses within the gut and beyond. Understanding the mechanisms underlying intestinal barrier dysfunction in these diverse disease contexts is crucial for the development of targeted therapeutic interventions aimed at restoring barrier integrity and ameliorating disease progression. Lipocalin-2 (LCN2) expression is significantly upregulated during episodes of intestinal inflammation, making it a pivotal indicator for gauging the extent of such inflammatory processes. Notably, however, LCN2 derived from distinct cellular sources, whether intestinal epithelial cells or immune cells, exhibits notably divergent functional characteristics. Furthermore, the multifaceted nature of LCN2 is underscored by its varying roles across different diseases, sometimes even demonstrating contradictory effects.

Systemic inflammation accelerates neurodegeneration in a rat model of Parkinson's disease overexpressing human alpha synuclein

Increasing efforts have been made to elucidate how genetic and environmental factors interact in Parkinson's disease (PD). In the present study, we assessed the development of symptoms on a genetic PD rat model that overexpresses human α-synuclein (Snca+/+) at a presymptomatic age, exposed to a pro-inflammatory insult by intraperitoneal injection of lipopolysaccharide (LPS), using immunohistology, high-dimensional flow cytometry, constant potential amperometry, and behavioral analyses. A single injection of LPS into WT and Snca+/+ rats triggered long-lasting increase in the activation of pro-inflammatory microglial markers, monocytes, and T lymphocytes. However, only LPS Snca+/+ rats showed dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc), associated with a reduction in the release of evoked dopamine in the striatum. No significant changes were observed in the behavioral domain. We propose our double-hit animal as a reliable model to investigate the mechanisms whereby α-synuclein and inflammation interact to promote neurodegeneration in PD.

Lipocalin-2 as a mediator of neuroimmune communication

Lipocalin-2, a neutrophil gelatinase-associated lipocalin, is a 25-kDa secreted protein implicated in a broad range of inflammatory diseases affecting the brain and periphery. It is a pleotropic protein expressed by various immune and nonimmune cells throughout the body. Importantly, the surge in lipocalin-2 levels in disease states has been associated with a myriad of undesirable effects, further exacerbating the ongoing pathological processes. In the brain, glial cells are the principal source of lipocalin-2, which plays a definitive role in determining their functional phenotypes. In different central nervous system pathologies, an increased expression of glial lipocalin-2 has been linked to neurotoxicity. Lipocalin-2 mediates a crosstalk between central and peripheral immune cells under neuroinflammatory conditions. One intriguing aspect is that elevated lipocalin-2 levels in peripheral disorders, such as cancer, metabolic conditions, and liver diseases, potentially incite an inflammatory activation of glial cells while disrupting neuronal functions. This review comprehensively summarizes the influence of lipocalin-2 on the exacerbation of neuroinflammation by regulating various cellular processes. Additionally, this review explores lipocalin-2 as a mediator of neuroimmune crosstalk in various central nervous system pathologies and highlights the role of lipocalin-2 in carrying inflammatory signals along the neuroimmune axis.

Frataxin deficiency shifts metabolism to promote reactive microglia via glucose catabolism

Immunometabolism investigates the intricate relationship between the immune system and cellular metabolism. This study delves into the consequences of mitochondrial frataxin (FXN) depletion, the primary cause of Friedreich's ataxia (FRDA), a debilitating neurodegenerative condition characterized by impaired coordination and muscle control. By using single-cell RNA sequencing, we have identified distinct cellular clusters within the cerebellum of an FRDA mouse model, emphasizing a significant loss in the homeostatic response of microglial cells lacking FXN. Remarkably, these microglia deficient in FXN display heightened reactive responses to inflammatory stimuli. Furthermore, our metabolomic analyses reveal a shift towards glycolysis and itaconate production in these cells. Remarkably, treatment with butyrate counteracts these immunometabolic changes, triggering an antioxidant response via the itaconate-Nrf2-GSH pathways and suppressing the expression of inflammatory genes. Furthermore, we identify Hcar2 (GPR109A) as a mediator involved in restoring the homeostasis of microglia without FXN. Motor function tests conducted on FRDA mice underscore the neuroprotective attributes of butyrate supplementation, enhancing neuromotor performance. In conclusion, our findings elucidate the role of disrupted homeostatic function in cerebellar microglia in the pathogenesis of FRDA. Moreover, they underscore the potential of butyrate to mitigate inflammatory gene expression, correct metabolic imbalances, and improve neuromotor capabilities in FRDA.

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

Neuroinflammation is a common pathological process in various neurological disorders, including stroke, Alzheimer's disease, Parkinson's disease, and others. It involves the activation of glial cells, particularly astrocytes, and the release of inflammatory mediators. Lipocalin-2 (Lcn-2) is a secretory protein mainly secreted by activated astrocytes, which can affect neuroinflammation through various pathways. It can also act as a pro-inflammatory factor by modulating astrocyte activation and polarization through different signaling pathways, such as NF-κB, and JAK-STAT, amplifying the inflammatory response and aggravating neural injury. Consequently, Lcn-2 and astrocytes may be potential therapeutic targets for neuroinflammation and related diseases. This review summarizes the current knowledge on the role mechanisms, interactions, and therapeutic implications of Lcn-2 and astrocytes in neuroinflammation.