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Background Neuroinflammation is a vital pathophysiological process during ischemic stroke. Activated astrocytes play a major role in inflammation. Lipocalin-2 (LCN2), secreted by activated astrocytes, promotes neuroinflammation. Pyroptosis is a pro-inflammatory form of programmed cell death that has emerged as a new area of research in stroke. Nevertheless, the potential role of LCN2 in astrocyte pyroptosis remains unclear. Methods An ischemic stroke model was established by middle cerebral artery occlusion (MCAO) in vivo. In this study, in vitro, oxygen–glucose deprivation and reoxygenation (O/R) were applied to cultured astrocytes. 24p3R (the LCN2 receptor) was inhibited by astrocyte-specific adeno-associated virus (AAV-GFAP-24p3Ri). MCC950 and Nigericin sodium salt (Nig) were used to inhibit or promote the activation of NLRP3 inflammasome pharmacologically, respectively. Histological and biochemical analyses were performed to assess astrocyte and neuron death. Additionally, the neurological deficits of mice were evaluated. Results LCN2 expression was significantly induced in astrocytes 24 h after stroke onset in the mouse MCAO model. Lcn2 knockout ( Lcn2 −/− ) mice exhibited reduced infarct volume and improved neurological and cognitive functions after MCAO. LCN2 and its receptor 24p3R were colocalized in astrocytes. Mechanistically, suppression of 24p3R by AAV-GFAP-24p3Ri alleviated pyroptosis-related pore formation and the secretion of pro-inflammatory cytokines via LCN2, which was then reversed by Nig-induced NLRP3 inflammasome activation. Astrocyte pyroptosis was exacerbated in Lcn2 −/− mice by intracerebroventricular administration of recombinant LCN2 (rLCN2), while this aggravation was restricted by blocking 24p3R or inhibiting NLRP3 inflammasome activation with MCC950. Conclusion LCN2/24p3R mediates astrocyte pyroptosis via NLRP3 inflammasome activation following cerebral ischemia/reperfusion injury.

Intervertebral disc degeneration (IVDD) is the primary factor contributing to low back pain (LBP). Unlike elderly patients, many young IVDD patients usually have a history of trauma or long-term abnormal stress, which may lead to local inflammatory reaction causing by immune cells, and ultimately accelerates degeneration. Research has shown the significance of M1-type macrophages in IVDD; nevertheless, the precise mechanism and the route by which it influences the function of nucleus pulposus cell (NPC) remain unknown. Utilizing a rat acupuncture IVDD model and an NPC degeneration model induced by lipopolysaccharide (LPS), we investigated the function of M1 macrophage-derived exosomes (M1-Exos) in IVDD both in vivo and in vitro in this study. We found that M1-Exos enhanced LPS-induced NPC senescence, increased the number of SA-β-gal-positive cells, blocked the cell cycle, and promoted the activation of P21 and P53. M1-Exos derived from supernatant pretreated with the exosome inhibitor GW4869 reversed this result in vivo and in vitro. RNA-seq showed that Lipocalin2 (LCN2) was enriched in M1-Exos and targeted the NF-κB pathway. The quantity of SA-β-gal-positive cells was significantly reduced with the inhibition of LCN2, and the expression of P21 and P53 in NPCs was decreased. The same results were obtained in the acupuncture-induced IVDD model. In addition, inhibition of LCN2 promotes the expression of type II collagen (Col-2) and inhibits the expression of matrix metalloproteinase 13 (MMP13), thereby restoring the equilibrium of metabolism inside the extracellular matrix (ECM) in vitro and in vivo. In addition, the NF-κB pathway is crucial for regulating M1-Exo-mediated NPC senescence. After the addition of M1-Exos to LPS-treated NPCs, p-p65 activity was significantly activated, while si-LCN2 treatment significantly inhibited p-p65 activity. Therefore, this paper demonstrates that M1 macrophage-derived exosomes have the ability to deliver LCN2, which activates the NF-κB signaling pathway, and exacerbates IVDD by accelerating NPC senescence. This may shed new light on the mechanism of IVDD and bring a fresh approach to IVDD therapy. Graphical Abstract

Background Cancer cachexia is a deadly wasting syndrome that accompanies various diseases (including ~ 50% of cancers). Clinical studies have established that cachexia is not a nutritional deficiency and is linked to expression of certain proteins ( e.g. , interleukin-6 and C-reactive protein), but much remains unknown about this often fatal syndrome. Methods First, cachexia was created in experimental mouse models of lung cancer. Samples of human lung cancer were used to identify the association between the serum lipocalin 2 (LCN2) level and cachexia progression. Then, mouse models with LCN2 blockade or LCN2 overexpression were used to ascertain the role of LCN2 upon ferroptosis and cachexia. Furthermore, antibody depletion of tissue-infiltrating neutrophils (TI-Neu), as well as myeloid-specific-knockout of Lcn2 , were undertaken to reveal if LCN2 secreted by TI-Neu caused cachexia. Finally, chemical inhibition of ferroptosis was conducted to illustrate the effect of ferroptosis upon tissue wasting. Results Protein expression of LCN2 was higher in the wasting adipose tissue and muscle tissues of experimental mouse models of lung cancer cachexia. Moreover, evaluation of lung cancer patients revealed an association between the serum LCN2 level and cachexia progression. Inhibition of LCN2 expression reduced cachexia symptoms significantly and inhibited tissue wasting in vivo. Strikingly, we discovered a significant increase in the number of TI-Neu in wasting tissues, and that these innate immune cells secreted high levels of LCN2. Antibody depletion of TI-Neu, as well as myeloid-specific-knockout of Lcn2 , prevented ferroptosis and tissue wasting in experimental models of lung cancer cachexia. Chemical inhibition of ferroptosis alleviated tissue wasting significantly and also prolonged the survival of cachectic mice. Conclusions Our study provides new insights into how LCN2-induced ferroptosis functionally impacts tissue wasting. We identified LCN2 as a potential target in the treatment of cancer cachexia.

Background Functions of astrocytes in the rehabilitation after ischemic stroke, especially their impacts on inflammatory processes, remain controversial. This study uncovered two phenotypes of astrocytes, of which one was helpful, and the other harmful to anoxic neurons after brain ischemia. Methods We tested the levels of inflammatory factors including TNF-a, IL-6, IL-10, iNOS, IL-1beta, and CXCL10 in primary astrocytes at 0 h, 6 h, 12 h, 24 h, and 48 h after OGD, grouped the hypoxia astrocytes into iNOS-positive (iNOS(+)) and iNOS-negative (iNOS(−)) by magnetic bead sorting, and then co-cultured the two groups of cells with OGD-treated neurons for 24 h. We further verified the polarization of astrocytes in vivo by detecting the co-localization of iNOS, GFAP, and Iba-1 on MCAO brain sections. Lentivirus overexpressing LCN2 and LCN2 knockout mice (#024630. JAX, USA) were used to explore the role of LCN2 in the functional polarization of astrocytes. 7.0-T MRI scanning and the modified Neurological Severity Score (mNSS) were used to evaluate the neurological outcomes of the mice. Results After oxygen-glucose deprivation (OGD), iNOS mRNA expression increased to the peak at 6 h in primary astrocytes, but keep baseline expression in LCN2-knockout astrocytes. In mice with transient middle cerebral artery occlusion (tMCAO), LCN2 was proved necessary for astrocyte classical activation. In LCN2 knockout mice with MCAO, no classically activated astrocytes were detected, and smaller infarct volumes and better neurological functions were observed. Conclusions The results indicated a novel pattern of astrocyte activation after ischemic stroke and lipocalin-2 (LCN2) plays a key role in polarizing and activating astrocytes.

Psoriasis is a common chronic inflammatory skin disease with unclear pathogenesis and limited treatment. Fire needling acupuncture is a distinctive acupuncture technique that involves the rapid insertion of red-hot needles into skin lesions or acupoints. It has been shown to exert anti-inflammatory and immunomodulatory effects and to effectively alleviate the clinical symptoms of psoriasis. This study aims to explore the underlying mechanisms of fire needling acupuncture in the treatment of psoriasis. Imiquimod was used to induce the psoriasis-like mouse model, and five groups were established: Control, Imiquimod (IMQ), IMQ + Methotrexate, IMQ + Fire needling acupuncture, and IMQ + Cl-amidine. Skin lesion severity and epidermal thickness were evaluated using the Psoriasis Area and Severity Index (PASI) and hematoxylin and eosin (H&E) staining. The levels of inflammatory cytokines (IL-23, IL-17, TNF-α, and IL-1β) in skin lesions were quantified by enzyme-linked immunosorbent assay (ELISA). The expression of epidermal proliferation and differentiation markers (Ki67 and K10), neutrophil surface marker (Ly6G), and neutrophil extracellular traps (NETs)-associated markers (MPO and Cit-H3) were evaluated by immunofluorescence and immunohistochemistry. In addition, the expression levels of TLR4, MyD88, NF-κB, p-NF-κB, and LCN2 in epidermis were quantified by Western blot analysis. Fire needling acupuncture significantly reduced PASI scores, epidermal thickness, and the levels of IL-23, IL-17, TNF-α, and IL-1β in psoriasis-like lesions. It also decreased Ki67 expression while increasing K10 expression in the epidermis. Moreover, the expression of Ly6G, MPO, and Cit-H3 in the lesions was reduced, and the protein levels of TLR4, MyD88, p-NF-κB, and LCN2 were downregulated in the epidermis after fire needling acupuncture treatment. Comparable effects were observed with methotrexate and Cl-amidine. Fire needling acupuncture effectively improves skin lesions, suppresses abnormal keratinocyte proliferation and differentiation, and alleviates local inflammation in imiquimod-induced psoriasis-like mice. These therapeutic effects may be attributed to reduced neutrophil infiltration and NETs formation, as well as inhibition of TLR4/MyD88/NF-κB/LCN2 pathway.

Background Neurotoxic microglia and astrocytes begin to activate and participate in pathological processes after spinal cord injury (SCI), subsequently causing severe secondary damage and affecting tissue repair. We have previously reported that photobiomodulation (PBM) can promote functional recovery by reducing neuroinflammation after SCI, but little is known about the underlying mechanism. Therefore, we aimed to investigate whether PBM ameliorates neuroinflammation by modulating the activation of microglia and astrocytes after SCI. Methods Male Sprague–Dawley rats were randomly divided into three groups: a sham control group, an SCI + vehicle group and an SCI + PBM group. PBM was performed for two consecutive weeks after clip-compression SCI models were established. The activation of neurotoxic microglia and astrocytes, the level of tissue apoptosis, the number of motor neurons and the recovery of motor function were evaluated at different days post-injury (1, 3, 7, 14, and 28 days post-injury, dpi). Lipocalin 2 (Lcn2) and Janus kinase-2 (JAK2)-signal transducer and activator of transcription-3 (STAT3) signaling were regarded as potential targets by which PBM affected neurotoxic microglia and astrocytes. In in vitro experiments, primary microglia and astrocytes were irradiated with PBM and cotreated with cucurbitacin I (a JAK2-STAT3 pathway inhibitor), an adenovirus (shRNA-Lcn2) and recombinant Lcn2 protein. Results PBM promoted the recovery of motor function, inhibited the activation of neurotoxic microglia and astrocytes, alleviated neuroinflammation and tissue apoptosis, and increased the number of neurons retained after SCI. The upregulation of Lcn2 and the activation of the JAK2-STAT3 pathway after SCI were suppressed by PBM. In vitro experiments also showed that Lcn2 and JAK2-STAT3 were mutually promoted and that PBM interfered with this interaction, inhibiting the activation of microglia and astrocytes. Conclusion Lcn2/JAK2-STAT3 crosstalk is involved in the activation of neurotoxic microglia and astrocytes after SCI, and this process can be suppressed by PBM.

Intervertebral disc degeneration (IVDD) is driven by persistent inflammation–oxidative stress that disrupts annulus fibrosus (AF) homeostasis. Guided by network pharmacology and docking, we prioritized the NF‐κB–LCN2 axis as a druggable target of wedelolactone (WDL). To achieve targeted modulation, we engineered a dual‐network ROS‐responsive hydrogel (WPG) in which a phenylboronic‐ester/PVA redox‐cleavable network interpenetrates a covalently crosslinked GelMA–elastin matrix, enabling mechanically robust yet stimulus‐triggered WDL release. WDL suppressed NF‐κB activation and downregulated LCN2 in both macrophages and AF cells. Conditioned‐medium co‐culture demonstrated that WDL disrupts macrophage‐derived LCN2‐mediated paracrine amplification, breaking the self‐sustaining inflammatory loop. Bulk RNA‐seq across both cell types revealed coordinated downregulation of NF‐κB – driven chemokine cascades and restoration of adhesion and ECM gene programs following WPG treatment. In a rat AF‐defect model, intradiscal WPG administration preserved disc height and T2‐weighted MRI signal, reduced MMP13 while increasing Collagen I and Aggrecan expression, suppressed nuclear P‐p65 and LCN2, and improved segment biomechanics—without eliciting adverse hematological or organ responses. Collectively, these findings establish that aligning molecular targeting (NF‐κB–LCN2 modulation) with the pathophysiological context via ROS‐gated delivery provides a synergistic strategy for AF repair and attenuation of IVDD progression. A mechanically robust, ROS‐responsive hydrogel is engineered to treat intervertebral disc degeneration by targeting the NF‐κB–LCN2 inflammatory feedback loop. By delivering wedelolactone specifically within oxidative niches, this system disrupts macrophage–disc cell crosstalk. This “pathology‐triggered” strategy restores extracellular matrix homeostasis, preserves disc structure, and recovers biomechanical function in vivo.

The lipocalin proteins are a large family of small extracellular proteins that demonstrate significant heterogeneity in sequence similarity and have highly conserved crystal structures. They have a variety of functions, including acting as carrier proteins, transporting retinol, participating in olfaction, and synthesizing prostaglandins. Importantly, they also play a critical role in human diseases, including cancer. Additionally, they are involved in regulating cellular homeostasis and immune response and dispensing various compounds. This comprehensive review provides information on the lipocalin family, including their structure, functions, and implications in various diseases. It focuses on selective important human lipocalin proteins, such as lipocalin 2 (LCN2), retinol binding protein 4 (RBP4), prostaglandin D2 synthase (PTGDS), and α1-microglobulin (A1M).

Background MicroRNAs (miRNAs) are implicated in the progression of ischemic stroke (IS) and bone marrow-derived mesenchymal stem cells (BMSCs)-derived exosomes play a role in IS therapy. Herein we hypothesized that the BMSCs-derived exosomes containing overexpressed miR-138-5p could protect the astrocytes following IS involved with lipocalin 2 (LCN2). Methods The differentially expressed gene related to IS was initially identified by bioinformatics analysis. miR-138-5p was predicted to regulate LCN2. The expression of miR-138-5p and LCN2 was altered in the oxygen-glucose deprivation (OGD)-induced astrocytes. Furthermore, the cell behaviors and inflammatory responses were evaluated both in astrocytes alone and astrocytes co-cultured with exosomes derived from BMSCs overexpressing miR-138-5p to explore the involvement of miR-138-5p and LCN2 in IS. Besides, middle cerebral artery occlusion (MCAO) mouse model was established to explore the effect of BMSCs-derived exosomal miR-138-5p in IS in vivo. Results LCN2 was highly expressed in IS. Besides, LCN2 was a target gene of miR-138-5p. BMSCs-derived exosomes could be endocytosed by astrocytes via co-culture. Overexpression of miR-138-5p promoted the proliferation and inhibited apoptosis of astrocytes injured by OGD, accompanied by the reduced expression of inflammatory factors, which was achieved by down-regulating LCN2. More importantly, BMSCs delivered miR-138-5p to the astrocytes via exosomes and BMSCs-derived exosomal miR-138-5p alleviated neuron injury in IS mice. Conclusion BMSCs-derived exosomal miR-138-5p reduces neurological impairment by promoting proliferation and inhibiting inflammatory responses of astrocytes following IS by targeting LCN2, which may provide a novel target for IS treatment.

Damage to white matter and myelin poses a significant challenge to neurological recovery in the chronic phase of intracerebral hemorrhage (ICH). The repair of myelin damage post-ICH largely depends on the activation and differentiation of oligodendrocyte precursor cells (OPCs) into oligodendrocytes, a process that is significantly influenced by the inflammatory microenvironment. Lipocalin-2 (Lcn2) regulate phenotypic transformation of microglia and thus modulates inflammation. However, the exact role of Lcn2 in facilitating myelin recovery during the chronic phase of ICH remains to be fully understood. To create the ICH model, autologous blood from male C57BL/6 and Lcn2 Cx3cr1 mice was utilized. Behavioral tests were conducted to evaluate neurological recovery. The differentiation of OPCs and extent of myelin recovery were assessed using OPC and myelin markers. A multi-factor inflammatory chip was employed to investigate potential molecular regulatory mechanisms. Additionally, the Lcn2 inhibitor ZINC-94/89 was administered to explore its potential in targeting Lcn2 for enhancing myelin recovery during the chronic phase of ICH. Knocking out Lcn2 in microglia significantly improved behavioral performance in chronic ICH mice, reduced inflammatory response, and enhanced myelin recovery. Both and experiments confirmed that Lcn2 knockout promoted microglia transformation to the M2 phenotype and enhanced OPCs differentiation. Mechanistically, Lcn2 knockout might affect Gdf-1 secretion in BV2 cells by modulating the JAK/STAT signaling pathway. Treatment with JAK inhibitors decreased Gdf-1 expression in BV2 cells, inhibiting OPCs migration and differentiation. Additionally, phosphorylation of Stat3 at Thr705 plays a critical role in enhancing Gdf-1 transcription and translation. Administration of the Lcn2 inhibitor ZINC-94/89 significantly improved behavioral performance, reduced inflammatory response, and promoted myelin recovery in chronic ICH mice. Lcn2 is crucial for myelin recovery in the chronic phase of ICH by modulating microglial phenotypes, thereby enhancing the migration and differentiation of OPCs. Administering an Lcn2 inhibitor early on could serve as a novel and effective strategy to boost recovery during this phase.