Sepsis is a life-threatening condition that arises from a poorly regulated inflammatory response to pathogenic organisms. Current treatments are limited to antibiotics, fluid resuscitation, and other supportive therapies. New targets for monitoring disease progression and therapeutic interventions are therefore critically needed. We previously reported that lipocalin-2 (Lcn2), a bacteriostatic mediator with potent pro-apoptotic activities, was robustly induced in sepsis. Other studies showed that Lcn2 was a predictor of mortality in septic patients. However, how Lcn2 is regulated during sepsis is poorly understood. We evaluated how IkBζ, an inducer of Lcn2, was regulated in sepsis using both the cecal ligation and puncture (CLP) and endotoxemia (LPS) animal models. We show that Nfkbiz, the gene encoding for IkBζ, was rapidly stimulated but, unlike Lcn2, whose expression persists during sepsis, mRNA levels of Nfkbiz decline to near basal levels several hours after its induction. In contrast, we observed that IkBζ expression remained highly elevated in septic animals following CLP but not LPS, indicating the occurrence of a CLP-specific mechanism that extends IkBζ half-life. By using aninhibitor of IkBζ, we determined that the expression of Lcn2 was largely controlled by IkBζ. Altogether, these data indicate that the high IkBζ expression in tissues likely contributes to the elevated expression of Lcn2 in sepsis. Since IkBζ is also capable of promoting or repressing other inflammatory genes, it might exert a central role in sepsis.

Lipocalin-2 (LCN2) has been implicated in promoting apoptosis and neuroinflammation in neurological disorders; however, its role in neural transplantation remains unknown. In this study, we cultured and differentiated Lund human mesencephalic (LUHMES) cells into human dopaminergic-like neurons and found that LCN2 mRNA was progressively induced in mouse brain after the intrastriatal transplantation of human dopaminergic-like neurons. The induction of LCN2 protein was detected in a subset of astrocytes and neutrophils infiltrating the core of the engrafted sites, but not in neurons and microglia. LCN2-immunoreactive astrocytes within the engrafted sites expressed lower levels of A1 and A2 astrocytic markers. Recruitment of microglia, neutrophils, and monocytes after transplantation was attenuated in LCN2 deficiency mice. The expression of M2 microglial markers was significantly elevated and survival of engrafted neurons was markedly improved after transplantation in LCN2 deficiency mice. Brain type organic cation transporter (BOCT), the cell surface receptor for LCN2, was induced in dopaminergic-like neurons after differentiation, and treatment with recombinant LCN2 protein directly induced apoptosis in dopaminergic-like neurons in a dose-dependent manner. Our results, therefore, suggested that LCN2 is a neurotoxic factor for the engrafted neurons and a modulator of neuroinflammation. LCN2 inhibition may be useful in reducing rejection after neural transplantation.

Keywords: Lipocalin-2; graft; neuroinflammation; neutrophil gelatinase-associated lipocalin; rejection; transplantation.

Psoriasis is the most prevalent inflammatory skin disorders, affecting 1-3% of the worldwide population. We previously reported that topical application of methyl 4-(adenin-9-yl)-2-hydroxybutanoate (DZ2002), a reversible S-adenosyl-l-homocysteine hydrolase (SAHH) inhibitor, was a viable treatment in murine psoriatic skin inflammation. In current study, we further explored the mechanisms of DZ2002 on keratinocyte dysfunction and skin infiltration, the key pathogenic events in psoriasis. We conducted genome-wide DNA methylation analysis in skin tissue from imiquimod (IMQ)-induced psoriatic and normal mice, demonstrated that topical administration of DZ2002 directly rectified aberrant DNA methylation pattern in epidermis and dermis of psoriatic skin lesion. Especially, DZ2002 differentially regulated DNA methylation of GATA3 and LCN2 promoters, which maintained keratinocytes differentiation and reduced inflammatory infiltration in psoriatic skin respectively. In vitro studies in TNF-α/IFN-γ-elicited HaCaT manifested that DZ2002 treatment rectified compromised keratinocyte differentiation via GATA3 enhancement and abated chemokine expression by reducing LCN2 production under inflammatory stimulation. Chemotaxis assays conducted on dHL-60 cells confirmed that suppression of LCN2 expression by DZ2002 was accompanied by CXCR1 and CXCR2 downregulation, and contributed to the inhibition of CXCL8-driven neutrophils migration. In conclusion, therapeutic benefits of DZ2002 are achieved through differentially regulating DNA methylation of GATA3 and LCN2 promoters in psoriatic skin lesion, which efficiently interrupt the pathogenic interplay between keratinocytes and infiltrating immune cells, thus maintains epidermal keratinocytes differentiation and prevents dermal immune infiltration in psoriatic skin.

Keywords: DNA methylation; DZ2002; Inflammatory infiltration; Keratinocyte; Psoriasis.

Background: Duodenal papilla carcinoma (DPC) is a rare malignancy of the gastrointestinal tract with high recurrence rate, and the pathogenesis of this highly malignant neoplasm is yet to be fully elucidated. This study aims to identify key genes to further understand the biology and pathogenesis underlying the molecular alterations driving DPC, which could be potential diagnostic or therapeutic targets.

Methods: Tumor samples of three DPC patients were collected and integrating RNA-seq analysis of tumor tissues and matched normal tissues were performed to discover differentially expressed genes (DEGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were carried out to understand the potential bio-functions of the DPC differentially expressed genes (DEGs). Protein-protein interaction (PPI) network was constructed for functional modules analysis and identification of hub genes. qRT-PCR of clinical samples was conducted to validate the expression level of the hub genes.

Results: A total of 110 DEGs were identified from our RNA-seq data, GO and KEGG analyses showed that the DEGs were mainly enriched in multiple cancer-related functions and pathways, such as cell proliferation, IL-17signaling pathway, Jak-STAT signaling pathway, PPAR signaling pathway. The PPI network screened out five hub genes including IL-6, LCN2, FABP4, LEP and MMP1, which were identified as core genes in the network and the expression value were validated by qRT-PCR. The hub genes identified in this work were suggested to be potential therapeutic targets of DPC.

Discussion: The current study may provide new insight into the exploration of DPC pathogenesis and the screened hub genes may serve as potential diagnostic indicator and novel therapeutic target.

Keywords: Biomarker; Differentially expressed genes; Duodenal papilla carcinoma; RNA-seq.

Purpose: Evidence is accumulating that lipocalin2 (LCN2) is implicated in insulin resistance and glucose homeostasis, but the underlying possible mechanisms remain unclear. This study is to investigate the possible linkage between LCN2 and AMP-activated protein kinase (AMPK) or forkhead transcription factor O1 (FoxO1), which influences insulin sensitivity and gluconeogenesis in liver.

Methods: LCN2 knockout (LCN2KO) mice and wild-type littermates were used to evaluate the effect of LCN2 on insulin sensitivity and hepatic gluconeogenesis through pyruvate tolerance test (PTT), glucose tolerance test (ipGTT), insulin tolerance test (ITT), and hyperinsulinemic-euglycemic clamps, respectively. LCN2KO mice and WT mice in vivo, and in vitro HepG2 cells were co-transfected with adenoviral FoxO1-siRNA (Ad-FoxO1-siRNA) or adenovirus expressing constitutively active form of AMPK (Ad-CA-AMPK), or dominant negative adenovirus AMPK (Ad-DN-AMPK), the relative mRNA and protein levels of two key gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6P) were measured.

Results: Improved insulin sensitivity and inhibited gluconeogenesis in the LCN2KO mice were confirmed by pyruvate tolerance tests and hyperinsulinemic-euglycemic clamps. Nuclear FoxO1 and its downstream genes PEECK and G6P were decreased in the livers of the LCN2KO mice, and AMPK activity was stimulated and directly phosphorylated FoxO1. In vitro, AMPK activity was inhibited in HepG2 cells overexpressing LCN2 leading to a decrease in phosphorylated FoxO1 and an increase in nuclear FoxO1.

Conclusion: The present study demonstrates that LCN2 regulates insulin sensitivity and glucose metabolism through inhibiting AMPK activity, and regulating FoxO1 and its downstream genes PEPCK/G6P, which regulate hepatic gluconeogenesis.

Keywords: AMP-activated protein kinase; Forkhead transcription factor O1; Gluconeogenesis; Insulin sensitivity; Lipocalin-2.

We previously reported that excess of deoxycorticosterone-acetate (DOCA)/salt-induced cardiac hypertrophy in the absence of hypertension in one-renin gene mice. This model allows us to study molecular mechanisms of high-salt intake in the development of cardiovascular remodeling, independently of blood pressure in a high mineralocorticoid state. In this study, we compared the effect of 5-wk low- and high-salt intake on cardiovascular remodeling and cardiac differential gene expression in mice receiving the same amount of DOCA. Differential gene and protein expression was measured by high-density cDNA microarray assays, real-time PCR and Western blot analysis in DOCA-high salt (HS) vs. DOCA-low salt (LS) mice. DOCA-HS mice developed cardiac hypertrophy, coronary perivascular fibrosis, and left ventricular dysfunction. Differential gene and protein expression demonstrated that high-salt intake upregulated a subset of genes encoding for proteins involved in inflammation and extracellular matrix remodeling (e.g., Col3a1, Col1a2, Hmox1, and Lcn2). A major subset of downregulated genes encoded for transcription factors, including myeloid differentiation primary response (MyD) genes. Our data provide some evidence that vascular remodeling, fibrosis, and inflammation are important consequences of a high-salt intake in DOCA mice. Our study suggests that among the different pathogenic factors of cardiac and vascular remodeling, such as hypertension and mineralocorticoid excess and sodium intake, the latter is critical for the development of the profibrotic and proinflammatory phenotype observed in the heart of normotensive DOCA-treated mice.

A correction to this paper has been published and can be accessed via a link at the top of the paper.

Multiple Sclerosis (MS) is a complex autoimmune neuro-inflammatory disorder characterized by persistent MS plaques in the central nervous system. Resolution of MS plaques is dependent on the remyelination competence of surviving oligodendrocytes and surrounding environment. Here, we assessed myelination modulators in a 100 MS patients against 77 healthy controls. Plasma fractions were used for the assessment of insulin growth factor binding protein1 (IGFBP1), brain-derived neurotrophic factor (BDNF), and lipocalin2 (LCN2) using a Luminex multiplex assay, whereas neurofilament light chain (NF-L) was assessed with an enzyme-linked immunosorbent assay. Circulating levels of IGFBP1, LCN2 and NF-L were significantly higher in MS patients (p<0.01). Whereas BDNF levels were significantly lower in MS patients (p=0.014). MS Female patients had significantly higher levels of IGFBP1 compared to male MS patients (p=0.006). MS patients treated with fingolimod had higher LCN2 levels compared to those on natalizumab (r=0.25, p=0.03). Higher NF-L levels associated with clinically isolated syndrome's (CIS) conversion into MS (p=0.002). We conclude that low BDNF and high LCN2 and NF-L levels are associated with MS pathogenesis, and high IGFBP1level is a biomarker for female MS only, suggesting different MS progression pathways between the sexes. LCN2 is a candidate predictor of response to natalizumab treatment, and NF-L is a candidate predictor of CIS conversion into MS.

The biological activities of molecules secreted into the serum of mice chronically irradiated with γ rays at low or medium dose rate (L/MDR) have not been well studied. In this work, the bioactive molecules found in the serum of chronically irradiated mice (dose rate: 0.0181 Gy/h) were characterized by a cell-based assay (CBA) using microarrays. This technique can predict changes in cytokine levels in serum by measuring gene expression profiles and analyzing molecular signaling pathways. Gene expression in cultured mouse embryo fibroblasts (MEFs) 1 day after addition of serum from nonirradiated or irradiated mice had different profiles. A high level of expression of lipocalin2 (Lcn2) was induced in MEFs upon addition of serum from MDR irradiated mice, and Lcn2 was used as a marker for identifying secreted molecules in serum. Based on microarray analysis of molecular pathways, we predicted that the enhanced gene expression of Lcn2 in MEFs might be caused by interleukin-1 (IL-1) in the serum of the irradiated mice, and that an IL-1α antibody could completely neutralize the enhanced gene expression of Lcn2 in MEFs. The increase in IL-1α levels in the serum from the irradiated mice was confirmed by ELISA experiments. However, an increase in IL-1β could not be detected. These results indicated that IL-1α was released into the serum of mice chronically exposed to a high dose of γ-ray radiation at MDR. We therefore believe that the CBA method using microarrays will be applicable for the screening of bioactive molecules in serum, which will be useful for detecting various diseases and metabolic changes.

SIP24 is, a 24 kDa superinducible protein, is an acute phase protein that is expressed in several tissues and organs and is identified in the human, mouse, and rat genome as lipocalin 2 (lcn2). This study investigated SIP24 expression by the rat uterus just before delivery and during postpartum involution. The distribution and levels of expression of SIP24 and myeloperoxidase (MPO) were compared by Western blot analysis and immunocytochemistry. The SIP24 level was high on day 22 of pregnancy and on days 1 and 2 postpartum, decreased on day 3 postpartum, and declined to low levels similar to those in nonpregnant rats by day 5 postpartum. SIP24 positive cells were identified by immunohistochemistry in the luminal and glandular epithelium on day 22 of pregnancy and on days 1, 2, 3, and 5 postpartum in addition to nonpregnant rats. Immunostaining was intense on day 22 of pregnancy and on days 1 and 2 postpartum. MPO also was identified in uterine tissues by immunohistochemistry. An evaluation of the SIP24 and MPO distribution and levels of expression in the rat uterus is consistent with the hypothesis that SIP24 modulates the neutrophil population by activities such as inducing their apoptosis.

Female rats were fed with ethanol extraction of Alismatis Rhizoma for 6 months to study its nephrotoxicity and molecular mechanism. HPLC was used to determine the components in ethanol extraction of Alismatis Rhizoma. An assessment of renal pathology was determined by HE staining. Meanwhile Western blot, immunohistochemical assay and q-PCR were used to assess the protein expression and mRNA level of Kim-1, clusterin, LCN2, osteopontin, ceruloplasmin and TIMP1 in rat kidney. Eight components were identified in ethanol extraction of Alismatis Rhizoma. Tubule-interstitial inflammation, renal tubular epithelial cell exfoliation and morphological changes of cell were observed in rat kidney. Comparing with control blank group, the protein expression of clusterin, Kim-1, LCN2, osteopontin and TIMP1 in rat kidney was significantly increased while the protein expression of ceruloplasmin was significantly decreased. The mRNA level of Kim-1, TIMP1, osteopontin, clusterin and LCN2 was significantly increased while the mRNA level of ceruloplasmin was significantly decreased. In this study, it was inferred that there is chronic toxicity in kidney by using high dosage of ethanol extraction of Alismatis Rhizoma for a long time. And the underlying molecular mechanism was related to regulate the protein expression of ceruloplasmin, clusterin, Kim-1, LCN2, osteopontin and TIMP1.

The kidney's inherent complexity has made identifying cell-specific pathways challenging, particularly when temporally associating them with the dynamic pathophysiology of acute kidney injury (AKI). Here, we combine renal cell-specific luciferase reporter mice using a chemoselective luciferin to guide the acquisition of cell-specific transcriptional changes in C57BL/6 background mice. Hydrogen peroxide generation, a common mechanism of tissue damage, was tracked using a peroxy-caged-luciferin to identify optimum time points for immunoprecipitation of labeled ribosomes for RNA-sequencing. Together, these tools revealed a profound impact of AKI on mitochondrial pathways in the collecting duct. In fact, targeting the mitochondria with an antioxidant, ameliorated not only hydrogen peroxide generation, but also significantly reduced oxidative stress and the expression of the AKI biomarker, LCN2. This integrative approach of coupling physiological imaging with transcriptomics and drug testing revealed how the collecting duct responds to AKI and opens new venues for cell-specific predictive monitoring and treatment.

Background: Hidradenitis Suppurativa (HS) is a chronic inflammatory disease with diverse manifestations ranging from nodules and abscesses to draining tunnels. Whether the underlying inflammation from lesions extends to relatively healthy-appearing adjacent perilesional and distant nonlesional skin has not been systematically evaluated.

Objective: We sought to characterize lesional, perilesional and nonlesional skin in HS patients.

Methods: Skin biopsy samples were collected under ultrasound guidance from active, untreated moderate-to-severe HS patients. Site-matched healthy volunteer control biopsies were used for comparison.

Results: RNA-sequencing demonstrated that HS skin clustered separately from healthy controls, with perilesional and lesion skin clustering together and away from nonlesional skin. Immunohistochemistry analysis identified psoriasiform hyperplasia with keratin 16 positivity in both perilesional and lesional skin, with comparable levels of CD3⁺, CD11c⁺ and Neutrophil Elastase⁺ cellular infiltration. There was a marked up-regulation of IL-17 signaling in perilesional and lesional skin. HS samples clustered based on the expression of Lipocalin-2 (LCN2), with samples with high LCN2 expression in the skin exhibiting a differing transcriptomic profile with significantly higher overall inflammation compared to those with low LCN2 levels.

Conclusions: Perilesional HS skin has a comparable transcriptomic and molecular profile as the lesional skin. HS can be grouped into two distinct subtypes based on molecular levels of LCN2 in the skin, with the LCN2-high subtype exhibiting a higher overall inflammatory burden and an upregulation of targetable cytokines. This is the first study to characterize a unique HS subtype (and a potential endotype) which may guide future therapeutic targets.

Keywords: Hidradenitis Suppurativa; IL-17 signaling; Lipocalin-2; lesional; neutrophils; nonlesional; perilesional.

Pulmonary emphysema, inflammation and senescence-like phenotype are pathophysiological characteristics of chronic obstructive pulmonary disease (COPD). Recently, a murine model of COPD has been established by inducing airway-specific overexpression of epithelial Na⁺ channel β subunit (βENaC-Tg mice). However, little is known about the histological and biochemical differences between βENaC-Tg mice and an existing acute emphysematous mouse model (elastase-induced model). Here, we first utilized whole lung image-based quantification method for histological analysis to determine auto-measure parameters, including alveolar area, alveolar perimeter, (major axis + minor axis)/2 and Feret diameter. Even though the extent of emphysema was similar in both models, the coefficient of variation (CV) of all histological parameters was smaller in βENaC-Tg mice, indicating that βENaC-Tg mice show homogeneous emphysema as compared with elastase-induced acute model. Expression analysis of lung tissue RNAs further revealed that elastase-induced model exhibits transient changes of inflammation markers (Kc, Il-6, Lcn2) and senescence-related markers (Sirt1, p21) at emphysema-initiation stage (1 day), which does not last until emphysema-manifestation stage (3 weeks); while the up-regulation is stable at emphysema-manifestation stage in βENaC-Tg mice (14-week old). Thus, these studies demonstrate that βENaC-Tg mice exhibit diffuse-type emphysema with stable expression of inflammatory and senescence-like markers.

Stroke is a leading cause of adult disability in the United States. However, limited number of molecularly targeted therapy exists for stroke. Recent studies have shown that Li-pocalin-2 (LCN2) is an acute phase protein mediating neuroinflammation after ischemic and hemorrhagic strokes. This review is an attempt to summarize some LCN2-related research findings and discuss its role in stroke.

Obesity represents a global health and economic burden, affecting millions of individuals worldwide. This pathology is associated with a chronic low‑grade inflammatory state that is partially responsible for the development of other cardiometabolic complications. Clinical studies have reported an association between high circulating levels of lipocalin‑2 (Lcn2) and increased body weight. Additionally, there is scientific evidence demonstrating the impact of maternal obesity on fetal programming. The latter and the fact that the authors previously found that Lcn2 and its receptor (24p3R) are expressed in the gonads of wild‑type rats, led to the analysis of their mRNA profile and cellular localization in gonads collected from the offspring of obese rats at 21 days postconception (dpc), and 0, 2, 4, 6, 12, 20 and 30 days postnatal (dpn) in the present study. Semi‑quantitative PCR revealed a statistically significant downregulation of Lcn2 and 24p3R mRNA at 21 dpc in the ovaries (P<0.01) and testicles (P<0.001) of the offspring of obese mothers. At 30 dpn, the relative expression of Lcn2 mRNA decreased significantly in the ovaries of the experimental group (P<0.05), while Lcn2 mRNA expression was not detectable in testicles. Regarding 24p3R, its mRNA was only significantly decreased at 21 dpc in ovaries of pups of obese mothers. At 30 dpn, the change in females was not significant. Conversely, in testicles, 24p3R mRNA levels increased slightly in the experimental group at 30 dpn. The Lcn2 protein signal was less intense in gonadal tissue sections from 30 dpn offspring of obese rats (P<0.001), whereas the 24p3R signal was downregulated in ovaries (P<0.001) and slightly upregulated in testicles. It was concluded that maternal obesity changes the expression of Lcn2 and 24p3R in the gonads of the offspring of obese rats, possibly through fetal programming. The consequences of this dysregulation for the offspring's gonadal function remains to be determined.

Acute ischemic stroke (AIS) is followed by a strong inflammatory response contributing to brain damage and making early diagnosis and treatment inevitable. Hence, obesity is a state of chronic inflammation with amplified oxidative stress; this study aimed to assess the role played by thrombomodulin (TM)/alarmin signaling pathway and copeptin in AIS initiation and severity in addition to the implication of abnormal body weight. The study was conducted on 50 participants; 30 were patients with AIS (15 overweight/obese and 15 normal weight), 10 were overweight/obese, and 10 were normal weight. Plasma TM, copeptin, high mobility group box1 (HMGB1), and lipocalin 2 (LCN2) levels were immunoassayed. Toll-like receptor 4 (TLR4) mRNA expression was evaluated by real-time PCR, National Institutes of Health Stroke Scale (NIHSS), carotid intima media thickness; atherogenic index and glycemic status were also assessed. TM, copeptin, HMGB1, and LCN2 levels were significantly increased in overweight/obese AIS patients and in AIS patients with NIHSS score ≥ 7 when compared to other groups (p value=, ˂ 0.001*). Receiver operating characteristic (ROC) curve elaborated HMGB-1 and LCN2 as the best biomarker for diagnosis and prediction of AIS severity, respectively. Regression analysis avails LCN2 and TM as best biomarker for AIS severity predication. In conclusion, these results highlighted detrimental role of alarmin signaling with increased adaptive response to block this pathway through TM in addition to increased copeptin level as an acute damage marker and their tight relation to WC not to BMI in AIS which clarify the implication of central adiposity.

Over the past century, obesity has developed into a paramount health issue that affects millions of people worldwide. Obese individuals have an increased risk to develop other metabolic disorders, such as insulin resistance and atherosclerosis, among others. Previously we determined that mice lacking stearoyl-CoA desaturase-1 (SCD1) enzyme specifically in the skin (SKO) were lean and protected from high-fat diet induced adiposity. Additionally, lipocalin 2 (Lcn2) mRNA was found to be 27-fold higher in the skin of SKO mice compared to control mice. Given reports suggesting that Lcn2 plays a role in protection against diet-induced weight gain, adiposity and insulin resistance, we hypothesized that deletion of Lcn2 alongside the skin-specific SCD1 deficiency would diminish the obesity resistance observed in SKO mice. To test this, we developed mice lacking SCD1 expression in the skin and also lacking Lcn2 expression globally and surprisingly, these mice did not gain significantly more weight than the SKO mice under high-fat diet conditions. Therefore, we conclude that Lcn2 does not mediate the protection against high-fat diet-induced adiposity observed in SKO mice.

BACKGROUND

The role of lipocalin 2 (LCN2) in type 2 diabetes mellitus (T2DM) needs to be fully elucidated. Moreover, bone has been demonstrated to modulate glucose metabolism via LCN2. We thus performed this study to investigate the associations of LCN2 with indexes of glucose metabolism in T2DM. The associations of LCN2 with bone metabolism were examined concurrently.

METHODS

Total 288 Chinese Han subjects entered in this study including 146 patients with T2DM and 142 subjects with normal glucose tolerance. Insulin resistance was assessed by HOMA-IR and.

Antibody-mediated glomerulonephritis (AGN) is a clinical manifestation of many autoimmune kidney diseases for which few effective treatments exist. Chronic inflammatory circuits in renal glomerular and tubular cells lead to tissue damage in AGN. These cells are targeted by the cytokine IL-17, which has recently been shown to be a central driver of the pathogenesis of AGN. However, surprisingly little is known about the regulation of pathogenic IL-17 signaling in the kidney. Here, using a well-characterized mouse model of AGN, we show that IL-17 signaling in renal tubular epithelial cells (RTECs) is necessary for AGN development. We also show that Regnase-1, an RNA binding protein with endoribonuclease activity, is a negative regulator of IL-17 signaling in RTECs. Accordingly, mice with a selective Regnase-1 deficiency in RTECs exhibited exacerbated kidney dysfunction in AGN. Mechanistically, Regnase-1 inhibits IL-17-driven expression of the transcription factor IκBξ and, consequently, its downstream gene targets, including Il6 and Lcn2. Moreover, deletion of Regnase-1 in human RTECs reduced inflammatory gene expression in a IκBξ-dependent manner. Overall, these data identify an IL-17-driven inflammatory circuit in RTECs during AGN that is constrained by Regnase-1.

Keywords: Autoimmune diseases; Cytokines; Immunology; Inflammation; Innate immunity.

Lipocalin 2 (LCN2) is a pleiotropic molecule that is induced in the central nervous system (CNS) in several acute and chronic pathologies. The acute induction of LCN2 evolved as a beneficial process, aimed at combating bacterial infection through the sequestration of iron from pathogens, while the role of LCN2 during chronic, non-infectious disease remains unclear, and recent studies suggest that LCN2 is neurotoxic. However, whether LCN2 is sufficient to induce behavioral and cognitive alterations remains unclear. In this paper, we sought to address the role of cerebral LCN2 on cognition in both acute and chronic settings. We demonstrate that LCN2 is robustly induced in the CNS during both acute and chronic inflammatory conditions, including LPS-based sepsis and cancer cachexia. In vivo, LPS challenge results in a global induction of LCN2 in the central nervous system, while cancer cachexia results in a distribution specific to the vasculature. Similar to these in vivo observations, in vitro modeling demonstrated that both glia and cerebral endothelium produce and secrete LCN2 when challenged with LPS, while only cerebral endothelium secrete LCN2 when challenged with cancer-conditioned medium. Chronic, but not short-term, cerebral LCN2 exposure resulted in reduced hippocampal neuron staining intensity, an increase in newborn neurons, microglial activation, and increased CNS immune cell infiltration, while gene set analyses suggested these effects were mediated through melanocortin-4 receptor independent mechanisms. RNA sequencing analyses of primary hippocampal neurons revealed a distinct transcriptome associated with prolonged LCN2 exposure, and ontology analysis was suggestive of altered neurite growth and abnormal spatial learning. Indeed, LCN2-treated hippocampal neurons display blunted neurite processes, and mice exposed to prolonged cerebral LCN2 levels experienced a reduction in spatial reference memory as indicated by Y-maze assessment. These findings implicate LCN2 as a pathologic mediator of cognitive decline in the setting of chronic disease.

Keywords: Cachexia; Cognitive decline; Gliosis; Hippocampus; Lipocalin 2; Sepsis; Spatial reference memory.