Molecular mechanism underlying persistent induction of LCN2 by lipopolysaccharide in kidney fibroblasts

Basic biology and roles of CEBPD in cardiovascular disease

CCAAT/enhancer-binding protein delta (CEBPD), as an evolutionarily conserved protein in mammals, belongs to the CEBP transcription factor family, which modulates many biological processes. The diversity of CEBPD functions partly depends on the cell type and cellular context. Aberrant CEBPD expression and activity are associated with multiple organ diseases, including cardiovascular diseases. In this review, we describe the basic molecular biology of CEBPD to understand its expression regulation, modifications, and functions. Here, we summarize the recent advances in genetically modified animals with CEBPD. Finally, we discuss the contribution of CEBPD to cardiovascular diseases and highlight the strategies for developing novel therapies targeting CEBPD.

Loss of SREBP-1c ameliorates iron-induced liver fibrosis by decreasing lipocalin-2

Sterol regulatory element-binding protein (SREBP)-1c is involved in cellular lipid homeostasis and cholesterol biosynthesis and is highly increased in nonalcoholic steatohepatitis (NASH). However, the molecular mechanism by which SREBP-1c regulates hepatic stellate cells (HSCs) activation in NASH animal models and patients have not been fully elucidated. In this study, we examined the role of SREBP-1c in NASH and the regulation of LCN2 gene expression. Wild-type and SREBP-1c knockout (1cKO) mice were fed a high-fat/high-sucrose diet, treated with carbon tetrachloride (CCl4), and subjected to lipocalin-2 (LCN2) overexpression. The role of LCN2 in NASH progression was assessed using mouse primary hepatocytes, Kupffer cells, and HSCs. LCN2 expression was examined in samples from normal patients and those with NASH. LCN2 gene expression and secretion increased in CCl4-induced liver fibrosis mice model, and SREBP-1c regulated LCN2 gene transcription. Moreover, treatment with holo-LCN2 stimulated intracellular iron accumulation and fibrosis-related gene expression in mouse primary HSCs, but these effects were not observed in 1cKO HSCs, indicating that SREBP-1c-induced LCN2 expression and secretion could stimulate HSCs activation through iron accumulation. Furthermore, LCN2 expression was strongly correlated with inflammation and fibrosis in patients with NASH. Our findings indicate that SREBP-1c regulates Lcn2 gene expression, contributing to diet-induced NASH. Reduced Lcn2 expression in 1cKO mice protects against NASH development. Therefore, the activation of Lcn2 by SREBP-1c establishes a new connection between iron and lipid metabolism, affecting inflammation and HSCs activation. These findings may lead to new therapeutic strategies for NASH.

The Unfolded Protein Response Is a Major Driver of LCN2 Expression in BCR-ABL- and JAK2V617F-Positive MPN

Lipocalin 2 (LCN2), a proinflammatory mediator, is involved in the pathogenesis of myeloproliferative neoplasms (MPN). Here, we investigated the molecular mechanisms of LCN2 overexpression in MPN. LCN2 mRNA expression was 20-fold upregulated in peripheral blood (PB) mononuclear cells of chronic myeloid leukemia (CML) and myelofibrosis (MF) patients vs. healthy controls. In addition, LCN2 serum levels were significantly increased in polycythemia vera (PV) and MF and positively correlated with JAK2V617F and mutated CALR allele burden and neutrophil counts. Mechanistically, we identified endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) as a main driver of LCN2 expression in BCR-ABL- and JAK2V617F-positive 32D cells. The UPR inducer thapsigargin increased LCN2 expression >100-fold, and this was not affected by kinase inhibition of BCR-ABL or JAK2V617F. Interestingly, inhibition of the UPR regulators inositol-requiring enzyme 1 (IRE1) and c-Jun N-terminal kinase (JNK) significantly reduced thapsigargin-induced LCN2 RNA and protein expression, and luciferase promoter assays identified nuclear factor kappa B (NF-κB) and CCAAT binding protein (C/EBP) as critical regulators of mLCN2 transcription. In conclusion, the IRE1-JNK-NF-κB-C/EBP axis is a major driver of LCN2 expression in MPN, and targeting UPR and LCN2 may represent a promising novel therapeutic approach in MPN.

Identification of gut microbiota and microbial metabolites regulated by an antimicrobial peptide lipocalin 2 in high fat diet-induced obesity

Lipocalin 2 (Lcn2), as an anti-microbial peptide is expressed in intestine, and the upregulation of intestinal Lcn2 has been linked to inflammatory bowel disease. However, the role of Lcn2 in shaping gut microbiota during diet-induced obesity (DIO) remains unknown. We found that short-term high fat diet (HFD) feeding strongly stimulates intestinal Lcn2 expression and secretion into the gut lumen. As the HFD feeding prolongs, fecal Lcn2 levels turn to decrease. Lcn2 deficiency accelerates the development of HFD-induced intestinal inflammation and microbiota dysbiosis. Moreover, Lcn2 deficiency leads to the remodeling of microbiota-derived metabolome, including decreased production of short-chain fatty acids (SCFAs) and SCFA-producing microbes. Most importantly, we have identified Lcn2-targeted bacteria and microbiota-derived metabolites that potentially play roles in DIO and metabolic dysregulation. Correlation analyses suggest that Lcn2-targeted Dubosiella and Angelakisella have a novel role in regulating SCFAs production and obesity. Our results provide a novel mechanism involving Lcn2 as an anti-microbial host factor in the control of gut microbiota symbiosis during DIO.

Alcohol decreases intestinal ratio of Lactobacillus to Enterobacteriaceae and induces hepatic immune tolerance in a murine model of DSS-colitis

Alcohol can potentiate disease in a mouse model of dextran sodium sulfate (DSS) colitis; however, the underlying mechanism remains to be established. In this study, we assessed whether the potentiated disease could be related to Enterobacteriaceae and Lactobacillus, as changes in their relative abundance can impact intestinal health. We also assessed whether the intestinal barrier is compromised after alcohol and DSS as it may increase bacterial translocation and liver inflammation. Mice were administered DSS followed by binge ethanol or water vehicle, generating four experimental groups: (Control+Vehicle, Control+Ethanol, DSS+Vehicle, DSS+Ethanol). DNA was isolated from colon and cecal contents followed by qPCR for levels of Enterobacteriaceae and Lactobacillus. Colon and liver sections were taken for histology. Intestinal epithelial cells were isolated from the colon for RNA expression. DSS+Ethanol cecal contents exhibited a 1 log increase in Enterobacteriaceae (p < .05), a 0.5 log decrease in Lactobacillus, and a 1.5 log decrease (p < .05) in the Lactobacillus:Enterobacteriaceae ratio compared to DSS+Vehicle, with similar trends in colon contents. These changes correlated with shorter colons and more weight loss. Irrespective of ethanol administration, DSS compromised the mucosal barrier integrity, however only DSS+Ethanol exhibited significant increases in circulating endotoxin. Furthermore, the livers of DSS+Ethanol mice had significantly increased levels of triglycerides, mononuclear cells, yet exhibited significantly depressed expression of liver inflammatory pathways, suggestive of tolerance induction, compared to mice receiving DSS+Vehicle. Our results suggest that ethanol after DSS colitis increases the intestinal burden of Enterobacteriaceae which may contribute to intestinal and liver damage, and the induction of immune tolerance.

Lipocalin-2 Predicts Long-Term Outcome of Normotensive Patients with Acute Pulmonary Embolism

Normotensive patients with acute pulmonary embolism (APE) are accompanied by heterogeneously adverse events. Responding to tissue injury, lipocalin-2 (LCN-2) is elevated in experimental APE model and associated with short-term prognosis. However, the prognostic value of LCN-2 in normotensive patients with APE for long-term major adverse events (MAEs) remains unknown. We evaluated the association of plasma LCN-2 levels with the median 467-day outcome in 170 normotensive patients with APE. We also assessed whether LCN-2 could improve risk stratification. MAEs consisted of mortality or recurrence of venous thromboembolism. During follow-up, 17 (10%) patients suffered from MAEs. These patients had higher LCN-2 levels compared with patients without MAEs (median: 13.97 vs. 8.55 ng/ml, P = 0.01). The proportion of MAEs in the intermediate-low-risk group (14.0%) was higher than that in the intermediate-high-risk group (5.3%). LCN-2 levels independently had prognostic value for MAEs in overall (HR = 3.40, 95% CI 1.46-7.90) and intermediate-risk group (HR = 3.88, 95% CI 1.63-9.23). LCN-2 also showed incremental value in overall (ΔC-index: 0.13, 95% CI 0.02-0.24; category-based NRI = 0.25, 95% CI 0.07-0.42) and intermediate-risk patients (ΔC-index: 0.13, 95% CI 0.05-0.31; category-based NRI = 0.44, 95% CI 0.24-0.65). Adding LCN-2 (cut-off value = 11 ng/ml) to the current risk algorithm improved MAEs of intermediate-risk reclassification (intermediate-high vs. intermediate-low = 25.6% vs. 6.0%, P = 0.002). Elevated plasma LCN-2 levels predict long-term MAEs among normotensive patients with APE. LCN-2 might be a useful biomarker for risk stratification in the intermediate-risk group.

Metformin alleviates nickel-induced autophagy and apoptosis via inhibition of hexokinase-2, activating lipocalin-2, in human bronchial epithelial cells

Autophagy is an intracellular recycling and degradation process for regulating tumor progression, survival and drug resistance. Nickel compounds have been identified as human carcinogens. However, the role of nickel-induced autophagy in lung carcinogenesis has not yet been fully elucidated. In this study, we determined that hexokinase 2 (HK2), which phosphorylates glucose and regulates autophagy, is the key mediator in nickel-induced autophagy in lung bronchial epithelial cells. We attempted to investigate the effects of the antidiabetic drug metformin on HK2 expression and lung cancer chemoprevention. Our results showed that metformin decreases nickel-induced autophagy and activation of apoptosis through inhibition of HK2 gene, protein and activity. Furthermore, we demonstrated that lipocalin 2 (LCN2), which is released by neutrophils at sites of infection and inflammation is involved in HK2-driven autophagy pathway. Knockdown of endogenous HK2 and LCN2 by shRNA reduced nickel-elicited autophagy and apoptosis, illustrating that metabolic alteration and inflammatory action are important in nickel-elicited carcinogenesis. We also determined the association between nickel-induced autophagy and apoptosis. Inhibition of nickel-induced autophagy abolished apoptotic cell death in chloroquine-treated, shLC3 Beas-2B cells and Atg5^−/− MFFs. From TGCA database and immunohistochemistry analysis, HK2 and LCN2 expression increased in lung squamous cell carcinoma and their related adjacent normal tissues. Taken together, our results demonstrated that metformin alleviates NiCl₂-induced autophagy and apoptosis via HK2-driven LCN2 activation in human bronchial epithelial cells. This novel mechanism provides a strategy for targeting nickel-elicited lung cancer progression, as well as for preventing HK2 cumulative damage triggered by environmental carcinogens.

Transcriptional study of hyperoxaluria and calcium oxalate nephrolithiasis in male rats: Inflammatory changes are mainly associated with crystal deposition

Hyperoxaluria associated with renal deposition of calcium oxalate (CaOx) crystals causes renal injury and inflammation leading to number of diseases including chronic kidney disease (CKD). It is however, not been possible to separate the renal consequences of hyperoxaluria from that of CaOx crystal deposition. We decided to utilize ethylene glycol (EG) model where hyperoxaluria and CaOx crystal deposition can be separated in time. To test our hypothesis, male rats were made hyperoxaluric by administering EG, rats were euthanized and kidneys were extracted on day 14, when occasional crystal is seen in the kidneys and day 28, when all animals have developed renal CaOx crystal deposits. Total RNA was extracted for microarray analysis and genome wide analysis of differentially expressed genes was performed to investigate differences between hyperoxaluria and crystal induced alterations in the kidneys. Immunohistochemical and Hematoxylin and Eosin (H&E) staining was also done for macromolecules with significant role in stone formation. All EG fed rats became hyperoxaluric by day 7, showed a few crystal deposits on day 14, and had heavy crystal deposition by day 28. There were significant changes in the expression of genes encoding for NADPH Oxidases; macromolecular crystallization modulators; genes involved in inflammasome activation; and osteogenic marker genes. Results demonstrate major differences between hyperoxaluria and CaOx crystal induced changes in the kidneys. Injury and inflammation are mainly associated with crystal deposition indicating significant role played by crystal retention.

TCF7L1 promotes skin tumorigenesis independently of β-catenin through induction of LCN2

The transcription factor TCF7L1 is an embryonic stem cell signature gene that is upregulated in multiple aggressive cancer types, but its role in skin tumorigenesis has not yet been defined. Here we document TCF7L1 upregulation in skin squamous cell carcinoma (SCC) and demonstrate that TCF7L1 overexpression increases tumor incidence, tumor multiplicity, and malignant progression in the chemically induced mouse model of skin SCC. Additionally, we show that downregulation of TCF7L1 and its paralogue TCF7L2 reduces tumor growth in a xenograft model of human skin SCC. Using separation-of-function mutants, we show that TCF7L1 promotes tumor growth, enhances cell migration, and overrides oncogenic RAS-induced senescence independently of its interaction with β-catenin. Through transcriptome profiling and combined gain- and loss-of-function studies, we identified LCN2 as a major downstream effector of TCF7L1 that drives tumor growth. Our findings establish a tumor-promoting role for TCF7L1 in skin and elucidate the mechanisms underlying its tumorigenic capacity.

E74-like factor 3 and nuclear factor-κB regulate lipocalin-2 expression in chondrocytes

KEY POINTS

E74-like factor 3 (ELF3) is a transcription factor regulated by inflammation in different physio-pathological situations. Lipocalin-2 (LCN2) emerged as a relevant adipokine involved in the regulation of inflammation. In this study we showed for the first time the involvement of ELF3 in the control of LCN2 expression and its cooperation with nuclear factor-κB (NFκB). Our results will help to better understand of the role of ELF3, NFκB and LCN2 in the pathophysiology of articular cartilage.

ABSTRACT

E74-like factor 3 (ELF3) is a transcription factor induced by inflammatory cytokines in chondrocytes that increases gene expression of catabolic and inflammatory mediators. Lipocalin 2 (LCN2) is a novel adipokine that negatively impacts articular cartilage, triggering catabolic and inflammatory responses in chondrocytes. Here, we investigated the control of LCN2 gene expression by ELF3 in the context of interleukin 1 (IL-1)-driven inflammatory responses in chondrocytes. The interaction of ELF3 and nuclear factor-κB (NFκB) in modulating LCN2 levels was also explored. LCN2 mRNA and protein levels, as well those of several other ELF3 target genes, were determined by RT-qPCR and Western blotting. Human primary chondrocytes, primary chondrocytes from wild-type and Elf3 knockout mice, and immortalized human T/C-28a2 and murine ATDC5 cell lines were used in in vitro assays. The activities of various gene reporter constructs were evaluated by luciferase assays. Gene overexpression and knockdown were performed using specific expression vectors and siRNA technology, respectively. ELF3 overexpression transactivated the LCN2 promoter and increased the IL-1-induced mRNA and protein levels of LCN2, as well as the mRNA expression of other pro-inflammatory mediators, in human and mouse chondrocytes. We also identified a collaborative loop between ELF3 and NFκB that amplifies the induction of LCN2. Our findings show a novel role for ELF3 and NFκB in the induction of the pro-inflammatory adipokine LCN2, providing additional evidence of the interaction between ELF3 and NFκB in modulating inflammatory responses, and a better understanding of the mechanisms of action of ELF3 in chondrocytes.

The function of miR-199a-5p/Klotho regulating TLR4/NF-κB p65/NGAL pathways in rat mesangial cells cultured with high glucose and the mechanism

Anti-aging protein Klotho may confer a renal protective effect via attenuating the nuclear factor-κB (NF-κB) p65 pathways activity. Besides, miR-199a-5p can promote gastric cancer by inhibition of Klotho protein expression. But little is known regarding to the role of miR-199a-5p/Klotho in regulating NF-κB p65 pathways in the pathogenesis of diabetic kidney disease (DKD). Thus, we explored Klotho and miR-199a-5p in terms of Toll-like receptor-4 (TLR4)/NF-κB p65/neutrophil gelatinase associated lipocalin (NGAL) signaling pathways in high glucose cultured mesangial cells (MCs). We found that high glucose increased miR-199a-5p expression, accompanied by the significantly decreased Klotho expression at both mRNA and protein. High glucose also activated TLR4/NF-κB p65/NGAL signaling pathways and promoted the downstream fibrosis and inflammatory reaction. Additionally, inhibition of miR-199a-5p or exogenous addition of Klotho restrained the activity of TLR4/NF-κB p65/NGAL signaling pathways, which in turn suppressed the inflammation and fibrosis in high glucose cultured MCs. This study provides a new basis to elucidate the protection mechanism of anti-aging protein Klotho in diabetic kidney. For the first time, our study prompts that miR-199a-5p can be used as a new therapeutic targets for DKD.

Sustained expression of lipocalin-2 during polymicrobial sepsis

Sepsis is a major healthcare problem and a leading cause of death worldwide. There is no dependable diagnosis, and treatment for this condition remains mainly supportive. The etiology of sepsis is related to an overwhelming inflammatory response. In this regard, the antimicrobial protein lipocalin-2 (Lcn2) has been associated with several inflammatory conditions, but its contribution to polymicrobial sepsis is unclear. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP), and Lcn2 mRNA levels and protein expression were measured in liver and lung tissues. We observed that Lcn2 expression was robustly induced in liver and lung of C57BL/6 J (B6) mice, and remained elevated during the stage of innate immune dysfunction observed in sepsis. This response was different in A/J mice, suggesting a contribution of the genetic background, probably due to differences in IL-10 expression between these two mouse strains. Indeed, IL-10 was found to regulate Lcn2 expression in both primary and J774A.1 macrophages. Thus, Lcn2 expression is highly regulated during CLP-induced sepsis, suggesting that this antimicrobial protein could have a role as a potential biomarker for the diagnosis of sepsis.

Mechanism and clinical evidence of lipocalin-2 and adipocyte fatty acid-binding protein linking obesity and atherosclerosis

Obesity is considered to be a chronic inflammatory state in which the dysfunction of adipose tissue plays a central role. The adipokines, which are cytokines secreted by adipose tissue, are key links between obesity and related diseases such as metabolic syndrome and atherosclerosis. LCN2 and A-FABP, both of which are major adipokines predominantly produced in adipose tissue, have recently been shown to be pivotal modulators of vascular function. However, different adipokines modulate the development of atherosclerosis in distinctive manners, which are partly attributable to their unique regulatory mechanisms and functions. This review highlights recent advances in the understanding of the role of two adipokines in mediating chronic inflammation and the pathogenesis of atherosclerosis.

The many faces of C/EBPδ and their relevance for inflammation and cancer

The CCAAT/enhancer binding protein delta (CEBPD, C/EBPδ) is a transcription factor that modulates many biological processes including cell differentiation, motility, growth arrest, proliferation, and cell death. The diversity of C/EBPδ's functions depends in part on the cell type and cellular context and can have opposing outcomes. For example, C/EBPδ promotes inflammatory signaling, but it can also inhibit pro-inflammatory pathways, and in a mouse model of mammary tumorigenesis, C/EBPδ reduces tumor incidence but promotes tumor metastasis. This review highlights the multifaceted nature of C/EBPδ's functions, with an emphasis on pathways that are relevant for cancer and inflammation, and illustrates how C/EBPδ emerged from the shadow of its family members as a fascinating “jack of all trades.” Our current knowledge on C/EBPδ indicates that, rather than being essential for a specific cellular process, C/EBPδ helps to interpret a variety of cues in a cell-type and context-dependent manner, to adjust cellular functions to specific situations. Therefore, insights into the roles and mechanisms of C/EBPδ signaling can lead to a better understanding of how the integration of different signaling pathways dictates normal and pathological cell functions and physiology.

Polymorphisms in the SUFU gene are associated with organ injury protection and sepsis severity in patients with Enterobacteriacea bacteremia

BACKGROUND

Organ injury including acute kidney injury (AKI) and acute lung Injury (ALI) are major contributors to mortality and morbidity in the setting of sepsis. Hedgehog pathway has been recognized as an important mediator in repair of organ injury. There are some clinical predictors associated with the development of organ injury in sepsis; however few host genetic risk factors have been identified and candidate genes for organ injury susceptibility and severity are largely unknown.

METHODS

A prospective cohort study in a tertiary care hospital included 250 adult hospitalized patients with Enterobacteriacea bacteremia. We selected a panel of 69 tagging SNPs for genes in the Hedgehog signaling pathway using the TagSNP functionality of the SNPInfo web server and designed a panel on the GoldenGate Veracode genotyping assay (Illumina). We confirmed Illumina data using Taqman allelic discrimination assays. We assessed SNPs in combination with clinical variables for associations with outcomes and organ injury.

RESULTS

Significant associations were identified using logistic regression models, controlling for age, race and gender. From the 69 tagging SNPs, 5 SNPs were associated with renal function and 2 with APACHEII score after false discovery rate correction. After multivariate analysis SNPs rs10786691 (p=0.03), rs12414407 (p=0.026), rs10748825 (p=0.01), and rs7078511 (p=0.006), all in the suppressor of fused homolog (SUFU) gene, correlated with renal function. Likewise, SUFU SNPs rs7907760 (p=0.009) and rs10748825 (p=0.029) were associated with APACHEII score. SNPs rs12414407 and rs1078825 are in linkage disequilibrium (LD) with rs2296590, a SNP in the 5'-UTR region that is within a predicted transcription factor bind site for CCAAT-enhancer-binding proteins. In multivariate analyses functional SNP rs2296590 was correlated with renal function (p=0.004) and APACHEII score (p=0.049).

CONCLUSIONS

Host susceptibility factors play an important role in sepsis development and sepsis related organ injury. Polymorphisms in the SUFU gene (encoding for a negative regulator of the hedgehog signaling pathway) are associated with protection from Enterobacteriacea bacteremia related organ injury and sepsis severity.