LECT2 protects mice against bacterial sepsis by activating macrophages via the CD209a receptor

Updates on the role of leukocyte cell-derived chemotaxin-2 in inflammation regulation and immunomodulation

Leukocyte cell-derived chemotaxin-2 (LECT2), originally identified as a novel neutrophil chemokine, is a multifunctional secreted factor primarily produced in hepatocytes. However, many studies have shown that LECT2 is a pleiotropic protein that not only exerts chemotaxis properties as a cytokine but also plays an important role in inflammatory regulation and immune regulation. Pathogens such as bacteria and the role of the host immune system are key factors in the inflammatory response. In antibacterial, LECT2 can directly destroy bacterial structure or affect the normal metabolism of bacteria to inactivate bacteria and can also achieve this effect by activating immune cells and regulating cytokines. In immunomodulation, LECT2 has neutrophil chemotactic activity and regulates the quantities of Natural killer T (NKT) cells, regulatory T cells, monocytes/macrophages, granulocytes, and/or the expression of associated cytokines, thereby influencing their effect in immune reaction. Inflammation and immune regulation are closely related to a variety of diseases, such as bacterial infection, liver cirrhosis, dermatitis, coronary atherosclerotic heart disease, and so on. This review summarizes the basic and clinical studies of LECT2 in antibacterial effects and its effects on immune cells to explore the mechanism of LECT in inflammatory regulation and immune regulation in physiological and pathological conditions better.

Discovery of Ll-CATH: a novel cathelicidin from the Chong'an Moustache Toad (Leptobrachium liui) with antibacterial and immunomodulatory activity

BACKGROUND

Cathelicidins are vital antimicrobial peptides expressed in diverse vertebrates, crucial for immunity. Despite being a new field, amphibian cathelicidin research holds promise.

RESULTS

We isolated the cDNA sequence of the cathelicidin (Ll-CATH) gene from the liver transcriptome of the Chong'an Moustache Toad (Leptobrachium liui). We confirmed the authenticity of the cDNA sequence by rapid amplification of cDNA ends and reverse transcription PCR, and obtained the Ll-CATH amino acid sequence using the Open Reading Frame Finder, an online bioinformatics tool. Its translated protein contained a cathelin domain, signal peptide, and mature peptide, confirmed by amino acid sequence. The comparative analysis showed that the mature peptides were variable between the amphibian species, while the cathelin domain was conserved. The concentration of Ll-CATH protein and the expression of its gene varied in the tissues, with the spleen showing the highest levels. The expression levels of Ll-CATH in different tissues of toads was significantly increased post infection with Aeromonas hydrophila. Chemically synthesized Ll-CATH effectively combated Proteus mirabilis, Staphylococcus epidermidis, Vibrio harveyi, V. parahaemolyticus, and V. vulnificus; disrupted the membrane of V. harveyi, hydrolyzed its DNA. Ll-CATH induced chemotaxis and modulated the expression of pro-inflammatory cytokine genes in RAW264.7 macrophages.

CONCLUSIONS

This study unveiled the antibacterial and immunomodulatory potential of amphibian cathelicidin, implying its efficacy against infections. Ll-CATH characterization expands our knowledge, emphasizing its in a bacterial infection therapy.

LECT2 mediates antibacterial immune response induced by Nocardia seriolae infection in the northern snakehead

Leukocyte-derived chemotaxin-2 (LECT2) is a multifunctional immunoregulator that plays several pivotal roles in the host's defense against pathogens. This study aimed to elucidate the specific functions and mechanisms of LECT2 (CaLECT2) in the northern snakehead (Channa argus) during infections with pathogens such as Nocardia seriolae (N. seriolae). We identified CaLECT2 in the northern snakehead, demonstrating its participation in the immune response to N. seriolae infection. CaLECT2 contains an open reading frame (ORF) of 459 bp, encoding a peptide of 152 amino acids featuring a conserved peptidase M23 domain. The CaLECT2 protein shares 62%-84 % identities with proteins from various other fish species. Transcriptional expression analysis revealed that CaLECT2 was constitutively expressed in all examined tissues, with the highest expression observed in the liver. Following intraperitoneal infection with N. seriolae, CaLECT2 transcription increased in the spleen, trunk kidney, and liver. In vivo challenge experiments showed that injecting recombinant CaLECT2 (rCaLECT2) could protect the snakehead against N. seriolae infection by reducing bacterial load, enhancing serum antibacterial activity and antioxidant capacity, and minimizing tissue damage. Moreover, in vitro analysis indicated that rCaLECT2 significantly enhanced the migration, respiratory burst, and microbicidal activity of the head kidney-derived phagocytes. These findings provide new insights into the role of LECT2 in the antibacterial immunity of fish.

Global research trends and hotspots for leukocyte cell-derived chemotaxin-2 from the past to 2023: a combined bibliometric review

Leukocyte cell-derived chemotaxin-2 (LECT2) is an important cytokine synthesized by liver. Significant research interest is stimulated by its crucial involvement in inflammatory response, immune regulation, disease occurrence and development. However, bibliometric study on LECT2 is lacking. In order to comprehend the function and operation of LECT2 in human illnesses, we examined pertinent studies on LECT2 investigation in the Web of Science database, followed by utilizing CiteSpace, VOSview, and Scimago Graphica for assessing the yearly quantity of papers, countries/regions involved, establishments, authors, publications, citations, and key terms. Then we summarized the current research hotspots in this field. Our study found that the literature related to LECT2 has a fluctuating upward trend. "Angiogenesis", "ALECT2", "diagnosis", and "biliary atresia" are the current investigative frontiers. Our findings indicated that liver diseases (e.g. liver fibrosis and hepatic cell carcinoma), systemic inflammatory disease, and amyloidosis are the current research focus of LECT2. The current LECT2 research outcomes are not exceptional. We hope to promote the scientific research of LECT2 and exploit its potential for clinical diagnosis and treatment of related diseases through a comprehensive bibliometric review.

Elevated serum levels of leukocyte cell-derived chemotaxin 2 are associated with the prevalence of metabolic syndrome

AIMS

Inflammation is central to the pathogenesis of metabolic syndrome (MetS). Leukocyte cell-derived chemotaxin 2 (LECT2) is constitutively secreted in response to inflammatory stimuli and oxidative stress contributing to tissue or systemic inflammation. We explored the relationship between LECT2 levels and MetS severity in humans and mice.

METHODS

Serum LECT2 levels were measured in 210 participants with MetS and 114 without MetS (non-MetS). LECT2 expression in the liver and adipose tissue was also examined in mice fed a high-fat diet (HFD) and genetically obese (ob/ob) mice.

RESULTS

Serum LECT2 levels were significantly higher in MetS participants than in non-MetS participants (7.47[3.36-17.14] vs. 3.74[2.61-5.82], P < 0.001). Particularly, serum LECT2 levels were significantly elevated in participants with hypertension, central obesity, diabetes mellitus (DM), hyperglycaemia, elevated triglyceride (TG) levels, and reduced high-density lipoprotein cholesterol (HDL-C) levels compared to those in participants without these conditions. Pearson's correlation analysis showed that serum LECT2 levels were positively associated with conventional risk factors in all patients. Moreover, LECT2 was positively associated with the number of MetS components (r = 0.355, P < 0.001), indicating that higher serum LECT2 levels reflected MetS severity. Multivariate regression analysis revealed that a one standard deviation increase in LECT2 was associated with an odds ratio of 1.52 (1.01-2.29, P = 0.044) for MetS prevalence after adjusting for age, sex, body mass index, waist circumference, smoking status, white blood cell count, fasting blood glucose, TG, total cholesterol, HDL-C, blood urea nitrogen, and alanine aminotransferase. Receiver operating characteristic curve analysis confirmed the strong predictive ability of serum LECT2 levels for MetS. The optimum serum LECT2 cut-off value was 9.05. The area under the curve was 0.73 (95% confidence interval 0.68-0.78, P < 0.001), with a sensitivity and specificity of 45.71% and 95.61%, respectively. Additionally, LECT2 expression levels were higher at baseline and dramatically enhanced in metabolic organs (e.g. the liver) and adipose tissue in HFD-induced obese mice and ob/ob mice.

CONCLUSIONS

Increased LECT2 levels were significantly and independently associated with the presence and severity of MetS, indicating that LECT2 could be used as a novel biomarker and clinical predictor of MetS.

Differential analysis of ovarian tissue between high and low-yielded laying hens in the late laying stage and the effect of LECT2 gene on follicular granulosa cells proliferation

The ovaries of high-yield laying hens exhibited signs of aging beyond 400 days of age, subsequently resulting in a decline in both egg production and egg quality. Oxidative stress, characterized by an increase in the production of reactive oxygen species (ROS), stands as one of the principal processes contributing to ovarian aging. Elevated ROS levels are implicated in the induction of apoptosis in granulosa cells (GCs), provoking mitochondrial impairment, and diminishing the capacity of the antioxidant defense system. This investigation stratified laying hens into two distinct groups, predicated upon their egg production levels: high-yield hens (HH) and low-yield hens (LL). The study focused on evaluating oxidative stress markers and identifying differentially expressed genes between these two groups. The findings revealed that the LL group exhibited follicular atresia, mitochondrial disruptions, and apoptotic occurrences in ovarian GCs. Notably, ROS levels, Malondialdehyde (MDA) concentrations, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) concentrations in ovarian tissue and follicular GCs were substantially higher in the HH group. Furthermore, the RNA-sequencing results unveiled differential expression of the LECT2 gene between the HH and LL groups. Consequently, an overexpression vector for the LECT2 gene was successfully constructed and introduced into GCs. The quantitative polymerase chain reaction (QPCR) analysis exhibited significant downregulation (p < 0.01) of key apoptotic genes such as Caspase-3 and C-myc and significant upregulation (p < 0.01) of BCL2 following the overexpression of the LECT2 gene in GCs. In conclusion, oxidative stress emerges as a pivotal factor influencing the laying traits of both high and low-yield laying hens. The accumulation of reactive oxygen species (ROS) within the ovaries precipitates apoptosis in GCs, subsequently leading to follicular atresia and a reduction in egg production. Furthermore, we employed RNA sequencing technology to examine the ovarian matrix tissue in high and low laying hens during the late phase of egg laying. Our analysis revealed a substantial upregulation of the LECT2 gene in the ovarian matrix tissue of high laying hens. This observation implies that the LECT2 gene exerts a pivotal influence on driving the proliferation and differentiation of follicular GCs, thereby exerting a crucial regulatory role in follicular development.

Loss of LECT2 promotes ovarian cancer progression by inducing cancer invasiveness and facilitating an immunosuppressive environment

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multifunctional cytokine that can bind to several receptors and mediate distinct molecular pathways in various cell settings. Changing levels of LECT2 have been implicated in multiple human disease states, including cancers. Here, we have demonstrated reduced serum levels of LECT2 in patients with epithelial ovarian cancer (EOC) and down-regulated circulating Lect2 as the disease progresses in a syngeneic mouse ID8 EOC model. Using the murine EOC model, we discovered that loss of Lect2 promotes EOC progression by modulating both tumor cells and the tumor microenvironment. Lect2 inhibited EOC cells' invasive phenotype and suppressed EOC's transcoelomic metastasis by targeting c-Met signaling. In addition, Lect2 downregulation induced the accumulation and activation of myeloid-derived suppressor cells (MDSCs). This fostered an immunosuppressive microenvironment in EOC by inhibiting T-cell activation and skewing macrophages toward an M2 phenotype. The therapeutic efficacy of programmed cell death-1 (PD-1)/PD-L1 pathway blockade for the ID8 model was significantly hindered. Overall, our data highlight multiple functions of Lect2 during EOC progression and reveal a rationale for synergistic immunotherapeutic strategies by targeting Lect2.

A Comparative Transcriptomic Study and Key Gene Targeting of Lamprey Gonadal Immune Response

The mammalian testis and ovary possess special immunocompetence, which is central to provide protection against pathogens. However, the innate immune responses to immune challenges in lamprey gonads are poorly understood. In this study, we extracted RNA from testis and ovary tissues of lampreys at 0 hour, 8 hours and 17 days after lipopolysaccharides (LPS) stimulation and performed transcriptome sequencing. While the transcriptome profiles of the two tissues were different for the most part, genes LIP, LECT2, LAL2, GRN, ITLN, and C1q were found to be the most significantly up-regulated genes in both. Quantitative Real-time PCR (qRT-PCR) analysis confirmed that these genes were upregulated after stimulation. Furthermore, immunohistochemical staining showed that these genes in lamprey gonads are expressed in high quantities and have a specific distribution. Taken together, our results suggest that these genes could play an essential role in response of the gonads to LPS induction. This research establishes a basis for investigating the immune mechanism of vertebrate gonads and presents a fresh concept for gaining insight into the evolutionary development of jawless vertebrates.

Bone morphogenetic protein 9 is a candidate prognostic biomarker and host-directed therapy target for sepsis

Defining next-generation immune therapeutics for the treatment of sepsis will involve biomarker-based therapeutic decision-making. Bone morphogenetic protein 9 (BMP9) is a cytokine in the transforming growth factor-β superfamily. Here, circulating BMP9 concentrations were quantified in two independent cohorts of patients with sepsis. Decreased concentrations of serum BMP9 were observed in the patients with sepsis at the time of admission as compared with healthy controls. Concentrations of BMP9 at the time of admission were also associated with 28-day mortality, because patients with sepsis at a higher risk of death had lower BMP9 concentrations. The mechanism driving the contribution of BMP9 to host immunity was further investigated using in vivo murine sepsis models and in vitro cell models. We found that BMP9 treatment improved outcome in mice with experimental sepsis. BMP9-treated mice exhibited increased macrophage influx into the peritoneal cavity and more efficient bacterial clearance than untreated mice. In vitro, BMP9 promoted macrophage recruitment, phagocytosis, and subsequent bacterial killing. We further found that deletion of the type 1 BMP receptor ALK1 in macrophages abolished BMP9-mediated protection against polymicrobial sepsis in vivo. Further experiments indicated that the regulation of macrophage activation by the BMP9-ALK1 axis was mainly mediated through the suppressor of mother against decapentaplegic 1/5 signaling pathway. Together, these results suggest that BMP9 can both serve as a biomarker for patient stratification with an independent prognostic value and be developed as a host-directed therapy for sepsis.

Antimicrobial Protein LECT2-b Helps Maintain Gut Microbiota Homeostasis via Selectively Targeting Certain Pathogenic Bacteria

Antimicrobial peptides/proteins (AMPs) constitute a critical component of gut immunity in animals, protecting the gut from pathogenic bacteria. However, the interactions between AMPs and gut microbiota remain elusive. In this study, we show that leukocyte-derived chemotaxin-2 (LECT2)-b, a recently discovered AMP, helps maintain gut homeostasis in grass carp (Ctenopharyngodon idella), one of the major farmed fish species globally, by directly regulating the gut microbiota. Knockdown of LECT2-b resulted in dysregulation of the gut microbiota. Specifically, LECT2-b deficiency led to the dominance of Proteobacteria, consisting of proinflammatory bacterial species, over Firmicutes, which includes anti-inflammatory bacteria. In addition, the opportunistic pathogenic bacteria genus Aeromonas became the dominant genus replacing the probiotic bacteria Lactobacillus and Bacillus. Further analysis revealed that this effect was due to the direct and selective inhibition of certain pathogenic bacterial species by LECT2-b. Moreover, LECT2-b knockdown promoted biofilm formation by gut microbiota, resulting in tissue damage and inflammation. Importantly, LECT2-b treatment alleviated the negative effects induced by LECT2-b knockdown. These findings highlight the crucial role of LECT2-b in maintaining the gut microbiota homeostasis and mucosal health. Overall, our study provides important data for understanding the roles of AMPs in the regulation of gut homeostasis in animals.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

Novel tripeptide RKH derived from Akkermansia muciniphila protects against lethal sepsis

OBJECTIVE

The pathogenesis of sepsis is complex, and the sepsis-induced systemic proinflammatory phase is one of the key drivers of organ failure and consequent mortality. Akkermansia muciniphila (AKK) is recognised as a functional probiotic strain that exerts beneficial effects on the progression of many diseases; however, whether AKK participates in sepsis pathogenesis is still unclear. Here, we evaluated the potential contribution of AKK to lethal sepsis development.

DESIGN

Relative abundance of gut microbial AKK in septic patients was evaluated. Cecal ligation and puncture (CLP) surgery and lipopolysaccharide (LPS) injection were employed to establish sepsis in mice. Non-targeted and targeted metabolomics analysis were used for metabolites analysis.

RESULTS

We first found that the relative abundance of gut microbial AKK in septic patients was significantly reduced compared with that in non-septic controls. Live AKK supplementation, as well as supplementation with its culture supernatant, remarkably reduced sepsis-induced mortality in sepsis models. Metabolomics analysis and germ-free mouse validation experiments revealed that live AKK was able to generate a novel tripeptide Arg-Lys-His (RKH). RKH exerted protective effects against sepsis-induced death and organ damage. Furthermore, RKH markedly reduced sepsis-induced inflammatory cell activation and proinflammatory factor overproduction. A mechanistic study revealed that RKH could directly bind to Toll-like receptor 4 (TLR4) and block TLR4 signal transduction in immune cells. Finally, we validated the preventive effects of RKH against sepsis-induced systemic inflammation and organ damage in a piglet model.

CONCLUSION

We revealed that a novel tripeptide, RKH, derived from live AKK, may act as a novel endogenous antagonist for TLR4. RKH may serve as a novel potential therapeutic approach to combat lethal sepsis after successfully translating its efficacy into clinical practice.

Histone methyltransferase SETD2 inhibits M1 macrophage polarization and glycolysis by suppressing HIF-1α in sepsis-induced acute lung injury

Sepsis is a severe syndrome caused by the imbalance of the host response to infection, accompanied by multiple organ damage, especially acute lung injury. SET Domain-Containing 2 (SETD2) is a methyltransferase catalyzing H3 lysine 36 trimethylation (H3K36me3) that regulates multiple biological processes. This study focused on explicating the action of SETD2 on macrophage function in sepsis and the precise mechanism involved. Enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction (RT-qPCR), and Western blotting were used to determine expression. Luciferase reporter assay and chromatin immunoprecipitation assay were conducted to detect the binding of SETD2 or H3K36me3 with the hypoxia-inducible factor 1, alpha subunit (Hif1a) gene. A sepsis-induced acute lung injury model was constructed via cecal ligation and puncture (CLP). SETD2 was decreased in RAW 264.7 cells stimulated by lipopolysaccharide (LPS). Besides, SETD2 suppressed M1 macrophage polarization and glycolysis caused by LPS. HIF-1α was enhanced in RAW 264.7 cells stimulated by LPS and inversely related to SETD2 expression. In addition, SETD2-catalyzed H3K36me3 bound to the Hif1a gene to modulate HIF-1α expression. Furthermore, Hif1a silencing suppressed Setd2 silencing-induced M1 macrophage polarization and glycolysis in RAW 264.7 cells. Moreover, overexpression of Setd2 inhibited CLP-induced lung injury and M1 macrophage polarization in mice. SETD2 suppressed M1 macrophage polarization and glycolysis via regulating HIF-1α through catalyzing H3K36me3 in sepsis.

Rapid genetic adaptation to a novel ecosystem despite a large founder event

Introduced and invasive species make excellent natural experiments for investigating rapid evolution. Here, we describe the effects of genetic drift and rapid genetic adaptation in pink salmon (Oncorhynchus gorbuscha) that were accidentally introduced to the Great Lakes via a single introduction event 31 generations ago. Using whole-genome resequencing for 134 fish spanning five sample groups across the native and introduced range, we estimate that the source population's effective population size was 146,886 at the time of introduction, whereas the founding population's effective population size was just 72-a 2040-fold decrease. As expected with a severe founder event, we show reductions in genome-wide measures of genetic diversity, specifically a 37.7% reduction in the number of SNPs and an 8.2% reduction in observed heterozygosity. Despite this decline in genetic diversity, we provide evidence for putative selection at 47 loci across multiple chromosomes in the introduced populations, including missense variants in genes associated with circadian rhythm, immunological response and maturation, which match expected or known phenotypic changes in the Great Lakes. For one of these genes, we use a species-specific agent-based model to rule out genetic drift and conclude our results support a strong response to selection occurring in a period gene (per2) that plays a predominant role in determining an organism's daily clock, matching large day length differences experienced by introduced salmon during important phenological periods. Together, these results inform how populations might evolve rapidly to new environments, even with a small pool of standing genetic variation.

Identification of hub genes in digestive system of mandarin fish (Siniperca chuatsi) fed with artificial diet by weighted gene co-expression network analysis

Mandarin fish (Siniperca chuatsi) is a carnivorous freshwater fish and an economically important species. The digestive system (liver, stomach, intestine, pyloric caecum, esophagus, and gallbladder) is an important site for studying fish domestication. In our previous study, we found that mandarin fish undergoes adaptive changes in histological morphology and gene expression levels of the digestive system when subjected to artificial diet domestication. However, we are not clear which hub genes are highly associated with domestication. In this study, we performed WGCNA on the transcriptomes of 17 tissues and 9 developmental stages and combined differentially expressed genes analysis in the digestive system to identify the hub genes that may play important functions in the adaptation of mandarin fish to bait conversion. A total of 31,657 genes in 26 samples were classified into 23 color modules via WGCNA. The modules midnightblue, darkred, lightyellow, and darkgreen highly associated with the liver, stomach, esophagus, and gallbladder were extracted, respectively. Tan module was highly related to both intestine and pyloric caecum. The hub genes in liver were cp, vtgc, c1in, c9, lect2, and klkb1. The hub genes in stomach were ghrl, atp4a, gjb3, muc5ac, duox2, and chia2. The hub genes in esophagus were mybpc1, myl2, and tpm3. The hub genes in gallbladder were dyst, npy2r, slc13a1, and slc39a4. The hub genes in the intestine and pyloric caecum were slc15a1, cdhr5, btn3a1, anpep, slc34a2, cdhr2, and ace2. Through pathway analysis, modules highly related to the digestive system were mainly enriched in digestion and absorption, metabolism, and immune-related pathways. After domestication, the hub genes vtgc and lect2 were significantly upregulated in the liver. Chia2 was significantly downregulated in the stomach. Slc15a1, anpep, and slc34a2 were significantly upregulated in the intestine. This study identified the hub genes that may play an important role in the adaptation of the digestive system to artificial diet, which provided novel evidence and ideas for further research on the domestication of mandarin fish from molecular level.

Proteins journey-from marine to freshwater ecosystem: blood plasma proteomic profiles of pink salmon Oncorhynchus gorbuscha Walbaum, 1792 during spawning migration

The pink salmon (Oncorhynchus gorbuscha) is a commercial anadromous fish species of the family Salmonidae. This species has a 2-year life cycle that distinguishes it from other salmonids. It includes the spawning migration from marine to freshwater environments, accompanied by significant physiological and biochemical adaptive changes in the body. This study reveals and describes variability in the blood plasma proteomes of female and male pink salmon collected from three biotopes-marine, estuarine and riverine-that the fish pass through in spawning migration. Identification and comparative analysis of blood plasma protein profiles were performed using proteomics and bioinformatic approaches. The blood proteomes of female and male spawners collected from different biotopes were qualitatively and quantitatively distinguished. Females differed primarily in proteins associated with reproductive system development (certain vitellogenin and choriogenin), lipid transport (fatty acid binding protein) and energy production (fructose 1,6-bisphosphatase), and males in proteins involved in blood coagulation (fibrinogen), immune response (lectins) and reproductive processes (vitellogenin). Differentially expressed sex-specific proteins were implicated in proteolysis (aminopeptidases), platelet activation (β- and γ-chain fibrinogen), cell growth and differentiation (a protein containing the TGF_BETA_2 domain) and lipid transport processes (vitellogenin and apolipoprotein). The results are of both fundamental and practical importance, adding to existing knowledge of the biochemical adaptations to spawning of pink salmon, a representative of economically important migratory fish species.

The emerging roles of leukocyte cell-derived chemotaxin-2 in immune diseases: From mechanisms to therapeutic potential

Leukocyte cell-derived chemotaxin-2 (LECT2, also named ChM-II), initially identified as a chemokine mediating neutrophil migration, is a multifunctional secreted factor involved in diverse physiological and pathological processes. The high sequence similarity of LECT2 among different vertebrates makes it possible to explore its functions by using comparative biology. LECT2 is associated with many immune processes and immune-related diseases via its binding to cell surface receptors such as CD209a, Tie1, and Met in various cell types. In addition, the misfolding LECT2 leads to the amyloidosis of several crucial tissues (kidney, liver, and lung, etc.) by inducing the formation of insoluble fibrils. However, the mechanisms of LECT2-mediated diverse immune pathogenic conditions in various tissues remain to be fully elucidated due to the functional and signaling heterogeneity. Here, we provide a comprehensive summary of the structure, the “double-edged sword” function, and the extensive signaling pathways of LECT2 in immune diseases, as well as the potential applications of LECT2 in therapeutic interventions in preclinical or clinical trials. This review provides an integrated perspective on the current understanding of how LECT2 is associated with immune diseases, with the aim of facilitating the development of drugs or probes against LECT2 for the theranostics of immune-related diseases.

Inflammation-related mRNA expression in patients with multiple myeloma undergoing hematopoietic stem cell mobilization

Mobilization of CD34+ cells is a key element in the therapy of patients with multiple myeloma undergoing autologous stem cell transplantation. The use of chemotherapy and the granulocyte colony-stimulating factor can significantly affect the expression of inflammation-related proteins and the migration of hematopoietic stem cells. We assessed the mRNA expression of selected proteins involved in the inflammatory landscape in MM patients (n=71). The aim of the study was to evaluate C-C motif chemokine ligand 3, 4, 5 (CCL3, CCL4, CCL5), leukocyte cell-derived chemotaxin 2 (LECT2), tumor necrosis factor (TNF), and formyl peptide receptor 2 (FPR2) levels in the course of mobilization and their role in the CD34+ collection efficacy. mRNA expression from peripheral blood plasma was evaluated by RT-PCR. We observed a deep decline in CCL3, CCL4, LECT2, and TNF mRNA expression on the day of the first apheresis (day A) as compared to baseline. A negative correlation was observed between CCL3, FPR2, LECT2, TNF level, and the CD34+ cells count in peripheral blood on day A, and the number of CD34+ cells obtained at first apheresis . Our results indicate that the investigated mRNAs significantly alter and may regulate the migration of CD34+ cells during mobilization. Moreover, in case of FPR2 and LECT2, the results obtained in patients differ from the murine models.

A small-molecule inhibitor of Keap1-Nrf2 interaction attenuates sepsis by selectively augmenting the antibacterial defence of macrophages at infection sites

BACKGROUND

Macrophages at infection sites are considered as the promising therapeutic targets to prevent sepsis development. The Nrf2/Keap1 system acts as a critical modulator of the antibacterial activity of macrophages. Recently, Keap1-Nrf2 protein-protein interaction (PPI) inhibitors have emerged as safer and stronger Nrf2 activators; however, their therapeutic potential in sepsis remains unclear. Herein, we report a unique heptamethine dye, IR-61, as a Keap1-Nrf2 PPI inhibitor that preferentially accumulates in macrophages at infection sites.

METHODS

A mouse model of acute lung bacterial infection was used to investigate the biodistribution of IR-61. SPR study and CESTA were used to detect the Keap1 binding behaviour of IR-61 in vitro and in cells. Established models of sepsis in mice were used to determine the therapeutic effect of IR-61. The relationship between Nrf2 levels and sepsis outcomes was preliminarily investigated using monocytes from human patients.

FINDINGS

Our data showed that IR-61 preferentially accumulated in macrophages at infection sites, enhanced bacterial clearance, and improved outcomes in mice with sepsis. Mechanistic studies indicated that IR-61 potentiated the antibacterial function of macrophages by activating Nrf2 via direct inhibition of the Keap1-Nrf2 interaction. Moreover, we observed that IR-61 enhanced the phagocytic ability of human macrophages, and the expression levels of Nrf2 in monocytes might be associated with the outcomes of sepsis patients.

INTERPRETATIONS

Our study demonstrates that the specific activation of Nrf2 in macrophages at infection sites is valuable for sepsis management. IR-61 may prove to be a Keap1-Nrf2 PPI inhibitor for the precise treatment of sepsis.

FUNDING

This work was supported by the National Natural Science Foundation of China (Major program 82192884), the Intramural Research Project (Grants: 2018-JCJQ-ZQ-001 and 20QNPY018), and the Chongqing National Science Foundation (CSTB2022NSCQ-MSX1222).

LECT2 modulates dendritic cell function after Helicobacter pylori infection via the CD209a receptor

BACKGROUND

Helicobacter pylori, a gram-negative bacterium persisting on the gastric mucosa, is involved in the pathogenesis of a variety of gastric diseases. Leukocyte cell-derived chemotaxin 2 (LECT2) treatment increased the phagocytic capacity of lymphocytes and improved immune function in bacterial infection. Whether the immune cells infected with H. pylori are affected by LECT2 is unclear.

METHODS

Bone marrow-derived dendritic cells (BMDCs) from wild-type C57BL/6 mice, CD209a knockout mice, or LECT2 knockout mice were exposed to H. pylori at a multiplicity of infection of 10 for 24 h. The maturity of DCs and the cytokines secreted by DCs were analyzed by flow cytometry, western blot, and real-time PCR. The signaling pathway underlying CD209a activation after LECT2 treatment were also detected.

RESULTS

LECT2 treatment promoted H. pylori-induced BMDC maturation and produced a high level of anti-inflammatory cytokine (IL-10) but a low level of pro-inflammatory cytokine (IL-23p40). Moreover, LECT2-pretreated DCs shifted the development of pro-inflammatory Th1/Th17 cells to Treg cells. CD209a mediated LECT2-induced maturation and secretion of DC in H. pylori-primed BMDCs. LECT2 was further confirmed to induce the secretion of certain cytokines via CD209a-JNK/P38 MAPK pathway.

CONCLUSION

This study reveals that LECT2 modulated the functions of H. pylori-primed DCs in a CD209a-dependent manner, which might hinder the clearance of H. pylori and contribute to its colonization.

Serum Leukocyte Cell-Derived Chemotaxin 2 (LECT2) Level Is Associated with Osteoporosis

OBJECTIVE

The aim of this study was to examine serum leukocyte cell-derived chemotaxin 2 (LECT2) levels in osteoporosis subjects to confirm its association with osteoporosis.

METHODS

A total of 204 adult subjects were recruited. Bone mineral densities (BMD) were assessed and blood samples were collected for measurements of biomedical parameters and the bone turnover markers. Serum LECT2 levels were measured by enzyme-linked immunosorbent assay. The relationships between serum LECT2 levels and other parameters were analyzed using the Spearman correlation coefficient.

RESULTS

Serum LECT2 levels were significantly increased in osteoporosis subjects over controls. We found a significantly negative correlation of serum LECT2 with BMD, 25-hydroxy-vitamin D, and creatinine and a significantly positive correlation with C-terminal telopeptide of type 1 collagen and total cholesterol.

CONCLUSION

Serum LECT2 levels were significantly upregulated in osteoporosis subjects and correlated with the severity of bone loss. Serum LECT2 could be a potential biomarker to assess the risk of bone loss.

Leukocyte Chemotactic Factor 2 Amyloidosis (ALECT2) Distribution in a Mexican Population

OBJECTIVES

To assess the prevalence of leukocyte cell-derived chemotactic 2 (LECT2), its organ involvement, and its clinical association in autopsies from an ethnically biased population.

METHODS

The tissues from all autopsies of individuals diagnosed with amyloidosis were reassessed and typed for amyloid light chain (AL) amyloidosis, amyloid A (AA) amyloidosis, transthyretin amyloidosis (ATTR), and leukocyte chemotactic factor 2 amyloidosis (ALECT2) by immunohistochemistry. Organ involvement was described and correlated with its clinical associations.

RESULTS

Of 782 autopsies, 27 (3.5%) had a confirmed diagnosis of amyloidosis. Of these, 14 (52%) corresponded to ALECT2, 5 (19%) to AL amyloidosis, 2 (7%) to ATTR amyloidosis, 1 (4%) to AA amyloidosis, and 5 (21%) as undetermined-type amyloidosis. The LECT2 amyloid deposits were found in the kidneys, liver, spleen, and adrenal glands in most individuals. Except for the kidneys, there were no clinical signs suggestive of amyloid deposition in most of the affected organs. LECT2 amyloidosis was not associated with the cause of death in any case. No cases had heart or brain involvement. Potential subclinical effects of amyloid deposition in organs such as adrenal glands and spleen require further study.

CONCLUSIONS

This autopsy study confirms the high prevalence of LECT2 amyloidosis in the Mexican population, with frequent amyloid deposition in the kidneys, liver, spleen, and adrenal glands.

Meteorin links the bone marrow hypoxic state to hematopoietic stem/progenitor cell mobilization

Hematopoietic stem/progenitor cells (HSPCs) are supported and regulated by niche cells in the bone marrow with an important characterization of physiological hypoxia. However, how hypoxia regulates HSPCs is still unclear. Here, we find that meteorin (Metrn) from hypoxic macrophages restrains HSPC mobilization. Hypoxia-induced factor 1α and Yin Yang 1 induce the high expression of Metrn in macrophages, and macrophage-specific Metrn knockout increases HSPC mobilization through modulating HSPC proliferation and migration. Mechanistically, Metrn interacts with its receptor 5-hydroxytryptamine receptor 2b (Htr2b) to regulate the reactive oxygen species levels in HSPCs through targeting phospholipase C signaling. The reactive oxygen species levels are reduced in HSPCs of macrophage-specific Metrn knockout mice with activated phospholipase C signaling. Targeting the Metrn/Htr2b axis could therefore be a potential strategy to improve HSPC mobilization for stem cell-based therapy.

A strategy of vascular-targeted therapy for liver fibrosis

BACKGROUND AND AIMS

No effective treatments are available for liver fibrosis. Angiogenesis is deeply involved in liver fibrogenesis. However, current controversial results suggest it is difficult to treat liver fibrosis through vascular targeting. There are three different microvessels in liver: portal vessels, liver sinusoids, and central vessels. The changes and roles for each of the three different vessels during liver fibrogenesis are unclear. We propose that they play different roles during liver fibrogenesis, and a single vascular endothelial cell (EC) regulator is not enough to fully regulate these three vessels to treat liver fibrosis. Therefore, a combined regulation of multiple different EC regulatory signaling pathway may provide new strategies for the liver fibrosis therapy. Herein, we present a proof-of-concept strategy by combining the regulation of leukocyte cell-derived chemotaxin 2 (LECT2)/tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 1 signaling with that of vascular endothelial growth factor (VEGF)/recombinant VEGF (rVEGF) signaling.

APPROACH AND RESULTS

The CCl₄ -induced mouse liver fibrosis model and NASH model were both used. During fibrogenesis, vascular changes occurred at very early stage, and different liver vessels showed different changes and played different roles: decreased portal vessels, increased sinusoid capillarization and the increased central vessels the increase of portal vessels alleviates liver fibrosis, the increase of central vessels aggravates liver fibrosis, and the increase of sinusoid capillarization aggravates liver fibrosis. The combinational treatment of adeno-associated viral vector serotype 9 (AAV9)-LECT2-short hairpin RNA (shRNA) and rVEGF showed improved therapeutic effects, but it led to serious side effects. The combination of AAV9-LECT2-shRNA and bevacizumab showed both improved therapeutic effects and decreased side effects.

CONCLUSIONS

Liver vascular changes occurred at very early stage of fibrogenesis. Different vessels play different roles in liver fibrosis. The combinational treatment of AAV9-LECT2-shRNA and bevacizumab could significantly improve the therapeutic effects on liver fibrosis.

Adipose tissue LECT2 expression is associated with obesity and insulin resistance in Korean women

OBJECTIVE

Leukocyte cell-derived chemotaxin 2 (LECT2) is an obesity-upregulated hepatokine inducing skeletal muscle insulin resistance. The study's aim was to explore whether LECT2 is expressed in human adipose tissue and whether the expression is dysregulated during obesity and associated with obesity-related metabolic disorders.

METHODS

This study measured metabolic parameters, serum LECT2, and expression of LECT2 and CD209, a gene encoding a putative receptor for LECT2, in abdominal subcutaneous and visceral adipose tissues in women with obesity (with or without type 2 diabetes) and women with normal weight. The expression/secretion of LECT2 and its putative effects were assessed in human adipocytes.

RESULTS

Adipose tissue LECT2 mRNA and serum LECT2 were higher in women with obesity and were significantly correlated with parameters related to insulin resistance. LECT2 was mainly expressed by adipocytes. Both LECT2 and CD209 expression was higher in adipocytes from women with obesity. Incubating adipocytes with substances mimicking the microenvironment of obesity adipose tissue increased LECT2 expression/secretion. LECT2 treatment of adipocytes suppressed insulin-stimulated Akt phosphorylation; it reduced adiponectin (ADIPOQ) and increased leptin (LEP) expression in a CD209-dependent manner.

CONCLUSIONS

This study demonstrates that LECT2 expression in adipose tissue is high in patients with obesity and associated with insulin resistance and suggests that adipocyte-derived LECT2 may contribute to adipose tissue dysfunction.

LECT2: A pleiotropic and promising hepatokine, from bench to bedside

LECT2 (leucocyte cell-derived chemotaxin 2) is a 16-kDa protein mainly produced by hepatocytes. It was first isolated in PHA-activated human T-cell leukaemia SKW-3 cells and originally identified as a novel neutrophil chemotactic factor. However, many lines of studies suggested that LECT2 was a pleiotropic protein, it not only functioned as a cytokine to exhibit chemotactic property, but also played multifunctional roles in some physiological conditions and pathological abnormalities, involving liver regeneration, neuronal development, HSC(haematopoietic stem cells) homeostasis, liver injury, liver fibrosis, hepatocellular carcinoma, metabolic disorders, inflammatory arthritides, systemic sepsis and systemic amyloidosis. Among the above studies, it was discovered that LECT2 could be a promising molecular biomarker and therapeutic target. This review summarizes LECT2-related receptors and pathways, basic and clinical researches, primarily in mice and human, for a better comprehension and management of these diseases in the future.

The Crosstalk Between Liver Sinusoidal Endothelial Cells and Hepatic Microenvironment in NASH Related Liver Fibrosis

Chronic liver injury can be caused by many factors, including virus infection, alcohol intake, cholestasis and abnormal fat accumulation. Nonalcoholic steatohepatitis (NASH) has become the main cause of liver fibrosis worldwide. Recently, more and more evidences show that hepatic microenvironment is involved in the pathophysiological process of liver fibrosis induced by NASH. Hepatic microenvironment consists of various types of cells and intercellular crosstalk among different cells in the liver sinusoids. Liver sinusoidal endothelial cells (LSECs), as the gatekeeper of liver microenvironment, play an irreplaceable role in the homeostasis and alterations of liver microenvironment. Many recent studies have reported that during the progression of NASH to liver fibrosis, LSECs are involved in various stages mediated by a series of mechanisms. Therefore, here we review the key role of crosstalk between LSECs and hepatic microenvironment in the progression of NASH to liver fibrosis (steatosis, inflammation, and fibrosis), as well as promising therapeutic strategies targeting LSECs.

Leukocyte cell-derived chemotaxin 2 is an antiviral regulator acting through the proto-oncogene MET

Retinoic acid-inducible gene (RIG)-I is an essential innate immune sensor that recognises pathogen RNAs and induces interferon (IFN) production. However, little is known about how host proteins regulate RIG-I activation. Here, we show that leukocyte cell-derived chemotaxin 2 (LECT2), a hepatokine and ligand of the MET receptor tyrosine kinase is an antiviral regulator that promotes the RIG-I-mediated innate immune response. Upon binding to MET, LECT2 induces the recruitment of the phosphatase PTP4A1 to MET and facilitates the dissociation and dephosphorylation of phosphorylated SHP2 from MET, thereby protecting RIG-I from SHP2/c-Cbl-mediated degradation. In vivo, LECT2 overexpression enhances RIG-I-dependent IFN production and inhibits lymphocytic choriomeningitis virus (LCMV) replication in the liver, whereas these changes are reversed in LECT2 knockout mice. Forced suppression of MET abolishes IFN production and antiviral activity in vitro and in vivo. Interestingly, hepatocyte growth factor (HGF), an original MET ligand, inhibits LECT2-mediated anti-viral signalling; conversely, LECT2-MET signalling competes with HGF-MET signalling. Our findings reveal previously unrecognized crosstalk between MET-mediated proliferation and innate immunity and suggest that targeting LECT2 may have therapeutic value in infectious diseases and cancer.

The innate antiviral immune response is an important defense against infection. Here, the authors show that leukocyte cell-derived chemotaxin 2 (LECT2) promotes RIG-I-mediated innate immune responses by preventing its degradation, and inhibits lymphocytic choriomeningitis virus replication in the liver.

LECT2 Is a Novel Antibacterial Protein in Vertebrates

In vertebrates, leukocyte-derived chemotaxin-2 (LECT2) is an important immunoregulator with conserved chemotactic and phagocytosis-stimulating activities to leukocytes during bacterial infection. However, whether LECT2 possesses direct antibacterial activity remains unknown. In this article, we show that, unlike tetrapods with a single LECT2 gene, two LECT2 genes exist in teleost fish, named LECT2-a and LECT2-b Using grass carp as a research model, we found that the expression pattern of grass carp LECT2-a (gcLECT2-a) is more similar to that of LECT2 in tetrapods, while gcLECT2-b has evolved to be highly expressed in mucosal immune organs, including the intestine and skin. Interestingly, we found that gcLECT2-b, with conserved chemotactic and phagocytosis-stimulating activities, can also kill Gram-negative and Gram-positive bacteria directly in a membrane-dependent and a non-membrane-dependent manner, respectively. Moreover, gcLECT2-b could prevent the adherence of bacteria to epithelial cells through agglutination by targeting peptidoglycan and lipoteichoic acid. Further study revealed that gcLECT2-b can protect grass carp from Aeromonas hydrophila infection in vivo, because it significantly reduces intestinal necrosis and tissue bacterial load. More importantly, we found that LECT2 from representative tetrapods, except human, also possesses direct antibacterial activities, indicating that the direct antibacterial property of LECT2 is generally conserved in vertebrates. Taken together, to our knowledge, our study discovered a novel function of LECT2 in the antibacterial immunity of vertebrates, especially teleost fish, greatly enhancing our knowledge of this important molecule.

Transcriptomic profiling of clobetasol propionate-induced immunosuppression in challenged zebrafish embryos

In the ecotoxicological hazard assessment of chemicals, the detection of immunotoxicity is currently neglected. This is mainly due to the complexity of the immune system and the consequent lack of standardized procedures and markers for the comprehensive assessment of immunotoxic modes of action. In this study, we present a new approach applying transcriptome profiling to an immune challenge with a mixture of pathogen-associated molecular patterns (PAMPs) in zebrafish embryos, analyzing differential gene expression during acute infection with and without prior exposure to the immunosuppressive drug clobetasol propionate (CP). While PAMP injection itself triggered biological processes associated with immune activation, some of these genes were more differentially expressed upon prior exposure to CP than by immune induction alone, whereas others showed weaker or no differential regulation in response to the PAMP stimulus. All of these genes responding differently to PAMP after prior CP exposure showed additivity of PAMP- and CP-induced effects, indicating independent regulatory mechanisms. The transcriptomic profiles suggest that CP impaired innate immune induction by attenuating the response of genes involved in antigen processing, TLR signaling, NF-КB signaling, and complement activation. We propose this approach as a powerful method for detecting gene biomarkers for immunosuppressive modes of action, as it was able to identify alternatively regulated processes and pathways in a sublethal, acute infection zebrafish embryo model. This allowed to define biomarker candidates for immune-mediated effects and to comprehensively characterize immunosuppression. Ultimately, this work contributes to the development of molecular biomarker-based environmental hazard assessment of chemicals in the future.

Soy Formula Is Not Estrogenic and Does Not Result in Reproductive Toxicity in Male Piglets: Results from a Controlled Feeding Study

Soy infant formula which is fed to over half a million infants per year contains isoflavones such as genistein, which have been shown to be estrogenic at high concentrations. The developing testis is sensitive to estrogens, raising concern that the use of soy formulas may result in male reproductive toxicity. In the current study, male White-Dutch Landrace piglets received either sow milk (Sow), or were provided milk formula (Milk), soy formula (Soy), milk formula supplemented with 17-beta-estradiol (2 mg/kg/d) (M + E2) or supplemented with genistein (84 mg/L of diet; (M + G) from postnatal day 2 until day 21. E2 treatment reduced testis weight (p < 0.05) as percentage of body weight, significantly suppressed serum androgen concentrations, increased tubule area, Germ cell and Sertoli cell numbers (p < 0.05) relative to those of Sow or Milk groups. Soy formula had no such effects relative to Sow or Milk groups. mRNAseq revealed 103 differentially expressed genes in the M + E2 group compared to the Milk group related to endocrine/metabolic disorders. However, little overlap was observed between the other treatment groups. These data suggest soy formula is not estrogenic in the male neonatal piglet and that soy formula does not significantly alter male reproductive development.

LECT-2 amyloidosis: what do we know?

Amyloidosis is a rare group of diseases characterized by abnormal folding of proteins and extracellular deposition of insoluble fibrils. It can be localized to one organ system or can have systemic involvement. The kidney is the most common organ to be involved in systemic amyloidosis often leading to renal failure and the nephrotic syndrome. The two most common types of renal amyloidosis are immunoglobulin light chain-derived amyloidosis (AL) and reactive amyloidosis (AA). A novel form of amyloidosis (ALECT2) derived from leukocyte chemotactic factor 2 (LECT-2) and primarily involving the kidneys was first described by Benson et al in 2008. The liver was subsequently identified as the second most common organ involved in ALECT2 amyloidosis. LECT-2 is a unique protein that can form amyloid deposits even in its unmutated form. Patients with ALECT2 present with minimal proteinuria in contrast to other forms of amyloidosis especially AL and AA. They may present with slightly elevated serum creatinine. Nephrotic syndrome and hematuria are rare. ALECT2 can be found in association with other types of amyloidosis as well as malignancies or autoimmune diseases. ALECT2 may be confused with amyloidosis associated with light and heavy chain monoclonal gammopathy if the immunofluorescence is positive with anti-light chain and anti-AA sera. The other organs involved are the duodenum, adrenal gland, spleen, prostate, gall bladder, pancreas, small bowel, parathyroid gland, heart, and pulmonary alveolar septa, but consistently uninvolved organs included brain and fibroadipose tissue. A renal biopsy along with characteristic features found on immunohistochemistry and mass spectrometry is diagnostic of ALECT2. ALECT2 should be suspected when all markers for AL and AA are negative. Proper diagnosis of ALECT2 can determine need for supportive care versus more aggressive interventions.

The molecular structure and role of LECT2 or CHM-II in arthritis, cancer, and other diseases

Leukocyte cell-derived chemotaxin-2 (LECT2 or LECT-2), also called chondromodulin II (ChM-II or CHM2) plays a versatile role in various tissues. It was first identified as a chemotactic factor to promote the migration of neutrophils. It was also reported as a hepatokine to regulate glucose metabolism, obesity, and nonalcoholic fatty liver disease. As a secreted factor, LECT2 binds to several cell surface receptors CD209a, Tie1, and Met to regulate inflammatory reaction, fibrogenesis, vascular invasion, and tumor metastasis in various cell types. As an intracellular molecule, it is associated with LECT2-mediated amyloidosis, in which LECT2 misfolding results in insoluble fibrils in multiple tissues such as the kidney, liver, and lung. Recently, LECT2 was found to be associated with the development of rheumatoid arthritis and osteoarthritis, involving the dysregulation of osteoclasts, mesenchymal stem cells, osteoblasts, chondrocytes, and endothelial cells in the bone microenvironment. LECT2 is implicated in the development of cancers, such as hepatocellular carcinoma via MET-mediated PTP1B/Raf1/ERK signaling pathways and is proposed as a biomarker. The mechanisms by which LECT2 regulates diverse pathogenic conditions in various tissues remain to be fully elucidated. Further research to understand the role of LECT2 in a tissue tropism-dependent manner would facilitate the development of LECT2 as a biomarker for diagnosis and therapeutic target.

Differentially expressed genes in the femur cartilage transcriptome clarify the understanding of femoral head separation in chickens

Locomotor problems are among one of the main concerns in the current poultry industry, causing major economic losses and affecting animal welfare. The most common bone anomalies in the femur are dyschondroplasia, femoral head separation (FHS), and bacterial chondronecrosis with osteomyelitis (BCO), also known as femoral head necrosis (FHN). The present study aimed to identify differentially expressed (DE) genes in the articular cartilage (AC) of normal and FHS-affected broilers by RNA-Seq analysis. In the transcriptome analysis, 12,169 genes were expressed in the femur AC. Of those, 107 genes were DE (FDR < 0.05) between normal and affected chickens, of which 9 were downregulated and 98 were upregulated in the affected broilers. In the gene-set enrichment analysis using the DE genes, 79 biological processes (BP) were identified and were grouped into 12 superclusters. The main BP found were involved in the response to biotic stimulus, gas transport, cellular activation, carbohydrate-derived catabolism, multi-organism regulation, immune system, muscle contraction, multi-organism process, cytolysis, leukocytes and cell adhesion. In this study, the first transcriptome analysis of the broilers femur articular cartilage was performed, and a set of candidate genes (AvBD1, AvBD2, ANK1, EPX, ADA, RHAG) that could trigger changes in the broiler´s femoral growth plate was identified. Moreover, these results could be helpful to better understand FHN in chickens and possibly in humans.

LECT2 Protects Nile Tilapia (Oreochromis niloticus) Against Streptococcus agalatiae Infection

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multifunctional cytokine that especially plays an important role in innate immune. However, the roles of LECT2 in the immune response of the economically important fish Nile tilapia (Oreochromis niloticus) against bacterial infection remains unclear. In this study, a lect2 gene from Nile tilapia (On-lect2) was identified, and its roles in the fish’s immune response against bacterial infection were determined and characterised. On-lect2 contains an open reading frame of 456 bp that encodes a peptide of 151 amino acids, as well as the conservative peptidase M23 domain. On-LECT2 is 62%–84% identical to other fish species and about 50% identical to mammals. The highest transcriptional level of On-lect2 was detected in the liver, whereas the lowest levels were detected in the other tissues. Moreover, the On-LECT2 protein is located mainly in the brain and head kidney. The transcriptional levels of On-lect2 substantially increased in the head kidney, brain, liver and spleen after Streptococcus agalactiae infection. Knockdown On-lect2 led to higher mortality due to liver necrosis or haemorrhage and splenomegaly. In vitro analysis indicated that the recombinant protein of On-LECT2 improved phagocytic activity of head kidney-derived macrophages. In vivo challenge experiments revealed several functions of On-LECT2 in the immune response of Nile tilapia against bacterial infection, including promotion of inflammation, reduction of tissue damages and improvement of survival rate.

LECT 2 Antagonizes FOXM1 Signaling via Inhibiting MET to Retard PDAC Progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with minimally effective treatments, highlighting the importance of developing novel biomarkers and therapeutic targets. Here, we disclosed the mechanisms that leukocyte cell-derived chemotaxin-2 (LECT2) modulates PDAC development using in vitro and in vivo models. LECT2 is downregulated in metastatic PDACs compared with the primary tumor, and its expression is correlated with multiple clinical pathologic features and prognosis. The absence promotes multiple malignant behaviors, including cell proliferation, epithelial-mesenchymal transition, migration, and invasion. In vivo studies showed that LECT2 overexpression inhibits tumor growth and lung metastasis. Mechanistically, LECT2 inhibits FOXM1 signaling by targeting HGF/MET to retard PDAC progression, revealing LECT2 as a promising biomarker and therapeutic target for PDAC in the future.

Biomarkers of drug-induced liver injury: a mechanistic perspective through acetaminophen hepatotoxicity

Introduction: Liver injury induced by drugs is a serious clinical problem. Many circulating biomarkers for identifying and predicting drug-induced liver injury (DILI) have been proposed.Areas covered: Biomarkers are mainly predicated on the mechanistic understanding of the underlying DILI, often in the context of acetaminophen overdose. New panels of biomarkers have emerged that are related to recovery/regeneration rather than injury following DILI. We explore the clinical relevance and limitations of these new biomarkers including recent controversies. Extracellular vesicles have also emerged as a promising vector of biomarkers, although the biological role for EVs may limit their clinical usefulness. New technological approaches for biomarker discovery are also explored.Expert opinion: Recent clinical studies have validated the efficacy of some of these new biomarkers, cytokeratin-18, macrophage colony-stimulating factor receptor, and osteopontin for DILI prognosis. Low prevalence of DILI is an inherent limitation to DILI biomarker development. Furthering mechanistic understanding of DILI and leveraging technological advances (e.g. machine learning/omics) is necessary to improve upon the newest generation of biomarkers. The integration of omics approaches with machine learning has led to novel insights in cancer research and DILI research is poised to leverage these technologies for biomarker discovery and development.

Leukocyte cell-derived chemotaxin 2 promotes the development of nonalcoholic fatty liver disease through STAT-1 pathway in mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD), whose pathogenesis remains unelucidated, has become an increasingly prevalent disease globally requiring novel treatment strategies. This study aims to explore the role of leukocyte cell-derived chemotaxin 2 (LECT2), one of the known hepatokines, in the development of NAFLD.

METHODS

The serum LECT2 level was evaluated in patients with NAFLD and male C57BL/6 mice fed a high-fat diet (HFD) for 8 weeks. Tail intravenous injection of adeno-associated virus that contained Lect2 short hairpin RNA or Lect2 overexpression plasmid was administered to mice to inhibit or increase hepatic Lect2 expression. Hepatic steatosis was evaluated by histological staining with haematoxylin and eosin and Oil Red O, and also by quantitative hepatic triglyceride measurements. RNA-seq was performed to discover the specific targets of LECT2 on NAFLD.

RESULTS

Serum and hepatic LECT2 levels were elevated in NAFLD patients and HFD-fed mice. Inhibition of hepatic Lect2 expression alleviated HFD-induced hepatic steatosis and inflammation, whereas hepatic overexpression of Lect2 aggravated HFD-induced hepatic steatosis and inflammation. RNA-seq and bioinformatical analysis suggested that the signal transducers and activators of transcription-1 (STAT-1) pathway might play an indispensable role in the interaction between LECT2 and NAFLD. A STAT-1 inhibitor could reverse the accumulation of hepatic lipids caused by Lect2 overexpression.

CONCLUSION

LECT2 expression is significantly elevated in NAFLD. LECT2 induces the occurrence and development of NAFLD through the STAT-1 pathway. LECT2 may be a potential therapeutic target for NAFLD.

LECT2 as a hepatokine links liver steatosis to inflammation via activating tissue macrophages in NASH

It remains unclear how hepatic steatosis links to inflammation. Leukocyte cell-derived chemotaxin 2 (LECT2) is a hepatokine that senses fat in the liver and is upregulated prior to weight gain. The aim of this study was to investigate the significance of LECT2 in the development of nonalcoholic steatohepatitis (NASH). In human liver biopsy samples, elevated LECT2 mRNA levels were positively correlated with body mass index (BMI) and increased in patients who have steatosis and inflammation in the liver. LECT2 mRNA levels were also positively correlated with the mRNA levels of the inflammatory genes CCR2 and TLR4. In C57BL/6J mice fed with a high-fat diet, mRNA levels of the inflammatory cytokines Tnfa and Nos2 were significantly lower in Lect2 KO mice. In flow cytometry analyses, the number of M1-like macrophages and M1/M2 ratio were significantly lower in Lect2 KO mice than in WT mice. In KUP5, mouse kupffer cell line, LECT2 selectively enhanced the LPS-induced phosphorylation of JNK, but not that of ERK and p38. Consistently, LECT2 enhanced the LPS-induced phosphorylation of MKK4 and TAB2, upstream activators of JNK. Hepatic expression of LECT2 is upregulated in association with the inflammatory signature in human liver tissues. The elevation of LECT2 shifts liver residual macrophage to the M1-like phenotype, and contributes to the development of liver inflammation. These findings shed light on the hepatokine LECT2 as a potential therapeutic target that can dissociate liver steatosis from inflammation.

Loss of bound zinc facilitates amyloid fibril formation of leukocyte-cell-derived chemotaxin 2 (LECT2)

Aggregation of the circulating protein leukocyte-cell-derived chemotaxin 2 (LECT2) causes amyloidosis of LECT2 (ALECT2), one of the most prevalent forms of systemic amyloidosis affecting the kidney and liver. The I40V mutation is thought to be necessary but not sufficient for ALECT2, with a second, as-yet undetermined condition being required for the disease. EM, X-ray diffraction, NMR, and fluorescence experiments demonstrate that LECT2 forms amyloid fibrils in vitro in the absence of other proteins. Removal of LECT2's single bound Zn2+ appears to be obligatory for fibril formation. Zinc-binding affinity is strongly dependent on pH: 9-13 % of LECT2 is calculated to exist in the zinc-free state over the normal pH range of blood, with this fraction rising to 80 % at pH 6.5. The I40V mutation does not alter zinc-binding affinity or kinetics but destabilizes the zinc-free conformation. These results suggest a mechanism in which loss of zinc together with the I40V mutation leads to ALECT2.

Hepatokines and metabolism: Deciphering communication from the liver

Background

The liver is a key regulator of systemic energy homeostasis and can sense and respond to nutrient excess and deficiency through crosstalk with multiple tissues. Regulation of systemic energy homeostasis by the liver is mediated in part through regulation of glucose and lipid metabolism. Dysregulation of either process may result in metabolic dysfunction and contribute to the development of insulin resistance or fatty liver disease.

Scope of review

The liver has recently been recognized as an endocrine organ that secretes hepatokines, which are liver-derived factors that can signal to and communicate with distant tissues. Dysregulation of liver-centered inter-organ pathways may contribute to improper regulation of energy homeostasis and ultimately metabolic dysfunction. Deciphering the mechanisms that regulate hepatokine expression and communication with distant tissues is essential for understanding inter-organ communication and for the development of therapeutic strategies to treat metabolic dysfunction.

Major conclusions

In this review, we discuss liver-centric regulation of energy homeostasis through hepatokine secretion. We highlight key hepatokines and their roles in metabolic control, examine the molecular mechanisms of each hepatokine, and discuss their potential as therapeutic targets for metabolic disease. We also discuss important areas of future studies that may contribute to understanding hepatokine signaling under healthy and pathophysiological conditions.

Genomic and functional characterization of the lect2 gene from Siniperca chuatsi

Mandarin fish (Siniperca chuatsi) is an important economic fish in China. Viral and bacterial diseases seriously affect the artificial culture of S. chuatsi. As a carnivorous fish, artificial feed domestication is also an important means to improve the scale of S. chuatsi culture. Therefore, the study of immunology and digestive physiology is very important to the industrial development of S. chuatsi. In this work, we analyzed the expression and function of the S. chuatsi leukocyte cell-derived chemotaxin 2 (Sc-lect2) gene on a basis of next generation, single-molecule long-read sequencing. Sc-lect2 was mainly expressed in the liver but barely expressed in the gill, skin, muscle, kidney, head kidney, brain, stomach, and intestine. When the fish were infected with infectious spleen and kidney necrosis virus and challenged with lipopolysaccharide and polyinosinic-polycytidylic acid, Sc-lect2 expression significantly increased by about 40, 17, and 7-fold, respectively, compared with unstimulated samples. We also found that Sc-lect2 increases by approximately 8-fold after the fish are fed an artificial diet. These results show that mandarin fish liver can not only digest food but also express specific immune genes. Changes in the diet can cause the differential expression of Sc-lect2 genes. Four Sc-lect2 interaction genes were differentially expressed in the skin or blood. Interestingly, miR-145-3p could inhibit Sc-lect2 gene expression by targeting its coding sequence region. One CpG island in the promoter region showed a high level of methylation, suggesting that high methylation does not affect Sc-lect2 gene expression in the liver.

Plasma half-life and tissue distribution of leukocyte cell-derived chemotaxin 2 in mice

Leukocyte cell-derived chemotaxin 2 (LECT2) is a hepatokine that causes skeletal muscle insulin resistance. The circulating levels of LECT2 are a possible biomarker that can predict weight cycling because they reflect liver fat and precede the onset of weight loss or gain. Herein, to clarify the dynamics of this rapid change in serum LECT2 levels, we investigated the in vivo kinetics of LECT2, including its plasma half-life and tissue distribution, by injecting ¹²⁵I-labelled LECT2 into ICR mice and radioactivity tracing. The injected LECT2 was eliminated from the bloodstream within 10 min (approximate half-life, 5 min). In the kidneys, the radioactivity accumulated within 10 min after injection and declined thereafter. Conversely, the radioactivity in urine increased after 30 min of injection, indicating that LECT2 is mainly excreted by the kidneys into the urine. Finally, LECT2 accumulated in the skeletal muscle and liver until 30 min and 2 min after injection, respectively. LECT2 accumulation was not observed in the adipose tissue. These findings are in agreement with LECT2 action on the skeletal muscle. The present study indicates that LECT2 is a rapid-turnover protein, which renders the circulating level of LECT2 a useful rapid-response biomarker to predict body weight alterations.

Thermoneutral Housing Temperature Improves Survival in a Murine Model of Polymicrobial Peritonitis

Regulatory guidelines mandate housing for laboratory mice at temperatures below their thermoneutral zone, creating chronic cold stress. However, increases in housing temperature could alter immune responses. We hypothesized housing mice at temperatures within their thermoneutral zone would improve sepsis survival and alter immune responses. Male C57BL/6 mice were housed at 22°C or 30°C after cecal ligation and puncture (CLP) for 10 days. Survival of mice housed at 30°C (78%) after CLP was significantly increased compared with mice housed at 22°C (40%). Experimental groups were repeated with mice euthanized at 0, 12, 24, and 48 h post-surgery to examine select immune parameters. Raising housing temperature minimally altered systemic, peritoneal, or splenic cell counts. However, IL-6 levels in plasma and peritoneal lavage fluid were significantly lower at 12 h post-surgery in mice housed at 30°C compared with 22°C. Bacterial colony counts from peritoneal lavage fluid were significantly lower in mice housed at 30°C and in vivo studies suggested this was the result of increased phagocytosis by neutrophils. As previously demonstrated, adoptive transfer of fibrocytes significantly increased sepsis survival compared with saline at 22°C. However, there was no additive effect when adoptive transfer was performed at 30°C. Overall, the results demonstrated that thermoneutral housing improves survival after CLP by increasing local phagocytic activity and technical revisions may be necessary to standardize the severity of the model across different housing temperatures. These findings stress the pronounced impact housing temperature has on the CLP model and the importance of reporting housing temperature.

Phagocytosis by Fibrocytes as a Mechanism to Decrease Bacterial Burden and Increase Survival in Sepsis

Fibrocytes are unique cells with innate and adaptive immune functions, but these mechanisms have not been fully explored. The aim of this study was to explain the mechanism by which adoptive transfer of exogenous fibrocytes improved bacterial clearance and increased sepsis survival. Initial flow cytometry-based, in vitro assays demonstrated phagocytosis by fibrocytes and intracellular bacterial killing was confirmed by direct plating of cell lysates after exposure to live bacteria. Intravenous adoptive transfer of fibrocytes at the time of cecal ligation and puncture (CLP) or 2 h after CLP in mice increased survivability. Decreased intraperitoneal bacterial burden was also observed. Quantification of peritoneal cell populations using flow cytometry demonstrated transferred and endogenous fibrocytes were significantly increased after CLP, while macrophage and neutrophil numbers were unchanged. To determine the impact in vivo, fluorescently labeled, killed bacteria were injected i.p. into mice 10 h after CLP or sham surgery ± adoptive transfer. Two hours later, flow cytometry of peritoneal cell populations after CLP alone revealed increased phagocytosis by macrophages, neutrophils, and endogenous fibrocytes. Transferred fibrocytes had significantly increased phagocytic activity in the septic peritoneum compared with sham and greater activity than any other cell type. Therefore, adoptive transfer may enhance bacterial clearance in early sepsis through the cumulative effects of endogenous and transferred fibrocytes rather than modulating the function of other endogenous phagocytes. Direct phagocytic activity coupled with previously described influences on T cell responses may explain the benefits of fibrocyte transfer in sepsis.

Delving into the amyloidogenic core of human leukocyte chemotactic factor 2

ALECT2 (leukocyte chemotactic factor 2) amyloidosis is one of the most recently identified amyloid-related diseases, with LECT2 amyloids commonly found in different types of tissues. Under physiological conditions, LECT2 is a 16 kDa multifunctional protein produced by the hepatocytes and secreted into circulation. The pathological mechanisms causing LECT2 transition into the amyloid state are still largely unknown. In the case of ALECT2 patients, there is no disease-causing mutation, yet almost all patients carry a common polymorphism that appears to be necessary but not sufficient to directly trigger amyloidogenesis. In this work, we followed a reductionist methodology in order to detect critical amyloidogenic "hot-spots" during the fibrillation of LECT2. By associating experimental and computational assays, this approach reveals the explicit amyloidogenic core of human LECT2 and pinpoints regions with distinct amyloidogenic properties. The fibrillar architecture of LECT2 polymers, based on our results, provides a wealth of detailed information about the amyloidogenic "hot-spot" interactions and represents a starting point for future peptide-driven intervention in ALECT2 amyloidosis.