Lipocalin-2 participates in sepsis-induced myocardial injury by mediating lipid accumulation and mitochondrial dysfunction

Lipocalin-2 Regulates Osteocyte Ferroptosis and Osteocyte-Osteoblast Crosstalk via Wnt Signaling to Control Bone Formation

Osteoporosis is a multifactorial disease, and emerging evidence suggests that iron overload contributes to its progression. Here, we identify Lipocalin-2 (LCN2), a cytokine secreted by bone cells with endocrine effects on other tissues, as a local regulator of osteocyte iron metabolism and a mediator of skeletal deterioration. Our findings reveal that LCN2 promotes iron accumulation, mitochondrial dysfunction, and ferroptosis in osteocytes in a process dependent on LCN2 receptor SLC22A17. Genetic ablation of Lcn2 (Dmp1-Cre; Lcn2 fl/fl ) in osteocytes mitigates their ferroptotic vulnerability by preserving mitochondrial integrity and limiting iron overload. Remarkably, LCN2 deletion enhances osteocyte dendricity and lacunocanalicular network, supporting their function in bone remodeling. Mechanistically, we demonstrate that Lcn2 ablation in osteocytes decreases DKK1 and SOST expression in bone, leading to increased Wnt/β-catenin signaling and osteoblast-driven bone formation. Using in vitro and in vivo approaches, we establish the LCN2-SLC22A17 axis as a key pathway linking iron homeostasis, osteocyte dysfunction, and skeletal remodeling. These findings provide insight into a previously unrecognized mechanism underlying iron-driven bone loss and suggest that targeting LCN2 could offer therapeutic potential for osteoporosis.

Targeting Lcn2 to Inhibit Myocardial Cell Ferroptosis is a Potential Therapy for Alleviating Septic Cardiomyopathy

Septic cardiomyopathy (SCM) represents a key feature of sepsis-associated cardiovascular failure, and ferroptosis is one of the essential causes of septic cardiac dysfunction. In this study, combined with omics analysis and in vivo experiments, we verified the damage of ferroptosis on cardiac tissue in septic mice and mined the target genes that can inhibit ferroptosis in cardiomyocytes. Lipocalin-2 (Lcn2) was identified to be associated with SCM progression via integrated transcriptomic and proteomic analyses. Sepsis was induced by cecal ligation and perforation (CLP) in mice. Ferroptosis and cardiac dysfunction were detected by pathological tissue staining and ELISA. However, after the knockout of Lcn2, cardiomyocyte ferroptosis was significantly suppressed, inflammatory infiltrates were reduced, reactive oxygen species (ROS) levels were lowered, mitochondrial damage was alleviated, and cardiac function was restored in CLP mice. In summary, this study found that Lcn2 can be a potential target for inhibiting ferroptosis in SCM. Targeting Lcn2 can effectively inhibit inflammation, improve mitochondrial dysfunction, inhibit cardiomyocyte ferroptosis, and alleviate SCM.

Activation of STAT6 in Intestinal Epithelial Cells Predisposes to Gut Inflammation

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) often associated with a Type 2 immune response. Although previous reports hint at a role for signal transducer and activator of transcription (STAT) 6 signaling in non-immune cells, the contribution of STAT6-activation particularly in intestinal epithelial cells (IECs) is still unknown. Dextran sodium sulfate (DSS)-induced colitis is a model for UC in mice that we applied here on animals with expression of a constitutively active version of STAT6 in IECs (VillinCre_STAT6vt mice). We report increased pathology and mortality due to enhanced and systemic inflammation in these mice. Bulk RNA sequencing of colonic tissue from naïve VillinCre_STAT6vt mice showed differential expression of more than 140 genes compared to control mice. Gene set enrichment analysis revealed STAT6-regulated expression of the unfolded protein response, MTORC- and MYC-signaling, and protein secretion pathways. A comparison of gene expression in the colon of naïve VillinCre_STAT6vt mice and a human single-cell RNA sequencing dataset of a patient cohort with IBD revealed overlapping changes in the epithelial and macrophage compartment compared to corresponding controls. In conclusion, we found that activation of STAT6 in the intestinal epithelium predisposes to exacerbated colitis and gut inflammation.

Exosomal ANXA2 facilitates ovarian cancer peritoneal metastasis by activating peritoneal mesothelial cells through binding with TLR2

BACKGROUND

Peritoneal dissemination of ovarian cancer (OvCa) can be largely attributed to the formation of a metastatic microenvironment driven by tumoral exosomes. Here, we aimed to elucidate the mechanisms through which exosomal annexin A2 (ANXA2) derived from OvCa cells induces an HPMC phenotypic shift in favour of peritoneal metastasis.

METHODS

Immunohistochemistry and orthotopic and intraperitoneal OvCa xenograft mouse models were used to clarify the relationship between tumour ANXA2 expression and peritoneal metastasis. Exosomes were isolated from OvCa cell lines via ultracentrifugation. Functional experiments on cell proliferation and motility, and western blot were performed to investigate the activation of HPMCs and its impact on tumour cell in vitro. High-throughput transcriptional sequencing and rescue experiments in which ANXA2 inhibitor (LCKLSL) or the toll-like receptor 2 (TLR2) inhibitor (C29) was used to co-culture the HPMCs with exosome were employed to identify the crucial functional molecules through which exosomal ANXA2 activates HPMCs. The impact of exosomal ANXA2-activated HPMCs on tumour progression was assessed via functional experiments.

RESULTS

Primary OvCa samples with high ANXA2 expression exhibited a stronger tendency to metastasize to the abdominal cavity. Tumoral ANXA2 promoted OvCa peritoneal metastasis through the secretion of exosomes carrying ANXA2. ANXA2-loaded exosomes activated HPMCs through exosomal ANXA2 binding to TLR2, shifting the phenotype of HPMCs towards mesenchymal cells, increasing their migration and invasion capacities, and elevating the expression of lipocalin 2 (LCN2). High LCN2 expression in HPMCs promoted OvCa cell adhesion, proliferation, motility, and lipid metabolism reprogramming.

CONCLUSION

Exosomal ANXA2 secreted by tumour cells activates HPMCs and induces the expression of LCN2, which in turn promotes the peritoneal metastasis of OvCa.

Lipocalin-2 promotes CKD vascular calcification by aggravating VSMCs ferroptosis through NCOA4/FTH1-mediated ferritinophagy

Vascular calcification (VC) is a common complication of chronic kidney disease (CKD), for which no effective therapies are available. Hyperphosphatemia, a feature of CKD, is a well-known inducer of VC. High phosphate (HP)-induced ferroptosis plays a crucial role in CKD-related VC (CKD-VC), but the mechanisms remain unclear. Lipocalin-2 (LCN2), an iron-trafficking protein, has been implicated in ferroptosis regulation. In the present study, the role of LCN2 as a potential mediator of CKD-VC was investigated. HP-induced LCN2 expression in the arteries of CKD-VC patients, animal models and vascular smooth muscle cells (VSMCs). LCN2 knockout (LCN2KO) mice and wild-type (WT) mice fed with a high adenine and phosphate (AP) diet were studied to explore CKD-VC. Compared with WT mice, LCN2KO mice showed an amelioration of the CKD-VC induced by the AP diet. The inhibition of LCN2 also alleviated HP-induced calcium deposition and phenotypic transition in VSMCs. Conversely, VSMCs-targeted LCN2 overexpression or recombinant LCN2 treatment exacerbated CKD-VC in vivo and in vitro. Mechanistically, nuclear receptor coactivator 4 (NCOA4)/ferritin heavy chain 1 (FTH1)-mediated ferritinophagy-dependent ferroptosis was involved in LCN2-mediated CKD-VC. Under HP conditions, LCN2 interacted with NCOA4, potentially accelerating the degradation of FTH1 and inducing ferroptosis. The inhibition of LCN2 may rescue the degradation of FTH1 and thus ameliorate ferroptosis, significantly suppressing VSMCs calcification. In summary, our study revealed a novel role for LCN2 induced ferritinophagy-dependent ferroptosis in CKD-VC, and targeting LCN2 might be a promising treatment for CKD-VC.

Energy metabolism: from physiological changes to targets in sepsis-induced cardiomyopathy

Sepsis is a systemic inflammatory response syndrome caused by a variety of dysregulated responses to host infection with life-threatening multi-organ dysfunction. Among the injuries or dysfunctions involved in the course of sepsis, cardiac injury and dysfunction often occur and are associated with the pathogenesis of hemodynamic disturbances, also defined as sepsis-induced cardiomyopathy (SIC). The process of myocardial metabolism is tightly regulated and adapts to various cardiac output demands. The heart is a metabolically flexible organ capable of utilizing all classes of energy substrates, including carbohydrates, lipids, amino acids, and ketone bodies, to produce ATP. The demand of cardiac cells for energy metabolism changes substantially in septic cardiomyopathy, with distinct etiological causes and different times. This review describes changes in cardiomyocyte energy metabolism under normal physiological conditions and some features of myocardial energy metabolism in septic cardiomyopathy and briefly outlines the role of the mitochondria as a center of energy metabolism in the septic myocardium, revealing that changes in energy metabolism can serve as a potential future therapy for infectious cardiomyopathy.

Utilizing omics technologies in the investigation of sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) is a common and high-mortality complication among critically ill patients. Uncertainties persist regarding the pathogenesis, pathophysiology, and diagnosis of SIC, underscoring the necessity to investigate potential biological mechanisms. With the rise of omics technologies, leveraging their high throughput and big data advantages, a systems biology perspective is employed to study the biological processes of SIC. This approach aids in gaining a better understanding of the disease's onset, progression, and outcomes, ultimately providing improved guidance for clinical practices. This review summarizes the currently applied omics technologies, omics studies related to SIC, and relevant omics databases.

Inhibition of Pyruvate Dehydrogenase Kinase 4 Protects Cardiomyocytes from lipopolysaccharide-Induced Mitochondrial Damage by Reducing Lactate Accumulation

Mitochondrial dysfunction is considered one of the major pathogenic mechanisms of sepsis-induced cardiomyopathy (SIC). Pyruvate dehydrogenase kinase 4 (PDK4), a key regulator of mitochondrial metabolism, is essential for maintaining mitochondrial function. However, its specific role in SIC remains unclear. To investigate this, we established an in vitro model of septic cardiomyopathy using lipopolysaccharide (LPS)-induced H9C2 cardiomyocytes. Our study revealed a significant increase in PDK4 expression in LPS-treated H9C2 cardiomyocytes. Inhibiting PDK4 with dichloroacetic acid (DCA) improved cell survival, reduced intracellular lipid accumulation and calcium overload, and restored mitochondrial structure and respiratory capacity while decreasing lactate accumulation. Similarly, Oxamate, a lactate dehydrogenase inhibitor, exhibited similar effects to DCA in LPS-treated H9C2 cardiomyocytes. To further validate whether PDK4 causes cardiomyocyte and mitochondrial damage in SIC by promoting lactate production, we upregulated PDK4 expression using PDK4-overexpressing lentivirus in H9C2 cardiomyocytes. This resulted in elevated lactate levels, impaired mitochondrial structure, and reduced mitochondrial respiratory capacity. However, inhibiting lactate production reversed the mitochondrial dysfunction caused by PDK4 upregulation. In conclusion, our study highlights the pathogenic role of PDK4 in LPS-induced cardiomyocyte and mitochondrial damage by promoting lactate production. Therefore, targeting PDK4 and its downstream product lactate may serve as promising therapeutic approaches for treating SIC.

Inhibition of Pyruvate Dehydrogenase Kinase 4 Attenuates Myocardial and Mitochondrial Injury in Sepsis-Induced Cardiomyopathy

BACKGROUND

Sepsis-induced cardiomyopathy (SIC) is a cardiac dysfunction caused by sepsis, with mitochondrial dysfunction being a critical contributor. Pyruvate dehydrogenase kinase 4 (PDK4) is a kinase of pyruvate dehydrogenase with multifaceted actions in mitochondrial metabolism. However, its role in SIC remains unknown.

METHODS

Serum PDK4 levels were measured and analyzed in 27 children with SIC, 30 children with sepsis, and 29 healthy children. In addition, for mice exhibiting SIC, the effects of PDK4 knockdown or inhibition on the function and structure of the myocardium and mitochondria were assessed.

RESULTS

The findings from the analysis of children with SIC revealed that PDK4 was significantly elevated and correlated with disease severity and organ injury. Nonsurvivors displayed higher serum PDK4 levels than survivors. Furthermore, mice with SIC benefited from PDK4 knockdown or inhibition, showing improved myocardial contractile function, reduced myocardial injury, and decreased mitochondrial structural injury and dysfunction. In addition, inhibition of PDK4 decreased the inhibitory phosphorylation of PDHE1α (pyruvate dehydrogenase complex E1 subunit α) and improved abnormal pyruvate metabolism and mitochondrial dysfunction.

CONCLUSIONS

PDK4 is a potential biomarker for the diagnosis and prognosis of SIC. In experimental SIC, PDK4 promoted mitochondrial dysfunction with increased phosphorylation of PDHE1α and abnormal pyruvate metabolism.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

LCN2 and ELANE overexpression induces sepsis

Sepsis is a syndrome characterized by a systemic inflammatory response due to the invasion of pathogenic microorganisms. The relationship between Lipocalin-2 (LCN2), elastase, neutrophil expressed (ELANE) and sepsis remains unclear. The sepsis datasets GSE137340 and GSE154918 profiles were downloaded from gene expression omnibus generated from GPL10558. Batch normalization, differentially expressed Genes (DEGs) screening, weighted gene co-expression network analysis (WGCNA), functional enrichment analysis, Gene Set Enrichment Analysis (GSEA), immune infiltration analysis, construction and analysis of protein-protein interaction (PPI) networks, Comparative Toxicogenomics Database (CTD) analysis were performed. Gene expression heatmaps were generated. TargetScan was used to screen miRNAs of DEGs. 328 DEGs were identified. According to Gene Ontology (GO), in the Biological Process analysis, they were mainly enriched in immune response, apoptosis, inflammatory response, and immune response regulation signaling pathways. In cellular component analysis, they were mainly enriched in vesicles, cytoplasmic vesicles, and secretory granules. In Molecular Function analysis, they were mainly concentrated in hemoglobin binding, Toll-like receptor binding, immunoglobulin binding, and RAGE receptor binding. In Kyoto Encyclopedia of Genes and Genomes (KEGG), they were mainly enriched in NOD-like receptor signaling pathway, Toll-like receptor signaling pathway, TNF signaling pathway, P53 signaling pathway, and legionellosis. Seventeen modules were generated. The PPI network identified 4 core genes (MPO, ELANE, CTSG, LCN2). Gene expression heatmaps revealed that core genes (MPO, ELANE, CTSG, LCN2) were highly expressed in sepsis samples. CTD analysis found that MPO, ELANE, CTSG and LCN2 were associated with sepsis, peritonitis, meningitis, pneumonia, infection, and inflammation. LCN2 and ELANE are highly expressed in sepsis and may serve as molecular targets.

Identification of immune-related genes in diagnosing retinopathy of prematurity with sepsis through bioinformatics analysis and machine learning

Background: There is increasing evidence indicating that immune system dysregulation plays a pivotal role in the pathogenesis of retinopathy of prematurity (ROP) and sepsis. This study aims to identify key diagnostic candidate genes in ROP with sepsis. Methods: We obtained publicly available data on ROP and sepsis from the gene expression omnibus database. Differential analysis and weighted gene correlation network analysis (WGCNA) were performed to identify differentially expressed genes (DEGs) and key module genes. Subsequently, we conducted functional enrichment analysis to gain insights into the biological functions and pathways. To identify immune-related pathogenic genes and potential mechanisms, we employed several machine learning algorithms, including Support Vector Machine Recursive Feature Elimination (SVM-RFE), Least Absolute Shrinkage and Selection Operator (LASSO), and Random Forest (RF). We evaluated the diagnostic performance using nomogram and Receiver Operating Characteristic (ROC) curves. Furthermore, we used CIBERSORT to investigate immune cell dysregulation in sepsis and performed cMAP analysis to identify potential therapeutic drugs. Results: The sepsis dataset comprised 352 DEGs, while the ROP dataset had 307 DEGs and 420 module genes. The intersection between DEGs for sepsis and module genes for ROP consisted of 34 genes, primarily enriched in immune-related pathways. After conducting PPI network analysis and employing machine learning algorithms, we pinpointed five candidate hub genes. Subsequent evaluation using nomograms and ROC curves underscored their robust diagnostic potential. Immune cell infiltration analysis revealed immune cell dysregulation. Finally, through cMAP analysis, we identified some small molecule compounds that have the potential for sepsis treatment. Conclusion: Five immune-associated candidate hub genes (CLEC5A, KLRB1, LCN2, MCEMP1, and MMP9) were recognized, and the nomogram for the diagnosis of ROP with sepsis was developed.

Lipocalin family proteins and their diverse roles in cardiovascular disease

The lipocalin (LCN) family members, a group of small extracellular proteins with 160-180 amino acids in length, can be detected in all kingdoms of life from bacteria to human beings. They are characterized by low similarity of amino acid sequence but highly conserved tertiary structures with an eight-stranded antiparallel β-barrel which forms a cup-shaped ligand binding pocket. In addition to bind small hydrophobic ligands (i.e., fatty acids, odorants, retinoids, and steroids) and transport them to specific cells, lipocalins (LCNs) can interact with specific cell membrane receptors to activate their downstream signaling pathways, and with soluble macromolecules to form the complex. Consequently, LCNs exhibit great functional diversity. Accumulating evidence has demonstrated that LCN family proteins exert multiple layers of function in the regulation of many physiological processes and human diseases (i.e., cancers, immune disorders, metabolic disease, neurological/psychiatric disorders, and cardiovascular disease). In this review, we firstly introduce the structural and sequence properties of LCNs. Next, six LCNs including apolipoprotein D (ApoD), ApoM, lipocalin 2 (LCN2), LCN10, retinol-binding protein 4 (RBP4), and Lipocalin-type prostaglandin D synthase (L-PGDS) which have been characterized so far are highlighted for their diagnostic/prognostic values and their potential effects on coronary artery disease and myocardial infarction injury. The roles of these 6 LCNs in cardiac hypertrophy, heart failure, diabetes-induced cardiac disorder, and septic cardiomyopathy are also summarized. Finally, their therapeutic potential for cardiovascular disease is discussed in each section.