MLKL signaling regulates macrophage polarization in acute pancreatitis through CXCL10

Exosomes Derived From Cerulein-Stimulated Pancreatic Acinar Cells Mediate Peritoneal Macrophage M1 Polarization and Pyroptosis via an miR-24-3p/MARCH3/NLRP3 Axis in Acute Pancreatitis

OBJECTIVES

Acute pancreatitis (AP) has a high incidence of hospitalizations, morbidity, and mortality worldwide. A growing number of studies on AP pathogenesis are based on cerulein-induced experimental model, which simulates human AP in vivo. It has been demonstrated that both pancreatic acinar cells and peritoneal macrophages are involved in pancreatic inflammation and damage. However, their connection has not been well understood.

METHODS

A cerulein-induced AP model was established on the pancreatic acinar cell line AR42J. Rat macrophages were isolated from the peritoneal cavity. The effects of cerulein-induced pancreatic exosomes on the peritoneal macrophage and pancreas in vivo and in vitro were examined. The underlying molecular mechanism was investigated by exploring the regulatory role of downstream molecules.

RESULTS

We found that exosomes derived from cerulein-treated AR42J cells induced rat peritoneal macrophage M1 polarization and pyroptosis. miR-24-3p was upregulated in cerulein-stimulated exosomes, whereas the miR-24-3p inhibitor counteracted the effect of pancreatic exosomes on peritoneal macrophage M1 polarization and pyroptosis. Furthermore, miR-24-3p inhibited March3 expression, whereas MARCH3 mediated NLRP3 ubiquitination in rat peritoneal macrophages, which, in turn, contributed to the apoptosis, reactive oxygen species production, and inflammation in AR42J cells.

CONCLUSIONS

Exosomes derived from cerulein-stimulated pancreatic acinar cells mediate peritoneal macrophage M1 polarization and pyroptosis via an miR-24-3p/MARCH3/NLRP3 axis in AP.

Age-related dysregulation of CXCL9/10 in monocytes is linked to impaired innate immune responses in a mouse model of Staphylococcus aureus osteomyelitis

BACKGROUND

Age-associated impairments in innate immunity are believed to be a causative factor responsible for severe pathogenesis of Staphylococcus aureus (S. aureus) infection in the bone tissue. However, the basis for age-associated decline in innate immune response upon S. aureus infection remains poorly understood.

RESULTS

Our transcriptional data (GEO: GSE166522) from a mouse model of S. aureus osteomyelitis show up-regulated CXCL9 and CXCL10 (CXCL9/10), which is further confirmed in vitro and in vivo by the present study. Notably, monocytes are a main source for CXCL9/10 production in bone marrow upon S. aureus challenge, but this response declines in middle-aged mice. Interestingly, conditional medium of bone marrow monocytes from middle-aged mice has a strikingly decreased effect on bactericidal functions of neutrophils and macrophages compares with that from young mice. We further show that activation of CXCL9/10-CXCR3 axis between monocytes and macrophages/neutrophils promotes the bactericidal function of the cells, whereas blocking the axis impairs such function. Importantly, treatment with either exogenous CXCL9 or CXCL10 in a middle-aged mice model enhances, while pharmacological inhibition of CXCR3 in young mice model impairs, bacterial clearance and bone marrow structure.

CONCLUSIONS

These findings demonstrate that bone marrow monocytes act as a critical promotor of innate immune response via the CXLCL9/10-CXCR3 axis upon S. aureus infection, and that the increased susceptibility to S. aureus infection in skeleton in an aged host may be largely attributable to the declined induction of CXCR9/10 in monocytes.

The Pivotal Role of Macrophages in the Pathogenesis of Pancreatic Diseases

The pancreas is an organ with both exocrine and endocrine functions, comprising a highly organized and complex tissue microenvironment composed of diverse cellular and non-cellular components. The impairment of microenvironmental homeostasis, mediated by the dysregulation of cell-to-cell crosstalk, can lead to pancreatic diseases such as pancreatitis, diabetes, and pancreatic cancer. Macrophages, key immune effector cells, can dynamically modulate their polarization status between pro-inflammatory (M1) and anti-inflammatory (M2) modes, critically influencing the homeostasis of the pancreatic microenvironment and thus playing a pivotal role in the pathogenesis of the pancreatic disease. This review aims to summarize current findings and provide detailed mechanistic insights into how alterations mediated by macrophage polarization contribute to the pathogenesis of pancreatic disorders. By analyzing current research comprehensively, this article endeavors to deepen our mechanistic understanding of regulatory molecules that affect macrophage polarity and the intricate crosstalk that regulates pancreatic function within the microenvironment, thereby facilitating the development of innovative therapeutic strategies that target perturbations in the pancreatic microenvironment.

The GgcxK325Q Mutation Does Not Affect the Calcium Homeostasis of the Epididymis and Male Fertility in Mice

A low-calcium microenvironment is imperative for spermatozoa maturation within the epididymis. Our previous work has shown that γ-glutamyl carboxylase (GGCX), the carboxylation enzyme of the matrix Gla protein (MGP), plays an essential role in epididymal calcium homeostasis and sperm maturation in rats and that the GGCX SNP mutation rs699664 was associated with asthenozoospermia (AZS) in humans. Here, we investigated the expression patterns of GGCX and MGP in the mouse epididymis and generated GgcxK325Q knock-in (KI) mice. We also tested the effects of this mutation on epididymal calcium homeostasis, sperm function, and male fertility in GgcxK325Q-/- mice. The results showed that both GGCX and MGP were enriched in all regions of the mouse epididymis, especially in the initial segment of the epididymis. Double immunofluorescence staining revealed that GGCX colocalized with MGP in the epithelial cells of the initial segment and caput regions as well as in the lumen of the corpus and cauda regions of the mouse epididymis. However, the GgcxK325Q-/- mice were fertile with normal epididymal morphology, sperm functions, and epididymal calcium concentration. Overall, our findings revealed that the GgcxK325Q mutation does not exert any discernible effect on male fertility in mice.

Identification and analysis of chemokine-related and NETosis-related genes in acute pancreatitis to develop a predictive model

Background: Chemokines and NETosis are significant contributors to the inflammatory response, yet there still needs to be a more comprehensive understanding regarding the specific molecular characteristics and interactions of NETosis and chemokines in the context of acute pancreatitis (AP) and severe AP (SAP). Methods: To address this gap, the mRNA expression profile dataset GSE194331 was utilized for analysis, comprising 87 AP samples (77 non-SAP and 10 SAP) and 32 healthy control samples. Enrichment analyses were conducted for differentially expressed chemokine-related genes (DECRGs) and NETosis-related genes (DENRGs). Three machine-learning algorithms were used for the identification of signature genes, which were subsequently utilized in the development and validation of nomogram diagnostic models for the prediction of AP and SAP. Furthermore, single-gene Gene Set Enrichment Analysis (GSEA) and Gene Set Variation Analysis (GSVA) were performed. Lastly, an interaction network for the identified signature genes was constructed. Results: We identified 12 DECRGs and 7 DENRGs, and enrichment analyses indicated they were primarily enriched in cytokine-cytokine receptor interaction, chemokine signaling pathway, TNF signaling pathway, and T cell receptor signaling pathway. Moreover, these machine learning algorithms finally recognized three signature genes (S100A8, AIF1, and IL18). Utilizing the identified signature genes, we developed nomogram models with high predictive accuracy for AP and differentiation of SAP from non-SAP, as demonstrated by area under the curve (AUC) values of 0.968 (95% CI 0.937-0.990) and 0.862 (95% CI 0.742-0.955), respectively, in receiver operating characteristic (ROC) curve analysis. Subsequent single-gene GESA and GSVA indicated a significant positive correlation between these signature genes and the proteasome complex. At the same time, a negative association was observed with the Th1 and Th2 cell differentiation signaling pathways. Conclusion: We have identified three genes (S100A8, AIF1, and IL18) related to chemokines and NETosis, and have developed accurate diagnostic models that might provide a novel method for diagnosing AP and differentiating between severe and non-severe cases.

Pervasive loss of regulated necrotic cell death genes in elephants, hyraxes, and sea cows (Paenungualta)

Gene loss can promote phenotypic differences between species, for example, if a gene constrains phenotypic variation in a trait, its loss allows for the evolution of a greater range of variation or even new phenotypes. Here, we explore the contribution of gene loss to the evolution of large bodies and augmented cancer resistance in elephants. We used genomes from 17 Afrotherian and Xenarthran species to identify lost genes, i.e., genes that have pseudogenized or been completely lost, and Dollo parsimony to reconstruct the evolutionary history of gene loss across species. We unexpectedly discovered a burst of gene losses in the Afrotherian stem lineage and found that the loss of genes with functions in regulated necrotic cell death modes was pervasive in elephants, hyraxes, and sea cows (Paenungulata). Among the lost genes are MLKL and RIPK3, which mediate necroptosis, and sensors that activate inflammasomes to induce pyroptosis, including AIM2, MEFV, NLRC4, NLRP1, and NLRP6. These data suggest that the mechanisms that regulate necrosis and pyroptosis are either extremely derived or potentially lost in these lineages, which may contribute to the repeated evolution of large bodies and cancer resistance in Paenungulates as well as susceptibility to pathogen infection.

Acute pancreatitis: pathogenesis and emerging therapies

Acute pancreatitis is a severe inflammatory disorder with limited treatment options. Improved understanding of disease mechanisms has led to new and potential therapies. Here we summarize what we view as some of the most promising new therapies for treating acute pancreatitis, emphasizing the rationale of specific treatments based on disease mechanisms. Targeted pharmacologic interventions are highlighted. We explore potential treatment benefits and risks concerning reducing acute injury, minimizing complications, and improving long-term outcomes. Mechanisms associated with acute pancreatitis initiation, perpetuation, and reconstitution are highlighted, along with potential therapeutic targets and how these relate to new treatments.

PRMT7-Dependent Transcriptional Activation of Hmgb2 Aggravates Severe Acute Pancreatitis by Promoting Acsl1-Induced Ferroptosis

Severe acute pancreatitis (SAP) is a highly fatal abdominal emergency, and its association with protein arginine methyltransferase 7 (PRMT7), the sole known type III enzyme responsible for the monomethylation of arginine residue, remains unexplored. In this study, we observe an increase in the PRMT7 levels in the pancreas of SAP mice and Cerulein-LPS-stimulated AR42J cells. Overexpression of Prmt7 exacerbated pancreatic damage in SAP, while the inhibition of PRMT7 improved SAP-induced pancreatic damage. Furthermore, PRMT7 overexpression promoted inflammation, oxidative stress, and ferroptosis during SAP. Mechanically, PRMT7 catalyzed monomethylation at histone H4 arginine 3 (H4R3me1) at the promoter region of high mobility group proteins 2 (HMGB2), thereby enhancing its transcriptional activity. Subsequently, HMGB2 facilitated Acyl CoA synthase long-chain family member 1 (ACSL1) transcription by binding to its promoter region, resulting in the activation of ferroptosis. Inhibition of PRMT7 effectively alleviated ferroptosis in Cerulein-LPS-induced AR42J cells by suppressing the HMGB2-ACSL1 pathway. Overall, our study reveals that PRMT7 plays a crucial role in promoting SAP through its regulation of the HMGB2-ACSL1 pathway to accelerate ferroptosis.

Tumor-associated macrophages: an effective player of the tumor microenvironment

Cancer progression is primarily caused by interactions between transformed cells and the components of the tumor microenvironment (TME). TAMs (tumor-associated macrophages) make up the majority of the invading immune components, which are further categorized as anti-tumor M1 and pro-tumor M2 subtypes. While M1 is known to have anti-cancer properties, M2 is recognized to extend a protective role to the tumor. As a result, the tumor manipulates the TME in such a way that it induces macrophage infiltration and M1 to M2 switching bias to secure its survival. This M2-TAM bias in the TME promotes cancer cell proliferation, neoangiogenesis, lymphangiogenesis, epithelial-to-mesenchymal transition, matrix remodeling for metastatic support, and TME manipulation to an immunosuppressive state. TAMs additionally promote the emergence of cancer stem cells (CSCs), which are known for their ability to originate, metastasize, and relapse into tumors. CSCs also help M2-TAM by revealing immune escape and survival strategies during the initiation and relapse phases. This review describes the reasons for immunotherapy failure and, thereby, devises better strategies to impair the tumor-TAM crosstalk. This study will shed light on the understudied TAM-mediated tumor progression and address the much-needed holistic approach to anti-cancer therapy, which encompasses targeting cancer cells, CSCs, and TAMs all at the same time.

PROTACs Targeting MLKL Protect Cells from Necroptosis

Mixed Lineage Kinase domain-Like pseudokinase (MLKL) is implicated in a broad range of diseases due to its role as the ultimate effector of necroptosis and has therefore emerged as an attractive drug target. Here, we describe the development of PROteolysis TArgeting Chimeras (PROTACs) as a novel approach to knock down MLKL through chemical means. A series of candidate degraders were synthesized from a high-affinity pyrazole carboxamide-based MLKL ligand leading to the identification of a PROTAC molecule that effectively degraded MLKL and completely abrogated cell death in a TSZ model of necroptosis. By leveraging the innate ability of these PROTACs to degrade MLKL in a dose-dependent manner, the quantitative relationship between MLKL levels and necroptosis was interrogated. This work demonstrates the feasibility of targeting MLKL using a PROTAC approach and provides a powerful tool to further our understanding of the role of MLKL within the necroptotic pathway.