PLD1 and PLD2 differentially regulate the balance of macrophage polarization in inflammation and tissue injury

PLD2 deletion ameliorates sepsis-induced cardiomyopathy by suppressing cardiomyocyte pyroptosis via the NLRP3/caspase 1/GSDMD pathway

OBJECTIVE

Sepsis-induced cardiomyopathy (SICM) is a life-threatening complication. Phospholipase D2 (PLD2) is crucial in mediating inflammatory reactions and is associated with the prognosis of patients with sepsis. Whether PLD2 is involved in the pathophysiology of SICM remains unknown. This study aimed to investigate the effect of PLD2 knockout on SICM and to explore potential mechanisms.

METHODS

The SICM model was established using cecal ligation and puncture in wild-type and PLD2-knockout mice and lipopolysaccharide (LPS)-induced H9C2 cardiomyocytes. Transfection with PLD2-shRNA lentivirus and a PLD2 overexpression plasmid were used to interfere with PLD2 expression in H9C2 cells. Cardiac pathological alterations, cardiac function, markers of myocardial injury, and inflammatory factors were used to evaluate the SICM model. The expression of pyroptosis-related proteins (NLRP3, cleaved caspase 1, and GSDMD-N) was assessed using western blotting, immunofluorescence, and immunohistochemistry.

RESULTS

SICM mice had myocardial tissue damage, increased inflammatory response, and impaired heart function, accompanied by elevated PLD2 expression. PLD2 deletion improved cardiac histological changes, mitigated cTNI production, and enhanced the survival of the SICM mice. Compared with controls, PLD2-knockdown H9C2 exhibits a decrease in inflammatory markers and lactate dehydrogenase production, and scanning electron microscopy results suggest that pyroptosis may be involved. The overexpression of PLD2 increased the expression of NLRP3 in cardiomyocytes. In addition, PLD2 deletion decreased the expression of pyroptosis-related proteins in SICM mice and LPS-induced H9C2 cells.

CONCLUSION

PLD2 deletion is involved in SICM pathogenesis and is associated with the inhibition of the myocardial inflammatory response and pyroptosis through the NLRP3/caspase 1/GSDMD pathway.

PLD2 deficiency alleviates endothelial glycocalyx degradation in LPS-induced ARDS/ALI

- Acute respiratory distress syndrome (ARDS)/acute lung injury (ALI) is a life-threatening condition marked by severe lung inflammation and increased lung endothelial barrier permeability. Endothelial glycocalyx deterioration is the primary factor of vascular permeability changes in ARDS/ALI. Although previous studies have shown that phospholipase D2 (PLD2) is closely related to the onset and progression of ARDS/ALI, its role and mechanism in the damage of endothelial cell glycocalyx remains unclear. We used LPS-induced ARDS/ALI mice (in vivo) and LPS-stimulated injury models of EA.hy926 endothelial cells (in vitro). We employed C57BL/6 mice, including wild-type and PLD2 knockout (PLD2-/-) mice, to establish the ARDS/ALI model. We applied immunofluorescence and ELISA to examine changes in syndecan-1 (SDC-1), matrix metalloproteinase-9 (MMP9), inflammatory cytokines (TNF-α, IL-6, and IL-1β) levels and the effect of external factors, such as phosphatidic acid (PA), 1-butanol (a PLD inhibitor), on SDC-1 and MMP9 expression levels. We found that PLD2 deficiency inhibits SDC-1 degradation and MMP9 expression in LPS-induced ARDS/ALI. Externally added PA decreases SDC-1 levels and increases MMP9 in endothelial cells, hence underlining PA's role in SDC-1 degradation. Additionally, PLD2 deficiency decreases the production of inflammatory cytokines (TNF-α, IL-6, and IL-1β) in LPS-induced ARDS/ALI. In summary, these findings suggest that PLD2 deficiency plays a role in inhibiting the inflammatory process and protecting against endothelial glycocalyx injury in LPS-induced ARDS/ALI.

Aging induces region-specific dysregulation of hormone synthesis in the primate adrenal gland

Adrenal glands, vital for steroid secretion and the regulation of metabolism, stress responses and immune activation, experience age-related decline, impacting systemic health. However, the regulatory mechanisms underlying adrenal aging remain largely uninvestigated. Here we established a single-nucleus transcriptomic atlas of both young and aged primate suprarenal glands, identifying lipid metabolism and steroidogenic pathways as core processes impacted by aging. We found dysregulation in centripetal adrenocortical differentiation in aged adrenal tissues and cells in the zona reticularis region, responsible for producing dehydroepiandrosterone sulfate (DHEA-S), were highly susceptible to aging, reflected by senescence, exhaustion and disturbed hormone production. Remarkably, LDLR was downregulated in all cell types of the outer cortex, and its targeted inactivation in human adrenal cells compromised cholesterol uptake and secretion of dehydroepiandrosterone sulfate, as observed in aged primate adrenal glands. Our study provides crucial insights into endocrine physiology, holding therapeutic promise for addressing aging-related adrenal insufficiency and delaying systemic aging.

The role and regulation of phospholipase D in metabolic disorders

Phospholipase D (PLD) is an enzyme that catalyzes the hydrolysis of phosphatidylcholine into phosphatidic acid and free choline. In mammals, PLD exists in two well-characterized isoforms, PLD1 and PLD2, and it plays pivotal roles as signaling mediators in various cellular functions, such as cell survival, differentiation, and migration. These isoforms are predominantly expressed in diverse cell types, including many immune cells, such as monocytes and macrophages, as well as non-immune cells, such as epithelial and endothelial cells. Several previous studies have revealed that the stimulation of these cells leads to an increase in PLD expression and its enzymatic products, potentially influencing the pathological responses in a wide spectrum of diseases. Metabolic diseases, exemplified by conditions, such as diabetes, obesity, hypertension, and atherosclerosis, pose significant global health challenges. Abnormal activation or dysfunction of PLD emerges as a potential contributing factor to the pathogenesis and progression of these metabolic disorders. Therefore, it is crucial to thoroughly investigate and understand the intricate relationship between PLD and metabolic diseases. In this review, we provide an in-depth overview of the functional roles and molecular mechanisms of PLD involved in metabolic diseases. By delving into the intricate interplay between PLD and metabolic disorders, this review aims to offer insights into the potential therapeutic interventions.

A newly developed PLD1 inhibitor ameliorates rheumatoid arthritis by regulating pathogenic T and B cells and inhibiting osteoclast differentiation

Phospholipase D1 (PLD1), which catalyzes the hydrolysis of phosphatidylcholine to phosphatidic acid and choline, plays multiple roles in inflammation. We investigated the therapeutic effects of the newly developed PLD1 inhibitors A2998, A3000, and A3773 in vitro and in vivo rheumatoid arthritis (RA) model. A3373 reduced the levels of LPS-induced TNF-α, IL-6, and IgG in murine splenocytes in vitro. A3373 also decreased the levels of IFN-γ and IL-17 and the frequencies of Th1, Th17 cells and germinal-center B cells, in splenocytes in vitro. A3373 ameliorated the severity of collagen-induced arthritis (CIA) and suppressed infiltration of inflammatory cells into the joint tissues of mice with CIA compared with vehicle-treated mice. Moreover, A3373 prevented systemic bone demineralization in mice with CIA and suppressed osteoclast differentiation and the mRNA levels of osteoclastogenesis markers in vitro. These results suggest that A3373 has therapeutic potential for RA.

Importance of PLD2 in an IL-23 driven psoriasiform dermatitis model and potential link to human psoriasis

Phospholipase D2 (PLD2), a major isoform of the PLD family, has been reported to regulate inflammatory responses. Thus far, the relevance of PLD2 in psoriasis, an inflammatory skin disease, has not been explored. In the current study, we examined PLD2 expression in the skin of psoriasis patients and the role of PLD2 in an interleukin (IL)-23-induced mouse model of psoriasiform dermatitis. Both in situ hybridization and bulk RNA sequencing showed PLD2 gene expression is significantly higher in lesional relative to non-lesional skin of psoriasis patients or the skin of healthy subjects. PLD2 expression is also enriched in residual lesions from patients on biologic therapies. Murine in vivo studies showed that PLD2 deficiency significantly reduced psoriasiform inflammation in IL-23-injected ears, as reflected by decreases in ear thickness, expression of defensin beta 4A and the S100 calcium binding protein A7A, macrophage infiltrate, and expression of CXCL10 and IL-6. However, the expression of type 17 cytokines, IL-17A and IL-17F, were not reduced. Dual knockout of PLD1 and PLD2 offered little additional protection compared to PLD2 knockout alone in the IL-23 model. In addition, pharmacological inhibition with a pan-PLD1/PLD2 inhibitor also suppressed IL-23-induced psoriasiform dermatitis. Bone-marrow-derived macrophages from wild type (WT) and PLD2 knockout (KO) mice exhibited little difference in viability and sensitivity to lipopolysaccharide and/or interferon gamma, or resiquimod (R848). PLD2 deficiency did not alter the differentiation and function of Th17 cells in an ex vivo study with splenocytes isolated from WT and PLD2 KO mice. Overall, these data suggest that PLD2 may play a role in the pathophysiology of psoriasis. Reducing macrophage infiltrate and cytokine/chemokine production might contribute to an anti-inflammatory effect observed in PLD2 knockout mice. Further studies are required to better understand the mechanisms by which PLD2 contributes to skin lesions in psoriasis patients and psoriasiform dermatitis models.

Choline metabolism underpins macrophage IL-4 polarization and RELMα up-regulation in helminth infection

Type 2 cytokines like IL-4 are hallmarks of helminth infection and activate macrophages to limit immunopathology and mediate helminth clearance. In addition to cytokines, nutrients and metabolites critically influence macrophage polarization. Choline is an essential nutrient known to support normal macrophage responses to lipopolysaccharide; however, its function in macrophages polarized by type 2 cytokines is unknown. Using murine IL-4-polarized macrophages, targeted lipidomics revealed significantly elevated levels of phosphatidylcholine, with select changes to other choline-containing lipid species. These changes were supported by the coordinated up-regulation of choline transport compared to naïve macrophages. Pharmacological inhibition of choline metabolism significantly suppressed several mitochondrial transcripts and dramatically inhibited select IL-4-responsive transcripts, most notably, Retnla. We further confirmed that blocking choline metabolism diminished IL-4-induced RELMα (encoded by Retnla) protein content and secretion and caused a dramatic reprogramming toward glycolytic metabolism. To better understand the physiological implications of these observations, naïve or mice infected with the intestinal helminth Heligmosomoides polygyrus were treated with the choline kinase α inhibitor, RSM-932A, to limit choline metabolism in vivo. Pharmacological inhibition of choline metabolism lowered RELMα expression across cell-types and tissues and led to the disappearance of peritoneal macrophages and B-1 lymphocytes and an influx of infiltrating monocytes. The impaired macrophage activation was associated with some loss in optimal immunity to H. polygyrus, with increased egg burden. Together, these data demonstrate that choline metabolism is required for macrophage RELMα induction, metabolic programming, and peritoneal immune homeostasis, which could have important implications in the context of other models of infection or cancer immunity.

Phospholipase D1 Attenuation Therapeutics Promotes Resilience against Synaptotoxicity in 12-Month-Old 3xTg-AD Mouse Model of Progressive Neurodegeneration

Abrogating synaptotoxicity in age-related neurodegenerative disorders is an extremely promising area of research with significant neurotherapeutic implications in tauopathies including Alzheimer's disease (AD). Our studies using human clinical samples and mouse models demonstrated that aberrantly elevated phospholipase D1 (PLD1) is associated with amyloid beta (Aβ) and tau-driven synaptic dysfunction and underlying memory deficits. While knocking out the lipolytic PLD1 gene is not detrimental to survival across species, elevated expression is implicated in cancer, cardiovascular conditions and neuropathologies, leading to the successful development of well-tolerated mammalian PLD isoform-specific small molecule inhibitors. Here, we address the importance of PLD1 attenuation, achieved using repeated 1 mg/kg of VU0155069 (VU01) intraperitoneally every alternate day for a month in 3xTg-AD mice beginning only from ~11 months of age (with greater influence of tau-driven insults) compared to age-matched vehicle (0.9% saline)-injected siblings. A multimodal approach involving behavior, electrophysiology and biochemistry corroborate the impact of this pre-clinical therapeutic intervention. VU01 proved efficacious in preventing in later stage AD-like cognitive decline affecting perirhinal cortex-, hippocampal- and amygdala-dependent behaviors. Glutamate-dependent HFS-LTP and LFS-LTD improved. Dendritic spine morphology showed the preservation of mushroom and filamentous spine characteristics. Differential PLD1 immunofluorescence and co-localization with Aβ were noted.

PLD2 deletion alleviates disruption of tight junctions in sepsis-induced ALI by regulating PA/STAT3 phosphorylation pathway

BACKGROUND

Increased inflammatory exudation caused by endothelium and endothelial junction damage is a typical pathological feature of acute respiratory distress syndrome/acute lung injury (ARDS/ALI). Previous studies have shown that phospholipase D2 (PLD2) can increase the inflammatory response and has a close relationship with the severity of sepsis-induced ALI and the mortality of sepsis, but its mechanism is unknown. This study explored the effect and mechanism of PLD2 deletion on the structure and function of endothelial tight junction (TJ) in lipopolysaccharide (LPS)-induced ALI.

METHODS

We used C57BL/6 mice (wild-type and PLD2 knockout (PLD2^-/-)) and human umbilical vein endothelial cell (HUVEC) models of sepsis-ALI. The pathological changes were evaluated by hematoxylin-eosin staining. Pulmonary vascular permeability was detected using wet-dry ratio, fluorescein isothiocyanate (FITC)-dextran, FITC-albumin, and immunoglobulin M concentration of bronchoalveolar lavage fluid. FITC-dextran and trans-endothelial electrical resistance assay were used to evaluate endothelial permeability on LPS-stimulated HUVECs. The mRNA expressions of TJ proteins were detected by real-time quantitative polymerase chain reaction. Then, protein levels were detected through Western blot analysis and immunofluorescence. The content of phosphatidic acid (PA), a downstream product of PLD2, was detected using an enzyme-linked immunosorbent assay kit.

RESULTS

PLD2 deficiency not only alleviated lung histopathological changes and improved pulmonary vascular permeability but also increased the survival rate of ALI mice. Knockout of PLD2 or treatment with the PLD2 inhibitor can reduce the damage of endothelial TJ proteins, namely, claudin5, occludin and zonula occludens protein-1, in sepsis-ALI mice and LPS-stimulated HUVECs. The level of the PLD2 catalytic product PA increased in LPS-stimulated HUVECs, and exogenous PA can reduce the TJ protein expression and increase signal transducer and activator of transcription 3 (STAT3) phosphorylation in vitro. Inhibition of STAT3 phosphorylation attenuated PA-induced degradation of endothelial TJs.

CONCLUSION

PLD2 knockout or inhibition may protect against LPS-induced lung injury by regulating the PA/STAT3 phosphorylation/endothelial TJ axis.

Exosomes from the Uterine Cavity Mediate Immune Dysregulation via Inhibiting the JNK Signal Pathway in Endometriosis

Endometriosis is a chronic inflammatory disease with an uncertain pathogenesis. Peritoneal immune dysregulation plays an important role in the pathogenesis of endometriosis. Exosomes are messengers of intercellular communication. This study mainly investigated the role of exosomes from the uterine cavity in endometriosis. Exosomes of the uterine aspirate fluid were isolated and cocultured with macrophages for 48 h. Flow cytometry was used to detect macrophage polarization. A Human MAPK Phosphorylation Antibody Array and Western blot were used to detect the phosphorylation of the MAPK pathway. A microRNA sequencing analysis was used to detect differentially expressed miRNAs. Our research found that exosomes of the uterine aspirate fluid from endometriosis could reduce the proportion of CD80⁺ macrophages. Additionally, it could inhibit the expression of P-JNK in macrophages. However, the JNK activator anisomycin could increase the proportion of CD80⁺ macrophages. In addition, exosomes of the uterine aspirate fluid from endometriosis could promote the migration and invasion of endometrial stromal cells by acting on macrophages. The expression of miR-210-3p was increased in both exosomes and the eutopic endometrium in patients with endometriosis through miRNA sequencing, which could also reduce the proportion of CD80⁺ macrophages. In summary, we propose that exosomes from the uterine cavity in patients with endometriosis may affect the phenotype of macrophages by inhibiting the JNK signaling pathway, thus mediating the formation of an immunological microenvironment conducive to the development of endometriosis.

Sexual dimorphism in gut microbiota dictates therapeutic efficacy of intravenous immunoglobulin on radiotherapy complications

INTRODUCTION

With the mounting number of cancer survivors, the complications following cancer treatment become novel conundrums and starve for countermeasures. Intravenous immunoglobulin (IVIg) is a purified preparation for immune-deficient and autoimmune conditions.

OBJECTIVES

Here, we investigated whether IVIg could be employed to fight against radiation injuries and explored the underlying mechanism.

METHODS

Hematopoietic or gastrointestinal (GI) tract toxicity was induced by total body or abdominal local irradiation. High-throughput sequencing was performed to analyze the gut microbiota configurations and gene expression profile of small intestine. The untargeted metabolomics of gut microbiome was assessed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analyses. Hydrodynamic-based gene delivery was used to knockdown the target genes in vivo.

RESULTS

Intravenous injection of IVIg protected against radiation-induced hematopoietic and GI tract toxicity in female mice but not in males. IVIg structured sex-characteristic gut microbiota configurations in abdominal irradiated mice. The irradiation enriched gut Lachnospiraceae in female mice but reduced those in males. IVIg injection combined with oral gavage of Lachnospiraceae or its metabolite hypoxanthine, alleviated radiation toxicity in male mice however, Lachnospiraceae or hypoxanthine alone failed to ameliorate the injuries. Abdominal local irradiation drove sex-distinct gene expression signatures in small intestine. Mechanistic investigation showed that replenishment of Lachnospiraceae or hypoxanthine offset abdominal radiation-reduced PLD1 expression in male mice. In females, irradiation elevated PLD1 expression. Deletion of PLD1 in GI tract of female mice erased the radioprotective effects of IVIg.

CONCLUSION

IVIg battles against radiation injuries in a sex-specific, gut microbiome-dependent way through Lachnospiraceae/hypoxanthine/PLD1 axis. Our findings provide a sex-precise therapeutic avenue to improve the prognosis of cancer patients with radiotherapy in pre-clinical settings.

Regulatory T Cells: Angels or Demons in the Pathophysiology of Sepsis?

Sepsis is a syndrome characterized by life-threatening organ dysfunction caused by the dysregulated host response to an infection. Sepsis, especially septic shock and multiple organ dysfunction is a medical emergency associated with high morbidity, high mortality, and prolonged after-effects. Over the past 20 years, regulatory T cells (Tregs) have been a key topic of focus in all stages of sepsis research. Tregs play a controversial role in sepsis based on their heterogeneous characteristics, complex organ/tissue-specific patterns in the host, the multi-dimensional heterogeneous syndrome of sepsis, the different types of pathogenic microbiology, and even different types of laboratory research models and clinical research methods. In the context of sepsis, Tregs may be considered both angels and demons. We propose that the symptoms and signs of sepsis can be attenuated by regulating Tregs. This review summarizes the controversial roles and Treg checkpoints in sepsis.

Exploration study on serum metabolic profiles of Chinese male patients with artificial stone silicosis, silicosis, and coal worker's pneumoconiosis

Long-term exposure to inhaled silica dust induces pneumoconiosis, which remains a heavy burden in developing countries. Modern industry provides new resources of occupational SiO₂ leading to artificial stone silicosis especially in developed countries. This study aimed to characterize the serum metabolic profile of pneumoconiosis and artificial stone silicosis patients. Our case-control study recruited 46 pairs of pneumoconiosis patients and dust-exposed workers. Nontargeted metabolomics and lipidomics by ultra-high-performance liquid chromatography-tandem mass spectrometry platform were conducted to characterize serum metabolic profile in propensity score-matched (PSM) pilot study. 54 differential metabolites were screened, 24 of which showed good screening efficiency through receiver operating characteristics (ROC) in pilot study and validation study (both AUC > 0.75). 4 of the 24 metabolites can predict pneumoconiosis stages, which are 1,2-dioctanoylthiophosphatidylcholine, phosphatidylcholine(O-18:1/20:1), indole-3-acetamide and l-homoarginine. Kynurenine, N-tetradecanoylsphingosine 1-phosphate, 5-methoxytryptophol and phosphatidylethanolamine(22:6/18:1) displayed the potential as specific biomarkers for artificial stone silicosis. Taken together, our results confirmed that tryptophan metabolism is closely related to pneumoconiosis and may be related to disease progression. Hopefully, our results could supplement the biomarkers of pneumoconiosis and provide evidence for the discovery of artificial stone silicosis-specific biomarkers.

Lipin-1-derived diacylglycerol activates intracellular TRPC3 which is critical for inflammatory signaling

Exposure to Gram-negative bacterial LPS exacerbates host immune responses and may lead to sepsis, a life-threatening condition. Despite its high mortality and morbidity, no drugs specifically directed to treating sepsis are currently available. Using human cell genetic depletion, pharmacological inhibition, live-cell microscopy and organelle-targeted molecular sensors we present evidence that the channel TRPC3 is activated intracellularly during macrophage exposure to LPS and is essential for Ca²⁺ release from internal stores. In this manner, TRPC3 participates in cytosolic Ca²⁺ elevations, activation of the transcription factor NF-κB and cytokine upregulation. We also report that TRPC3 is activated by diacylglycerol generated by the phosphatidic acid phosphatase lipin-1. In accord with this, lipin-1-deficient cells exhibit reduced Ca²⁺ responses to LPS challenge. Finally, pharmacological inhibition of TRPC3 reduces systemic inflammation induced by LPS in mice. Collectively, our study unveils a central component of LPS-triggered Ca²⁺ signaling that involves intracellular sensing of lipin-1-derived DAG by TRPC3, and opens new opportunities for the development of strategies to treat LPS-driven inflammation.

PLD1 and PLD2 differentially regulate the balance of macrophage polarization in inflammation and tissue injury

Phospholipase D (PLD) isoforms PLD1 and PLD2 serve as the primary nodes where diverse signaling pathways converge. However, their isoform‐specific functions remain unclear. We showed that PLD1 and PLD2 selectively couple to toll‐like receptor 4 (TLR4) and interleukin 4 receptor (IL‐4R) and differentially regulate macrophage polarization of M1 and M2 via the LPS–MyD88 axis and the IL‐4–JAK3 signaling, respectively. Lipopolysaccharide (LPS) enhanced TLR4 or MyD88 interaction with PLD1; IL‐4 induced IL‐4R or JAK3 association with PLD2, indicating isozyme‐specific signaling events. PLD1 and PLD2 are indispensable for M1 polarization and M2 polarization, respectively. Genetic and pharmacological targeting of PLD1 conferred protection against LPS‐induced sepsis, cardiotoxin‐induced muscle injury, and skin injury by promoting the shift toward M2; PLD2 ablation intensified disease severity by promoting the shift toward M1. Enhanced Foxp3⁺ regulatory T cell recruitment also influenced the anti‐inflammatory phenotype of Pld1^LyzCre macrophages. We reveal a previously uncharacterized role of PLD isoforms in macrophage polarization, signifying potential pharmacological interventions for macrophage modulation.