Apoptotic cells trigger the ABCA1/STAT6 pathway leading to PPAR-γ expression and activation in macrophages

KaiXinSan improves learning and memory impairment by regulating cholesterol homeostasis in mice overloaded with 27-OHC

Cholesterol and its oxidative products-oxysterols homeostasis- play a crucial role in maintaining cognitive function. Chinese medicine KaiXinSan (KXS) has demonstrated effectiveness in treating mental illness and regulating cognitive dysfunction of Alzheimer's disease (AD). The purpose of this article is to explore whether the KXS can enhance cognitive function by regulating cholesterol homeostasis. Employing the 27-hydroxy cholesterol (27-OHC) induced mice model of cognitive dysfunction and coculture model of assessment neurocyte damage, we investigated learning and memory abilities while concurrently addressing the reduction of neuronal cell damage through the regulation of cholesterol metabolism. 21 days of KXS treatment improved the learning and memory ability in mice 27-OHC-overloading by alleviating the exacerbated deposition of amyloid-β (Aβ), reducing inflammatory reactions, and mitigating synaptic plasticity damage. Additionally, it repaired myelin sheath function. More importantly, KXS significantly affects the metabolism of central cholesterol by substantially inhibiting the expression of liver X receptor (LXR), ATP-binding cassette transporter (ABCA1, ABCG1), apolipoprotein E (ApoE) and upregulated cytochrome P450 46A1(CYP46A1). Furthermore, KXS may alleviate 27-OHC-induced neuronal inflammation and apoptosis by promoting the conversion of cholesterol to 24-hydroxycholesterol (24-OHC) via CYP46A1 and suppressing cholesterol release from astrocyte cells. Altogether, our results demonstrate that KXS can prevent learning and memory impairments induced by 27-OHC loading. This effect may be related to its multitarget capability in promoting the conversion of excessive cholesterol to 24-OHC and maintaining a balance in cholesterol homeostasis and metabolism between neurons and astrocyte cells.

Engineering Efferocytosis-Mimicking Nanovesicles to Regulate Joint Anti-Inflammation and Peripheral Immunosuppression for Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by chronic inflammation of the synovial joints and the dysfunction of regulatory T cells (Tregs) in the peripheral blood. Therefore, an optimal treatment strategy should aim to eliminate the inflammatory response in the joints and simultaneously restore the immune tolerance of Tregs in peripheral blood. Accordingly, we developed an efferocytosis-mimicking nanovesicle that contains three functional factors for immunomodulating of efferocytosis, including "find me" and "eat me" signals for professional (macrophage) or non-professional phagocytes (T lymphocyte), and "apoptotic metabolite" for metabolite digestion. We showed that efferocytosis-mimicking nanovesicles targeted the inflamed joints and spleen of mice with collagen-induced arthritis, further recruiting and selectively binding to macrophages and T lymphocytes to induce M2 macrophage polarization and Treg differentiation and T helper cell 17 (Th17) recession. Under systemic administration, the efferocytosis-mimicking nanovesicles effectively maintained the pro-inflammatory M1/anti-inflammatory M2 macrophage balance in joints and the Treg/Th17 imbalance in peripheral blood to prevent RA progression. This study demonstrates the potential of efferocytosis-mimicking nanovesicles for RA immunotherapy.

Molecular Mechanisms and Therapeutic Potential of Resolvins in Cancer - Current Status and Perspectives

Resolvins are specialized pro-resolving mediators derived from omega-3 fatty acids that can suppress several cancer-related molecular pathways, including important activation of transcription parameters in the tumor cells and their microenvironment, inflammatory cell infiltration, cytokines as well as chemokines. Recently, an association between resolvins and an important anti-inflammatory process in apoptotic tumor cell clearance (efferocytosis) was shown. The inflammation status or the oncogene activation increases the risk of cancer development via triggering the transcriptional agents, including nuclear factor kappa-light-chain-enhancer of activated B cells by generating the pro-inflammatory lipid molecules and infiltrating the tumor cells along with the high level of pro-inflammatory signaling. These events can cause an inflammatory microenvironment. Resolvins might decrease the leukocyte influx into the inflamed tissues. It is widely accepted that resolvins prohibit the development of debris-triggered cancer via increasing the clearance of debris, especially by macrophage phagocytosis in tumors without any side effects. Resolvins D2, D1, and E1 might suppress tumor-growing inflammation by activation of macrophages clearance of cell debris in the tumor. Resolvin D5 can assist patients with pain during treatment. However, the effects of resolvins as anti-inflammatory mediators in cancers are not completely explained. Thus, based on the most recent studies, we tried to summarize the most recent knowledge on resolvins in cancers.

Regulatory mechanism underlying liver X receptor effects on the tumor microenvironment, inflammation and tumorigenesis

INTRODUCTION

Liver X receptors (LXRs) have emerged as novel targets for tumor treatment. LXRs within the tumor microenvironment show the capacity to impact tumorigenesis and tumor development by regulating the infiltration of immune cells and release of cytokines to moderate inflammation.

AREAS COVERED

In this review, we present a systematic description of recent progress in understanding the impact of LXRs on the tumor microenvironment and tumorigenesis. We also summarize the antitumor effects mediated by LXRs via their regulation of cytokine expression. Additionally, we discuss the limitations of LXR research in tumor studies to date.

EXPERT OPINION

Previous studies have demonstrated abnormal LXR expression in tumor tissues, and activation of LXRs has been shown to inhibit tumorigenesis and promote apoptosis in tumor cells. However, LXRs can also affect tumorigenesis by regulating immune cell functions within the tumor immune microenvironment. By summarizing the impact of LXRs on immune cells, we provide new insights into the multifaceted nature of LXRs as antitumor targets.

Cholesterol homeostasis in hair follicle keratinocytes is disrupted by impaired ABCA5 activity

The importance of cholesterol in hair follicle biology is underscored by its links to the pathogenesis of alopecias and hair growth disorders. Reports have associated defects in ABCA5, a membrane transporter, with altered keratinocyte cholesterol distribution in individuals with a form of congenital hypertrichosis, yet the biological basis for this defect in hair growth remains unknown. This study aimed to determine the impact of altered ABCA5 activity on hair follicle keratinocyte behaviour. Primary keratinocytes isolated from the outer root sheath of plucked human hair follicles were utilised as a relevant cell model. Following exogenous cholesterol loading, an increase in ABCA5 co-localisation to intracellular organelles was seen. Knockdown of ABCA5 revealed a dysregulation in cholesterol homeostasis, with LXR agonism leading to partial restoration of the homeostatic response. Filipin staining and live BODIPY cholesterol immunofluorescence microscopy revealed a reduction in endo-lysosomal cholesterol following ABCA5 knockdown. Analysis of oxysterols showed a significant increase in the fold change of 25-hydroxycholesterol and 7-β-hydroxycholesterol following cholesterol loading in ORS keratinocytes, after ABCA5 knockdown. These data suggest a role for ABCA5 in the intracellular compartmentalisation of free cholesterol in primary hair follicle keratinocytes. The loss of normal homeostatic response, following the delivery of excess cholesterol after ABCA5 knockdown, suggests an impact on LXR-mediated transcriptional activity. The loss of ABCA5 in the hair follicle could lead to impaired endo-lysosomal cholesterol transport, impacting pathways known to influence hair growth. This avenue warrants further investigation.

PSTPIP2 alleviates obesity associated adipose tissue inflammation and insulin resistance in diabetes mice through promoting M2 macrophage polarization via activation of PPARγ

BACKGROUND

Proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2) plays a role in inflammatory disease. In diabetes, very little is known about PSTPIP2 until now. Hence, this study aimed to determine PSTPIP2 functional role in diabetes.

METHODS

Diabetes mouse model was constructed by feeding high fat diet (HFD). Intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test were examined the glucose and insulin tolerance. The expression of genes and proteins was detected by quantitative real time PCR, immunohistochemistry and western blotting. The pathological changes of epididymal adipose tissues were examined by hematoxylin-eosin staining. RAW264.7 macrophages were treated with GW9662 (PPARγ antagonist). Flow cytometry examined the proportion of M1/M2 macrophages.

RESULTS

HFD enhanced the body weight, glucose and insulin tolerance, and inhibited PSTPIP2 expression in mice. PSTPIP2 overexpression alleviated glucose and insulin tolerance, reduced inflammation and macrophage accumulation in the epididymal adipose tissues of diabetic mice. The expression of iNOS and TNF-α was increased, the expression of IL-10 and Arg-1 was decreased in diabetic mice, which was abrogated by PSTPIP2 overexpression. In vitro, PSTPIP2 overexpression reduced the proportions of iNOS-positive cells and enhanced the proportions of CD206-positive cells in RAW264.7 cells. PPARγ and p-STAT6 were up-regulated, STAT6 was down-regulated in RAW264.7 cells. GW9662 impaired PSTPIP2 overexpression-mediated up-regulation of Arg-1, YM-1 and FIZZ1 in RAW264.7 cells.

CONCLUSION

PSTPIP2 alleviates obesity associated adipose tissue inflammation and insulin resistance in diabetic mice through promoting M2 macrophage polarization via activation of PPARγ, suggesting that PSTPIP2 is a prospective target for diabetes treatment.

Differential regulation of Type 1 and Type 2 mouse eosinophil activation by apoptotic cells

Eosinophils are multifunctional, evolutionary conserved leukocytes that are involved in a plethora of responses ranging from regulation of tissue homeostasis, host defense and cancer. Although eosinophils have been studied mostly in the context of Type 2 inflammatory responses, it is now evident that they participate in Type 1 inflammatory responses and can respond to Type 1 cytokines such as IFN-γ. Notably, both Type 1- and Type 2 inflammatory environments are characterized by tissue damage and cell death. Collectively, this raises the possibility that eosinophils can interact with apoptotic cells, which can alter eosinophil activation in the inflammatory milieu. Herein, we demonstrate that eosinophils can bind and engulf apoptotic cells. We further show that exposure of eosinophils to apoptotic cells induces marked transcriptional changes in eosinophils, which polarize eosinophils towards an anti-inflammatory phenotype that is associated with wound healing and cell migration. Using an unbiased RNA sequencing approach, we demonstrate that apoptotic cells suppress the inflammatory responses of eosinophils that were activated with IFN-γ + E. coli (e.g., Type 1 eosinophils) and augment IL-4-induced eosinophil activation (e.g., Type 2 eosinophils). These data contribute to the growing understanding regarding the heterogeneity of eosinophil activation patterns and highlight apoptotic cells as potential regulators of eosinophil polarization.

Identification of Diagnostic Biomarkers Associated with Stromal and Immune Cell Infiltration in Fatty Infiltration After Rotator Cuff Tear by Integrating Bioinformatic Analysis and Machine-Learning

Purpose

The present study aimed to explore potential diagnostic biomarkers for fatty infiltration (FI) of the rotator cuff muscles after rotator cuff tear (RCT) and investigate the influence of stromal and immune cell infiltration on this pathology.

Methods

The GSE130447 and GSE103266 datasets were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were identified, and gene set enrichment analyses were performed by R software. Two machine learning algorithms, random forest and multiple support vector machine recursive feature elimination (mSVM-RFE), were used to screen candidate biomarkers. The diagnostic value of the screened biomarkers was further validated by the area under the ROC curve (AUC) in the GSE103266 dataset. Murine microenvironment cell population counter (mMCP-counter) method was employed to estimate stromal and immune cell infiltration of FI. The correlation between biomarkers and infiltrated immune and stromal cell subsets was further analyzed.

Results

A total of 2123 DEGs were identified. The identified DEGs were predominantly linked to immune system process, extracellular matrix organization and PPAR signalling pathway. FABP5 (AUC = 0.958) and MGP (AUC = 1) were screened as diagnostic biomarkers of FI. Stromal and immune cell infiltration analysis showed that monocytes, mast cells, vessels, endothelial cells and fibroblasts may be related to the process of FI. FABP5 and MGP were positively correlated with vessels whereas negatively correlated with monocytes and mast cells.

Conclusion

FABP5 and MGP can serve as diagnostic biomarkers of FI after RCT, and stromal and immune cell infiltration may play a crucial role in this pathology.

Polyamine import and accumulation causes immunomodulation in macrophages engulfing apoptotic cells

Phagocytosis of apoptotic cells, termed efferocytosis, is critical for tissue homeostasis and drives anti-inflammatory programming in engulfing macrophages. Here, we assess metabolites in naive and inflammatory macrophages following engulfment of multiple cellular and non-cellular targets. Efferocytosis leads to increases in the arginine-derived polyamines, spermidine and spermine, in vitro and in vivo. Surprisingly, polyamine accumulation after efferocytosis does not arise from retention of apoptotic cell metabolites or de novo synthesis but from enhanced polyamine import that is dependent on Rac1, actin, and PI3 kinase. Blocking polyamine import prevents efferocytosis from suppressing macrophage interleukin (IL)-1β or IL-6. This identifies efferocytosis as a trigger for polyamine import and accumulation, and imported polyamines as mediators of efferocytosis-induced immune reprogramming.

Naringin improves sepsis-induced intestinal injury by modulating macrophage polarization via PPARγ/miR-21 axis

Naringin exhibited various pharmacological activities. However, its biological function and underlying mechanism in regulating macrophage polarization remain elusive. This study aimed to investigate the regulatory network between naringin and macrophage polarization in sepsis-induced intestinal injury. Cecal ligation and puncture (CLP) was used to establish the animal model of sepsis. Chromatin immunoprecipitation and a luciferase reporter assay were used to determine the interplay between peroxisome proliferator-activated receptor γ (PPARγ) and miR-21 promoter, as well as miR-21 and its target genes. Naringin enhanced the overall survival of septic mice and alleviated the CLP-induced inflammatory response and intestinal damage. This was accompanied by the increased expression of PPARγ in the intestines and the stimulation of ileal macrophages toward the M2 phenotype. Furthermore, in lipopolysaccharide-stimulated bone marrow-derived macrophages, naringin stimulated M2 polarization. Mechanistically, PPARγ inhibition attenuated the promotion of M2 polarization caused by naringin, and the naringin/PPARγ regulatory work was compromised by miR-21 inhibition. The present study suggested that naringin promoted M2 polarization via the PPARγ/miR-21 axis, thus relieving sepsis-induced intestinal injury. This study provides novel insights into the mechanism by which naringin alleviated sepsis-induced intestinal injury through regulation of macrophage polarization.

Deformable liposomal codelivery of vorinostat and simvastatin promotes antitumor responses through remodeling tumor microenvironment

The tumor microenvironment (TME) and its major component tumor-associated macrophages (TAM) play a pivotal role in the development of non-small cell lung cancer (NSCLC). An epigenetic drug-based combinatory therapeutic strategy was proposed and a deformable liposome system (D-Lipo) was developed for vorinostat and simvastatin codelivery for remodeling the TME. The application of deformable liposomes in systemic cancer drug delivery has been underexplored and its potential in cancer therapy is largely unknown. This work revealed that D-Lipo exhibited an enhanced intratumor infiltration ability. The proposed therapeutic strategy was characterized by a chemo-free regimen and TME remodeling function. D-Lipo efficiently inhibited the growth of the xenografted lung tumor. The anti-tumor mechanisms involved the repolarization of TAM from the M2 to M1 phenotype, anti-angiogenesis, and the consequent TME remodeling. As a result, the amounts of the anti-tumor M1 macrophages and the cytotoxic CD8+ T cells increased, while the amounts of the pro-tumor M2 macrophages and regulatory T cells (Tregs) reduced. It provides a promising avenue for epigenetic drug-based combination therapy for treating solid tumors.

Lipomatous Solitary Fibrous Tumors Harbor Rare NAB2-STAT6 Fusion Variants and Show Up-Regulation of the Gene PPARG, Encoding for a Regulator of Adipocyte Differentiation

Solitary fibrous tumors (SFTs) harbor activating NAB2-STAT6 gene fusions. Different variants of the NAB2-STAT6 gene fusion have been associated with distinct clinicopathologic features. Lipomatous SFTs are a morphologic variant of SFTs, characterized by a fat-forming tumor component. Our aim was to evaluate NAB2-STAT6 fusion variants and to further study the molecular genetic features in a cohort of lipomatous SFTs. A hybrid-capture-based next-generation sequencing panel was employed to detect NAB2-STAT6 gene fusions at the RNA level. In addition, the RNA expression levels of 507 genes were evaluated using this panel, and were compared with a control cohort of nonlipomatous SFTs. Notably, 5 of 11 (45%) of lipomatous SFTs in the current series harbored the uncommon NAB2 exon 4-STAT6 exon 4 gene fusion variant, which is observed in only 0.9% to 1.4% of nonlipomatous SFTs. Furthermore, lipomatous SFTs displayed significant differences in gene expression compared with their nonlipomatous counterparts, including up-regulation of the gene peroxisome proliferator activated receptor-γ (PPARG). Peroxisome proliferator activated receptor-γ is a nuclear receptor regulating adipocyte differentiation, providing a possible explanation for the fat-forming component in lipomatous SFTs. In summary, the current study provides a possible molecular genetic basis for the distinct morphologic features of lipomatous SFTs.

STAT6 Signaling Mediates PPARγ Activation and Resolution of Acute Sterile Inflammation in Mice

The signal transducer and activator of transcription 6 (STAT6) transcription factor promotes activation of the peroxisome proliferator-activated receptor gamma (PPARγ) pathway in macrophages. Little is known about the effect of proximal signal transduction leading to PPARγ activation for the resolution of acute inflammation. Here, we studied the role of STAT6 signaling in PPARγ activation and the resolution of acute sterile inflammation in a murine model of zymosan-induced peritonitis. First, we showed that STAT6 is aberrantly activated in peritoneal macrophages after zymosan injection. Utilizing STAT6^−/− and wild-type (WT) mice, we found that STAT6 deficiency further enhanced zymosan-induced proinflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-6, and macrophage inflammatory protein-2 in peritoneal lavage fluid (PLF) and serum, neutrophil numbers and total protein amount in PLF, but reduced proresolving molecules, such as IL-10 and hepatocyte growth factor, in PLF. The peritoneal macrophages and spleens of STAT6^−/− mice exhibited lower mRNA and protein levels of PPARγ and its target molecules over the course of inflammation than those of WT mice. The deficiency of STAT6 was shown to impair efferocytosis by peritoneal macrophages. Taken together, these results suggest that enhanced STAT6 signaling results in PPARγ-mediated macrophage programming, contributing to increased efferocytosis and inflammation resolution.

Probing intermolecular interactions and binding stability of kaempferol, quercetin and resveratrol derivatives with PPAR-γ: docking, molecular dynamics and MM/GBSA approach to reveal potent PPAR- γ agonist against cancer

Peroxisome Proliferator-Activated Receptors-γ (PPAR-γ), a ligand-activated transcription factor, suggested having anti-inflammatory effects by activating the target genes when bound to the ligand. Herein, we examined a conformational analysis of 8708 derivatives of Kaempferol, Quercetin, and Resveratrol, the prime activators of PPAR-γ molecular target by employing molecular docking and dynamic simulation pipeline to screen out potential agonists. The structure-based docking procedure performed by FlexX tool shortlisted high binding affinities of these derivatives of Kaempferol, Quercetin and Resveratrol with the protein receptor with a score of -38.94 kcal/mol (4'-Carboxy-5, 7-Dihydroxyflavone-CDHF), -41.63 kcal/mol (Demethyltorosaflavone D- DMTF) and -31.52 kcal/mol (Resveratrol-O-disulphate- RD) respectively, signifying the selected derivatives forms interactions like H-bond, Aromatic H-Bond, Pi-Pi stacking and salt bridges with PPAR-γ. The PPAR-γ-derivative complex was stabilized by intermolecular hydrogen bonds and stacking interactions. A greater interaction was significantly observed between the binding affinities of derivatives compared to the standards. Based on the root mean square deviation (RMSD) and root mean square fluctuation (RMSF) carried by the means of high-speed molecular dynamics (MD) and simulation of best-docked poses, the ligand, DMTF attained the most favored interaction with PPAR-γ. Thus, it appeared to have high chemical scaffold diversity and may confer high drug-likeness. The binding free energy (ΔG) led us to manifest Quercetin derivative to have a key role for PPAR-γ receptor. The result obtained clearly indicates the exploitation of the promising new drug leads that may further influence in synthesizing and analyzing the development as anti-cancer agonists.Communicated by Ramaswamy H. Sarma.

Lipid metabolism as a mechanism of immunomodulation in macrophages: the role of liver X receptors

Macrophages are immune myeloid cells with an extreme ability to modulate their phenotype in response to insults and/or pathogens. The immunomodulatory capacity of macrophages is also patent during development as they adapt their phenotype to the host tissue environment establishing the heterogeneous populations of tissue-resident macrophages. An important mechanism of immunomodulation in macrophages occurs through the regulation of transcriptional activity. Numerous transcription factors are associated with macrophage plasticity, among them, several nuclear receptors. The nuclear receptors Liver X Receptors (LXRα and LXRβ) have also revealed as active players during macrophage adaptations in diverse scenarios. This review will address the different mechanisms by which LXRs contribute to immunomodulation in macrophages by connecting lipid metabolism and immunity through transcriptional regulation.

PPAR signaling pathway in the first trimester placenta from in vitro fertilization and embryo transfer

Placenta is a temporary critical organ related to fetal development and pregnancy outcomes. And epidemiologic data demonstrate an increased risk of placental abnormality after in vitro fertilization and embryo transfer (IVF-ET). This study aims to explore the molecular mechanism for PPAR signaling pathway in placenta subjected to IVF-ET in the first trimester. Four first trimester placenta samples from double chorionic twins to single reduction in IVF-ET only because of oviducts factors. The other four control placenta samples from double chorionic twin were derived from those unplanned spontaneously conceived pregnancy after the legal termination. Affymetrix HG-U133 Plus 2.0 Array was performed to evaluate the global gene expressions. We confirmed microarray results from 10 significant differential genes using RT-qPCR. And 10 deregulated gene products were stained in the first trimester placenta by immunohistochemistry. These differentially expressed genes in IVF-ET placentas were submitted to functional annotation of clustering tools of bioinformatics resources and gene ontology enrichment analysis. Schematic representation of placental PPAR signaling pathway was labelled by Kyoto Encyclopedia of Genes and Genomes (KEGG). Analysis results of early placental PPAR signaling pathway gene expression from 8 women demonstrated 34 genes with a significant change in expression between IVF-ET and control group, 25 up-regulated; 9 down-regulated. KEGG pathway analysis indicated that IVF-ET manipulation extensively over-activated PPAR signaling pathway. Immune tolerance, trophoblast invasion, syncytia formation, lipid and glucose metabolism, inflammatory response and other complex biological functions were disturbed. RT-qPCR results and proteins staining intensity were consisted with microarray. Placental gene expressions and functions in PPAR signaling pathway were affected by IVF-ET treatment in the first trimester, which may offer a potential mechanism for the pathogenesis of various adverse outcomes during the perinatal period.