A novel immunomodulatory function of PHLPP1: inhibition of iNOS via attenuation of STAT1 ser727 phosphorylation in mouse macrophages

TGS1/PIMT regulates pro-inflammatory macrophage mediated paracrine insulin resistance: Crosstalk between macrophages and skeletal muscle cells

Macrophage-driven chronic low-grade inflammatory response is intimately associated with pathogenesis of insulin resistance and type 2 diabetes (T2D). However, the molecular basis for skewing of pro-inflammatory macrophage is still elusive. Here, we describe the mechanism and significance of TGS1/PIMT (PRIP-Interacting protein with Methyl Transferase domain) in regulating macrophage activation and polarization and its impact on the development of insulin resistance in skeletal muscle cells. We show altered expression of TGS1 in M1 polarized cultured macrophages, bone marrow-derived (BMDM) and adipose tissue macrophages. Moreover, in High Fat Diet (HFD)-fed mice enhanced TGS1 expression is predominantly localized to the nucleus of adipose tissue macrophages suggesting its potential functional role. Gain and loss of TGS1 expression in macrophage further established its role in the secretion of pro-inflammatory mediators. Mechanistically, TGS1 controls the transcription of numerous genes linked to inflammation by forming a complex with Histone Acetyl Transferase (HAT)-containing transcriptional co-activators CBP and p300. Functionally, TGS1 mediated macrophage inflammatory response induces the development of insulin resistance in skeletal muscle cells and adipocytes. Our findings thus demonstrate an unexpected contribution of TGS1 in the regulation of macrophage mediated inflammation and insulin resistance highlighting that TGS1 antagonism could be a promising therapeutic target for the management of inflammation and insulin resistance in T2D.

A Positive Causal Effect of Shrimp Allergy on Major Depressive Disorder Mediated by Allergy- and Immune-Related Pathways in the East Asian Population

BACKGROUND

Observational studies have implied a potential correlation between allergic diseases and major depressive disorder (MDD). However, the relationship is still inconclusive as it is likely to be interfered with by substantial confounding factors and potential reverse causality. The present study aimed to investigate causal correlation of the two diseases by a Mendelian randomization (MR) study and further elucidate the underlying molecular mechanisms.

METHODS

With the biggest summary datasets of a genome-wide association study (GWAS) in the East Asian population, we conducted a two-sample, bidirectional MR study to assess the causal correlation between shrimp allergy (SA) and MDD. Subsequently, we identified the pleiotropic genes' susceptibility to the two diseases at whole-genome and tissue-specific levels, respectively. Enriched GO sets and KEGG pathways were also discovered to elucidate the potential underlying mechanisms.

RESULTS

With the most suitable MR method, SA was identified as a causal risk factor for MDD based on three different groups of independent genetic instruments, respectively (p < 2.81 × 10-2). In contrast, we did not observe a significant causal effect of MDD on SA. The GWAS-pairwise program successfully identified seven pleiotropic genetic variants (PPA3 > 0.8), indicating that the two diseases indeed have a shared genetic basis. At a whole-genome level, the MAGMA program identified 44 pleiotropic genes, which were enriched in allergy-related pathways, such as antigen processing and presentation pathway (p = 1.46 × 10-2). In brain-specific tissue, the S-MultiXcan program found 17 pleiotropic genes that were significantly enriched in immune-related pathways and GO sets, including asthma-related pathway, T-cell activation-related, and major histocompatibility complex protein-related GO sets. Regarding whole-blood tissue, the program identified six pleiotropic genes that are significantly enriched in tolerance induction-related GO sets.

CONCLUSIONS

The present study for the first time indicated a significant causal effect of SA on the occurrence of MDD, but the reverse was not true. Enrichment analyses of pleiotropic genes at whole-genome and tissue-specific levels implied the involvement of allergy and immune-related pathways in the shared genetic mechanism of the two diseases. Elucidating the causal effect and the acting direction may be beneficial in reducing the incidence rate of MDD for the massive group of SA patients in the East Asian region.

PHLPPs: Emerging players in metabolic disorders

That reversible protein phosphorylation by kinases and phosphatases occurs in metabolic disorders is well known. Various studies have revealed that a multi-faceted and tightly regulated phosphatase, pleckstrin homology domain leucine-rich repeat protein phosphatase (PHLPP)-1/2 displays robust effects in cardioprotection, ischaemia/reperfusion (I/R), and vascular remodelling. PHLPP1 promotes foamy macrophage development through ChREBP/AMPK-dependent pathways. Adipocyte-specific loss of PHLPP2 reduces adiposity, improves glucose tolerance,and attenuates fatty liver via the PHLPP2-HSL-PPARα axis. Discoveries of PHLPP1-mediated insulin resistance and pancreatic β cell death via the PHLPP1/2-Mst1-mTORC1 triangular loop have shed light on its significance in diabetology. PHLPP1 downregulation attenuates diabetic cardiomyopathy (DCM) by restoring PI3K-Akt-mTOR signalling. In this review, we summarise the functional role of, and cellular signalling mediated by, PHLPPs in metabolic tissues and discuss their potential as therapeutic targets.

Minor Ginsenoside Rg2 and Rh1 Attenuates LPS-Induced Acute Liver and Kidney Damages via Downregulating Activation of TLR4-STAT1 and Inflammatory Cytokine Production in Macrophages

Ginsenosides have been reported to have various biological effects, such as immune regulation and anticancer activity. In this study, we investigated the anti-inflammatory role of a combination of Rg2 and Rh1, which are minor ginsenosides, in lipopolysaccharide (LPS)-stimulated inflammation. In vitro experiments were performed using the RAW264.7 cell line, and an in vivo model of inflammation was established using LPS-treated ICR mice. We employed Griess assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, quantitative reverse transcriptase-polymerase chain reaction, western blotting, immunofluorescence staining, and hematoxylin and eosin staining to evaluate the effect of Rg2 and Rh1. We found that Rg2 and Rh1 significantly decreased LPS-induced major inflammatory mediator production, inducible-nitric oxide synthase expression, and nitric oxide production in macrophages. Moreover, Rg2 and Rh1 combination treatment inhibited the binding of LPS to toll-like receptor 4 (TLR4) on peritoneal macrophages. Therefore, the combination of ginsenoside Rg2 and Rh1 suppressed inflammation by abolishing the binding of LPS to TLR4, thereby inhibiting the TLR4-mediated signaling pathway. The combined ginsenoside synergistically blocked LPS-mediated PKCδ translocation to the plasma membrane, resulting in p38-STAT1 activation and NF-κB translocation. In addition, mRNA levels of pro-inflammatory cytokines, including TNF-α, IL-1β, and IFN-β, were significantly decreased by combined ginsenoside treatment. Notably, the 20 mg/kg ginsenoside treatment significantly reduced LPS-induced acute tissue inflammation levels in vivo, as indicated by the tissue histological damage scores and the levels of biochemical markers for liver and kidney function from mouse serum. These results suggest that the minor ginsenosides Rg2 and Rh1 may play a key role in prevention of LPS-induced acute inflammation and tissue damage.

PHLPP1 counter-regulates STAT1-mediated inflammatory signaling

Inflammation is an essential aspect of innate immunity but also contributes to diverse human diseases. Although much is known about the kinases that control inflammatory signaling, less is known about the opposing phosphatases. Here we report that deletion of the gene encoding PH domain Leucine-rich repeat Protein Phosphatase 1 (PHLPP1) protects mice from lethal lipopolysaccharide (LPS) challenge and live Escherichia coli infection. Investigation of PHLPP1 function in macrophages reveals that it controls the magnitude and duration of inflammatory signaling by dephosphorylating the transcription factor STAT1 on Ser727 to inhibit its activity, reduce its promoter residency, and reduce the expression of target genes involved in innate immunity and cytokine signaling. This previously undescribed function of PHLPP1 depends on a bipartite nuclear localization signal in its unique N-terminal extension. Our data support a model in which nuclear PHLPP1 dephosphorylates STAT1 to control the magnitude and duration of inflammatory signaling in macrophages.

Rhizopus nigricans polysaccharide activated macrophages and suppressed tumor growth in CT26 tumor-bearing mice

In this study, a homogeneous polysaccharide (RPS-1) was extracted from liquid-cultured mycelia of Rhizopus nigricans. The weight-average molecular weight of RPS-1 was 1.617 × 10⁷ g/mol and structural characterization indicated that RPS-1 was a non-starch glucan which consisted of a backbone structure of (1→4)-linked α-d-glucopyranosyl residues substituted at the O-6 position with α-d-glucopyranosyl branches. RPS-1 stimulated the production of nitric oxide and tumor necrosis factor-α by triggering phosphorylation of mitogen-activated protein kinases and nuclear translocation of nuclear factor kappa B p65 in RAW 264.7 macrophage cells. Moreover, intragastric administration of RPS-1 improved the immune function of CT26 tumor-bearing mice and significantly inhibited the growth of transplanted tumor. In combination with 5-FU, RPS-1 enhanced antitumor activity of 5-FU and alleviated its toxicity on immune system. These findings suggested that RPS-1 has the potential for the development of functional foods and dietary supplements.

LPS depletes PHLPP levels in macrophages through the inhibition of SP1 dependent transcriptional regulation

We have previously reported that bacterial endotoxin LPS attenuates expression of PHLPP, a ser/thr phosphatase, at both transcript and protein levels in different immune cells, however the underlying molecular mechanism is unknown and is of significant interest. Here, in line with the decreased transcript levels upon LPS treatment, we observed that LPS caused significant reduction in PHLPP promoter activity. We observed that SP1, a transcription factor frequently associated with inflammation, was recruited to the PHLPP promoter region. Ectopic expression of SP1 enhanced both transcript and protein levels of PHLPP while knockdown of SP1 or pharmacological inhibition of SP1 DNA binding by mithramycin reduced PHLPP expression. Moreover, over-expression of SP1 co-activators CBP/p300 augmented SP1 driven PHLPP promoter activity. Of note, LPS treatment depleted SP1 and CBP protein levels due to which recruitment of SP1 to PHLPP promoter was reduced. Further, we found that re-introduction of SP1 restored promoter activity and transcript levels of PHLPP in LPS stimulated cells. Collectively, our data revealed the molecular mechanism underlying the regulation of PHLPP expression during LPS induced macrophage inflammatory response.

MicroRNA-712 restrains macrophage pro-inflammatory responses by targeting LRRK2 leading to restoration of insulin stimulated glucose uptake by myoblasts

Chronic inflammatory diseases such as insulin resistance, Type 2 diabetes, neurodegenerative diseases etc., are shown to be caused due to imbalanced activation states of macrophages. MicroRNAs which are transcriptional/post-transcriptional regulators of gene expression drive several pathophysiological processes including macrophage polarization. However the functional role of microRNAs in regulating inflammation induced insulin resistance is ill defined. In our current study we observed that the expression of miR-712 was reduced in macrophages exposed to LPS and IFN-γ. Ectopic expression of miR-712 in RAW 264.7 mouse macrophages impaired the expression of iNOS protein and secretion of pro-inflammatory cytokines such as TNF-α, IL-6 and IFN-β which in turn led to improved insulin stimulated glucose uptake in co-cultured L6 myoblasts. Mechanistically, we identified that miR-712 targets the 3'UTR of a potent inflammatory gene LRRK2 and dampens the phosphorylation of p38 and ERK1/2 kinases. Taken together, our data underscore the regulatory role of miR-712 in restoring insulin stimulated glucose uptake by myoblasts through down-regulating macrophage mediated inflammatory responses.

Role of PHLPP1 in inflammation response: Its loss contributes to gliomas development and progression

PH domain leucine-rich repeats protein phosphatase 1(PHLPP1) belongs to a novel family of Ser/Thr protein phosphatases: PHLPP serves as tumor suppressor in several cancers. However, little knowledge about the expression of PHLPP1 in human glioma tumor tissue and its role in inflammation response in glioma cells was known. Glioma samples were obtained from a total of 37 patients including 16 males and 21 females with surgical removal of the brain tumor. PHLPP1 protein and inflammatory cytokines were measured by Western blot analysis and immunohistochemistry while mRNA was determined by RT-PCR. The levels of inflammatory cytokines including TNF-α, IL-17, IL-1β in U251 glioma cells were evaluated by siRNA PHLPP1 and PHLPP1 addition. The loss of PHLPP1 expression occurs at high frequency in human gliomas. The highest mean values of PHLPP1 mRNA and protein were found in non-glioma brain tissues whereas the lowest mean values were found in those in glioblastoma with an increase of TNF-α, IL-17, IL-1β (p<0.05). PHLPP1 expression in human glioma was associated negatively with the severity of the tumor and inflammatory cytokines. siRNA PHLPP1 could increase the levels of inflammatory cytokines in U251 glioma cells while PHLPP1 addition could inhibit significantly inflammatory cytokines. We concluded that PHLPP1 played a suppression role in inflammatory response of glioma. The present study indicated that PHLPP1 could be used as a predictor for the prediction of the patients or as a therapeutic target for the treatment of human glioma.

MicroRNA-16 modulates macrophage polarization leading to improved insulin sensitivity in myoblasts

Uncontrolled inflammation leads to several diseases such as insulin resistance, T2D and several types of cancers. The functional role of microRNAs in inflammation induced insulin resistance is poorly studied. MicroRNAs are post-transcriptional regulatory molecules which mediate diverse biological processes. We here show that miR-16 expression levels are down-regulated in different inflammatory conditions such as LPS/IFNγ or palmitate treated macrophages, palmitate exposed myoblasts and insulin responsive tissues of high sucrose diet induced insulin resistant rats. Importantly, forced expression of miR-16 in macrophages impaired the production of TNF-α, IL-6 and IFN-β leading to enhanced insulin stimulated glucose uptake in co-cultured skeletal myoblasts. Further, ectopic expression of miR-16 enhanced insulin stimulated glucose uptake in skeletal myoblasts via the up-regulation of GLUT4 and MEF2A, two key players involved in insulin stimulated glucose uptake. Collectively, our data highlight the important role of miR-16 in ameliorating inflammation induced insulin resistance.

Regulatory effects of fisetin on microglial activation

Increasing evidence suggests that inflammatory processes in the central nervous system that are mediated by microglial activation play a key role in neurodegeneration. Fisetin, a plant flavonol commonly found in fruits and vegetables, is frequently added to nutritional supplements due to its antioxidant properties. In the present study, treatment with fisetin inhibited microglial cell migration and ROS (reactive oxygen species) production. Treatment with fisetin also effectively inhibited LPS plus IFN-γ-induced nitric oxide (NO) production, and inducible nitric oxide synthase (iNOS) expression in microglial cells. Furthermore, fisetin also reduced expressions of iNOS and NO by stimulation of peptidoglycan, the major component of the Gram-positive bacterium cell wall. Fisetin also inhibited the enhancement of LPS/IFN-γ- or peptidoglycan-induced inflammatory mediator IL (interlukin)-1 β expression. Besides the antioxidative and anti-inflammatory effects of fisetin, our study also elucidates the manner in fisetin-induced an endogenous anti-oxidative enzyme HO (heme oxygenase)-1 expression. Moreover, the regulatory molecular mechanism of fisetin-induced HO-1 expression operates through the PI-3 kinase/AKT and p38 signaling pathways in microglia. Notably, fisetin also significantly attenuated inflammation-related microglial activation and coordination deficit in mice in vivo. These findings suggest that fisetin may be a candidate agent for the development of therapies for inflammation-related neurodegenerative diseases.