Aryl hydrocarbon receptor is activated by glucose and regulates the thrombospondin-1 gene promoter in endothelial cells

Activation-induced thrombospondin-4 works with thrombospondin-1 to build cytotoxic supramolecular attack particles

Cytotoxic attack particles released by CTLs and NK cells include diverse phospholipid membrane and glycoprotein encapsulated entities that contribute to target cell killing. Supramolecular attack particles (SMAPs) are one type of particle characterized by a cytotoxic core enriched in granzymes and perforin surrounded by a proteinaceous shell including thrombospondin (TSP)-1. TSP-4 was also detected in bulk analysis of SMAPs released by CTLs; however, it has not been investigated whether TSP-4 contributes to distinct SMAP types or the same SMAP type as TSP-1 and, if in the same type of SMAP, whether TSP-4 and TSP-1 cooperate or compete. Here, we observed that TSP-4 expression increased upon CD8+ T cell activation while, surprisingly, TSP-1 was down-regulated. Correlative Light and Electron Microscopy and Stimulated Emission Depletion microscopy localized TSP-4 and TSP-1 in SMAP-containing multicore granules. Superresolution dSTORM revealed that TSP-4 and TSP-1 are usually enriched in the same SMAPs while particles with single-positive shells are rare. Retention Using Selective Hooks assays showed that TSP-4 localizes to the lytic granules faster than TSP-1 and promotes its accumulation therein. TSP-4 contributed to direct CTL-mediated killing, as previously shown for TSP-1. TSP-4 and TSP-1 were both required for latent SMAP-mediated cell killing, in which released SMAPs kill targets after removal of the CTLs. Of note, we found that chronic lymphocytic leukemia (CLL) cell culture supernatants suppressed expression of TSP-4 in CTL and latent SMAP-mediated killing. These results identify TSP-4 as a functionally important component of SMAPs and suggest that SMAPs may be targeted for immune suppression by CLL.

Aryl Hydrocarbon Receptor Pathway Augments Peritoneal Fibrosis in a Murine CKD Model Exposed to Peritoneal Dialysate

Key Points

CKD and high glucose–containing peritoneal dialysate alter peritoneal membrane contributing to peritoneal dialysis failure, with a poorly understood mechanism. CKD milieu activates the aryl hydrocarbon receptor pathway in the subperitoneal vasculature, increasing the peritoneal fibrosis and collagen deposition in humans and mice. An aryl hydrocarbon receptor inhibitor mitigates CKD and peritoneal dialysis–mediated peritoneal fibrosis, collagen deposition, and vasculogenesis in a mouse model.

Background

CKD is a proinflammatory and profibrotic condition and can independently alter the peritoneal membrane structure. Peritoneal dialysis (PD) results in profound alterations in the peritoneal membrane. The mechanisms contributing to the alterations of the peritoneal membrane structure in CKD milieu, along with PD, are poorly understood.

Methods

Here, we show that human CKD induces peritoneal membrane thickening, fibrosis, and collagen deposition and activates the aryl hydrocarbon receptor (AHR) pathway in the subperitoneal vasculature. Leveraging a novel model of PD in CKD mice, we confirm these CKD-induced changes in the peritoneal membrane, which are exacerbated on exposure to the peritoneal dialysate. Peritoneal dialysate further augmented the AHR activity in endothelial cells of peritoneal microvasculature in CKD mice.

Results

Treatment of CKD mice with an AHR inhibitor in peritoneal dialysate for 2 weeks resulted in a seven-fold reduction in AHR expression in the endothelial cells of subperitoneal capillaries, a five-fold decrease in subperitoneal space, and a nine-fold decrease in fibrosis and collagen deposition compared with vehicle-treated CKD mice. AHR inhibition reduced inflammation, subperitoneal neovascular areas, and its downstream target, tissue factor. The AHR inhibitor treatment normalized the peritoneal dialysate-induced proinflammatory and profibrotic cytokines, such as IL-6, monocyte chemoattractant protein-1, and macrophage inflammatory protein 1 levels, in CKD mice.

Conclusions

This study uncovers the activation of the AHR-cytokine axis in the endothelial cells of subperitoneal vessels in humans and mice with CKD, which is likely to prime the peritoneal membrane to peritoneal dialysate–mediated alterations. This study supports further exploration of AHR as a potential therapeutic target to preserve the structural and functional integrity of the peritoneal membrane in PD.

Kynurenine pathway in type 2 diabetes: Role of metformin

The Kynurenine pathway (KP) which is involved in the synthesis of nicotinamide adenine dinucleotide (NAD) from tryptophan (Trp) is intricate in the development of insulin resistance (IR) and type 2 diabetes (T2D). Inflammatory reactions in response to cardiometabolic disorders can induce the development of IR through the augmentation of KP. However, kynurenine (KYN), a precursor of kynurenic acid (KA) is increased following physical exercise and involved in the reduction of IR. Consequently, KP metabolites KA and KYN have anti-diabetogenic effects while other metabolites have diabetogenic effects. KP modulators, either inhibitors or activators, affect glucose homeostasis and insulin sensitivity in T2D in a bidirectional way, either protective or detrimental, that is not related to the KP effect. However, metformin through inhibition of inflammatory signaling pathways can reduce the activation of KP in T2D. These findings indicated a strong controversy regarding the role of KP in T2D. Therefore, the objectives of this mini review were to clarify how KP induces the development of IR and T2D. In addition, this review aimed to find the mechanistic role of antidiabetic drug metformin on the KP, and how KP modulators affect the pathogenesis of T2D.

Thrombospondin-1 Drives Cardiac Remodeling in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) face a high risk of cardiovascular disease. Previous studies reported that endogenous thrombospondin 1 (TSP1) involves right ventricular remodeling and dysfunction. Here we show that a murine model of CKD increased myocardial TSP1 expression and produced left ventricular hypertrophy, fibrosis, and dysfunction. TSP1 knockout mice were protected from these features. In vitro, indoxyl sulfate is driving deleterious changes in cardiomyocyte through the TSP1. In patients with CKD, TSP1 and aryl hydrocarbon receptor were both differentially expressed in the myocardium. Our findings summon large clinical studies to confirm the translational role of TSP1 in patients with CKD.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and kynurenine induce Parkin expression in neuroblastoma cells through different signaling pathways mediated by the aryl hydrocarbon receptor

Parkin regulates protein degradation and mitophagy in dopaminergic neurons. Deficiencies in Parkin expression or function lead to cellular stress, cell degeneration, and the death of dopaminergic neurons, which promotes Parkinson's disease. In contrast, Parkin overexpression promotes neuronal survival. Therefore, the mechanisms of Parkin upregulation are crucial to understand. We describe here the molecular mechanism of AHR-mediated Parkin regulation in human SH-SY5Y neuroblastoma cells. Specifically, we report that the human Parkin gene (PRKN) is transcriptionally upregulated by the aryl hydrocarbon receptor (AHR) through two different selective ligand-dependent pathways. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a stress-inducing AHR ligand, indirectly promotes PRKN transcription by inducing ATF4 expression via TCDD-mediated endoplasmic reticulum (ER) stress. In contrast, kynurenine, a nontoxic AHR agonist, induces PRKN transcription by promoting AHR binding to the PRKN promoter without activating ER stress. Our results demonstrate that AHR activation may be a potential pharmacological pathway to induce human Parkin, but such a strategy must carefully consider the choice of AHR ligand to avoid neurotoxic side effects.

Pathophysiological roles of thrombospondin-4 in disease development

Thrombospondin-4 (TSP-4) belongs to the extracellular matrix glycoprotein family of thrombospondins (TSPs). The multidomain, pentameric structure of TSP-4 allows its interactions with numerous extracellular matrix components, proteins and signaling molecules that enable its modulation to various physiological and pathological processes. Characterization of TSP-4 expression under development and pathogenesis of disorders has yielded important insights into mechanisms underlying the unique role of TSP-4 in mediating various processes including cell-cell, cell-extracellular matrix interactions, cell migration, proliferation, tissue remodeling, angiogenesis, and synaptogenesis. Maladaptation of these processes in response to pathological insults and stress can accelerate the development of disorders including skeletal dysplasia, osteoporosis, degenerative joint disease, cardiovascular diseases, tumor progression/metastasis and neurological disorders. Overall, the diverse functions of TSP-4 suggest that it may be a potential marker or therapeutic target for prognosis, diagnosis, and treatment of various pathological conditions upon further investigations. This review article highlights recent findings on the role of TSP-4 in both physiological and pathological conditions with a focus on what sets it apart from other TSPs.

Differential eigengene network analysis reveals benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin consensus regulatory network in human liver cell line HepG2

Aryl hydrocarbon receptor (AHR) is one of the main mediators of the toxic effects of benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, a vast number of BaP- and TCDD-affected genes may suggest a more complex transcriptional regulatory network driving common adverse effects of these two chemicals. Unlike TCDD, BaP is rapidly metabolized in the liver, yielding products with a questionable ability to bind and activate AHR. In this study, we used transcriptomics data from the BaP- and TCCD-exposed human liver cell line HepG2, and performed differential eigengene network analysis to understand the correlation among genes and to untangle the common regulatory mechanism in the action of BaP and TCDD. The genes were grouped into 11 meta-modules with an overall preservation of 0.72 and were also segregated into three consensus time clusters: 12, 24, and 48 h. The analysis showed that the consensus genes in each time cluster were either directly regulated by the AHR or the AHR-TF interactions. Some TFs form a direct physical interaction with AHR such as ESR1, FOXA1, and E2F1, whereas others, including CTCF, RXRA, FOXO1, CEBPA, CEBPB, and TP53 show an indirect interaction with AHR. The analysis of biological processes (BPs) identified unique and common BPs in BaP and TCDD samples, with DNA damage response detected in all three time points. In summary, we identified a consensus transcriptional regulatory network common for BaP and TCDD consisting of direct AHR targets and AHR-TF targets. This analysis sheds new light on the common mechanism of action of a genotoxic (BaP) and non-genotoxic (TCDD) chemical in liver cells.

Plasma aryl hydrocarbon receptor associated with epicardial adipose tissue in men: a cross-sectional study

BACKGROUND

Epicardial adipose tissue (EAT) is a type of ectopic fat with endocrine and paracrine functions. Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that responds to environmental stimuli. AhR expression is associated with obesity. In this cross-sectional study, we aimed to determine the relationship between circulating AhR concentrations and EAT.

METHODS

A total of 30 men with obesity and 23 age-matched men as healthy controls were enrolled. Plasma AhR concentrations were determined at fasting. The EAT thickness was measured on the free wall of the right ventricle from the basal short-axis plane by magnetic resonance imaging.

RESULTS

The participants with obesity had a higher plasma AhR level than the controls (81.0 ± 24.5 vs. 65.1 ± 16.4 pg/mL, P = 0.010). The plasma AhR level was positively correlated with EAT thickness (correlation coefficient = 0.380, P = 0.005). After adjusting for fasting glucose levels, plasma AhR levels were still significantly associated with EAT thickness (95% CI 0.458‒5.357, P = 0.021) but not with body mass index (P = 0.168).

CONCLUSION

Plasma AhR concentrations were positively correlated with EAT thickness on the free wall of the right ventricle in men. Further investigations are needed to evaluate the causal effects and underlying mechanisms between AhR and EAT.

The Role of Aryl Hydrocarbon Receptor in the Endothelium: A Systematic Review

Activation of the aryl hydrocarbon receptor (AhR) has been shown to be important in physiological processes other than detoxification, including vascular homeostasis. Although AhR is highly expressed in the endothelium, its function has been poorly studied. This systematic review aims to summarise current knowledge on the AhR role in the endothelium and its cardiovascular implications. We focus on endogenous AhR agonists, such as some uremic toxins and other agonists unrelated to environmental pollutants, as well as studies using AhR knockout models. We conclude that AhR activation leads to vascular oxidative stress and endothelial dysfunction and that blocking AhR signalling could provide a new target for the treatment of vascular disorders such as cardiovascular complications in patients with chronic kidney disease or pulmonary arterial hypertension.

Insight into the physiological and pathological roles of the aryl hydrocarbon receptor pathway in glucose homeostasis, insulin resistance, and diabetes development

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor that mediates the toxicities of several environmental pollutants. Decades of research have been carried out to understand the role of AhR as a novel mechanism for disease development. Its involvement in the pathogenesis of cancer, cardiovascular diseases, rheumatoid arthritis, and systemic lupus erythematosus have long been known. One of the current hot research topics is investigating the role of AhR activation by environmental pollutants on glucose homeostasis and insulin secretion, and hence the pathogenesis of diabetes mellitus. To date, epidemiological studies have suggested that persistent exposure to environmental contaminants such as dioxins, with subsequent AhR activation increases the risk of specific comorbidities such as obesity and diabetes. The importance of AhR signaling in various molecular pathways highlights that the role of this receptor is far beyond just xenobiotic metabolism. The present review aims at providing significant insight into the physiological and pathological role of AhR and its regulated enzymes, such as cytochrome P450 1A1 (CYP1A1) and CYP1B1 in both types of diabetes. It also provides a comprehensive summary of the current findings of recent research studies investigating the role of the AhR/CYP1A1 pathway in insulin secretion and glucose hemostasis in the pancreas, liver, and adipose tissues. This review further highlights the molecular mechanisms involved, such as gluconeogenesis, hypoxia-inducible factor (HIF), oxidative stress, and inflammation.

Diabetes downregulates the antimicrobial peptide psoriasin and increases E. coli burden in the urinary bladder

Diabetes is known to increase susceptibility to infections, partly due to impaired granulocyte function and changes in the innate immunity. Here, we investigate the effect of diabetes, and high glucose on the expression of the antimicrobial peptide, psoriasin and the putative consequences for E. coli urinary tract infection. Blood, urine, and urine exfoliated cells from patients are studied. The influence of glucose and insulin is examined during hyperglycemic clamps in individuals with prediabetes and in euglycemic hyperinsulinemic clamped patients with type 1 diabetes. Important findings are confirmed in vivo in type 2 diabetic mice and verified in human uroepithelial cell lines. High glucose concentrations induce lower psoriasin levels and impair epithelial barrier function together with altering cell membrane proteins and cytoskeletal elements, resulting in increasing bacterial burden. Estradiol treatment restores the cellular function with increasing psoriasin and bacterial killing in uroepithelial cells, confirming its importance during urinary tract infection in hyperglycemia. In conclusion, our findings present the effects and underlying mechanisms of high glucose compromising innate immunity.

Glucose promotes regulatory T cell differentiation to maintain intestinal homeostasis

Glucose, the critical energy source in the human body, is considered a potential risk factor in various autoimmune diseases when consumed in high amounts. However, the roles of glucose at moderate doses in the regulation of autoimmune inflammatory diseases and CD4+ T cell responses are controversial. Here, we show that while glucose at a high concentration (20% w/v) promotes intestinal inflammation, it suppresses colitis at a moderate dose (6% w/v), which increases the proportion of intestinal regulatory T (Treg) cells but does not affect effector CD4+ T cells. Glucose treatment promotes Treg cell differentiation but it does not affect Treg stability. Feeding glucose alters gut microbiota compositions, which are not involved in the glucose induction of Treg cells. Glucose promotes aryl hydrocarbon receptor (AhR) activation to induce Treg polarization. These findings reveal the different effects of glucose at different doses on the intestinal immune response.

Hexokinase 2 is a transcriptional target and a positive modulator of AHR signalling

The aryl hydrocarbon receptor (AHR) regulates the expression of numerous genes in response to activation by agonists including xenobiotics. Although it is well appreciated that environmental signals and cell intrinsic features may modulate this transcriptional response, how it is mechanistically achieved remains poorly understood. We show that hexokinase 2 (HK2) a metabolic enzyme fuelling cancer cell growth, is a transcriptional target of AHR as well as a modulator of its activity. Expression of HK2 is positively regulated by AHR upon exposure to agonists both in human cells and in mice lung tissues. Conversely, over-expression of HK2 regulates the abundance of many proteins involved in the regulation of AHR signalling and these changes are linked with altered AHR expression levels and transcriptional activity. HK2 expression also shows a negative correlation with AHR promoter methylation in tumours, and these tumours with high HK2 expression and low AHR methylation are associated with a worse overall survival in patients. In sum, our study provides novel insights into how AHR signalling is regulated which may help our understanding of the context-specific effects of this pathway and may have implications in cancer.

The BET Protein Inhibitor Apabetalone Rescues Diabetes-Induced Impairment of Angiogenic Response by Epigenetic Regulation of Thrombospondin-1

Aims: Therapeutic modulation of blood vessel growth holds promise for the prevention of limb ischemia in diabetic (DM) patients with peripheral artery disease (PAD). Epigenetic changes, namely, posttranslational histone modifications, participate in angiogenic response suggesting that chromatin-modifying drugs could be beneficial in this setting. Apabetalone (APA), a selective inhibitor of bromodomain (BRD) and bromodomain and extraterminal containing protein family (BET) proteins, prevents bromodomain-containing protein 4 (BRD4) interactions with chromatin thus modulating transcriptional programs in different organs. We sought to investigate whether APA affects angiogenic response in diabetes. Results: Compared with vehicle, APA restored tube formation and migration in human aortic endothelial cells (HAECs) exposed to high-glucose (HG) levels. Expression profiling of angiogenesis genes showed that APA prevents HG-induced upregulation of the antiangiogenic molecule thrombospondin-1 (THBS1). ChIP-seq and chromatin immunoprecipitation (ChIP) assays in HG-treated HAECs showed the enrichment of both BRD4 and active marks (H3K27ac) on THBS1 promoter, whereas BRD4 inhibition by APA prevented chromatin accessibility and THBS1 transcription. Mechanistically, we show that THBS1 inhibits angiogenesis by suppressing vascular endothelial growth factor A (VEGFA) signaling, while APA prevents these detrimental changes. In diabetic mice with hind limb ischemia, epigenetic editing by APA restored the THBS1/VEGFA axis, thus improving limb vascularization and perfusion, compared with vehicle-treated animals. Finally, epigenetic regulation of THBS1 by BRD4/H3K27ac was also reported in DM patients with PAD compared with nondiabetic controls. Innovation: This is the first study showing that BET protein inhibition by APA restores angiogenic response in experimental diabetes. Conclusions: Our findings set the stage for preclinical studies and exploratory clinical trials testing APA in diabetic PAD. Antioxid. Redox Signal. 36, 667-684.

Inhibition of Aryl Hydrocarbon Receptor Attenuates Hyperglycemia-Induced Hematoma Expansion in an Intracerebral Hemorrhage Mouse Model

Background

Hyperglycemia is associated with greater hematoma expansion (HE) and worse clinical prognosis after intracerebral hemorrhage (ICH). However, the clinical benefits of intensive glucose normalization remain controversial, and there are no approved therapies for reducing HE. The aryl hydrocarbon receptor (AHR) has been shown to participate in hyperglycemia‐induced blood–brain barrier (BBB) dysfunction and brain injury after stroke. Herein, we investigated the role of AHR in hyperglycemia‐induced HE in a male mouse model of ICH.

Methods and Results

CD1 mice (n=387) were used in this study. Mice were subjected to ICH by collagenase injection. Fifty percent dextrose was injected intraperitoneally 3 hours after ICH. AHR knockout clustered regularly interspaced short palindromic repeat was administered intracerebroventricularly to evaluate the role of AHR after ICH. A selective AHR inhibitor, 6,2′,4′‐trimethoxyflavone, was administered intraperitoneally 2 hours or 6 hours after ICH for outcome study. To evaluate the effect of AHR on HE, 3‐methylcholanthrene, an AHR agonist, was injected intraperitoneally 2 hours after ICH. The results showed hyperglycemic ICH upregulated AHR accompanied by greater HE. AHR inhibition provided neurological benefits by restricting HE and preserving BBB function after hyperglycemic ICH. In vivo knockdown of AHR further limited HE and enhanced the BBB integrity. Hyperglycemia directly activated AHR as a physiological stimulus in vivo. The thrombospondin‐1/transforming growth factor‐β/vascular endothelial growth factor axis partly participated in AHR signaling after ICH, which inhibited the expressions of BBB‐related proteins, ZO‐1 and Claudin‐5.

Conclusions

AHR may serve as a potential therapeutic target to attenuate hyperglycemia‐induced hematoma expansion and to preserve the BBB in patients with ICH.

CD47 and thrombospondin-1 regulation of mitochondria, metabolism, and diabetes

Thrombospondin-1 (TSP1) is the prototypical member of a family of secreted proteins that modulate cell behavior by engaging with molecules in the extracellular matrix and with receptors on the cell surface. CD47 is widely displayed on many, if not all, cell types and is a high-affinity TSP1 receptor. CD47 is a marker of self that limits innate immune cell activities, a feature recently exploited to enhance cancer immunotherapy. Another major role for CD47 in health and disease is to mediate TSP1 signaling. TSP1 acting through CD47 contributes to mitochondrial, metabolic, and endocrine dysfunction. Studies in animal models found that elevated TSP1 expression, acting in part through CD47, causes mitochondrial and metabolic dysfunction. Clinical studies established that abnormal TSP1 expression positively correlates with obesity, fatty liver disease, and diabetes. The unabated increase in these conditions worldwide and the availability of CD47 targeting drugs justify a closer look into how TSP1 and CD47 disrupt metabolic balance and the potential for therapeutic intervention.

Crosstalk between Tryptophan Metabolism via Kynurenine Pathway and Carbohydrate Metabolism in the Context of Cardio-Metabolic Risk-Review

Scientific interest in tryptophan metabolism via the kynurenine pathway (KP) has increased in the last decades. Describing its metabolites helped to increase their roles in many diseases and disturbances, many of a pro-inflammatory nature. It has become increasingly evident that KP can be considered an important part of emerging mediators of diabetes mellitus and metabolic syndrome (MS), mostly stemming from chronic systemic low-grade inflammation resulting in the aggravation of cardiovascular complications. An electronic literature search of PubMed and Embase up to March 2021 was performed for papers reporting the effects of tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), xanthurenic acid (XA), anthranilic acid (AA), and quinolinic acid (QA), focusing on their roles in carbohydrate metabolism and the cardiovascular system. In this review, we discussed the progress in tryptophan metabolism via KP research, focusing particular attention on the roles in carbohydrate metabolism and its complications in the cardiovascular system. We examined the association between KP and diabetes mellitus type 2 (T2D), diabetes mellitus type 1 (T1D), and cardiovascular diseases (CVD). We concluded that tryptophan metabolism via KP serves as a potential diagnostic tool in assessing cardiometabolic risk for patients with T2D.

Thrombospondin-4 mediates hyperglycemia- and TGF-beta-induced inflammation in breast cancer

Inflammation drives the growth of tumors and is an important predictor of cancer aggressiveness. CD68, a marker of tumor-associated macrophages (TAM), is routinely used to aid in prognosis and treatment choices for breast cancer patients. We report that thrombospondin-4 (TSP-4) mediates breast cancer inflammation and growth in mouse models in response to hyperglycemia and TGF-beta by increasing TAM infiltration and production of inflammatory signals in tumors. Analysis of breast cancers and noncancerous tissue specimens from hyperglycemic patients revealed that levels of TSP-4 and of macrophage marker CD68 are upregulated in diabetic tissues. TSP-4 was colocalized with macrophages in cancer tissues. Bone-marrow-derived macrophages (BMDM) responded to high glucose and TGF-beta by upregulating TSP-4 production and expression, as well as the expression of inflammatory markers. We report a novel function for TSP-4 in breast cancer: regulation of TAM infiltration and inflammation. The results of our study provide new insights into regulation of cancer growth by hyperglycemia and TGF-beta and suggest TSP-4 as a potential therapeutic target.

Detecting cell-type-specific allelic expression imbalance by integrative analysis of bulk and single-cell RNA sequencing data

Allelic expression imbalance (AEI), quantified by the relative expression of two alleles of a gene in a diploid organism, can help explain phenotypic variations among individuals. Traditional methods detect AEI using bulk RNA sequencing (RNA-seq) data, a data type that averages out cell-to-cell heterogeneity in gene expression across cell types. Since the patterns of AEI may vary across different cell types, it is desirable to study AEI in a cell-type-specific manner. Although this can be achieved by single-cell RNA sequencing (scRNA-seq), it requires full-length transcript to be sequenced in single cells of a large number of individuals, which are still cost prohibitive to generate. To overcome this limitation and utilize the vast amount of existing disease relevant bulk tissue RNA-seq data, we developed BSCET, which enables the characterization of cell-type-specific AEI in bulk RNA-seq data by integrating cell type composition information inferred from a small set of scRNA-seq samples, possibly obtained from an external dataset. By modeling covariate effect, BSCET can also detect genes whose cell-type-specific AEI are associated with clinical factors. Through extensive benchmark evaluations, we show that BSCET correctly detected genes with cell-type-specific AEI and differential AEI between healthy and diseased samples using bulk RNA-seq data. BSCET also uncovered cell-type-specific AEIs that were missed in bulk data analysis when the directions of AEI are opposite in different cell types. We further applied BSCET to two pancreatic islet bulk RNA-seq datasets, and detected genes showing cell-type-specific AEI that are related to the progression of type 2 diabetes. Since bulk RNA-seq data are easily accessible, BSCET provides a convenient tool to integrate information from scRNA-seq data to gain insight on AEI with cell type resolution. Results from such analysis will advance our understanding of cell type contributions in human diseases.

Detection of allelic expression imbalance (AEI), a phenomenon where the two alleles of a gene differ in their expression magnitude, is a key step towards the understanding of phenotypic variations among individuals. Existing methods detect AEI using bulk RNA sequencing (RNA-seq) data and ignore AEI variations among different cell types. Although single-cell RNA sequencing (scRNA-seq) has enabled the characterization of cell-to-cell heterogeneity in gene expression, the high costs have limited its application in AEI analysis. To overcome this limitation, we developed BSCET to characterize cell-type-specific AEI using the widely available bulk RNA-seq data by integrating cell-type composition information inferred from scRNA-seq samples. Since the degree of AEI may vary with disease phenotypes, we further extended BSCET to detect genes whose cell-type-specific AEIs are associated with clinical factors. Through extensive benchmark evaluations and analyses of two pancreatic islet bulk RNA-seq datasets, we demonstrated BSCET’s ability to refine bulk-level AEI to cell-type resolution, and to identify genes whose cell-type-specific AEIs are associated with the progression of type 2 diabetes. With the vast amount of easily accessible bulk RNA-seq data, we believe BSCET will be a valuable tool for elucidating cell type contributions in human diseases.

Detrimental activation of AhR pathway in cancer: an overview of therapeutic strategies

Sustained transcriptional activation of the aryl hydrocarbon receptor (AhR) promotes tumour growth and impairs the immune defence, at least for cutaneous melanoma and glioma. AhR ligands are produced by the tumour microenvironment (TME) and by the tumour itself (intracrine). The recent identification of interleukin-4-induced-1 (IL4I1), a parallel pathway to indoleamine 2 3-dioxygenase 1 (IDO1)/ tryptophan 2,3-dioxygenase (TDO), and its ability to generate AhR ligands, confirms that a complete inhibition of AhR ligand production might be difficult to reach. Here, we have focused on recent discoveries explaining the large varieties of AhR ligands and the functional consequences in terms of cancer cell plasticity and consecutive therapy resistance. We also examined therapeutic strategies targeting the AhR signalling pathway and their possible adverse effects. Since the end of 2019, two phase I clinical trials have investigated the ability of the AhR antagonist to 'reset' the immune system and re-sensitize the cancer cells to therapies by preventing their dedifferentiation.

The Secretive Liaison of Particulate Matter and SARS-CoV-2. A Hypothesis and Theory Investigation

As the novel coronavirus disease sweeps across the world, there is growing speculation on the role that atmospheric factors may have played on the different distribution of SARS-CoV-2, and on the epidemiological characteristics of COVID-19. Knowing the role that environmental factors play in influenza virus outbreaks, environmental pollution and, in particular, atmospheric airborne (particulate matter, PM) has been considered as a potential key factor in the spread and mortality of COVID-19. A possible role of the PM as the virus carrier has also been debated. The role of PM in exacerbating respiratory and cardiovascular disease has been well recognized. Accumulating evidence support the hypothesis that PM can trigger inflammatory response at molecular, cellular and organ levels. On this basis, we developed the hypothesis that PM may play a role as a booster of COVID-19 rather than as a carrier of SARS-CoV-2. To support our hypothesis, we analyzed the molecular signatures detected in cells exposed to PM samples collected in one of the most affected areas by the COVID-19 outbreak, in Italy. T47D human breast adenocarcinoma cells were chosen to explore the global gene expression changes induced by the treatment with organic extracts of PM 2.5. The analysis of the KEGG's pathways showed modulation of several gene networks related to the leucocyte transendothelial migration, cytoskeleton and adhesion system. Three major biological process were identified, including coagulation, growth control and immune response. The analysis of the modulated genes gave evidence for the involvement of PM in the endothelial disease, coagulation disorders, diabetes and reproductive toxicity, supporting the hypothesis that PM, directly or through molecular interplay, affects the same molecular targets as so far known for SARS-COV-2, contributing to the cytokines storm and to the aggravation of the symptoms triggered by COVID-19. We provide evidence for a plausible cooperation of receptors and transmembrane proteins, targeted by PM and involved in COVID-19, together with new insights into the molecular interplay of chemicals and pathogens that could be of importance for sustaining public health policies and developing new therapeutic approaches.

Indoxyl sulfate induces ROS production via the aryl hydrocarbon receptor-NADPH oxidase pathway and inactivates NO in vascular tissues

AIMS

The uremic toxin indoxyl sulfate (IS) was reported to be the cause of cardiovascular disease associated with chronic kidney disease. Therefore, we evaluated the direct influences of IS on vascular function, focusing on the superoxide anion (O₂^-) and nitric oxide (NO)/soluble guanylate cyclase (sGC) pathways.

MAIN METHODS

Isolated rat thoracic aortas with and without vascular endothelium were incubated with IS for 4 h in a physiological solution. In some experiments, several inhibitors were treated 30 min before the addition of IS. O₂^- production was measured by the chemiluminescence method, and the vascular reactivity to different vasorelaxants was examined using organ chamber technique.

KEY FINDINGS

1) Experiments using endothelium-intact vascular rings: IS significantly increased O₂^- production. The increase was suppressed by addition of the NADPH oxidase inhibitor apocynin, the antioxidant ascorbic acid and the aryl hydrocarbon receptor (AhR) inhibitor CH223191. Furthermore, IS attenuated the acetylcholine (ACh)-induced vasorelaxantion, which was suppressed by addition of the above drugs. 2) Experiments using endothelium-denuded vascular rings: IS significantly increased O₂^- production and also attenuated sodium nitroprusside (SNP)-induced vasorelaxation. These influences of IS were normalized only by ascorbic acid addition. On the other hand, IS did not affect the vasorelaxation by the sGC stimulator BAY 41-2272.

SIGNIFICANCE

This study suggested that IS causes O₂^- production in vascular tissues, thereby attenuating ACh- and SNP-induced vasorelaxation, probably through NO inactivation. Furthermore, it is reasonable to consider that IS-promoted O₂^- production in the presence of vascular endothelium is through binding to AhR and the activation of NADPH oxidase.

AHR Signaling Interacting with Nutritional Factors Regulating the Expression of Markers in Vascular Inflammation and Atherogenesis

There is strong evidence that exposure to fine particulate matter (PM_2.5) and a high-fat diet (HFD) increase the risk of mortality from atherosclerotic cardiovascular diseases. Recent studies indicate that PM_2.5 generated by combustion activates the Aryl Hydrocarbon Receptor (AHR) and inflammatory cytokines contributing to PM_2.5-mediated atherogenesis. Here we investigate the effects of components of a HFD on PM-mediated activation of AHR in macrophages. Cells were treated with components of a HFD and AHR-activating PM and the expression of biomarkers of vascular inflammation was analyzed. The results show that glucose and triglyceride increase AHR-activity and PM_2.5-mediated induction of cytochrome P450 (CYP)1A1 mRNA in macrophages. Cholesterol, fructose, and palmitic acid increased the PM- and AHR-mediated induction of proinflammatory cytokines in macrophages. Treatment with palmitic acid significantly increased the expression of inflammatory cytokines and markers of vascular injury in human aortic endothelial cells (HAEC) after treatment with PM_2.5. The PM_2.5-mediated activation of the atherogenic markers C-reactive protein (CRP) and S100A9, a damage-associated molecular pattern molecule, was found to be AHR-dependent and involved protein kinase A (PKA) and a CCAAT/enhancer-binding protein (C/EBP) binding element. This study identified nutritional factors interacting with AHR signaling and contributing to PM_2.5-induced markers of atherogenesis and future cardiovascular risk.

Urolithin A suppresses high glucose-induced neuronal amyloidogenesis by modulating TGM2-dependent ER-mitochondria contacts and calcium homeostasis

Hyperglycemia in diabetes mellitus (DM) patients is a causative factor for amyloidogenesis and induces neuropathological changes, such as impaired neuronal integrity, neurodegeneration, and cognitive impairment. Regulation of mitochondrial calcium influx from the endoplasmic reticulum (ER) is considered a promising strategy for the prevention of mitochondrial ROS (mtROS) accumulation that occurs in the Alzheimer's disease (AD)-associated pathogenesis in DM patients. Among the metabolites of ellagitannins that are produced in the gut microbiome, urolithin A has received an increasing amount of attention as a novel candidate with anti-oxidative and neuroprotective effects in AD. Here, we investigated the effect of urolithin A on high glucose-induced amyloidogenesis caused by mitochondrial calcium dysregulation and mtROS accumulation resulting in neuronal degeneration. We also identified the mechanism related to mitochondria-associated ER membrane (MAM) formation. We found that urolithin A-lowered mitochondrial calcium influx significantly alleviated high glucose-induced mtROS accumulation and expression of amyloid beta (Aβ)-producing enzymes, such as amyloid precursor protein (APP) and β-secretase-1 (BACE1), as well as Aβ production. Urolithin A injections in a streptozotocin (STZ)-induced diabetic mouse model alleviated APP and BACE1 expressions, Tau phosphorylation, Aβ deposition, and cognitive impairment. In addition, high glucose stimulated MAM formation and transglutaminase type 2 (TGM2) expression. We first discovered that urolithin A significantly reduced high glucose-induced TGM2 expression. In addition, disruption of the AIP-AhR complex was involved in urolithin A-mediated suppression of high glucose-induced TGM2 expression. Markedly, TGM2 silencing inhibited inositol 1, 4, 5-trisphosphate receptor type 1 (IP3R1)-voltage-dependent anion-selective channel protein 1 (VDAC1) interactions and prevented high glucose-induced mitochondrial calcium influx and mtROS accumulation. We also found that urolithin A or TGM2 silencing prevented Aβ-induced mitochondrial calcium influx, mtROS accumulation, Tau phosphorylation, and cell death in neuronal cells. In conclusion, we suggest that urolithin A is a promising candidate for the development of therapies to prevent DM-associated AD pathogenesis by reducing TGM2-dependent MAM formation and maintaining mitochondrial calcium and ROS homeostasis.

THBS1 (thrombospondin-1)

Thrombospondins are encoded in vertebrates by a family of 5 THBS genes. THBS1 is infrequently mutated in most cancers, but its expression is positively regulated by several tumor suppressor genes and negatively regulated by activated oncogenes and promoter hypermethylation. Consequently, thrombospondin-1 expression is frequently lost during oncogenesis and is correlated with a poor prognosis for some cancers. Thrombospondin-1 is a secreted protein that acts in the tumor microenvironment to inhibit angiogenesis, regulate antitumor immunity, stimulate tumor cell migration, and regulate the activities of extracellular proteases and growth factors. Differential effects of thrombospondin-1 on the sensitivity of normal versus malignant cells to ischemic and genotoxic stress also regulate the responses to tumors to therapeutic radiation and chemotherapy.

Thrombospondin-1: A Key Protein That Induces Fibrosis in Diabetic Complications

Fibrosis accompanies most common pathophysiological features of diabetes complications in different organs. It is characterized by an excessive accumulation of extracellular matrix (ECM) components, the response to which contributes to inevitable organ injury. The extracellular protein thrombospondin-1 (TSP-1), a kind of extracellular glycoprotein, is upregulated by the increased activity of some transcription factors and results in fibrosis by activating multiple pathways in diabetes. The results of studies from our team and other colleagues indicate that TSP-1 is associated with the pathological process leading to diabetic complications and is considered to be the most important factor in fibrosis. This review summarizes the molecular mechanism of increased TSP-1 induced by hyperglycemia and the role of TSP-1 in fibrosis during the development of diabetes complications.

Modulation of the peripheral blood transcriptome by the ingestion of probiotic yoghurt and acidified milk in healthy, young men

The metabolic health benefits of fermented milks have already been investigated using clinical biomarkers but the development of transcriptomic analytics in blood offers an alternative approach that may help to sensitively characterise such effects. We aimed to assess the effects of probiotic yoghurt intake, compared to non-fermented, acidified milk intake, on clinical biomarkers and gene expression in peripheral blood. To this end, a randomised, crossover study was conducted in fourteen healthy, young men to test the two dairy products. For a subset of seven subjects, RNA sequencing was used to measure gene expression in blood collected during postprandial tests and after two weeks daily intake. We found that the postprandial response in insulin was different for probiotic yoghurt as compared to that of acidified milk. Moreover changes in several clinical biomarkers were associated with changes in the expression of genes representing six metabolic genesets. Assessment of the postprandial effects of each dairy product on gene expression by geneset enrichment analysis revealed significant, similar modulation of inflammatory and glycolytic genes after both probiotic yoghurt and acidified milk intake, although distinct kinetic characteristics of the modulation differentiated the dairy products. The aryl hydrocarbon receptor was a major contributor to the down-regulation of the inflammatory genesets and was also positively associated with changes in circulating insulin at 2h after yoghurt intake (p = 0.05). Daily intake of the dairy products showed little effect on the fasting blood transcriptome. Probiotic yoghurt and acidified milk appear to affect similar gene pathways during the postprandial phase but differences in the timing and the extent of this modulation may lead to different physiological consequences. The functional relevance of these differences in gene expression is supported by their associations with circulating biomarkers.

Highly potent visnagin derivatives inhibit Cyp1 and prevent doxorubicin cardiotoxicity

Anthracyclines such as doxorubicin are highly effective chemotherapy agents used to treat many common malignancies. However, their use is limited by cardiotoxicity. We previously identified visnagin as protecting against doxorubicin toxicity in cardiac but not tumor cells. In this study, we sought to develop more potent visnagin analogs in order to use these analogs as tools to clarify the mechanisms of visnagin-mediated cardioprotection. Structure-activity relationship studies were performed in a zebrafish model of doxorubicin cardiomyopathy. Movement of the 5-carbonyl to the 7 position and addition of short ester side chains led to development of visnagin analogs with 1,000-fold increased potency in zebrafish and 250-fold increased potency in mice. Using proteomics, we discovered that doxorubicin caused robust induction of Cytochrome P450 family 1 (CYP1) that was mitigated by visnagin and its potent analog 23. Treatment with structurally divergent CYP1 inhibitors, as well as knockdown of CYP1A, prevented doxorubicin cardiomyopathy in zebrafish. The identification of potent cardioprotective agents may facilitate the development of new therapeutic strategies for patients receiving cardiotoxic chemotherapy. Moreover, these studies support the idea that CYP1 is an important contributor to doxorubicin cardiotoxicity and suggest that modulation of this pathway could be beneficial in the clinical setting.

Metformin accelerates wound healing in type 2 diabetic db/db mice

Wound healing impairment is increasingly recognized to be a consequence of hyperglycemia-induced dysfunction of endothelial precursor cells (EPCs) in type 2 diabetes mellitus (T2DM). Metformin exhibits potential for the improvement of endothelial function and the wound healing process. However, the underlying mechanisms for the observed beneficial effects of metformin application remain to be completely understood. The present study assessed whether metformin, a widely used therapeutic drug for T2DM, may accelerate wound closure in T2DM db/db mice. Genetically hyperglycemic db/db mice were used as the T2DM model. Metformin (250 mg/kg/day; intragastric) was administered for two weeks prior to EPC collection and wound model creation in db/db mice. Wound healing was evaluated by alterations in the wound area and the number of platelet endothelial cell adhesion molecule-positive cells. The function of the isolated bone marrow-derived EPCs (BM-EPCs) was assessed by a tube formation assay. The number of circulating EPCs, and the levels of intracellular nitric oxide (NO) and superoxide (O₂⁻) were detected by flow cytometry. Thrombospondin-1 (TSP-1) expression was determined by western blot analysis. It was observed that treatment with metformin accelerated wound healing, improved angiogenesis and increased the circulating EPC number in db/db mice. In vitro, treatment with metformin reversed the impaired BM-EPC function reflected by tube formation, and significantly increased NO production while decreasing O₂⁻ levels in BM-EPCs from db/db mice. In addition, TSP-1 expression was markedly attenuated by treatment with metformin in cultured BM-EPCs. Metformin contributed to wound healing and improved angiogenesis in T2DM mice, which was, in part, associated with stimulation of NO, and inhibition of O₂⁻ and TSP-1 in EPCs from db/db mice.

Induction of Colonic Regulatory T Cells by Mesalamine by Activating the Aryl Hydrocarbon Receptor

BACKGROUND & AIMS

Mesalamine is a first-line drug for treatment of inflammatory bowel diseases (IBD). However, its mechanisms are not fully understood. CD4⁺ Foxp3⁺ regulatory T cells (Tregs) play a potential role in suppressing IBD. This study determined whether the anti-inflammatory activity of mesalamine is related to Treg induction in the colon.

METHODS

We examined the frequencies of Tregs in the colons of wild-type mice, mice deficient for aryl hydrocarbon receptor (AhR^-/- mice), and bone marrow-chimeric mice lacking AhR in hematopoietic cells (BM-AhR^-/- mice), following oral treatment with mesalamine. We also examined the effects of mesalamine on transforming growth factor (TGF)-β expression in the colon.

RESULTS

Treatment of wild-type mice with mesalamine increased the accumulation of Tregs in the colon and up-regulated the AhR target gene Cyp1A1, but this effect was not observed in AhR^-/- or BM-AhR^-/- mice. In addition, mesalamine promoted in vitro differentiation of naive T cells to Tregs, concomitant with AhR activation. Mice treated with mesalamine exhibited increased levels of the active form of TGF-β in the colon in an AhR-dependent manner and blockade of TGF-β signaling suppressed induction of Tregs by mesalamine in the colon. Furthermore, mice pretreated with mesalamine acquired resistance to dextran sodium sulfate-induced colitis.

CONCLUSIONS

We propose a novel anti-inflammatory mechanism of mesalamine for colitis: induction of Tregs in the colon via the AhR pathway, followed by TGF-β activation.

Oral chromium picolinate impedes hyperglycemia-induced atherosclerosis and inhibits proatherogenic protein TSP-1 expression in STZ-induced type 1 diabetic ApoE-/- mice

Increasing evidence suggests thrombospondin-1 (TSP-1), a potent proatherogenic matricellular protein, as a putative link between hyperglycemia and atherosclerotic complications in diabetes. We previously reported that the micronutrient chromium picolinate (CrP), with long-standing cardiovascular benefits, inhibits TSP-1 expression in glucose-stimulated human aortic smooth muscle cells in vitro. Here, we investigated the atheroprotective action of orally administered CrP in type 1 diabetic apolipoprotein E-deficient (ApoE^−/−) mice and elucidated the role of TSP-1 in this process. CrP decreased lipid burden and neointimal thickness in aortic root lesions of hyperglycemic ApoE^−/− mice; also, smooth muscle cell (SMC), macrophage and leukocyte abundance was prevented coupled with reduced cell proliferation. Attenuated lesion progression was accompanied with inhibition of hyperglycemia-induced TSP-1 expression and reduced protein O-glycosylation following CrP treatment; also, PCNA and vimentin (SMC synthetic marker) expression were reduced while SM-MHC (SMC contractile marker) levels were increased. To confirm a direct role of TSP-1 in diabetic atherosclerosis, hyperglycemic TSP-1^−/−/ApoE^−/− double knockout mice were compared with age-matched hyperglycemic ApoE^−/− littermates. Lack of TSP-1 prevented lesion formation in hyperglycemic ApoE^−/− mice, mimicking the atheroprotective phenotype of CrP-treated mice. These results suggest that therapeutic TSP-1 inhibition may have important atheroprotective potential in diabetic vascular disease.

The Aryl Hydrocarbon Receptor Relays Metabolic Signals to Promote Cellular Regeneration

While sensing the cell environment, the aryl hydrocarbon receptor (AHR) interacts with different pathways involved in cellular homeostasis. This review summarizes evidence suggesting that cellular regeneration in the context of aging and diseases can be modulated by AHR signaling on stem cells. New insights connect orphaned observations into AHR interactions with critical signaling pathways such as WNT to propose a role of this ligand-activated transcription factor in the modulation of cellular regeneration by altering pathways that nurture cellular expansion such as changes in the metabolic efficiency rather than by directly altering cell cycling, proliferation, or cell death. Targeting the AHR to promote regeneration might prove to be a useful strategy to avoid unbalanced disruptions of homeostasis that may promote disease and also provide biological rationale for potential regenerative medicine approaches.

Leptin augments recruitment of IRF-1 and CREB to thrombospondin-1 gene promoter in vascular smooth muscle cells in vitro

We previously reported that high pathophysiological concentrations of leptin, the adipocyte-secreted peptide, upregulate the expression of a potent proatherogenic matricellular protein, thrombospondin-1 (TSP-1), in vascular smooth muscle cells. Moreover, this regulation was found to occur at the level of transcription; however, the underlying molecular mechanisms remain unknown. The goal of the present study was to investigate the specific transcriptional mechanisms that mediate upregulation of TSP-1 expression by leptin. Primary human aortic smooth muscle cell cultures were transiently transfected with different TSP-1 gene (THBS1) promoter-linked luciferase reporter constructs, and luciferase activity in response to leptin (100 ng/ml) was assessed. We identified a long THBS1 promoter (-1270/+750) fragment with specific leptin response elements that are required for increased TSP-1 transcription by leptin. Promoter analyses, protein/DNA array and gel shift assays demonstrated activation and association of transcription factors, interferon regulatory factor-1 (IRF-1) and cAMP response element-binding protein (CREB), to the distal fragment of the THBS1 promoter in response to leptin. Supershift, chromatin immunoprecipitation, and coimmunoprecipitation assays revealed formation of a single complex between IRF-1 and CREB in response to leptin; importantly, recruitment of this complex to the THBS1 promoter mediated leptin-induced TSP-1 transcription. Finally, binding sequence decoy oligomer and site-directed mutagenesis revealed that regulatory elements for both IRF-1 (-1019 to -1016) and CREB (-1198 to -1195), specific to the distal THBS1 promoter, were required for leptin-induced TSP-1 transcription. Taken together, these findings demonstrate that leptin promotes a cooperative association between IRF-1 and CREB on the THBS1 promoter driving TSP-1 transcription in vascular smooth muscle cells.

High-glucose environment increased thrombospondin-1 expression in keratinocytes via DNA hypomethylation

Diabetes is an important health issue because of its increasing prevalence and association with impaired wound healing. Epidermal keratinocytes with overexpressed antiangiogenic molecule thrombospondin-1 (TSP1) have been shown to impair proper wound healing. This study examined the potential involvement of keratinocyte-derived TSP1 on diabetic wound healing. Cultured human keratinocytes and diabetic rat model were used to evaluate the effect of high-glucose environment on TSP1 expression in epidermal keratinocytes, and the molecular mechanisms involved in the process were also studied. We demonstrated that high-glucose environment increased TSP1 expression in keratinocytes. In addition, increased oxidative stress induced DNA hypomethylation at the TSP1 promoter region in keratinocytes exposed to high-glucose environment. Similar findings were found in our diabetic rat model. Early antioxidant administration normalized TSP1 expression and global DNA methylation status in diabetic rat skin and improved wound healing in vivo. Because oxidative stress contributed to TSP1 DNA hypomethylation, early recognition of diabetic condition and timely administration of antioxidant are logical approaches to reduce complications associated with diabetes as alterations in epigenome may not be reversible by controlling glucose levels during the later stages of disease course.

Aryl Hydrocarbon Receptor Plays Protective Roles against High Fat Diet (HFD)-induced Hepatic Steatosis and the Subsequent Lipotoxicity via Direct Transcriptional Regulation of Socs3 Gene Expression

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor regulating the expression of genes involved in xenobiotic response. Recent studies have suggested that AhR plays essential roles not only in xenobiotic detoxification but also energy metabolism. Thus, in this study, we studied the roles of AhR in lipid metabolism. Under high fat diet (HFD) challenge, liver-specific AhR knock-out (AhR LKO) mice exhibited severe steatosis, inflammation, and injury in the liver. Gene expression analysis and biochemical study revealed thatde novolipogenesis activity was significantly increased in AhR LKO mice. In contrast, induction of suppressor of cytokine signal 3 (Socs3) expression by HFD was attenuated in the livers of AhR LKO mice. Rescue of theSocs3gene in the liver of AhR LKO mice cancelled the HFD-induced hepatic lipotoxicities. Promoter analysis established Socs3 as novel transcriptional target of AhR. These results indicated that AhR plays a protective role against HFD-induced hepatic steatosis and the subsequent lipotoxicity effects, such as inflammation, and that the mechanism of protection involves the direct transcriptional regulation ofSocs3expression by AhR.

Extracellular matrix structure

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network composed of collagens, proteoglycans/glycosaminoglycans, elastin, fibronectin, laminins, and several other glycoproteins. Matrix components bind each other as well as cell adhesion receptors forming a complex network into which cells reside in all tissues and organs. Cell surface receptors transduce signals into cells from ECM, which regulate diverse cellular functions, such as survival, growth, migration, and differentiation, and are vital for maintaining normal homeostasis. ECM is a highly dynamic structural network that continuously undergoes remodeling mediated by several matrix-degrading enzymes during normal and pathological conditions. Deregulation of ECM composition and structure is associated with the development and progression of several pathologic conditions. This article emphasizes in the complex ECM structure as to provide a better understanding of its dynamic structural and functional multipotency. Where relevant, the implication of the various families of ECM macromolecules in health and disease is also presented.

Aryl hydrocarbon receptor-dependent up-regulation of the heterodimeric amino acid transporter LAT1 (SLC7A5)/CD98hc (SLC3A2) by diesel exhaust particle extract in human bronchial epithelial cells

The heterodimeric L-type amino acid transporter (LAT) 1/CD98hc is overexpressed in lung cancers with a poor prognosis factor. Factors that contribute to LAT1/CD98hc overexpression in lung cells remain however to be determined, but the implication of atmospheric pollution can be suspected. The present study was therefore designed to analyze the effects of diesel exhaust particle (DEP) extract (DEPe) on LAT1/CD98hc expression in bronchial epithelial BEAS-2B cells. Exposure to DEPe up-regulated LAT1 and CD98hc mRNA levels in a concentration-dependent manner, with DEPe EC50 values (around 0.2 μg/mL) relevant to environmental situations. DEPe concomitantly induced LAT1/CD98hc protein expression and LAT1-mediated leucine accumulation in BEAS-2B cells. Inhibition of the aryl hydrocarbon receptor (AhR) pathway through the use of a chemical AhR antagonist or the siRNA-mediated silencing of AhR expression was next found to prevent DEPe-mediated induction of LAT1/CD98hc, indicating that this regulation depends on AhR, known to be activated by major chemical DEP components like polycyclic aromatic hydrocarbons. DEPe exposure was finally shown to induce mRNA expression and activity of matrix metalloproteinase (MMP)-2 in BEAS-2B cells, in a CD98hc/focal adhesion kinase (FAK)/extracellular regulated kinase (ERK) manner, thus suggesting that DEPe-mediated induction of CD98hc triggers activation of the integrin/FAK/ERK signaling pathway known to be involved in MMP-2 regulation. Taken together, these data demonstrate that exposure to DEPe induces functional overexpression of the amino acid transporter LAT1/CD98hc in lung cells. Such a regulation may participate to pulmonary carcinogenic effects of DEPs, owing to the well-documented contribution of LAT1 and CD98hc to cancer development.

Disruption of Ah Receptor Signaling during Mouse Development Leads to Abnormal Cardiac Structure and Function in the Adult

The Developmental Origins of Health and Disease (DOHaD) Theory proposes that the environment encountered during fetal life and infancy permanently shapes tissue physiology and homeostasis such that damage resulting from maternal stress, poor nutrition or exposure to environmental agents may be at the heart of adult onset disease. Interference with endogenous developmental functions of the aryl hydrocarbon receptor (AHR), either by gene ablation or by exposure in utero to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent AHR ligand, causes structural, molecular and functional cardiac abnormalities and altered heart physiology in mouse embryos. To test if embryonic effects progress into an adult phenotype, we investigated whether Ahr ablation or TCDD exposure in utero resulted in cardiac abnormalities in adult mice long after removal of the agent. Ten-months old adult Ahr^-/- and in utero TCDD-exposed Ahr^+/+ mice showed sexually dimorphic abnormal cardiovascular phenotypes characterized by echocardiographic findings of hypertrophy, ventricular dilation and increased heart weight, resting heart rate and systolic and mean blood pressure, and decreased exercise tolerance. Underlying these effects, genes in signaling networks related to cardiac hypertrophy and mitochondrial function were differentially expressed. Cardiac dysfunction in mouse embryos resulting from AHR signaling disruption seems to progress into abnormal cardiac structure and function that predispose adults to cardiac disease, but while embryonic dysfunction is equally robust in males and females, the adult abnormalities are more prevalent in females, with the highest severity in Ahr^-/- females. The findings reported here underscore the conclusion that AHR signaling in the developing heart is one potential target of environmental factors associated with cardiovascular disease.

Screening a mouse liver gene expression compendium identifies modulators of the aryl hydrocarbon receptor (AhR)

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the biological and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), dioxin-like compounds (DLC) as well as some drugs and endogenous tryptophan metabolites. Short-term activation of AhR can lead to hepatocellular steatosis, and chronic activation can lead to liver cancer in mice and rats. Analytical approaches were developed to identify biosets in a genomic database in which AhR activity was altered. A set of 63 genes was identified (the AhR gene expression biomarker) that was dependent on AhR for regulation after exposure to TCDD or benzo[a]pyrene and includes the known AhR targets Cyp1a1 and Cyp1b1. A fold-change rank-based test (Running Fisher's test; p-value ≤ 10(-4)) was used to evaluate the similarity between the AhR biomarker and a test set of 37 and 41 biosets positive or negative, respectively for AhR activation. The test resulted in a balanced accuracy of 95%. The rank-based test was used to identify factors that activate or suppress AhR in an annotated mouse liver/mouse primary hepatocyte gene expression database of ∼ 1850 comparisons. In addition to the expected activation of AhR by TCDD and DLC, AhR was activated by AP20189 and phenformin. AhR was suppressed by phenobarbital and 1,4-Bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP) in a constitutive activated receptor (CAR)-dependent manner and pregnenolone-16α-carbonitrile in a pregnane X receptor (PXR)-dependent manner. Inactivation of individual genes in nullizygous models led to AhR activation (Pxr, Ghrhr, Taf10) or suppression (Ahr, Ilst6st, Hnf1a). This study describes a novel screening strategy for identifying factors in mouse liver that perturb AhR in a gene expression compendium.

Ah Receptor Signaling Controls the Expression of Cardiac Development and Homeostasis Genes

Congenital heart disease (CHD) is the most common congenital abnormality and one of the leading causes of newborn death throughout the world. Despite much emerging scientific information, the precise etiology of this disease remains elusive. Here, we show that the aryl hydrocarbon receptor (AHR) regulates the expression of crucial cardiogenesis genes and that interference with endogenous AHR functions, either by gene ablation or by agonist exposure during early development, causes overlapping structural and functional cardiac abnormalities that lead to altered fetal heart physiology, including higher heart rates, right and left ventricle dilation, higher stroke volume, and reduced ejection fraction. With striking similarity between AHR knockout (Ahr(-/-)) and agonist-exposed wild type (Ahr(+/+)) embryos, in utero disruption of endogenous AHR functions converge into dysregulation of molecular mechanisms needed for attainment and maintenance of cardiac differentiation, including the pivotal signals regulated by the cardiogenic transcription factor NKH2.5, energy balance via oxidative phosphorylation and TCA cycle and global mitochondrial function and homeostasis. Our findings suggest that AHR signaling in the developing mammalian heart is central to the regulation of pathways crucial for cellular metabolism, cardiogenesis, and cardiac function, which are potential targets of environmental factors associated with CHD.

Trivalent chromium inhibits TSP-1 expression, proliferation, and O-GlcNAc signaling in vascular smooth muscle cells in response to high glucose in vitro

Trivalent chromium (Cr(3+)) is a mineral nutrient reported to have beneficial effects in glycemic and cardiovascular health. In vitro and in vivo studies suggest that Cr(3+) supplementation reduces the atherogenic potential and lowers the risk of vascular inflammation in diabetes. However, effects of Cr(3+) in vascular cells under conditions of hyperglycemia, characteristic of diabetes, remain unknown. In the present study we show that a therapeutically relevant concentration of Cr(3+) (100 nM) significantly downregulates a potent proatherogenic matricellular protein, thrombospondin-1 (TSP-1), in human aortic smooth muscle cells (HASMC) stimulated with high glucose in vitro. Promoter-reporter assays reveal that this downregulation of TSP-1 expression by Cr(3+) occurs at the level of transcription. The inhibitory effects of Cr(3+) on TSP-1 were accompanied by significant reductions in O-glycosylation of cytoplasmic and nuclear proteins. Using Western blotting and immunofluorescence studies, we demonstrate that reduced protein O-glycosylation by Cr(3+) is mediated via inhibition of glutamine: fructose 6-phosphate amidotransferase, a rate-limiting enzyme of the hexosamine pathway, and O-linked N-acetylglucosamine (O-GlcNAc) transferase, a distal enzyme in the pathway that controls intracellular protein O-glycosylation. Additionally, we found that Cr(3+) attenuates reactive oxygen species formation in glucose-stimulated HASMC, suggesting an antioxidant effect. Finally, we report an antiproliferative effect of Cr(3+) that is specific for high glucose and conditions triggering elevated protein O-glycosylation. Taken together, these findings provide the first cellular evidence for a novel role of Cr(3+) to modulate aberrant vascular smooth muscle cell function associated with hyperglycemia-induced vascular complications.

A mouse strain less responsive to dioxin-induced prostaglandin E2 synthesis is resistant to the onset of neonatal hydronephrosis

Dioxin is a ubiquitous environmental pollutant that induces toxicity when bound to the aryl hydrocarbon receptor (AhR). Significant differences in susceptibility of mouse strains to dioxin toxicity are largely accounted for by the dissociation constant of binding to dioxins of AhR subtypes encoded by different alleles. We showed that cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1), components of a prostanoid synthesis pathway, play essential roles in the onset of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced hydronephrosis of neonatal mice. Although C57BL/6J and BALB/cA mice harbor AhR receptors highly responsive to TCDD, they were found by chance to differ significantly in the incidence of TCDD-induced hydronephrosis. Therefore, the goal of the present study was to determine the molecular basis of this difference in susceptibility to TCDD toxicity. For this purpose, we administered C57BL/6J and BALB/cA dams' TCDD at an oral dose of 15 or 80 μg/kg on postnatal day (PND) 1 to expose pups to TCDD via lactation, and the pups' kidneys were collected on PND 7. The incidence of hydronephrosis in C57BL/6J pups (64%) was greater than in BALB/cA pups (0%, p < 0.05), despite similarly increased levels of COX-2 mRNA. The incidence of hydronephrosis in these mouse strains paralleled the levels of renal mPGES-1 mRNA and early growth response 1 (Egr-1) that modulates mPGES-1 gene expression, as well as PGE2 concentrations in urine. Although these mouse strains possess AhR alleles tightly bound to TCDD, their difference in incidence and severity of hydronephrosis can be explained, in part, by differences in the expression of mPGES-1 and Egr-1.

Revisiting the matricellular concept

The concept of a matricellular protein was first proposed by Paul Bornstein in the mid-1990s to account for the non-lethal phenotypes of mice with inactivated genes encoding thrombospondin-1, tenascin-C, or SPARC. It was also recognized that these extracellular matrix proteins were primarily counter or de-adhesive. This review reappraises the matricellular concept after nearly two decades of continuous investigation. The expanded matricellular family as well as the diverse and often unexpected functions, cellular location, and interacting partners/receptors of matricellular proteins are considered. Development of therapeutic strategies that target matricellular proteins are discussed in the context of pathology and regenerative medicine.

GTP cyclohydrolase I prevents diabetic-impaired endothelial progenitor cells and wound healing by suppressing oxidative stress/thrombospondin-1

Endothelial progenitor cell (EPC) dysfunction is a key contributor to diabetic refractory wounds. Endothelial nitric oxide synthase (eNOS), which critically regulates the mobilization and function of EPCs, is uncoupled in diabetes due to decreased cofactor tetrahydrobiopterin (BH4). We tested whether GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme of BH4 synthesis, preserves EPC function in type 1 diabetic mice. Type 1 diabetes was induced in wild-type (WT) and GTPCH I transgenic (Tg-GCH) mice by intraperitoneal injection of streptozotocin (STZ). EPCs were isolated from the peripheral blood and bone marrow of WT, Tg-GCH, and GTPCH I-deficient hph-1 mice. The number of EPCs was significantly lower in STZ-WT mice and hph-1 mice and was rescued in STZ Tg-GCH mice. Furthermore, GTPCH I overexpression improved impaired diabetic EPC migration and tube formation. EPCs from WT, Tg-GCH, and STZ-Tg-GCH mice were administered to diabetic excisional wounds and accelerated wound healing significantly, with a concomitant augmentation of angiogenesis. Flow cytometry measurements showed that intracellular nitric oxide (NO) levels were reduced significantly in STZ-WT and hph-1 mice, paralleled by increased superoxide anion levels; both were rescued in STZ-Tg-GCH mice. Western blot analysis revealed that thrombospondin-1 (TSP-1) was significantly upregulated in the EPCs of STZ-WT mice and hph-1 mice and suppressed in STZ-treated Tg-GCH mice. Our results demonstrate that the GTPCH I/BH4 pathway is critical to preserve EPC quantity, function, and regenerative capacity during wound healing in type 1 diabetic mice at least partly through the attenuation of superoxide and TSP-1 levels and augmentation of NO level.

Invoking the power of thrombospondins: regulation of thrombospondins expression

Increasing evidence suggests critical functions of thrombospondins (TSPs) in a variety of physiological and pathological processes. With the growing understanding of the importance of these matricellular proteins, the need to understand the mechanisms of regulation of their expression and potential approaches to modulate their levels is also increasing. The regulation of TSP expression is multi-leveled, cell- and tissue-specific, and very precise. However, the knowledge of mechanisms modulating the levels of TSPs is fragmented and incomplete. This review discusses the known mechanisms of regulation of TSP levels and the gaps in our knowledge that prevent us from developing strategies to modulate the expression of these physiologically important proteins.

The role of thrombospondin (TSP)-1 in obesity and diabetes

Matricellular proteins are extracellular macromolecules that do not serve a structural role, but when incorporated into the matrix, modulate cell:cell and cell:matrix interactions. The matricellular protein thrombospondin (TSP)-1, a potent angiostatic mediator and activator of transforming growth factor (TGF)-β, is upregulated in diabetes and obesity and may be involved in the pathogenesis of metabolic dysregulation and organ dysfunction. This manuscript discusses recently published observations on the role of TSP-1 in metabolic disease. In obesity models induced by a high-fat diet, adipose tissue TSP-1 upregulation induces inflammation and promotes weight gain and metabolic dysfunction. TSP-1 may have direct effects on adipocyte proliferation and fatty acid uptake. In diabetic subjects, TSP-1 upregulation in kidney, myocardium, and vascular tissue may promote dysfunction. In the myocardium, TSP-1 upregulation may transduce angiostatic signals inducing vascular rarefaction. Dissection of the functional domains involved in TSP-1 actions may lead to the development of peptide-based strategies for treatment of diabetes and its complications.