A succinate/SUCNR1-brush cell defense program in the tracheal epithelium

Host-derived succinate accumulates in the airways during bacterial infection. Here, we show that luminal succinate activates murine tracheal brush (tuft) cells through a signaling cascade involving the succinate receptor 1 (SUCNR1), phospholipase Cβ2, and the cation channel transient receptor potential channel subfamily M member 5 (TRPM5). Stimulated brush cells then trigger a long-range Ca2+ wave spreading radially over the tracheal epithelium through a sequential signaling process. First, brush cells release acetylcholine, which excites nearby cells via muscarinic acetylcholine receptors. From there, the Ca2+ wave propagates through gap junction signaling, reaching also distant ciliated and secretory cells. These effector cells translate activation into enhanced ciliary activity and Cl- secretion, which are synergistic in boosting mucociliary clearance, the major innate defense mechanism of the airways. Our data establish tracheal brush cells as a central hub in triggering a global epithelial defense program in response to a danger-associated metabolite.

Targeting of Scavenger Receptors Stabilin-1 and Stabilin-2 Ameliorates Atherosclerosis by a Plasma Proteome Switch Mediating Monocyte/Macrophage Suppression

BACKGROUND

Scavenger receptors Stabilin-1 (Stab1) and Stabilin-2 (Stab2) are preferentially expressed by liver sinusoidal endothelial cells. They mediate the clearance of circulating plasma molecules controlling distant organ homeostasis. Studies suggest that Stab1 and Stab2 may affect atherosclerosis. Although subsets of tissue macrophages also express Stab1, hematopoietic Stab1 deficiency does not modulate atherogenesis. Here, we comprehensively studied how targeting Stab1 and Stab2 affects atherosclerosis.

METHODS

ApoE-KO mice were interbred with Stab1-KO and Stab2-KO mice and fed a Western diet. For antibody targeting, Ldlr-KO mice were also used. Unbiased plasma proteomics were performed and independently confirmed. Ligand binding studies comprised glutathione-S-transferase-pulldown and endocytosis assays. Plasma proteome effects on monocytes were studied by single-cell RNA sequencing in vivo, and by gene expression analyses of Stabilin ligand-stimulated and plasma-stimulated bone marrow-derived monocytes/macrophages in vitro.

RESULTS

Spontaneous and Western diet-associated atherogenesis was significantly reduced in ApoE-Stab1-KO and ApoE-Stab2-KO mice. Similarly, inhibition of Stab1 or Stab2 by monoclonal antibodies significantly reduced Western diet-associated atherosclerosis in ApoE-KO and Ldlr-KO mice. Although neither plasma lipid levels nor circulating immune cell numbers were decisively altered, plasma proteomics revealed a switch in the plasma proteome, consisting of 231 dysregulated proteins comparing wildtype with Stab1/2-single and Stab1/2-double KO, and of 41 proteins comparing ApoE-, ApoE-Stab1-, and ApoE-Stab2-KO. Among this broad spectrum of common, but also disparate scavenger receptor ligand candidates, periostin, reelin, and TGFBi (transforming growth factor, β-induced), known to modulate atherosclerosis, were independently confirmed as novel circulating ligands of Stab1/2. Single-cell RNA sequencing of circulating myeloid cells of ApoE-, ApoE-Stab1-, and ApoE-Stab2-KO mice showed transcriptomic alterations in patrolling (Ccr2^-/Cx3cr1⁺⁺/Ly6C^lo) and inflammatory (Ccr2⁺/Cx3cr1⁺/Ly6C^hi) monocytes, including downregulation of proatherogenic transcription factor Egr1. In wildtype bone marrow-derived monocytes/macrophages, ligand exposure alone did not alter Egr1 expression in vitro. However, exposure to plasma from ApoE-Stab1-KO and ApoE-Stab2-KO mice showed a reverted proatherogenic macrophage activation compared with ApoE-KO plasma, including downregulation of Egr1 in vitro.

CONCLUSIONS

Inhibition of Stab1/Stab2 mediates an anti-inflammatory switch in the plasma proteome, including direct Stabilin ligands. The altered plasma proteome suppresses both patrolling and inflammatory monocytes and, thus, systemically protects against atherogenesis. Altogether, anti-Stab1- and anti-Stab2-targeted therapies provide a novel approach for the future treatment of atherosclerosis.

Disturbed flow-induced Gs-mediated signaling protects against endothelial inflammation and atherosclerosis

Atherosclerosis develops preferentially in areas of the arterial system, in which blood flow is disturbed. Exposure of endothelial cells to disturbed flow has been shown to induce inflammatory signaling, including NF-κB activation, which leads to the expression of leukocyte adhesion molecules and chemokines. Here, we show that disturbed flow promotes the release of adrenomedullin from endothelial cells, which in turn activates its G_s-coupled receptor calcitonin receptor–like receptor (CALCRL). This induces antiinflammatory signaling through cAMP and PKA, and it results in reduced endothelial inflammation in vitro and in vivo. Suppression of endothelial expression of Gα_s, the α subunit of the G-protein G_s; CALCRL; or adrenomedullin leads to increased disturbed flow–induced inflammatory signaling in vitro and in vivo. Furthermore, mice with induced endothelial-specific deficiency of Gα_s, CALCRL, or adrenomedullin show increased atherosclerotic lesions. Our data identify an antiinflammatory signaling pathway in endothelial cells stimulated by disturbed flow and suggest activation of the endothelial adrenomedullin/CALCRL/G_s system as a promising approach to inhibit progression of atherosclerosis.

Disturbed flow promotes the release of adrenomedullin from endothelial cells and activates Gs-mediated signaling, which reduces endothelial inflammation in vitro and in vivo.

Shear Stress-Induced miR-143-3p in Collateral Arteries Contributes to Outward Vessel Growth by Targeting Collagen V-α2

OBJECTIVE

Arteriogenesis, describing the process of collateral artery growth, is activated by fluid shear stress (FSS). Since this vascular mechanotransduction may involve microRNAs (miRNAs), we investigated the FSS-induced expression of vascular cell miRNAs and their functional impact on collateral artery growth during arteriogenesis. Approach and Results: To this end, rats underwent femoral artery ligation and arteriovenous anastomosis to increase collateral blood flow to maximize FSS and trigger collateral vessel remodeling. Five days after surgery, a miRNA expression profile was obtained from collateral tissue, and upregulation of 4 miRNAs (miR-24-3p, miR-143-3p, miR-146a-5p, and miR-195-5p) was verified by quantitative polymerase chain reaction. Knockdown of miRNAs at the same time of the surgery in an in vivo mouse ligation and recovery model demonstrated that inhibition of miR-143-3p only severely impaired blood flow recovery due to decreased arteriogenesis. In situ hybridization revealed distinct localization of miR-143-3p in the vessel wall of growing collateral arteries predominantly in smooth muscle cells. To investigate the mechanotransduction of FSS leading to the increased miR-143-3p expression, cultured endothelial cells were exposed to FSS. This provoked the expression and release of TGF-β (transforming growth factor-β), which increased the expression of miR-143-3p in smooth muscle cells in the presence of SRF (serum response factor) and myocardin. COL5A2 (collagen type V-α2)-a target gene of miR-143-3p predicted by in silico analysis-was found to be downregulated in growing collaterals.

CONCLUSIONS

These results indicate that the increased miR-143-3p expression in response to FSS might contribute to the reorganization of the extracellular matrix, which is important for vascular remodeling processes, by inhibiting collagen V-α2 biosynthesis.

Shear stress-induced endothelial adrenomedullin signaling regulates vascular tone and blood pressure

Hypertension is a primary risk factor for cardiovascular diseases including myocardial infarction and stroke. Major determinants of blood pressure are vasodilatory factors such as nitric oxide (NO) released from the endothelium under the influence of fluid shear stress exerted by the flowing blood. Several endothelial signaling processes mediating fluid shear stress-induced formation and release of vasodilatory factors have been described. It is, however, still poorly understood how fluid shear stress induces these endothelial responses. Here we show that the endothelial mechanosensitive cation channel PIEZO1 mediated fluid shear stress-induced release of adrenomedullin, which in turn activated its Gs-coupled receptor. The subsequent increase in cAMP levels promoted the phosphorylation of endothelial NO synthase (eNOS) at serine 633 through protein kinase A (PKA), leading to the activation of the enzyme. This Gs/PKA-mediated pathway synergized with the AKT-mediated pathways leading to eNOS phosphorylation at serine 1177. Mice with endothelium-specific deficiency of adrenomedullin, the adrenomedullin receptor, or Gαs showed reduced flow-induced eNOS activation and vasodilation and developed hypertension. Our data identify fluid shear stress-induced PIEZO1 activation as a central regulator of endothelial adrenomedullin release and establish the adrenomedullin receptor and subsequent Gs-mediated formation of cAMP as a critical endothelial mechanosignaling pathway regulating basal endothelial NO formation, vascular tone, and blood pressure.

β-Hydroxybutyrate protects from alcohol-induced liver injury via a Hcar2-cAMP dependent pathway

BACKGROUND & AIMS

Sterile inflammation resulting in alcoholic hepatitis (AH) occurs unpredictably after many years of excess alcohol intake. The factors responsible for the development of AH are not known but mitochondrial damage with loss of mitochondrial function are common features. Hcar2 is a G-protein coupled receptor which is activated by β-hydroxybutyrate (BHB). We aimed to determine the relevance of the BHB-Hcar2 pathway in alcoholic liver disease.

METHODS

We tested if loss of BHB production can result in increased liver inflammation. We further tested if BHB supplementation is protective in AH through interaction with Hcar2, and analyzed the immune and cellular basis for protection.

RESULTS

Humans with AH have reduced hepatic BHB, and inhibition of BHB production in mice aggravated ethanol-induced AH, with higher plasma alanine aminotransferase levels, increased steatosis and greater neutrophil influx. Conversely supplementation of BHB had the opposite effects with reduced alanine aminotransferase levels, reduced steatosis and neutrophil influx. This therapeutic effect of BHB is dependent on the receptor Hcar2. BHB treatment increased liver Il10 transcripts, and promoted the M2 phenotype of intrahepatic macrophages. BHB also increased the transcriptional level of M2 related genes in vitro bone marrow derived macrophages. This skewing towards M2 related genes is dependent on lower mitochondrial membrane potential (Δψ) induced by BHB.

CONCLUSIONS

Collectively, our data shows that BHB production during excess alcohol consumption has an anti-inflammatory and hepatoprotective role through an Hcar2 dependent pathway. This introduces the concept of metabolite-based therapy for AH.

LAY SUMMARY

Alcoholic hepatitis is a life-threatening condition with no approved therapy that occurs unexpectedly in people who consume excess alcohol. The liver makes many metabolites, and we demonstrate that loss of one such metabolite β-hydroxybutyrate occurs in patients with alcoholic hepatitis. This loss can increase alcohol-induced liver injury, and β-hydroxybutyrate can protect from alcohol-induced liver injury via a receptor on liver macrophages. This opens the possibility of metabolite-based therapy for alcoholic hepatitis.

P2Y₂ and Gq/G₁₁ control blood pressure by mediating endothelial mechanotransduction

Elevated blood pressure is a key risk factor for developing cardiovascular diseases. Blood pressure is largely determined by vasodilatory mediators, such as nitric oxide (NO), that are released from the endothelium in response to fluid shear stress exerted by the flowing blood. Previous work has identified several mechanotransduction signaling processes that are involved in fluid shear stress-induced endothelial effects, but how fluid shear stress initiates the response is poorly understood. Here, we evaluated human and bovine endothelial cells and found that the purinergic receptor P2Y2 and the G proteins Gq/G11 mediate fluid shear stress-induced endothelial responses, including [Ca2+]i transients, activation of the endothelial NO synthase (eNOS), phosphorylation of PECAM-1 and VEGFR-2, as well as activation of SRC and AKT. In response to fluid shear stress, endothelial cells released ATP, which activates the purinergic P2Y2 receptor. Mice with induced endothelium-specific P2Y2 or Gq/G11 deficiency lacked flow-induced vasodilation and developed hypertension that was accompanied by reduced eNOS activation. Together, our data identify P2Y2 and Gq/G11 as a critical endothelial mechanosignaling pathway that is upstream of previously described mechanotransduction processes and demonstrate that P2Y2 and Gq/G11 are required for basal endothelial NO formation, vascular tone, and blood pressure.

iTRAQ reveals candidate pancreatic cancer serum biomarkers: influence of obstructive jaundice on their performance

BACKGROUND

The aims of our study were to identify serum biomarkers that distinguish pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) patients from benign pancreatic disease patients and healthy subjects, and to assess the effects of jaundice on biomarker performance.

METHODS

Isobaric tags for relative and absolute quantification were used to compare pooled serum and pancreatic juice samples from a test set of 59 and 25 subjects, respectively. Validation was undertaken in 113 independent subjects.

RESULTS

Candidate proteins Complement C5, inter-α-trypsin inhibitor heavy chain H3, α1-β glycoprotein and polymeric immunoglobulin receptor were elevated in cancer, as were the reference markers CA19-9 and Reg3A. Biliary obstruction had a significant effect on the performance of the markers, in particular within the PDAC group where the presence of jaundice was associated with a significant increase in the levels of all six proteins (P<0.01). Consequently, in the absence of jaundice, proteins showed reduced sensitivity for PDAC patients over benign subjects and healthy controls (HCs). Similarly, in the presence of jaundice, markers showed reduced specificity for PDAC patients over benign subjects with jaundice. Combining markers enabled improved sensitivity for non-jaundiced PDAC patients over HCs and improved specificity for jaundiced PDAC patients over jaundiced benign disease subjects.

CONCLUSIONS

The presence-absence of jaundice in the clinical scenario severely impacts the performance of biomarkers for PDAC diagnosis and has implications for their clinical translation.

Endogenous metabolites as ligands for G protein-coupled receptors modulating risk factors for metabolic and cardiovascular disease

During the last decade, several G protein-coupled receptors activated by endogenous metabolites have been described. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Receptors of endogenous metabolites are expressed in taste cells, the gastrointestinal tract, adipose tissue, endocrine glands, immune cells, or the kidney and are therefore in a position to sense food intake in the gastrointestinal tract or to link metabolite levels to the appropriate responses of metabolic organs. Some of the receptors appear to provide a link between metabolic and neuronal or immune functions. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Tetracycline-inducible protein expression in pancreatic cancer cells: Effects of CapG overexpression

AIM: To establish stable tetracycline-inducible pancreatic cancer cell lines.

METHODS: Suit-2, MiaPaca-2, and Panc-1 cells were transfected with a second generation reverse tetracycline-controlled transactivator protein (rtTA2S-M2), under the control of either a cytomegalovirus (CMV) or a chicken β-actin promoter, and the resulting clones were characterised.

RESULTS: Use of the chicken (β-actin) promoter proved superior for both the production and maintenance of doxycycline-inducible cell lines. The system proved versatile, enabling transient inducible expression of a variety of genes, including GST-P, CYP2E1, S100A6, and the actin capping protein, CapG. To determine the physiological utility of this system in pancreatic cancer cells, stable inducible CapG expressors were established. Overexpressed CapG was localised to the cytoplasm and the nuclear membrane, but was not observed in the nucleus. High CapG levels were associated with enhanced motility, but not with changes to the cell cycle, or cellular proliferation. In CapG-overexpressing cells, the levels and phosphorylation status of other actin-moduating proteins (Cofilin and Ezrin/Radixin) were not altered. However, preliminary analyses suggest that the levels of other cellular proteins, such as ornithine aminotransferase and enolase, are altered upon CapG induction.

CONCLUSION: We have generated pancreatic-cancer derived cell lines in which gene expression is fully controllable.

Smad4 loss is associated with fewer S100A8-positive monocytes in colorectal tumors and attenuated response to S100A8 in colorectal and pancreatic cancer cells

S100A8 and its dimerization partner S100A9 are emerging as important chemokines in cancer. We previously reported that Smad4-negative pancreatic tumors contain fewer stromal S100A8-positive monocytes than their Smad4-positive counterparts. Here, we studied S100A8/A9-expressing cells in colorectal tumors relating their presence to clinicopathological parameters and Smad4 status. Two-dimensional gel electrophoresis (n = 12) revealed variation in the levels of S100A8 protein in colorectal cancer tumors, whereas immunohistochemical analysis (n = 313) showed variation in the numbers of stromal S100A8-positive and S100A9-positive cells. Loss of Smad4 expression was observed in 42/304 (14%) colorectal tumors and was associated with reduced numbers of S100A8-positive (P = 0.03) but not S100A9-positive stromal cells (P = 0.26). High S100A9 cell counts were associated with large tumor sizes (P = 0.0006) and poor differentiation grade (P = 0.036). However, neither S100A8 nor S100A9 cell counts predicted poor survival, except for patients with Smad4-negative tumors (P = 0.02). To address the impact of environmental S100A8/A9 chemokines on tumor cells, we examined the effects of exogenously added S100A8 and S100A9 proteins on cellular migration and proliferation of colorectal and pancreatic cancer cells. S100A8 and S100A9 enhanced migration and proliferation in Smad4-positive and Smad4-negative cancer cells. However, transient depletion of Smad4 resulted in loss of responsiveness to exogenous S100A8, but not S100A9. S100A8 and S100A9 activated Smad4 signaling as evidenced by phosphorylation of Smad2/3; blockade of the receptor for the advanced glycation end products inhibited this response. In conclusion, Smad4 loss alters the tumor's interaction with stromal myeloid cells and the tumor cells' response to the stromal chemokine, S100A8.

Dual-color proteomic profiling of complex samples with a microarray of 810 cancer-related antibodies

Antibody microarrays have the potential to enable comprehensive proteomic analysis of small amounts of sample material. Here, protocols are presented for the production, quality assessment, and reproducible application of antibody microarrays in a two-color mode with an array of 1,800 features, representing 810 antibodies that were directed at 741 cancer-related proteins. In addition to measures of array quality, we implemented indicators for the accuracy and significance of dual-color detection. Dual-color measurements outperform a single-color approach concerning assay reproducibility and discriminative power. In the analysis of serum samples, depletion of high-abundance proteins did not improve technical assay quality. On the contrary, depletion introduced a strong bias in protein representation. In an initial study, we demonstrated the applicability of the protocols to proteins derived from urine samples. We identified differences between urine samples from pancreatic cancer patients and healthy subjects and between sexes. This study demonstrates that biomedically relevant data can be produced. As demonstrated by the thorough quality analysis, the dual-color antibody array approach proved to be competitive with other proteomic techniques and comparable in performance to transcriptional microarray analyses.

Analysis of serum proteins by LC-MS/MS

Serum contains a vast array of proteins, some of which are specific to blood whilst others are secreted into blood from tissues and organs. The so-called tissue leakage factors reveal information about the tissue from which they originate and are therefore of great potential importance as disease biomarkers. There are already a number of blood-borne biomarkers in routine clinical use that aid in the diagnosis or management of cancer. However, there is a pressing need for additional markers, and new methods to find them are under development. Here we provide a protocol for serum protein profiling using liquid chromatography tandem mass spectrometry (LC-MS/MS). Included in this procedure, we detail the pre-processing steps of lipid and high-abundance protein removal. These procedures can also be employed up-stream of quantification methods such as isobaric tags for relative and absolute quantification (iTRAQ). Chapter 12 is devoted to the iTRAQ approach for quantifying proteins, and it is therefore not described in this chapter.

Pancreatic cancer: proteomic approaches to a challenging disease

PURPOSE OF REVIEW

To describe progress in the application of proteomic approaches to advance our understanding of the biology of pancreatic cancer as well as contribute potential protein biomarkers for this disease.

RECENT FINDINGS

Here we review proteomic studies relating to pancreatic cancer that have been published in the past 12 months. We describe novel techniques for the simplification of complex protein samples, focusing particularly on emerging methods for reducing the complexity of blood. We provide examples, where possible, of the application of these novel technologies to pancreatic cancer research.

SUMMARY

Both the range of proteomic-based approaches and their sensitivities for the detection of low-abundance proteins has increased. This provides promise that further research will yield insight into pancreatic cancer, including valuable information on proteins that may ultimately serve as biomarkers for pancreatic cancer.

Expression of glucose transporter isoforms and the insulin receptor during hamster preimplantation embryo development

During preimplantation development, embryos of many species are known to express up to five isoforms of the facilitative glucose transporter proteins (GLUT). Development of hamster blastocysts is inhibited by glucose. We therefore investigated GLUT isoform and insulin receptor (IR) expression in hamster preimplantation embryos cultured in glucose-free medium from the 8-cell stage onwards. We show that GLUT1, 3 and 8 mRNA are constitutively expressed from the 8-cell to the blastocyst stage. The IR is expressed from the morula stage onwards. Messenger RNA of the insulin-responsive GLUT4 was not detected at any stage. GLUT1 and 3 were localised by immunocytochemistry. GLUT1 was expressed in both embryoblast and trophoblast, in the latter, mainly in basal and lateral membranes directed towards the blastocoel and embryoblast. GLUT3 was exclusively localised in the apical membrane of trophoblast cells. We show that hamster preimplantation embryos express several GLUT isoforms thus closely resembling embryos of other mammalian species. Despite endogenous IR expression, the insulin-sensitive isoform GLUT4 was not expressed, indicating that the insulin-mediated glucose uptake known from classical insulin target cells may not be relevant for hamster blastocysts.

Confounding effect of obstructive jaundice in the interpretation of proteomic plasma profiling data for pancreatic cancer

It is well established that variation in sampling, processing and storage protocols can alter the levels of potential biomarkers in serum and plasma. Here, using pancreatic cancer as an example, we demonstrate that consideration of clinical parameters related to the patient's illness is equally important when seeking cancer-specific biomarkers. Bile duct-obstruction is a feature of pancreatic disease that can cause jaundice. Comparing patients with pancreatic cancer, chronic pancreatitis or biliary duct obstruction, we observed that the plasma levels of apolipoprotein A1, transthyretin, and apolipoprotein E, when examined in isolation, were each associated with pancreatic cancer. However, when the effect of bile duct obstruction was considered, only transthyretin levels were independently associated with cancer likelihood. Our results demonstrate the importance of accounting for disease-related confounding factors when analyzing data for the detection of cancer biomarkers.

Confounding effect of obstructive jaundice in the interpretation of proteomic plasma profiling data for pancreatic cancer

It is well established that variation in sampling, processing and storage protocols can alter the levels of potential biomarkers in serum and plasma. Here, using pancreatic cancer as an example, we demonstrate that consideration of clinical parameters related to the patient's illness is equally important when seeking cancer-specific biomarkers. Bile duct-obstruction is a feature of pancreatic disease that can cause jaundice. Comparing patients with pancreatic cancer, chronic pancreatitis or biliary duct obstruction, we observed that the plasma levels of apolipoprotein A1, transthyretin, and apolipoprotein E, when examined in isolation, were each associated with pancreatic cancer. However, when the effect of bile duct obstruction was considered, only transthyretin levels were independently associated with cancer likelihood. Our results demonstrate the importance of accounting for disease-related confounding factors when analyzing data for the detection of cancer biomarkers.

Cell lineage-specific signaling of insulin and insulin-like growth factor I in rabbit blastocysts

The insulin/IGF system plays a critical role in embryo growth and development. We have investigated the expression of insulin receptor (IR) and IGF-I receptor (IGF-IR) and the activation of their downstream pathways in rabbit 6-d-old blastocysts. IR was expressed in embryoblast (Em, inner cell mass) and trophoblast (Tr) cells, whereas IGF-IR was localized mainly in Em. Isoform A (IR-A) represents the main insulin isoform in blastocysts and was found in Em and Tr cells. IR-B was detectable only in Tr. IR/IGF-IR signaling pathways were analyzed after stimulation with insulin (17 nm) or IGF-I (1.3 nm) in cultured blastocysts. Insulin stimulated Erk1/2 in Em and Tr and Akt in Tr but not in Em. IGF-I activated both kinases exclusively in Em. The target genes c-fos (for MAPK kinase-1/Erk signaling) and phosphoenolpyruvate carboxykinase (PEPCK, for PI3K/Akt signaling) were also specifically regulated. Insulin down-regulated PEPCK RNA amounts in Tr by activation of the phosphatidylinositol 3-kinase/Akt pathway. Expression of c-fos by insulin and IGF-I was different with respect to time and fortitude of expression, mirroring again the specific IR and IGF-IR expression patterns in Em and Tr. Taken together, we show that IGF-I acts primarily mitogenic, an effect that is cell lineage-specifically restricted to the Em. By contrast, insulin is the growth factor of the Tr stimulating mitogenesis and down-regulating metabolic responses. As soon as blastocyst differentiation in Em and Tr has been accomplished, insulin and IGF-I signaling is different in both cell lineages, implying a different developmental impact of both growth factors.

Dioxin affects glucose transport via the arylhydrocarbon receptor signal cascade in pluripotent embryonic carcinoma cells

Intoxication by dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads, among other damages, to early embryo loss, fetal malformations, and cardiovascular toxicity. Apart from binding to the arylhydrocarbon receptor (AhR), the mechanism of TCDD-mediated embryo toxicity is still unclear. We investigated possible modes of a TCDD-mediated toxicity, particularly in glucose metabolism, in pluripotent P19 mouse embryonic carcinoma cells. Undifferentiated P19 cells were exposed to 1-100 nM TCDD and characterized for AhR signaling. For studying cell differentiation, P19 cells were exposed to 10 nM TCDD at stage of embryoid body formation, and analyzed on glucose metabolism and cardiac differentiation during the next 3 wk. TCDD treatment activated the AhR-signaling cascade within 1 h, confirmed by AhR translocation, induction of cytochrome P450 1A1 expression, and activation of the xenobiotic response element. Although cell viability and transcription of the cardiac marker protein alpha-myosin heavy chain were affected, TCDD did not inhibit the differentiation of P19 cells to pulsating cardiomyocytes. TCDD significantly down-regulated the expression levels of the glucose transporter (GLUT) isoforms 1 and 3. After 24-h TCDD treatment, GLUT1 was no longer localized in the plasma membrane of P19 cells. The impaired GLUT expression correlated with a lower glucose uptake in 5-d-old embryoid bodies. The TCDD effects were mediated by AhR, as shown by preculture with the AhR antagonist alpha-naphthoflavone. Our data demonstrate that an AhR-mediated disturbance in GLUT expression and insufficient glucose uptake may be major mechanisms in TCDD embryo toxicity.

Differential expression of glucose transporter isoforms during embryonic stem cell differentiation

In mouse blastocysts six facilitative glucose transporter isoforms (GLUT)1-4, 8 and 9 are expressed. We have used the mouse embryonic stem (ES) cell line D3 and spontaneously differentiating embryoid bodies (EB) to investigate GLUT expression and the influence of glucose during differentiation of early embryonic cells. Both ES cells and EBs (2d-20d) expressed GLUT1, 3, and 8, whereas the isoforms 2 and 4 were detectable exclusively in EBs. Differentiation-associated expression of GLUT was analyzed by double staining with stage-specific embryonic antigen (SSEA-1), cytokeratins (CK18, 19), nestin, and desmin. Similar to trophoblast cells in mouse blastocysts the outer cell layer of endoderm-like cells showed a high GLUT3 expression in early EBs. In 20-day-old EBs no GLUT3 protein and only minor GLUT3 mRNA amounts could be detected. A minimal glucose concentration of 5 mM applied during 2 and 8 days of EB culture resulted in up-regulated GLUT4, Oct-4 and SSEA-1 levels and a delay in EB differentiation. We conclude that GLUT expression depends on cellular differentiation and that the expression is modulated by glucose concentration. The developmental and glucose-dependent regulation of GLUT strongly suggests a functional role of glucose and glucose transporters in ES cell differentiation and embryonic development.

Insulin acts via mitogen-activated protein kinase phosphorylation in rabbit blastocysts

The addition of insulin during in vitro culture has beneficial effects on rabbit preimplantation embryos leading to increased cell proliferation and reduced apoptosis. We have previously described the expression of the insulin receptor (IR) and the insulin-responsive glucose transporters (GLUT) 4 and 8 in rabbit preimplantation embryos. However, the effects of insulin on IR signaling and glucose metabolism have not been investigated in rabbit embryos. In the present study, the effects of 170 nM insulin on IR, GLUT4 and GLUT8 mRNA levels, Akt and Erk phosphorylation, GLUT4 translocation and methyl glucose transport were studied in cultured day 3 to day 6 rabbit embryos. Insulin stimulated phosphorylation of the mitogen-activated protein kinase (MAPK) Erk1/2 and levels of IR and GLUT4 mRNA, but not phosphorylation of the phosphatidylinositol 3-kinase-dependent protein kinase, Akt, GLUT8 mRNA levels, glucose uptake or GLUT4 translocation. Activation of the MAPK signaling pathway in the absence of GLUT4 translocation and of a glucose transport response suggest that in the rabbit preimplantation embryo insulin is acting as a growth factor rather than a component of glucose homeostatic control.

Two insulin-responsive glucose transporter isoforms and the insulin receptor are developmentally expressed in rabbit preimplantation embryos

Glucose is the most important energy substrate for mammalian blastocysts. Its uptake is mediated by glucose transporters (GLUT). In muscle and adipocyte cells insulin stimulates glucose uptake by activation of the insulin receptor (IR) pathway and translocation of GLUT4. GLUT4 is expressed in bovine preimplantation embryos. A new insulin-responsive isoform, GLUT8, was recently described in mouse blastocysts. Thus, potentially, two insulin-responsive isoforms are expressed in early embryos. The mechanism of insulin action on embryonic cells, however, is still not clear. In the present study expression of IR, GLUT1, 2, 3, 4, 5 and 8 was studied in rabbit preimplantation embryos using RT-PCR, Western blotting and immunohistochemistry. The rabbit mRNA sequences for the complete coding region of IR, GLUT4 and a partial GLUT8 sequence were determined by RACE-PCR and sequencing. GLUT4 was expressed in 3-day-old morulae and in 4- and 6-day-old blastocysts. IR and GLUT8 transcripts were detectable only in blastocysts. Blastocysts also expressed GLUT1 and 3, but not GLUT2 and 5. Transcript numbers of GLUT4 and 8 were higher in trophoblast than in embryoblast cells. Translation of IR, GLUT4 and 8 proteins in blastocysts was confirmed by Western blotting. GLUT4 was localized mainly in the membrane and in the perinuclear region in trophoblast cells while in embryoblast cells its localization was predominantly in the perinuclear cytoplasm. The possible function(s) of two insulin-responsive isoforms, GLUT4 and GLUT8, in rabbit preimplantation embryos needs further investigation. It may not necessarily be linked to insulin-stimulated glucose transport.

Expression of the insulin-responsive glucose transporter isoform 4 in blastocysts of C57/BL6 mice

Glucose is the most important energy substrate for mammalian blastocysts. In preimplantation embryos glucose uptake is mainly mediated by facilitative glucose transporter molecules (GLUT). Employing RT-PCR in 3.5-day-old mouse blastocysts of strain C57/BL6 we have investigated the expression of the GLUT isoforms 1-4 and 8. We could not only detect GLUT 1, 3 and 8 but, in contrast to earlier studies, also the insulin-responsive isoform 4. GLUT2 was not expressed. The specificity for GLUT4 amplification was verified by sequence analysis. GLUT4 protein was localized by immunohistochemistry with two GLUT4 antibodies. It was found in ICM and trophoblast cells in the cytoplasmic compartment with a strong perinuclear staining. This is the first report on the expression of the insulin-sensitive GLUT4 isoform in mouse preimplantation embryos.