Aldehyde dehydrogenase 1 activity in the developing human pancreas modulates retinoic acid signalling in mediating islet differentiation and survival.

AIMS/HYPOTHESIS: Aldehyde dehydrogenase 1 (ALDH1), a human stem-cell marker, is an enzyme responsible for converting retinaldehydes to retinoic acids (RAs) to modulate cell differentiation. However, data on expression levels and functional roles of ALDH1 during human fetal pancreatic development are limited. The focus of this study was to characterise ALDH1 expression patterns and to determine its functional role in islet cell differentiation. METHODS: The presence of ALDH1 in the human fetal pancreas (8-22 weeks) was characterised by microarray, quantitative RT-PCR, western blotting and immunohistological approaches. Isolated human fetal islet-epithelial cell clusters were treated with ALDH1 inhibitors, retinoic acid receptor (RAR) agonists and ALDH1A1 small interfering (si)RNA. RESULTS: In the developing human pancreatic cells, high ALDH1 activity frequently co-localised with key stem-cell markers as well as endocrine transcription factors. A high level of ALDH1 was expressed in newly differentiated insulin(+) cells and this decreased as development progressed. Pharmacological inhibition of ALDH1 activity in human fetal islet-epithelial cell clusters resulted in reduced endocrine cell differentiation and increased cell apoptosis, and was reversed with co-treatment of RAR/RXR agonists. Furthermore, siRNA knockdown of ALDH1A1 significantly decreased RAR expression and induced cell apoptosis via suppression of the phosphoinositide 3-kinase (PI3K) pathway and activation of caspase signals. CONCLUSIONS/INTERPRETATION: Our findings indicate that ALDH1(+) cells represent a pool of endocrine precursors in the developing human pancreas and that ALDH1 activity is required during endocrine cell differentiation. Inhibition of ALDH1-mediated retinoid signalling impairs human fetal islet cell differentiation and survival.

Investigating the use of hair to assess polybrominated diphenyl ether exposure retrospectively.

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) are chemicals that are added to a variety of consumer products as flame-retardants and have been classified as emerging endocrine disruptors. They are persistent and have been detected in humans. Previous studies have suggested that hair is a suitable matrix for examining human exposure to organic pollutants such as PBDEs. It is believed that the majority of exposure is from our indoor environment. The aim of this study was to investigate the changes in PBDE patterns and levels along the hair shaft, by using segmental analysis to retrospectively assess long-term exposure over a 1-year period. METHODS: Questionnaires and hair samples from 65 women were collected at the Hospital for Sick Children, in Toronto, as part of a larger study. To assess long-term stability, hair samples were separated into 4- and 3-cm segments representing a 1-year period. Hair segments were analyzed for levels of 8 PBDE congeners, BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, BDE-183, and BDE-209 on gas chromatography-mass spectrometry (MS). A Friedman test was used to detect the differences in exposure among segments, and factors such as dietary habits, hair care routine, and site of residence were investigated to determine if they might affect hair levels. RESULTS: A significant increase (P < 0.0001) in total PBDEs was seen among segments moving from proximal (root end) to distal along the hair shaft (median in pg/mg): first (33.3), second (43.0), third (61.6), and fourth (75.5) segments. Significantly lower levels of PBDEs were observed in artificially colored hair samples (P = 0.032), and a significant increase in PBDE levels was observed in women who consumed meat on a daily basis as opposed to weekly consumption (P = 0.040). CONCLUSIONS: The increase in PBDEs along the hair shaft suggests that hair PBDEs may be influenced by diet and artificial coloring. More work is needed to validate the use of PBDEs in hair as a biomarker of long-term exposure.

Hair as a biomarker of systemic exposure to polybrominated diphenyl ethers.

The efficacy of using hair as a biomarker for exposure to polybrominated diphenyl ether (PBDE) flame retardants was assessed in humans and an animal model. Paired human hair and serum samples were obtained from adult men and women (n = 50). In parallel, hair, serum, liver, and fat were collected from adult male Sprague-Dawley rats exposed to increasing doses of the PBDE mixture found in house dust for 70 days via the diet. All samples were analyzed by GC-MS for eight common PBDEs: BDE-28, -47, -99, -100, -153, -154, -183, and -209. Paired human hair and serum samples had five congeners (BDE-28, -47, -99, -100, and -154) with significant individual correlations (0.345-0.566). In rat samples, BDE-28 and BDE-183 were frequently below the level of detection. Significant correlations were observed for BDE-47, -99, -100, -153, -154, and -209 in rat hair, serum, liver, and fat across doses, with r values ranging from 0.803 to 0.988; weaker correlations were observed between hair and other tissues when data from the lowest dose group or for BDE-209 were analyzed. Thus, human and rat hair PBDE measurements correlate strongly with those in alternative matrices, validating the use of hair as a noninvasive biomarker of long-term PBDE exposure.

Exposure of men living in the greater Montreal area to organophosphate esters: Association with hormonal balance and semen quality.

Exposure to organophosphate esters (OPEs) is extensive, yet few studies have investigated their association with hormone levels or semen quality. Here, we studied the association between urinary concentrations of OPEs and their metabolites with hormone levels and semen parameters in men (n = 117) predominantly in the 20-29 years age range who were recruited from the greater Montreal area between 2009 and 2012. Urine, serum, and semen samples were analyzed for OPEs, hormones, and semen quality, respectively. Bis(2-ethylhexyl) phosphate (BEHP), bis(2,4-di-tert-butylphenyl) hydrogen phosphate (B2,4DtBPP), tris(2-chloroisopropyl) phosphate (TCIPP), diphenyl phosphate (DPHP), bis (2-butoxyethyl) phosphate (BBOEP) and di-cresyl phosphate (DCPs) were detected in urine at a frequency ≥ 95%. The highest geometric mean concentration was observed for DPHP (18.54 ng/mL) and the second highest was B2,4DtBPP (6.23 ng/mL). Associations between a doubling in analyte concentrations in urine and hormone levels and semen quality parameters were estimated using multivariable linear regression. B2,4DtBPP levels were positively associated with total T3 (ß = 0.09; 95% CI: 0.01, 0.17). DPHP was inversely associated with estradiol (ß = -2.56; 95% CI: -5.00, -0.17), and TCIPP was inversely associated with testosterone (ß = -0.78; 95% CI: -1.40, -0.17). Concentrations of BCIPP were inversely associated with sperm concentrations (ß = -7.76; 95% CI: -14.40, -0.61), progressive motility (ß = - 4.98; 95% CI: -8.71, -1.09), and the sperm motility index (ß = -9.72; 95% CI: -17.71, -0.96). In contrast, urinary DPHP concentrations were positively associated with the sperm motility (ß = 4.37; 95% CI: 0.76, 8.12) and fertility indices (ß = 6.64; 95% CI: 1.96, 11.53). Thus, OPE detection rates were high and exposure to several OPEs was associated with altered hormone levels and semen parameters. The possibility that OPEs affect male reproduction warrants further investigation.

p75(NTR) induces apoptosis in medulloblastoma cells.

The classic medulloblastoma (CMB) and the desmoplastic medulloblastoma (DMB) subtypes represent the major medulloblastoma variants. In contrast to CMB, DMB display high levels of the low-affinity nerve growth factor receptor p75(NTR) . Given the reports of a better clinical course of DMB, we hypothesized that p75(NTR) might act as a tumor suppressor in medulloblastomas. In a large set of medulloblastomas, p75(NTR) was screened for mutations, and its mRNA expression and the DNA methylation status of its 5'-region were assessed. p75(NTR) immunostainings were performed in wild-type murine cerebella and medulloblastomas arising in patched heterozygous mice, and murine cerebellar granule cell precursors (GCP) were analyzed in vitro. Medulloblastoma cells engineered to express p75(NTR) were characterized flow cytometrically and morphologically. One CMB displayed a mutation of the p75(NTR) coding sequence. p75(NTR) mRNA levels clearly delineated DMB and CMB; however, CpG island hypermethylation was excluded as the cause of low p75(NTR) expression in CMB. Sonic Hedgehog-treated GCP showed elevated p75(NTR) expression, and strong expression of p75(NTR) was detected in the external granule cell layer of wild-type mice and in murine ptc(±) medulloblastomas. CMB cells overexpressing p75(NTR) displayed a significant increase in apoptosis. In summary, our data link activated Hedgehog signaling in DMB with p75(NTR) expression and characterize p75(NTR) as a biologically relevant inductor of apoptosis in MB.

Activation of Pancreatic Stellate Cells Is Beneficial for Exocrine but Not Endocrine Cell Differentiation in the Developing Human Pancreas.

Pancreatic stellate cells (PaSCs) are non-endocrine, mesenchymal-like cells that reside within the peri-pancreatic tissue of the rodent and human pancreas. PaSCs regulate extracellular matrix (ECM) turnover in maintaining the integrity of pancreatic tissue architecture. Although there is evidence indicating that PaSCs are involved in islet cell survival and function, its role in islet cell differentiation during human pancreatic development remains unclear. The present study examines the expression pattern and functional role of PaSCs in islet cell differentiation of the developing human pancreas from late 1st to 2nd trimester of pregnancy. The presence of PaSCs in human pancreata (8-22 weeks of fetal age) was characterized by ultrastructural, immunohistological, quantitative RT-PCR and western blotting approaches. Using human fetal PaSCs derived from pancreata at 14-16 weeks, freshly isolated human fetal islet-epithelial cell clusters (hIECCs) were co-cultured with active or inactive PaSCs in vitro. Ultrastructural and immunofluorescence analysis demonstrated a population of PaSCs near ducts and newly formed islets that appeared to make complex cell-cell dendritic-like contacts. A small subset of PaSCs co-localized with pancreatic progenitor-associated transcription factors (PDX1, SOX9, and NKX6-1). PaSCs were highly proliferative, with significantly higher mRNA and protein levels of PaSC markers (desmin, αSMA) during the 1st trimester of pregnancy compared to the 2nd trimester. Isolated human fetal PaSCs were identified by expression of stellate cell markers and ECM. Suppression of PaSC activation, using all-trans retinoic acid (ATRA), resulted in reduced PaSC proliferation and ECM proteins. Co-culture of hIECCs, directly on PaSCs or indirectly using Millicell® Inserts or using PaSC-conditioned medium, resulted in a reduction the number of insulin+ cells but a significant increase in the number of amylase+ cells. Suppression of PaSC activation or Notch activity during the co-culture resulted in an increase in beta-cell differentiation. This study determined that PaSCs, abundant during the 1st trimester of pancreatic development but decreased in the 2nd trimester, are located near ductal and islet structures. Direct and indirect co-cultures of hIECCs with PaSCs suggest that activation of PaSCs has opposing effects on beta-cell and exocrine cell differentiation during human fetal pancreas development, and that these effects may be dependent on Notch signaling.

beta1 integrin/FAK/ERK signalling pathway is essential for human fetal islet cell differentiation and survival.

beta1 integrin and collagen matrix interactions regulate the survival of cells by associating with focal adhesion kinase (FAK) and initiating MAPK/ERK signalling, but little is known about these signalling pathways during human fetal islet ontogeny. The purpose of this study was to investigate whether beta1 integrin/FAK activation of the MAPK/ERK pathway regulates human fetal islet cell expression of endocrine cell markers and survival. Isolated human (18-21 weeks fetal age) islet-epithelial cell clusters, cultured on collagen I, were examined using beta1 integrin blocking antibody, beta1 integrin siRNA and FAK expression vector. Perturbing beta1 integrin function in the human fetal islet-epithelial cell clusters resulted in a marked decrease in cell adhesion, in parallel with a reduction in the number of cells expressing PDX-1, insulin and glucagon (p < 0.05). beta1 integrin blockade disorganized focal adhesion contacts in the PDX-1(+) cells and decreased activation of FAK and ERK1/2 signalling in parallel with an increase in expression of cleaved caspases 9 and 3 (p < 0.01). Similar results were obtained following an siRNA knock-down of beta1 integrin expression. In contrast, over-expression of FAK not only increased phospho-ERK and the expression of PDX-1, insulin and glucagon (p < 0.05) but also abrogated the decreases in phospho-ERK and PDX-1 by beta1 integrin blockade. This study demonstrates that activation of the FAK/ERK signalling cascade by beta1 integrin is involved in the differentiation and survival of human fetal pancreatic islet cells.

Cytosolic prion protein is the predominant anti-Bax prion protein form: exclusion of transmembrane and secreted prion protein forms in the anti-Bax function.

Prion protein (PrP) prevents Bax-mediated cell death by inhibiting the initial Bax conformational change that converts cytosolic Bax into a pro-apoptotic protein. PrP is mostly a glycophosphatidylinositol-anchored cell surface protein but it is also retrotranslocated into cytosolic PrP (CyPrP) or can become a type 1 or type 2 transmembrane protein. To determine the form and subcellular location of the PrP that has anti-Bax function, we co-expressed various Syrian hamster PrP (SHaPrP) mutants that favour specific PrP topologies and subcellular localization with N-terminally green fluorescent protein tagged pro-apoptotic Bax (EGFP-Bax) in MCF-7 cells and primary human neurons. Mutants that generate both CyPrP and secreted PrP ((Sec)PrP) or only CyPrP have anti-Bax activity. Mutants that produce (Ctm)PrP or (Ntm)PrP lose the anti-Bax activity, despite their ability to also make (Sec)PrP. Transmembrane-generating mutants do not produce CyPrP and both normal and cognate mutant forms of CyPrP rescue against the loss of anti-Bax activity. (Sec)PrP-generating constructs also produce non-membrane attached (Sec)PrP. However, this form of PrP has minimal anti-Bax activity. We conclude that CyPrP is the predominant form of PrP with anti-Bax function. These results imply that the retrotranslocation of PrP encompasses a survival function and is not merely a pathway for the proteasomal degradation of misfolded protein.

Defective retrotranslocation causes loss of anti-Bax function in human familial prion protein mutants.

Prion protein (PrP) inhibits the activation of proapoptotic Bax in primary human neurons and MCF-7 cells. Because neuronal apoptosis occurs in human prion diseases, here we examine the anti-Bax function of familial PrP mutants. All Creutzfeldt-Jakob disease and fatal familial insomnia-associated prion protein mutations partially or completely lose the anti-Bax function in human neurons and, except for A117V and V203I, in MCF-7 cells. The ability of the mutants to protect against Bax-mediated cell death is divided into three groups: (1) group I, retention of anti-Bax function in both the Val129 and Met129 mutants; (2) group II, retention of anti-Bax function only in Val129 mutants; and (3) group III, reduction or no anti-Bax function in Val129 and Met129 mutants. The loss of anti-Bax function in these PrP mutants correlates completely with a significant decrease in the production of cytosolic PrP, a form of PrP shown previously to have anti-Bax function in human neurons. Cotransfection of the full-length PrP mutants with wild-type or mutant cytosolic PrP, but not with wild type full-length PrP, rescues the anti-Bax function of PrP. The results show that the failure of PrP mutants to produce cytosolic PrP is responsible for the loss of anti-Bax function and that the effect of the PrP mutants is dominant over wild-type PrP. Furthermore, these results imply that misfolded PrP that escapes retrotranslocation could accumulate at the cell surface and cause neuronal dysfunction.

Exposure to polybrominated diphenyl ethers and phthalates in healthy men living in the greater Montreal area: A study of hormonal balance and semen quality.

Studies investigating the associations between exposure of young men to polybrominated diphenyl ethers (PBDEs) or phthalates and hormone levels or semen quality have produced inconsistent results. Our goal was to investigate the association of exposure to PBDEs or phthalate metabolites with changes in markers of thyroid (TSH, free T3 and free T4) and reproductive function (sperm concentrations, motility, and quality; serum LH and testosterone) in 153 healthy young men from the greater Montreal area. Using covariate-adjusted models, we found that each 10-fold increase in BDE-47 was associated with lower TSH levels (-17.3%; 95% CI: -31.5, 0.0; p = 0.05). BDE-47 exposure was also associated with a decrease in sperm concentration (-19.7%; 95% CI: -36.8; 2.0; p = 0.07) and motility (-25.5%; 95% CI: -44.5, 0.1; p = 0.05). Trends towards decreases in these parameters were also observed in association with exposure to BDE-100 and the sum of BDE-47, -99, and -100 (∑3BDEs). These associations were not accompanied by effects on sperm chromatin quality, as assessed with the HT-COMET assay. There were no substantial associations between urinary phthalate metabolite concentrations, either individually or grouped by molecular weight or parent compound, and sperm quality parameters; however, there was a positive association between elevated MECCP and free T4 (0.98; 95% CI: 0.02, 1.94; p = 0.05). Inverse associations between BDE-47 and ∑3BDEs and free T3 and positive associations between MEHP and free T3 were stronger among individuals with BMI ≥ 25, suggesting that weight status may modify the effects of these endocrine disrupting chemicals.

Erratum: "A Case-Control Study of Maternal Polybrominated Diphenyl Ether (PBDE) Exposure and Cryptorchidism in Canadian Populations".

[This corrects the article DOI: 10.1289/EHP522.].

Phosphatidylinositol 3'-kinase/AKT signaling is activated in medulloblastoma cell proliferation and is associated with reduced expression of PTEN.

PURPOSE: Medulloblastomas represent the most frequent malignant brain tumors of childhood. They are supposed to originate from cerebellar neural precursor cells. Recently, it has been shown that Sonic Hedgehog-induced formation of medulloblastoma in an animal model is significantly enhanced by activation of the phosphatidylinositol 3'-kinase (PI3K) signaling pathway. EXPERIMENTAL DESIGN: To examine a role for PI3K/AKT signaling in the molecular pathogenesis of human medulloblastoma, we did an immunohistochemical study of the expression of Ser473-phosphorylated (p)-AKT protein in 22 medulloblastoma samples: All samples displayed p-AKT expression. To investigate if an activated PI3K/AKT pathway is required for medulloblastoma cell growth, we treated five human medulloblastoma cell lines with increasing concentrations of the PI3K inhibitor LY294002 and analyzed cellular proliferation and apoptosis. The antiproliferative effect could be antagonized by overexpressing constitutively active AKT. As the activation of PI3K/AKT signaling may be associated with alterations of the PTEN gene located at 10q23.3, a chromosomal region subject to frequent allelic losses in medulloblastoma, we screened PTEN for mutations and mRNA expression. RESULTS: Proliferation of all of the medulloblastoma cell lines was dependent on PI3K/AKT signaling, whereas apoptosis was not prominently affected. Allelic loss was detected in 16% of the cases. One medulloblastoma cell line was found to carry a truncating mutation in the PTEN coding sequence. Even more important, PTEN mRNA and protein levels were found to be significantly lower in medulloblastomas compared with normal cerebellar tissue of different developmental stages. Reduction of PTEN expression was found to be associated with PTEN promoter hypermethylation in 50% of the tumor samples. CONCLUSIONS: We conclude that activation of the PI3K/AKT pathway constitutes an important step in the molecular pathogenesis of medulloblastoma and that dysregulation of PTEN may play a significant role in this context.

A Case-Control Study of Maternal Polybrominated Diphenyl Ether (PBDE) Exposure and Cryptorchidism in Canadian Populations.

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) are flame retardants found in North American household products during the past four decades. These chemicals leach out in dust as products age, exposing individuals daily through inhalation and ingestion. Animal studies suggest that PBDEs disrupt sex hormones and adversely affect development of the reproductive system. OBJECTIVES: In the present study, we examined whether there is a link between maternal hair PBDE concentrations and the risk of cryptorchidism (undescended testes) in male infants; testis descent is known to be dependent on androgens. METHODS: Full-term male infants were recruited through clinics in Montreal, Toronto, and London, Canada. Boys with cryptorchidism at 3-18 months of age (n=137) were identified by pediatric urologists and surgeons; similar-aged controls (n=158) had no genitourinary abnormalities as assessed by pediatricians. Eight BDE congeners (BDE-28, -47, -99, -100, -153, -154, -183, -209) were measured by GC-MS (gas chromatography-mass spectrometry) in maternal hair samples collected at the time of recruitment. RESULTS: The ∑PBDE geometric mean for maternal hair was 45.35 pg/mg for controls and 50.27 pg/mg for cases; the concentrations of three BDEs (BDE-99, -100, and -154) were significantly higher in cases than controls in unadjusted models. In adjusted models, every 10-fold increase in the concentration of maternal hair BDE-99 [OR=2.53 (95% CI: 1.29, 4.95) or BDE-100 [OR=2.45 (95% CI: 1.31, 4.56)] was associated with more than a doubling in the risk of cryptorchidism. BDE-154 [OR=1.88 (95% CI: 1.08, 3.28) was also significant. CONCLUSIONS: Our results suggest that maternal exposure to BDE-99, -100, and -154 may be associated with abnormal migration of testes in the male fetus. This may be due to the anti-androgenic properties of the PBDEs. https://doi.org/10.1289/EHP522.

Role of DNA methylation in expression control of the IKZF3-GSDMA region in human epithelial cells.

Chromosomal region 17q12-q21 is associated with asthma and harbors regulatory polymorphisms that influence expression levels of all five protein-coding genes in the region: IKAROS family zinc finger 3 (Aiolos) (IKZF3), zona pellucida binding protein 2 (ZPBP2), ORMDL sphingolipid biosynthesis regulator 3 (ORMDL3), and gasdermins A and B (GSDMA, GSDMB). Furthermore, DNA methylation in this region has been implicated as a potential modifier of the genetic risk of asthma development. To further characterize the effect of DNA methylation, we examined the impact of treatment with DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) that causes DNA demethylation, on expression and promoter methylation of the five 17q12-q21 genes in the human airway epithelium cell line NuLi-1, embryonic kidney epithelium cell line 293T and human adenocarcinoma cell line MCF-7. 5-aza-dC treatment led to upregulation of expression of GSDMA in all three cell lines. ZPBP2 was upregulated in NuLi-1, but remained repressed in 293T and MCF-7 cells, whereas ORMDL3 was upregulated in 293T and MCF-7 cells, but not NuLi-1. Upregulation of ZPBP2 and GSDMA was accompanied by a decrease in promoter methylation. Moreover, 5-aza-dC treatment modified allelic expression of ZPBP2 and ORMDL3 suggesting that different alleles may respond differently to treatment. We also identified a polymorphic CTCF-binding site in intron 1 of ORMDL3 carrying a CG SNP rs4065275 and determined its methylation level. The site's methylation was unaffected by 5-aza-dC treatment in NuLi-1 cells. We conclude that modest changes (8-13%) in promoter methylation levels of ZPBP2 and GSDMA may cause substantial changes in RNA levels and that allelic expression of ZPBP2 and ORMDL3 is mediated by DNA methylation.

Stem cell factor/c-Kit interactions regulate human islet-epithelial cluster proliferation and differentiation.

Stem cell factor (SCF), a progenitor cell growth factor, binds to and activates the c-Kit receptor tyrosine kinase, which is critical for early stem cell differentiation in haematopoiesis and gametogenesis. Nothing is known regarding these interactions during islet development in the human fetal pancreas. The present study was to investigate whether an increase in c-Kit receptor activity in isolated human fetal islet-epithelial clusters, by giving exogenous SCF, would promote beta-cell development. In the intact fetal pancreas, SCF and c-Kit were observed co-localizing with cytokeratin 19 in both ductal and newly forming islet cells. Islet cells isolated from 14 to 16 weeks fetal pancreata were cultured with SCF (50 ng/ml) or vehicle for 48 h. We observed an increase in the number of c-Kit-, pancreatic and duodenal homeobox gene 1- (PDX-1-), insulin- and glucagon-expressing cells in the SCF-treated group (PDX-1 and insulin, p < 0.05). PDX-1 and c-Kit mRNA levels were also up-regulated in the SCF group (PDX-1, p < 0.05), with no change in preproinsulin or proglucagon gene expression. Co-localization of insulin with PDX-1 or c-Kit was observed frequently in SCF-treated cultures. A significantly (p < 0.05) greater proliferative capacity of islet-epithelial clusters was found in the SCF group in parallel with increased (p < 0.02) phosphorylation of Akt in a phosphatidylinositol-3 kinase (PI3K)-dependent manner. Our results demonstrate that SCF/c-Kit interactions are likely to be involved in mediating islet cell differentiation and proliferation during human fetal pancreatic development, and that phosphorylated Akt may have a role downstream of SCF/c-Kit signaling.

Role for beta1 integrin and its associated alpha3, alpha5, and alpha6 subunits in development of the human fetal pancreas.

The integrin receptors play a major role in tissue morphogenesis and homeostasis by regulating cell interactions with extracellular matrix proteins. We have examined the expression pattern of integrin subunits in the human fetal pancreas (8-20 weeks fetal age) and the relevance of beta1 integrin function for insulin gene expression and islet cell survival. Its subunits alpha3, alpha5, and alpha6 beta1 integrins are expressed in ductal cells at 8 weeks, before glucagon- and insulin-immunoreactive cells bud off; their levels gradually increase in both ductal cells and islet clusters up to 20 weeks. Colocalization of alpha3, alpha5 and alpha6 beta1 integrins with endocrine cell markers was frequently observed in 8- to 20-week fetal pancreatic cells. When the beta1 integrin receptor was functionally blocked in cultured islet-epithelial clusters with a beta1 immunoneutralizing antibody or following transient beta1 integrin small interfering RNA treatment, there was inhibition of cell adhesion to extracellular matrices, decreased expression of insulin, and increased cell apoptosis. These data offer evidence for dynamic and cell-specific changes in integrin expression during human pancreatic islet neogenesis. They also provide an initial insight into a molecular basis for cell-matrix interactions during islet development and suggest that beta1 integrin plays a vital role in regulating islet cell adhesion, gene expression, and survival.

Estrogen and androgen protection of human neurons against intracellular amyloid beta1-42 toxicity through heat shock protein 70.

Intracellular amyloidbeta peptide (iAbeta1-42) accumulates in the Alzheimer's disease brain before plaque and tangle formation (Gouras et al., 2000) and is extremely toxic to human neurons (Zhang et al., 2002). Here, we investigated whether androgen and estrogen could prevent iAbeta1-4) toxicity, because both these hormones have a wide range of neuroprotective actions. At physiological concentrations, 17-beta-estradiol, testosterone, and methyl testosterone reduce iAbeta1-42-induced cell death by 50% in neurons treated after the injection and by 80-90% in neurons treated 1 hr before the injection. The neuroprotective action of the hormones is mediated by receptors, because the estrogen receptor (ER) antagonist tamoxifen and the androgen receptor (AR) antagonist flutamide completely block the estrogen- and androgen-mediated neuroprotection, respectively. Transcriptional activity is required for the neuroprotective action, because dominant negative forms of the receptors that block the transcriptional activity of the ER and AR prevent estrogen- and androgen-mediated neuroprotection. Proteomics followed by Western blot analyses identified increased levels of heat shock protein 70 (Hsp70) in testosterone- and estrogen-treated human neurons. Comicroinjection of Hsp70 with the iAbeta1-42 blocks the toxicity of iAbeta1-42. We conclude that estrogen and androgens protect human neurons against iAbeta1-42 toxicity by increasing the levels of Hsp70 in the neurons.

Exploitation of astrocytes by glioma cells to facilitate invasiveness: a mechanism involving matrix metalloproteinase-2 and the urokinase-type plasminogen activator-plasmin cascade.

The presence of reactive astrocytes around glioma cells in the CNS suggests the possibility that these two cell types could be interacting. We addressed whether glioma cells use the astrocyte environment to modulate matrix metalloproteinase-2 (MMP-2), a proteolytic enzyme implicated in the invasiveness of glioma cells. We found that astrocytes in culture produce significant amounts of the pro-form of MMP-2 but undetectable levels of active MMP-2. However, after coculture with the U251N glioma line, astrocyte pro-MMP-2 was converted to the active form. The mechanism of pro-MMP-2 activation in glioma-astrocyte coculture was investigated and was found to involve the urokinase-type plasminogen activator (uPA)-plasmin cascade whereby uPA bound to uPA receptor (uPAR), leading to the conversion of plasminogen to plasmin. The latter cleaved pro-MMP-2 to generate its active form. Furthermore, key components (i.e., uPAR, uPA, and pro-MMP-2) were contributed principally by astrocytes, whereas the U251N glioma cells provided plasminogen. In correspondence with this biochemical cascade, the transmigration of U251N cells through Boyden invasion chambers coated with an extracellular matrix barrier was increased significantly in the presence of astrocytes, and this was inhibited by agents that disrupted the uPA-plasmin cascade. Finally, using resected human glioblastoma specimens, we found that tumor cells, but not astrocytes, expressed plasminogen in situ. We conclude that glioma cells exploit their astrocyte environment to activate MMP-2 and that this leads to the increased invasiveness of glioma cells.

p75 neurotrophin receptor protects primary cultures of human neurons against extracellular amyloid beta peptide cytotoxicity.

The cytotoxicity of extracellular amyloid beta peptide (Abeta) has been clearly demonstrated in many cell types. In contrast, primary human neurons in culture are resistant to extracellular Abeta-mediated toxicity. Here, we investigate the involvement of p75 neurotrophin receptor (p75NTR) in Abeta-treated human neurons. We find that Abeta1-40 and Abeta1-42, but not the reverse control peptide, Abeta40-1, rapidly increase the levels of p75NTR in a specific and dose-dependent manner. In contrast to observations in cell lines, enhanced expression of p75NTR in human neurons via a herpes simplex virus amplicon vector does not increase the susceptibility of neurons to Abeta. Unexpectedly, inhibition of p75NTR expression with an antisense expression construct or incubation of the cells with an antibody to the extracellular domain of p75NTR sensitizes human neurons to extracellular nonfibrillar or fibrillar Abeta1-42 cytotoxicity. Unlike intracellular Abeta, extracellular Abeta toxicity is independent of p53 and Bax activity. However, Abeta toxicity is inhibited by caspase inhibitors and the glycogen synthase kinase 3beta inhibitor lithium. Neuroprotection against Abeta is phosphatidylinositide 3-kinase dependent but Akt independent. These results are consistent with a neuroprotective role for p75NTR against extracellular Abeta toxicity in human neurons.

Epigenetic silencing of the HIC-1 gene in human medulloblastomas.

The HIC-1 (hypermethylated in cancer) candidate tumor suppressor gene is located on chromosome 17p13.3, a region frequently deleted in medulloblastomas (MBs). MBs arising in the cerebellum represent the most common malignant brain tumors in children. In this study we have analyzed the sequence, methylation, and expression status of the HIC-1 gene in MBs. Hypermethylation of the 5'UTR and/or second exon of HIC-1 was detected in 33/39 (85%) of MB biopsies and in 7/8 (88%) of MB cell lines by methylation-specific PCR. There was a significant correlation (p < 0.001) between HIC-1 methylation and lack of transcription as determined by competitive RT-PCR. Treatment of the MB cell lines Daoy and MEB-MED-8A with 5-aza-2'deoxycytidine led to re-expression of HIC-1 transcripts, indicating a silencing of HIC-1 by CpG island methylation. Mutation analysis of the coding region of HIC-1 revealed a single deletion leading to an in-frame deletion of 4 amino acids in the second exon of HIC-1 (1/68, 1.5%). Our data indicate that a significant number of MBs exhibit strikingly reduced HIC-1 expression caused by altered CpG island methylation. These data suggest that epigenetic silencing of HIC-1 may well contribute to the pathogenesis in the majority of MBs.