Tetracycline-regulated expression of VEGF-A in beta cells induces angiogenesis: improvement of engraftment following transplantation.

Early revascularization of pancreatic islet cells after transplantation is crucial for engraftment, and it has been suggested that vascular endothelial growth factor-A (VEGF-A) plays a significant role in this process. Although VEGF gene therapy can improve angiogenesis, uncontrolled VEGF secretion can lead to vascular tumor formation. Here we have explored the role of temporal VEGF expression, controlled by a tetracycline (TC)-regulated promoter, on revascularization and engraftment of genetically modified beta cells following transplantation. To this end, we modified the CDM3D beta cell line using a lentiviral vector to promote secretion of VEGF-A either in a TC-regulated (TET cells) or a constitutive (PGK cells) manner. VEGF secretion, angiogenesis, cell proliferation, and stimulated insulin secretion were assessed in vitro. VEGF secretion was increased in TET and PGK cells, and VEGF delivery resulted in angiogenesis, whereas addition of TC inhibited these processes. Insulin secretion by the three cell types was similar. We used a syngeneic mouse model of transplantation to assess the effects of this controlled VEGF expression in vivo. Time to normoglycemia, intraperitoneal glucose tolerance test, graft vascular density, and cellular mass were evaluated. Increased expression of VEGF resulted in significantly better revascularization and engraftment after transplantation when compared to control cells. In vivo, there was a significant increase in vascular density in grafted TET and PGK cells versus control cells. Moreover, the time for diabetic mice to return to normoglycemia and the stimulated plasma glucose clearance were also significantly accelerated in mice transplanted with TET and PGK cells when compared to control cells. VEGF was only needed during the first 2-3 weeks after transplantation; when removed, normoglycemia and graft vascularization were maintained. TC-treated mice grafted with TC-treated cells failed to restore normoglycemia. This approach allowed us to switch off VEGF secretion when the desired effects had been achieved. TC-regulated temporal expression of VEGF using a gene therapy approach presents a novel way to improve early revascularization and engraftment after islet cell transplantation.

Responsiveness of astrocytes in serum-free aggregate cultures to epidermal growth factor: dependence on the cell cycle and the epidermal growth factor concentration.

Serum-free aggregating cell cultures of fetal rat telencephalon treated with low doses (0.5 nM) of epidermal growth factor (EGF) showed a small, transient increase in DNA synthesis but no significant changes in total DNA and protein content. By contrast, treatment with high doses (13 nM) of EGF caused a marked stimulation of DNA synthesis as well as a net increase in DNA and protein content. The expression of the astrocyte-specific enzyme, glutamine synthetase, was greatly enhanced both at low and at high EGF concentrations. These results suggest that at low concentration EGF stimulates exclusively the differentiation of astrocytes, whereas at high concentration, EGF has also a mitogenic effect. Nonproliferating astrocytes in cultures treated with 0.4 microM 1-beta-D-arabinofuranosyl-cytosine were refractory to EGF treatment, indicating that their responsiveness to EGF is cell cycle-dependent. Binding studies using a crude membrane fraction of 5-day cultures showed a homogeneous population of EGF binding sites (Kd approximately equal to 2.6 nM). Specific EGF binding sites were found also in non-proliferating (and nonresponsive) cultures, although they showed slightly reduced affinity and binding capacity. This finding suggests that the cell cycle-dependent control of astroglial responsiveness to EGF does not occur at the receptor level. However, it was found that the specific EGF binding sites disappear with progressive cellular differentiation.

Variations in IB1/JIP1 expression regulate susceptibility of beta-cells to cytokine-induced apoptosis irrespective of C-Jun NH2-terminal kinase signaling.

We previously reported that interleukin-1beta (IL-1beta) alone does not cause apoptosis of beta-cells, whereas when combined with gamma-interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), it exerts a distinct apoptotic effect. Studies in beta-cell lines indicated that IL-1beta reduced expression of islet brain (IB)-1/JNK interacting protein (JIP)-1, a JNK scaffold protein with antiapoptotic action. We examined whether variations in IB1/JIP-1 expression in purified primary beta-cells affect their susceptibility to cytokine-induced apoptosis. Exposure to IL-1beta for 24 h decreased cellular IB1/JIP-1 content by 66 +/- 17%; this IL-1beta effect was maintained in the presence of TNF-alpha + IFN-gamma, which did not influence IB1/JIP-1 levels by themselves. Addition of IL-1beta to TNF-alpha + IFN-gamma increased apoptosis from 20 +/- 2% to 59 +/- 5%. A similar increase in TNF-alpha + IFN-gamma-induced apoptosis was produced by adenoviral expression of antisense IB1/JIP-1 and was not further enhanced by addition of IL-1beta, indicating that IL-1beta-mediated suppression of IB1/JIP-1 in beta-cells increases their susceptibility to cytokine-induced apoptosis. However, adenovirally mediated overexpression of IB1/JIP-1 also potentiated TNF-alpha + IFN-gamma-induced apoptosis, suggesting that the antiapoptotic effect of IB1/JIP-1 depends on well-defined cellular levels. We conclude that the IB1/JIP-1 level in beta-cells can control their susceptibility to apoptosis independent of JNK signaling.

In vivo transformation of mouse conventional CD8alpha+ dendritic cells leads to progressive multisystem histiocytosis

Division and proliferation of dendritic cells (DCs) have been proposed to contribute to homeostasis and to prolonged antigen presentation. Whether abnormal proliferation of dendritic cells causes Langerhans cell histiocytosis (LCH) is a highly debated topic. Transgenic expression of simian virus 40 (SV40) T antigens in mature DCs allowed their transformation in vivo while maintaining their phenotype, function, and maturation capacity. The transformed cells were differentiated splenic CD8 alpha-positive conventional dendritic cells with increased Langerin expression. Their selective transformation was correlated with higher steady-state cycling compared with CD8 alpha-negative DCs in wild-type and transgenic mice. Mice developed a DC disease involving the spleen, liver, bone marrow, thymus, and mesenteric lymph node. Surprisingly, lesions displayed key immunohistologic features of Langerhans cell histiocytosis, including expression of Langerin and absence of the abnormal mitoses observed in Langerhans cell sarcomas. Our results demonstrate that a transgenic mouse model with striking similarities to aggressive forms of multisystem histiocytosis, such as the Letterer-Siwe syndrome, can be obtained by transformation of conventional DCs. These findings suggest that conventional DCs may cause some human multisystem LCH. They can reveal shared molecular pathways for human histiocytosis between humans and mice

Differential sensitivity of GLUT1- and GLUT2-expressing beta cells to streptozotocin.

Streptozotocin injection in animals destroys pancreatic beta cells, leading to insulinopenic diabetes. Here, we evaluated the toxic effect of streptozotocin (STZ) in GLUT2(-/-) mice reexpressing either GLUT1 or GLUT2 in their beta cells under the rat insulin promoter (RIPG1 x G2(-/-) and RIPG2 x G2(-/-) mice, respectively). We demonstrated that injection of STZ into RIPG2 x G2(-/-) mice induced hyperglycemia (>20 mM) and an approximately 80% reduction in pancreatic insulin content. In vitro, the viability of RIPG2 x G2(-/-) islets was also strongly reduced. In contrast, STZ did not induce hyperglycemia in RIPG1 x G2(-/-) mice and did not reduce pancreatic insulin content. The viability of in vitro cultured RIPG1 x G2(-/-) islets was also unaffected by STZ. As islets from each type of transgenic mice were functionally indistinguishable, these data strongly support the notion that STZ toxicity toward beta cells depends on the expression of GLUT2.

Selective expression of a dominant-negative form of peroxisome proliferator-activated receptor in keratinocytes leads to impaired epidermal healing.

Many nuclear hormone receptors are involved in the regulation of skin homeostasis. However, their role in the epithelial compartment of the skin in stress situations, such as skin healing, has not been addressed yet. The healing of a skin wound after an injury involves three major cell types: immune cells, which are recruited to the wound bed; dermal fibroblasts; and epidermal and hair follicle keratinocytes. Our previous studies have revealed important but nonredundant roles of PPARalpha and beta/delta in the reparation of the skin after a mechanical injury in the adult mouse. However, the mesenchymal or epithelial cellular compartment in which PPARalpha and beta/delta play a role could not be determined in the null mice used, which have a germ line PPAR gene invalidation. In the present work, the role of PPARalpha was studied in keratinocytes, using transgenic mice that express a PPARalpha mutant with dominant-negative (dn) activity specifically in keratinocytes. This dn PPARalpha lacks the last 13 C terminus amino acids, binds to a PPARalpha agonist, but is unable to release the nuclear receptor corepressor and to recruit the coactivator p300. When selectively expressed in keratinocytes of transgenic mice, dn PPARalphaDelta13 causes a delay in the healing of skin wounds, accompanied by an exacerbated inflammation. This phenotype, which is similar to that observed in PPARalpha null mice, strongly suggests that during skin healing, PPARalpha is required in keratinocytes rather than in other cell types.

Mastoparan, a novel mitogen for Swiss 3T3 cells, stimulates pertussis toxin-sensitive arachidonic acid release without inositol phosphate accumulation

Mastoparan, a basic tetradecapeptide isolated from wasp venom, is a novel mitogen for Swiss 3T3 cells. This peptide induced DNA synthesis in synergy with insulin in a concentration-dependent manner; half-maximum and maximum responses were achieved at 14 and 17 microM, respectively. Mastoparan also stimulated DNA synthesis in the presence of other growth promoting factors including bombesin, insulin-like growth factor-1, and platelet-derived growth factor. The synergistic mitogenic stimulation by mastoparan can be dissociated from activation of phospholipase C. Mastoparan did not stimulate phosphoinositide breakdown, Ca2+ mobilization or protein kinase C-mediated phosphorylation of a major cellular substrate or transmodulation of the epidermal growth factor receptor. In contrast, mastoparan stimulated arachidonic acid release, prostaglandin E2 production, and enhanced cAMP accumulation in the presence of forskolin. These responses were inhibited by prior treatment with pertussis toxin. Hence, mastoparan stimulates arachidonic acid release via a pertussis toxin-sensitive G protein in Swiss 3T3 cells. Arachidonic acid, like mastoparan, stimulated DNA synthesis in the presence of insulin. The ability of mastoparan to stimulate mitogenesis was reduced by pertussis toxin treatment. These results demonstrate, for the first time, that mastoparan stimulates reinitiation of DNA synthesis in Swiss 3T3 cells and indicate that this peptide may be a useful probe to elucidate signal transduction mechanisms in mitogenesis.

Expression of intercellular adhesion molecule-1 in UVA-irradiated human skin cells in vitro and in vivo.

Ultraviolet A (UVA) radiation represents an important oxidative stress to human skin and certain forms of oxidative stress have been shown to modulate intercellular adhesion molecule-1 (ICAM-1) expression. ICAM-1 has been shown to play an important part in many immune reactions and the perturbations of this molecule by ultraviolet radiation could have implications in many inflammatory responses. An enhancement immunohistochemical method with avidin/biotin was used for analysing the early effects of UVA radiation on human cell cultures and human skin (340-400 nm). Both in vitro and in vivo data show that ICAM-1 staining in epidermal keratinocytes, which was expressed constitutively, decreased in a UVA dose-dependent manner. The decrease was most noted at 3-6 h following UVA radiation with some ICAM-1 staining returning by 48 h post-UVA. ICAM-1 positive staining in the dermis was specific for vascular structures and was increased 24 h after UVA radiation. Cultured dermal fibroblasts exhibited ICAM-1 staining which increased slightly within 6-48 h post-UVA radiation. As epidermal ICAM-1 expression is depleted following UVA radiation and dermal expression increases due to an increase in the vascular structures, ICAM-1 provides a valuable marker following UVA radiation in human skin that can be readily measured in situ.

Role of glast-positive glial cells during photoreceptor development

Purpose: Taking advantage of two transgenic lines, glast.DsRed and crx.gfp, that express fluorescent proteins in glial and photoreceptor cells respectively, we investigate the role of glast-positive glial cells (GPCs) in the survival/differentiation/proliferation of age-matched photoreceptor cells. Methods: Primary retinal cells were isolated from newborn transgenic mouse retina (glast.dsRed::crx.gfp) at postnatal day (P0/P1) and propagated in defined medium containing epidermal growth factor (EGF) and fibroblast growth factor 2 (bFGF). By flow-sorting another population of pure GPCs was isolated. Both populations were expanded and analyzed for the presence of specific retinal cell markers. Notably, the primary cell culture collected from the transgenic line glast.dsRed::crx.gfp showed a conspicuous presence of immature photoreceptors growing on top of GPCs. In order to reveal the role of such cells in the survival/differentiation/proliferation of photoreceptors we set up in vitro cultures of retina-derived cells that allowed long-term time-lapse recordings charting every cell division, death and differentiation event. To assess the regenerative potential of GPCs we challenged them with compounds mimicking retinal degeneration (NMU, NMDA, Zaprinast). Mass spectrometry (MS), immunostainings and other molecular approaches were performed to reveal adhesion molecules involved in the relationship between glial cells and photoreceptors. Results: Both primary cell lines were highly homogenous, with an elongated morphology and the majority expressed Müller glia markers (MG) such as glast, blbp, glt-1, vimentin, glutamine synthetase (GS), GFAP, cd44, mash1 and markers of reactive Müller glia such as nestin, pax6. Conversely, none of them were found positive for retinal neuron markers like tuj1, otx2, recoverin. Primary cultures of GPCs show the incapability of glial cells to give rise to photoreceptors in both wild type or degenerative environment. Furthermore, primary cultures of pure GPCs challenged with different compounds did not highlight the production of new glial cell-derived photoreceptors. Adhesion molecules involved in the contact between photoreceptors and glial cells are still under investigation. Conclusions: Primary glia cells do not give rise to photoreceptor cells in wt and degenerative conditions at least in vitro. The roles of glial cells seem to be more linked to the maintenance/proliferation of photoreceptor cells.

Loss of glucose-induced insulin secretion and GLUT2 expression in transplanted beta-cells.

Either 200 or 400 syngeneic islets were transplanted under the kidney capsule of normal or streptozocin-induced diabetic B6/AF1 mice. The diabetic mice with 400 islets became normoglycemic, but those with 200 islets, an insufficient number, were still diabetic after the transplantation (Tx). Two weeks after Tx, GLUT2 expression in the islet grafts was evaluated by immunofluorescence and Western blots, and graft function was examined by perfusion of the graft-bearing kidney. Immunofluorescence for GLUT2 was dramatically reduced in the beta-cells of grafts with 200 islets exposed to hyperglycemia. However, it was plentiful in grafts with 400 islets in a normoglycemic environment. Densitometric analysis of Western blots on graft homogenates demonstrated that GLUT2 protein levels in the islets, when exposed to chronic hyperglycemia for 2 weeks, were decreased to 16% of those of normal recipients. Moreover, these grafts had defective glucose-induced insulin secretion, while the effects of arginine were preserved. We conclude that GLUT2 expression in normal beta-cells is promptly down-regulated during exposure to hyperglycemia and may contribute to the loss of glucose-induced secretion of diabetes.

Type I IFNs at the interface between cutaneous immunity and epidermal remodeling.

Type I IFNs are key cytokines in antiviral host defense. Preferentially expressed by plasmacytoid dendritic cells, type I IFNs are induced by viral infection and in common skin wounds. In this issue, Tohyama et al. identify a new link between type I IFNs and epidermal remodeling, by showing that type I IFNs specifically upregulate IL-22R expression on keratinocytes and, thereby, IL-22-mediated Stat3 phosphorylation in keratinocytes. The findings suggest that type I IFNs play dual roles in human skin: first, they induce immune activation with the induction of IL-22-producing T cells; second, they provide the interface between immune activation and epidermal remodeling by increasing keratinocyte responsiveness to IL-22.

Stem cell-related "self-renewal" signature and high epidermal growth factor receptor expression associated with resistance to concomitant chemoradiotherapy in glioblastoma.

PURPOSE: Glioblastomas are notorious for resistance to therapy, which has been attributed to DNA-repair proficiency, a multitude of deregulated molecular pathways, and, more recently, to the particular biologic behavior of tumor stem-like cells. Here, we aimed to identify molecular profiles specific for treatment resistance to the current standard of care of concomitant chemoradiotherapy with the alkylating agent temozolomide. PATIENTS AND METHODS: Gene expression profiles of 80 glioblastomas were interrogated for associations with resistance to therapy. Patients were treated within clinical trials testing the addition of concomitant and adjuvant temozolomide to radiotherapy. RESULTS: An expression signature dominated by HOX genes, which comprises Prominin-1 (CD133), emerged as a predictor for poor survival in patients treated with concomitant chemoradiotherapy (n = 42; hazard ratio = 2.69; 95% CI, 1.38 to 5.26; P = .004). This association could be validated in an independent data set. Provocatively, the HOX cluster was reminiscent of a "self-renewal" signature (P = .008; Gene Set Enrichment Analysis) recently characterized in a mouse leukemia model. The HOX signature and EGFR expression were independent prognostic factors in multivariate analysis, adjusted for the O-6-methylguanine-DNA methyltransferase (MGMT) methylation status, a known predictive factor for benefit from temozolomide, and age. Better outcome was associated with gene clusters characterizing features of tumor-host interaction including tumor vascularization and cell adhesion, and innate immune response. CONCLUSION: This study provides first clinical evidence for the implication of a "glioma stem cell" or "self-renewal" phenotype in treatment resistance of glioblastoma. Biologic mechanisms identified here to be relevant for resistance will guide future targeted therapies and respective marker development for individualized treatment and patient selection.

Differences in glucose transporter gene expression between rat pancreatic alpha- and beta-cells are correlated to differences in glucose transport but not in glucose utilization.

Glucose exerts inverse effects upon the secretory function of islet alpha- and beta-cells, suppressing glucagon release and increasing insulin release. This diverse action may result from differences in glucose transport and metabolism between the two cell types. The present study compares glucose transport in rat alpha- and beta-cells. beta-Cells transcribed GLUT2 and, to a lesser extent, GLUT 1; alpha-cells contained GLUT1 but no GLUT2 mRNA. No other GLUT-like sequences were found among cDNAs from alpha- or beta-cells. Both cell types expressed 43-kDa GLUT1 protein which was enhanced by culture. The 62-kDa beta-cell GLUT2 protein was converted to a 58-kDa protein after trypsin treatment of the cells without detectable consequences upon glucose transport kinetics. In beta-cells, the rates of glucose transport were 10-fold higher than in alpha-cells. In both cell types, glucose uptake exceeded the rates of glucose utilization by a factor of 10 or more. Glycolytic flux, measured as D-[5(3)H]glucose utilization, was comparable in alpha- and beta-cells between 1 and 10 mmol/liter substrate. In conclusion, differences in glucose transporter gene expression between alpha- and beta-cells can be correlated with differences in glucose transport kinetics but not with different glucose utilization rates.

The function of a new regulator of epidermal differentiation, HOP, and pathomechanisms underlying epidermolytic hyperkeratosis

The process of epidermal differentiation involves proliferation, differentiation, migration and maturation of keratinocytes to form an impermeable barrier against water loss and outside environment. It is controlled by highly balanced regulatory machinery, involving many molecules that are still under investigation.Homeobox proteins are involved in body patterning and morphogenesis of organs and are studied as potentially good candidates to regulate this process. In the first project we investigated the role of a protein named HOP which belongs to a group of homeobox proteins. Even if HOP is a small protein almost completely composed of the homeodomain and without DNA binding capacity, it is considered as transcriptional regulator in different tissues. HOP interacts with serum response factor (SRF) and histone deacetylase type 2 (HDAC2). By microarray analysis we found that HOP expression increases in cultured human primary keratinocytes (NHK) which undergo calcium-induced differentiation. HOP protein was localized in granular layer of the epidermis of healthy individuals. Lack of HOP was demonstrated in psoriatic lesions, whereas a strong expression was demonstrated in the lesional skin of patients affected with lichen planus (LP). Since LP is characterized by hypergranulosis while psoriatic lesions by progressive lack of the granular layer, the obtained data indicated that HOP might have a potential function in granular layer of epidermis. To investigate HOP function, we inhibited its expression by using HOP specific StealthRNAi and we overexpressed HOP using lentiviral vectors in differentiating NHK. The conclusion of both experiments indicated that HOP positively regulates the expression of late differentiation markers, such as profilaggrin, loricrin and transglutaminase 1. The in vitro data were next confirmed in vivo using HOP knockout mouse model.The second part of my study involved analysis of mechanisms underlying the pathogenesis of epidermolytic hyperkeratosis (EHK). EHK is a genetic disorder characterized by erythema, skin blistering, keratinocyte hyperproliferation and hyperkeratosis. EHK is caused by mutations in keratin 1 or 10 (K1, K10) which are major structural proteins of differentiated keratinocytes and participate in the cellular scaffold formation. To investigate how the structural proteins carrying mutations alter cellular signaling, we established an in vitro model for EHK by overexpression of one of the most common K10 mutations reported so far (K10R156H), in primary human keratinocytes. In order to mimic the in vivo situation, mutated keratinocytes growing on silicone membranes were subjected to mechanical stretch. We observed strong collapse of KIF in K10R156H keratinocytes when subjected to stretch for 30 minutes. Our data demonstrated stronger activation of p38, a member of MAPK stress signaling pathways, in K10R156H when compared to control cells. We demonstrated also that K10R156H keratinocytes showed an induction of TNF-α and RANTES release in response to stretch.Taken together these studies characterize a novel regulator of epidermal differentiation - HOP and demonstrate new aspects implicated in the pathogenesis of EHK.