Reduction of endogenous TGF-beta increases proliferation of developing adrenal chromaffin cells in vivo

Stress Response Leading to Resistance in Glioblastoma-The Need for Innovative Radiotherapy (iRT) Concepts

Glioblastoma (GBM) is the most common and most aggressive malignant primary brain tumor in adults. In spite of multimodal therapy concepts, consisting of surgery, radiotherapy and chemotherapy, the median survival, merely 15–18 months, is still poor. Mechanisms for resistance of GBM to radio(chemo)therapy are not fully understood yet and due to the genetic heterogeneity within the tumor including radiation-resistant tumor stem cells, there are several factors leading to therapy failure. Recent research revealed that, hypoxia during radiation and miRNAs may adversely affect the therapeutic response to radiotherapy. Further molecular alterations and prognostic markers like the DNA-repair protein O6-methylguanine-DNA methyltransferase (MGMT), anti-apoptotic molecular chaperones, and/or the activity of aldehyde dehydrogenase 1 (ALDH1) have also been identified to play a role in the sensitivity to cytostatic agents. Latest approaches in the field of radiotherapy to use particle irradiation or dose escalation strategies including modern molecular imaging, however, need further evaluation with regard to long-term outcome. In this review we focus on current information about the mechanisms and markers that mediate resistance to radio(chemo)therapy, and discuss the opportunities of Innovative Radiotherapy (iRT) concepts to improve treatment options for GBM patients.

Tgfbeta2 and 3 are coexpressed with their extracellular regulator Ltbp1 in the early limb bud and modulate mesodermal outgrowth and BMP signaling in chicken embryos

Background

Transforming growth factor β proteins (Tgfβs) are secreted cytokines with well-defined functions in the differentiation of the musculoskeletal system of the developing limb. Here we have studied in chicken embryos, whether these cytokines are implicated in the development of the embryonic limb bud at stages preceding tissue differentiation.

Results

Immunohistochemical detection of phosphorylated Smad2 and Smad3 indicates that signaling by this pathway is active in the undifferentiated mesoderm and AER. Gene expression analysis shows that transcripts of tgfβ2 and tgfβ3 but not tgfβ1 are abundant in the growing undifferentiated limb mesoderm. Transcripts of tgfβ2 are also found in the AER, which is the signaling center responsible for limb outgrowth. Furthermore, we show that Latent Tgfβ Binding protein 1 (LTBP1), which is a key extracellular modulator of Tgfβ ligand bioavailability, is coexpressed with Tgfβs in the early limb bud. Administration of exogenous Tgfβs to limb buds growing in explant cultures provides evidence of these cytokines playing a role in the regulation of mesodermal limb proliferation. In addition, analysis of gene regulation in these experiments revealed that Tgfβ signaling has no effect on the expression of master genes of musculoskeletal tissue differentiation but negatively regulates the expression of the BMP-antagonist Gremlin.

Conclusion

We propose the occurrence of an interplay between Tgfβ and BMP signaling functionally associated with the regulation of early limb outgrowth by modulating limb mesenchymal cell proliferation.

The chromaffin vesicle: advances in understanding the composition of a versatile, multifunctional secretory organelle

Chromaffin vesicles (CV) are highly sophisticated secretory organelles synthesized in adrenal medullary chromaffin cells. They contain a complex mixture of structural proteins, catecholamine neurotransmitters, peptide hormones, and the relative processing enzymes, as well as protease inhibitors. In addition, CV store ATP, ascorbic acid, and calcium. During the last decades, extensive studies have contributed to increase our understanding of the molecular composition of CV. Yet, the recent development of biochemical and imaging procedures has greatly increased the list of CV-soluble constituents and opened new horizons as to the complexity of CV involvement in acute stress responses. Thus, a coherent picture of CV molecular composition is still to be drawn. This review article will provide a detailed account of the content of CV soluble molecules as it emerges from the most recent analytical studies. Moreover, this review article will attempt at focussing on the physiological and pathophysiological implications of the products released by CV.

Persistent expression of BMP-4 in embryonic chick adrenal cortical cells and its role in chromaffin cell development

Background

Adrenal chromaffin cells and sympathetic neurons both originate from the neural crest, yet signals that trigger chromaffin development remain elusive. Bone morphogenetic proteins (BMPs) emanating from the dorsal aorta are important signals for the induction of a sympathoadrenal catecholaminergic cell fate.

Results

We report here that BMP-4 is also expressed by adrenal cortical cells throughout chick embryonic development, suggesting a putative role in chromaffin cell development. Moreover, bone morphogenetic protein receptor IA is expressed by both cortical and chromaffin cells. Inhibiting BMP-4 with noggin prevents the increase in the number of tyrosine hydroxylase positive cells in adrenal explants without affecting cell proliferation. Hence, adrenal BMP-4 is likely to induce tyrosine hydroxylase in sympathoadrenal progenitors. To investigate whether persistent BMP-4 exposure is able to induce chromaffin traits in sympathetic ganglia, we locally grafted BMP-4 overexpressing cells next to sympathetic ganglia. Embryonic day 8 chick sympathetic ganglia, in addition to principal neurons, contain about 25% chromaffin-like cells. Ectopic BMP-4 did not increase this proportion, yet numbers and sizes of 'chromaffin' granules were significantly increased.

Conclusion

BMP-4 may serve to promote specific chromaffin traits, but is not sufficient to convert sympathetic neurons into a chromaffin phenotype.

Transforming growth factor-beta (TGF-beta) and programmed cell death in the vertebrate retina

Programmed cell death (PCD) is a precisely regulated phenomenon essential for the homeostasis of multicellular organisms. Developmental systems, particularly the nervous system, have provided key observations supporting the physiological role of PCD. We have recently shown that transforming growth factor-beta (TGF-beta) plays an important role in mediating ontogenetic PCD in the nervous system. As part of the central nervous system the developing retina serves as an ideal model system for investigating apoptotic processes during neurogenesis in vivo as it is easily accessible experimentally and less complex due to its limited number of different neurons. This review summarizes data indicating a pivotal role of TGF-beta in mediating PCD in the vertebrate retina. The following topics are discussed: expression of TGF-beta isoforms and receptors in the vertebrate retina, the TGF-beta signaling pathway, functions and molecular mechanisms of PCD in the nervous system, TGF-beta-mediated retinal apoptosis in vitro and in vivo, and interactions of TGF-beta with other pro- and anti-apoptotic factors.

Isoform-specific role of transforming growth factor-β2 in the regulation of proliferation and differentiation of murine adrenal chromaffin cells in vivo

Chromaffin cells, the neuroendocrine cells of the adrenal medulla, play an important role in molecular, cellular, and developmental neurobiology. Unlike the closely related sympathetic neurons, chromaffin cells are able to proliferate throughout their whole life span. Proliferation of chromaffin cells in vivo is thought to be regulated by the interaction of neurogenic and hormonal signals. Previous studies have shown that chromaffin cells synthesize and release transforming growth factor-betas (TGF-betas). In the present study, effects of TGF-betas on proliferation and differentiation of chromaffin cells in mouse adrenal chromaffin cells were investigated in a genetic mouse model. We observed a significant increase in the total number of tyrosine hydroxylase-positive (TH(+)) cells in Tgfbeta2(-/-) knockout mouse embryos at embryonic day (E) 18.5 compared with wild-type animals (Tgfbeta2(+/+)), but no changes in the number of TH(+) cells were observed in Tgfbeta3(-/-) mouse mutants. At E15.5, but not at E18.5, there was a marked increase in the number of proliferative cell nuclear antigen-positive chromaffin cells in Tgfbeta2(-/-) knockout embryos compared with the wild-type group. On the other hand, there was a clear decrease in the ratio of total number of phenylethanolamine-N-methyltransferase-positive cells to the total TH(+) in Tgfbeta2(-/-) mice embryos at E18.5 compared with wild-type animals. This is the first documentation of the physiological significance of the TGF-beta2, an isoform that has been suggested to play a role in the regulation of chromaffin cells proliferation and differentiation based on in vitro experiments.

Cerebellar deficits and hyperactivity in mice lacking Smad4

Smad4 is a central mediator of TGF-beta signals, which are known to play essential roles in many biological processes. Using a Cre-loxP approach to overcome early embryonic lethality, we have studied functions of TGF-beta/Smad4 signals in the central nervous system (CNS). No obvious deficits were detected in mice carrying the targeted disruption of Smad4 in the CNS. The overall morphology of the hippocampus appeared normal. There was no change in the proliferation of neuronal precursor cells, nor in several forms of synaptic plasticity. In contrast, deletion of Smad4 resulted in a marked decrease in the number of cerebellar Purkinje cells and parvalbumin-positive interneurons. Accompanied by the abnormality in the cerebellum, mutant mice also exhibited significantly increased vertical activity. Thus, our study reveals an unexpected role for Smad4 in cerebellar development and in the control of motor function.

Transforming growth factor-beta(s) are essential for the development of midbrain dopaminergic neurons in vitro and in vivo

Development of midbrain dopaminergic neurons is known to depend on inductive signals derived from the ventral midline, including Sonic hedgehog (Shh) as one of the identified molecules. Here we show that in addition to Shh, transforming growth factor (TGF)-beta is required for both induction and survival of ventrally located midbrain dopaminergic neurons. Like Shh, TGF-beta is expressed in early embryonic structures such as notochord and floor plate, as well as in the area where midbrain dopaminergic neurons are developing. Treatment of cells dissociated from the rat embryonic day (E) 12 midbrain floor with TGF-beta significantly increases the number of tyrosine hydroxylase (TH)-positive dopaminergic neurons within 24 hr. Neutralization of TGF-beta in vitro completely abolishes the induction of dopaminergic neurons. In the absence of TGF-beta, Shh cannot induce TH-positive neurons, and vice versa, neutralizing endogenous Shh abolishes the capacity of TGF-beta to induce dopaminergic neurons in vitro. Furthermore, neutralization of TGF-beta in vivo during chick E2-7 but not E4-7 resulted in a significant reduction in TH-positive neurons in the ventral midbrain floor but not in the locus coeruleus or diencephalon, which suggests that the TGF-beta is required for the induction of mesencephalic dopaminergic neurons with a critical time period at E2/E3. Furthermore, neutralization of TGF-beta between E6 and 10, a time period during maturation of mesencephalic dopaminergic neurons when no further inductive cues are required, also resulted in a significant loss of dopaminergic neurons, suggesting that TGF-beta is required for the promotion of survival of ventral midbrain dopaminergic neurons as well. Together, our results identify TGF-beta as an essential mediator for the induction and maintenance of midbrain dopaminergic neurons.

TGF-betas and their roles in the regulation of neuron survival

Transforming growth factor-betas (TGF-betas) are a still growing superfamily of cytokines with widespread distribution and diverse biological functions. They fall into several subfamilies including the TGF-betas 1, 2, and 3, the bone morphogenetic proteins (BMPs), the growth/differentiation factors (GDFs), activins and inhibins, and the members of the glial cell line-derived neurotrophic factor family. Following a brief description of their general roles and signaling in development, maintenance of homeostasis, and disease, we shall focus on their distribution in the CNS and their involvement in regulating neuron survival and death.

Generation of neuroendocrine chromaffin cells from sympathoadrenal progenitors: beyond the glucocorticoid hypothesis

The developmental diversification of neural crest-derived sympathoadrenal (SA) progenitor cells into neuroendocrine adrenal chromaffin cells and sympathetic neurons has been thought to be largely understood. Based on two decades of in vitro studies with isolated SA progenitor and chromaffin cells, it was widely assumed that chromaffin cell development crucially depends on glucocorticoid hormones provided by adrenal cortical cells. However, analysis of mice lacking the glucocorticoid receptor has revealed that the chromaffin cell phenotype develops largely normally in these mice, except for the induction of the adrenaline synthesizing enzyme phenylethylamine N-methyl transferase. In a search for novel candidate genes that might be involved in triggering the sympathetic neuron/chromaffin cell decision, we have studied putative contributions of transforming growth factor (TGF)-alpha, BMP-4, and the transcription factor MASH-1, molecules with distinct expressions in SA progenitor cells, in their migratory pathways and final destinations. TGF-beta2 and -beta3 and BMP-4 are highly expressed in the wall of the dorsal aorta and in the adrenal anlagen during and after immigration of SA progenitors but expressed at much lower levels in sympathetic ganglia. We found that neutralizing antibodies against all three TGF-beta isoforms applied to the chorionic-allantoic membrane (CAM) of quail embryos interfere with proliferation of immigrated adrenal chromaffin cells but do not affect their specific neuroendocrine ultrastructural phenotype. Grafting of noggin-producing cells to the CAM, which scavenges BMPs, interferes with visceral arch and limb development but does not overtly affect the chromaffin phenotype. The transcription factor MASH-1 promotes early differentiation of SA progenitors. Mice deficient for MASH-1 lack sympathetic ganglia, whereas the adrenal medulla previously has been reported to be present. We show here that most adrenal medullary cells in MASH-1(-/-) mice identified by Phox2b immunoreactivity lack the catecholaminergic marker tyrosine hydroxylase. More surprisingly, most cells do not contain chromaffin granules and display a neuroblast-like ultrastructure and show strongly enhanced expression of c-RET comparable to that observed in sympathetic ganglia. Together, our data suggest that TGF-betas and BMP-4 do not seem to be essential for chromaffin cell differentiation. In contrast with previous reports, however, MASH-1 apparently plays a crucial role in chromaffin cell development.

Adrenocorticotropic hormone in the aetiology and regression of neuroblastoma

Neuroblastoma is predominantly a paediatric neoplasm of the sympathetic nervous system. Despite the aggressive nature of the disease, spontaneous regression is frequently observed in infants diagnosed under the age of 12 months; especially with a specific stage referred to as stage 4s. Discovering the conditions, the elements, the mechanism and the indices behind this regression phenomenon could have therapeutic potential for prevention and cure. A review of the literature has implicated adrenocorticotropin hormone in both the aetiology and spontaneous regression of neuroblastoma. Manipulation of adrenocorticotropin hormone may offer hope for prevention and cure. Ingestible products such as retinoic acid, glycyrrhizic acid, salsolinol and ketoconazole acting in concert, could represent instrumental tools in a therapeutic manipulation process.

Transforming growth factor-beta 2 heterozygous mutant mice exhibit Cowper's gland hyperplasia and cystic dilations of the gland ducts (Cowper's syringoceles)

Analyses of mutant mice with a deletion for the transforming growth factor beta 2 (Tgfbeta2) gene revealed cysts in the perineal/scrotal region of male mice. We present evidence from in situ, light and electron microscopy that the cysts observed in Tgfbeta2+/- heterozygous mice males derive from Cowper's gland tissue. The Cowper's glands of Tgfbeta2+/- heterozygous mutant mice display all steps of glandular hyperplasia and cystic dilation. TGF-beta isoforms and TGF-beta receptor (TbetaR-II) were localized immunocytochemically in sections of Cowper's glands. TGF-beta2 and TGF-beta3 were located predominantly in myoepithelial cells of the Cowper's gland whereas the TbetaRII was found in the plasma membrane of the acinar cells. TUNEL-assays revealed that apoptotic cell death is significantly reduced in Cowper's glands of TgfbetaB2+/- heterozygous mutant mice. The fact that Tgfbeta2+/- heterozygous mutant mice exhibit hyperplasia of Cowper's gland epithelium and Cowper's gland cysts suggests a disturbance of epithelial-stromal interaction most likely due to reduced TGF-beta2 level, accompanied by a significant decrease in apoptosis.

Functional regeneration in a rat Parkinson's model after intrastriatal grafts of glial cell line-derived neurotrophic factor and transforming growth factor beta1-expressing extra-adrenal chromaffin cells of the Zuckerkandl's organ

Intrabrain transplantation of chromaffin cell aggregates of the Zuckerkandl's organ, an extra-adrenal paraganglion that has never been tested for antiparkinsonian treatment, induced gradual improvement of functional deficits in parkinsonian rats. These beneficial effects were related to long survival of grafted cells, striatal reinnervation, and enhancement of dopamine levels in grafted striatum. Grafted cells were not dopaminergics, but they expressed glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta(1). These factors were detected in the host striatal tissue, indicating that chromaffin cells secreted them after grafting. Because glial cell line-derived neurotrophic factor possesses neurorestorative properties over dopaminergic neurons, and transforming growth factor-beta(1) is a cofactor that potentiates the neurotrophic actions of GDNF, functional regeneration was likely caused by the chronic trophic action of neurotrophic factors delivered by long-surviving grafted cells. This work should stimulate research on the clinical applicability of transplants of the Zuckerkandl's organ in Parkinson's disease.

Reduction of endogenous TGF-beta does not affect phenotypic development of sympathoadrenal progenitors into adrenal chromaffin cells

Adrenal chromaffin cells and sympathetic neurons are related, but phenotypically distinct derivatives of the neural crest. Molecular cues that determine the chromaffin cell phenotype have not yet been identified; in contrast to a widely held belief, glucocorticoid signaling is apparently not relevant (Development 126 (1999) 2935). Transforming growth factor-betas (TGF-betas) regulate various aspects of embryonic development and are expressed in the environment of sympathoadrenal (SA) progenitor cells. We have previously shown that neutralization of endogenous TGF-beta from E4 to E8 in the quail embryo significantly increases numbers of adrenal tyrosine hydroxylase-positive cells. Whether endogenous TGF-beta may also be involved in influencing phenotypic development of adrenal chromaffin cells and their SA progenitors has not been analyzed. We now demonstrate that neutralization of endogenous TGF-beta1, -beta2 and -beta3 with a pan-anti-TGF-beta antibody in quail embryos during distinct time windows does not alter phenotypic development of chromaffin cells. In situ hybridizations revealed unaltered expression of neurofilament (NF-160), synaptotagmin I and neurexin I in adrenal glands. Likewise, the NF-associated antigen 3A10, and polyphosphorylated NF epitopes (RT 97) were unaltered. Most importantly, the typical ultrastructure of adrenal chromaffin cells including their large chromaffin secretory granules, a hallmark of the neuroendocrine phenotype, which distinguishes them from sympathetic neurons, was not affected. We therefore conclude that neutralization of endogenous TGF-beta influences chromaffin cell proliferation, but does not interfere with the development of the typical chromaffin cell phenotype.

Growth and neurotrophic factors regulating development and maintenance of sympathetic preganglionic neurons

The functional anatomy of sympathetic preganglionic neurons is described at molecular, cellular, and system levels. Preganglionic sympathetic neurons located in the intermediolateral column of the spinal cord connect the central nervous system with peripheral sympathetic ganglia and chromaffin cells inside and outside the adrenal gland. Current knowledge is reviewed of the development of these neurons, which share their origin with progenitor cells, giving rise to somatic motoneurons in the ventral horn. Their connectivities, transmitters involved, and growth factor receptors are described. Finally, we review the distribution and functions of trophic molecules that may have relevance for development and maintenance of preganglionic sympathetic neurons.

Targeted mutations of transforming growth factor-beta genes reveal important roles in mouse development and adult homeostasis

Transforming growth factors-beta (TGF-beta) are multifunctional molecules with profound biological effects in many developmental processes including regulation of cell proliferation, differentiation, cell adhesion, skeletal development, haematopoiesis, inflammatory responses, and wound healing. To learn about the role of TGF-beta in vivo, phenotypes of targeted mutations of molecules within the TGF-beta signalling pathway, TGF-beta1, -beta2, -beta3, TGF-beta receptor (TbetaR-II) and the signalling molecules SMAD2, SMAD3 and SMAD4, are discussed in this review. The three individual TGF-beta mutants show distinct and only partially overlapping phenotypes. In mice, targeted disruption of the TGF-beta1 gene results in diffuse and lethal inflammation about 3 weeks after birth, suggesting a prominent role of TGF-beta in the regulation of immune cell proliferation and extravasation into tissues. However, just half of the TGF-beta1 (-/-) conceptuses actually reach partuition due to defective haematopoiesis and endothelial differentiation. Targeted disruption of both TGF-beta2 and TGF-beta3 genes results in perinatal lethality. TGF-beta2 null mice exhibit a broad range of developmental defects, including cardiac, lung, craniofacial, limb, eye, ear and urogenital defects, whereas TGF-beta3 gene ablation results exclusively in defective palatogenesis and delayed pulmonary development. The TbetaR-II null phenotype closely resembles that of TGF-beta1 (-/-) conceptuses, which die in utero by E10.5. Loss of SMAD2 or SMAD4 results in related phenotypes: the mutants fail to form an organized egg cylinder, lack mesoderm required for gastrulation and die prior to E8.5. Together, gene ablation within the TGF-beta signalling pathway supports the notion of a prominent role of TGF-beta during development.

Functions of transforming growth factor-beta isoforms in the nervous system. Cues based on localization and experimental in vitro and in vivo evidence

This review briefly describes the cellular distribution and documented roles of the transforming growth factor (TGF)-beta isoforms TGF-beta2 and -beta3 in the central and peripheral nervous system. TGF-beta2 and -beta3 are coexpressed in developing radial glial and mature astroglial and Schwann cells, as well as in subpopulations of differentiated neurons, most prominently in cortical, hippocampal, and brainstem/spinal cord motor neurons. In vitro studies have suggested a number of potential, physiologically relevant functions for TGF-betas including regulation of astroglial cell proliferation, expression of adhesion molecules, survival promoting roles for neurons in combination with established neurotrophic factors, and differentiative actions on neurons.

The transforming growth factor-betas: structure, signaling, and roles in nervous system development and functions

Transforming growth factor-betas (TGF-betas) are among the most widespread and versatile cytokines. Here, we first provide a brief overview of their molecular biology, biochemistry, and signaling. We then review distribution and functions of the three mammalian TGF-beta isoforms, beta1, beta2, and beta3, and their receptors in the developing and adult nervous system. Roles of TGF-betas in the regulation of radial glia, astroglia, oligodendroglia, and microglia are addressed. Finally, we review the current state of knowledge concerning the roles of TGF-betas in controlling neuronal performances, including the regulation of proliferation of neuronal precursors, survival/death decisions, and neuronal differentiation.