Glial-derived Neurotropic Factor Research Articles

Creating new in vitro models to examine the role of Pkd1 in cell and tubular physiology

Autosomal dominant polycystic kidney disease (ADPKD) results from loss of function mutations in polycystin proteins PC1 and PC2 encoded by the PKD1 and PKD2 genes. ADPKD affects 1 in 400 to 1 in 1000 people worldwide, with approximately 50% of patients progressing to end stage renal disease. The physiological function of the polycystins and the mechanisms of cystogenesis remain largely unknown. In vitro models may provide the clearest possibility to understand the immediate cell biological effects of polycystin loss, without the confounding second order injury that occurs as cysts develop. Some of the hurdles to in vitro models include clonal variation, renal segment heterogeneity, and inconsistent growth in 3D culture conditions. To address this need, we isolated renal epithelial cells from either the cortex or the medulla of Pkd1flox/flox; Pax8-rtTA; tetO-7-Cre mice crossed with the immorto-mouse expressing the temperature sensitive SV40 large T antigen. We then cloned single cells into isogenic cell lines, one cortical and one medullary. We verified the induction of Pkd1 KO by treating the cells with either 10 ug/ml doxycycline to knock out (KO) Pkd1 or vehicle control. Treatment continued for 7 days, after which Pkd1 KO was confirmed by western blot. Next, we sought to functionally characterize the two new cell lines. When the cells were grown on transwell supports, cells formed epithelial tight junctions with a trans-epithelial resistance of 2467 ohms/cm2. Resistance increased to 3130 ohms/cm2 following Pkd1 KO in the medullary clone. We next measured the rate of media acidification with or without Pkd1 KO as a proxy for glucose utilization. Pkd1 KO cells acidified faster than controls in both clones. Next, we addressed their ability to grow into tubuloids or spheroids / cysts in 3D culture using multiple approaches. Cells were either 1) suspended directly in Matrigel and plated in a 96 well plate, 2) suspended in Matrigel droplets, with multiple droplets adhering to an individual well of a 6 well plate, 3) plated within a Matrigel “sandwich”, or 4) plated within a sandwich and pulsed with glial derived neurotropic factor (GDNF) for 48 hours. All clones suspended directly in Matrigel formed spheroids, with more and larger spheroids in the Matrigel droplet cultures. Similar results were observed in the cortical clone grown in the sandwich, however the Pkd1 KO medullary clone in the same culture conditions had several giant spheroid structures at least 3 times larger than any other organoid observed in control medullary cultures. Finally, cortical cultures grown in the sandwich and pulsed with GDNF revealed larger spheroid structures in the Pkd1 KO cells than the control structures. Medullary cultures grown with GDNF revealed complicated structures with lumens and tubuloid projections in the controls, and large hollow spheroid / cystic structures in the Pkd1 KO cultures. Taken together, these data support the Matrigel sandwich with GDNF pulse may be the most useful to interrogate physiological changes in the absence of Pkd1 expression. In summary, we have created two new clonal cell lines with inducible Pkd1 KO, with isogenic controls, and the ability to differentiate into complicated tubuloids or spheroids in a genotypical manner, that may help elucidate the most proximate events occuring in renal epithelial cells after the inactivation of Pkd1. U54 DK126114. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Neuropathology of the Basal Ganglia in SNCA Transgenic Rat Model of Parkinson's Disease: Involvement of Parvalbuminergic Interneurons and Glial-Derived Neurotropic Factor.

Parkinson’s disease (PD) is a neurodegenerative disease characterized by the accumulation of alpha-synuclein, encoded by the SNCA gene. The main neuropathological hallmark of PD is the degeneration of dopaminergic neurons leading to striatal dopamine depletion. Trophic support by a neurotrophin called glial-derived neurotrophic factor (GDNF) is also lacking in PD. We performed immunohistochemical studies to investigate neuropathological changes in the basal ganglia of a rat transgenic model of PD overexpressing alfa-synuclein. We observed that neuronal loss also occurs in the dorsolateral part of the striatum in the advanced stages of the disease. Moreover, along with the degeneration of the medium spiny projection neurons, we found a dramatic loss of parvalbumin interneurons. A marked decrease in GDNF, which is produced by parvalbumin interneurons, was observed in the striatum and in the substantia nigra of these animals. This confirmed the involvement of the striatum in the pathophysiology of PD and the importance of GDNF in maintaining the health of the substantia nigra.

Upregulated GDF-15 expression facilitates pancreatic ductal adenocarcinoma progression through orphan receptor GFRAL.

Growth and differentiation factor 15 (GDF-15) has been studied as an important hallmark of cancer. However, the receptor of GDF-15 in pancreatic cancer cell remains unclear. Here, we investigated its biological effects in pancreatic ductal adenocarcinoma (PDAC). We found that aberrant GDF-15 expression positively correlated with poor survival of PDAC patients. GDF-15 protein enhanced tumor cell proliferation in two pancreatic cancer lines, AsPC-1 and BxPC-3. Knockdown GDF-15 attenuated its biological function in vitro and reduced PDAC cell tumorigenesis upon xenotransplantation into nude mice. Moreover, we identified that glial-derived neurotropic factor family receptor α-like (GFRAL) was upregulated in PDAC tissues and positively correlated with GDF-15 expression. High GFRAL expression was significantly associated with poor survival in PDAC patients. Furthermore, we identified that the biological effects of GDF-15 are mediated by its receptor GFRAL which is present in PDAC cells. After overexpression GFRAL in pancreatic cancer cells, the effect of GDF-15 was significantly enhanced. Overall, our findings demonstrated that the GDF-15 secreted by PDAC cells, binds to GFRAL, itself localized in PDAC cells, to promote cancer cell growth and metastasis through the GDF-15/GFRAL signaling pathway.

Growth differentiation factor 15 (GDF15): A survival protein with therapeutic potential in metabolic diseases.

Growth Differentiation Factor 15 (GDF15), also known as NSAID activated gene-1 (NAG-1), is associated with a large number of biological processes and diseases, including cancer and obesity. GDF15 is synthesized as pro-GDF15, is dimerized, and is cleaved and secreted into the circulation as a mature dimer GDF15. Both the intracellular GDF15 and the circulating mature GDF15 are implicated in biological processes, such as energy homeostasis and body weight regulation. Although there have been many studies on GDF15, GFRAL, a member of the glial-derived neurotropic factor receptor α family, has only been recently identified as a receptor for mature GDF15. In this review, we focused on cancer and energy homeostasis along with obesity and body weight, and the effect of the identification of the GDF15 receptor in these investigations. In addition, the therapeutic potential of GDF15 as a pharmacological agent in obesity and other metabolic diseases was discussed.

Regenerated Sciatic Nerve Axons Stimulated through a Chronically Implanted Macro-Sieve Electrode.

Sieve electrodes provide a chronic interface for stimulating peripheral nerve axons. Yet, successful utilization requires robust axonal regeneration through the implanted electrode. The present study determined the effect of large transit zones in enhancing axonal regeneration and revealed an intimate neural interface with an implanted sieve electrode. Fabrication of the polyimide sieve electrodes employed sacrificial photolithography. The manufactured macro-sieve electrode (MSE) contained nine large transit zones with areas of ~0.285 mm2 surrounded by eight Pt-Ir metallized electrode sites. Prior to implantation, saline, or glial derived neurotropic factor (GDNF) was injected into nerve guidance silicone-conduits with or without a MSE. The MSE assembly or a nerve guidance conduit was implanted between transected ends of the sciatic nerve in adult male Lewis rats. At 3 months post-operation, fiber counts were similar through both implant types. Likewise, stimulation of nerves regenerated through a MSE or an open silicone conduit evoked comparable muscle forces. These results showed that nerve regeneration was comparable through MSE transit zones and an open conduit. GDNF had a minimal positive effect on the quality and morphology of fibers regenerating through the MSE; thus, the MSE may reduce reliance on GDNF to augment axonal regeneration. Selective stimulation of several individual muscles was achieved through monopolar stimulation of individual electrodes sites suggesting that the MSE might be an optimal platform for functional neuromuscular stimulation.

376. Overexpression of Pitx3 in the SNpc and Protection from MPTP Toxicity

In the brain, expression of the transcription factor Pituitary Homeobox 3 or Paired-Like Homeodomain Transcription Factor 3 (PITX3) is crucial to the development and maintenance of dopaminergic neurons. During brain development, PITX3 functions in concert with the transcription factors NURR1 and LMX1b to facilitate dopaminergic neuron maturation. In the mature brain, PITX3 promotes the dopaminergic phenotype by positively regulating tyrosine hydroxylase (TH), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2), either singly or in concert with NURR1. PITX3 also positively regulates expression of the pro-survival factors brain-derived neurotrophic factor (BDNF) and glial-derived neurotropic factor (GDNF). PITX3 is endogenously expressed in the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA). However, in Pitx3 null mouse models, perturbations of cell number are observed only in the SNpc, a situation that resembles the relative sparing of the VTA in early-stage Parkinson's disease (PD). Systemic administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in the degeneration of SN dopaminergic neurons via a mechanism thought to involve the inhibition of mitochondrial respiration and the generation of reactive oxygen species, both of which are implicated in the pathogenesis of PD. Recent work in muscle demonstrates that PITX3 regulates expression of antioxidant enzymes and genes involved in mitochondrial biogenesis via the transcription factor NRF1. We have overexpressed murine Pitx3 (or mCherry control) from the CMV promoter in the SN of C57BL/6J mice using an AAV2/10 viral vector, and tested for neuroprotection in a sub-chronic MPTP model of PD (5 × 20 mg/kg MPTP over 9 days) by assaying for striatal dopamine, stratial TH and DAT immunoreactivity, and SN neuronal number. We will present results from these assays and changes in expression of Pitx3 target genes (TH, DAT, VMAT2, BDNF and GDNF) after Pitx3 overexpression in the SN.

Treatment with glial derived neurotropic factor (GDNF) attenuates oxidative damages of spinal injury in rat model

Spinal cord injury (SCI) is a serious and debilitating issue being suffered by wide population worldwide. Extensive treatment approaches have been tested and being verified for their efficacy. Owing to the nature of central nervous system (CNS), the resident stem cells would be triggered in response to any sort of trauma with nerve factors as their communication signals. Apart from physical injuries, damages due to oxidative stress also need to be addressed while CNS repair mechanism takes place. This study looks at the potential of glial derived nerve factor (GDNF) in addressing the SCI in regard to oxidative damages. A total of 60 Wistar rats were clustered into five groups and GDNF at various concentrations was tested in each group. Assessments in terms of oxidative stress parameters were noted and analyzed accordingly. It was noted that GDNF had reduced oxidative damages and increased the levels of anti-oxidants in dose-dependent manner (p<0.05). Though treatment with 10mg/mL and 20mg/mL showed significant changes as compared to control group, these treatment modalities remained insignificant among each other. In conclusion, we demonstrated that GDNF exerted a neuro-protective effect on CNS by inducing anti-oxidants and reducing the levels of oxidative stress in SCI induced rat models.

Abstract 4999: Paracrine regulation of glioma invasion by astrocytes is mediated by glial derived neurothropic factor

Abstract Purpose: Glial cells have been shown to play a role in glioma progression. Here we investigate the mechanism by which astrocytes which are abundant in glioma tumors, promote cancer cell invasion. Experimental Design: In this study, we evaluated the effects of astrocytes on glioma biology both in vitro and in vivo and determined the downstream paracrine effect of glial derived neurotropic factor (GDNF) on tumor invasion. Results: Astrocytes conditioned media (ACM) significantly increased human and murine glioma cells migration compared to controls. This effect was inhibited when the activity of GDNF on glioma cells was blocked by RET-Fc chimera or anti-GDNF Ab and by siRNA directed against GDNF expression by astrocytes. Glioma cell incubation with ACM led to time dependent phosphorylation of the GDNF receptor, RET and downstream AKT phosphorylation. Tumor migration and GDNF-RET-AKT activation was inhibited by the RET small molecule inhibitor pyrazolopyrimidine-1 and by the AKT inhibitor LY294002. Finally, blocking of RET by pyrazolopyrimidine-1 or knockout of the RET co receptor GFRα1 in glioma cells reduced the size of brain tumors in immunocompetent mice. Conclusions: We suggest a mechanism by which astrocytes attracted to the glioma microenvironment facilitate brain invasion by secretion of GDNF and activation of RET/GFRα1 receptors expressed by the cancer cells. Note: This abstract was not presented at the meeting. Citation Format: Moran Amit, Ayelet Shabtay-Orbach, Yoav Binenbaum, Ziv Gil. Paracrine regulation of glioma invasion by astrocytes is mediated by glial derived neurothropic factor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4999. doi:10.1158/1538-7445.AM2014-4999

Repair of Spinal Cord Injury (SCI) Using Bone Marrow Stromal Cell Transfected with Adenoviral Vector Expressing Glial derived Neurotropic Factor (GDNF) in a Rat SCI Model

Back ground Subsequent to spinal cord injury many pathological changes may occur that could lead to inappropriate environment for repair. The Most important of such changes is the death of neurons. Exogenous administration of growth factors that modulate neuronal survival, synaptic plasticity, and neurotransmission has been proposed as a potential therapeutic treatment for SCI. Among these growth factors, GDNF is a peptide with pleiotropic survival and growth-promoting effects on neurons. In addition, GDNF induces the growth of motor and sensory axons and inhibits neuronal apoptosis. Adult stem cells may provide new strategies to treat SCI. Among various types of candidate stem cells, bone marrow stromal cells (BMSC) are promising because they have shown potential to neuronal differentiation and repair in damaged spinal cord. In this study, we aimed to improve results of treatment using combination of BMSC and GDNF features. Methods: Rats were divided randomly into four groups of six. Spinal cord injury was then performed under general anesthesia using the weight dropping method. The BMSCs were injected on 3th day of post-spinal cord injury. Group one included rats receiving normal saline, group two received BMSC, group three received BMSC infected with adenoviruses encoding the beta-galactosidase gene, and group four received BMSC infected with adenoviruses encoding the GDNF gene. A Basso, Beattie and Bresnahan (BBB) score test was performed for a period of four weeks. Two weeks before the end of BBB, biotin dextran amine was injected intracerebrally followed by tissue staining at the end of the fourth week. Results: There was a significant difference in BBB scores between groups one and four (p<0.05). BBB scale improved to 12.8 points group one, while it was 8.6 in the control. There were no significant differences between other groups. There were significant differences in axon counting between group one and other groups (p<0.0001). Also, there were significant differences in axon counting between group four with groups two and three (p<0.0001). Conclusion: Combined use of these methods (GDNF expressing BMSCs) showed better results in comparison with BMSC alone. In this study the two methods were used simultaneously. The time of injection of BMSCs is very important and so we suggest that other injection times be tested. Key words: BMSC, GDNF, Gene Therapy, Spinal cord injury.

Kit ligand and glial‐derived neurotrophic factor as alternative supplements for activation and development of ovine preantral follicles in vitro

In vitro growth of preantral follicles has the potential to produce considerable numbers of competent oocytes for use in medicine, agriculture, and even wildlife conservation. The critical regulatory role of growth factors and hormones in the development of preantral follicles has been established. This study investigated the effect of glial-derived neurotropic factor (GDNF) and kit ligand (KL) on the in vitro development of ovine preantral follicles. Results indicated that both GDNF and KL significantly improved activation of primordial follicles, similar to co-addition of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), which are commonly used for in vitro follicular development. Importantly, GDNF had a more profound effect on follicle health, development, and differentiation compared with KL alone. Furthermore, the combination of GDNF and KL in the presence of EGF and bFGF had a positive, synergic effect on health, development, and differentiation of preantral follicles, as determined by histological and hormonal assessments. The results of this study may provide a foundation for further studies that will unravel the molecular mechanisms of follicular development to further improve the current status of in vitro preantral follicle culture.

Brain and spinal cord affected by amyotrophic lateral sclerosis induce differential growth factors expression in rat mesenchymal and neural stem cells

Stem cell research raises hopes for incurable neurodegenerative diseases. In amyotrophic lateral sclerosis (ALS), affecting the motoneurones of the central nervous system (CNS), stem cell-based therapy aims to replace dying host motoneurones by transplantation of cells in disease-affected regions. Moreover, transplanted stem cells can serve as a source of trophic factors providing neuroprotection, slowing down neuronal degeneration and disease progression. To determine the profile of seven trophic factors expressed by mesenchymal stem cells (MSC) and neural stem cells (NSC) upon stimulation with CNS protein extracts from SOD1-linked ALS rat model. Culture of rat MSC, NSC and fibroblasts were incubated with brain and spinal cord extracts from SOD1(G93A) transgenic rats and mRNA expression of seven growth factors was measured by quantitative PCR. MSC, NSC and fibroblasts exhibited different expression patterns. Nerve growth factor and brain-derived neurotropic factor were significantly upregulated in both NSC and MSC cultures upon stimulation with SOD1(G93A) CNS extracts. Fibroblast growth factor 2, insulin-like growth factor and glial-derived neurotropic factor were upregulated in NSC, while the same factors were downregulated in MSC. Vascular endothelial growth factor A upregulation was restricted to MSC and fibroblasts. Surprisingly, SOD1(G93A) spinal cord, but not the brain extract, upregulated brain-derived neurotropic factor in MSC and glial-derived neurotropic factor in NSC. These results suggest that inherent characteristics of different stem cell populations define their healing potential and raise the concept of ALS environment in stem cell transplantation.

Protease Activated Receptors 1 and 4 Sensitize TRPV1 in Nociceptive Neurones

Protease-activated receptors (PAR1-4) are activated by proteases released by cell damage or blood clotting, and are known to be involved in promoting pain and hyperalgesia. Previous studies have shown that PAR2 receptors enhance activation of TRPV1 but the role of other PARs is less clear. In this paper we investigate the expression and function of the PAR1, 3 and 4 thrombin-activated receptors in sensory neurones. Immunocytochemistry and in situ hybridization show that PAR1 and PAR4 are expressed in 10 - 15% of neurons, distributed across all size classes. Thrombin or a specific PAR1 or PAR4 activating peptide (PAR1/4-AP) caused functional effects characteristic of activation of the PLCβ/PKC pathway: intracellular calcium release, sensitisation of TRPV1, and translocation of the epsilon isoform of PKC (PKCε) to the neuronal cell membrane. Sensitisation of TRPV1 was significantly reduced by PKC inhibitors. Neurons responding to thrombin or PAR1-AP were either small nociceptive neurones of the peptidergic subclass, or larger neurones which expressed markers for myelinated fibres. Sequential application of PAR1-AP and PAR4-AP showed that PAR4 is expressed in a subset of the PAR1-expressing neurons. Calcium responses to PAR2-AP were by contrast seen in a distinct population of small IB4+ nociceptive neurones. PAR3 appears to be non-functional in sensory neurones. In a skin-nerve preparation the release of the neuropeptide CGRP by heat was potentiated by PAR1-AP. Culture with nerve growth factor (NGF) increased the proportion of thrombin-responsive neurons in the IB4- population, while glial-derived neurotropic factor (GDNF) and neurturin upregulated the proportion of thrombin-responsive neurons in the IB4+ population. We conclude that PAR1 and PAR4 are functionally expressed in large myelinated fibre neurons, and are also expressed in small nociceptors of the peptidergic subclass, where they are able to potentiate TRPV1 activity.

Fundamentals of Neurogastroenterology: Basic Science

The focus of neurogastroenterology in Rome II was the enteric nervous system (ENS). To avoid duplication with Rome II, only advances in ENS neurobiology after Rome II are reviewed together with stronger emphasis on interactions of the brain, spinal cord, and the gut in terms of relevance for abdominal pain and disordered gastrointestinal function. A committee with expertise in selective aspects of neurogastroenterology was invited to evaluate the literature and provide a consensus overview of the Fundamentals of Neurogastroenterology textbook as they relate to functional gastrointestinal disorders (FGIDs). This review is an abbreviated version of a fuller account that appears in the forthcoming book, Rome III. This report reviews current basic science understanding of visceral sensation and its modulation by inflammation and stress and advances in the neurophysiology of the ENS. Many of the concepts are derived from animal studies in which the physiologic mechanisms underlying visceral sensitivity and neural control of motility, secretion, and blood flow are examined. Impact of inflammation and stress in experimental models relative to FGIDs is reviewed as is human brain imaging, which provides a means for translating basic science to understanding FGID symptoms. Investigative evidence and emerging concepts implicate dysfunction in the nervous system as a significant factor underlying patient symptoms in FGIDs. Continued focus on neurogastroenterologic factors that underlie the development of symptoms will lead to mechanistic understanding that is expected to directly benefit the large contingent of patients and care-givers who deal with FGIDs.

023.Drivers of germ cell differentiation

Spermatogenesis requires progression of a self-renewing male germline stem cell population through a precisely timed and ordered developmental sequence to form spermatozoa. For several years, we have been investigating the functional impact of signals on this progression by members of the TGFβ superfamily, follicle stimulating hormone and the bcl-2 family. For example, our lab and others have shown that activin A, bone morphogenetic protein (BMP)-4 and glial-derived neurotropic factor (GDNF) all modulate stem cell development and spermatogonial differentiation at the onset of spermatogenesis after birth. We are trying to understand how germ cells 'interpret' this plethora of competing signals to mediate maturation. Progression through successive maturation states in response to such signals requires the movement of proteins, including transcription factors, into the nucleus to implement changes in gene transcription. We are investigating the concept that regulated transport of proteins into the nucleus is one mechanism that governs spermatogenic differentiation, and we have focused on analysis of the major class of nuclear transport factors, the importins (IMPs). A diverse family comprising at least six different α forms and 20 different β forms in the mouse, the IMP proteins selectively bind a diverse range of cargo proteins and mediate their passage through the nuclear pore complex and into the nucleus. Our immunohistochemical and in situ hybridisation studies have demonstrated developmentally regulated expression of many IMPs in germ cells, in the fetus, in the neonate and in the adult. This suggests that they function to transport cargo required for discrete stages of spermatogenesis. Our recent studies examined the mouse embryonic gonad around the time when specification to form either a testis or an ovary occurs. The IMPβ3 protein is present in both male and female germ cells, but the subcellular localisation and expression patterns within these cell types is gender- and age-specific. We are currently exploring the functional significance of our observations.

Glial-Derived Neurotropic Factor and RET Gene Expression in Normal Human Anterior Pituitary Cell Types and in Pituitary Tumors

Glial-Derived Neurotropic Factor and RET Gene Expression in Normal Human Anterior Pituitary Cell Types and in Pituitary Tumors

Glial-derived neurotropic factor and RET gene expression in normal human anterior pituitary cell types and in pituitary tumors.

Glial-derived neurotropic factor (GDNF) signaling is mediated through a 2-component system consisting of the so-called GDNF receptor-alpha (GFRalpha1), which binds to GDNF. This complex activates the tyrosine kinase receptor RET. In this paper we demonstrate GDNF, GFRalpha1, and RET mRNA and protein expression in the human anterior pituitary gland. Double immunohistochemistry of anterior pituitary sections showed GDNF immunoreactivity in more than 95% of somatotrophs and to a lesser extent in corticotrophs (20%); it was almost absent in the remaining cell types. Also, although more than 95% of somatotrophs were stained for RET, no positive immunostaining could be detected in other cell types. Furthermore, we have looked for GDNF and RET in human pituitary adenomas of various hormonal phenotypes. Strong positive immunostaining was found for c-RET in all of the GH-secreting adenomas screened as well as in 50% of ACTH-producing adenomas. Positive immunostaining for GDNF was found in all of the GH-secreting adenomas and in 10% of the corticotropinomas. Lastly, we found strong positive immunostaining for GFRalpha1 in 90% of the somatotropinomas and 50% of the corticotropinomas as well as in 1 of 8 prolactinomas and 1 of 13 nonfunctioning adenomas. All of the remaining pituitary tumors screened were negative for RET, GDNF, and GFRalpha1. This study indicates that GDNF may well be acting in the regulation of somatotroph cell growth and/or cell function in the normal human anterior pituitary gland. The expression of RET in all of the somatotropinomas and in 50% of the ACTH-producing tumors implies that GDNF and RET could be involved in the pathogenesis of pituitary tumors.

Expression of c-ret promotes morphogenesis and cell survival in mIMCD-3 cells.

c-Ret, a protein tyrosine kinase receptor, and its ligand glial-derived neurotropic factor (GDNF) are critical for early regulation of ureteric bud development and nephrogenesis. To address whether c-ret directly initiates epithelial cell morphogenesis, the c-ret receptor was expressed in murine inner medullary collecting duct cells (mIMCD-3, a cell line of ureteric bud origin, which has no detectable endogenous c-ret expression). Stable expression of wild-type c-ret was found to yield a constitutively tyrosine-phosphorylated receptor, with no change after the addition of GDNF. Examination of mRNA from these cells demonstrated the message for endogenous GDNF, suggesting that c-ret was potentially being constitutively activated by an autocrine mechanism. When mIMCD-3 cells stably expressing the phosphorylated c-ret receptor were cultured in a type I collagen matrix, they exhibited little GDNF-independent or -dependent branching process formation at early time points compared with the known morphogen hepatocyte growth factor (HGF) (48 h; control, 0.33 +/- 0.33; GDNF, 1.0 +/- 0.58, P = nonsignificant; and HGF, 6.33 +/- 0.33 processes/20 cell clusters, P < 0.001), whereas extended culture (7 days) under serum-free conditions revealed a marked increase in cell survival and the spontaneous development of rudimentary branching process formation. Extended culture (7 days) of c-ret-expressing clones in type I collagen with the epithelial morphogens HGF and/or epidermal growth factor (EGF) resulted in the development of complex three-dimensional spiny cysts, whereas parental mIMCD-3 cells died under these conditions. We conclude that activated c-ret appears to mediate epithelial morphogenesis by prolonging cell survival and, in conjunction with activation of the morphogenic receptors c-met and the EGF receptor, initiates the events required for very early branching morphogenesis.

Endothelins, pseudo-obstruction and Hirschsprung’s disease

See article on page246 It has been known since the 1950s that the enteric nervous system is formed from cells that arise from the neural crest.1 The enteric neurones mainly...