Differential expression of glial cell line-derived neurotrophic factor family receptor alpha-2 isoforms in rat urinary bladder and intestine.

Neurturin (NTN) is a member of the glial cell line-derived (GDNF) family of neurotrophic factors, which act via a receptor complex composed of a signal transducing receptor, c-Ret and a glycosylphosphatidylinositol (GPI)-linked ligand binding receptor, GFRalpha. Different members of the GDNF family bind preferentially to one of four different GFRalpha receptors; NTN binds preferentially to the GFRalpha-2 receptor. Recent evidence has shown that three alternatively spliced isoforms of GFRalpha-2 occur in rodent tissues, including the rat brain, myenteric plexus and kidney, and several mouse tissues. Here we have examined the occurrence of GFRalpha-2 isoforms in the adult male rat urinary bladder by RT-PCR, in parallel with samples from the muscularis externa of the rat ileum. In contrast to the ileum, only a single GFRalpha-2 isoform, the smallest isoform, known as GFRalpha-2c, was detected in the rat urinary bladder. This differential expression of GFRalpha-2 transcripts in bladder and intestine may be related to differences in the roles of NTN in the two tissues and its actions on the neurons that innervate them.

Sub-cellular localisation of fukutin related protein in different cell lines and in the muscle of patients with MDC1C and LGMD2I.

MDC1C and LGMD2I are two allelic forms of muscular dystrophies caused by mutations in the gene encoding for fukutin related protein (FKRP). FKRP encodes for a putative glycosyltransferase, the precise function of which is unknown. However, the marked reduction of alpha-dystroglycan glycosylation in the muscle of MDC1C and LGMD2I patients suggests a role for FKRP in dystroglycan processing. Using a polyclonal antibody raised against FKRP we now show that endogenous FKRP locates to the Golgi apparatus of neuronal, oligodendroglial, and the cardiac muscle cell line H9c2. In differentiated C2C12 myotubes and in transverse sections of normal skeletal and cardiac muscle, endogenous FKRP surrounded the myonuclei. This localisation was unaffected in the skeletal muscle of patients with MDC1C and LGMD2I carrying various FKRP mutations. These observations imply a specific role for FKRP during striated muscle, neuronal and glial development and suggest that protein mis-localisation is not a common mechanism of disease in FKRP-related dystrophies.

G-protein Coupled Receptor Signaling in Pluripotent Stem Cell-derived Cardiovascular Cells: Implications for Disease Modeling.

Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies.

Identification of GFR alpha-2 isoforms in myenteric plexus of postnatal and adult rat intestine.

Glial cell line-derived neurotrophic factor family receptor alpha-2 (GFR alpha-2) is a GPI-linked receptor that preferentially binds neurturin (NTN), a member of the glial cell line-derived neurotrophic factor (GDNF) family. Three splice isoforms of GFR alpha-2 have been identified previously in mouse tissues, but the occurrence of splice isoforms in rats has not been described. The aim of this study was therefore to identify GFR alpha-2 splice isoforms in rat tissues using reverse transcription-polymerase chain reaction (RT-PCR) and gene cloning. Three isoforms were identified and sequenced, and named GFR alpha-2(a), (b) and (c), according to the nomenclature used for the previously identified mouse isoforms. The GFR alpha-2(a) and (b) isoforms were identical to those previously described in mice. The GFR alpha-2(c) isoform was novel. Sequences for GFR alpha-2(b) and (c) were deposited in the GenBank database (accession numbers GI: 16797788 and 16797786, respectively). All three isoforms were expressed in the brain, kidney, and intestine of both postnatal and adult rats.

Aberrant α-adrenergic hypertrophic response in cardiomyocytes from human induced pluripotent cells.

Cardiomyocytes from human embryonic stem cells (hESC-CMs) and induced pluripotent stem cells (hiPSC-CMs) represent new models for drug discovery. Although hypertrophy is a high-priority target, we found that hiPSC-CMs were systematically unresponsive to hypertrophic signals such as the α-adrenoceptor (αAR) agonist phenylephrine (PE) compared to hESC-CMs. We investigated signaling at multiple levels to understand the underlying mechanism of this differential responsiveness. The expression of the normal α1AR gene, ADRA1A, was reversibly silenced during differentiation, accompanied by ADRA1B upregulation in either cell type. ADRA1B signaling was intact in hESC-CMs, but not in hiPSC-CMs. We observed an increased tonic activity of inhibitory kinase pathways in hiPSC-CMs, and inhibition of antihypertrophic kinases revealed hypertrophic increases. There is tonic suppression of cell growth in hiPSC-CMs, but not hESC-CMs, limiting their use in investigation of hypertrophic signaling. These data raise questions regarding the hiPSC-CM as a valid model for certain aspects of cardiac disease.

Ageing of enteric neurons: oxidative stress, neurotrophic factors and antioxidant enzymes.

BACKGROUND: Ageing is associated with gastrointestinal dysfunction, which can have a major impact on quality of life of the elderly. A number of changes in the innervation of the gut during ageing have been reported, including neuronal loss and degenerative changes. Evidence indicates that reactive oxygen species (ROS) are elevated in ageing enteric neurons, but that neurotrophic factors may reduce generation of neuronal ROS. Two such factors, glial cell line derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) have also been found to protect enteric neurons against oxidative stress induced cell death of enteric ganglion cells in vitro. We have investigated the possible roles of neurotrophic factors further, by examining their expression in the gut during ageing, and by analysing their effects on antioxidant enzyme production in cultures of enteric ganglion cells. RESULTS: Analysis of the expression of GDNF and its receptors c-Ret and GFR α - 1 in rat gut by RT-PCR showed that expression continues throughout life and into ageing, in both ad libitum(AL) and calorically-restricted (CR) animals. Levels of expression of GDNF and GFR α - 1 were elevated in 24 month AL animals compared to 24 month CR animals, and to 24 CR and 6 month control animals respectively. The related factor Neurturin and its receptor GFR α - 2 were also expressed throughout life, the levels of the GFR - α-2(b) isoform were reduced in 24 m AL animals. Immunolabelling showed that c-Ret and GFR α - 1 proteins were expressed by myenteric neurons in ageing animals. GDNF, but not NT-3, was found to increase expression of Cu/Zn superoxide dismutase and catalase by cultured enteric ganglion cells. CONCLUSIONS: The neurotrophic factors GDNF and neurturin and their receptors continue to be expressed in the ageing gut. Changes in the levels of expression of GDNF , GFR α-1 and GFR α-2(b) isoform occurred in 24 m AL animals. GDNF, but not NT-3, increased the levels of antioxidant enzymes in cultured enteric ganglion cells, indicating a possible mechanism for the reported protective effect of GDNF against menadione-induced neuronal apoptosis in the ageing gut. Together these data suggest that GDNF family members may play a protective role in the gut throughout life, and support the suggestion that dysregulation of neurotrophic factor support could contribute to neuronal ageing in the gut.

Localization and functional analysis of the LARGE family of glycosyltransferases: significance for muscular dystrophy.

The dystroglycanopathies are a novel group of human muscular dystrophies due to mutations in known or putative glycosyltransferase enzymes. They share the common pathological feature of a hypoglycosylated form of alpha-dystroglycan, diminishing its ability to bind extracellular matrix ligands. The LARGE glycosyltransferase is mutated in both the myodystrophy mouse and congenital muscular dystrophy type 1D (MDC1D). We have transfected various cell lines with a variety of LARGE expression constructs in order to characterize their subcellular localization and effect on alpha-dystroglycan glycosylation. Wild-type LARGE co-localized with the Golgi marker GM130 and stimulated the production of highly glycosylated alpha-dystroglycan (hyperglycosylation). MDC1D mutants had no effect on alpha-dystroglycan glycosylation and failed to localize correctly, confirming their pathogenicity. The two predicted catalytic domains of LARGE contain three conserved DxD motifs. Systematically mutating each of these motifs to NNN resulted in the mislocalization of one construct, while all failed to have any effect on alpha-dystroglycan glycosylation. A construct lacking the transmembrane domain also failed to localize at the Golgi apparatus. These results indicate that LARGE needs to both physically interact with alpha-dystroglycan and function as a glycosyltransferase in order to stimulate alpha-dystroglycan hyperglycosylation. We have also cloned and overexpressed a homologue of LARGE, glycosyltransferase-like 1B (GYLTL1B). Like LARGE it localized to the Golgi apparatus and stimulated alpha-dystroglycan hyperglycosylation. These results suggest that GYLTL1B may be a candidate gene for muscular dystrophy and that its overexpression could compensate for the deficiency of both LARGE and other glycosyltransferases.