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Biomedical subjects

K E Davies

Publications and source records attributed to K E Davies.

At least 19 recordsLinked to original sources
PubMed2005

A and B utrophin in human muscle and sarcolemmal A-utrophin associated with tumours.

Utrophin is an autosomal homologue of dystrophin, abnormal expression of which is responsible for X-linked Duchenne and Becker muscular dystrophy. In normal mature muscle utrophin is confined to blood vessels, nerves and myotendinous and neuromuscular junctions. When dystrophin is absent utrophin is abundant on the sarcolemma. This has raised the possibility that up-regulation of utrophin may be of therapeutic benefit. Two full-length transcripts of utrophin, A and B, have been identified, which are regulated by alternatively spliced 5' promoters. In dystrophic mouse muscle, the A isoform is present on the sarcolemma, whereas the B form is confined to blood vessels. We show here using immunohistochemistry and human isoform-specific antibodies that A- and B-utrophin localisation is the same in human muscle. The A isoform is present on the sarcolemma of foetal human muscle fibres, regenerating fibres, fibres deficient in dystrophin and on blood vessels and neuromuscular junctions. B-utrophin is only detected on blood vessels. We also show that muscle adjacent to some soft tissue tumours shows increased sarcolemmal utrophin-A, showing that utrophin and dystrophin can simultaneously localise to the sarcolemma and raising the possibility that factor(s) from the tumour cells or accompanying inflammatory cells may have a role in regulating utrophin.

Adolescent↗
PubMed2005

Utrophin upregulation in Duchenne muscular dystrophy.

Duchenne Muscular Dystrophy (DMD) is a devastating, progressive muscle wasting disease for which there is currently no effective treatment. DMD is caused by mutations in the dystrophin gene many of which result in the absence of the large cytoskeletal protein dystrophin at the sarcolemma. Over-expression of utrophin, the autosomal paralogue of dystrophin, as a transgene in the mdx mouse (the mouse model of DMD) has demonstrated that utrophin can prevent the muscle pathology. Thus, up-regulation of utrophin in DMD muscle is a potential therapy for DMD. In this review we discuss recent advances in our understanding of the regulatory pathways controlling utrophin expression and the various approaches that have been applied to increasing the level of utrophin in the mdx mouse. These results are very encouraging and suggest that pharmacological up-regulation of utrophin may well be a feasible approach to therapy for DMD.

Animals↗
PubMed2003

Stromal cell-derived receptor 2 and cytochrome b561 are functional ferric reductases.

Iron has a variety of functions in cellular organisms ranging from electron transport and DNA synthesis to adenosine triphosphate (ATP) and neurotransmitter synthesis. Failure to regulate the homeostasis of iron can lead to cognition and demyelination disorders when iron levels are deficient, and to neurodegenerative disorders when iron is in excess. In this study we show that three members of the b561 family of predicted ferric reductases, namely mouse cytochrome b561 and mouse and fly stromal cell-derived receptor 2 (SDR2), have ferric reductase activity. Given that a fourth member, duodenal cytochrome b (Dcytb), has previously been shown to be a ferric reductase, it is likely that all remaining members of this family also exhibit this activity. Furthermore, we show that the rat sdr2 message is predominantly expressed in the liver and kidney, with low expression in the duodenum. In hypotransferrinaemic (hpx) mice, sdr2 expression in the liver and kidney is reduced, suggesting that it may be regulated by iron. Moreover, we demonstrate the presence of mouse sdr2 in the choroid plexus and in the ependymal cells lining the four ventricles, through in situ hybridization analysis.

Animals↗
PubMed2003

Protein expression changes in spinal muscular atrophy revealed with a novel antibody array technology.

Autosomal recessive proximal spinal muscular atrophy (SMA) is a severe neurodegenerative disease of childhood causing weakness and wasting secondary to motor neuron dysfunction. Over 97% of cases are caused by deletions or mutations within the survival motor neuron (SMN) gene. The SMN protein is highly expressed within brain, spinal cord and muscle, and is decreased in SMA patients. It has been shown to have an important role in RNA metabolism, but the reason for the specific motor neuron loss is still unclear. We have used a novel antibody array technology to look for differences in the expression patterns of primary muscle cultures from a type II SMA patient and a normal control. A relatively small number of differences were found within a group of proteins that function as both RNA binding proteins and transcription factors. Interactions between a number of these proteins are well established, and three of them bind in turn to p53 which interacts with SMN. A number of the changes were confirmed with western blot analysis both in the primary muscle cultures and in skeletal muscle samples from SMA patients and controls. Changes at the mRNA level were also confirmed with oligonucleotide arrays. These results suggest that a common transcription pathway may be altered in the disease state, and suggests that down-regulation of transcription factors contributes to SMA pathogenesis.

Adolescent↗
PubMed2003

Dystrophic phenotype of canine X-linked muscular dystrophy is mitigated by adenovirus-mediated utrophin gene transfer.

Utrophin is highly homologous and structurally similar to dystrophin, and in gene delivery experiments in mdx mice was able to functionally replace dystrophin. We performed mini-utrophin gene transfer in Golden Retriever dogs with canine muscular dystrophy (CXMD). Unlike the mouse model, the clinicopathological phenotype of CXMD is similar to that of Duchenne muscular dystrophy (DMD). We injected an adenoviral vector expressing a synthetic utrophin into tibialis anterior muscles of newborn dogs affected with CXMD and examined transgene expression by RNA and protein analysis at 10, 30 and 60 days postinjection in cyclosporin-treated and -untreated animals. Immunosuppression by cyclosporin was required to mitigate the immune response to viral and transgene antigens. RT-PCR analysis showed the presence of the exogenous transcript in the muscle of cyclosporin-treated and -untreated animals. The transgenic utrophin was efficiently expressed at the extrajunctional membrane in immunosuppressed dogs and this expression was stable for at least 60 days. We found reduced fibrosis and increased expression of dystrophin-associated proteins (DAPs) in association with muscle areas expressing the utrophin minigene, indicating that mini-utrophin can functionally compensate for lack of dystrophin in injected muscles. For this reason, utrophin transfer to dystrophin-deficient muscle appears as a promising therapeutic approach to DMD.

Adenoviridae↗
PubMed2002

Prevention of pathology in mdx mice by expression of utrophin: analysis using an inducible transgenic expression system.

Duchenne muscular dystrophy results from the absence of dystrophin, a cytoskeletal protein. Previously, we have shown in a transgenic mouse model of the disease (mdx) that high levels of expression of the dystrophin-related protein, utrophin can prevent pathology. We developed a new transgenic mouse model where muscle specific utrophin expression was conditioned by addition of tetracycline in water. Transgene expression was turned on at different time points: in utero, at birth, 10 and 30 days after birth. We obtained moderate levels of expression, variable from fibre to fibre (mosaicism) but sufficient to induce a correct localization of the dystro-sarcoglycan complex. Histology revealed a reduction of necrotic foci and of the percentage of centronucleated fibres, which remained still largely above the normal level. Isometric force was not improved but the resistance to eccentric contractions was significantly stronger. When utrophin expression was activated 30 days after birth, improvements were marginal, suggesting that the age at which utrophin therapy is initiated could be an important factor. Our results also provide an unexpected insight into the pathogenesis of the dystrophinopathies. We observed a complete normalization of the characteristics of the mechano-sensitive/voltage-independent Ca(2+) channels (occurrence, open probabilities and Ca(2+) currents), while the classical markers of dystrophy were still abnormal. These observations question the role of increased Ca(2+) channel activity in initiating the dystrophic process. The new model shows that utrophin therapy, initiated after birth, can be effective, but the extent of correction of the various symptoms of dystrophinopathy critically depends on the amount of utrophin expressed.

Animals↗
PubMed2002

Cloning and developmental expression analysis of ltd-1, the Caenorhabditis elegans homologue of the mouse kyphoscoliosis (ky) gene.

We have characterized the developmental expression pattern of the Caenorhabditis elegans homologue of the mouse ky gene. The Ky protein has a putative key function in muscle development and has homologues in invertebrates, fungi and a cyanobacterium. The C. elegans Ky homologue gene has been named ltd-1 for LIM and transglutaminase domains gene. The LTD-1::GFP construct is expressed in developing hypodermal cells from the twofold stage embryo through adulthood. These data define the ltd-1 gene as a novel marker for C. elegans epithelial cell development.

Amino Acid Sequence↗
PubMed2002

A quantitative study of bioenergetics in skeletal muscle lacking utrophin and dystrophin.

Muscle energetics and function were investigated in the hindlimb of mice lacking dystrophin (mdx), utrophin and dystrophin (utr-dys) and controls (C57Bl/10) using 31P and 1H magnetic resonance techniques, electrical nerve stimulation and direct biochemical analysis. At rest, [adenosine triphosphate] and [total creatine] were lowest in utr-dys, while [inorganic phosphate] was elevated. Calculated [adenosine diphosphate] was 3-fold higher in mdx and 5-fold higher in utr-dys than in controls, consistent with an increased adenosine triphosphate requirement for ion pump activity. During stimulation, force production was low only in utr-dys, and this was reflected in the bioenergetic changes. Initial recovery rates of [phosphocreatine] and [adenosine diphosphate] after stimulation were rapid in all groups, indicative of normal mitochondrial adenosine triphosphate production in utr-dys and mdx. Recovery of pH was slow in utr-dys. The data indicate that the severe abnormalities which are present in the absence of utrophin and dystrophin leave basic muscle energetics intact and appear confined to processes involving the sarcolemma.

Adenosine Diphosphate↗
PubMed2001

The role of basal and myogenic factors in the transcriptional activation of utrophin promoter A: implications for therapeutic up-regulation in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is an X-linked recessive muscle wasting disease caused by the absence of a muscle cytoskeletal protein, dystrophin. Utrophin is the autosomal homologue of dystrophin. We previously demonstrated that overexpression of utrophin in the muscles of dystrophin-null transgenic mice completely prevented the phenotype arising from dystrophin deficiency. Two independently regulated promoters control utrophin expression and the upstream promoter (promoter A) is synaptically regulated in muscle. In this study, we have investigated basal regulation and myogenic induction of promoter A. Interactions between Ap2 and Sp1 and their cognate DNA motifs are critical for basal transcription from the minimal promoter region. During differentiation of C2C12 myoblasts in vitro, a 2-fold increase in A-utrophin mRNA level was observed. Expression of a reporter gene, whose transcription was driven by a 1.3 kb promoter A fragment, paralleled expression of the endogenous transcript. Myogenic induction mapped to a conserved upstream muscle-specific E-box, which was shown to bind myogenic regulatory factors, transactivating the promoter up to 18-fold in transient assays. This study provides a basis for further understanding the regulatory mechanisms that control utrophin expression in muscle and may facilitate the development of reagents to effect therapeutic up-regulation of utrophin in DMD.

5' Flanking Region↗
PubMed2001

A novel mechanism for modulating synaptic gene expression: differential localization of alpha-dystrobrevin transcripts in skeletal muscle.

Alpha-dystrobrevin is a dystrophin-related and -associated protein that is involved in synapse maturation and is required for normal muscle function. There are three protein isoforms in skeletal muscle, alpha-dystrobrevin-1, -2, and -3 that are encoded by the single alpha-dystrobrevin gene. To understand the role of these proteins in muscle we have investigated the localisation and transcript distribution of the different alpha-dystrobrevin isoforms. Alpha-dystrobrevin-1 and -2 are concentrated at the neuromuscular junction and are both recruited into agrin-induced acetylcholine receptor clusters in cultured myotubes. We also demonstrate that all alpha-dystrobrevin mRNAs are transcribed from a single promoter in skeletal muscle. However, only transcripts encoding alpha-dystrobrevin-1 are preferentially accumulated at postsynaptic sites. These data suggest that the synaptic accumulation of alpha-dystrobrevin-1 mRNA occurs posttranscriptionally, identifying a novel mechanism for synaptic gene expression. Taken together, these results indicate that different isoforms possess distinct roles in synapse formation and possibly in the pathogenesis of muscular dystrophy.

Agrin↗
PubMed2001

Characterisation of novel point mutations in the survival motor neuron gene SMN, in three patients with SMA.

We report two novel mutations in three cases of spinal muscular atrophy (SMA), including two distant cousins who followed an unexpectedly severe course. Diagnosis was confirmed by reduced SMN protein and full-length SMN mRNA levels. Sequencing of the non-deleted SMN1 gene revealed a single G insertion at the end of exon 1 in the two cousins and a novel G275S exon 6 missense mutation in the milder case.

Child↗
PubMed2001

Activation of calcineurin and stress activated protein kinase/p38-mitogen activated protein kinase in hearts of utrophin-dystrophin knockout mice.

Dilated cardiomyopathy is a common complication of Duchenne and Becker muscular dystrophies, which are caused by mutations in the dystrophin gene. The mdx mouse is an animal model for Duchenne muscular dystrophy (DMD) and shows mildly dystrophic changes in the heart. By contrast, the utrophin-dystrophin knockout (dko) mouse shows severe dystrophic changes in cardiac muscle, that more closely resembles DMD cardiomyopathy than mdx mouse. However the pathogenesis of development has not been fully understood. Recently many reports have revealed that calcineurin and stress activated protein kinase (SAPK)/p38-mitogen activated protein kinase (MAPK) hypertrophic signalling pathways are associated with the development of some forms of hypertrophic and dilated cardiomyopathies. These signalling pathways may have some roles in the development of dystrophin-deficient cardiomyopathy. Here we report that calcineurin and SAPK/p38-MAPK signalling pathways were constantly activated in dko hearts, but the activation varied in mdx hearts. The pathogenesis of the development of dystrophin-deficient cardiomyopathy may be associated with the activation of these signalling pathways.

Age Factors↗
PubMed2001

Non-toxic ubiquitous over-expression of utrophin in the mdx mouse.

Duchenne muscular dystrophy (DMD) is an inherited, severe muscle wasting disease caused by the loss of the cytoskeletal protein, dystrophin. Patients usually die in their late teens or early twenties of cardiac or respiratory failure. We have previously demonstrated that the dystrophin related protein, utrophin is able to compensate for the loss of dystrophin in the mdx mouse, the mouse model of the disease. Expression of a utrophin transgene under the control of an HSA promoter results in localization of utrophin to the sarcolemma and prevents the muscle pathology. Here we show that the over-expression of full-length utrophin in a broad range of tissues is not detrimental in the mdx mouse. These findings have important implications for the feasibility of the up-regulation of utrophin in therapy for DMD since they suggest that tissue specific up-regulation may not be necessary.

Aging↗
PubMed2001

Obesity and day-case surgery.

Day-case surgery is increasing in popularity and more patients with multiple medical problems are being considered as suitable for this approach. However, the current recommendations exclude morbidly obese patients (body mass index > 35 kg.m(-2)). We present a review of 258 morbidly obese patients who have received treatment in our day-surgery unit. Our experience does not show any significant increase in unplanned admission rates or postoperative complications. In conclusion, we feel that morbid obesity alone should not be an exclusion criterion for day-case surgery.

Aftercare↗
PubMed2001

Spinal muscular atrophy.

The spinal muscular atrophies are a group of mostly inherited disorders selectively affecting the lower motor neuron. There is a wide degree of clinical and genetic heterogeneity that must be taken into account when giving prognostic information. Autosomal recessive childhood proximal SMA is the commonest form and is due to mutations in a gene encoding a novel protein, SMN, that appears to play a critical role in RNA metabolism but has also been shown to interact with actin-binding proteins and mediators of programmed cell death. The identification of the genetic basis of SMA has resulted in advances for prenatal diagnosis and in new insights into motor neuron biology. The chromosomal location of two of the rarer dominant forms of SMA has been found. Identification of the molecular pathophysiology of lower motor neuron syndromes can be expected to aid in the development of therapy for these disabling disorders.

Adult↗
PubMed2001

Role of beta-dystrobrevin in nonmuscle dystrophin-associated protein complex-like complexes in kidney and liver.

beta-Dystrobrevin is a dystrophin-related and -associated protein that is highly expressed in brain, kidney, and liver. Recent studies with the kidneys of the mdx3Cv mouse, which lacks all dystrophin isoforms, suggest that beta-dystrobrevin, and not the dystrophin isoforms, may be the key component in the assembly of complexes similar to the muscle dystrophin-associated protein complexes (DPC) in nonmuscle tissues. To understand the role of beta-dystrobrevin in the function of nonmuscle tissues, we generated beta-dystrobrevin-deficient (dtnb(-/-)) mice by gene targeting. dtnb(-/-) mice are healthy, fertile, and normal in appearance. No beta-dystrobrevin was detected in these mice by Western blotting or immunocytochemistry. In addition, the levels of several beta-dystrobrevin-interacting proteins, namely Dp71 isoforms and the syntrophins, were greatly reduced from the basal membranes of kidney tubules and liver sinusoids and on Western blots of crude kidney and liver microsomes of beta-dystrobrevin-deficient mice. However, no abnormality was detected in the ultrastructure of membranes of kidney and liver cells or in the renal function of these mice. beta-Dystrobrevin may therefore be an anchor or scaffold for Dp71 and syntrophin isoforms, as well as other associating proteins at the basal membranes of kidney and liver, but is not necessary for the normal function of these mice.

Alleles↗
PubMed2000

Disruption of SMN function by ectopic expression of the human SMN gene in Drosophila.

Spinal muscular atrophy is a neurodegenerative disorder caused by mutations or deletions in the survival motor neuron (SMN) gene. We have cloned the Drosophila ortholog of SMN (DmSMN) and disrupted its function by ectopically expressing human SMN. This leads to pupal lethality caused by a dominant-negative effect, whereby human SMN may bind endogenous DmSMN resulting in non-functional DmSMN/human SMN hetero-complexes. Ectopic expression of truncated versions of DmSMN and yeast two-hybrid analysis show that the C-terminus of SMN is necessary and sufficient to replicate this effect. We have therefore generated a system which can be utilized to carry out suppressor and high-throughput screens, and provided in vivo evidence for the importance of SMN oligomerization for SMN function at the level of an organism as a whole.

Amino Acid Sequence↗