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Biomedical subjects

M S Clark

Publications and source records attributed to M S Clark.

At least 55 records · Page 3Linked to original sources
PubMed1997

The role of molecular chaperones in mitochondrial protein import and folding.

Molecular chaperones play a critical role in many cellular processes. This review concentrates on their role in targeting of proteins to the mitochondria and the subsequent folding of the imported protein. It also reviews the role of molecular chaperons in protein degradation, a process that not only regulates the turnover of proteins but also eliminates proteins that have folded incorrectly or have aggregated as a result of cell stress. Finally, the role of molecular chaperones, in particular to mitochondrial chaperonins, in disease is reviewed. In support of the endosymbiont theory on the origin of mitochondria, the chaperones of the mitochondrial compartment show a high degree of similarity to bacterial molecular chaperones. Thus, studies of protein folding in bacteria such as Escherichia coli have proved to be instructive in understanding the process in the eukaryotic cell. As in bacteria, the molecular chaperone genes of eukaryotes are activated by a variety of stresses. The regulation of stress genes involved in mitochondrial chaperone function is reviewed and major unsolved questions regarding the regulation, function, and involvement in disease of the molecular chaperones are identified.

Animals↗
PubMed1997

Tissue-specific glucocorticoid regulation of tryptophan hydroxylase mRNA levels.

A potential long-term target of glucocorticoid modulation of serotonin (5-HT) production is tryptophan hydroxylase (TPH) gene expression. However, studies on TPH gene expression have been hampered by the extremely low levels of TPH mRNA in the brain, and there have been contradictory reports on the effects of glucocorticoids on 5-HT levels. To overcome these obstacles, we have developed a sensitive competitive RT-PCR assay to directly measure TPH mRNA levels from the rat brain. We observed a tissue-specific modulation of TPH mRNA levels in the melatonin producing pineal gland and the serotonin producing raphe nuclei of the brain. Following chronic treatment of adrenalectomized rats with the synthetic glucocorticoid dexamethasone for 1 week, there was a 16-fold increase in TPH mRNA in the pineal gland that was contrasted by a decrease in TPH mRNA to 16% of the control levels in the brain. To address the mechanism of dexamethasone repression of TPH mRNA levels, we then tested a serotonergic neuronal-like cell line derived from rat thyroid C cells. Dexamethasone caused a rapid decrease in TPH mRNA levels to approximately 20% of control values in CA77 C cells. This was measured by both competitive RT-PCR and a standard hybridization assay, which confirmed the validity of the RT-PCR assay. Furthermore, the reduction of TPH mRNA levels was associated with a decrease in 5-HT levels in the CA77 C cells. Hence, glucocorticoids may alter serotonin and melatonin biosynthetic capacity by cell-specific modulation of the TPH gene.

Animals↗
PubMed1997

Exercise profile and subsequent mortality in an elderly Australian population.

Although the importance of exercise as a public health issue is increasingly recognised, little attention has been paid to exercise in very old people. We examined exercise patterns in 1788 subjects aged 70 years and over who were participating in the Australian Longitudinal Study of Ageing. In the two weeks before interview, 39 per cent of subjects had taken no exercise and only four per cent had exercised vigorously. When compared with those who took no exercise, exercisers were more likely to be male and younger, to self-report better health, to be former smokers and regular alcohol users. Mortality rates at two years follow-up were inversely related to the level of exercise at baseline. This research indicates that exercise is important for the very old as well as younger groups.

Aged↗
PubMed1997

Abnormal illness behaviour in rehabilitation from stroke.

OBJECTIVE: To examine the effect of abnormal illness behaviour (AIB) on rehabilitation outcome following stroke. DESIGN: A longitudinal design, with assessments on admission to and discharge from rehabilitation, and six and 12 months after discharge. SETTING: The study was undertaken in the rehabilitation unit at Repatriation General Hospital, in Adelaide, South Australia. SUBJECTS: Ninety-four 12-month stroke survivors who had undergone an inpatient rehabilitation programme. MAIN OUTCOME MEASURES: AIB was assessed using the Illness Behaviour Questionnaire. Additional psychological measurements comprised the Zung Self-Rating Depression Scale, General Health Questionnaire, and a visual analogue mood scale. Functional ability was assessed with the Australian ADL Index, and lifestyle activities with the Frenchay Activities Index. RESULTS: Cluster analysis of discharge data was used to define a rule for identifying patients with AIB. AIB was apparent in nearly 30% of patients at discharge, and persisted for 12 months. Patients with AIB scored more poorly than non-AIB patients on functional, social and psychological indicators. CONCLUSIONS: AIB emerged as a key determinant of long-term disability. It is important to consider why AIB develops during rehabilitation, and how to identify patients at risk.

Activities of Daily Living↗
PubMed1997

SB 202026: a novel muscarinic partial agonist with functional selectivity for M1 receptors.

The finding that ascending cholinergic systems are severely degenerated in Alzheimer's disease has driven the search for a cholinomimetic therapy. Adverse effects observed with cholinesterase inhibitors and high-efficacy muscarinic agonists led us to design compounds with an improved profile. SB 202026 (R-(Z)-(+)-alpha-(methoxyimino)-1-azabicyclo[2.2.2] octane-3-acetonitrile) displaced [3H]-oxotremorine-M from muscarinic receptors in the rat brain with high affinity (IC50 = 14 nM), a potency similar to that of oxotremorine-M itself (IC50 = 13 nM), but exhibited low affinity for cholinergic nicotinic receptors and other neuroreceptors. In studies using cloned human muscarinic receptors, SB 202026 possessed approximately equal affinity in displacing [3H]-quinuclidinyl benzilate from all muscarinic receptor subtypes. In functional models in vitro, SB 202026 caused maximal depolarization of the rat superior cervical ganglion at low concentrations (300 nM) (M1-mediated effect), while producing a lower maximal effect than the high-efficacy agonists oxotremorine-M and carbachol on M2-mediated release of ACh and M3-mediated smooth muscle contraction (guinea pig ileum), respectively. The functional selectivity and partial agonist profile seen in vitro were reflected in vivo through potent cognition-related activity (M1-induced increase in hippocampal EEG power) combined with low efficacy, compared with arecoline or oxotremorine, on induction of bradycardia (M2-mediated response), hypotension (via M3-mediated vasorelaxation) and tremor (thought to be mediated by M3 receptors). The foregoing profile of SB 202026 predicted that cognition-enhancing activity would be achieved at doses below those that initiate undesirable side effects, and this has subsequently been demonstrated in rodents, marmosets and humans.

Acetylcholine↗
PubMed1996

Thyroid parafollicular cells. An accessible model for the study of serotonergic neurons.

Serotonergic neurons play key roles in modulating a wide variety of behavioral and homeostatic processes. However, there is a paucity of good model systems to study these neurons at a molecular level. In this review we will present evidence that cell lines derived from an unexpected source, thyroid parafollicular cells (PF) (also called C cells), fit the criteria for use as models for the study of serotonergic neurons. A strength of PF cell lines over other cell lines is that the parental PF cells have serotonergic properties and a neuronal potential that is consistent with their neural crest origin. Furthermore, PF cells and PF cell lines are capable of expressing the fundamental properties of serotonergic neurons, including: (1) serotonin (5-HT) biosynthesis by tryptophan hydroxylase (TPH), (2) vesicular 5-HT storage and regulated release, (3) expression of a 5-HT autoreceptor, and (4) expression of the 5-HT transporter. In this review, we will focus primarily on the serotonergic and neuronal properties of the rat CA77 PF cell line and the parental rat PF cells. The applicability of CA77 cells for molecular analyses will be described. First, their use for studies on the glucocorticoid regulation of the TPH gene will be discussed. Second, control of the calcitonin/calcitonin gene-related peptide (CT/CGRP) gene will be discussed, with particular emphasis on the application of serotonergic drugs in treating migraine headaches. These examples highlight the versatility of thyroid PF cell lines as a system for studying the control of both serotonin biosynthesis and physiological actions.

Animals↗
PubMed1996

Expression and development of a functional plasmalemmal 5-hydroxytryptamine transporter by thyroid follicular cells.

5-Hydroxytryptamine (5-HT) is synthesized and secreted by thyroid parafollicular (PF) cells. As all PF granules contain 5-HT, it is released whenever PF cells secrete. Because 5-HT stimulates follicular (F) cells and can modulate their response to TSH, 5-HT has been proposed to be a paracrine PF to F cell transmitter. This role would require a thyroid mechanism to rapidly inactivate 5-HT. A 5-HT transporter (SERT) in the plasma membrane of serotonergic neurons inactivates neuronal 5-HT. We thus tested the hypothesis that this molecule is expressed in the thyroid. Messenger RNA encoding SERT was demonstrated in both the human thyroid and a rat F cell line (FRTL-5). SERT immunoreactivity was detected in rat F, but not PF, cells. Transporter-mediated uptake of [3H]5-HT by F cells arose early in development (E13 in mice) and was maintained in adult life in mice, guinea pigs, bats, and rats (FRTL-5 cells). These observations indicate that a functional SERT is expressed in the thyroid, not by the 5-HT-secreting PF cells, but by their putative F cell targets.

Aging↗
PubMed1995

Aggregation state and neurotoxic properties of Alzheimer beta-amyloid peptide.

The behaviour of synthetic batches of beta-amyloid (beta A) 1-40 peptide in solution has been studied. The effects of beta A1-40 on a PC12 cell toxicity assay was dependent upon the time of preincubation of an aqueous solution of the peptide before application to the cells. Fibrillization of the beta A1-40, quantitatively assessed by the binding of Congo red to amyloid fibrils, also increased in a time dependent manner over the 168 h incubation period studied. The degree of Congo red binding, in the absence of any preincubation, differed between two synthetically distinct batches of the peptide. The rate of development of fibril formation during subsequent incubation also differed between the two batches and appeared to parallel the effects on cell viability. Infra-red spectroscopic analysis revealed beta-sheet formation for both batches and other more subtle conformational differences between the peptides. Electron microscope examination of the batches of beta A1-40 confirmed the difference in occurrence and development of fibrils. At high magnification, fibrils of both batches exhibited a helical structure. The results suggest that the development of neurotoxicity of beta A1-40 is related to the fibrillar state of the peptide.

Alzheimer Disease↗
PubMed1995

The Adelaide Activities Profile: a measure of the life-style activities of elderly people.

A new instrument for the measurement of life-style activities of the elderly is described. The Adelaide Activities Profile (AAP) was developed in response to the shortcomings of the Frenchay Activities Index. The AAP was validated on a random sample of 1799 people aged 70 years and over, living outside of institutional care. Principal components factor analysis revealed four consistent factors from which four scales were derived; these scales were named domestic chores, household maintenance, service to others, and social activities. Analyses demonstrated the construct validity of the four life-style scales by showing them to be differentially sensitive to a range of domestic, health and social circumstances. It was concluded that the distinct and meaningful clusters of activities represented by the AAP scales should have broad application as health and social indicators.

Activities of Daily Living↗
PubMed1995

Competence and performance in activities of daily living of patients following rehabilitation from stroke.

Indices of activities of daily living (ADL) are commonly criticized for failing to yield other than functional information. We suggest an alternative approach in which tested functional ability (ADL competence) is distinguished from actual behaviour (ADL performance). A method of making these assessments, based on the Australian ADL Index, was trialled in a longitudinal study involving 130 patients admitted for rehabilitation following stroke. Twelve months after discharge from rehabilitation the total ADL performance score was higher, that is to say worse, than the total ADL competence score; further, there was no significant agreement between the competence and performance ratings for nine of the 17 activities. It appears that ADL competence and ADL performance can be distinguished both theoretically and empirically. Two case studies illustrate the usefulness of the performance assessment. We recommend the ADL performance assessment as an outcome measure in rehabilitation.

Activities of Daily Living↗
PubMed1995

Induction of a serotonergic and neuronal phenotype in thyroid C-cells.

We have investigated whether rat thyroid C-cells can acquire a phenotype similar to serotonergic neurons. C-cells are neural crest derived endocrine cells with some intrinsic neuronal and serotonergic properties. A relatively simple isolation scheme yielded cultures of about 50% initial purity, as measured by fluorescence activated cell sorting. These enriched C-cells could extend neurites up to 550 microns on a laminin-containing substratum in the presence of NGF. The cultured C-cells expressed neurofilaments and this expression was enhanced by NGF treatment. The C-cells also expressed two markers of the sympathoadrenal neural crest lineage, the mammalian achaete scute homolog-1 (MASH-1) transcription factor, and the B2 cell surface antigen. Interestingly, MASH-1 was not detectable after the C-cells were placed in culture, which is consistent with neuronal differentiation, since MASH-1 is only expressed in neuronal progenitors prior to differentiation. We then demonstrated that C-cells possess the fundamental features of serotonergic neurons: synthesis and secretion, uptake, and feedback control. The enriched C-cells, as well as the CA77 C-cell line, showed 5-HT immunostaining, expression of tryptophan hydroxylase mRNA, 5-HT1B autoreceptor mRNA, and 5-HT transporter mRNA and activity. NGF greatly induced 5-HT transporter activity as determined by sensitivity to sertraline, a selective 5-HT reuptake inhibitor. Based on these results, we propose that thyroid C-cells are derived from a vagal sympathoadrenal progenitor, similar to serotonergic enteric neurons, and can undergo neuronal transdifferentiation. Hence, these cells should provide suitable and convenient models for molecular and cellular studies on serotonergic neurons.

Animals↗
PubMed1993

Neural expression of a novel alternatively spliced and polyadenylated Gs alpha transcript.

We have isolated an alternative transcript of the rat Gs alpha signal transduction protein gene, referred to as Gs alpha N1. Gs alpha N1 was isolated by differential hybridization screening of genes induced upon dexamethasone treatment of the neuronal-like CA77 rat thyroid C-cell line. The 1-kilobase Gs alpha N1 transcript is generated by alternative splicing and polyadenylation of a novel terminal exon. This exon lies 800 base pairs downstream of exon 3 in the Gs alpha gene. Dexamethasone differentially induced Gs alpha N1 severalfold relative to Gs alpha mRNA in the CA77 cells, similar to the bias seen with alternative processing of the calcitonin/calcitonin gene-related peptide transcript. In addition to the differential regulation by dexamethasone, the expression pattern of Gs alpha N1 in rat tissues differed markedly from Gs alpha. Gs alpha N1 mRNA was much more abundant in the brain, with intermediate levels in skeletal muscle and very low levels in other tissues. This was in contrast to the more ubiquitously expressed Gs alpha mRNA. Within the brain, Gs alpha N1 was particularly abundant in discrete regions of the brainstem and hypothalamus that modulate autonomic functions. Examination of rat embryos demonstrated that Gs alpha is expressed in both brain and nonneural tissue at least 1 day before Gs alpha N1 mRNA could be detected in the embryonic brain. Based on the regulated expression of the Gs alpha N1 transcript and previous studies on G alpha proteins, the predicted Gs alpha N1 protein may potentially modulate several heterotrimeric G protein functions in the nervous system.

Alternative Splicing↗
PubMed1992

Synthesis and muscarinic activities of quinuclidin-3-yltriazole and -tetrazole derivatives.

The synthesis of 15 methyl or unsubstituted 1,2,3-triazoles, 1,2,4-triazoles, and tetrazoles additionally substituted with a 1-azabicyclo[2.2.2]octan-3-yl group is described. The potency and efficacy of these compounds as muscarinic ligands were determined in radioligand binding assays using [3H]oxotremorine and [3H]quinuclidinyl benzilate. Potency and efficacy were found in compounds in which the azole moiety was attached to the azabicyclic ring either through a carbon atom or a nitrogen atom. Electrostatic potential maps of both the C-linked and the novel N-linked series of compounds were calculated. A relationship between position and depth of the electrostatic minima relative to the azabicyclic ring and the potency and efficacy of the compounds was determined.

Animals↗
PubMed1991

Comparison of azabicyclic esters and oxadiazoles as ligands for the muscarinic receptor.

The link between the cognitive deficit associated with Alzheimer type dementia and the loss of cholinergic function in the disease provides a basis for examining muscarinic agonists as potential therapeutic agents. This paper describes the design and synthesis of novel azabicyclic methyl esters as ligands for the muscarinic receptor. Replacement of the methyl ester by a 3-methyl-1,2,4-oxadiazole ring produces potent metabolically more stable muscarinic agonists capable of penetrating the central nervous system. These compounds generally show improved affinity relative to the corresponding methyl esters. 3-Methyl-1,2,4-oxadiazole 7b has an affinity 4 times that of acetylcholine. Receptor affinity is discussed in relation to the size and geometry of the azabicyclic ring and the electronic properties of the heteroaromatic ring.

Aminoquinolines↗