Award details

Control of muscle contraction in Caenorhabditis elegans of relevance to human malignant hyperthermia, exertional heatstroke and muscle ageing.

Reference	BB/M00032X/1
Principal Investigator / Supervisor	Professor Ian Hope
Co-Investigators / Co-Supervisors	Dr Marie-Anne Shaw
Institution	University of Leeds
Department	Sch of Biology
Funding type	Research
Value (£)	396,565
Status	Completed
Type	Research Grant
Start date	19/01/2015
End date	18/07/2018
Duration	42 months

Abstract

The ryanodine receptor is the channel through which calcium ions flow out of the sarcoplasmic reticulum to trigger muscle contraction. Human genetics suggests the control of this channel is more complicated than we currently appreciate but relevant to numerous myopathies and muscle ageing. However, being over 5000 amino acids long and an integral membrane protein makes the ryanodine receptor difficult to study. The C. elegans ryanodine receptor is strongly conserved with the vertebrate homologues throughout its length, suggesting the control systems are also conserved, but provides a tractable model subject. C. elegans strains will be created with single amino acid changes as in the compromised ryanodine receptor variants associated with human malignant hyperthermia. The reaction of the genetically modified individuals to drugs, that trigger malignant hyperthermia, and to environments, that trigger genetically related conditions, will be assessed. A few such strains amongst those constructed so far do respond in a manner reminiscent of the human situation. Other strains, where no such sensitive state is detected, will nevertheless be sensitized to second site genetic changes affecting proteins involved in regulating the ryanodine receptor. A forward genetic screen will be undertaken and mutants that now respond to a triggering drug, dependent on the modified ryanodine receptor, will be isolated. The mutations in these strains will be determined by whole genome sequencing to identify genes involved in novel regulatory mechanisms acting on the ryanodine receptor. A link between ryanodine receptor function and muscle ageing has been suggested repeatedly. Muscle ageing rates will be measured in mutants isolated and upon knockout / knockdown of other genes previously linked with ryanodine receptor function. This work may well lead eventually to treatments for various human medical conditions associated with cardiac and skeletal muscle and to delay muscle ageing.

Summary

Muscle contraction depends on molecular filaments pulling past each other to shorten the length of the cell. This relative movement is triggered by an elevation of calcium ions in the cytoplasm around the filaments. Most of this calcium comes from a membrane bound organelle called the sarcoplasmic reticulum within the muscle cell. The channel through which the calcium ions cross the sarcoplasmic reticulum membrane is a protein called the ryanodine receptor. When a nerve excites a muscle cell to contract, the ryanodine receptor channel is opened to the flow of calcium ions. The channel must close to allow the calcium ions to be pumped back into the sarcoplasmic reticulum for the muscle to relax. The ryanodine receptor is a huge integral membrane protein making it difficult to study, but the genetics of various human conditions suggest the control of the channel is more complicated than we currently appreciate. Genetic approaches taken in a suitable model system make such difficult subjects tractable. One powerful model system in biological study, with which genetic approaches can be readily pursued, is the nematode worm Caenorhabditis elegans. At a molecular genetic level all animals are much more similar than might have been expected from outward appearances. By studying this nematode worm we have already found out about many important aspects of fundamental biology. Like vertebrates, C. elegans locomotion depends on neural excitation of muscle cells. C. elegans also has a ryanodine receptor, with structure very similar to the ryanodine receptor of vertebrates, including humans, and the control mechanisms will also be conserved. The C. elegans ryanodine receptor will be modified in the same way as in human conditions where the ryanodine receptor of some individuals, susceptible to malignant hyperthermia, appears compromised. The reaction of the worms, with such modified ryanodine receptors, to conditions that cause a problem response in susceptible people will be assessed. A few such worm models have already been constructed to test the approach and some of these do respond to triggering agents in a manner reminiscent of the human condition. This adds support to the validity of using C. elegans as a model for this topic of study. Further models, with different ryanodine receptor variants, will be constructed and the response of all model strains to triggering agents will be fully assessed. The worm models that do not show such reactions will nevertheless be partially compromised and provide a sensitized background state in which additional genetic changes, of direct relevance to ryanodine receptor function, can be revealed. The additional genetic changes are likely to affect proteins involved in controlling the activity of the ryanodine receptor. Therefore, random mutations will be created across the genome in the sensitized strains of C. elegans and mutants which now respond to the triggering agent, dependent on the modified ryanodine receptor, will be screened for. Characterization of the mutations in these mutant strains will identify genes and encoded proteins with roles in control of the ryanodine receptor function that had not been previously appreciated. Identifying novel regulatory mechanisms acting on the ryanodine receptor may well lead to medical treatments for various human medical conditions associated with cardiac and skeletal muscle. Previous studies in C. elegans and mammals have repeatedly suggested a link between ryanodine receptor function and muscle ageing, the decreased capacity for muscle contraction in older animals. The short lifespan of C. elegans has made this species a leading subject for ageing research. Muscle ageing rates will be measured in mutants isolated in the ryanodine receptor compromised background. Similar assays will be applied for other genes previously linked with ryanodine function. Possible subjects for research into delaying muscle ageing will thereby be identified.

Impact Summary

The proposed project concerns advancing our basic biological knowledge of the control of calcium homeostasis and muscle function. As such the value of the work lies primarily and initially within academic impact. The findings from the project will contribute to the national and global body of scientific knowledge upon which the knowledge economy is built. More specifically, the advancement of our understanding of these fundamental biological processes will be relevant to the important issues of the ageing of populations that is becoming an increasing problem worldwide. This project is timely in that it will explore the mechanisms underlying the recent associations between variants of the ryanodine receptor and muscle ageing. Reduced skeletal muscle function in the aged is a major determinant of well-being, dependency on support services, morbidity and mortality. A delay in muscle ageing would be of direct benefit in improving human healthspan. A better understanding of ryanodine receptor biology and of calcium balance maintenance within muscle cells with age appears likely to provide the knowledge upon which treatments to delay muscle ageing will be developed. The remarkable conservation of biological processes at the molecular level means studying this subject in the tractable model system Caenorhabditis elegans will yield knowledge of relevance across the animal kingdom, including to human biology. Recent research has also found a link between the ryanodine receptor in cardiac muscle and various heart dysfunctions. Although the proposed project is focussed on the variants of ryanodine receptor found in skeletal muscle, findings concerning the operation of this ion channel will also be relevant to advancing our basic knowledge of cardiac muscle biology as the C. elegans ryanodine receptor is orthologous to both cardiac and skeletal muscle ryanodine receptors. Heart dysfunction is also an increasing problem with the ageing of our populations. Defects in the ryanodine receptor have been linked with various other medical conditions that are not associated with age, such as exertional rhabdomyolysis and exertional heatstroke. Improvements in our basic understanding of the control of the function of this ion channel may well provide the basis for diagnosis, prophylaxis or treatment of all these conditions. A more immediate beneficiary of the proposed research is likely to be patients requiring general anaesthesia. A better knowledge of the genetic basis of malignant hyperthermia, and genetic associations beyond the ryanodine receptor, will contribute to the further implementation of personalized medicine in routine anaesthetic practice to lead to increased safety of anaesthesia. Improvements in diagnostics will reduce costs associated with cancelled operations and high dependency postoperative care. These benefits could be realised very quickly for small numbers of high-risk patients as new genetic knowledge can be translated into diagnostic tests in a matter of months. In the longer term, this research could contribute to the development of a screening test applicable to the 10% of the population requiring general anaesthesia each year, around 5 million people in the UK alone. Such a screening test would have potential for commercial exploitation.

Committee	Research Committee C (Genes, development and STEM approaches to biology)
Research Topics	Ageing
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

I accept the terms and conditions of use (opens in new window)

export PDF file

back to list new search