Summary
Central core disease, multi-minicore disease and malignant hyperthermia have
been linked to point mutations in the gene encoding the skeletal muscle sarcoplasmic
reticulum calcium release channel (ryanodine receptor), which is localized on human
chromosome 19 (RYR1). The ryanodine receptor is a key protein involved in the
regulation of the intracellular calcium concentration in muscle cells and plays a crucial
role in muscle contraction, releasing the calcium from the sarcoplasmic reticulum after
plasma membrane depolarization. Central core disease and multi-minicore disease are
neuromuscular disorders characterized by hypotonia during infancy, muscle weakness
and delayed motor development. They differ in their clinical phenotypes and modes of
inheritance. Central core disease is a relatively mild, slowly progressive autosomal
dominant myopathy, characterized histologically by the presence of centrally located
cores running the length of the muscle fibres. Multi-minicore disease is a more severe,
rare, autosomal recessive congenital myopathy characterized histologically by the
presence of multiple cores in only a small number of sarcomeres. The subclinical
myopathy malignant hyperthermia is a potentially fatal pharmacogenetic disorder
occurring in predisposed individuals when they are exposed to volatile anaesthetics and
depolarizing muscle relaxants such as suxamethonium. The study of the functional
properties of ryanodine receptor channels carrying mutations linked to neuromuscular
disorders is important from a diagnostic point of view but also to understand the basic
pathophysiological mechanism leading to these different diseases. In fact understanding
the mechanisms leading to dysregulation of calcium homeostasis is of fundamental
importance if one is to develop a pharmacological treatment to improve the quality of life
of affected patients. To date there are no effective therapies for the treatment of muscle
weakness in central core disease and multi-minicore disease patients, while for malignant
hyperthermia presymtomatic diagnosis is fundamental.
Our working hypothesis is that decrease of sarco(endo)plasmic reticulum Ca2+
load via leaky ryanodine receptor channels and/or alteration of calcium influx via store
operated channels or excitation-coupled Ca2+ entry, may account for the phenotype of
patients with Central Core Disease, including muscle weakness and abnormal secretion of
inflammatory cytokines from muscle cells and cells of the immune system. In this
project we will set out to test the validity of our hypothesis by directly investigating the
mechanisms activating calcium influx during depolarization of myotubes from normal
individuals and from patients with Central Core Disease. In addition, we will measure
how calcium influx in human dendritic cells is involved in activation of the ryanodine
receptor providing signals leading to their maturation.