The type 1 ryanodine receptor or RyR1 is among the calcium release channels in skeletal muscles required in muscle contraction. It regulates the release of calcium ions from the sarcoplasmic reticulum, an organelle that stores calcium ions within muscle cells, which is a very important factor in muscle operation.
Malfunctions of the RyR1 protein can be triggered by mutations and may produce an extremely wide range of effects on the channel; these effects are manifested in severe muscular disorders, including malignant hyperthermia (MH) and central core disease (CCD). MH is an autosomal dominant inherited disease characterised by high fever and muscle contractures in response to inhaled anaesthetic agents in patients harbouring gain of function RyR1 mutation.
CCD is one of the inherited myopathies which cause muscle weakness and myopathy due to loss-of-function RyR1 variants. These effects prove the significance of RyR1 as well as the proper functioning of the calcium channels to the muscles.
Although the current studies emphasised the vast intraluminal space of RyR1, where majority of mutations were identified, little was known about the involvement of the fifth transmembrane domain (S5) in channel activation and development of muscular dystrophies. Fortunately, in a new study published on 18 September, in Communications Biology the Japanese scientists focused on this gap of knowledge and studied the mutation in the S5 segment of the RyR1 that led to MH and CCD.
The research team including the leading researcher with the Associate Professor of Takashi Murayama from Juntendo University, and his team of Nagomi Kurebayashi, Associate Professor at Juntendo University and the team including Associate Professor of Haruo Ogawa and Graduate student of Yuya Otori of Kyoto University aimed at identifying the connection between S5 mutation and muscle disorder.
Heterologously expressed RyR1 proteins with the specific mutations were examined in HEK293 cells, a human embryonic kidney cell line. To evaluate consequences of mutations on calcium release kinetics they quantified caffeine-stimulated calcium release.
In addition, they maintained resting cytoplasmic and ER calcium levels by Fluo-4 AM (green-fluorescent calcium indicator) and R-CEPIA1er, respectively. A functional RyR1 assay using fluorescently labelled ryanodine was made to assess the binding of the channels and their activity levels. Furthermore, the depolarization-induced calcium release (DICR) device was employed in the determination of calcium release in the RyR1 channel.
Thus, this investigation helps longitudinally explain how mutations in S5 distort channel function and by extension the perspective on calcium signalling in muscle physiology proves beneficial. According to Murayama and Ogawa, these research investigations offer a start in the right direction for the development of new drugs to treat muscle diseases as a result of RyR1 mutations.
Reference:
Dual role of the S5 segment in type 1 ryanodine receptor channel gating, Communications Biology (2024). DOI: 10.1038/s42003-024-06787-1
