Vaishnavi Kardale, Bioinformatics Centre, Savitribai Phule Pune University
Every two seconds somewhere in the world a person has a stroke. A stroke is studied to happen when a part of the brain is deceived by the blood supply. This blockage depletes that part of the brain with oxygen. The lack of oxygen damages the brain. If treatment is delayed the brain cells may die causing permanent damage. Stroke is the leading cause of long-term disability. It reduces mobility in more than half of stroke survivors over the age of 65. Patients who suffer a stroke are unable to use their arms usually on one side of the body that is affected. Commonly experienced symptoms are abnormally tight and stiff muscles that resist stretching.
The present study of interest:
A study at Northwestern University and Shirley Ryan Ability Lab found that to adapt to the impairment in the arm, muscles lose sarcomere- their smallest building block. Muscle sarcomere consists of two main proteins- actin and myosin. These two proteins work together to produce force.
The research was published in the National Academy of Arts and Sciences. Previous studies in animals have found that muscle length adapts to functional demands. This means if a muscle is not as functional it will lose its sarcomere leading to a decrease in its length. No such study was carried out in humans until now. In this study, three non-invasive medical imaging techniques were used:
- MRI to measure the volume of muscle
- Ultrasound to measure the bundles of muscle fibers
- Two-photon microscopy to measure the microscopic muscle sarcomere.
The researchers compared results from seven stroke patients with four healthy individuals. Since stroke usually affects one side of the body, the researchers also compared the images of the affected side with the unaffected side.
What did the study find?
The study found that the affected biceps had less volume, shorter muscle fibre, and comparable sarcomere length. The affected biceps had fewer sarcomeres compared to the unaffected biceps. The differences between a healthy participant’s arm and a stroke patient’s arm were massive. These differences were attributed to stroke.
The researchers hope that their study can improve the rehabilitation technique to rebuild muscle sarcomere and help to ease muscle tightening and shortening.
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Reference:
- Adkins, A.N., Dewald, J.P.A., Garmirian, L.P.G, et al. (2021) Serial sarcomere number is substantially decreased within the paretic biceps brachii in individuals with chronic hemiparetic stroke. PNAS.https://doi.org/10.1073/pnas.2008597118
- The in-text image of actin and myosin filaments has been extracted from Servier Medical Art.
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