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Is Upper Arm Post-Stroke Spasticity Related to Reduced Muscle Repair Potential? Comparison of Muscle Stem Cell Population between Stroke Patients and Control Group
Olga Politikou, MD1, Richard L. Lieber, PhD2, Raji Pichika, PhD3, Andreas Spittler, MD1, Oskar C. Aszmann, MD, PhD4 and Andrea Domenighetti, PhD5, (1)Medical University of Vienna, Vienna, Austria, (2)Department of Orthopaedics, Northwestern University, Chicago, IL, (3)Shirley Ryan AbilityLab, Chicago, IL, (4)CD Laboratory for Restoration of Extremity Function, Division of Plastic and Reconstructive Surgery, Medical University of Vienna, Vienna, Austria, (5)Northwestern University, Chicago, IL

Introduction: Satellite cells (SC), a group of mononuclear, self-renewing adult muscle stem cells residing between sarcolemma and basal lamina, are the precursors responsible for muscle regenerative process. Previous studies demonstrated a reduced SC population in spastic hamstring muscles of children with cerebral palsy but it is still unknown whether this finding is secondary to muscle contractures or is primarily related to the disease itself and contributes to contracture development. Our goal was to determine whether upper extremity spastic contracted muscles from stroke patients also present a reduced SC population, which could preclude them from sufficient functional recovery after contracture release or intervention on nerve level, such as hyperselective neurotomy.
Methods: In this pilot study, we compared the percentage of SC populations in pronator teres (PT) and flexor carpi ulnaris (FCU) muscle from stroke patients obtained during spasticity reduction surgery (n=4; 3 females, 1 male; age range 37-72y; post-stroke interval 2 - 5 years) and from control participants who underwent ulnar nerve release at the elbow (n=2; 1 male, 1 female, age 45 and 56y). After two-step enzymatic digestion and trituration of muscle biopsies, cell suspensions were stained with appropriate cell surface markers to differentiate SC population (NCAM/CD56-positive and Integrin-β1/CD29-positive) from hematopoietic and stromal cell types (PTPRC/CD45-positive and PECAM1/CD31-positive) using flow cytometry. The sorted SC population was expanded and differentiated in vitro using low serum media. Seventy-two hours later, cells were fixed and stained for the differentiation marker alpha-actinin (ACTA2) and DAPI to label the nuclei.
Results: In spastic PT and FCU muscles from stroke patients, SCs represented 0.6% (SD 0.3%) of the whole cell population, while in intact muscles of control participants SCs were 0.8% (SD 0.3 %), with no statistical difference between groups (Fig. 1A). Our preliminary data also suggest that sorted SCs from spastic muscles have maintained muscle growth and repair potential as illustrated from their capacity to proliferate, expand and differentiate into multi-nucleated myotubes (i.e. newly forming muscle fibers) in vitro (Fig. 1B).
Conclusion: In contrast to contractured muscles in children with cerebral palsy, SC content of muscles involved in post-stroke spasticity seem to maintain their numbers and ability to proliferate and differentiate. Our findings provide a new insight in the pathophysiology of post-stroke spasticity and may guide appropriate treatment choice.


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