Cellular modelling to understand altered muscle growth in children with Cerebral Palsy

Cerebral palsy (CP) is one of the most common conditions leading to lifelong childhood physical disability, affecting approximately 1.6 in 1000 live births. CP is characterised firstly by neural deficits caused by a non-progressive lesion in the immature brain, and secondly by musculoskeletal problems that progress with age. Clinical symptoms of the neural and muscular impairments mainly involve spasticity, increased stiffness and contractures, muscle weakness and decreased functional ability such as disturbed gait. Furthermore, literature reported muscle alterations of CP patients in comparison to typically developing (TD) children both at macroscopic (e.g., reduced muscle volume and longer tendons) and microscopic levels (e.g., fibrotic tissue accumulation, hypertrophic extracellular matrix and reduced satellite cell (SC) numbers). Unfortunately, the onset and development of these muscle alterations are not well understood, because data from young patients with CP, i.e., < 10 years of age, have been scarce. Additionally, the role of muscle stem cells, involved in all post-natal regeneration and remodelling processes, have been poorly described in the context of CP.

In this PhD research work, we aimed to improve insights in the muscle pathology of young children with CP by investigating the in vitro biological features of multiple muscle stem cell populations. The first objective was to characterise multiple stem cell populations for their proliferation and differentiation potential, extracted from muscle biopsies that were collected using the muscle microbiopsy technique. The second objective was to further quantitatively assess alterations in SC differentiation and explore potential involved gene pathways.

Based on muscle microbiopsies from the calf muscle (Medial Gastrocnemius) of young 17 patients with CP (3-9 years of age), and 13 age-matched typically developing (TD) children, we observed altered differentiation features based on fusion index, myotube morphology and nuclear positioning. Unprecedently, a smaller subgroup of subjects (TD: n = 3, CP: n = 6) was also included for stem cell analysis of the hamstring muscle (Semitendinosus), which showed for both TD and CP lower myogenic capacities based on the SC fusion index. Uniquely, 4 patients with CP were enrolled before and after botulinum toxin (BoNT) treatment and longitudinal analysis suggested lower SC representation and lower myogenic potency after BoNT.

In conclusion, this PhD project provided evidence on the involvement of stem cells in the CP muscle pathology and paved the way for a broader application of the muscle microbiopsy to characterise adult stem cells in CP and other muscle related pathologies. Further research is needed to investigate this SC phenotype and identify specific pathways contributing to the CP muscle pathology.