Heparan sulfate controls skeletal muscle differentiation and motor functions

Background: Heparan sulfate (HS) is a sulfated linear polysaccharide on cell surfaces that plays an important role in physiological processes. HS is present in skeletal muscles but its detailed role in this tissue remains unclear. Methods: We examined the role of HS in the differentiation of C2C12 cells, a mouse myoblast cell line. We also phenotyped the impact of HS deletion in mouse skeletal muscles on their functions by using Cre-loxP system. Results: CRISPR-Cas9-dependent HS deletion or pharmacological removal of HS dramatically impaired myoblast differentiation of C2C12 cells. To confirm the importance of HS in vivo, we deleted Ext1, which encodes an enzyme essential for HS biosynthesis, specifically in the mouse skeletal muscles (referred to as mExt1CKO mice). Treadmill and wire hang tests demonstrated that mExt1CKO mice exhibited muscle weakness. The contraction of isolated soleus muscles from mExt1CKO mice was also impaired. Morphological examination of mExt1CKO muscle tissue under light and electron microscopes revealed smaller cross sectional areas and thinner myofibrils. Finally, a model of muscle regeneration following BaCl₂ injection into the tibialis anterior muscle of mice demonstrated that mExt1CKO mice had reduced expression of myosin heavy chain and an increased number of centronucleated cells. This indicates that muscle regeneration after injury was attenuated in the absence of HS expression in muscle cells. Significance: These results demonstrate that HS plays an important role in skeletal muscle function by promoting differentiation.