LARGE glycans on dystroglycan function as a tunable matrix scaffold to prevent dystrophy

Area of Science:

• Cell Biology
• Biochemistry
• Developmental Biology

Background:

• The cell surface glycan coat is vital for cellular functions and highly dynamic.
• The enzyme like-acetylglucosaminyltransferase (LARGE) adds repeating polysaccharide units (LARGE-glycan) to dystroglycan, essential for its extracellular matrix receptor function.
• Defects in LARGE-glycan lead to muscular dystrophies, but the precise role of glycan chain length remains unclear.

Purpose of the Study:

• To investigate the cellular function of the LARGE-glycan repeat and its correlation with muscular dystrophy.
• To determine how LARGE-glycan chain extension influences dystroglycan's extracellular matrix binding capacity.
• To elucidate the role of LARGE-glycan in skeletal muscle development and regeneration.

Main Methods:

• Studied coordinated upregulation of Large and dystroglycan in differentiating mouse muscle.
• Utilized synthesized LARGE-glycan repeats to assess binding capacity with extracellular matrix ligands.
• Blocked Large upregulation during mouse muscle regeneration to observe effects on dystroglycan and muscle function.

Main Results:

• Coordinated upregulation of Large and dystroglycan promotes rapid extension of LARGE-glycan chains.
• Increased LARGE-glycan chain length directly correlates with enhanced binding to extracellular matrix ligands.
• Blocking Large upregulation during muscle regeneration results in reduced LARGE-glycan, leading to basement membrane defects, immature neuromuscular junctions, and muscle dysfunction.
• Patients with severe muscular dystrophy exhibit fewer LARGE-glycan repeats.

Conclusions:

• The LARGE-glycan on dystroglycan acts as a tunable scaffold for extracellular matrix proteins.
• The extension of LARGE-glycan chains is essential for normal skeletal muscle function and integrity.
• Dysfunctional LARGE-glycan extension contributes to the pathogenesis of muscular dystrophy.