Tubular aggregates: sarcoplasmic reticulum origin, calcium storage ability, and functional implications

Area of Science:

• Biochemistry
• Cell Biology
• Neuromuscular Disorders

Background:

• Autosomal dominant myopathy can affect muscle fiber types.
• Tubular aggregates are a pathological finding in some myopathies.
• Sarcoplasmic reticulum (SR) proteins like Ca-pump and calsequestrin are crucial for muscle calcium homeostasis.

Purpose of the Study:

• To investigate the role of tubular aggregates in calcium handling in autosomal dominant myopathy.
• To examine the expression and reactivity of SR Ca-pump protein and calsequestrin in affected muscle fibers.
• To assess the calcium loading capacity of muscle fibers with tubular aggregates.

Main Methods:

• Immunofluorescent staining of muscle biopsy specimens using antibodies against SR Ca-pump protein and calsequestrin.
• Assessment of Ca2+ loading ability in chemically skinned muscle fibers.
• Analysis of tubular aggregates for reactivity with antibodies and calcium uptake.

Main Results:

• Type 1 and type 2 muscle fibers showed differential reactivity to anti-Ca-pump protein IgG but similar reactivity to anti-calsequestrin antibody.
• Tubular aggregates exhibited high reactivity with both antibodies.
• Tubular aggregates served as sites for calcium accumulation, increasing the Ca loading capacity of affected fibers via ATP-dependent uptake.

Conclusions:

• Tubular aggregates in autosomal dominant myopathy are sites of significant calcium accumulation.
• These aggregates enhance the calcium loading capacity of affected muscle fibers.
• The findings contribute to understanding calcium dysregulation in myopathies.