Plasminogen activator activity in differentiating rat myoblasts.

Area of Science:

• Cell Biology
• Biochemistry
• Muscle Physiology

Background:

• Skeletal muscle cells in culture exhibit both secreted and membrane-bound plasminogen activator (PA) activity.
• The role of PA in skeletal muscle cell differentiation and maturation remains unclear.

Purpose of the Study:

• To investigate the effect of dexamethasone on PA activity in primary skeletal muscle cell cultures and a myogenic cell line.
• To determine the role of PA in the fusion process of skeletal muscle cells.

Main Methods:

• Primary skeletal muscle cells and the L-8 myogenic cell line were cultured with and without dexamethasone.
• PA activity was measured in conditioned media and on cell membranes.
• Creatine phosphokinase (CPK) activity and protein content were assessed.
• Cell viability and fusion were evaluated.
• Reactivation of PA activity in conditioned media was tested using SDS, trypsin, and acidification.

Main Results:

• Dexamethasone significantly reduced both secreted and membrane-bound PA activity in primary skeletal muscle cells, along with cytosolic CPK and protein content, without affecting cell fusion or viability.
• The suppressive effect of dexamethasone was dependent on exposure time, with maximal reduction observed after 4 days.
• Conditioned media from dexamethasone-treated cells showed no inhibition of plasmin or PA, and activity could be restored by SDS or trypsin treatment, but not acidification.
• In contrast, dexamethasone had no effect on PA activity in the L-8 myogenic cell line, regardless of fusion status.

Conclusions:

• Dexamethasone modulates PA activity in primary skeletal muscle cells, suggesting a regulatory role for this hormone.
• The findings indicate that plasminogen activator is not essential for the fusion and maturation processes of skeletal muscle cells.
• The differential response of primary cultures versus the L-8 cell line suggests distinct regulatory mechanisms or cell-specific properties.