Endogenous cathepsin B inhibitor activity in normal and myopathic red and white skeletal muscle

Area of Science:

• Biochemistry
• Muscle Physiology
• Nutritional Science

Background:

• Degenerative muscle diseases have obscure primary chemical lesions.
• Vitamin E deficiency causes nutritional muscular myopathy in animals.
• Lysosomal endoproteinases like cathepsin B play roles in muscle tissue.

Purpose of the Study:

• To investigate cathepsin B activity and its endogenous inhibitor levels in vitamin E-deficient muscular myopathy.
• To determine if altered cathepsin B activity is a primary defect in this condition.

Main Methods:

• Assessed cathepsin B activity in red and white skeletal muscles of guinea pigs.
• Measured endogenous cathepsin B inhibitor activity in the same muscle tissues.
• Corrected cathepsin B activity for inhibitor levels.

Main Results:

• A twofold increase in cathepsin B activity was observed in white muscles of vitamin E-deficient animals.
• Normal and control groups showed significantly higher cathepsin B inhibitor activity compared to deficient animals.
• Corrected cathepsin B specific activity in deficient muscle was not significantly different from normal or control tissues.

Conclusions:

• The increased cathepsin B activity in vitamin E-deficient muscle is likely due to reduced inhibitor levels, not a primary enzyme abnormality.
• This suggests that altered regulation of cathepsin B, rather than its intrinsic activity, is involved in nutritional muscular myopathy.