NF-kappaB functions in stromal fibroblasts to regulate early postnatal muscle development

Area of Science:

• Muscle biology
• Developmental biology
• Cellular signaling

Background:

• Classical NF-kappaB (NF-kappaB) activity inhibits skeletal muscle myogenesis.
• Previous studies suggest NF-kappaB involvement in early postnatal skeletal muscle development.
• RelA/p65 knockout mice exhibit increased myofiber numbers, hinting at NF-kappaB's regulatory role.

Purpose of the Study:

• Investigate the role of NF-kappaB in early postnatal skeletal muscle development.
• Elucidate the cellular localization and function of NF-kappaB during muscle growth.
• Determine the impact of NF-kappaB modulation on myogenic gene expression and myoblast fusion.

Main Methods:

• Utilized genetic manipulation (p65 deficiency, IKKbeta deletion) and pharmacological inhibition (IkappaB alpha-SR) to repress NF-kappaB activity.
• Analyzed skeletal muscle tissue from early postnatal mice at different developmental time points.
• Assessed myofiber number, myogenic gene expression, and cellular localization of NF-kappaB activity.
• Investigated the role of NF-kappaB in regulating inducible nitric-oxide synthase (iNOS) expression in fibroblasts.

Main Results:

• Repression of NF-kappaB led to increased total fiber numbers and upregulated myogenic gene products.
• NF-kappaB activity decreased progressively in postnatal muscle, shifting from myofibers to stromal fibroblasts.
• NF-kappaB in fibroblasts regulates inducible nitric-oxide synthase (iNOS) expression.
• iNOS expression is crucial for myoblast fusion during skeletal muscle maturation.

Conclusions:

• NF-kappaB acts as a negative regulator of myogenesis but also plays a positive role in muscle development.
• NF-kappaB signaling in stromal fibroblasts regulates iNOS, which is essential for myoblast fusion.
• This study expands the understanding of NF-kappaB's dual role in skeletal muscle development, impacting both myogenesis inhibition and hypertrophy stimulation.