NF-κB Signaling Regulates Physiological and Pathological Chondrogenesis

Area of Science:

• Molecular biology
• Immunology
• Developmental biology

Background:

• Nuclear factor-kappa B (NF-κB) is a crucial transcription factor regulating genes involved in cell proliferation, apoptosis, inflammation, and immune responses.
• NF-κB activation occurs via two main pathways: the classical pathway (involving IκBα degradation) and the alternative pathway (involving NF-κB-inducing kinase, NIK).
• The mouse growth plate, essential for bone development, comprises distinct zones: resting, proliferative, prehypertrophic, and hypertrophic.

Purpose of the Study:

• To elucidate the distinct roles of NF-κB classical and alternative pathways in cartilage development and pathogenesis of joint diseases.
• To investigate the expression and function of NF-κB components, such as p65 (RelA) and RelB, in the growth plate and during inflammatory conditions.

Main Methods:

• Analysis of NF-κB pathway components (p65/RelA, RelB, NIK) expression in mouse growth plate cartilage.
• Examination of the effects of classical NF-κB inhibition on growth hormone (GH) and insulin-like growth factor (IGF-1) signaling, cell proliferation, and bone morphogenetic protein 2 (BMP2) expression.
• Review of NF-κB involvement in the pathogenesis of rheumatoid arthritis (RA) and osteoarthritis (OA) models.

Main Results:

• The classical NF-κB pathway component, p65 (RelA), is expressed throughout the cartilage layer of the growth plate.
• Inhibition of the classical NF-κB pathway suppressed GH/IGF-1 signaling, reduced cell proliferation, decreased BMP2 expression, and promoted apoptosis.
• NF-κB classical pathways regulate inflammatory cytokine production (TNFα, IL-1β, IL-6, IL-17), implicated in RA pathogenesis.
• The alternative NF-κB pathway, involving RelB, is crucial for chondrocyte generation in the proliferative zone during development and contributes to RA and OA pathogenesis.

Conclusions:

• NF-κB plays a dual role in cartilage biology, governing normal development and pathological destruction.
• The classical and alternative NF-κB pathways exhibit distinct functions in chondrogenesis and inflammatory joint diseases.
• Modulation of NF-κB signaling presents a potential therapeutic target for managing cartilage-related disorders like RA and OA.