Cathepsin K inhibition renders equine bone marrow nucleated cells hypo-responsive to LPS and unmethylated CpG stimulation in vitro.

This study examines enzyme cathepsin K’s role in bone degradation and immune response, focusing on how its inhibition impacts inflammatory responses in equine bone marrow nucleated cells. The researchers found that by limiting cathepsin K, cell vitality is promoted, apoptosis is reduced, and cytokine secretion is decreased, which can affect the immune response.

Cathepsin K and its Role

• Cathepsin K (CatK) is a key enzyme involved in bone degradation. It’s also known to play a role in immune response.
• The researchers set out to investigate how inhibition of this enzyme might interact with and affect bone marrow nucleated cells in horses, focusing particularly on inflammatory responses.

The Methodology and Objectives

• The study uses two models of inflammation: stimulation with lipopolysaccharide (LPS) and unmethylated CpG.
• The objectives were to observe whether CatK inhibition changes cytokine secretion (specifically IL-1β, IL-6, and TNF-α) of stimulated bone marrow nucleated cells, and whether changes occur in the expression of surface markers on these cells, and the MHC II molecule within an environment of CatK inhibition.

Findings and Conclusion

• It was found that inhibiting CatK promotes cell viability and reduces cell apoptosis, which is the process of programmed cell death in organisms.
• The inhibition also resulted in significant decrease of cytokine secretion by the bone marrow nucleated cells, whether they were triggered or untriggered. This indicates that CatK might have a role to play in immune responses.
• The study also reported a change in the expression of MHC II molecule, which has crucial immunological functions, such as presenting peptides derived from extracellular proteins.
• The researchers draw the conclusion that inhibiting CatK affects the responsiveness of bone marrow nucleated cells in horses to inflammation induced by toll-like receptor 4 (TLR4) and toll-like receptor 9 (TLR9).
• The conclusion suggests further implications for the proteolytic activity of CatK in the MyD88 pathway which is essential for transmitting toll-like receptor signals, and/or in subsequent proteolytic events necessary for the secretion of cytokines.