Traditionally, interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) have been regarded as classical proinflammatory and bone resorptive cytokines. Nevertheless, a few recent publications give evidence for inhibitory effects of TNF- α on osteoclastogenesis. The aim of this work was to analyse the effects of IL-1β, IL-6 and TNF-α on osteoclastogenesis and cathepsin K expression in primary murine bone marrow osteoclast cultures. Primary murine bone marrow cell cultures from 2-3 month old HIM:OF-1 mice were supplemented with 1,25 dihydroxy vitamin D3 to induce osteoclatogenesis and combined or individually treated with the proinflammatory cytokines IL-1β, IL-6 and TNF-α. After a culture period of one week, cells were stained for tartrate resistant acid phosphatase (TRAP), mRNA levels of cathepsin K, RANKL and OPG were determined by real-time-PCR, and protein expression of cathepsin K was assessed by immunofluorescence staining. Combined treatment and treatment with the individual cytokines led to a significant decrease in the number of generated osteoclasts as assessed by TRAP staining, whereas protein expression and mRNA expression of cathepsin K were not influenced. However, there was as trend towards a lower cathepsin K mRNA expression in cultures individually treated with interleukin-6 or TNF-α, and a lower RANKL/OPG mRNA ratio in cultures individually treated with TNF-α. We conclude, that in our experimental setting the proinflammatory cytokines IL-1β, IL-6 and TNF-α decrease the generation of osteoclasts, but have not significant effect on mRNA or protein expression of cathepsin K.
Disclosure: The authors declared no competing interests. This work was supported by Merck Sharp & Dohme Ges.m.b.h.