Expression of mRNA for IL1β, IL6 and TGFβ1 in developing human bone and cartilage

Abstract

Using in situ hybridization, we investigated the expression of mRNA for interleukin-1β (IL1β), interleukin-6 (IL6), and transforming growth factor- β-1 (TGFβ1) in sections of developing bone in human osteophytes. The expression was related to the cellular activity of alkaline phosphatase to aid in the identification of pre-osteoblast populations. IL1β mRNA was localized in active osteoblasts within distinct areas of intramembranous ossification. However, the expression was sporadic and appeared to occur at a specific stage of the osteoblast life cycle. There was no IL1β mRNA expression in any cell types during endochondral ossification. IL6 mRNA expression was located within pre-osteoblasts and in newly differentiated and matrix-secreting osteoblasts; expression was absent or reduced in flattened, inactive osteoblasts. Weak or no IL6 expression was observed in chondroblasts and chondrocytes, respectively. However, there was a close association between IL6 mRNA expression and the differentiation of mesenchymal cells into osteoblasts. TGFβ1 expression was localized to osteoblasts apposed to bone or cartilage matrix; the intensity of expression correlated with matrix secretion. Chondroblasts and chondrocytes expressed lower but significant levels of TGFβ1 mRNA; the expression was lost with the progression to calcifying cartilage. The three cytokines studied were differentially expressed both temporally and spatially, suggesting different roles for each in osteoblast and chondrocyte function.