Expression of markers of activity in cultured human osteoblasts: effects of interleukin-4 and interleukin-13.

Cytokines regulate proliferation, differentiation and activation of osteoblasts. Interleukin-4 (IL-4) and interleukin-13 (IL-13) takes part in this regulation by inhibiting proliferation and by enhancement of interleukin-6 (IL-6) formation in cultured human osteoblasts (hOBs). In the present study we have investigated the effects of IL-4 and IL-13 on markers of osteoblastic activity in isolated hOBs. Treatment with either IL-4 or IL-13 (1-100 pM) stimulated the formation of alkaline phosphatase (ALP) dose-dependently, detected by enzyme reaction and histochemistry. IL-4 and IL-13 also induced an increase in the secretion of procollagen type I carboxypeptide (PICP) from cultured hOBs, measured by RIA. Osteocalcin secretion measured by ELISA-technique was unaffected. The rate of mineralization, assessed by von Kossa and Alizarin Red staining, was clearly enhanced in hOBs stimulated by IL-4 or IL-13. In conclusion IL-4 and IL-13 exert multiple effects on osteoblast activity in cultured hOBs. Stimulation of ALP secretion together with enhanced collagen secretion and mineralization suggests that IL-4 and IL-13 also have the capacity to maintain hOBs in a differentiated, productive phase.