IFNß impairs extracellular matrix formation leading to inhibition of mineralization by effects in the early stage of human osteoblast differentiation.

ABSTRACT

Osteoimmunology is an emerging field of research focused on the interaction of the immune system and bone. In this study we demonstrate that human osteoblasts are sensitive to the immune cytokine interferon (IFN)ß. Osteoblasts respond to IFNß as shown by the induction of several known IFN target genes such as interferon-induced (IFI) proteins (IFIT1, IFI44L), interferon-stimulated gene factor 3 (ISGF3) complex and the induction of IFNß itself. We demonstrated that IFNß has severe inhibitory effects on mineralization of osteoblast-derived extracellular matrix (ECM). Analysis of the timing of the IFNß effects revealed that committed osteoblasts in early stage of differentiation are most sensitive to IFNß inhibition of mineralization. A single IFNß treatment was as effective as multiple treatments. During the progress of differentiation osteoblasts become desensitized for IFNß. This pinpoints to a complex pattern of IFNß sensitivity in osteoblasts. Focusing on early osteoblasts, we showed that IFNß decreased gene expression of ECM-related genes, such as type I Collagen (COL1A1), fibronectin (FN1), fibullin (FBLN1), fibrillin (FBN2), and laminin (LAMA1). Additionally, ECM produced by IFNß-treated osteoblasts contained less collagen protein. IFNß stimulated gene expression of osteopontin (OPN), annexin2 (ANXA2), and hyaluronan synthase 1 (HAS1), which are important factors in the adhesion of hematopoietic stem cells (HSC) in the HSC niche. In conclusion, IFNß directly modifies human osteoblast function by inhibiting ECM synthesis eventually resulting in delayed bone formation and mineralization and induces a HSC niche supporting phenotype. These effects are highly dependent on timing of treatment in the early phase of osteoblast differentiation.