IFNβ signaling inhibits osteogenesis in human SLE bone marrow

Bone marrow mesenchymal stem cells are multipotent adult stem cells that can differentiate into osteoblasts, adipocytes, and chondrocytes. Our recently published data demonstrate that systemic lupus erythematous bone marrow mesenchymal stem cells produce increased quantities of interferon β based on a positive feedback loop involving the innate signaling molecule mitochondrial antiviral signaling protein. Moreover, this pathway contributes to human systemic lupus erythematous bone marrow mesenchymal stem cell senescence-like features. Here we investigate the differentiation defects of systemic lupus erythematous bone marrow mesenchymal stem cells and the potential for therapeutic interventions.

The six systemic lupus erythematous patients recruited in this study satisfy the American College of Rheumatology 1997 classification criteria for systemic lupus erythematous. Systemic Lupus Erythematous Disease Activity Index-2K was used to determine disease activity. Systemic lupus erythematous bone marrow mesenchymal stem cells were isolated with Ficoll centrifugation and phenotyped using flow cytometry. In vitro studies included real-time polymerase chain reaction and western blotting.

We compared six age-paired bone marrow aspirates from healthy controls and systemic lupus erythematous patients. Systemic lupus erythematous bone marrow mesenchymal stem cells display significantly reduced alkaline phosphatase staining, as well as reduced expression of osteogenic markers alkaline phosphatase, Runt-related transcription factor 2, and bone sialoprotein. When healthy bone marrow mesenchymal stem cells were treated with interferon β for 6 hours, expression of these same osteogenic markers was markedly reduced. Conversely the application of interferon β neutralizing antibody enhanced the expression of osteoblastogenesis markers. When the underlying mechanisms for interferon β inhibition of osteoblastogenesis were investigated, we found that IFNβ pre-treatment activates the inhibitory Smad6 and Smad7 expression through JAK1/STAT1, leading to reduced Smad1 phosphorylation and nuclear translocation.

Our present work suggests that interferon β affects osteogenesis. By revealing the essential role of interferon β on systemic lupus erythematous bone marrow mesenchymal stem cell differentiation, our study sheds light on systemic lupus erythematous pathogenesis and provides a new potential therapeutic target for the bone complications found in systemic lupus erythematous.