Effects of cortisol and bone morphogenetic protein-2 on stromal cell differentiation: correlation with CCAAT-enhancer binding protein expression

Abstract

Bone marrow stroma contain pluripotential cells with the potential to differentiate into various mesenchymal cell lineages. We compared the effect of cortisol and bone morphogenetic protein-2 (BMP-2) on the differentiation of murine ST-2 stromal cells into mature osteoblasts or adipocytes. ST-2 cells were cultured for 3-27 days in the presence of 10% fetal bovine serum, 100 microg/mL ascorbic acid, and 5 mmol/L beta-glycerolphosphate in the presence or absence of cortisol at 1 micromol/L or BMP-2 at 1 nmol/L. Untreated ST-2 cells expressed high levels of alkaline phosphatase activity (APA) 15 days after confluence, and this was followed by the appearance of mineralized nodules after 24 days. BMP-2 accelerated and intensified the appearance of cells expressing APA and the presence of mineralized nodules. In contrast, cortisol decreased APA, prevented the formation of mineralized nodules, and induced a cellular phenotype characteristic of adipocytes. Untreated stromal cells expressed osteocalcin, Cbfa1, type I collagen, and alkaline phosphatase mRNA. BMP-2 increased osteocalcin and alkaline phosphatase mRNA, whereas cortisol suppressed their expression, as well as Cbfa1 and type I collagen transcripts. Cortisol enhanced, and BMP-2 downregulated, peroxisome proliferator-activated receptor gamma 2 and adipsin transcripts. The C/EBP transcription factors regulate genes critical for adipocytic and osteoblastic differentiation. Cortisol increased the expression of C/EBP alpha, beta, delta, and gamma mRNA levels, whereas BMP-2 had minor effects on C/EBP expression. In conclusion, BMP-2 accelerates the differentiation of stromal cells toward an osteoblastic phenotype, whereas glucocorticoids induce their differentiation toward an adipocytic phenotype.