Novel expression of Bone Morphogenic Protein 10 (BMP10) in lymphocytes

Abstract

The bone morphogenic protein family (~20 BMPs in humans), are members of the transforming growth factor-β (TGF-β) superfamily. BMPs have been shown to exert important roles during development and organogenesis by delivering positional information in both vertebrates and invertebrates. We had previously observed early induction of mRNA for BMP10 in rat B cells soon after Aggregatibacter actinomycetemcomitans (Aa) bacterial infection, in studies conducted in a rat model for human periodontal disease. However, prior to the onset of bone resorption, BMP10 mRNA precipitously declined. Being the first demonstration that mRNA for BMP10 is expressed by lymphocytes, we examined the expression of BMP10, at the protein level. Peripheral blood lymphocytes from humans, rats and mice were purified, by micro-immunomagnetic bead separation, into B cell, CD4, and CD8 T cell fractions. Flow cytometry analysis conducted with anti-BMP10 antibody revealed cellular expression of BMP10 in all the fractions examined. Interestingly, activation of CD4 T cells by Con A, rodent B cells by LPS, or human B cells by S. Aureus, resulted in drastic shut-down of BMP10 expression at mRNA and protein levels. In conclusion, our studies demonstrate, for the first time, that lymphocytes express BMP10 protein. Furthermore, while activation of B cells by bacterial antigen induced early BMP10 expression, further chronic stimulation resulted in decline in BMP10 expression. Intriguingly, mitogen stimulation of B cells and CD4 T cells, led to a drastic reduction in BMP10 expression at mRNA and protein levels, suggesting that BMP10 might be a novel marker for naïve lymphocytes.