BMP2, BMP4, noggin, BMPRIA, BMPRIB, and BMPRII are differentially expressed in the adult rat spinal cord

Abstract

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor β (TGF-β) superfamily. BMPs, such as BMP2 and BMP4, exert its biological functions by interacting with membrane bound receptors belonging to the serine/threonine kinase family including bone morphogenetic protein receptor I (BMPRIA, BMPRIB) and type II (BMPRII). Functions of BMPs are also regulated in the extracellular space by secreted antagonistic regulators such as noggin. Although BMP2, BMP4, noggin, BMPRIA, BMPRIB, and BMPRII expressions have been well described in the central nervous system, little information is available for their expressions in the spinal cord. We, thus, investigated these protein expressions in the adult rat spinal cord using immunohistochemistry. Here, we show that BMP2, BMP4, noggin, BMPRIA, BMPRIB, and BMPRII are widely and differentially expressed in the spinal cord. Besides abundant BMP2, BMP4, noggin, BMPRIA, BMPRIB, and BMPRII protein expressions in neurons, we detected them also in astrocytes, oligodendrocytes, and ependymal cells. In addition, we found BMPRIA, BMPRIB, and BMPRII protein expressions in microglia. Interestingly, we also observed that these proteins are strongly expressed in many kinds of axons in both ascending and descending tracts. These data indicate that BMP2, BMP4, noggin, BMPRIA, BMPRIB, and BMPRII proteins are more widely expressed in the adult spinal cord than previously reported, and their continued abundant expressions in the adult spinal cord strongly support the idea that BMP signaling plays pivotal roles in the adult spinal cord.