BMP4 and chronic kidney disease: In this study, the immunohistochemical results showed that BMP-2 protein was barely expressed in the normal aorta but strongly expressed in the tunica media of the aorta in CKD rats, whereas BMP-4 was weakly expressed in the normal aorta, and positive staining of BMP-4 protein was observed in almost the whole wall of the aorta in CKD rats.