Abstract

Background: Bone Morphogenetic Protein (BMP)-7 is protective in different animal models of acute and chronic kidney
disease. Its role in human kidneys, and in particular hypertensive nephrosclerosis, has thus far not been described.
Methods: BMP-7 mRNA was quantified using real-time PCR and localised by immunostaining in tissue samples
from normal and nephrosclerotic human kidneys. The impact of angiotensin (AT)-II and the AT-II receptor
antagonist telmisartan on BMP-7 mRNA levels and phosphorylated Smad 1/5/8 (pSmad 1/5/8) expression was
quantified in proximal tubular cells (HK-2). Functional characteristics of BMP-7 were evaluated by testing its
influence on TGF-b induced epithelial-to-mesenchymal transition (EMT), expression of TGF-b receptor type I
(TGF-bRI) and phosphorylated Smad 2 (pSmad 2) as well as on TNF-a induced apoptosis of proximal tubular cells.
Results: BMP-7 was predominantly found in the epithelia of the distal tubule and the collecting duct and was less
abundant in proximal tubular cells. In sclerotic kidneys, BMP-7 was significantly decreased as demonstrated by
real-time PCR and immunostaining. AT-II stimulation in HK-2 cells led to a significant decrease of BMP-7 and
pSmad 1/5/8, which was partially ameliorated upon co-incubation with telmisartan. Only high concentrations of
BMP-7 (100 ng/ml) were able to reverse TNF-a-induced apoptosis and TGF-b-induced EMT in human proximal
tubule cells possibly due to a decreased expression of TGF-bRI. In addition, BMP-7 was able to reverse
TGF-b-induced phosphorylation of Smad 2.
Conclusions: The findings suggest a protective role for BMP-7 by counteracting the TGF-b and TNF-a-induced
negative effects. The reduced expression of BMP-7 in patients with hypertensive nephrosclerosis may imply loss of
protection and regenerative potential necessary to counter the disease.