Antagonism of BMP4 signaling disrupts smooth muscle investment of the ureter and ureteropelvic junction.
OBJECTIVE
Congenital ureteropelvic junction obstruction has been associated with aberrant ureteral smooth muscle organization. Recent evidence has shown that BMP4 may be involved in ureteral morphogenesis. We determined whether the disruption of BMP4 signaling results in abnormal smooth muscle investment of the ureter and ureteropelvic junction.


METHODS
We used a Cre mediated Bmp4 knockout system to conditionally excise the Bmp4 gene in developing mouse embryos. Kidney rudiments were isolated from embryos at varying gestational ages from WT and conditional knockout mice. Metanephric kidney explants were cultured in the presence or absence of the BMP antagonist Noggin. Agarose beads pre-incubated with Gremlin, another BMP antagonist, were used for localized disruption of BMP signaling. Frozen sections and whole metanephric explants were then analyzed by immunofluorescence.


RESULTS
Bmp4 gene excision resulted in a dose dependent loss of ureteral smooth muscle. Antagonism of BMP signaling inhibited ureteral smooth muscle investment in a dose dependent manner and was paralleled by a dose dependent decrease in the immediate downstream targets of BMP signaling, phosphorylated Smad1, 5 and 8. Localized antagonism of BMP resulted in the focal disruption of ureteral smooth muscle investment.


CONCLUSIONS
We report that decreased BMP signaling, whether by the loss of BMP4 in vivo or direct antagonism in vitro, results in a gradual reduction of the normal, well organized coat of smooth muscle surrounding the ureter. Our results also suggest that this occurs via a direct Smad dependent pathway. This raises the possibility that abnormalities in BMP4 signaling may have a role in the development of congenital ureteropelvic junction obstruction.
Wang
Gerald J
GJ
Departments of Urology and Physiology and Biophysics (ABA, DL), New York-Presbyterian Hospital, Weill Medical College of Cornell University, New York, New York, USA.
Brenner-Anantharam
Andrea
A
Vaughan
E Darracott
ED
Herzlinger
Doris
D
D000818:Animals; D055415:Bone Morphogenetic Protein 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000494:pharmacology; D005260:Female; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D007682:Kidney Pelvis / Q000196:embryology*; D051379:Mice; D009130:Muscle, Smooth / Q000196:embryology*; D014513:Ureter / Q000196:embryology*; D014517:Ureteral Obstruction / Q000209:etiology*; D000099176:Noggin Protein; D016207:Cytokines
D055415:Bone Morphogenetic Protein 4; D002352:Carrier Proteins; D036341:Intercellular Signaling Peptides and Proteins; D000099176:Noggin Protein; C525810:Bmp4 protein, mouse; C113178:Grem1 protein, mouse; D016207:Cytokines