BMP4 uses several different effector pathways to regulate proliferation and differentiation in the epithelial and mesenchymal tissue compartments of the developing mouse ureter

Abstract

Heterozygous loss of Bmp4 results both in humans and mice in severe malformation of the urinary tract. These defects have at least partially been attributed to loss of expression of Bmp4 in the ureteric mesenchyme, yet the cellular and molecular function of this signal as well as its effector pathways in this tissue have remained incompletely resolved. Here, we show that mice with a conditional deletion of Bmp4 in the ureteric mesenchyme exhibited hydroureter and hydronephrosis at newborn stages due to functional and physical ureter obstruction. Proliferation in both the mesenchymal and epithelial progenitor pools was severely reduced and smooth muscle cell and urothelial differentiation programs were not activated. Epithelial expression of P-ERK1/2, P-AKT and P-P38, and mesenchymal expression of P-SMAD1/5/9, P-P38 and P-AKT were abrogated. Pharmacological inhibition and activation experiments in ureter cultures defined AKT as the most relevant downstream effector for epithelial and mesenchymal proliferation as well as for epithelial differentiation. Epithelial proliferation and differentiation were also influenced by P-38 and ERK1/2, while SMAD signaling, together with AKT and P-38, were required for smooth muscle cell differentiation. Our analysis suggests that BMP4 is the signal that couples the proliferation and differentiation programs in the epithelial and mesenchymal tissue compartments of the developing ureter by different downstream effectors, most importantly AKT and SMAD.

A SHH-FOXF1-BMP4 signaling axis regulating growth and differentiation of epithelial and mesenchymal tissues in ureter development

“…BMP4 did not rescue SMC differentiation in these settings arguing that FOXF1 acts upstream of and in concert with BMP4 in this program. While this study was in progress, we showed that loss of Bmp4 in the ureteric mesenchyme resulted in a complete loss of epithelial and mesenchymal proliferation and differentiation further supporting the notion that BMP4 mediates HH signaling and FOXF1 activity in the ureteric mesenchyme [ 51 ].…”

TBX2 and TBX3 act downstream of canonical WNT signaling in patterning and differentiation of the mouse ureteric mesenchyme

“…Alternatively, reduced SHH or WNT signaling input may have lowered Foxf1 expression (Bohnenpoll et al, 2017b). As FOXF1 and BMP4 are both independently required for SMC differentiation in the ureter (Bohnenpoll et al, 2017b;Mamo et al, 2017), we suggest that their reduced expression and activity, respectively, largely accounts for the delayed and reduced onset of SMC differentiation in Tbx2/3cDKO ureters.…”

“…Loss of Tbx2 and Tbx3 in the UM disrupts ureter peristalsis Tbx2/3cDKO ureters did not present the dilatation phenotype described in other mutants with reduced SMC investment (Bohnenpoll et al, 2017b;Mamo et al, 2017;Trowe et al, 2012), so we questioned whether peristalsis was affected. We isolated E18.5 ureters and cultured them for 6 days in a transwell setting, monitoring contraction frequency and intensity daily ( Fig.…”

“…At E11.5, SHH activates a SMO-dependent pathway in the UM that is required for survival of cells in the outer layer, for proliferation and SMC differentiation of cells of the inner layer, and also for urothelial proliferation and differentiation. The proliferation and differentiation functions of SHH signaling are mediated by the forkhead transcription factor FOXF1, which, in turn, induces expression of and synergizes with BMP4 in SMC differentiation (Bohnenpoll et al, 2017b;Mamo et al, 2017). At E12.5, WNT7B and WNT9B activate the canonical WNT pathway in cells of the inner mesenchymal layer, disruption of which results in reduced proliferation and failed SMC differentiation of these cells, and expansion of the adventitial fate to the inner layer (Trowe et al, 2012).…”

Delayed onset of smooth muscle cell differentiation leads to hydroureter formation in mice with conditional loss of the zinc finger transcription factor gene Gata2 in the ureteric mesenchyme

“…To identify molecular changes that may cause defective SMC differentiation in Gata2cKO ureters, we screened (using in situ hybridisation) for activity of pathways and expression of genes that have been implicated in this programme: Ptch1 , target of SHH signalling ; Bmp4 ; Id2 , target of BMP signalling ; Axin2 , target of WNT signalling ; Rarb , target of RA signalling ; and the transcription factor genes Foxf1 , Tbx18 , Tszh3 , and Sox9 . At E14.5, all of these genes were expressed in the inner UM of mutant ureters as in the control except for Tbx18 , Tshz3 , and Rarb , which were up‐regulated (supplementary material, Figure S9).…”