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The role of PKA activation in the branching morphogenesis of the ureteric bud


Development of the embryonic kidney initiates with the formation of the ureteric bud (UB) from the Wolffian duct (WD) and proceeds as the UB and the MM reciprocally induce the growth and differentiation of one another. Branching morphogenesis of the UB is crucial for the development of the overall structure of the kidney, and defects in this process are correlated to many renal diseases. Studies over the past two decades have identified numerous molecules involved in the process of UB branching. However, the influence that these molecular interactions have on branching still remains unclear. Among these branching signaling molecules, the activation of protein kinase A (PKA) has been implicated in epithelial cell branching and UB outgrowth from the WD (Gupta et al., 1999; Santos et al., 1993; Tee et al., 2010). Here, an approach combining biological network analysis and compound screen was utilized to investigate the mechanisms by which PKA interacts with other molecules to regulate UB branching. Activation of PKA by dibutyryl cyclic adenosine monophosphate (dbcAMP) was shown to inhibit UB branching in in vitro systems, including 3D UB cell culture, isolated UB culture, and whole embryonic kidney (WEK) culture. Using network analysis and compound screen, it was hypothesized that the inhibitory effect of PKA activation on UB branching via TGF-[beta]1 or cyclic AMP is mediated through p38 MAPK and NF-[kappa]B. The proposed pathway involving TGF-[beta]1, PKA, p38 MAPK, and NF- [kappa]B was subsequently validated in 3D UB cell culture, with TGF-[beta]1 being an upstream activator of PKA, and p38 MAPK and NF-[kappa]B being downstream effectors of PKA

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