Protein Kinase A (PKA) Signaling in the Cystogenesis and Dedifferentiation of Proximal Tubules

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Project Summary Autosomal dominant polycystic kidney disease (ADPKD) affects more than 600,000 people in the USA and is caused by mutations primarily in genes PKD1 and PKD2. In ADPKD, cysts and fibrosis replace the renal parenchyma leading to renal pathology and failure. Currently, in the USA there are no approved therapies to stop or slow cyst growth. Increased levels of second messenger cAMP is one of the key initial events associated with PKD mutations. cAMP activates multiple signaling pathways including the Protein Kinase A (PKA) pathway that results in phosphorylation of transcription factor Creb and other substrates. Cysts may arise from different tubular segments in PKD such as proximal tubules (PTs) and collecting ducts (CDs). Potential therapies to modulate cAMP/PKA signaling in CD-derived cysts are under clinical trials however, strategies to control cAMP/PKA signaling in PT-derived cysts remain largely undefined. Furthermore, early interventions during childhood to reduce cystic burden have been recommended to preserve maximum renal function. Available data suggest that PT-derived cysts predominate in the developing kidney. Our recently published studies suggest that cAMP-mediated PKA activation plays a key role in the cystogenesis of PTs of the developing kidneys. Our studies also suggest that PKA contributes to the dedifferentiation of PT cystic segments of the developing and developed kidney, a process known to contribute to cystogenesis. Proximity of PKA to cAMP makes it a suitable therapeutic target however, the direct role of PKA in PT cystogenesis has not been investigated. The objective of this proposal is to test the overarching hypothesis that aberrant cAMP/PKA signaling is a key factor driving PT de-differentiation that promotes cyst formation in the kidney. This hypothesis will be tested in the following two aims. Aim 1: Examine the direct effect of PKA in the dedifferentiation of PTs in culture. We will determine whether modulation of PKA activity in in vitro cultures is sufficient and/or necessary for PT dedifferentiation as an early step to cystogenesis. Aim 2: Determine the effects of constitutive PKA activation on the cystogenesis and dedifferentiation of PTs in vivo. We will determine whether constitutive activation of PKA in differentiated PTs is sufficient to induce their de-differentiation, leading to cystogenesis as well as initiate multi-faceted cellular responses such as fibrosis and inflammation-associated changes from the surrounding renal parenchyma. These studies will define a direct novel role of PKA in the dedifferentiation and cystogenesis of PT and establish PKA as a potential therapeutic target. These studies will lay the foundation for the future studies that will determine whether modulation of PKA activity in PTs exacerbates or ameliorates cystogenesis and dedifferentiation in a PKD mouse model. Future studies will also focus to identify novel substrates of PKA implicated in the dedifferentiation and cystogenesis of PTs.