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Published on: September 1, 2015
Ectopic Phosphorylated Creb Marks Dedifferentiated Proximal Tubules in Cystic Kidney Disease
Pawan Puri1, Caitlin M Schaefer1, Daniel Bushnell1
1Division of Nephrology, Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
Abstract:
Ectopic cAMP signaling is pathologic in polycystic kidney disease; however, its spatiotemporal actions are unclear. We characterized the expression of phosphorylated Creb (p-Creb), a target and mediator of cAMP signaling, in developing and cystic kidney models. We also examined tubule-specific effects of cAMP analogs in cystogenesis in embryonic kidney explants. In wild-type mice, p-Creb marked nephron progenitors (NP), early epithelial NP derivatives, ureteric bud, and cortical stroma; p-Creb was present in differentiated thick ascending limb of Henle, collecting duct, and stroma; however, it disappeared in mature NP-derived proximal tubules. In Six2cre;Frs2αFl/Fl mice, a renal cystic model, ectopic p-Creb stained proximal tubule-derived cystic segments that lost the differentiation marker lotus tetragonolobus lectin. Furthermore, lotus tetragonolobus lectin-negative/p-Creb-positive cyst segments (re)-expressed Ncam1, Pax2, and Sox9 markers of immature nephron structures and dedifferentiated proximal tubules after acute kidney injury. These dedifferentiation markers were co-expressed with p-Creb in renal cysts in Itf88 knockout mice subjected to ischemia and Six2cre;Pkd1Fl/Fl mice, other renal cystogenesis models. 8-Br-cAMP addition to wild-type embryonic kidney explants induced proximal tubular cystogenesis and p-Creb expression; these effects were blocked by co-addition of protein kinase A inhibitor. Thus p-Creb/cAMP signaling is appropriate in NP and early nephron derivatives, but disappears in mature proximal tubules. Moreover, ectopic p-Creb expression/cAMP signaling marks dedifferentiated proximal tubular cystic segments. Furthermore, proximal tubules are predisposed to become cystic after cAMP stimulation.
Insights
Ectopic cAMP signaling, marked by phosphorylated CREB (p-Creb), drives cyst formation in polycystic kidney disease by promoting proximal tubule dedifferentiation. This signaling is normally absent in mature proximal tubules but reactivates during cystogenesis.
Area of Science:
- Molecular Biology
- Nephrology
- Cell Biology
Background:
- Ectopic cyclic adenosine monophosphate (cAMP) signaling is implicated in polycystic kidney disease (PKD) pathogenesis.
- The precise spatiotemporal roles of cAMP signaling in kidney development and disease remain incompletely understood.
- Phosphorylated CREB (p-Creb) is a key mediator of cAMP signaling, making its expression a valuable marker.
Purpose of the Study:
- To characterize the expression patterns of p-Creb in developing and cystic kidney models.
- To investigate the tubule-specific effects of cAMP analogs on cystogenesis.
- To elucidate the role of p-Creb/cAMP signaling in proximal tubule dedifferentiation and cyst formation.
Main Methods:
- Immunohistochemical analysis of p-Creb expression in wild-type and genetically engineered mouse models of renal cystic disease (Six2cre;Frs2αFl/Fl, Itf88 knockout, Six2cre;Pkd1Fl/Fl).
- Assessment of differentiation markers (lotus tetragonolobus lectin) and dedifferentiation markers (Ncam1, Pax2, Sox9) in kidney tissues.
- In vitro studies using embryonic kidney explants treated with cAMP analogs (8-Br-cAMP) and protein kinase A inhibitors.
Main Results:
- In wild-type kidneys, p-Creb is detected in nephron progenitors and early derivatives but absent in mature proximal tubules.
- Ectopic p-Creb expression was observed in proximal tubule-derived cysts, co-occurring with loss of differentiation markers and re-expression of immature markers.
- cAMP analog treatment induced proximal tubular cystogenesis and p-Creb expression in embryonic kidney explants, effects blocked by kinase inhibition.
Conclusions:
- p-Creb/cAMP signaling is developmentally regulated, present in early nephron structures but absent in mature proximal tubules.
- Ectopic p-Creb expression signifies dedifferentiation of proximal tubules and is a hallmark of renal cystogenesis.
- Proximal tubules are susceptible to cAMP-induced cyst formation, highlighting a potential therapeutic target in PKD.
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