Genetic analysis conducted during the previous funding period defined two stages where Notch signals play an important role in kidney biology. The first essential function of Notch is during nephron segmentation. Notch2 signals block distal identities and promote proximal tubule (PT) and podocyte (POD) identities either cell autonomously or inducing them in neighboring cells. This activity is required only transiently, becoming dispensable after S-shaped body (SB) formation. A second important function of Notch signals is to act as gatekeepers of renal tubular epithelial homeostasis during adulthood;in their absence, cysts and renal dysfunction develop spontaneously in a substantial fraction of outbred animals with some cysts containing cells that continue to divide and develop papillary adenomas, thought to be the precursor for papillary renal cell carcinoma (PRCC). Injury increases the frequency of cyst and papillary adenoma formation. While these findings explain why reduced Notch2 signaling in humans causes Alagille syndromes (AGS), and suggest that elevating Notch1 activity in such patients should improve health, they do not establish if/how Notch signals direct the acquisition of PT and POD fates. We will take advantage of cell lineage tracing tools prepared during the previous funding period to address the issue of whether the cellular organization in the SB, at the time of Notch2 activation, underlies the organization of nephron sub-structures in the adult nephron and map the potential of de-differentiated renal PT recovering from injury in the adult. These fate mapping studies will allow us to ask if SB cells experiencing Notch activity are fated to become PT, POD, neither, or both, and if de-differentiated adult renal epithelial cells are fate-restricted or oligopotential. The results will direct our subsequent search for genes capable of enhancing POD and PT regeneration in injured adults.
In Aim 2, we will ask how these cells acquire their fates.
In Aim 3, we will determine the mechanistic contribution of Notch loss to cyst and adenoma formation in adults.
In Aim 4, we will develop strategies to transiently augment Notch1 activity in AGS and PRCC with the translational goal of developing clinical interventions aimed at compensating for Notch signal reduction reduction in AGS.
We find that mutations reducing Notch activity that do not result in developmental abnormalities nonetheless contribute to formation of cysts later in life, 30% of which will develop renal adenomas resembling human papillary renal carcinoma. Since Notch reduction therapy is being considered in adult humans, a full, mechanistic elucidation of the role Notch signaling plays during renal development and its role in maintenance of adult renal tubules continues to be of great scientific and clinical importance.
|Kopan, Raphael; Chen, Shuang; Liu, Zhenyi (2014) Alagille, Notch, and robustness: why duplicating systems does not ensure redundancy. Pediatr Nephrol 29:651-7|
|Boyle, Scott C; Liu, Zhenyi; Kopan, Raphael (2014) Notch signaling is required for the formation of mesangial cells from a stromal mesenchyme precursor during kidney development. Development 141:346-54|
|Kopan, Raphael; Chen, Shuang; Little, Melissa (2014) Nephron progenitor cells: shifting the balance of self-renewal and differentiation. Curr Top Dev Biol 107:293-331|
|Liu, Zhenyi; Chen, Shuang; Boyle, Scott et al. (2013) The extracellular domain of Notch2 increases its cell-surface abundance and ligand responsiveness during kidney development. Dev Cell 25:585-98|
|Liu, Zhiyong; Liu, Zhenyi; Walters, Bradley J et al. (2013) In vivo visualization of Notch1 proteolysis reveals the heterogeneity of Notch1 signaling activity in the mouse cochlea. PLoS One 8:e64903|
|Barak, Hila; Surendran, Kameswaran; Boyle, Scott C (2012) The role of Notch signaling in kidney development and disease. Adv Exp Med Biol 727:99-113|
|Vooijs, Marc; Liu, Zhenyi; Kopan, Raphael (2011) Notch: architect, landscaper, and guardian of the intestine. Gastroenterology 141:448-59|
|Pellegrinet, Luca; Rodilla, Veronica; Liu, Zhenyi et al. (2011) Dll1- and dll4-mediated notch signaling are required for homeostasis of intestinal stem cells. Gastroenterology 140:1230-1240.e1-7|
|Liu, Zhenyi; Turkoz, Ahu; Jackson, Erin N et al. (2011) Notch1 loss of heterozygosity causes vascular tumors and lethal hemorrhage in mice. J Clin Invest 121:800-8|
|Barak, Hila; Boyle, Scott C (2011) Organ culture and immunostaining of mouse embryonic kidneys. Cold Spring Harb Protoc 2011:pdb.prot5558|
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