br Results br Discussion Here
Discussion Here, by comparing the WT CSCs with normal kidney development, we discover two surprising fundamental concepts. First, in terms of lineage hierarchy, the CSC may not correspond to the earliest normal stem cell but rather to a more differentiated progeny. Second, heterogeneity that mirrors renal stem cell differentiation is present in the homogeneous-appearing WT blastema. Our earlier observations (Pode-Shakked et al., 2013) disclosed high similarity between WT CSCs and early renal stem cells. These observations were based on propagation of trilineage human WT, in which the relationship of the CSC to tumor bulk includes a comparison to blastema and also to mature elements, placing the CSC as an undifferentiated renal cell type. Our ability to examine pure blastema Xns enabled stringent comparison of WT CSCs to the undifferentiated tumor bulk and the unraveling of the findings. Indeed, the importance of the fine-tuning of our system is manifested when comparing WT CSCs to parental l-name manufacturer (i.e., hFK and pWT), disclosing a relatively undifferentiated phenotype. This precise understanding of the relation between the WT CSC and embryonic renal differentiation affords insights from both oncologic and developmental aspects. Multiple studies have highlighted the relationship between CSCs and their differentiated progeny (Reya et al., 2001), including WT CSCs, and their ability to generate tubular structures and glomeruloid bodies (Little, 2005; Pode-Shakked and Dekel, 2011; Pode-Shakked et al., 2013). Nevertheless, the dedifferentiated progeny arising from ALDH1+ WT CSCs, represented by the bulk of the blastema and characterized by higher SIX2 and lower E-Cadherin, illustrates mechanisms for WT and progression. Interestingly, partial reprogramming by pluripotent stemness factors has been recently implicated in generation of a Wilms’-like tumor in vivo (Ohnishi et al., 2014). Hypothetically, dedifferentiation of WT CSCs may also account for the nonrenal mesenchymal elements observed in WT. This notion is strengthened by the fact that developmental lineages are already specified in the MM, and no common nephron epithelial-stromal progenitor cell has been documented (Brown et al., 2013; Kobayashi et al., 2008; Pleniceanu et al., 2010; Self et al, 2006). Our work may suggest a revision to the concept that the earliest transformed renal stem cell capable of giving rise to differentiated progeny is the tumor-initiating cell. Alternatively, the WT cell of origin and WT CSCs responsible for tumor propagation may not be the same cell. Resolution of this matter utilizing a transgenic animal model of WT generation that employs specific CRE drivers of renal stem cells (e.g., SIX2) might be complicated because WT CSCs express some levels of SIX2 and WT1. Finally, from the developmental aspect, it remains to be determined how NCAM1+ human nephron progenitors isolated from the hFK and representing more committed epithelial progenitors than uninduced MM (Harari-Steinberg et al., 2013) are relevant for WT once transformed. From a more practical aspect, the unequivocal limiting-dilution xenotransplantation data, illustrating ALDH1+ WT CSCs as critical for continued propagation of WT blastema Xns, highlight the WT CSC as a therapeutic target. We previously suggested anti-NCAM1-targeted therapy as a useful means for WT eradication (Pode-Shakked et al., 2013). Clearly, the NCAM1 expression domain exceeds that of the WT CSC. In this regard, our genomic and proteomic data disclose several specific pathways (e.g., NF-κB, Wnt, PI3K, and mTOR) previously implicated in stemness acquisition (Armstrong et al., 2006; Huang et al., 2012; Katoh and Katoh, 2007; Shostak and Chariot, 2011) as highly operative in WT CSCs. Thus, global analysis not only sheds light on the WT CSC as possessing enhanced stemness alongside a more differentiated renal phenotype but also pinpoints interventions such as mTOR and epidermal growth factor receptor inhibition that may prove beneficial in WT CSC eradication.