Modeling renal progenitors - defining the niche

Targeting Strategies for Renal Cancer Stem Cell Therapy

Renal cell carcinoma (RCC) is an intractable genitourinary malignancy that accounts for approximately 4% of adult malignancies. Currently, there is no approved targeted therapy for RCC that has yielded durable remissions, and they remain palliative in intent. Emerging evidence has indicated that renal tumorigenesis and RCC treatment-resistance may originate from renal cancer stem cells (CSCs) with tumor-initiating capacity (CSC hypothesis). A better understanding of the mechanism underlying renal CSCs will help to dissect RCC heterogeneity and drug treatment efficiency, to promote more personalized and targeted therapies. In this review, we summarized the stem cell characteristics of renal CSCs. We outlined the targeting strategies and challenges associated with developing therapies that target renal CSCs angiogenesis, immunosuppression, signaling pathways, surface biomarkers, microRNAs and nanomedicine. In conclusion, CSCs are an important role in renal carcinogenesis and represent a valid target for treatment of RCC patients.

Dissecting the Interaction of FGF8 with Receptor FGFRL1

In mammals, the novel protein fibroblast growth factor receptor-like 1 (FGFRL1) is involved in the development of metanephric kidneys. It appears that this receptor controls a crucial transition of the induced metanephric mesenchyme to epithelial renal vesicles, which further develop into functional nephrons. FGFRL1 knockout mice lack metanephric kidneys and do not express any fibroblast growth factor (FGF) 8 in the metanephric mesenchyme, suggesting that FGFRL1 and FGF8 play a decisive role during kidney formation. FGFRL1 consists of three extracellular immunoglobulin (Ig) domains (Ig1-Ig2-Ig3), a transmembrane domain and a short intracellular domain. We have prepared the extracellular domain (Ig123), the three individual Ig domains (Ig1, Ig2, Ig3) as well as all combinations containing two Ig domains (Ig12, Ig23, Ig13) in recombinant form in human cells. All polypeptides that contain the Ig2 domain (Ig123, Ig12, Ig23, Ig2) were found to interact with FGF8 with very high affinity, whereas all constructs that lack the Ig2 domain (Ig1, Ig3, Ig13) poorly interacted with FGF8 as shown by ELISA and surface plasmon resonance. It is therefore likely that FGFRL1 represents a physiological receptor for FGF8 in the kidney and that the ligand primarily binds to the Ig2 domain of the receptor. With Biacore experiments, we also measured the affinity of FGF8 for the different constructs. All constructs containing the Ig2 domain showed a rapid association and a slow dissociation phase, from which a K_D of 2–3 × 10⁻⁹ M was calculated. Our data support the hypothesis that binding of FGF8 to FGFRL1 could play an important role in driving the formation of nephrons in the developing kidney.

Functional domains of the FgfrL1 receptor

FgfrL1 is a novel growth factor receptor that is primarily expressed in musculoskeletal tissues and the kidney. FgfrL1-deficient mice have a malformed diaphragm and no kidneys. Such animals die immediately after birth because they are not able to inflate their lungs. The FgfrL1 molecule is composed of three extracellular Ig domains, a transmembrane helix and a short intracellular domain. To investigate the contribution of each of these domains to the function of the novel receptor, we generated mice with deletions of the individual domains. Mice lacking the intracellular domain are viable and phenotypically normal. Mice lacking the first (N-terminal) Ig domain are also viable and normal, but have a reduced life span. Mice lacking the Ig2 or the Ig3 domain are born alive, but die within 24 ​h after birth. Ig2-deficient animals exhibit substantially smaller kidneys than wild-type littermates and contain a lower number of glomeruli. Ig3-deficient mice completely lack metanephric kidneys. Interestingly, both the Ig2 and the Ig3-deficient animals show only minor alterations in the diaphragm, which still enables them to inflate their lungs after birth. Our results demonstrate that the principal function of the FgfrL1 receptor is to control the growth of the metanephric kidneys by regulating nephrogenesis. It appears that this function is primarily accomplished by the Ig3 domain with some contribution of the Ig2 domain. It is conceivable that the two domains interact with an Fgf ligand and another molecule from the surface of neighboring cells to induce condensation of the metanephric mesenchyme to renal epithelia and glomeruli.

Kidney-differentiated cells derived from Lowe Syndrome patient's iPSCs show ciliogenesis defects and Six2 retention at the Golgi complex

Lowe syndrome is an X-linked condition characterized by congenital cataracts, neurological abnormalities and kidney malfunction. This lethal disease is caused by mutations in the OCRL1 gene, which encodes for the phosphatidylinositol 5-phosphatase Ocrl1. While in the past decade we witnessed substantial progress in the identification and characterization of LS patient cellular phenotypes, many of these studies have been performed in knocked-down cell lines or patient's cells from accessible cell types such as skin fibroblasts, and not from the organs affected. This is partially due to the limited accessibility of patient cells from eyes, brain and kidneys. Here we report the preparation of induced pluripotent stem cells (iPSCs) from patient skin fibroblasts and their reprogramming into kidney cells. These reprogrammed kidney cells displayed primary cilia assembly defects similar to those described previously in cell lines. Additionally, the transcription factor and cap mesenchyme marker Six2 was substantially retained in the Golgi complex and the functional nuclear-localized fraction was reduced. These results were confirmed using different batches of differentiated cells from different iPSC colonies and by the use of the human proximal tubule kidney cell line HK2. Indeed, OCRL1 KO led to both ciliogenesis defects and Six2 retention in the Golgi complex. In agreement with Six2's role in the suppression of ductal kidney lineages, cells from this pedigree were over-represented among patient kidney-reprogrammed cells. We speculate that this diminished efficacy to produce cap mesenchyme cells would cause LS patients to have difficulties in replenishing senescent or damaged cells derived from this lineage, particularly proximal tubule cells, leading to pathological scenarios such as tubular atrophy.

3D Culture Supports Long-Term Expansion of Mouse and Human Nephrogenic Progenitors

Transit-amplifying nephron progenitor cells (NPCs) generate all of the nephrons of the mammalian kidney during development. Their limited numbers, poor in vitro expansion, and difficult accessibility in humans have slowed basic and translational research into renal development and diseases. Here, we show that with appropriate 3D culture conditions, it is possible to support long-term expansion of primary mouse and human fetal NPCs as well as NPCs derived from human induced pluripotent stem cells (iPSCs). Expanded NPCs maintain genomic stability, molecular homogeneity, and nephrogenic potential in vitro, ex vivo, and in vivo. Cultured NPCs are amenable to gene targeting and can form nephron organoids that engraft in vivo, functionally couple to the host's circulatory system, and produce urine-like metabolites via filtration. Together, these findings provide a technological platform for studying human nephrogenesis, modeling and diagnosing renal diseases, and drug discovery.