Paraprotein-Related Kidney Disease: Glomerular Diseases Associated with Paraproteinemias.

Paraproteins are monoclonal Igs that accumulate in blood as a result of abnormal excess production. These circulating proteins cause a diversity of kidney disorders that are increasingly being comanaged by nephrologists. In this review, we discuss paraprotein-related diseases that affect the glomerulus. We provide a broad overview of diseases characterized by nonorganized deposits, such as monoclonal Ig deposition disease (MIDD), proliferative GN with monoclonal Ig deposits (PGNMID), and C3 glomerulopathy, as well as those characterized by organized deposits, such as amyloidosis, immunotactoid glomerulopathy, fibrillary GN, and cryoglobulinemic GN, and rarer disorders, such as monoclonal crystalline glomerulopathies, paraprotein-related thrombotic microangiopathies, and membranous-like glomerulopathy with masked IgGκ deposits. This review will provide the nephrologist with an up to date understanding of these entities and highlight the areas of deficit in evidence and future lines of research.

Modelling kidney disease with CRISPR-mutant kidney organoids derived from human pluripotent epiblast spheroids.

Human-pluripotent-stem-cell-derived kidney cells (hPSC-KCs) have important potential for disease modelling and regeneration. Whether the hPSC-KCs can reconstitute tissue-specific phenotypes is currently unknown. Here we show that hPSC-KCs self-organize into kidney organoids that functionally recapitulate tissue-specific epithelial physiology, including disease phenotypes after genome editing. In three-dimensional cultures, epiblast-stage hPSCs form spheroids surrounding hollow, amniotic-like cavities. GSK3ß inhibition differentiates spheroids into segmented, nephron-like kidney organoids containing cell populations with characteristics of proximal tubules, podocytes and endothelium. Tubules accumulate dextran and methotrexate transport cargoes, and express kidney injury molecule-1 after nephrotoxic chemical injury. CRISPR/Cas9 knockout of podocalyxin causes junctional organization defects in podocyte-like cells. Knockout of the polycystic kidney disease genes PKD1 or PKD2 induces cyst formation from kidney tubules. All of these functional phenotypes are distinct from effects in epiblast spheroids, indicating that they are tissue specific. Our findings establish a reproducible, versatile three-dimensional framework for human epithelial disease modelling and regenerative medicine applications.

Nephron organoids derived from human pluripotent stem cells model kidney development and injury.

Kidney cells and tissues derived from human pluripotent stem cells (hPSCs) may enable organ regeneration, disease modeling and drug screening. We report an efficient, chemically defined protocol for differentiating hPSCs into multipotent nephron progenitor cells (NPCs) that can form nephron-like structures. By recapitulating metanephric kidney development in vitro, we generate SIX2+ SALL1+ WT1+ PAX2+ NPCs with 90% efficiency within 9 days of differentiation. The NPCs possess the developmental potential of their in vivo counterparts and form PAX8+ LHX1+ renal vesicles that self-organize into nephron structures. In both two- and three-dimensional culture, NPCs form kidney organoids containing epithelial nephron-like structures expressing markers of podocytes, proximal tubules, loops of Henle and distal tubules in an organized, continuous arrangement that resembles the nephron in vivo. We also show that this organoid culture system can be used to study mechanisms of human kidney development and toxicity.

Directed Differentiation of Pluripotent Stem Cells into Kidney.

Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), represent an ideal substrate for regenerating kidney cells and tissue lost through injury and disease. Recent studies have demonstrated the ability to differentiate PSCs into populations of nephron progenitor cells that can organize into kidney epithelial structures in three-dimensional contexts. While these findings are highly encouraging, further studies need to be performed to improve the efficiency and specificity of kidney differentiation. The identification of specific markers of the differentiation process is critical to the development of protocols that effectively recapitulate nephrogenesis in vitro. In this review, we summarize the current studies describing the differentiation of ESCs and iPSCs into cells of the kidney lineage. We also present an analysis of the markers relevant to the stages of kidney development and differentiation and propose a new roadmap for the directed differentiation of PSCs into nephron progenitor cells of the metanephric mesenchyme.

Regenerating the nephron with human pluripotent stem cells.

PURPOSE OF REVIEW: Nephrogenesis in humans is limited to the period of embryonic kidney development in utero, with no new nephrons formed after birth. Although the kidneys possess the capacity to self-repair segments of the nephron, nephron loss from acute or chronic kidney injury is irreversible and results in impaired function. Human pluripotent stem cells (PSCs), including embryonic stem cells and induced pluripotent stem cells, are an attractive source of cells to regenerate nephron progenitor cells (NPCs) and ultimately functional kidney tissue. NPCs are found exclusively during the period of embryonic development, but their nephron-forming capacity makes them an ideal cell population to regenerate with PSCs. RECENT FINDINGS: Significant progress has been made in the effort to direct the differentiation of human PSCs into NPCs. Differentiation protocols designed to recapitulate the complex process of kidney organogenesis in vitro can generate cells that express characteristic NPC markers and these cells can assemble into three-dimensional nephron-like structures. Additional studies are required to evaluate the functionality of these putative kidney cells and to test their ability to integrate into three-dimensional organized kidney tissue structures, either spontaneously or facilitated by bioengineered structures or scaffolds with appropriate matrix materials. SUMMARY: The successful recreation of human nephrons from PSCs would offer a novel therapeutic approach to treating patients with kidney disease.

Membranous nephropathy as a manifestation of graft-versus-host disease: association with HLA antigen typing, phospholipase A2 receptor, and C4d.

Glomerulopathy is an uncommon but increasingly recognized complication of hematopoietic cell transplantation. It typically manifests as membranous nephropathy, less commonly as minimal change disease, and rarely as proliferative glomerulonephritis. There is evidence to suggest that these glomerulopathies might represent manifestations of chronic graft-versus-host disease. In this report, we focus on membranous nephropathy as the most common form of glomerulopathy after hematopoietic cell transplantation. We present a case of membranous nephropathy that developed 483 days post-allogeneic hematopoietic stem cell transplantation in a patient with a history of acute graft-versus-host disease. We also share our experience with 4 other cases of membranous nephropathy occurring after allogeneic hematopoietic stem cell transplantation. Clinicopathologic correlates, including the association with graft-versus-host-disease, HLA antigen typing, glomerular deposition of immunoglobulin G (IgG) subclasses, subepithelial colocalization of IgG deposits with phospholipase A2 receptor staining, C4d deposition along the peritubular capillaries, and treatment, are discussed with references to the literature.

Directed differentiation of pluripotent stem cells to kidney cells.

Regenerative medicine affords a promising therapeutic strategy for the treatment of patients with chronic kidney disease. Nephron progenitor cell populations exist only during embryonic kidney development. Understanding the mechanisms by which these populations arise and differentiate is integral to the challenge of generating new nephrons for therapeutic purposes. Pluripotent stem cells (PSCs), comprising embryonic stem cells, and induced pluripotent stem cells (iPSCs) derived from adults, have the potential to generate functional kidney cells and tissue. Studies in mouse and human PSCs have identified specific approaches to the addition of growth factors, including Wnt and fibroblast growth factor, that can induce PSC differentiation into cells with phenotypic characteristics of nephron progenitor populations with the capacity to form kidney-like structures. Although significant progress has been made, further studies are necessary to confirm the production of functional kidney cells and to promote their three-dimensional organization into bona fide kidney tissue. Human PSCs have been generated from patients with kidney diseases, including polycystic kidney disease, Alport syndrome, and Wilms tumor, and may be used to better understand phenotypic consequences of naturally occurring genetic mutations and to conduct "clinical trials in a dish". The capability to generate human kidney cells from PSCs has significant translational applications, including the bioengineering of functional kidney tissue, use in drug development to test compounds for efficacy and toxicity, and in vitro disease modeling.

Rapid and efficient differentiation of human pluripotent stem cells into intermediate mesoderm that forms tubules expressing kidney proximal tubular markers.

Human pluripotent stem cells (hPSCs) can generate a diversity of cell types, but few methods have been developed to derive cells of the kidney lineage. Here, we report a highly efficient system for differentiating human embryonic stem cells and induced pluripotent stem cells (referred to collectively as hPSCs) into cells expressing markers of the intermediate mesoderm (IM) that subsequently form tubule-like structures. Treatment of hPSCs with the glycogen synthase kinase-3ß inhibitor CHIR99021 induced BRACHYURY(+)MIXL1(+) mesendoderm differentiation with nearly 100% efficiency. In the absence of additional exogenous factors, CHIR99021-induced mesendodermal cells preferentially differentiated into cells expressing markers of lateral plate mesoderm with minimal IM differentiation. However, the sequential treatment of hPSCs with CHIR99021 followed by fibroblast growth factor-2 and retinoic acid generated PAX2(+)LHX1(+) cells with 70%-80% efficiency after 3 days of differentiation. Upon growth factor withdrawal, these PAX2(+)LHX1(+) cells gave rise to apically ciliated tubular structures that coexpressed the proximal tubule markers Lotus tetragonolobus lectin, N-cadherin, and kidney-specific protein and partially integrated into embryonic kidney explant cultures. With the addition of FGF9 and activin, PAX2(+)LHX1(+) cells specifically differentiated into cells expressing SIX2, SALL1, and WT1, markers of cap mesenchyme nephron progenitor cells. Our findings demonstrate the effective role of fibroblast growth factor signaling in inducing IM differentiation in hPSCs and establish the most rapid and efficient system whereby hPSCs can be differentiated into cells with features characteristic of kidney lineage cells.

Reduced ciliary polycystin-2 in induced pluripotent stem cells from polycystic kidney disease patients with PKD1 mutations.

Heterozygous mutations in PKD1 or PKD2, which encode polycystin-1 (PC1) and polycystin-2 (PC2), respectively, cause autosomal dominant PKD (ADPKD), whereas mutations in PKHD1, which encodes fibrocystin/polyductin (FPC), cause autosomal recessive PKD (ARPKD). However, the relationship between these proteins and the pathogenesis of PKD remains unclear. To model PKD in human cells, we established induced pluripotent stem (iPS) cell lines from fibroblasts of three ADPKD and two ARPKD patients. Genetic sequencing revealed unique heterozygous mutations in PKD1 of the parental ADPKD fibroblasts but no pathogenic mutations in PKD2. Undifferentiated PKD iPS cells, control iPS cells, and embryonic stem cells elaborated primary cilia and expressed PC1, PC2, and FPC at similar levels, and PKD and control iPS cells exhibited comparable rates of proliferation, apoptosis, and ciliogenesis. However, ADPKD iPS cells as well as somatic epithelial cells and hepatoblasts/biliary precursors differentiated from these cells expressed lower levels of PC2 at the cilium. Additional sequencing confirmed the retention of PKD1 heterozygous mutations in iPS cell lines from two patients but identified possible loss of heterozygosity in iPS cell lines from one patient. Furthermore, ectopic expression of wild-type PC1 in ADPKD iPS-derived hepatoblasts rescued ciliary PC2 protein expression levels, and overexpression of PC1 but not a carboxy-terminal truncation mutant increased ciliary PC2 expression levels in mouse kidney cells. Taken together, these results suggest that PC1 regulates ciliary PC2 protein expression levels and support the use of PKD iPS cells for investigating disease pathophysiology.

Onco-nephrology: AKI in the cancer patient.

AKI is common in patients with cancer, and it causes interruptions in therapy and increased hospital length of stay, cost, and mortality. Although cancer patients are susceptible to all of the usual causes of AKI in patients without cancer, there are a number of AKI syndromes that occur more frequently or are unique to this patient population. AKI also confers substantially increased risk of short-term death, and the ability to reverse AKI portends a better outcome in some cancers, such as multiple myeloma. Several trends in oncology, including increased survival, better supportive care, older patients who have received multiple chemotherapy regimens, and new therapeutic options, are driving an increase in the numbers of cancer patients who develop AKI. As a result, nephrologists should be increasingly familiar with the diagnosis, management, and treatment of AKI in this setting. Here, we summarize recent data on epidemiology of AKI in cancer patients, describe the most common AKI syndromes in this population, and highlight emerging areas in the growing field of onconephrology.

Jak3-independent trafficking of the common gamma chain receptor subunit: chaperone function of Jaks revisited.

Janus kinases (Jaks) play an essential role in cytokine signaling and have been reported to regulate plasma membrane expression of their cognate receptors. In this study, we examined whether Jak3 and the common gamma chain (gamma(c)) reciprocally regulate their plasma membrane expression. In contrast to interleukin-2Ralpha, gamma(c) localized poorly to the plasma membrane and accumulated in endosomal-lysosomal compartments. However, gamma(c) was expressed at comparable levels on the surface of cells lacking Jak3, and plasma membrane turnover of gamma(c) was independent of Jak3. Nonetheless, overexpression of Jak3 enhanced accumulation of gamma(c) at the plasma membrane. Without gamma(c), Jak3 localized in the cytosol, whereas in the presence of the receptor, it colocalized with gamma(c) in endosomes and at the plasma membrane. Although the Jak FERM domain is necessary and sufficient for receptor binding, the requirement for full-length Jak3 in gamma(c) membrane trafficking was remarkably stringent; using truncation and deletion mutants, we showed that the entire Jak3 molecule was required, although kinase activity was not. Thus, unlike other cytokine receptors, gamma(c) does not require Jak3 for receptor membrane expression. However, full-length Jak3 is required for normal trafficking of this cytokine receptor/Jak pair, a finding that has important structural and clinical implications.