Organogenesis for kidney regeneration

Potency of Human Urine-Derived Stem Cells for Renal Lineage Differentiation

Kidney is one of the most difficult organs for regeneration. Several attempts have been performed to regenerate renal tissue using stem cells, the results were not satisfactory. Urine is major product of kidney and contains cells from renal components. Moreover, urine-derived stem cells (USCs) can be easily obtained without any health risks throughout a patient's entire life. Here, we evaluated the utility of USCs for renal tissue regeneration. In this study, the ability of USCs to differentiate into renal lineage cells was compared with that of adipose tissue-derived stem cells (ADSCs) and amniotic fluid-derived stem cells (AFSCs), with respect to surface antigen expression, morphology, immunocytochemistry, renal lineage gene expression, secreted factors, immunomodulatory marker expression, in vivo safety, and renal differentiation potency. Undifferentiated USCs were positive for CD44 and CD73, negative for CD34 and CD45, and formed aggregates after 3 weeks of renal differentiation. Undifferentiated USCs showed high SSEA4 expression, while renal-differentiated cells expressed PAX2, WT1, and CADHERIN 6. In the stem/renal lineage-associated gene analysis, OCT4, SSEA4, and CD117 were significantly downregulated over time, while PAX2, LIM1, PDGFRA, E-CADHERIN, CD24, ACTB, AQP1, OCLN, and NPHS1 were gradually upregulated. In the in vivo safety evaluation, renal-differentiated USCs did not show abnormal histology. These findings demonstrated that USCs have a similar MSC potency, renal lineage-differentiation ability, immunomodulatory effects, and in vivo safety as ADSCs and AFSCs, and showed higher levels of growth factor secretion for paracrine effects. Therefore, urine and USCs can be one of good cell sources for kidney regeneration.

Current Bioengineering and Regenerative Strategies for the Generation of Kidney Grafts on Demand

Currently in the USA, one name is added to the organ transplant waiting list every 15 min. As this list grows rapidly, fewer than one-third of waiting patients can receive matched organs from donors. Unfortunately, many patients who require a transplant have to wait for long periods of time, and many of them die before receiving the desired organ. In the USA alone, over 100,000 patients are waiting for a kidney transplant. However, it is a problem that affects around 6% of the word population. Therefore, seeking alternative solutions to this problem is an urgent work. Here, we review the current promising regenerative technologies for kidney function replacement. Despite many approaches being applied in the different ways outlined in this work, obtaining an organ capable of performing complex functions such as osmoregulation, excretion or hormone synthesis is still a long-term goal. However, in the future, the efforts in these areas may eliminate the long waiting list for kidney transplants, providing a definitive solution for patients with end-stage renal disease.

Assembling Kidney Tissues from Cells: The Long Road from Organoids to Organs

The field of regenerative medicine has witnessed significant advances that can pave the way to creating de novo organs. Organoids of brain, heart, intestine, liver, lung and also kidney have been developed by directed differentiation of pluripotent stem cells. While the success in producing tissue-specific units and organoids has been remarkable, the maintenance of an aggregation of such units in vitro is still a major challenge. While cell cultures are maintained by diffusion of oxygen and nutrients, three- dimensional in vitro organoids are generally limited in lifespan, size, and maturation due to the lack of a vascular system. Several groups have attempted to improve vascularization of organoids. Upon transplantation into a host, ramification of blood supply of host origin was observed within these organoids. Moreover, sustained circulation allows cells of an in vitro established renal organoid to mature and gain functionality in terms of absorption, secretion and filtration. Thus, the coordination of tissue differentiation and vascularization within developing organoids is an impending necessity to ensure survival, maturation, and functionality in vitro and tissue integration in vivo. In this review, we inquire how the foundation of circulation is laid down during the course of organogenesis, with special focus on the kidney. We will discuss whether nature offers a clue to assist the generation of a nephro-vascular unit that can attain functionality even prior to receiving external blood supply from a host. We revisit the steps that have been taken to induce nephrons and provide vascularity in lab grown tissues. We also discuss the possibilities offered by advancements in the field of vascular biology and developmental nephrology in order to achieve the long-term goal of producing transplantable kidneys in vitro.

Current Bioengineering Methods for Whole Kidney Regeneration

Kidney regeneration is likely to provide an inexhaustible source of tissues and organs for immunosuppression-free transplantation. It is currently garnering considerable attention and might replace kidney dialysis as the ultimate therapeutic strategy for renal failure. However, anatomical complications make kidney regeneration difficult. Here, we review recent advances in the field of kidney regeneration, including (i) the directed differentiation of induced pluripotent stem cells/embryonic stem cells into kidney cells; (ii) blastocyst decomplementation; (iii) use of a decellularized cadaveric scaffold; (iv) embryonic organ transplantation; and (v) use of a nephrogenic niche for growing xenoembryos for de novo kidney regeneration from stem cells. All these approaches represent potentially promising therapeutic strategies for the treatment of patients with chronic kidney disease. Although many obstacles to kidney regeneration remain, we hope that innovative strategies and reliable research will ultimately allow the restoration of renal function in patients with end-stage kidney disease.

Renal primordia activate kidney regenerative events in a rat model of progressive renal disease

New intervention tools for severely damaged kidneys are in great demand to provide patients with a valid alternative to whole organ replacement. For repairing or replacing injured tissues, emerging approaches focus on using stem and progenitor cells. Embryonic kidneys represent an interesting option because, when transplanted to sites such as the renal capsule of healthy animals, they originate new renal structures. Here, we studied whether metanephroi possess developmental capacity when transplanted under the kidney capsule of MWF male rats, a model of spontaneous nephropathy. We found that six weeks post-transplantation, renal primordia developed glomeruli and tubuli able to filter blood and to produce urine in cyst-like structures. Newly developed metanephroi were able to initiate a regenerative-like process in host renal tissues adjacent to the graft in MWF male rats as indicated by an increase in cell proliferation and vascular density, accompanied by mRNA and protein upregulation of VEGF, FGF2, HGF, IGF-1 and Pax-2. The expression of SMP30 and NCAM was induced in tubular cells. Oxidative stress and apoptosis markedly decreased. Our study shows that embryonic kidneys generate functional nephrons when transplanted into animals with severe renal disease and at the same time activate events at least partly mimicking those observed in kidney tissues during renal regeneration.

Adult stem cells and cardiac regeneration

There is worldwide demand for therapies to promote the robust repair and regeneration with maximum regain of function of particular tissues and organs damaged by disease or injury. The potential role of adult stem cells has been highlighted by an increasing number of in vitro and in vivo studies. Nowhere is this more evident than in adult stem cell-based therapies being explored to promote cardiac regeneration. In spite of encouraging advances, significant challenges remain.

Differentiation of human pluripotent stem cells into nephron progenitor cells in a serum and feeder free system

Objectives

Kidney disease is emerging as a critical medical problem worldwide. Because of limited treatment options for the damaged kidney, stem cell treatment is becoming an alternative therapeutic approach. Of many possible human stem cell sources, pluripotent stem cells are most attractive due to their self-renewal and pluripotent capacity. However, little is known about the derivation of renal lineage cells from human pluripotent stem cells (hPSCs). In this study, we developed a novel protocol for differentiation of nephron progenitor cells (NPCs) from hPSCs in a serum- and feeder-free system.

Materials and Methods

We designed step-wise protocols for differentiation of human pluripotent stem cells toward primitive streak, intermediate mesoderm and NPCs by recapitulating normal nephrogenesis. Expression of key marker genes was examined by RT-PCR, real time RT-PCR and immunocytochemistry. Each experiment was independently performed three times to confirm its reproducibility.

Results

After modification of culture period and concentration of exogenous factors, hPSCs can differentiate into NPCs that markedly express specific marker genes such as SIX2, GDNF, HOXD11, WT1 and CITED1 in addition to OSR1, PAX2, SALL1 and EYA1. Moreover, NPCs possess the potential of bidirectional differentiation into both renal tubular epithelial cells and glomerular podocytes in defined culture conditions. In particular, approximately 70% of SYN-positive cells were obtained from hPSC-derived NPCs after podocytes induction. NPCs can also form in vitro tubule-like structures in three dimensional culture systems.

Conclusions

Our novel protocol for hPSCs differentiation into NPCs can be useful for producing alternative sources of cell replacement therapy and disease modeling for human kidney diseases.

Structural links between the renal stem/progenitor cell niche and the organ capsule

A special feature of the renal stem/progenitor cell niche is its always close neighborhood to the capsule during organ development. To explore this link, neonatal kidney was investigated by histochemistry and transmission electron microscopy. For adequate contrasting, fixation of specimens was performed by glutaraldehyde including tannic acid. The immunohistochemical data illustrate that renal stem/progenitor cells are not distributed randomly but are positioned specially to the capsule. Epithelial stem/progenitor cells are found to be enclosed by the basal lamina at a collecting duct (CD) ampulla tip. Only few layers of mesenchymal cells are detected between epithelial cells and the capsule. Most impressive, numerous microfibers reacting with soybean agglutinin, anti-collagen I and III originate from the basal lamina at a CD ampulla tip and line between mesenchymal stem/progenitor cells to the inner side of the capsule. This specific arrangement holds together both types of stem/progenitor cells in a cage and fastens the niche as a whole at the capsule. Electron microscopy further illustrates that the stem/progenitor cell niche is in contact with a tunnel system widely spreading between atypical smooth muscle cells at the inner side of the capsule. It seems probable that stem/progenitor cells are supplied here by interstitial fluid.

Re-engineering development to instruct tissue regeneration

With few exceptions, tissue regeneration strategies based on the conventional combination of cells, scaffolding materials, and soluble factors (tissue engineering) have introduced a rather limited clinical impact. While it is being recognized that the nonconvincing benefits of engineered grafts require more fundamental knowledge on mechanisms of action and potency factors, the attempt to mimic and recapitulate developmental events has inspired an evolution of the paradigm. In the context of skeletal regeneration, a "developmental engineering" approach has been advocated to generate intermediate grafts (i.e., hypertrophic cartilage templates) which, as suggested by limb developmental biology, are capable of autonomous spatial and temporal evolution into fully functional bone organs. However, limited consideration has been given to the fact that the recipient site within adult organisms may not be compatible with well-established developmental processes. This can be due to the possibly restricted function of resident progenitors, to the critical mechanical and physical boundary conditions of mature organs, or to the strong role of inflammatory signals and immune cells at repair sites. We thus propose that predictable, orderly, and durable tissue regeneration should be based on a "developmental RE-engineering" paradigm, with the challenge to instruct the execution of developmental programs in the context of an adult system.