The use of stem cells has enabled the successful generation of simple organs. However, anatomically complicated organs such as the kidney have proven more refractory to stem-cell-based regenerative techniques. Given the limits of allogenic organ transplantation, an ultimate therapeutic solution is to establish self-organs from autologous stem cells and transplant them as syngrafts back into donor patients. To this end, we have striven to establish an in vitro organ factory to build up complex organ structures from autologous adult stem cells by using the kidney as a target organ. Cultivation of human mesenchymal stem cells in growing rodent embryos enables their differentiation within a spatially and temporally appropriate developmental milieu, facilitating the first step of nephrogenesis. We show that a combination of whole-embryo culture, followed by organ culture, encourages exogenous human mesenchymal stem cells to differentiate and contribute to functional complex structures of the new kidney.

Given the limits of allogenic organ transplantation, an ultimate therapeutic solution is to establish a self-organ from autologous stem cells and transplant them as syngrafts back into donor patients. It was reported previously that human mesenchymal stem cells (hMSC) that are cultivated in growing rodent embryos can differentiate within a spatially and temporally appropriate developmental milieu, facilitating the first step of nephrogenesis. As another step toward clinical application, the system was modified for progression to complete functional organogenesis. Rat embryos (E11.5) were isolated from uteri, and bone marrow–derived hMSC, which were transfected adenovirally with glial cell line–derived neurotrophic factor and retrovirally with LacZ, were implanted into the nephrogenic site. Forty-eight hours later, ureteric buds were elongated and initial branching was completed. The metanephroi were dissected out, developed further using in vitro organ culture for 24 h, transplanted into the omentum of a uninephrectomized rat, and grown for 2 wk. They enlarged and exhibited normal kidney structure and ultrastructure. hMSC-derived LacZ-positive cells were identified throughout the regenerated kidney and were morphologically identical to resident renal cells. Transplantation of developing metanephroi into the LacZ transgenic rat revealed that neo-kidney vasculature originated from the host circulation. Finally, fluid was collected from expanded ureters, and urea nitrogen and creatinine were measured. Levels were much higher in these fluids compared with transplanted rat sera (840.3 ± 184.6 versus 30.4 ± 10.8 and 10.1 ± 3.1 versus 0.3 ± 0.2 mg, respectively), suggesting that the neo-kidney may produce urine. Taken together, these findings suggest that hMSC can differentiate into a mature renal structure with the potential to replace lost kidney function.

Patients with chronic kidney disease (CKD) and dialysis have higher mortality than those without, and cardiovascular disease (CVD) is the main cause of death. As CVD is caused by several mechanisms, insulin resistance plays an important role in CVD. This review summarizes the importance and mechanism of insulin resistance in CKD and discusses the current evidence regarding insulin resistance in patients with CKD and dialysis. Insulin resistance has been reported to influence endothelial dysfunction, plaque formation, hypertension, and dyslipidemia. A recent study also reported an association between insulin resistance and cognitive dysfunction, non-alcoholic fatty liver disease, polycystic ovary syndrome, and malignancy. Insulin resistance increases as renal function decrease in patients with CKD and dialysis. Several mechanisms increase insulin resistance in patients with CKD, such as chronic inflammation, oxidative stress, obesity, and mineral bone disorder. There is the possibility that insulin resistance is the potential future target of treatment in patients with CKD.

Significance: Worldwide, the number of patients with end-stage renal disease requiring renal replacement therapy is increasing because of the shortage of donor organs. We have successfully generated functional kidneys from human stem cells using the organogenic niche method. However, for these kidneys to have clinical application, a urinary excretion pathway is necessary. Using pigs, we demonstrated our stepwise peristaltic ureter system, showing that it resolves important problems regarding the construction of the urine excretion pathway and the long-term growth of the stem cell-generated embryonic kidneys.

It has been suggested that low nephron number contributes to glomerular hypertension and hyperperfusion injury in progressive chronic kidney disease (CKD). The incidence of CKD in Japan is among the highest in the world, but the reasons remain unclear. We estimated total nephron (glomerular) number (Nglom _TOTAL ) as well as numbers of nonsclerosed (Nglom _NSG ) and globally sclerosed glomeruli (Nglom _GSG ), and the mean volume of nonsclerosed glomeruli (Vglom _NSG ) in Japanese normotensive, hypertensive, and CKD subjects and investigated associations between these parameters and estimated glomerular filtration rate (eGFR). Autopsy kidneys from age-matched Japanese men (9 normotensives, 9 hypertensives, 9 CKD) had nephron number and Vglom _NSG estimated using disector/fractionator stereology. Subject eGFR, single-nephron eGFR (SNeGFR), and the ratio SNeGFR/Vglom _NSG were calculated. Nglom _NSG in Japanese with hypertension (392,108 ± 87,605; P < 0.001) and CKD (268,043 ± 106,968; P < 0.001) was less than in normotensives (640,399 ± 160,016). eGFR was directly correlated with Nglom _NSG ( r = 0.70, P < 0.001) and inversely correlated with Vglom _NSG ( r = –0.53, P < 0.01). SNeGFR was higher in hypertensives than normotensives ( P = 0.03), but was similar in normotensives and CKD, while the ratio SNeGFR/Vglom _NSG was similar in normotensives and hypertensives but markedly reduced in CKD. Nephron number in Japanese with hypertension or CKD was low. This results in a higher SNeGFR in hypertensives compared with normotensive and CKD subjects, but lowered SNeGFR/Vglom _NSG in CKD subjects, suggesting that changes in GFR are accommodated by glomerular hypertrophy rather than glomerular hypertension. These findings suggest glomerular hypertrophy is a dominant factor in maintenance of GFR under conditions of low nephron number.

Animal fetuses and embryos may have applications in the generation of human organs. Progenitor cells may be an appropriate cell source for regenerative organs because of their safety and availability. However, regenerative organs derived from exogenous lineage progenitors in developing animal fetuses have not yet been obtained. Here, we established a combination system through which donor cells could be precisely injected into the nephrogenic zone and native nephron progenitor cells (NPCs) could be eliminated in a time- and tissue-specific manner. We successfully achieved removal of Six2+ NPCs within the nephrogenic niche and complete replacement of transplanted NPCs with donor cells. These NPCs developed into mature glomeruli and renal tubules, and blood flow was observed following transplantation in vivo. Furthermore, this artificial nephron could be obtained using NPCs from different species. Thus, this technique enables in vivo differentiation from progenitor cells into nephrons, providing insights into nephrogenesis and organ regeneration.