In vitro generation of renal tubular epithelial cells from fibroblasts: implications for precision and regenerative medicine in nephrology

A Novel Protocol for Culturing Polarized Proximal Tubular Epithelial Cells from Kidney Biopsies: Enhancing Platforms for Drug Excretion and Nephrotoxicity Studies

The kidneys are integral to homeostasis but are susceptible to nephrotoxic compounds. Proximal tubular epithelial cells (PTECs) mediate drug metabolism and transport and are widely used in preclinical studies. However, commercial PTECs are limited in availability and physiological relevance. This study aimed to develop a novel, reliable protocol for isolating and culturing PTECs from human kidney biopsies. Primary PTECs were isolated from kidney biopsies of two patients (MFUM-RPTEC-1 and MFUM-RPTEC-2). Their morphology, population doubling time, transepithelial electrical resistance (TEER), and phenotypic markers were evaluated. Polarization and transporter expression were analyzed using cells cultured on Transwell inserts. Colonies formed within 24-48 h, with confluence reached by 8-10 days and dome (hemicyst) formation by day 13. TEER values peaked at 190 Ω/cm2 after 7-14 days, confirming tight junction formation. Immunostaining identified characteristic markers (e.g., SGLT2, OAT1/3, OCT2, P-gp, MRP4, MATE1, N-cadherin, ZO-1, CK-18). Cells cultured on Transwell plates exhibited native polarization, expressing transporters crucial for drug excretion on apical and basolateral surfaces. We present two robust protocols for isolating and characterizing PTECs, offering a scalable method to obtain functional, polarized cells from scarce biopsy material. The isolated PTECs, therefore, present a valuable platform for preclinical studies, especially for drug excretion testing through the expressed transporters. Drug competition for these transporters during tubular secretion is also a common cause of nephrotoxicity.

Expression levels and stoichiometry of Hnf1β, Emx2, Pax8 and Hnf4 influence direct reprogramming of induced renal tubular epithelial cells

Generation of induced renal epithelial cells (iRECs) from fibroblasts offers great opportunities for renal disease modeling and kidney regeneration. However, the low reprogramming efficiency of the current approach to generate iRECs has hindered potential therapeutic application and regenerative approach. This could be in part attributed to heterogeneous and unbalanced expression of reprogramming factors (RFs) Hnf1β (H1), Emx2 (E), Pax8 (P), and Hnf4α (H4) in transduced fibroblasts. Here, we establish an advanced retroviral vector system that expresses H1, E, P, and H4 in high levels and distinct ratios from bicistronic transcripts separated by P2A. Mouse embryonic fibroblasts (MEFs) harboring Cdh16-Cre; mT/mG allele are utilized to conduct iREC reprogramming via directly monitoring single cell fate conversion. Three sets of bicistronic RF combinations including H1E/H4P, H1H4/EP, and H1P/H4E have been generated to induce iREC reprogramming. Each of the RF combinations gives rise to distinct H1, E, P, and H4 expression levels and different reprogramming efficiencies. The desired H1E/H4P combination that results in high expression levels of RFs with balanced stoichiometry. substantially enhances the efficiency and quality of iRECs compared with transduction of separate H1, E, P, and H4 lentiviruses. We find that H1E/H4P-induced iRECs exhibit the superior features of renal tubular epithelial cells, as evidenced by expressing renal tubular-specific genes, possessing endocytotic arrogation activity and assembling into tubules along decellularized kidney scaffolds. This study establishes H1E/H4P cassette as a valuable platform for future iREC studies and regenerative medicine.

Great potential of renal progenitor cells in kidney: From the development to clinic

The mammalian renal organ represents a pinnacle of complexity, housing functional filtering units known as nephrons. During embryogenesis, the depletion of niches containing renal progenitor cells (RPCs) and the subsequent incapacity of adult kidneys to generate new nephrons have prompted the formulation of protocols aimed at isolating residual RPCs from mature kidneys and inducing their generation from diverse cell sources, notably pluripotent stem cells. Recent strides in the realm of regenerative medicine and the repair of tissues using stem cells have unveiled critical signaling pathways essential for the maintenance and generation of human RPCs in vitro. These findings have ushered in a new era for exploring novel strategies for renal protection. The present investigation delves into potential transcription factors and signaling cascades implicated in the realm of renal progenitor cells, focusing on their protection and differentiation. The discourse herein elucidates contemporary research endeavors dedicated to the acquisition of progenitor cells, offering crucial insights into the developmental mechanisms of these cells within the renal milieu and paving the way for the formulation of innovative treatment modalities.

Urinary nephrospheres indicate recovery from acute kidney injury in renal allograft recipients - a pilot study

Background

Acute kidney injury represents a major threat to the transplanted kidney. Nevertheless, these kidneys have the potential to fully recover. Tubular regeneration following acute kidney injury is driven by the regenerative potential of tubular cells originating from a tubular stem cell pool. We investigated urinary sediments of acute kidney injury transplanted patients and compared it to those of non-transplanted patients. Thereby we discovered tubular cell agglomerates, which have not been described in vivo. We hypothesized that these so-called nephrospheres were associated with recovery from acute kidney injury.

Methods

Urine sediment of 45 kidney-transplanted and 19 non-transplanted individuals was investigated. Nephrospheres were isolated and stained for several molecular markers including aquaporin 1 (AQP1) and calcium sensing receptor (CASR). Nephrospheres were cultured to examine their growth behavior in vitro. In addition, quantitative PCR for CASR, AQP1, and podocin (NPHS2) was performed.

Results

Nephrospheres were excreted in the urine of 17 kidney-transplant recipients 7 days after onset of acute kidney injury and were detectable over several days until kidney function was recovered to baseline creatinine levels. None were found in the urine of non-transplanted individuals. Nephrospheres were either AQP1+/CASR+ or AQP1−/CASR+ and could be cultured for 27 days. Mitotic cells could still be visualized after 17 days in culture. Quantitative PCR detected AQP1 in both kidney-transplanted and non-transplanted individuals during the phase of creatinine decline. As a limitation qPCR was only performed for the entire urinary sediment.

Conclusions

Nephrospheres are three dimensional tubular cell agglomerates which appeared in urine of kidney transplant recipients recovering from acute kidney injury. Appearance of nephrospheres in urine was independent of the duration after kidney transplantation. Nephrospheres proliferated in cell culture and kept expressing kidney specific marker. Presence of nephrospheres in urine showed a specificity of 100% and a sensitivity of 60.71% for recovery.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1454-3) contains supplementary material, which is available to authorized users.

Reversibility of irreversible aging

Most multicellular organisms are known to age, due to accumulation of damage and other deleterious changes over time. These changes are often irreversible, as organisms, humans included, evolved fully differentiated, irreplaceable cells (e.g. neurons) and structures (e.g. skeleton). Hence, deterioration or loss of at least some cells and structures should lead to inevitable aging of these organisms. Yet, some cells may escape this fate: adult somatic cells may be converted to partially reprogrammed cells or induced pluripotent stem cells (iPSCs). By their nature, iPSCs are the cells representing the early stages of life, indicating a possibility of reversing the age of cells within the organism. Reprogramming strategies may be accomplished both in vitro and in vivo, offering opportunities for rejuvenation in the context of whole organisms. Similarly, older organs may be replaced with the younger ones prepared ex vivo, or grown within other organisms or even other species. How could the irreversibility of aging of some parts of the organism be reconciled with the putative reversal of aging of the other parts of the same organism? Resolution of this question holds promise for dramatically extending lifespan, which is currently not possible with traditional genetic, dietary and pharmacological approaches. Critical issues in this challenge are the nature of aging, relationship between aging of an organism and aging of its parts, relationship between cell dedifferentiation and rejuvenation, and increased risk of cancer that goes hand in hand with rejuvenation approaches.