Tubular epithelial progenitors are excreted in urine during recovery from severe acute kidney injury and are able to expand and differentiate in vitro

• Published in: PeerJ (San Francisco, CA) CA), 2022-10, Vol.10, p.e14110, Article e14110
• Main Authors: Gerges, Daniela, Hevesi, Zsofia, Schmidt, Sophie H, Kapps, Sebastian, Pajenda, Sahra, Geist, Barbara, Schmidt, Alice, Wagner, Ludwig, Winnicki, Wolfgang
• Format: Article
• Language: English
• Subjects: Acute kidney injury (AKI); Acute Kidney Injury - metabolism; Antibodies; Apoptosis; Aquaporin 1; Aquaporin 6; Biochemistry; Cell Biology; Cell culture; Cell differentiation; Cytology; Dialysis; Differentiation; Epithelial cells; Gene expression; Humans; Immunofluorescence; Internal Medicine; Ischemia; Ischemia - metabolism; Kidney; Kidney diseases; Kidney transplantation; Kidney Tubules, Proximal - metabolism; Morphology; Nephrology; Nephrosphere; Neprilysin; Neprilysin - metabolism; Pathology; Patients; Pax8 protein; Progenitor cells; Proteins; Renal function; Stem cells; Transplants & implants; Tubular epithelial progenitors; Tubular regeneration; Tumors; Urine
• ISSN: 2167-8359; 2167-8359
• DOI: 10.7717/peerj.14110

Acute kidney injury (AKI) is a serious condition associated with chronic kidney disease, dialysis requirement and a high risk of death. However, there are specialized repair mechanisms for the nephron, and migrated committed progenitor cells are the key players. Previous work has described a positive association between renal recovery and the excretion of tubular progenitor cells in the urine of kidney transplant recipients. The aim of this work was to describe such structures in non-transplanted AKI patients and to focus on their differentiation. Morning urine was obtained from four patients with AKI stage 3 and need for RRT on a consecutive basis. Urine sediment gene expression was performed to assess which part of the tubular or glomerular segment was affected by injury, along with measurement of neprilysin. Urine output and sediment morphology were monitored, viable hyperplastic tubular epithelial clusters were isolated and characterized by antibody or cultured . These cells were monitored by phase contrast microscopy, gene, and protein expression over 9 days by qPCR and confocal immunofluorescence. Furthermore, UMOD secretion into the supernatant was quantitatively measured. Urinary neprilysin decreased rapidly with increasing urinary volume in ischemic, toxic, nephritic, and infection-associated AKI, whereas the decrease in sCr required at least 2 weeks. While urine output increased, dead cells were present in the sediment along with debris followed by hyperplastic agglomerates. Monitoring of urine sediment for tubular cell-specific gene transcript levels NPHS2 (podocyte), AQP1 and AQP6 (proximal tubule), and SLC12A1 (distal tubule) by qPCR revealed different components depending on the cause of AKI. Confocal immunofluorescence staining confirmed the presence of intact nephron-specific epithelial cells, some of which appeared in clusters expressing AQP1 and PAX8 and were 53% positive for the stem cell marker PROM1. Isolated tubule epithelial progenitor cells were grown , expanded, and reached confluence within 5-7 days, while the expression of AQP1 and UMOD increased, whereas PROM1 and Ki67 decreased. This was accompanied by a change in cell morphology from a disproportionately high nuclear/cytoplasmic ratio at day 2-7 with mitotic figures. In contrast, an apoptotic morphology of approximately 30% was found at day 9 with the appearance of multinucleated cells that were associable with different regions of the nephron tubule by marker proteins. At the