#1805 Renal progenitor cells isolated from urine of IgA nephropathy patients formed renal spheroids that can recapitulate the typical IgA1 deposition
Authors: Giannuzzi Francesca , Picerno Angela , Maiullari Silvia , Montenegro Francesca , Cicirelli Antonella , Stasi Alessandra , Franzin Rossana , Pertosa Giovanni , Rossini Michele , Leo Vincenzo D I , Gesualdo Loreto , Sallustio Fabio 
Published: May 2024

Abstract

Background and Aims
Recent developments in stem cell biology have made it possible to create spheroids and kidney organoids from human and mouse pluripotent stem cells and renal stem cells. Spheroids are a suitable in vitro model for studies of drug studies and can transform into organoids whose rapidly developing field has proven useful in simulating nephrotoxicity, kidney disorders, and kidney development. However, to date in all studies the generation of organoids and tubuloids required the use of sophisticated and complex differentiation protocols involving external administration of several growth factors and needs compliance with a precise and specific timescale.
Here we showed for the first time that human adult renal progenitor cells (ARPCs) can be isolated from urines of healthy subjects (HS) or IgA Nephropathy (IgAN) patients and can form spheroids generating very long tubule-like structures naturally, without the external use of chemokines or growth factors to artificially induce the process and recapitulating the IgA1 deposition that is the typical characteristic of the disease.

Method
Spheroids and tubule-like structures were characterized by whole-mounting and frozen section immunofluorescence (IF) assays and by Flow Cytometry Analysis using CD133, NanoG, Oct3/4, GATA-3, SSEA4, CD249, Aminopepidase N, ZO-1, Uromodulin, and Lotus Tetragonolobus Lectin (LTL) antibodies. ELISA was used to determine the renin secretion and CAM assays to determine ARPCs and ARPC-derived Spheroids angiogenic properties. PKH-26 labeling was used for their in vitro and in vivo tracking. Serum of HS and IgAN patients in culture with spheroids was used to recapitulate the disease and IgA1 deposits were measured by IF.

Results
ARPC-derived spheroids reflected the renal progenitor properties and recapitulated organoids generating very long tubule-like structures that expressed structural and functional renal tubule markers such as CD249, Aminopepidase N, ZO-1, Uromodulin, and LTL and in some cases shared many structural similarities with some regions of nephrons, such as the distal convoluted tubule, the loop of Henle and proximal convoluted tubules.
Moreover, ARPC-derived spheroids secreted elevated levels of renin and, as the cellular counterpart, showed angiogenic properties. To study the proof of concept that ARPC-derived spheroids can be used to establish in vitro models recapitulating renal diseases, we generated IgAN patient-specific renal spheroids using the ARPC mixed cell population method. ARPC-derived spheroids of IgAN patients showed deposits of IgA1 already after four days of culture with patient serum (p = 0.004) and, with a different pattern, after 8 and 15 days (p = 0.0029 and p = 0.0012, respectively). The IgA1 deposition resembled that in the glomeruli of patients diagnosticated with IgAN. In contrast, no positive signal was detected in either IgAN spheroids in culture with FBS, or with inactivated IgAN serum, as well as in spheroids derived from urine of HS in culture with IgAN serum.

Conclusion
The ability of ARPCs to form spheroids and differentiate into tubular-like structures without the need for external chemokines or growth factors is a significant advancement in the field, even more considering that these cells can be isolated from the urine of patients. These findings open up new possibilities for the regenerative medicine in studying kidney development, disease mechanisms, and regenerative therapy development for renal disorders.