SEMINAR:Monitoring renal physiology with advanced in vitro kidney models

Guest: Idil Orhon, Radboud University Medical Center

Title: Monitoring renal physiology with advanced in vitro kidney models

Date/Time: 24 April 2024, 13.40

Location: FENS G035

Abstract: The kidney consists of different segments that are essential in maintaining homeostasis throughout the body, including regulating electrolyte and water balance. The last segment of the kidney tubules is called the collecting duct (CD), where finetuning of sodium and water reabsorption occurs. A dysfunction of this process can lead to nephrogenic diabetes insipidus (NDI) that causes the inability to concentrate urine which can lead to patients excreting urine from 3 to 20 liters per day with risk of severe dehydration. It is known that NDI is caused by dysfunction of the water channel aquaporin 2 (AQP2) or the vasopressin 2 receptor (V2R) in the CD. Despite promising results of pre-clinical experiments, clinical trials often fail due to ineffectiveness or side-effects. Recent developments in organoid research promise to study kidney (patho)physiology with increased translational value compared to conventional in vitro research models.

Tubuloids are kidney organoid models that are derived from adult stem cells and consist of epithelial cells from different segments of the kidney tubules. Tubuloid cells have high resemblance to their in vivo counterparts in terms of morphology and a mature expression profile of distal part of the nephron. By utilizing these tubuloid models, we show that tubuloids are capable of functional CD-specific sodium and water transport regulation under control of physiological stimuli and (inhibitory) diuretics that are commonly used in the clinic. Single cell RNAseq results show that tubuloids can be differentiated towards the thick ascending limb (TAL), distal convoluted tubule(DCT and the collecting duct (CD).

Differentiated tubuloids showed significantly increased expression of these segment specific markers, including key sodium transporters NKCC2 (TAL), NCC (DCT), the sodium channel ENaC (CD) and water transport channels AQP2 (CD), AQP3 and AQP4. Radioactive tracer 22Na+ was used to study sodium reabsorption by renal ion transporters and channels, confirming that endogenous sodium channels in tubuloids reabsorb Na+ in a diuretic dependent manner. Physiological stimulation of tubuloids by desmopressin , the analog of vasopressin, resulted in upregulation of AQP2 signaling in a vasopressin 2 receptor (V2R) dependent manner. Following these findings, we performed 3D swelling assays to confirm the functional water transport capabilities. These functional assays confirmed that CD tubuloids are indeed capable of increasing water transport within the lumen of tubules and thereby respond to stimuli by swelling.

By combining these functional sodium and water transport assays with the versatile tubuloid model, we propose that distal tubule differentiated tubuloids are suitable models to study kidney-specific behavior which can enable personalized medicine and studies on (rare) kidney diseases.

Bio: Idil Orhon is currently a senior postdoc in the department of medical biosciences in Radboud University medical Center in Nijmegen, Netherlands. She received her bachelor from Sabanci University in 2009 in Biological sciences and Bioengineering with a minor in chemistry. She then went to Paris, France for her masters in Cell Biology. She received her PhD in Cell Biology in 2014 cum laude in the group of Prof. Patrice Codogno where she studied the Interplay between autophagy and the primary cilium: Role in mechanical stress integration in kidney epithelial cells. She continued her research in the Netherlands with her postdoc in the group of Prof. Fulvio Reggiori, where she studied the role of autophagy in stem cell self-renewal in the context of salivary gland stem cells using salivary gland organoids. She then followed her passion in kidney physiology and organoids which brought her to Radboudumc in the group of Prof. Joost Hoenderop, where she has focused on (patho)physiological kidney modeling using kidney organoids. Dr. Orhon has published articles such as Nature, Nature Cell Biology and Autophagy. She is passionate about autophagy, the kidney and animal-free in vitro modeling.