#930 Elevated glucose in kidney organoids induces epithelial detachment driven by proinflammatory cytokines
Authors: Spennati Giulia , Regier Mary C , Ward Heather H , Das Vivek , Karihaloo Anil , Freedman Benjamin S 
Published: May 2024

Abstract

Background and Aims
Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease affecting 40% of diabetics. The pathogenesis of DKD is linked with inflammation, altered metabolism, and hemodynamic change but the relationship between these factors is not well understood. Proteinuria and albuminuria are common features, suggesting that impairments in the renal glomerular filtration barrier may be among the primary disease initiators. Limited DKD models are available, which has hampered our disease understanding and the ability to develop new therapies. Therefore, creating an in-vitro model that harbors multiple renal cell types organized in their natural complex arrangement becomes an attractive option to fill in this gap. Here, we conducted a systematic investigation of the effects of high glucose on kidney organoids, with the goal of understanding whether these cultures can reflect specific features relevant to DKD.

Method
To evaluate the effect of high glucose, kidney organoids were differentiated until maturation (day 21) in standard glucose and then switched for six days to concentrations of 5.5, 11, 33 and 100 mM. Then, to test the effect of proinflammatory cytokines on the injury phenotypes we switched organoids, at day 21, in control glucose condition (11 mM) ± TNFα or high glucose (33 mM) ± inhibitors (TNFα). Morphology was analysed via immunostaining, LDH and live/dead assay were used for toxicity, qPCR and western blotting to investigate differences in gene and protein expression, and mannose was used as an osmotic control. scRNA-seq of organoid in 11 vs 33 mM was conducted to gain insight into the molecular mechanism(s) contributing to the high glucose.

Results
Organoids remain well preserved in glucose up to 11 mM whereas organoids cultured in 33 and 100 mM showed a ∼30% reduction in overall organoid number between days 3 and 6. Moreover, in high glucose (33 and 100 mM), we observed an increase in the number of small, single PODXL+ cells surrounding the main organoid body, suggesting detachment from the podocyte clusters that normally form in organoids (Fig. A). To quantify it, we divided the total PODXL+ area into two sub-regions, classified as intact area and detached area, and calculated their ratio (Fig. B). Results indicated a 2-fold reduction of the intact vs detached area between 11 and 33 mM (p = 0.0011), suggesting that organoids undergo a spreading process under the influence of high glucose (Fig. C). Comparison of equimolar glucose vs mannose, live/dead and LDH assays identify a non-osmotic and non-apoptotic cause of the injury. ScRNA-seq analysis identified TNF-α as an upregulated pathway, which was confirmed with qPCR (p = 0.0131). Comparison of organoids at 11mM ± TNFα indicated that TNFα addition sensitizes podocytes to detachment at lower glucose levels, specifically, we identified a 4-fold reduction of the PODXL+ intact vs detached area at 11 mM ± TNFα (p &lt; 0.0001), Fig. D. To further validate these findings and investigate possible therapeutic strategies, organoids were cultured with 33 mM glucose with TNF-α inhibitor and we identified a protective effect of the inhibitor which prevented the podocyte spreading phenotype at 33 mM glucose (Fig. E).

Conclusion
Our experiments identify an injury phenotype under high glucose concentrations, in kidney organoids, characterized by podocyte detachment from the main organoid body. Moreover, no osmotic or toxicity effect was observed. Importantly, this phenotype resembles disease features identified in diabetic patients, where podocyte loss and detachment from the glomerular basement membrane is associated with pathophysiology. We identified a correlation between the injury phenotype, characterized by epithelial detachment, and proinflammatory cytokine upregulation, which is driven by high glucose, and we have shown it can be targeted therapeutically. Therefore, this new experimental model in-vitro offers up new insights into the pathophysiology of diabetes and its complications, and represents a new platform to screen for therapeutics.