#4286 ACCUMULATION OF MALADAPTIVE TUBULAR EPITHELIAL CELLS (TECS) IS UBIQUITOUS IN CKD AND REPRESENTS A COMMON INITIATING MECHANISM OF DISEASE PROGRESSION
Authors: Olson Eric , Bohnenpoll Tobias , Pospiech Johannes , Michel Niklas , Mcconnell Mark , Cox Jennifer , Kuo Jay , Radresa Olivier , King Andrew , Andag Uwe 
Published: June 2023

Abstract

Background and Aims
Interstitial fibrosis, tubular atrophy and inflammation are common final pathways to end-stage kidney disease (ESKD), contributing to progressive nephron loss and functional decline in most chronic kidney diseases (CKD), including those considered to be glomerular in origin. Disease-associated maladaptive TECs have been described in rodent models1 and are characterized by a failed repair phenotype that contributes to tubulointerstitial fibrosis and inflammation. The contribution of equivalent maladaptive cell states to human CKD progression remains poorly described. The aim of this study was to characterize maladaptive TECs in the NURTuRE CKD cohort to assess their abundance and potential role in initiating inflammation and fibrosis in a large and heterogeneous patient population.

Method
Human maladaptive TECs were identified in an scRNA-Seq dataset (GSE171314) from IgA nephropathy patients by scoring cells with a TNF activation and a mouse proximal tubule failed repair (FR) gene signature[1]. The results were validated in a scRNA-Seq dataset (GSE171458) from patients with membranous nephropathy. Marker genes for these human maladaptive TEC clusters were derived using the Seurat R package and the top 50 candidates were combined into cell state-specific signatures. Single-sample signature scores were calculated for 310 kidney biopsy transcriptomes from various CKD etiologies in the NURTuRE cohort. Signature scores were correlated with eGFR and used in a time-to-event analysis (40% decline in eGFR or occurrence of ESRD) to predict renal event-free survival.

Results
Analysis of independent human scRNA-Seq datasets and scoring with TNF activation and mouse proximal tubule FR gene signatures revealed two distinct maladaptive TEC states associated with different tubular segments. A cluster of cells (FR-PT) with increased TNF activation and mouse FR signature expression were identified that clustered adjacent to proximal TECs, suggesting a lineage relationship. A second cluster of cells (DT2) with increased TNF activation was clustered adjacent to thick ascending limb (TAL) cells, suggesting distal tubule lineage. Both maladaptive TEC clusters were detected at low levels in healthy controls but increased in CKD. FR-PT and DT2 cells are characterized by a pro-fibrotic and pro-inflammatory gene expression and likely represent a source of signalling molecules mediating stromal crosstalk in the kidney fibrotic microenvironment. To investigate their abundance in CKD, signature expression in NURTuRE kidney biopsy transcriptomes was summarized into a sample-level score. Signature scores for FR-PT and DT2 cells were generally elevated in all CKD etiologies with substantial variation within disease groups. Inverse correlation of eGFR with the scores suggested an accumulation of maladaptive TECs with kidney function decline, largely independent of primary diagnosis (Fig. 1). Pseudotime analysis revealed that this accumulation accompanied or preceded increases in myofibroblast and immune cell gene expression, suggesting a mechanism that may be driving disease initiation and progression. Importantly, high expression of the FR and DT2 signatures was associated with a decrease in renal event-free survival (Fig. 2), further supporting their relevance to human disease progression.

Conclusion
This study suggests an important role for an accumulation of maladaptive TECs in CKD progression. These cells are observed in every CKD etiology that was included in this study, suggesting that targeting these cells could be an effective strategy to preserve kidney function broadly in CKD. Identification of surrogate blood or urine biomarker would allow for the identification of patients with increased levels of these cells regardless of disease etiology.