Knock-out of Adam 10 in mCCDcl1 of gives in sight into the effects of Notch pathway disruption for kidney collecting ductcell plasticity

The kidney cortical collecting duct (CCD) is responsible for the fine tuning of sodium, volume, and acid-base homeostasis, and comprises of principal and intercalated cells (PCs and ICs) as well as a newly discovered ‘intermediate’ cell type (1). Plasticity between PCs and ICs has been reported previously in mice in which genes for factors implicated in the Notch pathway, such as Adam10, have been knocked out (KO) (2). In vivo, disruption of the Notch pathway leads to a decreasing PC:IC ratio. The self-immortalized mouse CCD cell line, mCCDcl1, shows functional characteristics of PCs and a response to physiological concentrations of hormones such as aldosterone; it also has been shown to express both PC and IC markers, a phenotype transmitted through single cell cloning (3). These characteristics make mCCDcl1 cells a useful platform for the study of plasticity in the CCD. Adam10 was knocked out in mCCDcl1 cells using CRISPR-Cas9 technology and independent clones were isolated and expanded for study. Despite mCCDcl1 cells being polyploid, our strategy enabled all alleles for each gene to be successfully targeted. Clones were cultured on Transwell filters over 10 days and their electrophysiological properties measured (trans-epithelial resistance Rte, voltage Vte, calculated short-circuit current Isc). Both Adam10 KO clones showed a slightly reduced baseline Rte compared to control (0.90±0.19 kΩ.cm2 vs 1.12±0.18 kΩ.cm2) but a complete reduction in baseline Isc (0.3±0.1 μA/cm2 vs -8.1±0.4 μA/cm2 for control) as well as aldosterone response, decreased by 95% (fold change 0.19±0.03 down 3.70±0.11 for control). Single-cell RNA sequencing principal component analysis shows different clustering of KO clones compared to WT. Potentially explaining the loss of sodium transport function, a significant drop in expression for the gamma subunit of the epithelial sodium channel (γ-ENaC) (between ~40% and ~60% depending on the cluster) was detected in the KO clones, as well as a decrease in the expression of 11ßHSD2 (between ~20% and ~60%). Immunostaining in KO clones confirmed the decrease in expression of γ-ENaC and showed an altered distribution and localisation of γ-ENaC, Aqp2, and V-ATPase B1 compared to WT mCCDcl1, overall suggesting a loss of polarisation. These data suggest that genomic modification of mCCDcl1 cells provides an effective means to investigate the mechanisms through which CCD cells mediate their plasticity and can identify new pathways involved in regulating cell phenotype as well as specific effects of pathway disruption on collecting duct cells functions. (1) Park et al.; Single-cell transcriptomics of the mouse kidney reveals potential cellular targets of kidney disease; Science; 360: 758-763, 2018. (2) Guo et al.; Adam10 Mediates the Choice between Principal Cells and Intercalated Cells in the Kidney; JASN; 26: 149-159, 2015. (3) Assmus et al.; mCCDcl1 cells show plasticity consistent with the ability to transition between principal and intercalated cells; AJP-renal; 314 (5): 820-831, 2018.