SOX9 switch links regeneration to fibrosis at the single-cell level in mammalian kidneys

Abstract

The steps governing healing with or without fibrosis within the same microenvironment are unclear. After acute kidney injury (AKI), injured proximal tubular epithelial cells activate SOX9 for self-restoration. Using a multimodal approach for a head-to-head comparison of injury-induced SOX9 lineages, we identified a dynamic SOX9 switch in repairing epithelia. Lineages that regenerated epithelia silenced SOX9 and healed without fibrosis (SOX9 on-off ). By contrast, lineages with unrestored apicobasal polarity maintained SOX9 activity in sustained efforts to regenerate, which were identified as a SOX9 on-on Cadherin6 pos cell state. These reprogrammed cells generated substantial single-cell WNT activity to provoke a fibroproliferative response in adjacent fibroblasts, driving AKI to chronic kidney disease. Transplanted human kidneys displayed similar SOX9/CDH6/WNT2B responses. Thus, we have uncovered a sensor of epithelial repair status, the activity of which determines regeneration with or without fibrosis.

Spatiotemporal Landscape of Kidney Tubular Responses to Glomerular Proteinuria

“…For better visualization of the images, contrast and brightness were modified and applied to all parts of the figures equally. Fluorescent signals from each marker were normalized from min (50) to max (51) for each animal to plot tubule regions of interest depending on the level of each marker expression. For histochemical images, signals were thresholded to remove background fluorescence and count all pixels above the threshold as a positive staining for the marker.…”

“…To further assess to what extent gene expression profiles in proteinuric states are specific to this condition, we compared the results with published data from a previous study of IRI. 49,50 For the IRI mice, data were obtained at two time points: early (4, 12, 64, and 96 hours) and late (14 days, 28 days, and 6 weeks) (Supplemental Figure 7). Comparison of the datasets revealed an acute dedifferentiation and subsequent partial recovery of all three segments of the proximal tubule (S1-3) in IRI, in contrast to the selective and sustained loss of S2/3 cells observed in proteinuria.…”

“…To investigate the spatial relationship between protein reabsorption and other transport functions along the mouse proximal tubule, we began by performing an unbiased analysis of gene expression data in control C57BL/ 6J mice, generated by single-nucleus RNAseq in a previous study on the effects of ischemia-reperfusion injury (IRI) 49,50 (Supplemental Table 1). We present gene expression analysis in C57BL/6J mice because these were the strain used for intravital imaging experiments, but similar results were obtained in the FVB background of POD-ATTAC mice (Supplemental Figure 1).…”