Ureteral functional and cellular changes caused by obstruction in unilateral ureteral obstructed mouse model

Ureter obstruction disrupts ureteral peristalsis causing kidney drainage cessation and hydronephrosis development. Currently, the molecular mechanisms driving obstruction-induced ureteral aperistalsis are unknown. Transient receptor potential (TRP) channels were previously shown to regulate intestinal peristalsis, which shares numerous physiological characteristics to ureteral peristalsis. We therefore hypothesized that TRP channels may play a role in the regulation of ureteral peristalsis and dysfunction following obstruction. Using a unilateral ureteral obstruction (UUO) mouse model, we tested the effect of TRP channel inhibitors on normal mouse renal pelvis spontaneous contraction using a myograph. To further validate their role in regulating peristalsis, the impact of obstruction on the expression of candidate TRP channels was tested. In addition, single-cell RNA sequencing (scRNA-seq) was used to study specific cellular changes in gene expression including TRP channels in the mouse ureter and renal pelvis. Overall, Trpc5 was downregulated while Trpc6 and Trpc4 were significantly upregulated in 3-day obstructed mouse ureters and renal pelvis compared to the contralateral unobstructed samples. Downregulation in Trpc5 expression in obstructed ureters is consistent with our hypothesis. In contrast, Trpc6 and Trpv4 upregulation is consistent with fibrosis and distension. However, 7-day obstructed samples showed no significant changes in candidate TRP channels expression. In addition, in myograph experiments, TRP channel inhibitors (especially TRPV2 and TRPC5) significantly reduced renal pelvis spontaneous contractions frequency. On the other hand, scRNA-seq experiments showed that all cells identified in the mouse ureter and renal pelvis are modulated by obstruction. In obstructed mouse ureter and renal pelvis, genes that are associated with fibrosis and epithelial mesenchymal transition (EMT) were upregulated in addition to increased expression of gene sets involved in smooth muscle contraction. Regarding TRP channels expression in smooth muscle cells, only Trpv2 showed a possible trend toward significance to be downregulated in obstructed samples. In addition, we found a unique mesenchymal cell type found only in obstructed ureters that is predicted to trigger angiogenesis and rebuild the ureter to its normal state. Overall, TRP channels probably regulate ureteral peristalsis while obstruction appears to modulate not only smooth muscle cells, but all cell types found in the ureter and renal pelvis.