Recurrence of steroid-resistant nephrotic syndrome (SRNS) is thought to be due to an unknown “circulating factor”, the identity of which has so far remained elusive. Our previous work suggests a signaling role for protease-activated receptor-1 (PAR-1), leading to impaired podocyte function. Here, we show that relapse nephrotic plasma (NP), but not paired remission plasma, induced a pro-fibrotic response. This change was inhibited by PAR-1 inhibitors, but not by TGF-β1 inhibition. Four PAR-1 inhibitors demonstrated distinct antagonistic properties. The phosphorylation of VASP and JNK in a 3D spheroid model (GlomSpheres) and kidney organoids corroborated the finding from a 2D ciPods model. Functionally, relapse NP induced podocyte motility, and podocyte loss from spheroids both of which were also selectively rescued by PAR-1 inhibitors. Also, it induced the loss of podocyte-specific markers in kidney organoids. We propose that the circulating factor acts as a pro-fibrotic effector by activating PAR-1, leading to increased podocyte injury.
