Injury-induced paracrine effects on the podocyte's transcriptome

Although injury in glomerular disease might only damage a subset of podocytes in any given glomerulus, the response of the healthy neighboring podocytes to the injured podocytes oftentimes determines the course of the disease. To investigate this relationship, we designed a dual-chamber open microfluidic coculture device to specifically examine paracrine signaling from podocytes undergoing targeted injury by either adriamycin, puromycin aminonucleoside, or a cytopathic antipodocyte antibody to healthy podocytes. Global transcriptomic analysis measured by RNA sequencing revealed shared and unique pathways between the three forms of targeted injury, with temporal differences in the transcriptomic responses to each form of injury. Transcriptional changes also showed that paracrine-induced injury to neighboring podocytes was similar to the targeted-injured podocytes and was specific for each podocyte injury model. In silico ligand-receptor analysis of ligands secreted by the insult-targeted podocytes and receptors expressed by the responsive, paracrine-injured counterparts identified 19 candidate mediator pairs that were shared among the three injury models. Several of these were enriched in patients with histological evidence of glomerular injury present in the Nephrotic Syndrome Study Network (NEPTUNE). One-factor-at-a-time candidate approaches validated the ability of these candidate pathways to mediate aspects of the podocyte injury models. Finally, an all-inclusive, comprehensive investigation of this signaling space using a systematic Design-of-Experiment analysis revealed that transforming growth factor-β1 (TGF-β1) signaling is a critical mediator of mitochondrial dysfunction during podocyte injury. Together, these findings define a new concept for future studies to understand the pathways involved in animal models and ultimately human studies.NEW & NOTEWORTHY From a clinical perspective, it is ideal if yet unknown common pathways could be therapeutically targeted in different forms of injury in diseases of podocytes, and if there were mitigation strategies to minimize further damage to yet unaffected podocytes. The results of the current studies showed that there are indeed common responses to different experimental forms of podocyte injury and identified common paracrine signaling from injured podocytes that adversely affects the neighboring healthy podocyte population.