Arginase-1 Expressing Macrophages and Myofibroblasts Interact to Regulate IGF1-Dependent Tubule Repair

Background: Following acute kidney injury, successful regeneration of tubular epithelium is essential to restore normal kidney function. We have previously reported that arginase-1 expressing macrophages in the outer medulla promote tubular proliferation following ischemic injury, however the mechanism of this effect remained unidentified. Methods: Arginase-1 + macrophage-dependent proliferative signals and their cellular source were determined by cell sorting and single-cell transcriptional profiling at 2 days post injury in mice subjected to ischemia-reperfusion injury (IRI) and in vitro using transwell coculture of macrophages and renal cells. Results: Quantitative PCR analysis of outer medullary RNA on day 2 post-IRI in wild type and macrophage-specific arginase1 null ( Arg1 mko ) mice identified Insulin-like growth factor -1 ( Igf1 ) as the epithelial growth factor significantly upregulated in an arginase 1 -dependent manner after kidney injury. Single-cell RNA sequencing analysis of mouse kidneys, human kidney biopsies, and sorted outer medullary cells identified myofibroblasts and endothelial cells as potential cellular sources of IGF-1. In vitro studies showed that myofibroblast and endothelial cell expression of Igf1 was dependent on macrophage arginase-1 expression, and that myofibroblast-secreted IGF1 induced epithelial cell IGF1 receptor activation and proliferation. Consistent with this, in vivo activation of the IGF1 receptor on surviving S3 proximal tubule cells after injury was dependent on macrophage Arg1 expression. Conclusions: Our results demonstrate that alternatively activated macrophages signal cooperatively with myofibroblasts and possibly endothelial cells to coordinate local IGF1 secretion and proliferative tubule repair at sites of epithelial cell loss after kidney injury. These findings support an important role of activated myofibroblasts in effective tubule repair.