Arginase-1 Expressing Macrophages Interact with Myofibroblasts to Regulate Insulin-Like Growth Factor-1-Dependent...

Insulin-like growth factor-1 is upregulated in the injured outer stripe of the kidney only if Arginase-1 (Arg1)-expressing macrophages are present. Arg1-expressing macrophages induce myofibroblasts and endothelial cells of the outer stripe to express insulin-like growth factor-1 rather than making it themselves. Myofibroblast-expressed insulin-like growth factor-1 induces proximal tubule insulin-like growth factor-1 receptor activation and subsequent proliferation.

Following AKI, 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 after ischemic injury; however, the mechanism of this effect remained unidentified.

Arginase-1 + macrophage-dependent proliferative signals and their cellular source were determined by cell sorting and single-cell transcriptional profiling at 2 days postinjury in mice subjected to ischemia-reperfusion injury and in vitro using transwell coculture of macrophages and renal cells.

Quantitative PCR analysis of outer medullary RNA on day 2 post-ischemia-reperfusion injury in wild type and macrophage-specific arginase-1 null ( Arg1mko ) 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 IGF1. 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.

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.