Ptprz Signaling, Tubule and Macrophage-Mediated Renal Injury and Subsequent Chronic Kidney Disease [macrophages]

Background: Macrophages and tubular epithelial cell interactions are integral in kidney ischemia-incited interstitial inflammation leading to acute kidney injury (AKI). Ischemia/reperfusion injury (I/R) triggers tubular epithelial cells to express IL-34, a macrophage growth factor, that promotes AKI and subsequent CKD. IL-34 engages the cognate receptor, c-FMS, expressed by macrophages, and the recently discovered Protein-Tyrosine Phosphatase Z (Ptprz). Ptprz, binds to multiple ligands other than IL-34 that progressively increase their expression in kidneys after I/R. Methods: We tested the hypothesis that signaling through Ptprz promotes macrophage-mediated AKI and subsequent CKD, by comparing Ptprz knockout (KO) with wild-type (WT) mice after I/R. Results: Ptprz was expressed by leukocytes and in tubular epithelial cells after I/R in mice. Using Ptprz KO mice we determined that during AKI and CKD renal pathology, and loss of renal function were ameliorated. Ptprz-dependent mechanisms mediated: (i) tubular epithelial cell expression of chemokines that fostered macrophage and T cell rich renal inflammation, and (ii) tubule injury and apoptosis, that resulted in the loss of tubules and interstitial fibrosis during CKD. As macrophages release mediators that induce tubular epithelial cell apoptosis, thus Ptprz-dependent mechanisms promote tubule damage. These findings are translational, as after I/R in human kidney transplants, PTPRZ and PTPRZ ligands were upregulated and expressed by the same cell populations as in mice. Moreover, PTPRZ levels in sera were elevated in kidney transplant patients. Conclusion: Intra-renal Ptprz-dependent macrophage and tubular epithelial cell mediated mechanisms promote AKI and subsequent CKD.