Introduction: Kidney injury is clinically classified as crescentic glomerulonephritis (CrGN) when ≥50% of the glomeruli in a biopsy sample contain crescentic lesions. However, current strategies, such as systemic immunosuppressive therapy and plasmapheresis for CrGN, are partially effective, and these drugs have considerable systemic side effects. Hence, targeted therapy to prevent glomerular crescent formation and expansion remains an unmet clinical need.
Areas covered: Hyperproliferative parietal epithelial cells (PECs) are the main constituent cells of the glomerular crescent with cell-tracing evidence. Crescents obstruct the flow of primary urine, pressure the capillaries, and degenerate the affected nephrons. We reviewed the markers of PEC activation and proliferation, potential therapeutic effects of thrombin and thrombin receptor inhibitors, and how podocytes cross-talk with PECs. These experiments may help identify potential early specific targets for the prevention and treatment of glomerular crescentic injury.
Expert opinion: Inhibiting PEC activation and proliferation in CrGN can alleviate glomerular crescent progression, which has been supported by preclinical studies with evidence of genetic deletion. Clarifying the outcome of PEC transformation to the podocyte phenotype and suppressing thrombin, thrombin receptors, and PEC hyperproliferation in early therapeutic strategies will be the research goals in the next ten years.
Keywords: CD44; CD74; CD9; Parietal epithelial cells; glomerular crescent.
It is clinically classified as crescentic glomerulonephritis (CrGN) when more than 50% of the glomeruli of the kidney in a biopsy sample contain crescentic lesions (crescent shaped injuries). However, current strategies, such as immunosuppressive therapy and plasmapheresis (the removal, treatment and returning of blood) for CrGN, are partially effective, and these drugs have considerable side effects. In order to seek targeted therapy for CrGN, we reviewed the current research evidences. First, the hyperproliferative parietal epithelial cells (PECs) are the main cells within the glomerular crescent seen with cell-tracing evidence. The activated PECs can express specific markers and altered biological characteristics, such as cell growth and multiplication, migration, and extracellular matrix production. CD44, CD74, CD9, and pERK-1/2 are specific markers for PEC activation, and also as the potential therapeutic targets with evidence of gene knockout and inhibitor. Second, during the formation of glomerular crescents, PECs grow and multiply also through cross-talking with podocyte cells by the AngII/SDF-1/CXCR4/ERK1/2, HB-EGF/EGFR/JAK/STAT3, and PDGF/PDGFR signaling pathways, suggesting that the intervention of key molecules in these disease processes may be promising therapeutic targets for CrGN. Third, thrombin and protease-activated receptors (PARs) participate in the excessive proliferation of PEC through activation of the coagulation cascade reaction, PAR-1 and PAR-2. Therefore, anticoagulation therapy, especially inhibition of PAR-1 and PAR-2, is expected to be an effective strategy for the early prevention and treatment of CrGN. The drug vorapaxar selectively antagonizes PAR-1 and is the most promising candidate. These findings will not only improve the outlook for CrGN treatment, but will also help in the treatment of other glomerular diseases with crescentic lesions. [Figure: see text].