Nature and mediators of parietal epithelial cell activation in glomerulonephritides of human and rat

Bowman's capsule parietal epithelial cell activation occurs in several human proliferative glomerulonephritides. The cellular composition of the resulting hyperplastic lesions is controversial, although a population of CD133⁺CD24⁺ progenitor cells has been proposed to be a major constituent. Mediator(s) involved in proliferation and migration of progenitor cells into the Bowman's space have been poorly explored. In a series of 36 renal biopsies of patients with proliferative and nonproliferative glomerulopathies, dysregulated CD133⁺CD24⁺ progenitor cells of the Bowman's capsule invade the glomerular tuft exclusively in proliferative disorders. Up-regulation of the CXCR4 chemokine receptor on progenitor cells was accompanied by high expression of its ligand, SDF-1, in podocytes. Parietal epithelial cell proliferation might be sustained by increased expression of the angiotensin II (Ang II) type-1 (AT₁) receptor. Similar changes of CXCR4, SDF-1, and AT₁ receptor expression were found in Munich Wistar Frömter rats with proliferative glomerulonephritis. Moreover, an angiotensin-converting enzyme inhibitor normalized CXCR4 and AT₁ receptor expression on progenitors concomitant with regression of crescentic lesions in a patient with crescentic glomerulonephritis. These results suggest that glomerular hyperplastic lesions derive from the proliferation and migration of renal progenitors in response to injured podocytes. The Ang II/AT₁ receptor pathway may participate, together with SDF-1/CXCR4 axis, to the dysregulated response of renal precursors. Thus, targeting the Ang II/AT₁ receptor/CXCR4 pathways may be beneficial in severe forms of glomerular proliferative disorders.