Mitogenic action of lysophosphatidic acid in proximal tubular epithelial cells obtained from voided human urine

Focal tubular cell multiplication at sites on an injured nephron is a criti cal event in the recovery phase following acute tubular necrosis. During th is process, numerous viable tubular cells exfoliate and are shed into the u rine. Lysophosphatidic acid (LPA) is generated in the plasma membrane of in jured cells and acts as an intercellular mediator of various biological pro cesses, including inflammation, proliferation and repair. In the present st udy, exfoliated proximal tubule (PT) cells were isolated from human urine a nd the mitogenic effects of LPA were investigated as a model of repair and proliferation following renal injury. LPA stimulated a 23.5% increase in DN A synthesis, a 29.4% increase in cell number and an 86.6% decrease in cAMP content. All of these responses were pertussis toxin sensitive, indicating the involvement of G(i)-type G-proteins in LPA signalling. Conversely, the LPA-induced DNA synthesis and the decrease in intracellular cAMP content we re insensitive to wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), suggesting a mitogenic response via PI3K-independent mechanisms. F urthermore, we detected specific mRNA transcripts for the recently cloned h uman LPA-receptors, endothelial differentiation gene (Edg)-2 and Edg-4 (Edg -2 much greater than Edg-4) by reverse transcription-PCR in PT cells. Our d ata suggest that LPA may behave as a local growth factor in PT cells follow ing tubular injury.