Phenotypic profiles of cultured glomerular cells following repeated cyclesof hydrocarbon injury

Background. The glomerulus has been implicated as a target of hydrocarbon i njury in vitro and in vivo. In the present studies, the phenotypic profiles of cultured rat glomerular cells (GCs) following repeated cycles of hydroc arbon injury were evaluated. Cultured GCs were incubated for 24 hours with benzo[a]pyrene (BaP; 3 mu mol/L), a prototypical polycyclic aromatic hydroc arbon, and were allowed to recover overnight before two additional cycles o f chemical challenge during serial propagation in vitro. At the end of this regimen, control cultures were characterized by predominance of fusiform c ells that grew in "hills and valleys," while GCs subjected to hydrocarbon i njury displayed an epithelial morphology characterized by a rounded, polygo nal shape clearly distinct from that normally exhibited by glomerular mesan gial cells (GMCs) in culture. Methods. Indirect immunofluorescent detection of cell markers was conducted to identify cells of mesenchymal or epithelial origin. Measurements of DNA synthesis and cell number were performed to determine proliferative capaci ties of the different cell types in response to hydrocarbon challenge. Results. Immunofluorescence studies revealed that control GC cultures conta ined mostly alpha-smooth muscle (SM) actin-positive cells, with a few(5.1% +/- 2.6) E-cadherin-positive cells occasionally identified. In contrast, Ba P-treated cultures exhibited a mixed cell population in which E-cadherin-po sitive cells were predominant (66.6% +/- 4.1). Single-cell cloning of naive cultures of GCs yielded four clones, three of which exhibited a fusiform m orphology and were OI-SM actin positive (SCC 1 through SCC 3) and one (SCC 4E) that exhibited epithelial characteristics similar to those found in hyd rocarbon-treated cultures. Immunofluorescence studies showed that epithelia l cells in hydrocarbon-treated cultures, as well as SCC 4E-derived clones, were vimentin positive and cytokeratin negative, characteristics similar to glomerular visceral epithelial cells (GVECs). DNA synthesis and cell proli feration in done SCC 1 were decreased following acute BaP challenge, while growth rates in SCC 4E-derived clones were unaffected by hydrocarbon injury . Repeated cycles of hydrocarbon challenge in clonal populations yielded di fferent profiles of DNA synthesis, with significant decreases in SCC 1 and no changes in SCC 4E. Conclusions. These observations suggest that hydrocarbon injury induces dif ferential responses in cells of the glomerulus, resulting in inhibition of GMCs and selective growth advantage of GVECs. These alterations are reminis cent of critical events described in the pathogenesis of focal segmental gl omerulosclerosis and raise important questions about the pathogenesis of hy drocarbon-induced nephropathies.