Dynamics of glial fibrillary acidic protein distribution in cultured glomerular podocytes and mesangial cells of the rat kidney

Glial fibrillary acidic protein (GFAP) has recently been shown to be expres sed in the glomerular podocytes and mesangial cells (MC) of kidney (Buniati an et al (1998) Biol Cell 90, 53-61). The different localization of GFAP in podocytes and MC has raised the question whether this might reflect specif ic cellular functions. To address this question, in the present study podoc ytes and MC in early (2, 3 day-old), prolonged (5, 7 day-old) and late (14, 21 day-old) primary cultures from outgrowths of glomerular explants were u sed. Double-immunolabeling studies demonstrated that podocytes transiently acquire myofibroblastic features, characterized by the expression of smooth muscle alpha-actin (SMAA) and increased perinuclear reaction of GFAP in pr olonged cultures. The morphological differentiation of cobblestone-like pod ocytes into process-bearing cells was followed by loss of the myofibroblast ic marker, SMAA, de novo expression of desmin, and distribution of GFAP, vi mentin and desmin into the processes. Ln late culture, GFAP and SMAA were n early absent from the podocytes which maintained the cobblestone-like morph ology. By contrast, the myofibroblastic features gained by MC during prolon ged culturing increased with time. A myofibroblast-like cytoskeleton of pod ocytes and MC similar to that of healthy astrocytes suggests an increased s pectrum of functional activities of these cells during the acquisition of m yofibroblastic features. Ln addition, the present study provides a new comb ination of biochemical and biological features by which podocytes and MC ca n be distinguished in culture. (C) 1999 Editions scientifiques et medicales Elsevier SAS.