Differentiated phenotype of glomerular mesangial cells in nodular culture. Kitamura, Masanori, Tetsuya Mitarai, Ryuji Nagasawa, and Naoki Maruyama. Department of Medicine and Institute of Urology and Nephrology, University College London Medical School, London, UK, Department of Internal Medicine, Saitama Medical Center, Saitama Medical School, Saitama, Japan, Department of Molecular Pathology, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan
APStracts 2:0188F, 1995.
Prolonged culture of glomerular mesangial cells forms nodular structures composed of cells and surrounding extracellular matrix, which may mimic the situation in the glomerular mesangium of the kidney. The aim of this study was to investigate whether nodule -associated cells (NAC) exhibit a different phenotype to nodule -unassociated cells (NUC) in vitro. As phenotypic markers for rat mesangial cells, we examined mitogenic activity, expression of [alpha]-smooth muscle actin, and production of extracellular matrix constituents. Autoradiographic and immunohistochemical analyses revealed that NAC showed far less mitogenesis than NUC, like mesangial cells in the normal glomerulus. Immunofluorescence study and Northern blot analysis showed that [alpha]-smooth muscle actin, a marker of mesangial cell activation/dedifferentiation, was strongly expressed in NUC but faint in NAC. When nodules were dissolved by trypsinization, the dispersed NAC regained both active mitogenesis and [alpha]-smooth muscle actin expression, suggesting that the altered phenotype was reversible. Northern blot analysis revealed that the ratio of type IV collagen versus type I collagen expression, a marker of mesangial cell differentiation, was elevated in NAC compared to NUC. This phenotypic shift towards differentiation was associated with up-regulation of transforming growth factor-b1. These findings demonstrate that mesangial cells in nodules exhibit a phenotype which is distinct from that of cells in two-dimensional cultures. We hypothesize that, as a differentiated feature, cultured mesangial cells have the ability to create an appropriate three -dimensional cyto-architecture which resembles the glomerular mesangium. 

Received 4 April 1995; accepted in final form 16 October 1995.
APS Manuscript Number F114-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95