Mechanism for the negative regulation of cell proliferation by ganglioside GM3 in high glucose-treated glomerular mesangial cells.

We recently identified ganglioside GM3 as a modulator of glomerular hypertrophy in streptozotocin-induced diabetic rats (Life Sci., 72: 1997-2006, 2003). This study examined whether alteration of ganglioside GM3 expression could modulate the high glucose-induced proliferation of glomerular mesangial cells (GMCs). GMCs isolated from rat kidneys were cultured under normal (5.6 mM) or high (25 mM) glucose condition for 24-72 hrs. Cell proliferation was predominantly stimulated when GMCs were cultured with high glucose as well as 20 microM of d-threo-PDMP, an inhibitor of ganglioside biosynthesis, for 24 hrs, whereas raising ambient glucose significantly reduced the mesangial sialic acid contents. Based upon mobility on high-performance thin-layer chromatography (HPTLC), GMCs showed a complex pattern of ganglioside expression that consisted of three major components of gangliosides, mainly GM3. High glucose induced a significant reduction of ganglioside expression with apparent changes in the composition of major ganglioside GM3, and semi-quantitative analysis by HPTLC showed that ganglioside GM3 was reduced to 62% of GMCs cultured under normal glucose condition. A prominent immunofluorescence microscopy using anti-GM3 monoclonal antibody also showed a dramatic disappearance of immunoreactivity in high glucose-treated GMCs. Moreover, high glucose significantly lowered the Km values of GM3 synthase (16 microM vs. 49 microM), but did not change the Vmax. These results provide the pathophysiological relationship between the high glucose-induced proliferation of GMCs and the decreased expression of ganglioside GM3, indicating a mechanism for the negative regulation of mesangial proliferation by ganglioside GM3. This mechanism may play an important role in the development of diabetic glomerulopathy.