Gangliosides GM1 and GM2 Stimulate Vascular Smooth Muscle Cell Growth and the Mitogen-Activated Protein Kinase Signaling Transduction Pathway
The gangliosides GM1, GM2 and GM3 appear to be involved in the development of cardiovascular diseases. However, little is known about the direct effects of gangliosides on vascular smooth muscle cell growth (VSMC) growth and mitogenic signal transduction pathway. Stimulation of quiescent VSMCs with GM1 (5, 20, 50 and 100 μM) resulted in a dose-dependent increase in [3H]thymidine incorporation from 41±3.5 (basal value) to 64±3.7, 69.6±7.1, 180±11 and 190±10.7 (mean±SE, n=3), respectively. GM3 (1 to 50 μM) had no effects on DNA synthesis whereas 100 μM GM3 caused a reduction in DNA synthesis from 41±3.5 to 12 ±1.4 cpm/μg protein (mean±SE, n=3). Stimulation of quiescent VSMCs with 50 μM GM1 and GM2 caused a 95±7% and 100±4% increase in cell counts (mean±SE, n=3) whereas 50 μM GM3 had no effects. Phosphorylated (activated) MAP kinases were detected by the enhanced chemiluminescence western blotting method using a phospho-specific extracellular signal-response kinases (ERK)1/2 antibody, a phospho-specific p38 MAPK antibody and a phospho-specific c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPK) (the p54 and p46 isoforms) antibody. Stimulation of the cells with 50 μM GM1 and GM2 for 1 to 30 min resulted in time-dependent increase of phosphorylated ERK1/2 and p54/p46 with a maximum at 15 min (5-fold increase). The effect of GM1 and GM2 on the ERK1/2 and JNK/SAPK was also dose-dependent with maximal effect at 50 μM. Gangliosides had no effect on p38 MAPK phosphorylation. Treatment of the cells with 100 ng/ml pertussis toxin (PTX) (Gi protein inhibitor) and 20 μM PD 98059 (MEK inhibitor) caused a complete inhibition of the phosphorylation of the ERK1/2 and JNK/SAPK. We conclude that the gangliosides may be involved in the development of cardiovascular diseases via proliferation of VSMCs. Furthermore, like bioactive lipids, gangliosides are able to stimulate the MAP kinase pathway via a PTX-sensitive Gi coupled receptor.