Shedding of growth-suppressive gangliosides from glomerular mesangial cells undergoing apoptosis.
BACKGROUND
Apoptosis of glomerular mesangial cells is a common feature in several types of glomerular diseases. However, its pathophysiologic significance is not known. We recently identified gangliosides as a major growth-inhibitory substance in the conditioned medium of mesangial cells. In this report, we tested whether biologically distinct forms of cell fate, apoptosis and necrosis, could modulate ganglioside shedding from mesangial cells.


METHODS
Mesangial cells were exposed to low (10 to 40 mJ/cm2) and high (400 mJ/cm2) doses of ultraviolet light to induce apoptosis and necrosis, respectively. Conditioned media were collected and examined for its growth-inhibitory activity for mesangial cells. Ganglioside shedding was analyzed using metabolic labeling and thin-layer chromatography (TLC).


RESULTS
Shedding of gangliosides as well as growth-inhibitory activity in the conditioned medium predominantly increased when mesangial cells were undergoing apoptosis in contrast to that of viable or necrotic mesangial cells. The inhibitory substance in the conditioned medium from apoptotic mesangial cells completely fulfilled the characteristic criteria of gangliosides. This substance was less than 3 kD and was sensitive to neuraminidase digestion. Shedding of gangliosides from mesangial cells reduced significantly when apoptosis was inhibited by overexpression of antiapoptotic gene, Bcl-XL. In addition, ganglioside shedding also increased when mesangial cells were exposed to other inducers of apoptosis for mesangial cells (i.e., H2O2 and staurosporin).


CONCLUSIONS
These results provide the novel link between masangial cell apoptosis and increased release of gangliosides that potentially suppress mesangial cell proliferation and thus indicate a mechanism for the negative regulation of mesangial cell growth by apoptosis.
Tsuboi
Nobuo
N
Department of Internal Medicine, Institute of DNA Medicine, Jikei University School of Medicine, Minato-Ku, Tokyo, Japan. nobuotsuboi@aol.com
Utsunomiya
Yasunori
Y
Kawamura
Tetsuya
T
Kikuchi
Tetsuro
T
Hosoya
Tatsuo
T
Ohno
Tsuneya
T
Yamada
Hisashi
H
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005732:Gangliosides / Q000378:metabolism* / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology* / Q000378:metabolism; D006131:Growth Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008297:Male; D009336:Necrosis; D016877:Oxidants / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019311:Staurosporine / Q000494:pharmacology; D014466:Ultraviolet Rays; D051020:bcl-X Protein
C494813:Bcl2l1 protein, rat; D017077:Culture Media, Conditioned; D004791:Enzyme Inhibitors; D005732:Gangliosides; D006131:Growth Inhibitors; D016877:Oxidants; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D006861:Hydrogen Peroxide; D019311:Staurosporine