Sphingosine 1-phosphate stimulates rat mesangial cell proliferation from outside the cells.
BACKGROUND
Proliferation of mesangial cells (MCs) is the initial step in glomerulonephritis, and platelet-derived mediators have been shown to play a significant role in this proliferation. Sphingosine 1-phosphate (S1P), one of the sphingolipids, is abundantly stored in platelets and is released upon stimulation. We examined the effects of S1P and related sphingolipids on the cell fate of cultured MCs in order to elucidate potential roles of these lipid mediators in glomerulonephritis.


METHODS
Cell proliferation was evaluated by bromodeoxy uridine (BrdU) incorporation together with MTS assay. Apoptosis of MCs was evaluated by examining annexin V staining and typical morphological changes in nuclei. We also examined the metabolism of [(3)H]sphingosine in MCs in either the presence or absence of platelet-derived growth factor (PDGF). The expression of endothelial differentiation genes (edg), which are the cell surface receptors for S1P in MCs, was examined by RT-PCR.


RESULTS
S1P, but not the other sphingolipids, stimulated MC proliferation. In contrast, dimethylsphingosine (DMS) induced apoptosis in the MCs. The amount of sphingosine (Sph) converted into S1P was small and was not affected by PDGF. This observation suggested that Sph kinase activity producing S1P from Sph was low in the MCs. Furthermore, expression of edg-1, -2 and -5 in MCs was confirmed by RT-PCR.


CONCLUSIONS
Our observations suggest that S1P stimulates MC proliferation from outside the cells, and not as a second messenger for PDGF. The modulation of MC fate with sphingolipids may provide possible strategies for the treatment of glomerulonephritis.
Hanafusa
Norio
N
Division of Nephrology and Endocrinology, University of Tokyo School of Medicine, Tokyo, Japan.
Yatomi
Yutaka
Y
Yamada
Koei
K
Hori
Yuichi
Y
Nangaku
Masaomi
M
Okuda
Toshihiro
T
Fujita
Toshiro
T
Kurokawa
Kiyoshi
K
Fukagawa
Masafumi
M
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects*; D008246:Lysophospholipids; D051381:Rats; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D008246:Lysophospholipids; C060506:sphingosine 1-phosphate; D004247:DNA; C061800:N,N-dimethylsphingosine; D013110:Sphingosine