Pressure-induced expression of monocyte chemoattractant protein-1 through activation of MAP kinase.
BACKGROUND
In glomerular hypertension, mesangial cells (MC) are subjected to at least two physical forces: a high pressure and mechanical stretch. In 5/6 nephrectomized rat, a model of progressive glomerular sclerosis associated with glomerular hypertension, monocyte chemoattractant protein-1 (MCP-1) is expressed in glomeruli, suggesting the possible role of MCP-1 in the pathogenesis of glomerular sclerosis; however, whether pressure directly affects MCP-1 expression remains undetermined. Here we examined the effects of pressure on MCP-1 expression in cultured rat MC and the signal transduction pathways that lead to MCP-1 expression.


METHODS
Pressure was applied to MC by instilling compressed helium gas into sealed plates. MCP-1 mRNA and protein levels in MC were detected by reverse transcription-polymerase chain reaction (RT-PCR) or Northern blotting and ELISA or Western blotting, respectively. Mitogen-activated protein (MAP) kinase activity was measured with the catalytic activity of p42/p44 MAP kinase and anti-phospho p42/p44 MAP kinase antibody. A transient transfection assay that specifically modulates MAP kinase kinase (MEK) activity was carried out.


RESULTS
MCs subjected to external pressure expressed MCP-1 mRNA rapidly and transiently with the peak level noted at 10 minutes and 80 mm Hg pressure. MCP-1 protein levels in cell lysates and culture medium also significantly increased after pressure loading. Pressure rapidly increased the phosphorylation level and activity of p42/p44 MAP kinase. Treatment of MC with a MAP kinase kinase (MEK) inhibitor, PD98059, suppressed levels of both pressure-induced MAP kinase activities and MCP-1 mRNA expression. The constitutively activated type of MEK1 induced MCP-1 expression (13.7-fold) even in non-pressurized MC.


CONCLUSIONS
Our results indicate that pressure per se can induce MCP-1 via activation of MAP kinase pathway, suggesting that glomerular hypertension might be involved in the progression of renal diseases through the expression of MCP-1 in MC.
Suda
T
T
The Second Department of Internal Medicine, University of Occupational and Environmental Health, School of Medicine, 1-1 Iseigaoka, Yahatanishi, Kitakyushu 807-8555, Japan.
Osajima
A
A
Tamura
M
M
Kato
H
H
Iwamoto
M
M
Ota
T
T
Kanegae
K
K
Tanaka
H
H
Anai
H
H
Kabashima
N
N
Okazaki
M
M
Nakashima
Y
Y
D000818:Animals; D018932:Chemokine CCL2 / Q000235:genetics* / Q000378:metabolism; D004789:Enzyme Activation; D005920:Glomerular Mesangium / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D011312:Pressure; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar
D018932:Chemokine CCL2; D012333:RNA, Messenger; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases