BMK1 is activated in glomeruli of diabetic rats and in mesangial cells by high glucose conditions.
BACKGROUND
High glucose causes renal cell injury through various signal transduction pathways, including mitogen-activated protein (MAP) kinases cascades. Big MAP kinase 1 (BMK1), also known as extracellular signal-regulated kinase 5 (ERK5), is a recently identified MAP kinase family member and was reported to be sensitive to osmotic and oxidative stress. However, the role of BMK1 in diabetic nephropathy has not been elucidated yet.


METHODS
We investigated whether BMK1 is activated in the glomeruli of Otsuka Long Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus in comparison with the control Long Evans Tokushima Otsuka (LETO) rats. We also examined the effect of high glucose on BMK1 activity in cultured rat mesangial cells.


RESULTS
BMK1 and ERK1/2 but not p38 were activated in the glomeruli of OLETF rats, which showed diabetic nephropathy at 52 weeks of age. High glucose, in addition to a high concentration of raffinose, caused rapid and significant activation of BMK1 in rat mesangial cells. MAP kinase/ERK kinase (MEK) inhibitors, U0126 and PD98059, both inhibited BMK1 activation by high glucose in a concentration-dependent manner. Protein kinase C (PKC) inhibition by GF109203X and PKC down-regulation with long-time phorbol myristate acetate (PMA) treatment both inhibited BMK1 and Src kinase activation. Src kinase inhibitors, herbimycin A and PP2, also inhibited high glucose-induced BMK1 activation. PKC inhibitors, Src inhibitors and MEK inhibitors, all inhibited cell proliferation by high glucose. Finally, transfection of dominant-negative MEK5, which is an upstream regulator of BMK1, abolished the BMK1-mediated rat mesangial cell proliferation stimulated by high glucose.


CONCLUSIONS
In the present study, we demonstrated that high glucose activates BMK1 both in vivo and in vitro. It was suggested that high glucose induces PKC- and c-Src-dependent BMK1 activation. It could not be denied that BMK1 activation is induced through an osmotic stress-sensitive mechanism. BMK1-mediated mesangial cell growth may be involved in the pathogenesis of diabetic nephropathy.
Suzaki
Yuki
Y
Department of Pharmacology and Pediatrics, The University of Tokushima School of Medicine, Tokushima, Japan. yoshizu@basic.med.tokushima-u.ac.jp
Yoshizumi
Masanori
M
Kagami
Shoji
S
Nishiyama
Akira
A
Ozawa
Yuichi
Y
Kyaw
Moe
M
Izawa
Yuki
Y
Kanematsu
Yasuhisa
Y
Tsuchiya
Koichiro
K
Tamaki
Toshiaki
T
D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D000081247:CSK Tyrosine-Protein Kinase; D002478:Cells, Cultured; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology*; D003928:Diabetic Nephropathies / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000187:drug effects / Q000201:enzymology; D005947:Glucose / Q000494:pharmacology; D048671:MAP Kinase Kinase 5 / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D048054:Mitogen-Activated Protein Kinase 7 / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D009930:Organic Chemicals / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D020334:Rats, Inbred OLETF; D019061:src-Family Kinases
D002070:Butadienes; D004791:Enzyme Inhibitors; D009570:Nitriles; D009930:Organic Chemicals; C466090:PD 98058; C113580:U 0126; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; D011493:Protein Kinase C; D048054:Mitogen-Activated Protein Kinase 7; D048671:MAP Kinase Kinase 5; C482565:Map2k5 protein, rat; D005947:Glucose