Serine/threonine kinase, Cot/Tpl2, regulates renal cell apoptosis in ischaemia/reperfusion injury.
OBJECTIVE
Cot/Tpl2, a serine/threonine (Ser/Thr) protein kinase, has been classified as a member of the mitogen-activated protein kinase (MAPK) family, and is known to have a pleiotropic role. Many studies have reported the involvement of Cot/Tpl2, mainly as a member of the Toll-like receptor (TLR) 4 signalling pathway in lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha (TNF-alpha) production. At the same time, it is also related to the caspase-dependent apoptotic pathway. Thus, the role of Cot/Tpl2 in ischaemia/reperfusion injury (IRI) in which TNF-alpha and apoptosis are the major pathogenetic factors was studied.


METHODS
IRI was induced in wild type (Cot/Tpl2(+/+)) mice and in Cot/Tpl2-deficient (Cot/Tpl2(-/-)) mice. The extent of tubular injury and renal function were studied. TNF-alpha production, neutrophil infiltration and apoptosis were also compared between the two groups.


RESULTS
Cot/Tpl2(-/-) mice had preserved renal function compared with wild type mice in IRI. Although Cot/Tpl2 was phosphorylated in IRI and in the cultured tubular epithelial cells (TEC) after stimulation with LPS and hydrogen peroxide, there were no significant differences in terms of TNF-alpha production, neutrophil infiltration or MAPK activation between Cot/Tpl2(+/+) and Cot/Tpl2(-/-) mice. In contrast, Cot/Tpl2(-/-) mice showed obviously reduced terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling positive cells and cleaved caspase-3 positive cells. Furthermore, Cot/Tpl2-deficient TECs demonstrated significantly less caspase-3 activation after hydrogen peroxide stimulation with comparable caspase-9 activation to wild type TEC.


CONCLUSIONS
Cot/Tpl2 did not function as a member of MAPK family, but as a promoter of apoptosis in IRI. These results suggest that Cot/Tpl2 could be a possible therapeutic target in IRI.
Department of Nephrology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Takaaki
T
Yaomura
Naotake
N
Tsuboi
Yoshinori
Y
Urahama
Akinori
A
Hobo
Kenji
K
Sugimoto
Jun
J
Miyoshi
Tetsuya
T
Matsuguchi
Kannagi
K
Reiji
Seiichi
S
Matsuo
Yukio
Y
Yuzawa
D000818:Animals; D017209:Apoptosis; D007668:Kidney / Q000166:cytology / Q000201:enzymology*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015427:Reperfusion Injury / Q000201:enzymology* / Q000503:physiopathology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; D020930:MAP Kinase Kinase Kinases; C069937:MAP3K8 protein, human