Serine/threonine kinase, Cot/Tpl2, regulates renal cell apoptosis in ischaemia/reperfusion injury

Aim: 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-α (TNF-α) 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-α 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-α 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-α 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. Conclusion: 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.