Dexamethasone-induced cardioprotection: A role for the phosphatase MKP-1? W.-J. Fan, S. Genade, A. Genis, B. Huisamen, A. Lochner ⁎ Division of Medical Physiology, Department of Biomedical Sciences, Faculty of Health Sciences, University of Stellenbosch, South Africa abstract article info Article history: Received 11 September 2008 Accepted 27 March 2009 Keywords: Dexamethasone Isolated rat heart Ischaemia/reperfusion MKP-1 expression p38 MAPK ERK42/44 PKB/Akt Aims: Previous studies suggested that p38 MAPK activation during sustained myocardial ischaemia and reperfusion was harmful. We hypothesize that attenuation of p38MAPK activity via dephosphorylation by the dual-specificity phosphatase MKP-1 should be protective against ischaemia/reperfusion injury. Since the glucocorticoid, dexamethasone, induces the expression of MKP-1, the aim of this study was to determine whether upregulation of this phosphatase by dexamethasone protects the heart against ischaemia/reperfusion injury. Main methods: Male Wistar rats were treated with dexamethasone (3 mg/kg/day ip) for 10 days, before removal of the hearts for Western blot (ip Dex -P) or perfusion in the working mode (ip Dex + P). Hearts were subjected to 20 min global or 35 min regional ischaemia (36.5 °C) and 30 or 120 min reperfusion. In a separate series, dexamethasone (1 μM) was added to the perfusate for 10 min (Pre + Dex) before or after (Rep+ Dex) ischaemia. Key findings: Dexamethasone, administered intraperitoneally or added directly to the perfusate, significantly improved post-ischaemic functional recovery and reduced infarct size compared to untreated controls (p b 0.05). These were associated with enhanced up-regulation of MKP-1 protein expression (arbitrary units (mean± SD): Untreated: 1; ip Dex -P: 2.59 ± 0.22; ip Dex + P: 1.51 ± 0.22; Pre + Dex: 4.11 ± 0.73, Rep + 15′Dex: 1.51 ± 0.14; untreated vs. all groups, p b 0.05) and attenuation of p38 MAPK activation (p b 0.05) in all dexamethasone-treated groups, except for Rep+10′Dex. ERK and PKB/Akt activation were unchanged. Significance: Dexamethasone-induced cardioprotection was associated with upregulation of the phospha- tase MKP-1 and inactivation of pro-apoptotic p38 MAPK. © 2009 Elsevier Inc. All rights reserved. Introduction It is well-established that the mitogen-activated protein kinases and particularly p38 MAPK are activated by myocardial ischaemia and reperfusion (for a review see Steenbergen 2002). The role of p38 MAPK in ischaemic injury is, however, very controversial: while some studies (Weinbrenner et al. 1997; Mocano et al. 2000) provided evidence that activation of p38 MAPK is beneficial, many others demonstrated that activation of this kinase during ischaemia/reperfusion aggravates lethal injury (for a review see Bassi et al. 2008). Confounding factors which may have contributed to these conflicting data are (i) the transient activation of p38 MAPK which occurs during early aerobic perfusion before induction of ischaemia (ii) the fact that dimethylsulphoxide (DMSO) which is routinely used as vehicle for SB203580, an inhibitor of p38 MAPK, has anti-oxidant properties (Bell et al. 2008) and (iii) the perfusion procedure used (Langendorff mode with or without balloon or working heart), which may profoundly affect kinase phosphorylation (Stenslokken et al. 2009). In our laboratory, it has been demonstrated that activation of p38 MAPK occurs transiently during a multi-cycle preconditioning protocol (Marais et al. 2001), acting as a trigger (Sanada et al. 2001), while attenuation of its activation during sustained ischaemia is associated with cardioprotection in isolated rat hearts (Marais et al. 2001; Moolman et al. 2006) and cardiomyocytes (Mackay and Mochley-Rosen 1999; Ma et al. 1999). In contrast to these numerous studies on p38 MAPK activation in cardioprotection, very little is known about dephosphorylation of this kinase by the appropriate phosphatases and their role, if any, in ischaemia/reperfusion. The mitogen-activated protein kinase phosphatases (MKPs) con- stitute a family of 11 dual-specificity phosphatases that inactivate the MAPKs by dephosphorylation of specific Thr/Tyr residues. For example, the phosphatase MKP-1 preferentially inactivates p38 MAPK, then JNK and to a lesser extent ERK (Franklin et al. 1998). Wu and Bennet (2005) demonstrated that in fibroblasts MKP-1 promotes cell survival by attenuating stress-responsive MAPK-mediated apoptosis. Upregulation of MKP-1 has also been shown to be associated with cardioprotection by long-chain fatty acids (Engelbrecht et al. 2005). In addition, it has been reported that transgenic mice overexpressing MKP-1 were partially protected, whereas gene-targeted mice show greater injury after ischaemia–reperfusion (Kaiser et al. 2004). We hypothesized that inactivation of p38 MAPK during ischaemia/ reperfusion by upregulation of MKP-1 should be cardioprotective. MPK- 1 is experimentally induced by growth factors (Juhasz et al. 2004), oxidative stress (Guyton et al. 1996), arachidonic acid (Metzler et al. 1998), 12-0-tetradecanoylphorbol-13-acetate (Bokemeyer et al. 1998) and the glucocorticoid dexamethasone (Lasa et al. 2002; Kassel et al. Life Sciences 84 (2009) 838–846 ⁎ Corresponding author. Dept Biomedical Sciences, PO Box 19063, Tygerberg 7505, South Africa. E-mail address: alo@sun.ac.za (A. Lochner). 0024-3205/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.lfs.2009.03.014 Contents lists available at ScienceDirect Life Sciences journal homepage: www.elsevier.com/locate/lifescie