Differential activation of mitogen-activated protein kinases in acute, intermittent and chronic myocardial hypoxia in vivo

a risk factor for cardiovascular surgery. However, the underlying molecular mechanisms are unknown. We investigated the role of MAPKs in CH compared with acute (AH) and intermittent (IH) hypoxia. We used a novel type of normobaric hypoxic chamber that permits to study the animals under true CH conditions (ie, no cage opening for feeding and animal care). In contrast, most previous stud-ies involved daily opening of cages and, hence, results actually referred to IH (ie, prolonged hypoxia with short daily periods of reoxygenation) rather than true CH. Methods: Adult rats were subdivided into 4 groups: normoxia (N; O2 fraction= 21%), AH (O2 fraction=10% for 1h), CH and IH (n=6/group). CH and IH rats were housed in a normobaric hypoxic chamber (O2 fraction =10%), but IH rats were exposed to room air for 1h/day. After 2 weeks, CH and IH hearts were excised and homogenized for extraction of cytosolic and nuclear proteins to determine activation (phosphorylation) of c-Jun NH2-terminal kinases (JNK), extracellular signal-regulated kinases (ERK), and p38 MAPK byWestern blot. JNK and p38 MAPK activities were also determined by in vitro kinase assays. Mitochondria were isolated to determine the subcellular distribution of cytochrome C and the anti-apoptotic factor Bcl-2. Cardiomyocyte apoptosis was determined by TUNEL. Results: AH was associated with significant (p<0.05) activation of JNK (3.4-fold) and p38 MAPK (3.7-fold), IH with that of JNK (2.3-fold) and ERK (1.7-fold), and CH with that of p38 MAPK alone (3.3-fold). JNK and p38 MAPK in vitro kinase assays were consistent with these MAPK activation patterns. Cardiomyocyte apoptosis was increased 2.2-fold in IH and 4-fold in CH. There were no differences in the mitochondrial release of cytochrome C as well as expression and subcellular distribution of Bcl-2 among groups. Conclusions: AH, IH and CH are associated with differential MAPK activation in rat hearts in vivo. p38 MAPK activation is associated with cardiomyocyte apoptosis in CH, whereas JNK and ERK activation may be associated with cardioprotection in IH. Results of ongoing in vivo experiments using selective inhibitors of JNK and p38 MAPK in the intermittent and chronic hypoxia models will also be presented to further characterize the effects of differential MAPK activation on cardiomyocyte apoptosis under these conditions.