Abstract 9: Nuclear and Mitochondrial Translocation of Phosphorylated PKCδAssociates With Tunel-positive and Urocortin-negative Staining in the Human Heart From Diabetic Patients Undergoing On-pump Cardiac Surgery
BACKGROUND: Diabetes mellitus worsens postsurgical outcomes in patients undergoing on-pump cardiac surgery (OPCS) by unclear mechanisms.
AIMS: To investigate the cardio-protective role and the mechanism of action of urocortin (Ucn), with respect to PKCϵ and PKCδ expression, activation and relocation in diabetic patients (DMP) versus non-diabetic patients (NDMP) undergoing OPCS.
METHODS: Two sequential biopsies were obtained from the right atrium of 27 DMP and 22 NDMP undergoing OPCS at the start of grafting (internal control) and 10 minutes after release of the aortic clamp.
RESULTS: In NDMP, post-cardioplegic induction of Ucn was documented both at the mRNA (255% of basic levels; p<0.05) and protein level (four-fold increase; p<0.01). Conversely, in DMP pre-cardioplegic levels of Ucn were 50% lower than those of NDMP, while post-cardioplegic induction was not observed. In NDMP, cardioplegic arrest also increased the expression levels of PKC-ϵ mRNA (225% of basic level) and protein (2-fold rise), while overexpression of PKC-δ was not documented. On the contrary, DMP exhibited a reversed pattern of PKCϵ/δ induction with frank overexpression of PKCδ(mRNA:269% of basic level; protein:2.4-fold increase; p<0.01) and non-significant overexpression of PKCϵ. Phosphorylation (2.9-fold increase) and mitochondrial relocation of PKCϵ was mainly detected in post-cardioplegic samples from NDMP, while nuclear and mitochondrial translocation of activated PKCδ (2.4-fold increase) was mainly documented in post-cardioplegic samples from DMP. Apoptosis, assessed by TUNEL staining, was over 2-fold higher in post-cardioplegic samples from DMP (6.5±1.8%) than NDMP (2.9±0.7%). Importantly, enhanced PKCϵ/mitochondria colocalization was observed in viable myocytes showing positive staining for Ucn, while apoptotic myocytes exhibiting nuclear and mitochondrial relocation of PKCδ were systematically Ucn-negative.
CONCLUSIONS: In DMP cardioplegic arrest failed to induce myocyte overexpression of Ucn, which was associated with induction, activation, nuclear and mitochondrial relocation of PKCδ, finally resulting in apoptosis. Failure to overexpress Ucn makes the DMP more susceptible to apoptosis and may contribute to adverse postsurgical outcomes.