Abstract 447: Myristoylation of Protein Kinase C Beta II Peptide Inhibitor Facilitates Rapid Attenuation of Phorbol 12-myristate 13-acetate in Activated Superoxide Release in Isolated Rat Polymorphonuclear Leukocytes

Protein kinase C beta II (PKCβII) activates polymorphonuclear leukocyte (PMN) superoxide (SO) production via NADPH oxidase (NOX-2) phosphorylation to exacerbate myocardial ischemia/reperfusion (I/R) injury. In prior studies, myristoylation (myr) of PKCβII peptide inhibitor (N-myr-SLNPEWNET; myr-PKCβII-), which disrupts PKCβII translocation/phosphorylation of NOX-2, was shown to dose-dependently attenuate PMN SO release induced by phorbol 12-myristate 13-acetate (PMA), a broad-spectrum PKC agonist. However, the role of myr on the inhibitory effects of myr-PKCβII- has yet to be elucidated. We hypothesized that myr-PKCβII peptide activator (N-myr-SVEIWD; myr-PKCβII+) would augment, myr-PKCβII- would attenuate, and scrambled myr-PKCβII- (N-myr-WNPESLNTE; myr-PKCβII-scram), a control for myr, would not affect PMA-induced PMN SO release compared to unconjugated peptides and nontreated controls. Rat PMNs (5х10 6 ) were incubated for 15 min at 37 o C in the presence/absence of SO dismutase (SOD; 10 μg/mL), unconjugated PKCβII+/-, myr-PKCβII+/-, or myr-PKCβII-scram (all 20 μM). SO release was measured by the change in absorbance at 550 nm via ferricytochrome c reduction after PMA (100 nM) stimulation for 390 sec. Data were analyzed by ANOVA using Student-Newman-Keuls post hoc analysis. Myr-PKCβII- significantly attenuated SO release (0.30±0.02; n=27; p<0.05) compared to nontreated controls (0.46±0.01; n=73), myr-PKCβII+ (0.46±0.03; n=25), unconjugated PKCβII+ (0.43±0.04; n=15), PKCβII- (0.43±0.02; n=22) and myr-PKCβII-scram (0.65±0.04; n=22). SOD (n=8), which rapidly converts SO to H 2 O 2 , significantly reduced absorbance by 94±7%, indicating that absorbance increased mainly due to PMA stimulation. Cell viability (trypan blue exclusion) was similar in all groups (94±2%). Unexpectedly, myr-PKCβII-scram significantly stimulated the highest increase in absorbance compared to all groups (p<0.01). Future studies will determine whether myr-PKCβII-scram augments absorbance by a different mechanism. Results suggest that myr improves myr-PKCβII- delivery compared to unconjugated PKCβII- but does not affect inhibition of PMA-induced PMN SO release. Myr-PKCβII- may thus effectively limit inflammation-induced I/R injury.

Abstract 445: Myristoylated Protein Kinase C Beta II Peptide Inhibitor Attenuates Hypoxia-Reoxygenation Injury in Human Umbilical Vein Endothelial Cells

Endothelial dysfunction as a result of ischemia/reperfusion (I/R) injury contributes to local organ damage in heart attack patients. In vascular cells, NADPH oxidase (NOX) and the mitochondrial electron transport chain are initiating sources of reactive oxygen species (ROS) during I/R injury. Protein kinase C beta II (PKCβII) is an attractive therapeutic target due to its phosphorylation of p66Shc to enhance mitochondrial-derived ROS production and p47 phox to promote ROS release from NOX. In previous studies, a cell-permeable myristoylated PKCβII peptide inhibitor (N-myr-SLNPEWNET; myr-PKCβII-) has been shown to improve post-reperfusion cardiac function and reduce infarct size in rat myocardial I/R injury. The decrease in myocardial I/R injury with myr-PKCβII- may in part be attributed to improved vascular endothelial function. Due to myr-PKCβII- peptide sequence being highly conserved among mammalian species, we hypothesize that myr-PKCβII- will confer protection by directly inhibiting ROS production from NOX and mitochondria in human umbilical endothelial cells (HUVECs) subjected to hypoxia/reoxygenation (H/R) mediated injury. HUVECs, cultured in gelatin-coated 96-well plates, were subjected to 24h hypoxia and 24h reoxygenation in a Billups-Rothenburg chamber with 1% O 2 , 5% CO 2 , and balance nitrogen. Myr-PKCβII- (20 μM) was administered at the beginning of the 24h reoxygenation period. Cell viability was assessed using tetrazolium-salt (WST-8) colorimetric assay with a microplate reader (450 nm) and normalized against the normoxia control group. Data were analyzed using Student-Newman-Keuls post-hoc analysis. At the 24h reoxygenation period, cell viability (%) was significantly reduced to 78±2% (n=5; p<0.05) in the non-treated H/R group compared to normoxia controls (n=5). Myr-PKCβII- significantly improved HUVEC survival (95±4%; n=5) compared to non-treated H/R controls (n=5; p<0.01) which were not significantly different from normoxia controls. The data suggest that PKCβII inhibition promotes cell survival possibly due to directly attenuating NOX and mitochondrial derived ROS in cells subjected to H/R conditions. Further studies are needed to determine cell survival potential under more severe H/R mediated injury.

Inhibition of protein kinase C beta phosphorylation activates nuclear factor-kappa B and improves postischemic recovery in type 1 diabetes

Peripheral artery disease (PAD) is a major health problem and is caused by atherosclerosis in arteries outside the heart leading to impaired blood flow. The presence of diabetes significantly increases the likelihood of having worse outcomes in PAD, and the molecular mechanisms involved are poorly understood. Hyperglycemia in diabetes activates the nuclear factor-kappa B (NF-κB) pathway, and chronic inflammation in diabetes is associated with vascular complications. Ischemia also activates NF-κB signaling that is important for perfusion recovery in experimental PAD. We hypothesized that prolonged exposure of endothelial cells to high glucose in diabetes impairs ischemic activation of the NF-κB pathway and contributes to poor perfusion recovery in experimental PAD. We assessed the effect of high glucose and ischemia on canonical and non-canonical NF-κB activation in endothelial cells and found both conditions activate both pathways. However, exposure of endothelial cells to high glucose impairs ischemia-induced activation of the canonical NF-κB pathway but not the non-canonical pathway. We probed an array of antibodies against signaling proteins in the NF-κB pathway to identify proteins whose phosphorylation status are altered in endothelial cells exposed to high glucose. Protein kinase C beta (PKCβ) was among the proteins identified, and its role in impaired ischemia-induced activation of NF-κB during hyperglycemia has not been previously described. Inhibition of PKCβ improves ischemia-induced NF-κB activation in vitroand in vivo. It also improves perfusion recovery in diabetic mice following experimental PAD. Thus, in diabetes, PKCβ phosphorylation contributes to impaired ischemic activation of NF-κB and likely a mechanism contributing to poor PAD outcomes. Impact statement Diabetes worsens the outcomes of peripheral arterial disease (PAD) likely in part through inducing chronic inflammation. However, in PAD, recovery requires the nuclear factor-kappa B (NF-κB) activation, a known contributor to inflammation. Our study shows that individually, both ischemia and high glucose activate the canonical and non-canonical arms of the NF-κB pathways. We show for the first time that prolonged high glucose specifically impairs ischemia-induced activation of the canonical NF-κB pathway through activation of protein kinase C beta (PKCβ). Accordingly, inhibition of PKCβ restores the ischemia-induced NF-κB activity both in vitroin endothelial cells and in vivoin hind limbs of type 1 diabetic mice and improves perfusion recovery after experimental PAD. Thus, this study provides a mechanistic insight into how diabetes contributes to poor outcomes in PAD and a potential translational approach to improve PAD outcomes.