Ami P. Raval

RESVERATROL PRETREATMENT PROTECTS RAT BRAIN FROM CEREBRAL ISCHEMIC DAMAGE VIA A SIRTUIN 1-UNCOUPLING PROTEIN 2 PATHWAY

Resveratrol is a natural polyphenol found in grapes and wine and has been associated with protective effects against cardiovascular diseases. In vitro, both resveratrol preconditioning (RPC) and ischemic preconditioning (IPC) require activation of sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, to induce neuroprotection against cerebral ischemia. In the present study, we tested two hypotheses: (a) that neuroprotection against cerebral ischemia can be induced by RPC in vivo; and (b) that RPC neuroprotection involves alterations in mitochondrial function via the SIRT1 target mitochondrial uncoupling protein 2 (UCP2). IPC was induced by 2 min of global ischemia (temporary bilateral carotid artery occlusion with hypotension), and RPC, by i.p. injection of resveratrol at 10, 50 and 100 mg/kg dosages. Forty-eight hours later, we compared the neuroprotective efficacy of RPC and IPC in vulnerable cornu ammonis 1 hippocampal pyramidal neurons using a rat model of asphyxial cardiac arrest (ACA). SIRT1 activity was measured using a SIRT1-specific fluorescent enzyme activity assay. In hippocampal mitochondria isolated 48 h after IPC or RPC, we measured UCP2 levels, membrane potential, respiration, and the mitochondrial ATP synthesis efficiency (ADP/O ratio). Both IPC and RPC induced tolerance against brain injury induced by cardiac arrest in this in vivo model. IPC increased SIRT1 activity at 48 h, while RPC increased SIRT1 activity at 1 h but not 48 h after treatment in hippocampus. Resveratrol significantly decreased UCP2 levels by 35% compared to sham-treated rats. The SIRT1-specific inhibitor sirtinol abolished the neuroprotection afforded by RPC and the decrease in UCP2 levels. Finally, RPC significantly increased the ADP/O ratio in hippocampal mitochondria reflecting enhanced ATP synthesis efficiency. In conclusion, in vivo resveratrol pretreatment confers neuroprotection similar to IPC via the SIRT1-UCP2 pathway.

RESVERATROL MIMICS ISCHEMIC PRECONDITIONING IN THE BRAIN

Recent studies in a variety of species including mammals showed that resveratrol (trans-3, 5, 4″-trihydroxystibene) treatment and caloric restriction increased silent information regulator 2/sirtuin 1 activity, which mediated increase in life span/cell survival. Resveratrol is a naturally occurring phytoalexin and a well-documented cardioprotective agent. Similarly, ischemic preconditioning (IPC) has been shown to be both cardio- and cerebroprotective against subsequent ischemic insults. A major emphasis in this field is to understand the molecular mechanisms that mediate this phenomenon. The goal of this study was to define whether resveratrol can emulate IPC neuroprotection against cerebral ischemia. Employing an in vitro model of cerebral ischemia, the organotypic hippocampal slice culture, we report that resveratrol pretreatment mimics IPC via the SIRT1 pathway. Blockade of SIRT1 activation by sirtinol after IPC or resveratrol pretreatment abolished their neuroprotection. A better understanding of the mechanisms by which resveratrol induces ischemic tolerance in a prophylactic manner may provide a novel therapy against stroke or neurosurgical procedures.

Protein Kinase C δ Mediates Cerebral Reperfusion Injury In Vivo

Protein kinase C (PKC) has been implicated in mediating ischemic and reperfusion damage in multiple organs. However, conflicting reports exist on the role of individual PKC isozymes in cerebral ischemic injury. Using a peptide inhibitor selective for δPKC, δV1-1, we found that δPKC inhibition reduced cellular injury in a rat hippocampal slice model of cerebral ischemia [oxygen-glucose deprivation (OGD)] when present both during OGD and for the first 3 hr of reperfusion. We next demonstrated peptide delivery to the brain parenchyma after in vivo delivery by detecting biotin-conjugatedδV1-1 and by measuring inhibition of intracellular δPKC translocation, an indicator of δPKC activity. Delivery of δV1-1 decreased infarct size in an in vivo rat stroke model of transient middle cerebral artery occlusion. Importantly, δV1-1 had no effect when delivered immediately before ischemia. However, delivery at the onset, at 1 hr, or at 6 hr of reperfusion reduced injury by 68, 47, and 58%, respectively. Previous work has implicated δPKC in mediating apoptotic processes. We therefore determined whether δPKC inhibition altered apoptotic cell death or cell survival pathways in our models. We found that δV1-1 reduced numbers of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells, indicating decreased apoptosis, increased levels of phospho-Akt, a kinase involved in cell survival pathways, and inhibited BAD (Bcl-2-associated death protein) protein translocation from the cell cytosol to the membrane, indicating inhibition of proapoptotic signaling. These data support a deleterious role for δPKC during reperfusion and suggest that δV1-1 delivery, even hours after commencement of reperfusion, may provide a therapeutic advantage after cerebral ischemia.

Ischemic Preconditioning Targets the Respiration of Synaptic Mitochondria via Protein Kinase Cε

In the brain, ischemic preconditioning (IPC) diminishes mitochondrial dysfunction after ischemia and confers neuroprotection. Activation of ε protein kinase C (εPKC) has been proposed to be a key neuroprotective pathway during IPC. We tested the hypothesis that IPC increases the levels of εPKC in synaptosomes from rat hippocampus, resulting in improved synaptic mitochondrial respiration. Preconditioning significantly increased the level of hippocampal synaptosomal εPKC to 152% of sham-operated animals at 2 d of reperfusion, the time of peak neuroprotection. We tested the effect of εPKC activation on hippocampal synaptic mitochondrial respiration 2 d after preconditioning. Treatment with the specific εPKC activating peptide, tat-ψεRACK (tat-ψε-receptor for activated C kinase), increased the rate of oxygen consumption in the presence of substrates for complexes I, II, and IV to 157, 153, and 131% of control (tat peptide alone). In parallel, we found that εPKC activation in synaptosomes from preconditioned animals resulted in altered levels of phosphorylated mitochondrial respiratory chain proteins: increased serine and tyrosine phosphorylation of 18 kDa subunit of complex I, decreased serine phosphorylation of FeS protein in complex III, increased threonine phosphorylation of COX IV (cytochrome oxidase IV), increased mitochondrial membrane potential, and decreased H2O2 production. In brief, ischemic preconditioning promoted significant increases in the level of synaptosomal εPKC. Activation of εPKC increased synaptosomal mitochondrial respiration and phosphorylation of mitochondrial respiratory chain proteins. We propose that, at 48 h of reperfusion after ischemic preconditioning, εPKC is poised at synaptic mitochondria to respond to ischemia either by direct phosphorylation or activation of the εPKC signaling pathway.

Epsilon Protein Kinase C Mediated Ischemic Tolerance Requires Activation of the Extracellular Regulated Kinase Pathway in the Organotypic Hippocampal Slice

Ischemic preconditioning (IPC) promotes brain tolerance against subsequent ischemic insults. Using the organotypic hippocampal slice culture, we conducted the present study to investigate (1) the role of adenosine A1 receptor (A1AR) activation in IPC induction, (2) whether epsilon protein kinase C (ɛPKC) activation after IPC is mediated by the phosphoinositol pathway, and (3) whether ɛPKC protection is mediated by the extracellular signal-regulated kinase (ERK) pathway. Our results demonstrate that activation of A1AR emulated IPC, whereas blockade of the A1AR during IPC diminished neuroprotection. The neuroprotection promoted by the A1AR was also reduced by the ɛPKC antagonist. To determine whether ɛPKC activation in IPC and A1AR preconditioning is mediated by activation of the phosphoinositol pathway, we incubated slices undergoing IPC or adenosine treatment with a phosphoinositol phospholipase C inhibitor. In both cases, preconditioning neuroprotection was significantly attenuated. To further characterize the subsequent signal transduction pathway that ensues after ɛPKC activation, mitogen-activated protein kinase kinase was blocked during IPC and pharmacologic preconditioning (PPC) (with ɛPKC, NMDA, or A1AR agonists). This treatment significantly attenuated IPC- and PPC-induced neuroprotection. In conclusion, we demonstrate that ɛPKC activation after IPC/PPC is essential for neuroprotection against oxygen/glucose deprivation in organotypic slice cultures and that the ERK pathway is downstream to ɛPKC.

Ischemic preconditioning ameliorates excitotoxicity by shifting glutamate/γ-aminobutyric acid release and biosynthesis

Excitotoxicity is recognized to play a major role in cerebral ischemia‐induced cell death. The main goal of the present study was to define whether our model of ischemic preconditioning (IPC) promotes a shift from excitatory to inhibitory neurotransmission during the test ischemia to diminish metabolic demand during the reperfusion phase. We also determined whether γ‐aminobutyric acid (GABA) played a role in IPC‐induced neuroprotection. Ten minutes of cerebral ischemia was produced by tightening the carotid ligatures bilaterally following hypotension. Samples of microdialysis perfusate, representing extracellular fluid, were analyzed for amino acid content by HPLC. IPC promoted a robust release of GABA after lethal ischemia compared with control rats. We also observed that the activity of glutamate decarboxylase (the predominant pathway of GABA synthesis in the brain) was higher in the IPC group compared with control and ischemic groups. Because GABAA receptor up‐regulation has been shown to occur following IPC, and GABAA receptor activation has been implicated in neuroprotection against ischemic insults, we tested the hypothesis that GABAA or GABAB receptor activation was neuroprotective during ischemia or early reperfusion by using an in vitro model (organotypic hippocampal slice culture). Administration of the GABAB agonist baclofen during test ischemia and for 1 hr of reperfusion provided significant neuroprotection. We concluded that increased GABA release in preconditioned animals after ischemia might be one of the factors responsible for IPC neuroprotection. Specific activation of GABAB receptor contributes significantly to neuroprotection against ischemia in organotypic hippocampal slices.

ɛPKC phosphorylates the mitochondrial K+ATP channel during induction of ischemic preconditioning in the rat hippocampus

Neuroprotection against cerebral ischemia conferred by ischemic preconditioning (IPC) requires translocation of epsilon protein kinase C (epsilonPKC). A major goal in our laboratory is to define the cellular targets by which epsilonPKC confers protection. We tested the hypothesis that epsilonPKC targets the mitochondrial K(+)(ATP) channel (mtK(+)(ATP)) after IPC. Our results demonstrated a rapid translocation of epsilonPKC to rat hippocampal mitochondria after IPC. Because in other tissues epsilonPKC targets mtK(+)(ATP) channels, but its presence in brain mitochondria is controversial, we determined the presence of the K(+)(ATP) channel-specific subunits (Kir6.1 and Kir6.2) in mitochondria isolated from rat hippocampus. Next, we determined whether mtK(+)(ATP) channels play a role in the IPC induction. In hippocampal organotypic slice cultures, IPC and lethal ischemia were induced by oxygen-glucose deprivation. Subsequent cell death in the CA1 region was quantified using propidium iodide staining. Treatment with the K(+)(ATP) channel openers diazoxide or pinacidil 48 h prior to lethal ischemia protected hippocampal CA1 neurons, mimicking the induction of neuroprotection conferred by either IPC or epsilonPKC agonist-induced preconditioning. Blockade of mtK(+)(ATP) channels using 5-hydroxydecanoic acid abolished the neuroprotection due to either IPC or epsilonPKC preconditioning. Both ischemic and epsilonPKC agonist-mediated preconditioning resulted in phosphorylation of the mtK(+)(ATP) channel subunit Kir6.2. After IPC, selective inhibition of epsilonPKC activation prevented Kir6.2 phosphorylation, consistent with Kir6.2 as a phosphorylation target of epsilonPKC or its downstream effectors. Our results support the hypothesis that the brain mtK(+)(ATP) channel is an important target of IPC and the signal transduction pathways initiated by epsilonPKC.

The Arctic Ground Squirrel Brain Is Resistant to Injury From Cardiac Arrest During Euthermia

Background and Purpose— Hetereothermic mammals tolerate hypoxia during euthermy and torpor, and evidence suggests this tolerance may extend beyond hypoxia to cerebral ischemia. During hibernation, CA1 hippocampal neurons endure extreme fluctuations in cerebral blood flow during transitions into and out of torpor as well as reductions in cerebral blood flow during torpor. In vitro studies likewise show evidence of ischemia tolerance in hippocampal slices harvested from euthermic ground squirrels; however, no studies have investigated tolerance in a clinically relevant model of in vivo global cerebral ischemia. The purpose of the present study was to test the hypothesis that the euthermic Arctic ground squirrel (AGS; Spermophillus parryii) is resistant to injury from asphyxial cardiac arrest (CA). Methods— Estrous-matched female rats were used as a positive control. Female euthermic AGS and rats were subjected to 8-minute CA. At the end of 7 days of reperfusion, AGS and rats were fixed for histopathological assessment. Results— In rats subjected to CA, the number of ischemic neurons was significantly higher (P<0.001) compared with control rats in hippocampus and striatum. Cortex was mildly injured. Surprisingly, neuronal counts in AGS were not significantly different in CA and control groups in these brain regions. Conclusion— These data demonstrate that AGS are remarkably tolerant to global cerebral ischemia during euthermia. A better understanding of the mechanisms by which AGS tolerate severe reductions in blood flow during euthermia may provide novel neuroprotective strategies that may translate into significant improvements in human patient outcomes after CA.

EF1α and RPL13a represent normalization genes suitable for RT-qPCR analysis of bone marrow derived mesenchymal stem cells

BackgroundRT-qPCR analysis is a widely used method for the analysis of mRNA expression throughout the field of mesenchymal stromal cell (MSC) research. Comparison between MSC studies, both in vitro and in vivo, are challenging due to the varied methods of RT-qPCR data normalization and analysis. Therefore, this study focuses on putative housekeeping genes for the normalization of RT-qPCR data between heterogeneous commercially available human MSC, compared with more homogeneous populations of MSC such as MIAMI and RS-1 cells.ResultsEight genes including; ACTB, B2M, EF1α, GAPDH, RPL13a, YWHAZ, UBC and HPRT1 were tested as possible housekeeping genes based on their expression level and variability. EF1α and RPL13a were validated for RT-qPCR analysis of MIAMI cells during expansion in varied oxygen tensions, endothelial differentiation, neural precursor enrichment, and during the comparison with RS-1 cells and commercially available MSC. RPL13a and YWHAZ were validated as normalization genes for the cross-species analysis of MIAMI cells in an animal model of focal ischemia. GAPDH, which is one of the most common housekeeping genes used for the normalization of RT-qPCR data in the field of MSC research, was found to have the highest variability and deemed not suitable for normalization of RT-qPCR data.ConclusionsIn order to make comparisons between heterogeneous MSC populations, as well as adult stem cell like MSC which are used in different laboratories throughout the world, it is important to have a standardized, reproducible set of housekeeping genes for RT-qPCR analysis. In this study we demonstrate that EF1α, RPL13a and YWHAZ are suitable genes for the RT-qPCR analysis and comparison of several sources of human MSC during in vitro characterization and differentiation as well as in an ex vivo animal model of global cerebral ischemia. This will allow for the comparative RT-qPCR analysis of multiple MSC populations with the goal of future use in animal models of disease as well as tissue repair.

Traditional Risk Factors Are Not Major Contributors to the Variance in Carotid Intima-Media Thickness

Background and Purpose— Carotid intima-media thickness (cIMT) was a widely accepted ultrasound marker of subclinical atherosclerosis in the past. Although traditional risk factors may explain ≈50% of the variance in plaque burden, they may not explain such a high proportion of the variance in IMT, especially when measured in plaque-freel ocations. We aimed this study to identify individuals with cIMT unexplained by traditional risk factors for future environmental and genetic research. Methods— As part of the Northern Manhattan Study, 1790 stroke-free individuals (mean age, 69±9 years; 60% women; 61% Hispanic; 19% black; 18% white) were assessed for cIMT using B-mode carotid ultrasound. Multiple linear regression models were evaluated: (1) incorporating prespecified traditional risk factors; and (2) including less traditional factors, such as inflammation biomarkers, adiponectin, homocysteine, and kidney function. Standardized cIMT residual scores were constructed to select individuals with unexplained cIMT. Results— Mean total cIMT was 0.92±0.09 mm. The traditional model explained 11% of the variance in cIMT. Age (7%), male sex (3%), glucose (<1%), pack-years of smoking (<1%), and low-density lipoprotein cholesterol (<1%) were significant contributing factors. The model, including inflammatory biomarkers, explained 16% of the variance in cIMT. Adiponectin was the only additional significant contributor to the variance in cIMT. We identified 358 individuals (20%) with cIMT unexplained by the investigated risk factors. Conclusions— Vascular risk factors explain only a small proportion of variance in cIMT. Identification of novel genetic and environmental factors underlying unexplained subclinical atherosclerosis is of utmost importance for future effective prevention of vascular disease.