Differential effects of delta and epsilon protein kinase C in modulation of postischemic cerebral blood flow

Abstract

Cerebral ischemia causes cerebral blood flow (CBF) derangements resulting in neuronal damage by enhanced protein kinase C delta (δPKC) levels leading to hippocampal and cortical neuronal death after ischemia. Contrarily, activation of εPKC mediates ischemic tolerance by decreasing vascular tone providing neuroprotection. However, whether part of this protection is due to the role of differential isozymes of PKCs on CBF following cerebral ischemia remains poorly understood. Rats pretreated with a δPKC specific inhibitor (δV1-1, 0.5 mg/kg) exhibited attenuation of hyperemia and latent hypoperfusion characterized by vasoconstriction followed by vasodilation of microvessels after two-vessel occlusion plus hypotension. In an asphyxial cardiac arrest (ACA) model, rats treated with δ V1-1 (pre- and postischemia) exhibited improved perfusion after 24 h and less hippocampal CA1 and cortical neuronal death 7 days after ACA. On the contrary, εPKC-selective peptide activator, conferred neuroprotection in the CA1 region of the rat hippocampus 30 min before induction of global cerebral ischemia and decreased regional CBF during the reperfusion phase. These opposing effects of δ v. εPKC suggest a possible therapeutic potential by modulating CBF preventing neuronal damage after cerebral ischemia.

Fig. 10.1

In vivo imaging of cerebral blood vessels using 2-photon microscopy (2-PM). Rats were injected with fluorescein isothiocyanate (FITC)-dextran (0.2 mg/kg) shown in green (a, b). Images were captured at 20× (a) and 200× (b) of a particular cortical blood vessel. Blood flow measurements using linescans from single vessels (linescans at 512 Hz) were used to determine red blood cell (RBC) flow (c). RBC flow values were calculated based on the slope of the shadows (measured using NIH Image J) produced by RBCs when traversed through the blood vessel. Pretreatment with δV1-1-induced attenuation of hypoperfusion 24 h after ACA. Rats pretreated (30 min) with δV1-1 after 24 h of ACA signifi cantly enhanced CBF by 700% as compared to tat peptide (vehicle) (d). In a separate set of experiments, δV1-1 was administered directly after 6 min of ACA and CBF changes were monitored. CBF was enhanced 45 and 60 min after ACA by 311 and 314%, respectively, as compared to tat peptide (e). For more details, please see Lin et al. [8]

Fig. 10.2

δV1-1 inhibits δPKC translocation in cortical lysates. Pretreatment with δV1-1 in the rat inhibited δPKC translocation after 6 min of ACA with a 61% reduction in protein as compared to tat peptide (vehicle) detected by Western blot analysis. For more details, please see Lin et al. [8]

Fig. 10.3

Rats pretreated with ψεRACK reduced cerebral reperfusion after 2-VO. A bolus IV injection of ψεRACK 30 min before ischemia reduced postischemic hyperemia by 30% as compared to tat peptide 25 min after 2-VO detected via laser-Doppler flowmetry. For more details, please see Della-Morte et al. [9]