The Protein Kinase C Activator Phorbol Myristate Acetate Decreases Brain Edema by Aquaporin 4 Downregulation after Middle Cerebral Artery Occlusion in the Rat

Abstract

The protein kinase C activator phorbol 12-myristate 13-acetate (PMA) is known to interact with aquaporin 4 (AQP 4), a water-selective transporting protein that is abundant in astrocytes, and has experimentally been found to decrease osmotically-induced cell swelling. The purpose of this study was to examine whether PMA reduces brain edema following focal ischemia induced by middle cerebral artery (MCA) occlusion by modulation of AQP4 expression. Male Sprague-Dawley rats were randomly assigned to either sham surgery (n ¼ 6), or a continuous intravenous infusion of vehicle (1% dimethylsulfoxide), followed by MCA occlusion (n ¼ 18), and administration of PMA at 50 mg=kg (n ¼ 6) or at 200 mg=kg (n ¼ 6) starting 60 min before or 30 min (200 mg=kg; n ¼ 6) or 60 min (200 mg=kg; n ¼ 6) after MCA occlusion. Cerebral blood flow was monitored with laser Doppler over the MCA territory, and confirmed a 70% reduction during occlusion. After a 2-h period of ischemia and 2 h of reperfusion, the animals were sacrificed for assessment of brain water content and sodium and potassium concentration. AQP4 expression was assessed by immunoblotting and quantified by densitometry (n ¼ 24). Statistical analysis was performed by ANOVA followed by Tukey's post-hoc test. PMA treatment at 200 mg=kg significantly reduced brain water concentration in the infarcted area when started 60 min before or 30 min after occlusion ( p < 0.001 and p ¼ 0.022, respectively), and prevented the subsequent sodium shift ( p < 0.05). PMA normalized the AQP4 upregulation in ischemia ( p ¼ 0.021). A downregulation of AQP4 in the ischemic area paralleling the reduction in brain edema formation following PMA treatment suggests that the effect was mediated by AQP4 modulation.

Hydrogen sulfide induces neuroprotection against experimental stroke in rats by down-regulation of AQP4 via activating PKC

“…Activation of PKC with phorbol myristate acetate decreases brain edema by down-regulation of AQP4 after MCAO in the rat (Fazzina et al, 2010). Similar to their investigations, in our study, inhalation of H 2 S significantly decreased brain edema, and concomitantly inhibited the expression of AQP4.…”

Astragaloside IV reduces cerebral edema post-ischemia/reperfusion correlating the suppression of MMP-9 and AQP4

“…Brain water content and cerebral edema were also reduced significantly through down-regulation of AQP4 by an exogenouslytreated protein kinase C activator (Fazzina et al, 2010). Additionally, brain edema can be prevented in AQP4 null mice in models of cytotoxic edema models such as ischemic stroke, water intoxication, and acute bacterial meningitis (Manley et al, 2000;Papadopoulos and Verkman, 2005).…”

Real-Time Monitoring of Changes in Brain Extracellular Sodium and Potassium Concentrations and Intracranial Pressure after Selective Vasopressin-1a Receptor Inhibition following Focal Traumatic Brain Injury in Rats

“…AQP4 is the predominant water channel in the brain and has a significant role in the pathophysiology of brain edema. [32][33][34][35][36] Evidence suggests V1aR regulate the expression and function of AQP4, 17,22,37 although the mechanism is still elusive. 17,22,[29][30][31] Recently, we explored the hypothesis that selective V1aR inhibition by the non-peptide antagonist SR49059 30,38 can reduce brain edema in animal models of middle cerebral artery occlusion 22,39 and TBI.…”