A small molecule AMPK activator protects the heart against ischemia-reperfusion injury.

AMP-activated protein kinase (AMPK) is a stress signaling enzyme that orchestrates the regulation of energy-generating and -consuming pathways. Intrinsic AMPK activation protects the heart against ischemic injury and apoptosis, but whether pharmacologic AMPK stimulation mitigates ischemia-reperfusion damage is unknown. The aims of this study were to determine whether direct stimulation of AMPK using a small molecule activator, A-769662, attenuates myocardial ischemia-reperfusion injury and to examine its cardioprotective mechanisms. Isolated mouse hearts pre-treated with A-769662 had better recovery of left ventricular contractile function (55% vs. 29% of baseline rate-pressure product; p=0.03) and less myocardial necrosis (56% reduction in infarct size; p<0.01) during post-ischemic reperfusion compared to control hearts. Pre-treatment with A-769662 in vivo attenuated infarct size in C57Bl/6 mice undergoing left coronary artery occlusion and reperfusion compared to vehicle (36% vs. 18%, p=0.025). Mouse hearts with genetically inactivated AMPK were not protected by A-769662, indicating the specificity of this compound. Pre-treatment with A-769662 increased the phosphorylation and inactivation of eukaryotic elongation factor 2 (eEF2), preserved energy charge during ischemia, delayed the development of ischemic contracture, and reduced myocardial apoptosis and necrosis. A-769662 also augmented endothelial nitric oxide synthase (eNOS) activation during ischemia, which partially attenuated myocardial stunning, but did not prevent necrosis. AMPK is a therapeutic target that can be stimulated by a direct-acting small molecule in order to prevent injury during ischemia-reperfusion. The use of AMPK activators may represent a novel strategy to protect the heart and other solid organs against ischemia.

Eph-dependent tyrosine phosphorylation of ephexin1 modulates growth cone collapse.

Ephs regulate growth cone repulsion, a process controlled by the actin cytoskeleton. The guanine nucleotide exchange factor (GEF) ephexin1 interacts with EphA4 and has been suggested to mediate the effect of EphA on the activity of Rho GTPases, key regulators of the cytoskeleton and axon guidance. Using cultured ephexin1-/- mouse neurons and RNA interference in the chick, we report that ephexin1 is required for normal axon outgrowth and ephrin-dependent axon repulsion. Ephexin1 becomes tyrosine phosphorylated in response to EphA signaling in neurons, and this phosphorylation event is required for growth cone collapse. Tyrosine phosphorylation of ephexin1 enhances ephexin1's GEF activity toward RhoA while not altering its activity toward Rac1 or Cdc42, thus changing the balance of GTPase activities. These findings reveal that ephexin1 plays a role in axon guidance and is regulated by a switch mechanism that is specifically tailored to control Eph-mediated growth cone collapse.

Short-term enhancement of visual field sensitivity in glaucomatous eyes following surgical intraocular pressure reduction.

PURPOSE: To examine the hypothesis that surgical intraocular pressure (IOP) reduction leads to enhancement of visual field (VF) sensitivity in glaucomatous eyes. DESIGN: Prospective case-control study. METHODS: Patients with uncontrolled IOP requiring trabeculectomy or aqueous drainage device were enrolled. Controls consisted of medically treated glaucoma patients with stable IOP and no change in medical therapy during follow-up. Two baseline preoperative VFs and 3 follow-up VF examinations at 1, 2, and 3 months postoperatively were used for analysis. The same number of VF examinations measured within an 18-month interval was used for control eyes. VF locations with significant change were defined as exceeding 95% test-retest confidence limits based upon the mean sensitivity using the 2 baseline VF exams. The number of significantly changing locations per eye and changes in mean and pattern standard deviation (PSD) from the mean baseline fields were compared between groups using a Poisson generalized estimating equation model. RESULTS: Thirty eyes of 30 surgically treated glaucoma patients and 41 eyes of 28 stable controls were enrolled. Postoperative IOP was decreased at follow-up 3 compared with baseline (P < .001) in the surgical eyes, but was similar in control eyes (P = .92). At follow-up 3, the number of test locations improving in central (P = .014) and peripheral (P = .019) VF locations was significantly greater in the surgical eyes. The number of eyes with improved PSD at follow-up 3 was significantly greater in the surgical eyes compared with controls (P = .02). CONCLUSIONS: Short-term enhancement of central and peripheral VF sensitivity occurs after surgical reduction of IOP in glaucomatous eyes and may represent a potential biomarker for retinal ganglion cell response to therapeutic interventions in glaucoma.