Jamie W. Meyer

A central role for the endothelial NADPH oxidase in atherosclerosis

An increasing body of evidence has demonstrated that NADPH oxidase plays a critical role in several early steps leading toward the development of atherosclerosis. These effects appear to be carried out by both the ability of O2 − to act as a small second messenger molecule, and potentially the oxidation of low density lipoprotein by O2 −. We describe a model for the initiation and development of atherosclerosis that suggests targeted inhibition of NADPH oxidase as a powerful site for prevention and treatment of this disease.

Mice With a Null Mutation in the NHE1 Na+-H+ Exchanger Are Resistant to Cardiac Ischemia-Reperfusion Injury

Abstract— Pharmacological studies indicate that Na+-H+ exchanger isoform 1 (NHE1) plays a central role in myocardial ischemia-reperfusion injury; however, confirmation by alternative methods is lacking. To address this issue, we examined the role of NHE1 in ischemia-reperfusion injury using gene-targeted NHE1-null mutant (Nhe1−/−) mice. Nhe1−/− and wild-type hearts were perfused in a Langendorff apparatus in both the absence and presence of the NHE1 inhibitor eniporide, subjected to 40 minutes of ischemia and 30 minutes of reperfusion, and the effects of genetic ablation or inhibition of NHE1 on hemodynamic, biochemical, and pathological changes were assessed. In the absence of eniporide, left ventricular developed pressure, end-diastolic pressure, and coronary flow were significantly less impaired in Nhe1−/− hearts relative to wild-type hearts, and release of lactate dehydrogenase, morphological damage, and ATP depletion were also significantly less. In the presence of eniporide, however, wild-type hearts were significantly protected and there were no significant differences between the two genotypes with respect to cardiac performance, lactate dehydrogenase release, or morphological damage. Furthermore, the presence or absence of eniporide had no apparent effect on the degree of cardioprotection observed in Nhe1−/− hearts. These data demonstrate that genetic ablation of NHE1 protects the heart against ischemia-reperfusion injury. In addition to providing direct evidence that confirms previous pharmacological studies indicating a role for NHE1 in ischemia-reperfusion injury, these results suggest that the long-term absence of NHE1 does not elicit major compensatory changes that might negate the cardioprotective effects of blocking its activity over the short-term.

Impaired Cardiac Contractility in Mice Lacking Both the AE3 Cl-/HCO3-Exchanger and the NKCC1 Na+-K+-2Cl¯ Cotransporter : EFFECTS ON Ca2+ HANDLING AND PROTEIN PHOSPHATASES

To analyze the cardiac functions of AE3, we disrupted its gene (Slc4a3) in mice. Cl(-)/HCO3(-) exchange coupled with Na+-dependent acid extrusion can mediate pH-neutral Na+ uptake, potentially affecting Ca2+ handling via effects on Na+/Ca2+ exchange. AE3 null mice appeared normal, however, and AE3 ablation had no effect on ischemia-reperfusion injury in isolated hearts or cardiac performance in vivo. The NKCC1 Na+-K+-2Cl(-) cotransporter also mediates Na+ uptake, and loss of NKCC1 alone does not impair contractility. To further stress the AE3-deficient myocardium, we combined the AE3 and NKCC1 knock-outs. Double knock-outs had impaired contraction and relaxation both in vivo and in isolated ventricular myocytes. Ca2+ transients revealed an apparent increase in Ca2+ clearance in double null cells. This was unlikely to result from increased Ca2+ sequestration, since the ratio of phosphorylated phospholamban to total phospholamban was sharply reduced in all three mutant hearts. Instead, Na+/Ca2+ exchanger activity was found to be enhanced in double null cells. Systolic Ca2+ was unaltered, however, suggesting more direct effects on the contractile apparatus of double null myocytes. Expression of the catalytic subunit of protein phosphatase 1 was increased in all mutant hearts. There was also a dramatic reversal, between single null and double null hearts, in the carboxymethylation and localization to the myofibrillar fraction, of the catalytic subunit of protein phosphatase 2A, which corresponded to the loss of normal contractility in double null hearts. These data show that AE3 and NKCC1 affect Ca2+ handling, PLN regulation, and expression and localization of major cardiac phosphatases and that their combined loss impairs cardiac function.