Loss of ischemic preconditioning's cardioprotection in aged mouse hearts is associated with reduced gap junctional and mitochondrial levels of connexin 43

Abstract

Boengler K, Konietzka I, Buechert A, Heinen Y, Garcia-Dorado D, Heusch G, Schulz R. Loss of ischemic preconditioning's cardioprotection in aged mouse hearts is associated with reduced gap junctional and mitochondrial levels of connexin 43. Am J Physiol Heart Circ Physiol 292: H1764 -H1769, 2007. First published December 1, 2006; doi:10.1152/ajpheart.01071.2006 is localized at left ventricular (LV) gap junctions and in cardiomyocyte mitochondria. A genetically induced reduction of Cx43 as well as blockade of mitochondrial Cx43 import abolishes the infarct size (IS) reduction by ischemic preconditioning (IP). With progressing age, Cx43 content in ventricular and atrial tissue homogenates is reduced. We now investigated whether or not 1) the mitochondrial Cx43 content is reduced in aged mice hearts and 2) IS reduction by IP is lost in aged mice hearts in vivo. Confirming previous results, sarcolemmal Cx43 content was reduced in aged (Ͼ13 mo) compared with young (Ͻ3 mo) C57Bl/6 mice hearts, whereas the expression levels of protein kinase C ⑀ and endothelial nitric oxide synthase remained unchanged. Also in mitochondria isolated from aged mice LV myocardium, Western blot analysis indicated a 40% decrease in Cx43 content compared with mitochondria isolated from young mice hearts. In young mice hearts, IP by one cycle of 10 min ischemia and 10 min reperfusion reduced IS (% of area at risk) following 30 min regional ischemia and 120 min reperfusion from 67.7 Ϯ 3.3 (n ϭ 17) to 34.2 Ϯ 6.6 (n ϭ 5, P Ͻ 0.05). In contrast, IP's cardioprotection was lost in aged mice hearts, since IS in nonpreconditioned (57.5 Ϯ 4.0, n ϭ 10) and preconditioned hearts (65.4 Ϯ 6.3, n ϭ 8, P ϭ not significant) was not different. In conclusion, mitochondrial Cx43 content is decreased in aged mouse hearts. The reduced levels of Cx43 may contribute to the age-related loss of cardioprotection by IP. left ventricle; infarct size; translocase of the outer membrane 20 BRIEF PERIODS OF ischemia-reperfusion delay the development of cell death from a subsequent prolonged episode of ischemiareperfusion, a phenomenom known as ischemic preconditioning (IP; for review see Refs. 10 and 34). Connexin 43 (Cx43) is essential for cardioprotection (36). The cardioprotection by ischemic or pharmacological preconditioning with diazoxide is abolished both in in situ hearts and in isolated cardiomyocytes from heterozygous Cx43-deficient mice (17,23,37). Apart from its localization at the sarcolemma, Cx43 is also detected at the inner membrane of cardiomyocyte mitochondria (3, 32), i.e., in cell organelles that are central for triggering/mediating the cardioprotection by IP (21,26,28). Indeed, the reduction of mitochondrial Cx43 by geldanamycin, which inhibits heat shock protein 90 and thereby decreases the translocation of Cx43 to the mitochondria, abolishes the infarct size reduction by diazoxide otherwise seen in isolated rat hearts (32).Reactive oxygen species (ROS), which are partially produced by uncoupling of oxidative phosphorylation, trigger IP's cardioprotecti...

Middle age aggravates myocardial ischemia through surprising upholding of complex II activity, oxidative stress, and reduced coronary perfusion

“…The gap junction connexin 43 content has been tightly involved in the development of rigor tension, since it facilitates cell-to-cell communication and generalization of the behavior of a cell minority to the total cellular population of the heart. It is known to be decreased with aging, starting precisely at middle duration of the lifespan (Boengler et al 2007). Since middle age reduces the gap junction connexin 43 content, excess proton accumulated in the most metabolically active cells should not be easily diffused in the less active cells, which should delay PFK inhibition in these last cells and allow the upholding of their metabolic activity.…”

The late phase of preconditioning and its natural clinical application—gene therapy

“…The effect of aging on PC is unclear. Some studies [27,28,29] but not others [30] support the concept that the early PC response is absent in old animals. Aging abolishes the late phase of ischemia-induced PC in mice [31] but not the late phase of opioid-induced late PC in rats [32].…”

Loss of Anti-Arrhythmic Effect of Vagal Nerve Stimulation on Ischemia-Induced Ventricular Tachyarrhythmia in Aged Rats

“…The annealing temperature was 61.8°C, 54.9°C and 54.7°C for Cx43, eNOS and GAPDH, respectively. The expression level of Cx43 mRNA was normalized with eNOS mRNA because there was no significant difference between adult rats and aged rats (Boengler et al 2007) and GAPDH mRNA expression.…”

“…It has been reported that vagal nerve stimulation (VNS) exerts an anti-arrhythmic effect by preserving phosphorylated Cx43 in a rat model of MI (Ando et al 2005). However, previous reports found that the expression of Cx43 protein is decreased in the ventricles of aged rats (Boengler et al 2006(Boengler et al , 2007(Boengler et al , 2009). Whether VNS can exert an anti-arrhythmic effect during acute MI in aged rats remains unknown.…”