Mitochondrial protein and HSP70 signaling after ischemia in hypothermic-adapted hearts augmented with glucose

Abstract

. Mitochondrial protein and HSP70 signaling after ischemia in hypothermic-adapted hearts augmented with glucose. Am. J. Physiol. 277 (Regulatory Integrative Comp. Physiol. 46): R11-R17, 1999.-Hypothermia improves resistance to subsequent ischemia in the cardioplegic-arrested heart (CAH). This adaptive process produces mRNA elevation for heat shock protein (HSP) 70-1 and mitochondrial proteins, adenine nucleotide translocator (ANT 1 ), and ␤-F 1 -ATPase. Glucose in cardioplegia also enhances myocardial protection. These processes might be linked to reduced ATP depletion. To assess for synergism between these protective processes, isolated rabbit hearts (n ϭ 91) were perfused at 37°C and exposed to ischemic cardioplegic arrest for 2 h. Hearts were in four groups: control (C), hypothermia adapted (H) perfused to 31°C 20 min before ischemia, 22 mM glucose (G) in cardioplegia, and hypothermic adaptation and glucose (HG). Developed pressure (DP), dP/dt max , and pressure-rate product (PRP) improved (P Ͻ 0.05) in G, H, and HG compared with C during reperfusion. DP and PRP were elevated in HG over H and G. ATP was higher in G, H, and HG, although no additional increase in HG over H was found. Lactate and CO 2 production were elevated in G only. The mRNA expression for HSP70-1, ANT 1 , and ␤-F 1 -ATPase was elevated severalfold in H and HG, but not G over C during reperfusion. In conclusion, glucose provides additional functional improvement in H. Additionally, neither ATP levels nor anaerobic metabolism are linked to mRNA expression for HSP70, ANT 1 , or ␤-F 1 -ATPase in CAH. stress response; RNA; cardiac surgery METABOLIC ALTERATIONS, resulting from a brief hypothermic exposure, improve resistance to subsequent ischemic and reperfusion injury at warmer temperatures. Decreased ATP depletion during ischemia represents a prominent feature of hypothermic adaptation. This results from a hypothermia-induced reduction in ATP use, which persists during subsequent warm ischemia (10). Characteristics of this adaptive process include enhanced postischemic gene expression for specific stress-related proteins and constitutive mitochondrial membrane proteins (10). The response of these transcript levels emulates expression induced by cold stress in cold-adapted tissues from hibernating species (5).Preservation of ATP appears to be closely linked to improved postischemic function after cardioplegic arrest and reperfusion after hypothermic adaptation in the isolated rabbit heart model (10). However, it remains unclear whether a causative relationship exists between ATP maintenance and enhancement of the heat shock protein (HSP) response or preservation of signaling for mitochondrial biogenesis.Other metabolic strategies can also improve ATP preservation during cardioplegic arrest and ischemia in an isolated perfused heart. Specifically, glucose, provided in the cardioplegia, promotes anaerobic ATP synthesis and limits ischemic ATP depletion (9). In this study, we propose two hypotheses. First, glucose in cardioplegia further augments...

Hypothermia preserves myocardial function and mitochondrial protein gene expression during hypoxia

“…Hybridization of the mRNA probes for ␤F 1 -ATPase (6) and ANT 1 has been previously reported in this rabbit model (19,21,22). A representative Northern blot illustrating ␤F 1 -ATPase and ANT 1 is shown in Fig.…”

“…Previous work in this laboratory showed that hypothermia applied to no-flow ischemia reduces lactate production and lactate-H ϩ cotransporter flux (18)(19)(20)(21). Thus one may presume that hypothermia-induced alterations in anaerobic metabolism provide a protective mechanism against injury from no-flow ischemia.…”

“…Thus one may presume that hypothermia-induced alterations in anaerobic metabolism provide a protective mechanism against injury from no-flow ischemia. This contention can be challenged, because glucose provided in cardioplegia during no-flow normothermic or hypothermic conditions paradoxically enhances glycolysis and lactate accumulation while promoting improvements in contractile performance after reperfusion (19,20).…”

“…lactate; mitochondrial membrane protein; myocardial ischemia; reperfusion EVALUATION OF HYPOTHERMIC myocardial protection has occurred predominantly in experimental models employing reductions in coronary flow to reduce oxygen supply. Exposure to mild or moderate hypothermic insult promotes cross-tolerance to variable forms of subsequent injury, particularly those produced by ischemia and/or reperfusion (19,21). A reduction in ATP utilization rate initiated by hypothermia persists during rewarming and plays a central role in preserving myocardial function after ischemia and reperfusion (20).…”

“…A reduction in ATP utilization rate initiated by hypothermia persists during rewarming and plays a central role in preserving myocardial function after ischemia and reperfusion (20). Hypothermic ATP preservation may promote specific molecular responses observed during reperfusion in the isolated rabbit heart model, including stabilization of steady-state mRNA levels for nuclear-encoded mitochondrial membrane proteins, enhanced induction of the stress protein heat shock protein-70 (HSP70) (19,21,22) and promotion of signaling for antiapoptotic pathways (18).…”