The AMPK Activator Aicar Ameliorates Age-Dependent Myocardial Injury in Murine Hemorrhagic Shock

Abstract

The development of myocardial dysfunction in patients with hemorrhagic shock is significantly impacted by the patient age. AMP-activated protein kinase (AMPK) is a pivotal orchestrator of energy homeostasis, which coordinates metabolic recovery after cellular stress. We investigated whether AMPK-regulated pathways are age-dependent in hemorrhage-induced myocardial injury and whether AMPK activation by 5-amino-4-imidazole carboxamide riboside (AICAR) affords cardioprotective effects. Anesthetized C57/BL6 young (3–5 months old) and mature male mice (9–12 months old) were subjected to hemorrhagic shock by blood withdrawing followed by resuscitation with shed blood and Lactated Ringer’s solution. Mice were sacrificed at 3 hours after resuscitation, and plasma and hearts were harvested for biochemical assays. Vehicle-treated mature mice exhibited higher myocardial injury and higher levels of plasma biomarkers of cardiovascular injury (endocan and follistatin) when compared with young mice. Cardiac cell mitochondrial structure was also markedly impaired in vehicle-treated mature mice when compared to young mice. At molecular analysis, an increase of the phosphorylated catalytic subunit pAMPKα was associated with nuclear translocation of the peroxisome proliferator-activated receptor γ co-activator-α in young, but not mature mice. No changes in autophagy were observed as evaluated by the conversion of the light-chain (LC)3B-I protein to LC3B-II form. Treatment with AICAR ameliorated myocardial damage in both age groups. However, AICAR therapeutic effects were less effective in mature mice compared to young mice and involved distinct mechanisms of action. Thus, our data demonstrate that during hemorrhagic shock AMPK-dependent metabolic mechanisms are important for mitigating myocardial injury. However, these mechanisms are less competent with age.

Metformin ameliorates gender-and age-dependent hemodynamic instability and myocardial injury in murine hemorrhagic shock

“…These data are in apparent discrepancy with our previous data demonstrating that another AMPK activator, AICAR, was able to provide beneficial effects in both young and adult male mice [20,21]. It must be noted, however, that the molecular mechanisms of metformin may extend beyond the activation of the AMPK metabolic pathway.…”

“…It consists of three subunits: one catalytic α-subunit, which is activated by phosphorylation, and two regulatory β- andγ subunits [14,16,40]. Consistent with our previous findings [20], we observed that there was an age-dependent dysregulation of AMPK activation in the cytosol and nuclear compartments in hearts of male mice after hemorrhagic shock. On the contrary, in female mice of both ages pAMPKα was significantly elevated in the cytosol, but not the nuclear compartment.…”

“…We have previously reported that in murine models of hemorrhagic shock the degree of severity and pathophysiologic characteristics of myocardial and lung injury are age-dependent [20,21]. In this study, we have extended our investigation to gender-related responses and we have demonstrated that male gender is also a variable for heightened cardiovascular inflammation and injury.…”

“…Either the left or right femoral artery was cannulated (PE-10 tube) and connected to a blood pressure transducer (PowerLab, ADInstruments, Colorado Springs, CO) for measurement of mean arterial blood pressure (MABP) and heart rate (HR). Hemorrhagic shock was induced by blood removal until mean arterial blood pressure (MABP) reached 30±5 mmHg [20–22]. The mice were kept in this MABP range for 90 minutes by additional blood removal or small volume transfusion.…”

“…In previous experimental studies, we have demonstrated that AMPK-dependent metabolic mechanisms become dysfunctional with aging and correlate with myocardial and lung injury in mature adult male mice when compared with young animals after hemorrhagic shock [20,21]. To further understand the underlying molecular mechanisms of cardiovascular function during hemorrhagic shock, the purpose of our study was to investigate both age- and gender-dependent mechanisms of the hemodynamic compromise and systemic inflammatory response in a clinically relevant model of hemorrhagic shock in young (3–5 months old) and middle-aged mature (9–12 months old) mice.…”