Aged Mouse Hearts Research Articles

Overexpression of MnSOD reduces oxidative stress and pro‐apoptotic signaling in the aging mouse heart

The aging heart is characterized by increased oxidative stress and cell loss via apoptosis and necrosis. Aging increases apoptotic signaling (e.g., Bax, caspase-3 cleavage), in the heart while caloric restriction and exercise retard apoptosis. The Mn isoform of superoxide dismutase (Mn-SOD) may reduce oxidative stress, ischemia-reperfusion injury, and apoptosis. We hypothesized that MnSOD overexpression using a transgenic mouse model would reduce markers of oxidative stress and apoptosis in the aging left ventricle. Hearts were extracted from young (8 mo) wild type (YWT), young MnSOD transgenic (YTg), old (28 mo) wild-type (OWT), & old MnSOD transgenic (OTg) mice. Higher MnSOD protein expression in the left ventricle was confirmed in both young YTg and OTg. Pro-apoptotic Bax and cleaved caspase-3 as well as oxidative stress marker 4-hydroxynonenal adducts (4-HNE) were measured using Western blot analysis. Total hydroperoxides were determined using the ferrous oxide-xylenol orange technique. Aging increased 4-HNE (+37%), while MnSOD overexpression reduced both 4-HNE (−36%) and total hydroperoxides (−27%) in the OTg left ventricle. Cleaved caspase-3 levels were greater (+27%) in OWT than YWT, while MnSOD overexpression reduced cleaved caspase-3 levels (−40%). In addition, Bax protein expression was 32% lower in OTg than OWT. These data indicate that MnSOD overexpression reduces oxidative stress and pro-apoptotic signaling in the aging mouse heart. Supported by Texas American Heart Association (GIA # 0555064Y)

T-Cell Receptor Vβ8.1 Peptide Reduces Coxsackievirus-Induced Cardiopathology in Aged Mice

Viral myocarditis is an important cause of heart failure and cardiomyopathy. Immunosenescence, characterized by a dramatic reduction in immune responsiveness, can increase susceptibility to cardiopathology from viral infections. The T-cell receptor (TCR) Vbeta 8.1 peptide, a 16-mer peptide, has shown immuno-regulating and immunostimulating effects in viral-induced immunodeficiency. In our study, 18-mo-old C57Bl/6 female mice were treated twice with TCR Vbeta8.1 peptide and 10 d before sacrifice were injected ip with coxsackievirus B3. Cardiac histopathology was assessed for lesion severity. Splenocyte cyto-kine production (interleukin-2, -4, -6, interferon-gamma) and heart viral titers were determined. Our data suggest that immunosenescence suppressed both T helper (Th1) and Th2 cytokine production and that treatment with TCR Vbeta8.1 peptide induced cytokine stimulation close to levels seen in young mice. Nontreated aged mice developed some degree of myocarditis (75% mild and 25% severe), whereas only 35% of the peptide-treated aged group developed cardiopathology, with 25% being mild and 10% severe. Heart tissue from nontreated aged mice infected with coxsackievirus had a higher viral titer than hearts of aged mice equally infected but treated with the peptide. In conclusion, TCR Vbeta8.1 peptide induced immunoregulation, and inhibited or reduced coxsackievirus B3-induced cardiopathology in aged mice.

Chronic exposure to morphine produces a marked cardioprotective phenotype in aged mouse hearts

Aging is often associated with decreased myocardial ischemic tolerance. We recently reported that chronic preconditioning produced by continuous exposure to morphine affords a profound cardioprotective phenotype in young mice. In this study, we determined if chronic exposure to morphine retained its ability to precondition the myocardium in the young or aged heart. Young (10–14 weeks) or aged (24–26 months) C57/BL6 mice were untreated, administered morphine acutely (30 μM), or implanted with a morphine pellet (75 mg) for 5 days prior to heart isolation and perfusion. Following equilibration, perfused hearts were subjected to 25 min ischemia and 45 min reperfusion. Untreated hearts from both young and aged mice displayed marked contractile dysfunction and LDH release following reperfusion. Acute infusion of morphine improved recovery of end-diastolic pressure and developed pressure in young ( P<0.05 vs. untreated) but not senescent hearts. Hearts from mice exposed to morphine for 5 days displayed a further improvement in post-ischemic contractile function ( P<0.05 vs. acute treatment), and a marked reduction in post-ischemic LDH efflux ( P<0.05 vs. untreated) in both young and senescent hearts. These data demonstrate that aged hearts maintain the ability to be preconditioned by chronic exposure to morphine in the absence of acute protection.

Age-associated Differences in Cardiovascular Inflammatory Gene Induction during Endotoxic Stress

Upon physiological stress, families of stress response genes are activated as natural defense mechanisms. Here, we show that induction of specific inflammatory genes is significantly dysregulated and altered in the heart of aged (24--26-month-old) versus young (4-month-old) mice experimentally challenged with a bacterial endotoxin, lipopolysaccharide (LPS, 1.5 mg/kg of body mass). Whereas the LPS-mediated induction of cardiac mRNA for tumor necrosis factor alpha or inducible nitric-oxide synthase showed no age-associated differences, the induction of interleukin-1 beta (IL-1 beta) and intracellular adhesion molecule-1 was modestly extended with aging, and the induction of IL-6 was significantly prolonged with aging. This age-associated phenomenon occurred gradually from 4 to 17 months of age and became more evident after 23 months of age. The age-associated augmentation of the cardiac IL-6 induction was also dramatic at the protein level. Immunohistochemically, the LPS-induced cardiac IL-6 was localized mainly in the microvascular walls. Aged but not young mice showed a high mortality rate during these experiments. These results demonstrate that endotoxin-mediated induction of specific inflammatory genes in cardiovascular tissues is altered with aging, which may be causally related to the increased susceptibility of aged animals to endotoxic stress.

Impaired lusitropy-frequency in the aging mouse: role of Ca(2+)-handling proteins and effects of isoproterenol.

We examined the relationship between age-associated lusitropic impairment, heart rate, and Ca(2+)-handling proteins and assessed the efficacy of increasing left ventricular (LV) relaxation via beta-adrenergic stimulation in adult and aging mouse hearts. LV function was measured in isolated, isovolumic blood-perfused hearts from adult (5 mo), old (24 mo), and senescent (34 mo) mice. Hearts were paced from 5 to 10 Hz, returned to 7 Hz, exposed to 10(-6) M isoproterenol, and paced again from 7 to 10 Hz. Age-related alterations in Na(+)/Ca(2+) exchanger (NCX), sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a), and phospholamban (PLB) levels were assessed by immunoblot. Despite preserved contractile performance, aging caused impaired lusitropy. Increased pacing caused an elevation in end-diastolic pressure that progressively worsened with age. The time constant of isovolumic pressure decay (tau) was significantly prolonged in old and senescent hearts compared with adults. Relative to adult hearts, the SERCA2a-to-PLB ratios were reduced 68 and 69%, and NCX were reduced 37 and 58% in old and senescent hearts, respectively. Isoproterenol completely reversed the age-associated lusitropic impairments. These data suggest that impaired lusitropy in aging mouse hearts is related to a decreased rate of cytosolic Ca(2+) removal and that accelerating SR Ca(2+) resequestration via beta-adrenergic stimulation can reverse this impairment.

Carnitine palmitoyl transferase-I activity in the aging mouse heart

We investigated the influence of age on carnitine palmitoyl transferase-I (CPT-I, EC 2.3.1.21) activity in the mouse heart. There was an age-associated decrease in CPT-I activity from 2 to 26 months ( P = 0.006). We studied the effect of oxygen-derived radicals on CPT-I activity. Mitochondria from 2-month-old mouse hearts exposed to different concentrations of hydrogen peroxide (H 2O 2) showed a dose-related decrease in CPT-I activity ( P < 0.002). To determine the possible reversibility of the age change in CPT-I activity, we studied the effect of oral administration of propionyl-L-carnitine (PLC). Oral pretreatment of middle-aged (18-month-old) mice with PLC resulted in a 37% increase of basal CPT-I activity ( P < 0.05) compared to age-matched untreated animals, and restored it to a level similar to that of 2-month-old mice. Pretreatment of senescent (26-month-old) mice with PLC, however, showed no significant change in basal CPT-I activity. It is possible that the age-related decrease in CPT-I activity may result from an in vivo accumulation of oxygen-derived radical damage. It appears that the age change in CPT-I activity in 18- but not in the 26-month-old mice is reversible with PLC.

Voluntary wheel running exercise and monoamine levels in brain, heart and adrenal glands of aging mice

The goals of this study were to examine the effects of three months of voluntary wheel-running exercise on life span, whole body and brain, heart and adrenal weights and biogenic amine content (norepinephrine, dopamine, epinephrine and serotonin) in three age groups of male mice. The three groups consisted of mature (9 months), middle-aged (19 months), and old (27–29 months) mice. No significant differences in weight were found between control and exercise or age. The oldest mice had a survival rate of 69% for the exercise group and 43% for the age matched controls when the exercise phase was completed. Locomotor activity was significantly reduced for the old mice compared to the middle-age and mature mice. Only the mature (12 months of age at sacrifice) exercised mice showed a cardiac and adrenal hypertrophy (about 10%). There was a moderate increase in norepinephrine content in the ventral hypothalamus of the brain with exercise (significant at 12 months of age). Biogenic amine content in other regions of the brain (brain stem and forebrain minus hypothalamus) was not affected by age and/or exercise. There was a significant decrease in heart norepinephrine content with exercise in old mice (30–32 months). Adrenal gland norepinephrine content was significantly increased by exercise at 12 months of age and decreased at 22 months of age. Our results suggest that an increase in norepinephrine content in the hypothalamus might be a manifestation of an adaptation to the increased demands upon hypothalamic noradrenergic terminals imposed by prolonged exercise. It is also apparent that aging and exercise alters the amounts of sympathetic transmitter of the heart and adrenal glands. Such alteration may be beneficial to the aging brain by retaining norepinephrine stores that normally decline with age.

Effects of long-term running stress on the ultrastructure of the aging mouse heart.

Apical regions of the left ventricular myocardium of female C57BL/6J mice, aged between 6 and 27 months, that had been subjected to endurance running for 2, 10 or 15 months, were examined by light and electron microscopy. Focal degenerative changes were found in myocytes of these experimental mice, including loss of myofibrils, erosion of myocytes and changes in nuclei, lipofuscin content and mitochondria. The interstitial connective tissue showed an increase in collagen in aged myocardia. Endurance-trained runners frequently showed signs of platelet aggregation or microthrombi in small capillaries associated with myocytes. These were most common in endurance-trained middle-aged and very elderly mice, but were not found in sedentary age-matched controls. Our experiments indicate that running stress may be damaging to cardiac tissue in aged animals. Our findings may be of significance in helping the understanding of the development and the etiology of stress-induced cardiovascular damage in the elderly.

Glycogenolysis during anoxia in aged mouse heart.

Myocardial glycogen mobilization in response to anoxia has been studied in open-chested C57Bl/6NCrl male mice 6 and 24 months of age. During the 1st minute without oxygen, old animals utilized glycogen more rapidly than did young animals. However, during the 2nd minute of anoxia, young animals continued to utilize cardiac glycogen, whereas old animals did not. A direct correlation was noted between glycogen utilization and activation of myocardial phosphorylase activity (A+B forms). Moreover total myocardial phosphorylase declined during anoxia in old animals while showing no significant change in their younger counterparts. This age-related defect in glycogen mobilization suggests altered tolerance to anoxia in aged animals. The inability to mobilize myocardial glycogen may stem from the existence of an altered form of phosphorylase or from an altered environment in the aged heart.

Comparison of cytoplasmic superoxide dismutase in liver, heart and brain of aging rats and mice

Comparisons of the specific activity of cytoplasmic superoxide dismutase, in homogenates of liver, brain and heart demonstrate considerably reduced activity in livers of aging rats and mice, a very small reduction in specific activity in the heart and no reduction in the brain of aging animals. Antisera elicited in rabbits against purified superoxide dismutase from liver of either young or old rats revealed complete cross-reactivity with the heart and brain enzymes. They also exhibited complete cross-reactivity with the mouse enzymes from all three organs. This finding has, for the first time, enabled a comparison of possible age-dependent alterations in the same enzyme antigen in different cell types. Despite the differences in age-related changes in specific activity in homogenates of liver, heart and brain the enzyme shows a considerable decline in catalytic activity per antigenic unit in all three organs in both aging rats and mice.