SummaryEvidence suggests that aging, per se , is a major risk factor for cardiac dysfunction. Oxidative modification of cardiac proteins by non-enzymatic glycation, i.e. advanced glycation endproducts (AGEs), has been implicated as a causal factor in the aging process. This study was designed to examine the role of aging on cardiomyocyte contractile function, cardiac protein oxidation and oxidative modification. Mechanical properties were evaluated in ventricular myocytes from young (2-month) and aged (24 -26-month) mice using a MyoCam® system. The mechanical indices evaluated were peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening/relengthening (± ± ± ± dL/dt). Oxidative stress and protein damage were evaluated by glutathione and glutathione disulfide (GSH/GSSG) ratio and protein carbonyl content, respectively. Activation of NAD(P)H oxidase was determined by immunoblotting. Aged myocytes displayed a larger cell cross-sectional area, prolonged TR90, and normal PS, ± ± ± ± dL/ dt and TPS compared with young myocytes. Aged myocytes were less tolerant of high stimulus frequency (from 0.1 to 5 Hz) compared with young myocytes. Oxidative stress and protein oxidative damage were both elevated in the aging group associated with significantly enhanced p47 phox but not gp91 phox expression. In addition, level of cardiac AGEs was ∼ ∼ ∼ ∼ 2.5-fold higher in aged hearts than young ones determined by AGEs-ELISA. A group of proteins with a molecular range between 50 and 75 kDa with pI of 4 -7 was distinctively modified in aged heart using one-or two-dimension SDS gel electrophoresis analysis. These data demonstrate cardiac diastolic dysfunction and reduced stress tolerance in aged cardiac myocytes, which may be associated with enhanced cardiac oxidative damage, level of AGEs and protein modification by AGEs.

Ceylan-Isik, Asli F., Karissa H. LaCour, and Jun Ren. Sex difference in cardiomyocyte function in normal and metallothionein transgenic mice: the effect of diabetes mellitus. J Appl Physiol 100: 1638-1646, 2006. First published January 12, 2006 doi:10.1152/japplphysiol.01273.2005.-Evidence suggests a sex difference in intrinsic physiological and diabetic myocardial contractile function related to antioxidant properties of female ovarian hormones. This study was designed to examine the effect of cardiac overexpression of antioxidant metallothionein on intrinsic and diabetic cardiomyocyte function. Weight-matched wildtype (FVB) and metallothionein transgenic mice of both sexes were made diabetic with streptozotocin (220 mg/kg). Contractile and intracellular Ca 2ϩ properties were evaluated including peak shortening (PS), time to PS, time to 90% relengthening (TR90), maximal velocity of shortening or relengthening (ϮdL/dt), fura-2 fluorescence intensity change, and Ca 2ϩ decay rate. Akt and transcription factor c-Jun levels were evaluated by Western blot. Myocytes from female FVB mice exhibited lower PS, ϮdL/dt, and fura-2 fluorescence intensity change, prolonged time to PS, TR 90, and Ca 2ϩ decay compared with male FVB mice. Interestingly, this sex difference was not present in metallothionein mice. Diabetes depressed PS, ϮdL/dt and caffeineinduced Ca 2ϩ release, as well as prolonged TR90 and Ca 2ϩ decay in male FVB mice, whereas it only reduced PS in female FVB mice. These diabetic dysfunctions were nullified by metallothionein in both sexes. Females displayed elevated Akt phosphorylation and reduced c-Jun phosphorylation. Diabetes dampened Akt phosphorylation in male FVB mice and enhanced c-Jun in both sexes. Diabetes-induced alterations in Akt phosphorylation and c-Jun were abolished by metallothionein. The sex difference in Akt phosphorylation but not c-Jun levels was reversed by metallothionein. These data indicate that antioxidant capacity plays an important role in sex differences in both intrinsic and diabetic cardiomyocyte contractile properties possibly related to phosphorylation of Akt and c-Jun. myocyte shortening; Akt; c-Jun DIABETIC CARDIOMYOPATHY, a unique deterioration of myocardial function found in the diabetic population, is a prominent form of diabetic complications independent of macro-and microvascular complications of diabetes mellitus (9, 23). It is characterized by impaired ventricular contraction, relaxation, and wall compliance (9,23,24,41). Both clinical and experimental evidence has revealed impaired intracellular Ca 2ϩ homeostasis, reduced contractility, prolonged duration of contraction and relaxation associated with enhanced free radical accumulation, and oxidative damage in the heart (7,9,11,12,22,24,31,32,41). Interestingly, a "female advantage" exists in premenopausal women with regard to the propensity and severity of diabetic heart diseases (23, 35, 36). Sex differences in myocardial and cardiomyocyte contractile function have long been established, mainly manifested as differe...

1. Clinical, epidemiological and experimental evidence suggests a 'female advantage' in the progression of cardiovascular diseases, including diabetic cardiomyopathy. It is speculated that this 'gender bias' may be due to gender-related differences in sex hormones and intrinsic myocardial contractile properties. 2. The present study was designed to examine the impact of diabetes and gender on cardiac contractile function and activation of the cardiac survival signalling molecule Akt. Short-term (2 weeks) diabetes was induced in adult mice of both genders with streptozotocin (STZ). Mechanical and intracellular Ca(2+) properties of isolated ventricular myocytes were evaluated using an IonOptix MyoCam system (IonOptix Corporation, Milton, MA, USA). Total and phosphorylated Akt were evaluated using western blot analysis. 3. Female mouse myocytes displayed smaller peak shortening (PS) amplitude and maximal velocity of shortening/relengthening (+/-dL/dt), longer time to PS and time to 90% relengthening compared with male counterparts. Diabetes significantly reduced PS, +/-dL/dt, prolonged TR(90), delayed intracellular Ca(2+) clearing and reduced sarcoplasmic reticulum (SR) Ca(2+) release in male mouse myocytes. All these abnormalities, with the exception of SR Ca(2+), release were masked by the female gender. 4. The negative staircase of PS with increased stimulus frequency (from 0.1 to 5.0 Hz) and protein carbonyl damage were comparable among all animal groups. 5. Female gender and diabetes independently enhanced phosphorylation of Akt without affecting total Akt expression. Interestingly, STZ-induced short-term diabetes failed to elicit additional phosphorylation of Akt in female hearts. 6. In summary, the present data revealed that STZ induced impaired cardiac contractile function and altered intracellular Ca(2+) handling in males, but not females, partially due to intrinsic mechanical differences and Akt activation status between genders.

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