Search

Pressure overload-induced cardiac hypertrophy leads to decreased contractile performance, frequently progressing to heart failure. Cardiac hypertrophy and heart failure can be accompanied by the so-called sick thyroid syndrome, resulting in decreased serum T(3) levels along with decreased expression of thyroid hormone receptors (TRalpha1 and TRbeta1) and sarco(endo)plasmic reticulum Ca-ATPase (SERCA). Because the binding of T(3) occupied receptors to the thyroid response elements in the SERCA promotor can increase gene expression, we wanted to determine whether increasing TR expression in the hypertrophied heart could also improve SERCA expression and cardiac function. Mice subjected to aortic constriction to generate pressure overload-induced hypertrophy were also subjected to gene therapy using adeno-associated virus (AAV) expressing either TRalpha1 or TRbeta1, with LacZ expressing AAV serving as control. After 8 wk of aortic constriction, a similar degree of hypertrophy was observed in all three groups; however, mice treated with TRalpha1 or TRbeta1 showed improved contractile function. Administration of a physiological dose of T(3) increased serum T(3) levels only into the lower range of normal. This T(3) dose, with or without AAV TR treatment, did not result in any significant increase in contractile performance. Calcium transients measured in isolated myocytes also exhibited an enhanced rate of decay associated with TRalpha1 or TRbeta1 treatment. Western blot analysis showed increased SERCA expression in the TRalpha1- or TRbeta1-treated groups relative to the LacZ-treated control group. These results demonstrate that increasing TR expression in the hypertrophied heart is associated with an improvement in contractile function and increased SERCA expression.

Inducible heat shock protein 70 (HSP70i) has been shown to exert a protective effect in hearts subjected to ischemia-reperfusion. Although studied in heat-shocked animals and in transgenic mice that constitutively overexpress the protein, the therapeutic application of the protein in the form of a viral vector-mediated HSP70i expression has not been widely examined. Accordingly, we have examined the effects of HSP70i delivered in vivo to the left ventricular free wall of the heart via viral gene therapy in mice. The affect of virally mediated HSP70i expression in preserving cardiac function following ischemia-reperfusion was examined after short-term expression (5-day adenovirus mediated) and long-term expression (8-mo adeno-associated virus mediated) in mice by subjecting ex vivo Langendorff perfused hearts to a regime of ischemia-reperfusion. Both vectors were capable of increasing HSP70i expression in the heart, and neither vector had any effect on cardiac function during aerobic (preischemic) perfusion when compared with corresponding controls. In contrast, both adenovirus-mediated and adeno-associated virus-mediated expression of HSP70i improved the contractile recovery of the heart after 120 min of reperfusion following ischemia. This study demonstrates the feasibility of using both short- and long-term expression of virally mediated HSP70i as a therapeutic intervention against cardiac ischemia-reperfusion injury.

Although it is known that insulin-dependent (type 1) diabetes results in depressed contractile performance associated with diminished sarcoendoplasmic reticular Ca2+-ATPase (SERCA2a) activity, findings in insulin-resistant (type 2) diabetes suggest a less clear association. The db/db insulin-resistant mouse model exhibits decreased cardiac performance both in situ and in isolated ex vivo working hearts. In this study, contractile performance and calcium transients were measured in Langendorff-perfused hearts and isolated cardiac myocytes. Diabetic (db/db) mouse hearts demonstrated decreased rates of contraction, relaxation, and pressure development. Calcium transients from isolated myocytes revealed significantly lower diastolic and systolic levels of calcium in diabetic hearts. Furthermore, the decay rate of the calcium transient was significantly reduced in diabetic myocytes, suggesting a diminished capacity for cytosolic calcium removal not associated with a change in sodium-calcium exchanger activity. Calcium leakage from the sarcoplasmic reticulum (SR) measured using tetracaine was significantly increased in diabetic myocytes. Western blot analysis indicated only a small decrease in SERCA2a expression in diabetic mice, but a large increase in phospholamban expression. Expression of the ryanodine receptor did not differ between groups. In conclusion, the decreased contractile function observed in the db/db diabetic mouse model appears to be related to decreased calcium handling by the SR.

Objective: Prolonged cardiac contraction and relaxation in hypothyroidism are in part related to diminished expression of the gene coding for the calcium pump of the sarcoplasmic reticulum (SERCA2a). Therefore, we examined whether or not transgenic SERCA2a gene expression in mice may compensate for the cardiac effects of hypothyroidism., Methods: SERCA2a mRNA and protein were analyzed from hearts of euthyroid and hypothyroid mice of wild-type or SERCA2a transgene status. Contractile function was studied in isolated left ventricular papillary muscles., Results: We found significant decreases of SERCA2a mRNA and protein levels in hearts of hypothyroid wild-type mice in comparison with euthyroid wild-type mice (controls). Papillary muscles from hypothyroid wild-type mice showed significant increases in time to peak contraction and relaxation times compared with controls. In contrast, SERCA2a mRNA and protein levels were significantly higher in hypothyroid SERCA2a transgenic mice than in hypothyroid wild-type mice. The transgene led to a functional improvement by compensating for the prolonged contraction and relaxation of papillary muscles., Conclusions: Our murine model of hypothyroidism revealed decreases in SERCA2a gene expression accompanied by prolonged contraction and relaxation of papillary muscles, and an improvement of the contractile phenotype due to compensated SERCA2a gene expression in SERCA2a transgenic mice.