Key result
Cardiac-directed AC(VI) expression increases myocyte cAMP production ~160% in response to forskolin.
Why the study?
Previous models using constitutively active transgenes for cardiac-directed AC(VI) expression may have confounding interactions during development, necessitating a controlled expression model.
Absolute Event Rate: 39% vs 15%
p-value: p=0.004
Controlled cardiac-directed expression of AC(VI) in a transgenic mouse model successfully increases cardiac myocyte cAMP generation and left ventricular contractile function.
New inducible ACVI model avoids developmental confounds; leaves open translation to human HF therapy.
OBJECTIVE: We have previously shown that cardiac-directed expression of adenylycyclase type VI (AC(VI)) increases heart function in transgenic mice, and improves heart function and survival in murine cardiomyopathy. However, a potential problem of crossbreeding paradigms that use lines with two constitutively active transgenes is that results can be obfuscated by interactions between transgenes during growth and development. METHODS: To develop a model that could be used subsequently to address this generic problem, transgenic mice with tetracycline (tet)-regulated cardiac-specific expression of AC(VI) were generated. In this transgenic strain, the expression of a tet-controlled transactivator (tTA) was under control of the rat alpha-myosin heavy chain promoter. Expression of the AC(VI) gene was driven by a tet-response element (TRE) and a minimal CMV promoter. RESULTS: Homogenates of hearts showed no change in AC(VI) protein content during tet suppression (doxycycline), confirming successful suppression of transgene expression. Removal of tet suppression for 10 days was associated with a 10-fold increase in cardiac AC(VI) protein content. A similar increase in mRNA was observed (Northern blot analysis). The estimated half-life of newly synthesized cardiac AC(VI) protein was 2-3 days. Isolated cardiac myocytes from animals that had tet-suppression removed for 10 days showed increased cAMP production in response to forskolin stimulation (Transgene Off: 15+/-6 fmol/microg; Transgene On: 39+/-14 fmol/microg; n=5 each group; P=0.004) and also to isoproterenol stimulation (Transgene Off: 20+/-5 fmol/microg; Transgene On: 31+/-12 fmol/microg; n=5 each group; P=0.035) and hearts isolated from these animals showed marked increased left ventricular peak dP/dt in response to dobutamine stimulation (P=0.009) indicating that inducible cardiac AC(VI) is functionally coupled and recruitable. CONCLUSION: We have generated transgenic mice with controlled cardiac-specific expression of AC(VI), provided detailed information regarding the kinetics of transgene expression and suppression and estimated the half-life of cardiac AC(VI) protein to be 2-3 days. Finally, we have shown, for the first time, that controlled cardiac-directed expression of a transgene can increase cardiac myocyte cAMP generation and left ventricular contractile function.
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Gao et al. (2002) studied Transgenic mice model for cardiac function. Controlled cardiac-directed expression of AC(VI) (removal of tet suppression) vs. Tet suppression (Transgene Off) was evaluated on cAMP production in response to forskolin stimulation (fmol/microg) (p=0.004). Controlled cardiac-directed expression of AC(VI) significantly increased cardiac myocyte cAMP production in response to forskolin stimulation (39+/-14 vs 15+/-6 fmol/microg; P=0.004).
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