Influence of myocardial damage on gene expression of cyclic adenosine monophosphate signal transduction in rats

Abstract

Objective To investigate the relationship between alteration of gene in cyclic adenosine monophosphate（cAMP） signal transduction system in rats after myocardial damage and changes of cardiac function and ventricular remodeling. Methods Twenty eight male Wistar rats weighing 220 g to 250 g were randomly divided into three groups： acute myocardial damage group（AMD, n = 10）, chronic myocardial damage group （CMD,n = 9 ） and sham-operation group （control, n = 9）. Animal model of acute myocardial damage was established by ligation of rats left coronary artery in the AMD and the CMD groups. Rats in control group were treated similarly, except that the coronary suture was not tied. Hemodynamics and echocardiography were measured before rats were sacrificed 24 hours after operation in control and AMD groups but those in CMD groups were sacrificed 8 weeks later. Cadiocyte apoptosis were estimated by TUNEL method, cAMP levels in heart were tested by radioimmunity and the mRNA expressions for inducible cAMP early repressor （ICER）, cAMP response element binding protein （CREB）, phosphodiesterase 3A （PDE3A） and bcl-2 were assayed by real-time quantitative reverse transcriptase polymerase chain reaction （RT-PCR）. Results The difference of left ventricular end diastolic diameter （LVEDD）, left ventricular end diastolic pressure（LVEDP）, maximal rising and falling rate of ventricular pressure,left ventricular systolic pressure （LVSP）, eject fraction （EF） and fraction shortening （FS） were statistically significant among the three groups（F = 285.9, 196.8, 83.2, 80.4, 54.9, 196.6, 95.2, all P 〈 0.01）. LVEDD[（7.03 ±0.28）, （8.20 ± 0.27）mm] and LVEDP[（11.19 ± 2.89）, （19.76 ± 3.34）mmHg] in AMD and CMD groups were significantly increased, compared with those in control group[ （5.05 ± 0.30）mm, （- 5.62 ± 3.01 ）mmHg, all P 〈0.01 ]. While maximal rising rate[ （2964 ± 449）, （2214 ± 434）mmHg/s] and falling rate[（- 2617 ± 441）,（- 1891± 424）mmHg/s] of left ventricular pressure, LVSP[ （94.19 ± 4.03）, （85.85 ± 6.39）mmHg], EF[ （41.6 ±5.9）%, （35.9 ± 4.1 ）%] and FS[ （36.9 ± 4.6）%, （23.1 ± 4.9）%] of left ventricular in the two groups were lower than those in control[（4759 ± 406）mmHg/s, （- 4327 ± 388）mmHg/s, （116.29 ± 8.25）mmHg, （80.9 ± 5.6）%,（53.1 ± 4.3）%, all P 〈 0.01 ]. These changes in CMD group were more significant than those in AMD groups（P 〈0.05 or P 〈 0.01 ）. The difference of apoptotic index, cAMP and expression of ICER, CREB, PDE3A mRNA and bcl-2 mRNA were statistically significant among the three groups（F= 172.5, 141.0, 540.8, 246.8, 165.1, 563.9,all P〈 0.01 ）. Apoptotic index[ （32.8 ± 4.2）‰, （18.4 ± 3.9）‰] and cAMP in heart[ （9.95 ± 0.30）, （5.60 ± 0.25）nmol/kg] in AMD and CMD groups were increased compared to control group[ （3.9 ± 1.7）‰, （2.48 ± 0.29）nmol/kg,all P 〈 0.01 ], and those in CMD group were lower than in AMD group（all P 〈 0.01 ）. Expression of ICER mRNA （1.434 ± 0.093, 0.942 ± 0.076） and CREB mRNA（5.70 ± 0.50, 2.64 ± 0.51） in AMD and CMD groups were higher, and expression of PDE3A mRNA（48.98 ± 8.14, 16.68 ± 8.46） were lower than those in control group （0.154 ± 0.063, 1.08 ± 0.35, 105.94 ± 12.61, all P 〈 0.01 ）. The three genes in CMD group were fewer than those in AMD group（all P 〈 0.01 ）. bcl-2 mRNA was up regulated in AMD group（4.55 ± 0.27） and was down regulated in CMD group（0.35 ± 0.15） compared to control（2.18 ± 0.30, all P〈 0.01）. Conclusions There is PDE3A-ICER positive-feedback loop leading to myocyte apoptosis and heart failure after myocardial damage. The downregulation of PDE3A mRNA observed in chronic myocardial damage may play a causative role in the progression of ventricular remodeling and heart failure, in part, by inducing ICER mRNA and promoting cardiac myocyte dysfunction. Key words: Myocardial damage; Inducible cyclic adenosine monophosphate early repressor; Phosphodiesterase 3A; Cyclic adenosine monophosphate