Transforming Growth Factor-β Function Blocking Prevents Long-Term Intensive Exercise Training-induced Cardiac Fibrosis in Rat Model

Abstract

Background: Long-term intensive exercise training induces myocardial fibrosis, which acts as an arrhythmogenic substrate. Transforming growth factor (TGF)-β pathway causes myocardial fibrosis in various cardiac diseases. The purposes of this study were to: 1) confirm vigorous exercise-induced cardiac fibrosis and 2) examine the effect of TGF-β function blocking on cardiac structure/function and pathologic collagen deposition in a chronic intensive exercise rat model. Methods: Male Wistar rats weighing 100 to 125 g were randomly assigned to three groups: time-matched sedentary control (S-control, n=10), exercise+dimethyl sulfoxide (DMSO) [exercise control (E-control, n=5; one dropped out)] and exercise+TGF-β antagonist (TGF-β function blocking group, n=5). The exercise groups performed intensive exercise on a treadmill for 12 weeks after two weeks of conditioning. Transthoracic echocardiography was performed at the beginning and at the endpoint of exercise training under anesthesia. At the endpoint, the hearts were harvested after euthanasia and weighed. Collagen deposition in all cardiac chambers was quantified after Masson’s Trichrome stain. Biochemical studies [ribonucleic acid (RNA) of TGF-β1, fibronectin-1, matrix metalloproteinase-2 (MMP-2), of tissue inhibitors of metalloproteinase-1 (TIMP-1), collagen-Ia1, -Ia2 and –IIIa1 in all four cardiac chambers] for pathologic collagen deposition were performed with real-time polymerase chain reaction. Results: Chronic intensive exercise training (the E-control and TGF-β function blocking group) results in less increase in body weight and left ventricular (LV) wall thickening and dilation (p<0.05 for all) without significant change in ejection fraction or heart weight compared with the S-control group. Myocardial fibrosis quantity significantly increased in all cardiac chambers in the E-control group (p<0.001 compared to S-control). Of note, in the TGF-β function blocking group, pathologic collagen deposition was significantly lower than the E-control group (p<0.001) in all cardiac chambers. RNA analysis results were variable: TGF-β did not differ significantly among the three groups; MMP-2 values from left ventricle (LV) and right atrium (RA) were significantly lower in the S-control compared with the E-control (p<0.001 in LV and p=0.006 in RA) and TGF-β function blocking group (p=0.005 in LV and p=0.006 in RA), whereas other values were did not differ in intergroup comparison. Figronectin-1 values were similar in all cardiac chambers and TIMP values from LV and RA were significantly lower in the S-control group than the E-control (p=0.020 in LV and p=0.002 in RA) and TGF-β function blocking group (p=0.045 in LV and p=0.004 in RA), while other values were not remarkable. Collagen-Ia1, -Ia2 and IIIa1 values from LV and RA were significantly lower in the S-control group than the E-control group (p=0.019, p<0.001 and p=0.005 for LV and p=0.004, p<0.001 and p=0.010 for RA, respectively). When comparing values between the E-control and TGF-β function blocking group, no collagen subtypes differed significantly. Comparing the S-control and TGF-β function blocking group, collagen-Ia1 from RA (p=0.005), collagen-Ia2 from RA (p=0.001) and collagen-IIIa1 from LV (p=0.010) were significantly lower. Conclusion: TGF-β function blocking ameliorates the heart fibrosis induced by long-term intensive exercise training in animals, without impact on cardiac structure and function.

서론: 장기간 수행하는 고강도 운동이 심장 부정맥을 유발하는 심근 섬유화와 연관이 있다는 임상적, 역학적 관찰 결과들이 최근 보고되고 있다. 한편, transforming growth factor (TGF)-β pathway 는 여러 심장 질환에서 심근 섬유화에 중대한 역할을 한다. 본 연구의 목적은: 1) 고강도 운동 유발성 심근 섬유화의 발생을 백서 모델에서 확인하고, 2) 그러한 모델에서 TGF-β 의 기능 억제가 심장의 구조와 기능 및 병적인 심근 섬유화의 감소에 영향을 줄 수 있는지 확인하는 것이다. 방법: 몸무게 100~125 g 의 백서 (Wistar rat) 를 무작위로 3군으로 배정하였다: 시간 통제의 무운동 대조군 (n=10), dimethyl sulfoxide (DMSO) 를 위약으로 투여한 운동 대조군 (n=5, 1 마리 중도 탈락) 및 TGF-β 길항제를 투여한 운동 실험군 (n=5). 운동을 시행한 군들은 2주간의 적응기간을 거친 후 트레드밀에서 12주간 36 m/s 의 속도로 ...