Overexpression of TFAM or Twinkle Increases mtDNA Copy Number and Facilitates Cardioprotection Associated with Limited Mitochondrial Oxidative Stress

Abstract

BackgroundMitochondrial DNA (mtDNA) copy number decreases in animal and human heart failure (HF), yet its role in cardiomyocytes remains to be elucidated. Thus, we investigated the cardioprotective function of increased mtDNA copy number resulting from the overexpression of human transcription factor A of mitochondria (TFAM) or Twinkle helicase in volume overload (VO)-induced HF.Methods and ResultsTwo strains of transgenic (TG) mice, one overexpressing TFAM and the other overexpressing Twinkle helicase, exhibit an approximately 2-fold equivalent increase in mtDNA copy number in heart. These TG mice display similar attenuations in eccentric hypertrophy and improved cardiac function compared to wild-type (WT) mice without any deterioration of mitochondrial enzymatic activities in response to VO, which was accompanied by a reduction in matrix-metalloproteinase (MMP) activity and reactive oxygen species after 8 weeks of VO. Moreover, acute VO-induced MMP-2 and MMP-9 upregulation was also suppressed at 24 h in both TG mice. In isolated rat cardiomyocytes, mitochondrial reactive oxygen species (mitoROS) upregulated MMP-2 and MMP-9 expression, and human TFAM (hTFAM) overexpression suppressed mitoROS and their upregulation. Additionally, mitoROS were equally suppressed in H9c2 rat cardiomyoblasts that overexpress hTFAM or rat Twinkle, both of which exhibit increased mtDNA copy number. Furthermore, mitoROS and mitochondrial protein oxidation from both TG mice were suppressed compared to WT mice.ConclusionsThe overexpression of TFAM or Twinkle results in increased mtDNA copy number and facilitates cardioprotection associated with limited mitochondrial oxidative stress. Our findings suggest that increasing mtDNA copy number could be a useful therapeutic strategy to target mitoROS in HF.

Mitochondrial Transcription Factor A's role in heart failure.

“…Through analysis of heart weight/body weight ratio, we observe a reduction in cardiac hypertrophy with TFAM overexpression (Fig.17). Our results are similar to the current literature In AVF induced HF models, TFAM overexpression reduced protease activity and cardiac hypertrophy (Ikeda et al 2015). Studies show that TFAM overexpression attenuates cardiac dilation and dysfunction in myocardial infarction induced heart failure models (Ikeuchi et al 2005).…”

“…Furthermore, we observed a significant weight gain, which we deemed a result of edema, in the WT-TAC model compared to the control. Other papers have found similar results in HF models (Veeraveedu et al 2017;Ikeda et al 2015).…”

“…Though other groups administered 200 micromolar H2O2 to HL-1 cardiomyocytes we experienced increased cell death and standardized the treatment. In AV fistula volume-overload (VO) heart failure, TFAM overexpression suppressed MMP up regulation and limited mitochondrial oxidative stress (Ikeda et al 2015).…”

“…In vivo studies have analyzed the effects of TFAM over-expression, showing decreased myocyte hypertrophy, oxidative stress, protease expression, apoptosis, interstitial fibrosis, increased mtDNA copy number, and cardiomyocyte stability in myocardial infarction/heart failure models (Ikeuchi et al 2005;Ikeda et al 2015;Kang, Kim, and Hamasaki 2007;Hayashi et al 2008). Additionally, TFAM protected cells from oxidative stress in many in vitro models (Thomas et al 2012;Xu et al 2009;Aguirre-Rueda et al 2015).…”

The role of mitochondria in cardiac development and protection

“…As a rather puzzling observation, the overexpression of TFAM or Twinkle protects mouse cardiomyocytes against ischemia [112,113] as well as high levels of oxidative stress [28,114]. While overexpression of these factors seems to have a mild deleterious effect on OXHPHOS [115], they also increase mtDNA copy number and induce high levels of recombination [28,91].…”