Mitofilin downregulation/Loss favors the initiation and development of dilated cardiomyopathy that progresses to acute heart failure and cardiac arrest
Authors: Draeger Derrick , Feng Yanshen C. , Bopassa Jean C. 
Published: May 2022

Rational

Heart failure (HF) is a clinical syndrome characterized by a constellation of symptoms that are caused by a structural and/or functional cardiac abnormality, ultimately resulting in reduced cardiac output and/or elevated intracardiac pressures. Despite the fact that many cardiovascular diseases end in HF, the condition too often fails to attract the awareness and emphasis it deserves. Worryingly, the mechanisms leading to HF are still not clearly defined. Therefore, research to decipher mechanisms of cardiac decompensation in HF with reduced ejection fraction (HFrEF) and to identify new treatments is urgently needed.

Objective

The objective of this study is to determine the role of the mitochondrial inner membrane protein (Mitofilin/Mic60), which plays a crucial role in maintaining mitochondrial cristae morphology, downregulation and loss in the onset and progression of HF and in increasing the prevalence of sudden death in the mouse.

Material and methods

We developed a Mitofilin‐floxed mouse model and crossed this mouse with a transgenic mouse that expresses Tamoxifen inducible Myh6‐Cre recombinase to generate a cardiomyocyte‐specific Mitofilin KO (cMitofilin‐/‐) mouse. Kaplan Meier Curve was used to determine the rate of mice survival, mitochondrial integrity was measured by analyzing cristae morphology and ROS production was assessed using amplex red method. The calcium retention capacity (CRC) required to induce mitochondrial permeability transition pore opening was measured using calcium green dye. Cardiac function was measured by echocardiography and Mic60 mRNA assessed by qRT‐PCR.

Results

We found an dramatic increase in sudden cardiac death in cMitofilin‐/‐ mice within 5 days post Tamoxifen treatment. Mitofilinfl+/fl++Cre(+) mice treated TAM (cMitofilin‐/‐) displayed significantly increase in cardiac size and reduction of cardiac function indicative of acute dilated cardiomyopathy (DCM) compared to vehicle. cMitofilin‐/‐mice showed mitochondrial cristae disruption and dysfunction including reduced mitochondrial CRC and increased ROS production compared to WT. We observed that full‐body Mitofilin‐/‐ mice do not survive after multiple crossing of full‐body heterozygote Mitofilin+/‐ mice, suggesting that a single allele expression of Mitofilin is sufficient to rescue the DCM phenotype. To determine the role of Mitofilin downregulation in DCM, we compared Mitofilin levels in WT mice treated with Doxorubicin (DOX) versus vehicle. DOX is a highly effective anticancer drug that causes acute ventricular dysfunction, and may induce late‐onset cardiomyopathy and HF. We found a dramatic reduction of Mitofilin in DOX‐treated animals that exhibited a higher death rate versus controls; this finding was associated with an increase in mitochondrial oxidative stress and dysfunction. Furthermore, mice treated with DOX displayed a decrease in Mitofilin mRNA, suggesting reduced Mitofilin expression during HF is at least in part mediated by Mitofilin transcriptional dysregulation. Interestingly, Mitofilin overexpression in H9c2 cardiomyocytes prevented DOX‐induced increase in cell survival.

Conclusion

. Together, these results indicate that Mitofilin downregulation/loss induces the onset and progression of DCM that is associated with HF and cardiac arrest. Our results provide a better understanding of mitochondrial‐dependent mechanism of DCM and represent a novel potential therapeutic target against DCM and HF.