Analysis of Systolic Cardiac Function in PERM1-knockout Mice: Insights from A Retrospective Study in Large Cohorts of Animals

Abstract

Several groups demonstrated that PERM1 is a positive regulator of mitochondrial bioenergetics in the heart. However, discrepant results have emerged with regard to whether PERM1 loss-of-function affect cardiac contractility. Here we present data from a retrospective study collecting echocardiography data from all Perm1 knockout (Perm1-KO) mice and their wildtype (WT) littermates used for various molecular biological experiments in our lab between April of 2022 and September of 2023. This yielded an atypically large number of subjects per group, 84 WT mice and 88 Perm1-KO mice. We analyzed Echo-derived parameters of left ventricular (LV) systolic function. The ejection fraction (EF) was 65.43±7.13 in WT vs. 53.98±8.80 in Perm1-KO yielding p < 0.00000000000000004 using unpaired t-test. Other parameters which reached statistically significant difference between WT and Perm1-KO (at p < 0.05) included LV fractional shortening, LV diastolic and systolic diameters, LV anterior and posterior systolic wall thickness, LV posterior wall systolic thickening, stroke volume, and cardiac output. Changes caused by constitutive Perm1-KO can be conceptualized as reduced contractility partially compensated by increased LV circumference. This study provides a strong evidence that Perm1-KO causes a specific remodeling of cardiac contractility and provides retrospective power analysis which can be useful for future prospective studies.

Keywords: PERM1; cardiac contractility; echocardiography; ejection fraction; power analysis.

Figure 1. Frequency distribution histograms for selected parameters of systolic function.

Frequency distribution histograms for EF (A), CO (B) and LVPW thickening (C) obtained in WT and Perm1-KO mice. Note that all distributions are unimodal and roughly bell-shaped. There is a big overlap in all distributions between WT and KO, yet the differences between means are statistically significant.

Figure 2. The analysis of correlation between EF and CO and between LV diameter in diastole and EF.

Perm1 deletion does not change the relationship between EF and CO (A) and between LV diameter in diastole and EF (B). In both WT and Perm1-KO mice, there is no correlation between EF and CO (A), and there is a strong negative correlation between LV diameter in diastole and EF (B).

Figure 3. Echocardiographic images representing the extremes in the distribution of EF in WT and Prem1-KO groups.

PSAX M-mode images representing the mice with the lowest (A) and the highest (B) value of EF in the WT group, and the lowest (C) and the highest (D) value of EF in the KO group. Note that despite the very big differences in EF values, these mice, representing the extreme ends of EF distributions, achieve similar levels of CO.

Figure 4. Retrospective analysis of p-value versus average group size.

The p-value for unpaired two-sided t-test was computed as if measured each time the sample size increased due to additional experiments. The value of negative logarithm of p value increases approximately linearly with the average group size, and after group size reaches a critical number, the p-value remains at the level < 0.05.