Sex Differences in Myocardial Histology, Gene Expression, and Myocardial Recovery in Recent-Onset Cardiomyopathy

Non-ischemic cardiomyopathy of recent onset (ROCM) has favorable rates of recovery but carries significant morbidity including a leading cause of cardiac transplantation. Left ventricular end diastolic diameter (LVEDD) dilatation as well as inflammation on endomyocardial biopsy (EMB) appear to be some of the strongest predictors of subsequent recovery.^1,2 In contrast, fibrosis is associated with poorer outcomes.² Sex differences have been observed among ROCM patients. Whether the degree of cardiac remodeling or endomyocardial histology differs by sex, and whether this contributes to apparent differences in recovery has not been previously evaluated.

We examined ventricular remodeling, endomyocardial histology, and gene expression among sexes in the Intervention in Myocarditis and Acute Cardiomyopathy (IMAC) 1 and 2 trials. All subjects had non-ischemic cardiomyopathy with a left ventricular ejection fraction (LVEF) ≤ 40% at entry and symptoms of less than 6 months in duration. Subjects underwent angiography or noninvasive screening to exclude coronary artery disease and transthoracic echocardiography to rule out valvular heart disease. Informed consent was obtained from all subjects, and protocols were approved by the institutional review boards of all participating centers. LVEF was quantified at entry and 6 months by echocardiography (IMAC2) or nuclear scan (IMAC1). The primary assessment of LVEF improvement was the LVEF at 6 months, and the change in LVEF defined as the difference in LVEF from entry to six months. The degree of remodeling was defined by left ventricular end diastolic diameter indexed for body surface area (LVEDDi). A total of 104 subjects had available EMBs and 20 subjects underwent additional gene expression as previously reported in an analysis of cytokine expression and recovery.³ Fas, fas ligand, fas-associated death domain-like interleukin-1 beta converting enzyme (FLICE), tumor necrosis factor (TNF)-α and TNF-receptor (TNFR1) expression were assessed by RNase protection assay. These factors were normalized to a consistently active gene, glyceraldehyde 3-phosphate dehydrogenase (GADPH).

The total cohort of 104 subjects included 59% (n = 62) males and 41% (n = 42) females, with mean age of 43 years and LVEF at entry 0.25 ± 0.08. NYHA functional class (I/II/III/IV) at entry was similar 11/43/30/16% among men 11/43/30/16% and 5/38/36/21% women, respectively. Comparisons by sex revealed similar time to presentation, symptoms duration and medical therapy at entry. Among participants in this analysis that underwent endomyocardial biopsy, men had significantly more fibrosis (41/62 (66%) vs. 19/42 (45%), p = 0.03) as compared to women. Men had more myocyte hypertrophy (35/62 (56%) vs. 17/42 (40%), p = 0.11), and less cellular inflammation or myocarditis (7/62 (11%) vs 10/42 (24%), p = 0.09) as compared to women.

Comparisons of remodeling alone by sex revealed no significant differences once indexed to body surface area (men: 3.2 ± 0.7, women: 3.3 ± 0.7, p = 0.38). In comparing EF improvement by sex, women had significantly better LVEF at 6 months (0.44± 0.16 vs. 0.37 ± 0.15, p = 0.03). There was no significant differences with respect to LVEF at entry (women: 0.27±0.09 vs. men: 0.24±0.08, p = 0.10).

Among the subgroup of available EMB’s (n= 20), several pro-apoptotic ligands and receptors demonstrated lower expression in women when compared to men including tumor necrosis factor receptor-1 (TNFR1) (women 1.53% (IQR 1.45,1.76) vs. for men 1.91% (1.67, 2.17), p=0.01), Fas receptor (0.26% (0.23, 0.28) vs. 0.13% (0.11, 0.24), p = 0.01), fas-associated death domain-like interleukin-1-beta converting enzyme (FLICE) (0.12% (0.09, 0.15) vs. 0.16% (0.13, 0.20), p 0.039) as compared to men. Women also had lower gene expression of TNF-α which approached significance (0.09% (0.07, 0.13) vs. (0.13% (0.11, 0.15), p = 0.058). (Figure 1)

Figure 1. Sex Differences in Gene Expression.

Values are displayed at % of glyceraldehyde 3-phosphate dehydrogenase (GADPH). *p<0.05.

This study found women with ROCM had less fibrosis and corresponding lower cardiac tissue gene expression of several pro-apoptotic factors including fas ligand, FLICE, and TNFR1, as compared to their male counterparts. Further, women had significantly better LVEF at 6 months despite similar entry LVEF and LVEDDi.

There are several possible mechanisms which may explain these sex differences. Our study did not reveal differences in duration of symptoms or presentation to care. Prior studies have suggested a predominant role of female sex hormones, primarily estrogen, which protects against myocardial injury. Estrogen has multiple protective roles for the cardiomyocyte, including repression of angiotensin-II-stimulated calcineurin activity that normally causes hypertrophy as well as preventing SMAD2 and SMAD3 fibrosis-inducing gene transcription.⁴ Further, studies note that the loss of estrogen protection against cardiac hypertrophy and fibrosis in post-ovariectomized animal models can be relatively recapitulated with exogenous estrogen supplementation.⁵ In looking at sex differences in EMB histology and gene expression in our study, women may be less likely to progress to apoptosis and irreversible cell injury and thus may be more likely to recover ventricular function after an acute myopathy. Further studies exploring which protective mechanisms lead to the relative decreases in pro-apoptotic tissue expression in cardiomyocytes as observed in this and other studies may help to target pathways for preservation.