Project 2: Gene-by-sex interactions in heart failure with preserved ejection fraction (HFpEF) PROJECT SUMMARY Our laboratory has been interested in the basis of sex differences in cardiometabolic traits for the past two decades. We use a “system genetics” approach that integrates clinical and molecular traits in the context of genetic variation. For studies in mice we use a resource called the Hybrid Mouse Diversity Panel (HMDP) that has a number of advantages for studies of complex traits. Our proposal is fucused on a poorly understood, but common form of heart failure, called heart failure with preserved ejection fraction (HFpEF). It is characterized by diastolic dysfunction and preserved ejection fraction, distinct from heart failure with reduced ejection fraction (HFrEF). HFpEF is a highly complex disorder with multiple comorbidities, including obesity, diabetes, hypertension, and inflammation. It is highly heterogenous and has a significant environmental component, making human studies difficult. Consistent epidemiological data demonstrate that women are about twice as likely to develop HFpEF as compared to men. They also tend to present with more symptom burden, including significantly increased diastolic dysfunction and enhanced left ventricle stiffness. However, the nature of sex differences remains unclear. Because of the complexity of the syndrome, we have used a mouse model of HFpEF that involves feeding mice a high fat diet and a nitric oxide synthase inhibitor. Our strategy is to perform systems genetics analyses using this model in the HMDP and from this develop hypotheses that can be tested in human cohorts. Our results thus far in mice have revealed that females tend to be more susceptible to diastolic dysfunction and other HFpEF traits than males, consistent with the human epidemiological data. Aim 1 is directed at understanding sex differences in HFpEF traits, particularly in the heart, at the molecular level. A long- term goal is to model sex-specific biologic networks that can be generalized to humans. Aim 2 is directed at understanding the cause of the sex differences. We have previously obtained evidence that sex hormones explain, in part, the sex differences in HFpEF susceptibility and we now propose to examine sex chromosomes using the Four Core Genotypes (FCG). During the course of our studies, we discovered that, in heart, males have higher levels of mitochondrial function than do females, and we have proposed that this may explain the sex difference. In Aim 3, we will now test this hypothesis by examining the roles of estrogen receptor alpha and sex chromosomes in mitochondrial functions. We will also characterize in detail the mitochondrial enzyme, ACSL6, that we have identified as causal for HFpEF.