Recent increases in physical inactivity and obesity are accompanied by an increased incidence of heart failure with preserved ejection fraction (HFpEF). While obesity and type 2-diabetes mellitus (T2DM) are thought to contribute to the pathophysiology of the diastolic dysfunction frequently observed in these patients, the underlying mechanisms are only poorly understood and therapy of HFpEF therefore remains highly empirical. Moreover, the mechanistic insights obtained to date are mainly based on studies with male mice and virtually nothing is known in about the pathophysiology in female. Because the disease is particularly frequent in the female population after menopause, the overall aim of our research is to identify novel gender-specific mechanisms that protect against diastolic dysfunction.
It is well-known that 17β-estradiol (E2) has direct beneficial effects in the ischemic or pressure-overloaded heart via the estrogen receptor (ER)α and ERβ. Recently, it was discovered that the orphan G protein-coupled receptor 30 specifically mediates non-genomic effects of E2 and it therefore was renamed to "G protein-coupled estrogen receptor" (GPER). The GPER has been implicated in regulating metabolism and inflammation, two important features of metabolic disease, but its role in obesity-related cardiac dysfunction has not been investigated.
The proposed project therefore has the following aims:
Aim 1: To analyze the effects of gender and ovarian hormones on cardiac hemodynamics in obese mice.
Aim 2: To analyze gender-specific mechanisms of cardiac dysfunction in high fat/high sucrose (HFD)-induced obesity.
Aim 3: To analyze the role of the GPER in regulating cardiac inflammation, metabolism and function after HFD feeding.
For aim 1, we will use echocardiography, pressure volume loop analysis and the ex vivo working heart setup to analyze cardiac metabolism and hemodynamic function in male, female, and OVX-female mice on a HFD.
For aim 2, we will test whether
- OVX-HFD increases inflammatory responses and thereby increases fibrosis and decreases diastolic function.
- mTOR, either directly or indirectly via its effects on PKC, alters titin's phosphorylation and isoform expression.
- gender-related differences in calcium handling along with reduced sarcoplasmic reticulum Ca2+ATPase (SERCA2a) expression contribute to cardiac dysfunction.
- gender-related differences in glucose uptake and/or autophagy lead to a changed energy status, which in turn explains a decline in contractile and relaxation performance of the heart of OVX-obese mice, in particular under energy-demanding conditions such as dobutamine- or pacing-induced stress.
For aim 3, the GPER agonist G-1 will be applied in ex vivo working heart as well as in vivo experiments.
With the proposed experiments we hope to test the hypotheses that (1) enhanced cardiac inflammatory responses in ovariectomized obese female mice lead to decreased cardiac compliance by increasing fibrosis, (2) impaired glucose metabolism and autophagy in obesity cause reduced cardiac relaxation during diastole, effects that are worsened after ovariectomy, (3) G-1 can be used therapeutically to prevent inflammation-induced fibrosis and to ameliorate glucose metabolism. Moreover, our model will be analyzed with RNA-seq profiling approaches to identify potential novel targets. Our anticipated new insights into the mechanisms that cause diastolic dysfunction in female and male models will hopefully contribute to stratified strategies that will increase the healthy lifespan of both genders. |
