Estrogen receptor beta and adiponectin as targets in cardiovascular and metabolic disease
Open Access
- Author:
- Tomicek, Nanette J.
- Graduate Program:
- Physiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- None
- Committee Members:
- Donna Hope Korzick, Dissertation Advisor/Co-Advisor
Donna Hope Korzick, Committee Chair/Co-Chair
Charles H Lang, Committee Member
Roger John Mccarter, Committee Member
Ramesh Ramachandran, Special Member - Keywords:
- aging
female
coronary heart disease
metabolic syndrome
adipose - Abstract:
- Coronary heart disease (CHD) remains the leading cause of morbidity and mortality in aged women, with a 2- to 3-fold increase in incidence following menopause. The loss of estrogen (E2) has been implicated as a defining factor for reduced cardioprotection, yet estrogen replacement therapy (ERT) fails to reduce cardiovascular morbidity and mortality in postmenopausal women. Moreover, the combined effects of aging and E2-deficiency contribute to a unique high risk state for metabolic dysregulation which further drives cardiovascular disease risk in aged women. Closer examination of both direct and indirect effects of E2 and estrogen receptor (ER) signaling in the context of aging and E2-deficiency is needed to help identify relevant targets for therapeutic intervention in post-menopausal women. The adipokine, adiponectin (APN), has been identified as a biomarker for CHD risk and may be influenced by aging, adiposity, and ERβ. The series of four studies described herein was designed to investigate ER-signaling disruptions in metabolic and cardiac tissues as well as characterize attenuations in APN signaling capacity in a model of aging and E2-deficiency, the Fischer 344 (F344) female rat. The aim of the first study (Chapter 3) was to determine the effects of acute ERβ activation on ischemia/reperfusion (I/R) injury in adult, aged, and aged E2-deficient female rats. Hearts were isolated from adult (6 mo), aged (24 mo), and aged ovariectomized (OVX) rats and subjected to 47 min of global I and 60 min of R. Rats were acutely treated with the ERβ-agonist diarylpropionitrile (DPN) or vehicle 45 min prior to I/R. Acute treatment with DPN had no effect on functional recovery following I/R injury in adult, aged, or aged OVX female rats. The aim of the second study (Chapter 4) was to determine if age-associated E2-deficiency is associated with alterations in the ERα/ERβ ratio in visceral adipose tissue and skeletal muscle of female rats. We also sought to characterize changes in intra-adipocyte and circulating APN. Visceral adipose and skeletal muscle was isolated from adult and aged rats with and without OVX. ERβ protein increased in adipose of aged and aged OVX rats and ERα increased in both adipose and gastrocnemius of aged OVX rats (p<0.05). Intra-adipocyte APN was increased and circulating APN concentration decreased in aged OVX vs adult OVX rats (p<0.05). Downstream APN targets, adiponectin receptor 2 (adipoR2), and the activated AMP-dependant kinase (pAMPK)/total AMPK ratio all decreased with age (p<0.05). Collectively, the data described in Chapter 4 suggests age-associated increases in ERβ in adipose, reduced circulating APN, and alterations in APN downstream effectors might conspire to create a metabolic phenotype associated with reduced cardioprotection. In the third study (Chapter 5) we employed a direct in vitro approach to assess the effects of ERβ overexpression on APN in an adipocyte-like cell culture model, 3T3-L1 cells. Cells were transfected with ERβ plasmid construct for 24 h. Post-transfection ERβ mRNA was increased 1000-fold, yet protein levels were unchanged. In a second experiment DPN was utilized to activate ERβ in differentiated 3T3-L1 cells. However, due to lack of ER responsiveness, the effects of ERβ activation on APN production or secretion in vitro were not elucidated. The aim of the fourth study (Chapter 6) was to determine if APN treatment is effective in conferring direct cardioprotection in the female rat heart and also to characterize changes in downstream cardiac APN targets associated with aging, E2-deficiency, and a high fat diet. Hearts were isolated from adult, aged, and aged OVX rats as described in Chapter 3 and were infused with 9 μg of APN or vehicle upon ischemia. APN infusion was successful in improving left ventricular developed pressure (LVDP) and end diastolic pressure (EDP) following I/R injury in all groups (p<0.05). No change in AMPK phosphorylation was observed in APN vs control I/R groups. In a subset of perfused control hearts isolated from rats consuming a high fat diet for 20 weeks total AMPK and AdipoR1 protein was decreased by 20% and increased by 50%, respectively relative to chow fed rats (p<0.05), which suggests APN-resistance. A summary of the key findings in the collection of four studies described follows. 1) Cardiac ERβ does not likely play a role in cardioprotection in the female F344 myocardium. 2) Defects in APN secretion are associated with increased ERβ in visceral adipose tissue of aged and aged OVX female rats. Unfortunately, a causal link between ERβ and APN could not be evaluated presently in vivo or in vitro models. 3) APN treatment improves post-ischemic function in the F344 female rat heart and APN or downstream APN effectors may be relevant therapeutic targets for combating CHD risk and mortality in aged women. However, high fat consumption may negate the protective effect of APN given the APN-resistant phenotype observed in aged female rats on a high fat diet.