NOVEL 3-DIMENSIONAL ELECTRON MICROSCOPIC ANALYSIS OF MITOCHONDRIAL MORPHOLOGY IN AGED AND ISCHEMIC FEMALE RAT HEART

Open Access
Author:
Henry, Jessica Behin
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Dr. Donna Korzick, Thesis Supervisor
  • Dr. Gong Chen, Honors Advisor
Keywords:
  • ischemic injury
  • mitochondria
  • aging
  • menopause
  • heart
Abstract:
Cardiovascular disease (CVD) prevalence and mortality increase with age for men and women. However, postmenopausal women experience a two-fold increase in risk of CHD compared to premenopausal women. These statistics suggest that estrogen (E2) is cardioprotective, however, estrogen replacement therapy is contraindicated in postmenopausal women highlighting the importance of alternative therapeutic targets. Following ischemia/reperfusion (I/R) injury, mitochondria undergo ultrastructure damage that impacts their ability to produce ATP and prevent cell death. Studying mitochondrial dynamics and quality control can provide insight into mitochondrial compensatory mechanisms after I/R injury, such as Drp1-mediated fission and mitophagy. Serial block-face scanning electron microscopy (SBFSEM) can provide many advantages for studying alterations in mitochondrial morphology, but its utilization to investigate age-associated E2-deficiency is untested. In vivo coronary artery ligation (CAL; 55 min I, 6 hr R) was used to generate cardiac I/R injury in adult (5-6 mo) and aged ovarectomized (22-24 mo) female rats. Following perfusion fixation, cardiac samples were imaged by SBFSEM and analyzed to evaluate mitochondrial density, mitochondrial volume, and qualitative ultrastructural parameters. Additionally, western blotting was performed to assess mitochondrial Drp1 levels. Decreased mitochondrial volume and increased mitochondrial density with concurrent increases in the presence of autophagasomes and Drp1 in the adult, but not aged female heart during reperfusion. Collectively, the results suggest for the first time, deficient fission-mediated mitophagy in the aged female heart with I/R injury. These results further suggest that SBFSEM is an effective approach to study mitochondria under conditions of I/R injury. That alterations in mitochondrial quality control occur in the aged, E2-deficient heart provides a possible mechanism for reduced functional recovery after an ischemic event in post-menopausal women.