Impact of age-associated estrogen deficiency on innate immune responses to myocardial ischemic injury in the female rat heart

Open Access
Author:
Jackson, Morgan A
Graduate Program:
Physiology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 19, 2017
Committee Members:
  • Donna Korzick, Thesis Advisor
  • Kumble Sandeep Prabhu, Committee Member
  • Catharine Ross, Committee Member
Keywords:
  • heart
  • aging
  • estrogen
  • inflammation
  • macrophage
  • ischemia reperfusion injury
Abstract:
Post-menopausal women exhibit reduced tolerance to myocardial ischemia reperfusion injury. Few studies have examined the effects of age-associated estrogen deficiency on innate inflammatory responses, which largely determine the extent of ischemic damage and the efficacy of wound healing. To assess the combined impact of age and estrogen loss on innate inflammatory response to myocardial I/R, adult (5 – 6 mo) and aged ovariectomized (OVX at 15 mo, aged to 24 mo) female F344 rats underwent coronary artery ligation (CAL) to induce ischemia-reperfusion injury. Both adult (n = 26) and MO OVX (n = 29) rats underwent either 31 min or 55 min of ischemia, followed by 10 min, 6 h, 24 h, or 72 h of reperfusion. Rat serum was collected and used to measure baseline and post-I/R circulating inflammatory cytokine concentrations. Immunohistochemistry staining of left ventricle (LV) sections was used to detect infiltrating immune cells. Western blot analysis of homogenized LV samples was conducted to assess changes in expression of proteins associated with the inflammatory response, including pro-caspase-1 and p20. Further, cultured macrophages derived from bone marrow (BMDM) and spleen (SM) of non-ischemic adult and MO OVX rats were stimulated for either 6 or 24 h with a combination of LPS and IFNγ or vehicle in order to assess macrophage polarization and function. BMDM cultured from aged, estrogen deficient rats exhibited blunted production of IL-1β (p<0.05) and IL-6 (p<0.05) following 24 h stimulation with LPS and IFNγ compared to macrophages cultured from young adults. Similarly, MO OVX SM showed blunted production of IL-1β (p<0.01) following 6 h incubation with LPS and IFNγ, suggesting age-associated estrogen deficiency may impair macrophage responses to acute inflammatory stimuli. Additionally MO OVX rats exhibited elevated baseline serum concentrations of IL-10 (p<0.05) and TNFα (p<0.05) relative to adult counterparts. Further, age-associated estrogen deficiency resulted in increased production of IL-1β (p<0.05) and TNFα (p<0.05) relative to adults, following 6 h and 10 min reperfusion respectively. Taken together, these findings suggest aging and estrogen withdrawal combined may contribute to the development of a chronic inflammatory phenotype, which could potentiate an exacerbated inflammatory response in the female rat heart.