Alpha1-adrenergic receptor activation mimics ischemic postconditioning in cardiac myocytes

• Main Author: Janota, Danielle M
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2014
• Subjects: Biology; Biomedical engineering; Cellular biology; Molecular biology
• ISBN: 1321476450; 9781321476453

Ischemic postconditioning has been shown to reduce injury in response to ischemia/reperfusion. Because of limitations on the clinical use of ischemic postconditioning protocols, pharmacological agents that elicit a postconditioning (PostC) effect are highly desired. Previous studies have shown that stimulation of alpha1-adrenergic receptors (α1-ARs) is cardioprotective, thus, the first aim of this dissertation was to examine the effects of post-ischemic stimulation of α1-ARs on cardiac myocyte cell death. Adult rat ventricular myocytes and HL-1 cardiac myocytes were subjected to simulated ischemia-reperfusion injury. Cell membrane permeability, evaluated by measuring released lactate dehydrogenase (LDH) or propidium iodide uptake (PI), was used as an estimate of cell death. Lower amounts of LDH and PI uptake were detected when α1-ARs were stimulated at the onset of reperfusion. Further, lower levels of apoptosis were measured using TUNEL and DNA laddering to evaluate DNA cleavage and Annexin V staining to evaluate outer membrane phosphatidylserine. Prior studies suggest that increased autophagy following ischemia is protective. The second aim of this dissertation was to determine whether post-ischemic α1-AR stimulation inhibits cardiac myocyte death through modulation of autophagy. α1-AR-mediated reductions in cell death were reversed in the presence of ATG inhibitor, 3-Methyladenine. Western blot for autophagosomal marker, LC3-II indicated modulation of autophagy, and two methods were used to measure autophagic flux. LC3-II turnover examined with and without autophagosome-lysosome fusion inhibitor chloroquine revealed an increase in autophagic flux or induction. HL-1 cells transfected with plasmid to express a tandem fluorescent-tagged LC3 molecule also indicated an increase in autophagic flux or induction. Finally, the third aim of this dissertation was to examine the molecular pathways stimulated by α1-ARs that lead to decreased cell death. PI fluorescence assays indicated possible involvement of ERK1/2, PKC, and PLC. Western blotting to detect phosphorylated ERK1/2 or Akt at various time points was not conclusive. Overall, these results suggest that α1-AR stimulation at the onset of reperfusion reduces cardiac myocyte death, an effect that appears to be dependent upon increased induction of autophagy. ERK1/2, PKC, and PLC activation are potential pathways involved in α1-AR-mediated cell survival.