Age-associated shifts in cardiac gene transcription and transcriptional responses to ischemic stress.

Aged hearts exhibit reduced tolerance to ischemia-reperfusion, together with altered structure and post-ischemic remodelling. The molecular bases of such changes are unclear. Using cDNA microarrays and quantitative RT-PCR we characterized shifts in gene expression patterns with aging in normoxic and post-ischemic (20 min global ischemia, 60 min reperfusion) murine hearts (young: 2-4 months; aged: 16-18 months). We identified an age-associated up-regulation of transcripts involved in cell death, oxygen transport and metabolism in normoxic hearts. Down-regulated transcripts were involved in transporter activity, protein binding and hydrolase activity, changes in MAPK, WNT and TGF-beta signalling with aging were also observed. Ischemic stress generated a much greater degree of contractile impairment and cellular damage in aged vs. young hearts. This was associated with a substantially modified transcriptional response, with selective changes in Ca2+, WNT, NOTCH and G-protein coupled receptor signalling paths in aged vs. young hearts. Despite some common responses to ischemia in young and aged hearts (induction of heat shock protein transcripts), aging selectively modified ischemic responses of immediate early genes, and genes involved in modulating apoptosis and remodelling/angiogenesis. In summary, aging is associated with shifts in cardiovascular gene expression consistent with the phenotypic features of older hearts. Reduced tolerance with age may be related to modification of signalling (particularly WNT and TGF-beta), and shifts in expression of immediate early genes, and genes important in control of cell death/survival, angiogenesis, and cardiac remodelling.

Effects of aging and ischemia on adenosine receptor transcription in mouse myocardium.

The well-documented age-related change in ischemic tolerance may result from impaired adenosine-mediated cardioprotection. Additionally, ischemia itself may potentially modify adenosine signalling, contributing to the post-ischemic phenotype. This study investigates age- and ischemia-dependent changes in adenosine receptor transcript levels (Adora) for the A(1), A(2A), A(2B), and A(3) receptor subtypes in mouse myocardium. Hearts from young (2-4 months) and moderately aged (16-18 months) mice were subjected to 20-min ischemia and 45-min reperfusion. Ischemic tolerance was impaired in aged hearts, which recovered less than 30% ventricular pressure development (compared with approximately 70% in young hearts), and lost 2-fold higher levels of lactate dehydrogenase during reperfusion (reflecting cellular disruption). Real-time PCR analyses revealed an age-related decline in Adora3 levels and induction of Adora2B. Curiously, this effect was mimicked by ischemia, which acutely reduced Adora3 levels and induced Adora2B in young (but not old) hearts. In contrast, in aged hearts ischemia selectively reduced levels of Adora1 transcript ( approximately 2-fold) without altering transcript levels for the other receptors. These results demonstrate selective modulation of cardioprotective adenosine receptor transcription by both aging and ischemia. Reduced A(3) adenosine receptor transcription may contribute to impaired ischemic tolerance in aged hearts, whereas changes in Adora transcription induced by ischemia may impact on the post-ischemic phenotype at later time points.

Effects of A1 adenosine receptor overexpression on normoxic and post-ischemic gene expression.

OBJECTIVES: To identify potential molecular genetic determinants of cardiovascular ischemic tolerance in wild-type and transgenic hearts overexpressing A(1) adenosine receptors (A(1)ARs). METHODS: cDNA microarrays were used to explore expression of 1824 genes in wild-type hearts and ischemia-tolerant mouse hearts overexpressing A(1)ARs. RESULTS: Overexpression of A(1)ARs reduced post-ischemic contractile dysfunction, limited arrhythmogenesis, and reduced necrosis by approximately 80% in hearts subjected to 30 min global ischemia 60 min reperfusion. Cardioprotection was abrogated by acute A(1)AR antagonism, and only a small number (19) of genes were modified by A(1)AR overexpression in normoxic hearts. Ischemia-reperfusion significantly altered expression of 75 genes in wild-type hearts (14 induced, 61 down-regulated), including genes for metabolic enzymes, structural/motility proteins, cell signaling proteins, defense/growth proteins, and regulators of transcription and translation. A(1)AR overexpression reversed the majority of gene down-regulation whereas gene induction was generally unaltered. Additionally, genes involved in cell defence, signaling and gene expression were selectively modified by ischemia in transgenic hearts (33 induced, 10 down-regulated), possibly contributing to the protected phenotype. Real-time PCR verified changes in nine selected genes, revealing concordance with array data. Transcription of the A(1)AR gene was also modestly reduced post-ischemia, consistent with impaired functional sensitivity to A(1)AR stimulation CONCLUSIONS: Data are presented regarding the early post-ischemic gene profile of intact heart. Reduced A(1)AR transcription is observed which may contribute to poor outcome from ischemia. A(1)AR overexpression selectively modifies post-ischemic gene expression, potentially contributing to ischemic-tolerance.