Age- and Sex-Dependent Caveolar Gene Expression in Normoxic and Post-Ischemic Mouse Hearts

Age and sex modify myocardial I-R tolerance with caveolar invaginations in the plasma membrane shown to be important determinants of ischemic tolerance as well as responsiveness to cardioprotective stimuli. Caveolar membrane domains are formed by variety of coat proteins including those of caveolins, cavins and Popeye domain-containing family of proteins. Expression of these proteins are unclear in the aging male and female myocardium. Expression of caveolae-associated transcripts and proteins were assayed in normoxic and post-ischemic (20 min ischemia/60 min reperfusion) myocardium from 8-, 16-, 32- and 48-week old male and female mice (C57Bl/6). Using cultured HL-1 cells, the reliance of acute A ₁ Adenosine Receptor agonism on caveolae was also assessed, a known stress tolerance determinant that reside in caveolae. Significant down-regulation of chief caveolae transcripts Cav3 and Cavin1 correlated with 38%-52% reductions in Caveolin-3 & Cavin-1 protein in normoxic middle-aged hearts (respectively), congruent with age-related repression of caveolins in other tissue types. For females, caveolae-related genes were largely stable with aging which were consistent with previous findings that middle-aged female hearts display increase stress tolerance as measured by LDH release following I-R. Age thus appears to suppress transcription/expression of caveolar proteins critical to myocardial responses to stress and protective stimuli, an effect more pronounced in male vs. female myocardium. These age-dependent shifts in caveolar coat protein expression was associated with exaggerated contractile dysfunction associated evident at 32- and 48-weeks (vs. 8 weeks) in male hearts, but not associated with impaired recovery in 32 and 48-weeks (vs. 8 and 16 weeks) in females. In HL-1 cardiomyocytes subject to simulated ischemia-reperfusion, acute A ₁ AR agonism with 100 nM 2-chloro-N6-cyclopentyadenosine (CCPA) resulted in cytoprotection evident by significantly decreased LDH release (by ̴20%), which was abolished by caveolae & cholesterol depletion agent methyl-β-cyclodextrin (MβCD, 1 mM), suggesting caveolar involvement in protective signaling.