Abstract Body (Do not enter title and authors here): Introduction:
Hibernation or aestivation involve physiologic and molecular adaptations across species that enhance survival under extreme conditions. These include reduced respiratory or heart rate and blood flow, resembling an ischemic state, but without any significant tissue damage. Similarly, the neonatal heart also exhibits protective adaptations against ischemia-reperfusion injury (IRI), resembling hibernation/aestivation. In contrast, adult non-hibernating mammals poorly tolerate ischemia-reperfusion, partly due to excess lactate and H⁺ from anaerobic glycolysis, accelerating ATP depletion used to maintain intracellular pH, resulting in poor cardiac function.
Hypothesis:
We hypothesized that loss of the cardiac maturation RNA splicing factor RBFOX1 could promote a less mature (neonatal-like) cardiomyocyte state in adult mice, mimicking molecular changes seen during hibernation/aestivation, improving tolerance to IRI.
Methods:
We used the Alberta snail as a model for hibernation/aestivation and both male and female heart-specific RBFOX1 deficient mice to assess molecular signalling, along with IRI, utilizing the ex-vivo Langendorff working heart model with radiolabelled substrates to measure metabolic alterations.
Results:
We found increased circulating ketones in the hemolymph of aestivating snails, as well as decreased RBFOX1 levels and markers of less mature cardiomyocytes (i.e., decreased Hoxb13 and Meis1) in snail tissue. RBFOX1 deficient mice had normal cardiac function, but less mature cardiomyocytes, characterized by sarcomere disassembly, stemness marker expression, and increased mono-nucleated cardiomyocytes. Furthermore, RBFOX1-deficient cardiomyocytes had increased levels of glycolytic, ketone oxidation, and fatty acid oxidation rate-limiting enzymes as well as increased L-type Ca²⁺ channels and sodium-hydrogen exchangers. These molecular metabolic changes resulted in an increase in baseline glycolysis rates for RBFOX1-deficient hearts, while after 20 minutes of global ischemia they had improved cardiac work recovery and increased post-IR glycolysis and ketone oxidation rates, while fatty-acid oxidation and glucose oxidation rates remained similar to control hearts.
Conclusions:
Loss of RBFOX1 appears to be an evolutionarily conserved mechanism in aestivating snails and non-hibernating neonatal mice that allows for improved tolerance to IRI through increased glycolysis, ketone oxidation and H⁺ clearing in non-hibernating adult mice.