Intense light-elicited up-regulation of miR-21 facilitates glycolysis and cardioprotection in a Per2-dependent mechanism

A wide search for ischemic preconditioning (IP) mechanisms of cardioprotection
identified the light elicited circadian rhythm protein Period 2 (Per2) to be
cardioprotective.  Studies on cardiac
metabolism found a key role for light elicited Per2 in mediating metabolic
dependence on carbohydrate metabolism. To profile Per2 mediated pathways
following IP of the mouse heart, we performed a genome array and identified 352
abundantly expressed and well-characterized Per2 dependent micro RNAs. One prominent result of our in silico analysis for cardiac Per2 dependent micro RNAs revealed a
selective role for miR-21 in the regulation of hypoxia and metabolic
pathways. Based on this Per2 dependency, we subsequently found a diurnal
expression pattern for miR-21 with higher miR-21 expression levels at Zeitgeber
time (ZT) 15 compared to ZT3.  Gain or
loss of function studies for miR-21 using miRNA mimics or miRNA inhibitors and a
Seahorse Bioanalyzer uncovered a critical role of miR-21 for cellular glycolysis,
glycolytic capacity, and glycolytic reserve. Exposing mice to intense light, a
strategy to induce Per2, led to a robust induction of cardiac miR-21 tissue
level and decreased infarct sizes, which was abolished in miR-21-/-
mice. Similarly, first translational studies in humans using intense blue light
exposure for 5 days in healthy volunteers resulted in increased plasma miR-21 levels
which was associated with increased phosphofructokinase activity, the rate-limiting
enzyme in glycolysis. Together, we identified miR-21 as cardioprotective downstream
target of Per2 and suggest intense light therapy as a potential strategy to
enhance miR-21 activity and subsequent carbohydrate metabolism in humans.