Ischemia/reperfusion (IR) initiates various cellular and
molecular changes often resulting in myocardial infarction and cardiac
dysfunction. Inhibition of enzymes that are involved in cell pathology could be
potential therapeutic targets especially phosphodiesterases. Pharmacological
preconditioning (PC) with tadalafil, a PDE5A inhibitor enhances protein kinaseG-1 (PKG-I) activity resulting in stem cell survival and cardioprotection. PC
protection has two different phases, an early (2 h) and late (24 h).
However,
the mechanism of protection during these phases remained grossly unknown.
Mesenchymal stem cells (MSC) from adult male Fischer-344 rats were pre-treated
with tadalafil (100 μM) for an hour and subjected to 2 h of hypoxia (1% O2)
followed by reoxygenation (HR: in vitro model mimicking ischemia/reperfusion).
We observed increased MSC survival with reduced cell cytotoxicity as
revealed by low LDH release and trypan blue staining respectively in tadalafil
treated cells upon HR; decrease in TUNEL positivity as well as caspases
activity ; an increase in pAKT/AKT, iNOS, eNOS and pGSK3β/GSK3β during
early protection phase of PC. This protection seemed to be a spontaneous
adaptive response of MSCs against HR and was independent of tadalafil whereas
an increase in Bcl2/Bax was tadalafil dependent; during late phase, we
observed phosphorylation of STAT3 at serine727 leading to its entry inside the
nucleus and binding onto the promoter of PKG-I by 3 fold (P<0.05).
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