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Regular Manuscript

Endogenous Hedgehog expression contributes to myocardial ischemia reperfusion-induced injury

¹ Academic Medical Center
² University of Maastricht
³ University of Groningen

^* To whom correspondence should be addressed. E-mail: m.f.bijlsma{at}amc.uva.nl.

	Abstract

The developmentally important hedgehog (Hh) pathway is activated in ischemic tissue and exogenously administered Sonic hedgehog (Shh) supports tissue repair following cardiac ischemia. Hence, it is currently assumed that the endogenous increase in Shh during ischemia serves a beneficial role in limiting cardiac tissue damage. To prove or refute this hypothesis, we treated mice with the smoothened (Smo) inhibitor cyclopamine to block the Hh pathway during myocardial ischemia-reperfusion. The experimental induction of myocardial ischemia resulted in activation of the Hh pathway, and hallmark features of myocardial damage such as left ventricular dilatation and reduced cardiac output. Unexpectedly, cyclopamine treatment ameliorated left ventricular dilatation and cardiac output. As the beneficial effect of exogenous Shh was suggested to depend on reduced apoptosis, increased vascularization and reduced fibrosis, we subsequently assessed the effect of cyclopamine on these processes. Vascularization was similar in cyclopamine- and control treated animals, but increased apoptosis and reduced fibrosis were observed in the cyclopamine treated animals. Thus, Hh seems to exert a dualistic action in cardiac ischemia in which high exogenous levels are able to foster tissue repair, whereas endogenous Hh seems to be deleterious.

Key Words: ischemic heart disease, hedgehog, development, reperfusion