Abstract 3923: NF2/Merlin Promotes Apoptosis and Ischemic Injury Through Activation of Mst1
Neurofibromatosis 2 (NF2)/merlin is a membrane associated protein and a known tumor suppressor. Recent work in Drosophila has provided evidence that NF2/merlin can promote activation of the hippo pathway. Hippo signaling inhibits cell growth and promotes apoptosis in the fly, and we have previously shown that the mammalian homologue of hippo, Mst1, has a similar function in the heart. We therefore sought to determine whether NF2/merlin can mediate activation of Mst1, thereby promoting apoptosis of cardiac myocytes. Our findings demonstrate that expression of NF2 in cultured cardiac myocytes is sufficient to increase phosphorylation of Mst1 (2.9±0.2-fold, p<0.05), indicative of its activation. Expression of NF2 also induces cardiac myocyte apoptosis (4.8±1.7-fold, p<0.05). Further, NF2-induced apoptosis is significantly reduced by co-expression of kinase-inactive Mst1 (61±12% decrease vs. NF2, p<0.05), implicating Mst1 in this response. To examine the importance of endogenous NF2 in ischemic injury, we first examined whether ischemia/reperfusion (I/R) alters NF2 expression/activation. We found that in vivo I/R (30min/2hr) increases NF2 expression (3.2±1.3-fold vs. sham, p<0.05) and activation (phosphorylation decreased 61±17% vs. sham, p<0.05) as determined by immunoblot. Cardiac-specific knockout (KO) mice were used to determine the role of endogenous NF2 in I/R injury. Global I/R (30min/1hr) was performed using the Langendorff method and infarct size determined. Hearts from NF2 KO mice had significantly reduced infarct size compared to WT littermates (24.6±5.5% vs. 46.9±8.4%, p<0.05). Functional recovery was also measured. Following 60 min of reperfusion, function of KO hearts was comparable to baseline, but was significantly decreased in WT hearts. Percent recovery from baseline for LVDP, dp/dt max, and dp/dt min were 81.7±13.1%, 81.5±14.6% and 89.5±15.1% respectively for KO hearts compared to 21.7±12.7%, 16.4±8.6%, and 28.1±12.9% in WT hearts. WT hearts also showed greater LVEDP compared to KO hearts (5.7±1.6-fold vs. 2.6±0.4-fold, p<0.05). These data demonstrate the proapoptotic capacity of NF2 through its ability to signal to Mst1 in cardiac myocytes, ultimately impacting ischemic injury and cardiac function.
This research has received full or partial funding support from the American Heart Association, National Center.