A new Mfn-2 related synthetic peptide promotes vascular smooth muscle cell apoptosis via regulating the mitochondrial apoptotic pathway by inhibiting Akt signaling

Restenosis after angioplasty is a major challenge for the treatment of coronary artery diseases. Facilitation of vascular smooth muscle cell (VSMC) apoptosis may be an attractive approach to decrease the incidence of restenosis. We synthesized a 16-amino acid mitofusin-2 (Mfn-2) gene related peptide (MRSP) based on the sequence of the p21^ras signature motif, the smallest functional sequence of the Mfn-2 gene with proapoptotic properties in VSMC. We investigated whether MRSP enhanced apoptotic activities to inhibit VSMC accumulation and neointimal hyperplasia in rats with carotid balloon injury.

VSMCs were treated with different concentrations of MRSP, the PI3K agonist 740 Y-P and the inhibitor LY294002. Cell apoptosis and related pathway molecules were assessed. MRSP was also given to rats with carotid artery balloon injury. Neointimal hyperplasia and cell apoptotic pathways were detected.

In vitro experiments revealed that MRSP treatment significantly increased VSMC apoptosis and induced increases in procaspase-9 cleavage, caspase-3 activation, cytochrome c release from mitochondria to the cytoplasm and the Bax/Bcl-2 ratio but not caspase-8 expression, indicating that the mitochondrial apoptotic cascade was activated by MRSP, which might be attributed to suppression of the PI3K/Akt signaling pathway. We further found that the PI3K agonist 740 Y-P prevented and that the inhibitor LY294002 strengthened the proapoptotic effects of MRSP. MRSP strongly inhibited neointimal hyperplasia and VSMC accumulation, but increased VSMC apoptosis in the vascular wall after balloon injury. Moreover, MRSP substantially enhanced Bax and cleaved caspase-3 expression and decreased Bcl-2 levels in intima, accompanied by decreased levels of phosphorylated Akt and PI3K in vivo.

Taken together, the present study showed that MRSP treatment results in a strong proapoptotic effect by activating the mitochondrial apoptotic cascade through suppression of the PI3K/Akt pathway.