Role of Akt signaling pathway in delayed cerebral vasospasm after subarachnoid hemorrhage in rats.
Akt plays an important role in cell survival, proliferation, apoptosis and other activities. It also has been involved in maintaining smooth muscle cell contraction phenotypes in vitro and in vivo. Recent studies have focused on the inhibition of Akt in acute vasospasm and neuronal apoptosis after subarachnoid hemorrhage (SAH). However, its role in delayed cerebral vasospasm (DCVS) has not been reported. In this study, using a "two-hemorrhage" rat model of SAH, we examined the expression of p-Akt and the formation of vasospasm in the basilar arteries. To investigate the possible role of Akt in phenotypic switching, we performed immunohistochemical staining to examine expressions of SMα-actin and proliferating cell nuclear antigen (PCNA), markers of smooth muscle phenotypic switching. We found that the basilar arteries exhibited vasospasm after SAH and that vasospasm became most severe on day 7 after SAH. Elevated protein expression of p-Akt was detected 4 days after SAH induction, peaked on day 7, and recovered on day 21, which was in a parallel time course to the development of DCVS. Moreover, results of immunohistochemical staining revealed enhanced expression of PCNA but gradual reduction in expression of SMα-actin from day 1 to day 7 after SAH; then, the expressions of PCNA and SMα-actin gradually recovered until day 21. These results support a novel mechanism in which the Akt signaling pathway plays an important role in the proliferation of smooth muscle cells (SMCs) rather than inducing phenotype switching in basilar arteries, which promotes the development of DCVS after SAH.