Role of MAPK in chronic cerebral vasospasm
Introduction
Cerebral vasospasm is a major factor contributing to the poor outcome in patients suffering subarachnoid hemorrhage (SAH) [1], [2], [3]. The main features of cerebral vasospasm are delayed onset, prolonged contraction of major cerebral arteries, and resistance to most known vasodilators. The pathogenesis of vasospasm remains unclear even though prolonged smooth muscle contraction, histological changes of the arterial wall, and the inflammatory or immunological reaction might all be involved [4], [5]. The signal transduction pathways in the cerebral arteries during cerebral vasospasm are related at least to smooth muscle contraction [4], [5].
Many extracellular stimuli (including growth factors, hormones, stress, elevated temperature and G-protein coupled receptor agonists) initiate the phosphorylation cascades leading to the activation of mitogen-activated protein kinase (p44/42 MAPK) [6]. p44/42 MAPK activation may lead to an expression of the early genes, such as c-jun or c-fos, thus leading to the cellular proliferation [6]. p44/42 MAPK can cause the phosphorylation of caldesmon, thus promoting prolonged contraction [7]. It has been reported in several in vitro studies that p44/42 MAPK is involved in the prolonged contraction of the cerebral arteries, caused by hemolysate and endothelin-1 [8], [9], [10], the most important causative agents for vasospasm. In this study, we used an established canine double hemorrhage model of SAH to evaluate the role of p44/42 MAPK in the pathogenesis of vasospasm. This study tests the therapeutic values of the p44/42 MEK kinase inhibitor PD98059 in the reversal of vasospasm.
Section snippets
Subarachnoid hemorrhage model
Thirty-six adult mongrel dogs of either sex, weighing 18–24 kg, were used in this canine double-hemorrhage model. The dogs were anesthetized with thiopental (10 mg/kg) and mechanically ventilated during the procedures. Each dog's body temperature was maintained at 37 °C with a heating blanket, and a 4 F catheter was inserted into the femoral artery to monitor mean arterial blood pressure and blood gases. Experimental SAH was induced according to the method described by Varsos et al. [11].
Time course of cerebral vasospasm
The caliber of the basilar artery was calculated as the ratio of the mean basilar artery diameter on day 3–7, as a percentage of that on day 0. Fig. 1 shows the examples of angiograms from three dogs sacrificed on day 3, 5 and 7.
p44/42 MAPK immunoprecipitation
The time course of the p44/42 MAPK immunoprecipitation was calculated as the ratio of the sample to MAPK immunoprecipitation from normal dogs. Fig. 2A demonstrates examples of Western blot from samples of four dogs sacrificed on day 0 (no blood injection), day 3, 5, and
Discussion
In the present study we demonstrated that (a) p44/42 MAPK immunoprecipitation was enhanced after blood injection and corresponds to angiographic vasospasm. (b) PD98059 significantly reduced p44/42 MAPK immunoprecipitation and angiographic vasospasm.
Acknowledgements
This work was partially supported by a grant-in-aid to J.H.Z. from the American Heart Association, and a grant from American Heart Association Bugher Foundation for Stroke Award.
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