PKC and Rho in vascular smooth muscle: Activation by BOXes and SAH CSF

Abstract

Cerebral vasospasm (CV) remains a significant cause of delayed neurological deficit and ischemic damage after subarachnoid hemorrhage (SAH), despite intensive research effort. The current lack of an effective therapeutic approach is somewhat due to our lack of understanding regarding the mechanism by which this pathological constriction develops. Recent evidence implicates bilirubin oxidation products (BOXes) in the etiology of CV after SAH: BOXes are found in cerebrospinal fluid from SAH patients with symptomatic or angiographically visible vasospasm (CSF V ) but not in CSF from SAH patients with no vasospasm (CSF C ). We have previously published research suggesting that the etiology of CV comprises two components: a physiological stimulation to constrict and a pathological failure to relax. Both these components are elicited by CSF V , but not CSF C , and BOXes synthesized in the laboratory potentiate physiological constriction in arterial smooth muscle in vitro, and elicit contraction in pial arteries in vivo. In this paper, we will present our results concerning the action of BOXes on arterial smooth muscle constriction, compared with CSF V . We will also present evidence implicating temporal changes in PKC isoforms and Rho expression in both BOXes-and CSF V -elicited smooth muscle responses. Keywords INTRODUCTIONWorldwide, subarachnoid hemorrhage (SAH) and its sequel, cerebral vasospasm (CV), kill or seriously debilitate an estimated 1.2 million people, of both genders, and all ages and ethnic groups annually (1). In the United States alone, complications from SAH, including increased length of hospital stay, increased treatment intensity level, requirement for long-term care and intensive rehabilitation are estimated to have cost 500 million dollars in 2000 (2). The pathological constriction of cerebral vessels that occurs during CV may lead to ischemia, infarction or death (3,4) and the 3-10 days between the initial hemorrhage and onset of CV potentially affords the clinician a therapeutic window (5). Unfortunately, despite considerable research efforts, the etiology of CV is still unknown, and appears to be a complex combination of events (3,6-10) Our research indicates that the intractable vasoconstriction seen in CV after SAH is a combination of a physiological protein kinase C-mediated contraction, followed by a pathological failure to relax, mediated by Rho-mediated inhibition of myosin light chain Send correspondence to: Dr Gail Pyne-Geithman, Department of Neurology, University of Cincinnati, 2324 Vontz Center, 3125 Eden Avenue, Cincinnati, OH USA NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript phosphatase (9,11). Bilirubin oxidation products (BOXes) may be responsible for one or both of these events (12-14).The literature records a bewildering array of molecules that may be implicated in the etiology of CV after SAH. They include endothelin (15), hemoglobin (7,16), bilirubin and it's oxidation products (17-19), arachidonic acid and it's peroxidized metabolites...

Bilirubin Oxidation End Products Directly Alter K+ Channels Important in the Regulation of Vascular Tone

“…While the molecular and cellular targets of BOXes are yet to be fully revealed, a recent study shows that BOXes exert their action in part by regulating PKC and GTPase Rho A (Pyne-Geithman et al 2008). Our results here demonstrate that BOXes profoundly inhibit the Slo1 BK channel activity in a lysine-dependent manner and suggest that the inhibitory effect of BOXes on the channel could contribute to the vasoconstrictive effect of BOXes.…”

“…The evidence therefore supports the idea that BOXes are important in development of delayed cerebral vasospasm; however, the effectors or molecular targets of BOXes are only beginning to be revealed. Thus far, PKC and the small GTPase Rho A have been suggested as direct or indirect effectors of BOXes (Pyne-Geithman et al 2008). It is not known whether BOXes affect other cell constituents.…”

Complement activation and disease: protective effects of hyperbilirubinaemia

“…High levels of free radicals, produced in blood clots found around blood vessels after subarachnoid haemorrhage, may oxidize bilirubin to BOXes (bilirubin oxidized products) which act on vascular smooth muscle cells causing, or contributing to, chronic vasoconstriction and vasospasm (reviewed in [91]). BOXes may be responsible for one or both events associated with cerebral vasospasm after subarachnoid haemorrhage, including a PKC (protein kinase C)-mediated contraction and a failure to relax due to Rho-mediated inhibition of MLCP (myosin light-chain phosphatase) [92]. However, the pathophysiology of the haemorrhage-induced vasoconstriction is still not fully understood, and other aggravating factors may be involved in causing cerebral vasospasm [92], thus hindering its treatment and prevention [93].…”

“…BOXes may be responsible for one or both events associated with cerebral vasospasm after subarachnoid haemorrhage, including a PKC (protein kinase C)-mediated contraction and a failure to relax due to Rho-mediated inhibition of MLCP (myosin light-chain phosphatase) [92]. However, the pathophysiology of the haemorrhage-induced vasoconstriction is still not fully understood, and other aggravating factors may be involved in causing cerebral vasospasm [92], thus hindering its treatment and prevention [93].…”

Genetics of Cerebral Vasospasm

“…Rho-kinase also phosphorylates myosin light chain directly, generating sustained contraction in a similar manner as the Ca 2+ /calmodulin-dependent MLC kinase pathway [125]. Rho-kinase has been shown to be involved in the pathogenesis of both coronary and cerebral vasospasm [124, 126–131]. Oxyhemoglobin from SAH activates Rho/Rho-kinase signaling [127].…”