Protein kinase cdelta and alpha are involved in the development of vasospasm after subarachnoid hemorrhage

Protein kinase C-inhibition reduces critical weight loss and improves functional outcome after experimental subarachnoid haemorrhage

OBJECTIVES

Subarachnoid haemorrhage (SAH) carries a high burden of morbidity and mortality. One in three patients develop vasospasm, which is associated with Delayed Cerebral Ischemia. The pathophysiology includes vasoconstrictor receptor upregulation in cerebral arteries. The protein kinase C - inhibitor RO-31-7549 reduces the expression of several vasoconstrictor receptors and normalizes cerebral blood flow in experimental SAH but functional and behavioural effects are unknown. This study was undertaken to analyse functional outcomes up to 14 days after experimental SAH.

MATERIALS AND METHODS

54 male rats were randomised to experimental SAH or sham, using the pre-chiasmatic, single injection model, and subsequent treatment or vehicle. 42 remained for final analysis. The animals were euthanized on day 14 or when reaching a humane endpoint. The primary endpoint was overall survival, defined as either spontaneous mortality or when reaching a predefined humane endpoint. The secondary outcomes were differences in the rotating pole test, weight, open field test, novel object recognition and qPCR of selected inflammatory markers.

RESULTS

In the vehicle group 6/15 rats reached the humane endpoint of >20 % weight loss compared to 1/14 in the treatment group. This resulted in a significant reduced risk of early euthanasia due to >20 % weight loss of HR 0.15 (0.03-0.66, p = 0.04). Furthermore, the treatment group did significantly better on the rotating pole test, RR 0.64 (0.47-0.91, p = 0.02).

CONCLUSION

RO-31-7549 improved outcomes in terms >20 % weight loss and rotating pole performance after experimental SAH and could be investigated.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

The important role of connexin 43 in subarachnoid hemorrhage-induced cerebral vasospasm

Background

Gap junctions are involved in the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH). However, the specific roles and regulatory functions of related connexin isoforms remain unknown. The aim of this study was to investigate the importance of connexin 43 (Cx43) in CVS and determine whether Cx43 alterations are modulated via the protein kinase C (PKC) signaling transduction pathway.

Methods

Oxyhemoglobin (OxyHb)-induced smooth muscle cells of basilar arterial and second-injection model in rat were used as CVS models in vitro and in vivo. In addition, dye transfer assays were used for gap junction-mediated intercellular communication (GJIC) observation in vitro and delayed cerebral ischemia (DCI) was observed in vivo by perfusion-weighted imaging (PWI) and intravital fluorescence microscopy.

Results

Increase in Cx43 mediated the development of SAH-induced CVS was found in both in vitro and in vivo CVS models. Enhanced GJIC was observed in vitro CVS model, this effect and increased Cx43 were reversed by preincubation with specific PKC inhibitors (chelerythrine or GF 109203X). DCI was observed in vivo on day 7 after SAH. However, DCI was attenuated by pretreatment with Cx43 siRNA or PKC inhibitors, and the increased Cx43 expression in vivo was also reversed by Cx43 siRNA or PKC inhibitors.

Conclusions

These data provide strong evidence that Cx43 plays an important role in CVS and indicate that changes in Cx43 expression may be mediated by the PKC pathway. The current findings suggest that Cx43 and the PKC pathway are novel targets for developing treatments for SAH-induced CVS.

Alteration of basilar artery rho-kinase and soluble guanylyl cyclase protein expression in a rat model of cerebral vasospasm following subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The vasoconstrictor endothelin-1 (ET-1) has been implicated in the pathogenesis of cerebral vasospasm following subarachnoid hemorrhage (SAH). Previous results showed that CGS 26303, an endothelin converting enzyme (ECE) inhibitor, effectively prevented and reversed arterial narrowing in animal models of SAH. In the present study, we assessed the effect of CGS 26303 on neurological deficits in SAH rats. The involvement of vasoactive pathways downstream of ET-1 signaling in SAH was also investigated.

METHODS

Sprague-Dawley rats were divided into five groups (n = 6/group): (1) normal control, (2) SAH, (3) SAH+vehicle, (4) SAH+CGS 26303 (prevention), and (5) SAH+CGS 26303 (reversal). SAH was induced by injecting autologous blood into cisterna magna. CGS 26303 (10 mg/kg) was injected intravenously at 1 and 24 hr after the initiation of SAH in the prevention and reversal protocols, respectively. Behavioral changes were assessed at 48 hr after SAH. Protein expression was analyzed by Western blots.

RESULTS

Deficits in motor function were obvious in the SAH rats, and CGS 26303 significantly improved the rate of paraplegia. Expressions of rho-kinase-II and membrane-bound protein kinase C- δ and rhoA were significantly increased, while those of soluble guanylyl cyclase α 1 and β 1 as well as protein kinase G were significantly decreased in the basilar artery of SAH rats. Treatment with CGS 26303 nearly normalized these effects.

CONCLUSIONS

These results demonstrate that the rhoA/rho-kinase and sGC/cGMP/PKG pathways play pivotal roles in cerebral vasospasm after SAH. It also shows that ECE inhibition is an effective strategy for the treatment of this disease.

Role of bilirubin oxidation products in the pathophysiology of DIND following SAH

Despite intensive research efforts, by our own team and many others, the molecules responsible for acute neurological damage following subarachnoid hemorrhage (SAH) and contributing to delayed ischemic neurological deficit (DIND) have not yet been elucidated. While there are a number of candidate mechanisms, including nitric oxide (NO) scavenging, endothelin-1, protein kinase C (PKC) activation, and rho kinase activation, to name but a few, that have been investigated using animal models and human trials, we are, it seems, no closer to discovering the true nature of this complex and enigmatic pathology. Efforts in our laboratory have focused on the chemical milieu present in hemorrhagic cerebrospinal fluid (CSF) following SAH and the interaction of the environment with the molecules generated by SAH and subsequent events, including NO scavenging, immune response, and clot breakdown. We have identified and characterized a group of molecules formed by the oxidative degradation of bilirubin (a clot breakdown product) and known as BOXes (bilirubin oxidation products). We present a synopsis of the characterization of BOXes as found in human SAH patients' CSF and the multiple signaling pathways by which BOXes act. In summary, BOXes are likely to play an essential role in the etiology of acute brain injury following SAH, as well as DIND.

The roles of early brain injury in cerebral vasospasm following subarachnoid hemorrhage: from clinical and scientific aspects

Cerebral vasospasm research has been focused on investigating the mechanisms of prolonged delayed vasoconstriction of cerebral arteries following subarachnoid hemorrhage (SAH). However, it has been clarified that induction of significant vasodilation of such arteries does not lead to better overall outcomes in SAH patients. On the other hand, early brain injury, such as cortical spreading depression, early cortical depolarization waves, and impairment of neurovascular coupling, is seen acutely after SAH and may play a significant role in early impairment of brain function following SAH. These results clearly indicate that it is time to reconsider what causes this early brain damage and dictates patient outcome following SAH; classical delayed cerebral vasospasm following SAH might be an epiphenomenon. It is of utmost importance to investigate whether early brain injury and delayed cerebral vasospasm correlate with each other following SAH or are independent. Recent results of cerebral vasospasm research indicates future directions, and such investigations would lead to better outcome for SAH patients.

Calcium and potassium channels in experimental subarachnoid hemorrhage and transient global ischemia

Healthy cerebrovascular myocytes express members of several different ion channel families which regulate resting membrane potential, vascular diameter, and vascular tone and are involved in cerebral autoregulation. In animal models, in response to subarachnoid blood, a dynamic transition of ion channel expression and function is initiated, with acute and long-term effects differing from each other. Initial hypoperfusion after exposure of cerebral vessels to oxyhemoglobin correlates with a suppression of voltage-gated potassium channel activity, whereas delayed cerebral vasospasm involves changes in other potassium channel and voltage-gated calcium channels expression and function. Furthermore, expression patterns and function of ion channels appear to differ between main and small peripheral vessels, which may be key in understanding mechanisms behind subarachnoid hemorrhage-induced vasospasm. Here, changes in calcium and potassium channel expression and function in animal models of subarachnoid hemorrhage and transient global ischemia are systematically reviewed and their clinical significance discussed.

Mechanisms underlying potentiation of endothelin-1-induced myofilament Ca(2+) sensitization after subarachnoid hemorrhage

Increased vascular smooth muscle contractility has an important role in the development of cerebral vasospasm after subarachnoid hemorrhage (SAH). Myofilament Ca(2+) sensitivity is a major determinant of smooth muscle contractility. We investigated changes in the Ca(2+)-sensitizing effect of endothelin-1 (ET-1) and the mechanisms underlying ET-1-induced Ca(2+) sensitization after SAH using a rabbit SAH model. After SAH, the contractile response to ET-1 was enhanced, and the ET(A) receptor expression was upregulated in the basilar artery. In α-toxin-permeabilized preparations, ET-1 induced enhanced and prolonged contraction after SAH, suggesting that ET-1-induced Ca(2+) sensitization is potentiated after SAH. Endothelin-1-induced Ca(2+) sensitization became less sensitive to inhibitors of Rho-associated coiled-coil protein kinase (ROCK) and protein kinase C (PKC) after SAH. The expression of PKCα, ROCK2, PKC-potentiated phosphatase inhibitor of 17 kDa (CPI-17) and myosin phosphatase target subunit 1 (MYPT1) was upregulated, and the level of phosphorylation of CPI-17 and MYPT1 was elevated after SAH. This study demonstrated for the first time that the Ca(2+)-sensitizing effect of ET-1 on myofilaments is potentiated after SAH. The increased expression and activity of PKCα, ROCK2, CPI-17, and MYPT1, as well as the upregulation of ET(A) receptor expression are suggested to underlie the enhanced and prolonged Ca(2+) sensitization induced by ET-1.

Roles of signal transduction mechanisms in cerebral vasospasm following subarachnoid hemorrhage: overview

The concept of "cortical spreading depression" following subarachnoid hemorrhage (SAH) drastically tends to change the direction of vasospasm research. It has been rather confuse whether classical idea, delayed long-lasting major cerebral arterial contraction is real cerebral vasospasm or it occurs just after SAH and classical arterial contraction is an epiphenomenon. However, it is true that such sustained arterial contraction occurs following SAH, and the mechanisms still remain unclear. Intracellular signal transduction plays a pivotal role in long-lasting arterial contraction. Although scientific research advances, each role of signal transduction system has been getting clarified; overview or interrelations among such systems have to be more investigated. Based on the previous results, some aspect or part of streams of interrelation of signal transduction systems can be getting clearer. Such way to clarify the overview is extremely important to understand the real mechanisms of long-lasting arterial contraction following SAH ("classical cerebral vasospasm").

Reduced Ca2+ spark activity after subarachnoid hemorrhage disables BK channel control of cerebral artery tone

Intracellular Ca(2+) release events ('Ca(2+) sparks') and transient activation of large-conductance Ca(2+)-activated potassium (BK) channels represent an important vasodilator pathway in the cerebral vasculature. Considering the frequent occurrence of cerebral artery constriction after subarachnoid hemorrhage (SAH), our objective was to determine whether Ca(2+) spark and BK channel activity were reduced in cerebral artery myocytes from SAH model rabbits. Using laser scanning confocal microscopy, we observed ∼50% reduction in Ca(2+) spark activity, reflecting a decrease in the number of functional Ca(2+) spark discharge sites. Patch-clamp electrophysiology showed a similar reduction in Ca(2+) spark-induced transient BK currents, without change in BK channel density or single-channel properties. Consistent with a reduction in active Ca(2+) spark sites, quantitative real-time PCR and western blotting revealed decreased expression of ryanodine receptor type 2 (RyR-2) and increased expression of the RyR-2-stabilizing protein, FKBP12.6, in the cerebral arteries from SAH animals. Furthermore, inhibitors of Ca(2+) sparks (ryanodine) or BK channels (paxilline) constricted arteries from control, but not from SAH animals. This study shows that SAH-induced decreased subcellular Ca(2+) signaling events disable BK channel activity, leading to cerebral artery constriction. This phenomenon may contribute to decreased cerebral blood flow and poor outcome after aneurysmal SAH.

The relaxant effect of okadaic acid on canine basilar artery involves activation of PKCalpha and phosphorylation of the myosin light chain at Thr-9

Vasodilator responses induced by okadaic acid were investigated in canine basilar artery precontracted with 80 mM KCl. Okadaic acid (1 microM) relaxed the artery and this relaxant effect was partially inhibited by Gö6976, a conventional protein kinase C inhibitor, and calphostin C, an inhibitor of conventional and novel PKCs. Rottlerin, a specific inhibitor of PKCdelta, did not influence okadaic acid's effect. KCl increased phosphorylation of 20,000-Dalton myosin light chain (MLC(20)) at Ser-19. Okadaic acid additionally increased MLC(20) phosphorylation at Thr-18 and Thr-9, resulting in triphosphorylation of MLC(20). This phosphorylation was inhibited by Gö6976. Okadaic acid stimulated phosphorylation of PKCalpha and 17,000-Dalton PKC-potentiated inhibitory phosphoprotein (CPI-17), and Gö6976 inhibited these phosphorylations. These results suggest that okadaic acid's relaxant effect involves MLC(20) triphosphorylation through a direct phosphorylation by PKCalpha and an indirect phosphorylation by inhibition of myosin light chain phosphatase through PKCalpha-mediated CPI-17 phosphorylation.

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

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 (CSFV) but not in CSF from SAH patients with no vasospasm (CSFC). 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 CSFV, but not CSFC, 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 CSFV. We will also present evidence implicating temporal changes in PKC isoforms and Rho expression in both BOXes- and CSFV-elicited smooth muscle responses.

Heparin-binding EGF-like growth factor mediates oxyhemoglobin-induced suppression of voltage-dependent potassium channels in rabbit cerebral artery myocytes

Oxyhemoglobin (OxyHb) can suppress voltage-dependent K(+) channel (K(V)) currents through protein tyrosine kinase activation, which may contribute to cerebral vasospasm following subarachnoid hemorrhage. Here we have tested the hypothesis that shedding of heparin-binding EGF-like growth factor (HB-EGF) and the resulting activation of the tyrosine kinase EGF receptor (EGFR) underlie OxyHb-induced K(V) channel suppression in the cerebral vasculature. With the use of the conventional whole cell patch-clamp technique, two EGFR ligands, EGF and HB-EGF, were found to mimic OxyHb-induced K(V) suppression in rabbit cerebral artery myocytes. K(V) current suppression by OxyHb or EGF ligands was eliminated by a specific EGFR inhibitor, AG-1478, but was unaffected by PKC inhibition. Compounds (heparin and CRM-197) that specifically interfere with HB-EGF signaling eliminated OxyHb-induced K(V) suppression, suggesting that HB-EGF is the EGFR ligand involved in this pathway. HB-EGF exists as a precursor protein that, when cleaved by matrix metalloproteases (MMPs), causes EGFR activation. MMP activation was detected in OxyHb-treated arteries by gelatin zymography. Furthermore, the MMP inhibitor (GM-6001) abolished OxyHb-induced K(V) current suppression. We also observed K(V) current suppression due to EGFR activation in human cerebral artery myocytes. In conclusion, these data demonstrate that OxyHb induces MMP activation, causing HB-EGF shedding and enhanced EGFR activity, ultimately leading to K(V) channel suppression. We propose that EGFR-mediated K(V) suppression contributes to vascular pathologies, such as cerebral vasospasm, and may play a more widespread role in the regulation of regional blood flow and peripheral resistance.

Protein kinase C inhibition prevents upregulation of vascular ET(B) and 5-HT(1B) receptors and reverses cerebral blood flow reduction after subarachnoid haemorrhage in rats

The pathogenesis of cerebral ischaemia after subarachnoid haemorrhage (SAH) still remains elusive. The purpose of the present study was to examine whether specific protein kinas C (PKC) inhibition in rats could alter the transcriptional SAH induced Endothelin (ET) type B and 5-hydroxytryptamine type 1B (5-HT(1B)) receptor upregulation and prevent the associated cerebral blood flow (CBF) reduction. The PKC inhibitor RO-31-7549 or vehicle was injected intracisternally after the induced SAH in rats (n=3 to 10 in each groups for each method). The involvement of the PKC isoforms was investigated with Western blot; only PKCdelta and PKCalpha subtypes were increased after SAH RO-31-7549 treatment abolished this. At 2 days after the SAH basilar and middle cerebral arteries were harvested and the contractile response to endothelin-1 (ET-1; ET(A) and ET(B) receptor agonist) and 5-carboxamidotryptamine (5-CT; 5-HT(1) receptor agonist) were investigated with a myograph. The contractile responses to ET-1 and 5-CT were increased (P<0.05) after SAH compared with sham operated rats. In parallel, the ET(B) and 5-HT(1B) receptor mRNA and protein expression were significantly elevated after SAH, as analysed by quantitative real-time polymerase chain reaction and immunohistochemistry, respectively. Administration of RO-31-7549 prevented the upregulated contraction elicited by application of ET-1 and 5-CT in cerebral arteries and kept the ET(B) and 5-HT(1B) receptor mRNA and protein levels at pre-SAH levels. Regional and global CBF evaluated by an autoradiographic technique were reduced by 60%+/-4% after SAH (P<0.05) and prevented by treatment with RO-31-7549. Our study suggests that PKC plays an important role in the pathogenesis of cerebral ischaemia after SAH.

Stretch-induced triphosphorylation of myosin light chain and myogenic tone in canine basilar artery

The relationship between phosphorylation of 20,000 Da myosin light chain (MLC20) and contraction in response to mechanical stretch was investigated in the canine basilar artery. A slow stretch (at a rate of 1 mm/s and a stimulus period for 15 min) increased triphosphorylated MLC20 despite lowered intracellular calcium concentration and mechanical activities, such as myogenic tone, shortening velocity and stiffness of the artery. Nicardipine, a Ca2+ channel blocker, and ML-9, a myosin light chain kinase (MLCK) inhibitor, partially inhibited the stretch-induced MLC20 phosphorylation. The remained phosphorylation was further reduced by calphostin C, a protein kinase C (PKC) inhibitor. Y-27632, a Rho-kinase inhibitor, inhibited phosphorylation of myosin light chain phosphatase and attenuated MLC20 phosphorylation. These results suggest that slow stretch induces triphosphorylation of MLC20, which is mediated by MLCK, PKC, and Rho-kinase, and that the triphosphorylation of MLC20 does not result in myogenic contraction, rather seems to counteract it.

Cerebral vasospasm: a consideration of the various cellular mechanisms involved in the pathophysiology

The cellular mechanisms responsible for cerebral vasospasm (CVS) occurring after subarachnoid hemorrhage (SAH) have been of major interest over the past 50 years. The present review describes how each of the discrete anatomic components that comprise the cerebral artery may contribute to the pathology of CVS. The blood extravasated after SAH is hemolyzed and undergoes degradation with resultant production of free radicals, known to be powerful initiators of vascular damage. An inflammatory response is generated activating both leukocytes and platelets with subsequent release of inflammatory agents. The cerebral artery affected by CVS undergoes phenotypic change involving both the endothelial and smooth muscle cells. In the endothelium the production of nitric oxide and prostacyclin is affected. In the smooth muscle cells signal transduction pathways that enhance the function of the contractile proteins and induce the upregulation of contractile receptors are activated. In parallel, there is evidence that nervous reflex pathways involving the trigeminal ganglion and the hypothalamus are activated. However, the relative contributions of each of the systems are speculative. Therapy may be directed at disrupting the cascade leading from the SAH insult to CVS or at overcoming the dysfunction incurred by CVS; possible therapeutical interventions are considered.

Co-expression/co-location of S100 proteins (S100B, S100A1 and S100A2) and protein kinase C (PKC-beta, -eta and -zeta) in a rat model of cerebral basilar artery vasospasm

OBJECT

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhages (SAH) involve a number of members of the protein kinase C (PKC) family. However, whereas calcium is thought to play a number of major roles in the pathophysiology of SAH, a number of PKCs function independently of calcium. We recently emphasized the potential role of the calcium-binding S100 proteins in a 'double haemorrhage' rat model of SAH-induced vasospasm. A number of S100 proteins are known to interfere directly with PKC, or indirectly with PKC substrates. We therefore investigated whether specific S100 proteins and PKCs are co-expressed/co-located in a rat model of SAH-induced vasospasm.

METHODS AND RESULTS

SAH-induced vasospasm in rats (by means of a double cisternal injection of autologous blood from a rat femoral artery) distinctly modified the expression levels of calcium-dependent PKC-alpha and PKC-beta and calcium-independent PKC-eta and PKC-zeta in endothelial and smooth-muscle cells. The RNA levels of these four PKC isotypes were determined by quantitative RT-PCR. The present study reveals that, in endothelial cells, the S100B expression/location correlate well with those of PKC-eta, and those of S100A1 with PKC-beta. In smooth-muscle cells S100A2 expression/location correlate with those of PKC-eta, and those of S100B with PKC-zeta.

CONCLUSION

The present data argue in favour of a joint action of the S100 protein network and the PKC signalling pathway during cerebral vasospasm.

Biomechanical and phenotypic changes in the vasospastic canine basilar artery after subarachnoid hemorrhage

Because it has been argued that active myogenic tone prolongs cerebral vasospasm for >2 wk after subarachnoid hemorrhage (SAH), we attempted to identify the mechanism that plays the main role in sustaining the prolonged cerebral vasospasm. We especially focused on the roles of biomechanical and phenotypic changes in the cerebral arteries in the mechanisms of prolonged vasospasm after SAH. We used the basilar arteries from a “two-hemorrhage” canine model to make serial measurements of maximal contraction capacity and arterial stiffness (papaverine-insensitive tone) until day 28. We also examined hematoxylin-eosin-stained vasospastic canine basilar arteries for histological changes and immunohistochemically examined them for expression of myosin heavy chain isoforms (SMemb, SM1, and SM2), which are markers of smooth muscle phenotypic changes. Changes in collagen concentration in canine basilar arteries were also measured. Angiographic cerebral vasospasm persisted until day 14 and then gradually diminished; artery diameter returned to the control diameters on day 28. Maximal contraction capacity decreased until day 21 and showed some recovery by day 28. Arterial stiffness, on the other hand, progressed until day 28. Histological examination revealed medial thickening and increased connective tissue until day 21 and a return to control findings by day 28. The increased connective tissue was not accompanied by changes in collagen concentration, suggesting a role of some other protein in the increase in connective tissue. Immunohistochemical studies with anti-SMemb, anti-SM1, and anti-SM2 antibodies showed enhanced expression of SMemb from day 7 to day 21 and disappearance of SM1 and SM2 on days 14 and 21. The changes in myosin heavy chain isoform expression returned to normal on day 28. The above results indicate that biomechanical and phenotypic changes may play a pivotal role in sustaining cerebral vasospasm for >2 wk after SAH, with minimal changes in active myogenic arterial tone.

Signaling mechanisms in cerebral vasospasm

The elusive nature of events that sustain cerebral vasospasm after subarachnoid hemorrhage resulting from a ruptured aneurysm presents major challenges in designing effective therapies for this frequently devastating condition. Protracted cerebral artery constriction entails several dynamic components in intracellular signaling events initiated by endothelial factors, products of hemolysate, and numerous kinases, as well as increased intracellular Ca(2+). The rationale for potential treatment modalities and their efficacy are discussed in this brief review.

Vascular smooth muscle function: The physiology and pathology of vasoconstriction

Vascular smooth muscle is the contractile component of arteries and veins. The control of contraction and relaxation is dependent upon intracellular and extracellular signals. Abnormal contractions can cause and or contribute to pathology such as hypertension, ischemia and infarction. In this review, we address the vascular pathogenesis associated with hypertension and subarachnoid hemorrhage induced cerebral vasospasm. Hypertension is a multifactorial disease with many causes and a profound impact on the cardiovascular system, whereas subarachnoid hemorrhage induced cerebral vasospasm is a pathological vasoconstriction often causing infarction that is thought to be 'caused' by a factor or factors in the CSF following the hemorrhage. However, the mechanism by which the vessels are constricted is unknown. Although the causes for these two pathological vasoconstrictions remain to be determined, we conclude that the common denominator is that these contractile changes result in pathology with devastating consequences to human health.

Interactive role of protein kinase C-delta with rho-kinase in the development of cerebral vasospasm in a canine two-hemorrhage model

BACKGROUND

We previously reported that protein kinase C (PKC)-delta was initially translocated from the cytosol to the membrane fraction (on day 4), followed by PKC-alpha, with the progression of cerebral vasospasm after subarachnoid hemorrhage (SAH) on day 7. Rho/Rho-kinase pathways have also been proposed to be involved in the vasospasm. Thus we investigated the interactive role of Rho-kinase and PKC in the development of cerebral vasospasm after SAH.

METHODS

The cerebral vasospasm was produced using a 'two-hemorrhage' canine model. The animals were treated with Y-27632, a Rho-kinase inhibitor, and rottlerin, a PKC-delta inhibitor, both injected into the cisterna magna.

RESULTS

Y-27632 inhibited the vasospasm, 20-kDa myosin light chain (MLC20) phosphorylation, and PKC-delta translocation after the second injection of autologous blood on day 4. In contrast, Y-27632 did not affect the vasospasm on day 7. Rottlerin also inhibited the vasospasm on day 4, but had no effect on MLC20 phosphorylation and RhoA translocation. The vasospasm was accompanied with the phosphorylation of caldesmon (CaD), an actin-linked regulatory protein, which was strongly attenuated by Y-27632 and rottlerin. The application of PKC-delta to skinned strips of isolated canine basilar arteries caused a contraction and an increase in CaD phosphorylation.

CONCLUSION

The development of cerebral vasospasm after SAH (on day 4) is caused by at least two mechanisms: one involves MLC20 phosphorylation mediated by the inhibition of MLC20 phosphatase by Rho-kinase, and the other CaD phosphorylation mediated by the activation of PKC-delta by Rho-kinase, which results in the alleviation of the inhibition by CaD of myosin Mg2+-ATPase activity.

[Regulatory role of mechanical stress response in cellular function: development of new drugs and tissue engineering]

The investigation of mechanotransduction in the cardiovascular system is essentially important for elucidating the cellular and molecular mechanisms involved in not only the maintenance of hemodynamic homeostasis but also etiology of cardiovascular diseases including arteriosclerosis. The present review summarizes the latest research performed by six academic groups, and presented at the 75th Annual Meeting of the Japanese Pharmacological Society. Technology of cellular biomechanics is also required for research and clinical application of a vascular hybrid tissue responding to pulsatile stress. 1) Vascular tissue engineering: Design of pulsatile stress-responsive scaffold and in vivo vascular wall reconstruction (T. Matsuda); 2) Cellular mechanisms of mechanosensitive calcium transients in vascular endothelium (M. Oike et al.); 3) Cross-talk of stimulation with fluid flow and lysophosphatidic acid in vascular endothelial cells (K. Momose et al.); 4) Mechanotransduction of vascular smooth muscles: Rate-dependent stretch-induced protein phosphorylations and contractile activation (K. Obara et al.); 5) Lipid mediators in vascular myogenic tone (I. Laher et al.); and 6) Caldiomyocyte regulates its mechanical output in response to mechanical load (S. Sugiura et al.).

20-Hydroxyeicosatetraenoic acid potentiates stretch-induced contraction of canine basilar artery via PKC alpha-mediated inhibition of KCa channel

1. The present study was undertaken to elucidate whether PKCalpha plays a role in the mechanism of the stretch-induced contraction potentiated by 20-hydroxyeicosatetraenoic acid (20-HETE). The effects of 20-HETE on the canine basilar artery were compared with those of iberiotoxin, a blocker of large conductance Ca(2+)-activated K(+) channels (K(Ca) channels), as this blocker was shown earlier to sensitize these arteries to mechanical stretch. 2. Slow stretch at rates of 0.1 to 3 mm s(-1) did not produce any contraction in normal physiological solution. 3. In the presence of 20-HETE, the slow stretch could produce contraction, which was inhibited by nicardipine, a 1,4-dihydropyridine Ca(2+) channel blocker, and gadolinium, a blocker of stretch-activated cation channels. 4. 20-HETE inhibited whole-cell K(+) current and depolarized the membrane by approximately 10 mV. These effects of 20-HETE were similar to those of iberiotoxin. 5. Calphostin C, an inhibitor of protein kinase C (PKC), inhibited the action of 20-HETE, but not that of iberiotoxin. 6. In response to 20-HETE PKCalpha isoform was translocated from the cytosol to the membrane fraction, which translocation was inhibited by calphostin C. 7. These results suggest that 20-HETE induced sensitization of the canine basilar artery to stretch was caused by PKCalpha-mediated inhibition of K(Ca) channel activity.

Inhibitory effects of protein kinase C on inwardly rectifying K+- and ATP-sensitive K+ channel-mediated responses of the basilar artery

BACKGROUND AND PURPOSE

The structurally related, inwardly rectifying K+ (K(IR)) channel and the ATP-sensitive K+ (K(ATP)) channel are important modulators of cerebral artery tone. Although protein kinase C (PKC) activators have been shown to inhibit these channels with the use of patch-clamp electrophysiology, effects of PKC on K+ channel function in intact cerebral blood vessels are unknown. We therefore tested whether pharmacological alteration of PKC activity affects cerebral vasodilator responses to K(IR) and/or K(ATP) channel activators in vivo.

METHODS

We measured changes in basilar artery diameter using a cranial window preparation in anesthetized rats. In addition, intracellular recordings of smooth muscle membrane potential were made in isolated basilar arteries.

RESULTS

K+ (5 to 15 mmol/L) and aprikalim (1 to 10 micromol/L) each elicited reproducible vasodilatation. The PKC activator phorbol-12,13-dibutyrate (PdBu) (50 nmol/L) inhibited responses to K+ (by 40% to 55%) and aprikalim (by 40% to 70%), whereas responses to papaverine were unaffected. The PKC inhibitor calphostin C (0.1 micromol/L) augmented responses to K+ (by 2- to 3-fold) and aprikalim (2-fold) but not papaverine. In addition, K+ (5 mmol/L) and aprikalim (3 micromol/L) each hyperpolarized the basilar artery. PdBu inhibited these responses to aprikalim by 45% but had no effect on K+-induced hyperpolarization.

CONCLUSIONS

These data suggest that both basal and stimulated PKC activity inhibit K(IR) and K(ATP) channel-mediated cerebral vasodilatation in vivo. The inhibitory effect on K(ATP) channel-mediated vasodilatation occurs at least partly by inhibition of hyperpolarization mediated by K(ATP) channels. PKC inhibits K+-induced vasodilatation without affecting hyperpolarization, suggesting that the inhibitory effect of PKC on vasodilator responses to K+ does not involve altered K(IR) channel function.

[Role of protein kinase C isozymes in cellular functions and pathological conditions]

Protein kinase C (PKC) is a superfamily of lipid-dependent protein Ser/Thr kinases consisting of at least 10 isozymes. The present article summarizes the papers presented at the congress symposium of the 74th Annual Meeting of the Japanese Pharmacological Society, in which six special topics regarding PKC isozyme-dependent cellular functions and pathological disorders were discussed. Using a GFP-tagged PKC expression technique, each PKC subtype was suggested to vary its targeting-site in each cell in response to each stimulus and that the targeting to the specific compartment is necessary for the specific cellular responses (NS). A cardioprotective agent, JTV519, was shown to attenuate post-ischemic myocardial injury by mimicking ischemic preconditioning through specific activation of PKC delta (YK). Using an antisense technique, PKC alpha and delta/epsilon were shown to be necessary for gene expression of inducible NO synthase by interleukin-1, one of the proinflammatory cytokines, by a stimulated transactivation of NF-kappa B (TH). In canine cerebral artery, PKC delta and PKC alpha play important roles in the development and the maintenance of vasospasm induced by subarachnoid hemorrhage, respectively (SN); and stretch-induced MLC20 phosphorylation involves MLCK and PKC alpha but not PKC delta activities facilitated by inactivation of myosin phosphatase through Rho activity (KO & KN). To clarify the role of PKC isozymes in insulin resistance, the effects of insulin on glucose uptake, PKC isozyme activation and PI3K activation in rat adipocytes were shown and then platelet PKC beta activation in diabetic patients with various diabetic complications, including diabetic retinopathy, was reported (TI). These studies will promisingly open the way to a new era for the development of novel drugs controlling an isozyme-specific activity of the protein kinase C superfamily and improvement in the knowledge about the role of the protein kinase in health and disease.

Protein kinase C and cerebral vasospasm

Twenty-five years after the discovery of protein kinase C (PKC), the physiologic function of PKC, and especially its role in pathologic conditions, remains a subject of great interest with 30,000 studies published on these aspects. In the cerebral circulation, PKC plays a role in the regulation of myogenic tone by sensitization of myofilaments to calcium. Protein kinase C phosphorylates various ion channels including augmenting voltage-dependent Ca2+ channels and inhibiting K+ channels, which both lead to vessel contraction. These actions of PKC amplify vascular reactivity to different agonists and may be critical in the regulation of cerebral artery tone during vasospasm. Evidence accumulated during at least the last decade suggest that activation of PKC in cerebral vasospasm results in a delayed but prolonged contraction of major arteries after subarachnoid hemorrhage. Most of the experimental results in vitro or in animal models support the view that PKC is involved in cerebral vasospasm. Implication of PKC in cerebral vasospasm helps explain increased arterial narrowing at the signal transduction level and alters current perceptions that the pathophysiology is caused by a combination of multiple receptor activation, hemoglobin toxicity, and damaged neurogenic control. Activation of protein kinase C also interacts with other signaling pathways such as myosin light chain kinase, nitric oxide, intracellular Ca2+, protein tyrosine kinase, and its substrates such as mitogen-activated protein kinase. Even though identifying PKC revolutionized the understanding of cerebral vasospasm, clinical advances are hampered by the lack of clinical trials using selective PKC inhibitors.

Glycated serum albumin-induced vascular smooth muscle cell proliferation through activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway by protein kinase C

Proliferation of vascular smooth muscle cells (VSMC) contributes to the pathogenesis of atherosclerosis, and glycated serum albumin (GSA, Amadori adduct of albumin) might be a mitogen for VSMC proliferation, which may further be associated with diabetic vascular complications. In this study, we investigated the involvement of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK), and protein kinase C (PKC), in GSA-stimulated mitogenesis, as well as the functional relationship between these factors. VSMC stimulation with GSA resulted in a marked activation of ERK. The MAPK kinase (MEK) inhibitor, PD98059, blocked GSA-stimulated MAPK activation and resulted in an inhibition of GSA-stimulated VSMC proliferation. GSA also increased PKC activity in VSMC in a dose-dependent manner. The inhibition of PKC by the PKC inhibitors, GF109203X and Rottlerin (PKCdelta specific inhibitor), as well as PKC downregulation by phorbol 12-myristate 13-acetate (PMA), inhibited GSA-induced cell proliferation and blocked ERK activation. This indicates that phorbol ester-sensitive PKC isoforms including PKCdelta are involved in MAPK activation. Thus, we show that the MAPK cascade is required for GSA-induced proliferation, and that phorbol ester-sensitive PKC isoforms contribute to cell activation and proliferation in GSA-stimulated VSMC.