Donate Help Contact The AHA Sign In Home
American Heart Association
Circulation Research
Search: search_blue_button Advanced Search
« Previous Article | Table of Contents | Next Article »
Circulation Research. 2006;99:238-239
doi: 10.1161/01.RES.0000236798.01988.5d
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Liao, J. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Liao, J. K.
Related Collections
Right arrowRelated Article
(Circulation Research. 2006;99:238.)
© 2006 American Heart Association, Inc.

Editorials

Rho-Kinase

A Potential Link Between Hypercholesterolemia and Abnormal Vascular Smooth Muscle Contraction

James K. Liao

From the Vascular Medicine Research Unit, Cardiovascular Division, Brigham and Women’s Hospital and Harvard Medical School, Boston, Mass.

Correspondence to James K. Liao, MD, Brigham and Women’s Hospital, 65 Landsdowne St, Rm 275, Cambridge, MA 02139. E-mail jliao{at}rics.bwh.harvard.edu



See related article, pages 299–306


Key Words: cholesterol • Rho kinase • calcium • smooth muscle • contraction

Although elevated serum cholesterol levels and hypertension are independent risk factors for cardiovascular disease, far too often they are manifested in the same individual.1 Whether this is a coincidental finding between 2 highly prevalent risk factors or perhaps because of some mechanistic link between these 2 processes is unclear. Regardless, the concomitant treatment of hypercholesterolemia and hypertension has yielded additive and possibly synergistic reductions in cardiovascular events.2

Previous studies attempting to link hypercholesterolemia with abnormal vascular smooth muscle (SMC) contractions have focused on the endothelium. Hypercholesterolemia and atherosclerosis impair the production and/or availability of endothelium-derived NO, leading to endothelial dysfunction and abnormal vascular reactivity.3–5 Indeed, acute lowering of serum cholesterol with low-density lipoprotein-apheresis or with statin therapy improves endothelium-dependent relaxations.6–8 These findings suggest that the endothelium serves as the primary mediator of the inhibitory effect of hypercholesterolemia on vascular motor function. The direct effect of cholesterol on SMC, however, is less well understood as endothelium-independent vasorelaxations to nitroprusside are often unaltered in hypercholesterolemia or in patients with atherosclerosis.6,8,9

In the present study, Morikage et al extend the effects of cholesterol on vascular reactivity to changes in SMC contractions.10 They showed that elevated serum cholesterol levels were associated with increased calcium sensitization of SMC through the sphingosylphosphorylcholine (SPC)/Rho-kinase (ROCK)-mediated pathway in humans and rabbits. This enhanced SMC contraction was observed only with ROCK activator SPC and not with phenylephrine or potassium; was accompanied by minimal changes in intracellular calcium concentration; and was unaffected by addition of the eNOS inhibitor, NG-monomethyl-L-arginine, or removal of the endothelium. However, the SMC contraction was abolished by addition of the ROCK inhibitor, Y27632, or by applying a dominant-negative mutant of ROCK (dn-ROK) to the cytosol of permeabilized SMC. Interestingly, Y27632 and dn-ROK had no effect on calcium-dependent SMC contraction, suggesting calcium sensitization of SMC rather than calcium-induced SMC contraction by cholesterol. The authors conclude that cholesterol enhances calcium sensitivity of SMC to SPC via ROCK and suggest that this may be a mechanism by which hypercholesterolemia could precipitate vasospasms or perhaps increase the risk for hypertension.

ROCK plays a central role in diverse cellular functions such as SMC contraction, stress fiber formation, and cell migration and proliferation.11 Presently, 2 ROCK isoforms have been identified, ROCK1 and ROCK2.12–15 ROCK1 and ROCK2 share an overall 65% homology in amino-acid sequence and 92% homology in their kinase domains.11 Thus, pharmacological inhibitors of ROCK such as Y-27632, fasudil (HA1077), and hydroxyfasudil, which target their ATP-dependent kinase domains, can inhibit both ROCK1 and ROCK2. Furthermore, at higher concentrations, Y-27632 can also inhibit protein kinase C–related kinase-2, protein kinase N, and citron kinase,16 whereas fasudil can inhibit protein kinase A and protein kinase C.17 Physiologically, ROCKs can be activated by serum lysopholipids such as lysophosphatidic acid, sphingosine-1 phosphate, and SPC, which stimulate RhoGEF and lead to the formation of active GTP-bound Rho GTPases.11 ROCKs are serine-threonine protein kinases and immediate downstream targets of Rho GTPases.18,19 They control the assembly of the actin cytoskeleton, increase calcium sensitization, and enhance cell contractility by phosphorylating a variety of proteins, such as myosin light chain phosphatase, LIM kinases, adducin, and ezrin-radixin-moesin proteins.11 Indeed, inhibition of ROCK prevents cerebral ischemia,20 coronary vasospasm,21 hypertension,22,23 and atherosclerosis.24 Thus, it is likely that SPC-induced calcium sensitization and the subsequent enhanced contractions of SMC, as demonstrated in the present study by Morikage et al, is mediated by ROCK.10

Immunolocalization and cell-fractionation studies of ROCKs, especially ROCK2, have shown that this protein is distributed mainly in the cytoplasm.14,25 Activated ROCK2 partly translocates from the cytoplasm to membranes. For example, a small amount of ROCK2 has been found in the membrane fraction, and some immunostaining is detectable at the cell periphery or membranes of growing cells.26 In the present study, SPC-induced translocation of cytosolic ROCK to the cell membrane and SMC contractions were blocked by depletion of cellular cholesterol with ß-cyclodextrin and the subsequent loss of cholesterol-enriched lipid rafts. These findings suggest that translocation of ROCK to lipid rafts is essential for its function and that cholesterol enhances this process. Thus, cholesterol primes SMC in terms of enhancing ROCK-mediated calcium sensitivity by facilitating ROCK translocation to cholesterol-enriched lipid rafts. Clinically, calcium sensitization of SMC by ROCK is observed in patients with hypertension,22,23 and as shown in the present study, in patients with hypercholesterolemia.10

Although cholesterol may be necessary for ROCK-mediated effects, several questions remain. Because most studies have used ROCK inhibitors, which cannot discriminate between ROCK1 and ROCK2, it is unknown what the relative importance of ROCK isoforms is in calcium sensitization of SMC. Perhaps future studies with isoform-specific ROCK inhibitors or ROCK-deficient mice will shed light on this matter. Furthermore, it is not known whether patients who have lower serum cholesterol levels or who received lipid-lowering therapy have decreased membrane ROCK and lipid rafts, and if so, whether this is associated with decreased blood pressure. Although blood pressure was not monitored as frequently in previous lipid-lowering trials with statins as with hypertensive trials, none of lipid-lowering trials have ever shown a clear reduction in blood pressure with statin therapy. Thus, further studies are required to determine whether the priming effect of cholesterol on ROCK-mediated calcium sensitivity of SMC contributes clinically to higher blood pressure. Unless these questions are addressed, it remains to be determined whether ROCK is an important therapeutic target for hypertension in patients with and without hypercholesterolemia.


*    Acknowledgments
 
Sources of Funding

Supported by National Institutes of Health grant HL052233.

Disclosures

None.


*    Footnotes
 
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.


*    References
up arrowTop
 *References
 

  1. Poulter NR, Wedel H, Dahlof B, Sever PS, Beevers DG, Caulfield M, Kjeldsen SE, Kristinsson A, McInnes GT, Mehlsen J, Nieminen M, O’Brien E, Ostergren J, Pocock S; ASCOT Investigators. Role of blood pressure and other variables in the differential cardiovascular event rates noted in the Anglo-Scandinavian Cardiac Outcomes Trial-Blood Pressure Lowering Arm (ASCOT-BPLA). Lancet. 2005; 366: 907–913.[CrossRef][Medline] [Order article via Infotrieve]
  2. Sever PS, Dahlof B, Poulter NR, Wedel H, Beevers G, Caulfield M, Collins R, Kjeldsen SE, Kristinsson A, McInnes GT, Mehlsen J, Nieminen M, O’Brien E, Ostergren J; ASCOT investigators. Prevention of coronary and stroke events with atorvastatin in hypertensive patients who have average or lower-than-average cholesterol concentrations, in the Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm (ASCOT-LLA): a multicentre randomised controlled trial. Lancet. 2003; 361: 1149–1158.[CrossRef][Medline] [Order article via Infotrieve]
  3. Harrison DG, Freiman PC, Armstrong ML, Marcus ML, Heistad DD. Alterations of vascular reactivity in atherosclerosis. Circ Res. 1987; 61 (5 Pt 2): II74–II80.[Medline] [Order article via Infotrieve]
  4. Liao JK, Shin WS, Lee WY, Clark SL. Oxidized low-density lipoprotein decreases the expression of endothelial nitric oxide synthase. J Biol Chem. 1995; 270: 319–324.[Abstract/Free Full Text]
  5. Ohara Y, Peterson TE, Harrison DG. Hypercholesterolemia increases endothelial superoxide anion production. J Clin Invest. 1993; 91: 2546–2551.[Medline] [Order article via Infotrieve]
  6. Anderson TJ, Meredith IT, Yeung AC, Frei B, Selwyn AP, Ganz P. The effect of cholesterol-lowering and antioxidant therapy on endothelium-dependent coronary vasomotion. N Engl J Med. 1995; 332: 488–493.[Abstract/Free Full Text]
  7. Tamai O, Matsuoka H, Itabe H, Wada Y, Kohno K, Imaizumi T. Single LDL apheresis improves endothelium-dependent vasodilatation in hypercholesterolemic humans. Circulation. 1997; 95: 76–82.[Abstract/Free Full Text]
  8. Treasure CB, Klein JL, Weintraub WS, Talley JD, Stillabower ME, Kosinski AS, Zhang J, Boccuzzi SJ, Cedarholm JC, Alexander RW. Beneficial effects of cholesterol-lowering therapy on the coronary endothelium in patients with coronary artery disease. N Engl J Med. 1995; 332: 481–487.[Abstract/Free Full Text]
  9. Ludmer PL, Selwyn AP, Shook TL, Wayne RR, Mudge GH, Alexander RW, Ganz P. Paradoxical vasoconstriction induced by acetylcholine in atherosclerotic coronary arteries. N Engl J Med. 1986; 315: 1046–1051.[Abstract]
  10. Morikage N, Kishi H, Sato M, Guo F, Shirao S, Yano T, Soma M, Hamano K, Esato K, Kobayashi S. Cholesterol primes vascular smooth muscle to induce Ca2+-sensitization mediated by a sphingosylphosphorylcholine-Rho-kinase pathway: possible role for membrane raft. Circ Res. 2006; 99: 299–306.[Abstract/Free Full Text]
  11. Riento K, Ridley AJ. Rocks: multifunctional kinases in cell behaviour. Nat Rev Mol Cell Biol. 2003; 4: 446–456.[CrossRef][Medline] [Order article via Infotrieve]
  12. Amano M, Ito M, Kimura K, Fukata Y, Chihara K, Nakano T, Matsuura Y, Kaibuchi K. Phosphorylation and activation of myosin by Rho-associated kinase (Rho-kinase). J Biol Chem. 1996; 271: 20246–20249.[Abstract/Free Full Text]
  13. Leung T, Chen XQ, Manser E, Lim L. The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton. Mol Cell Biol. 1996; 16: 5313–5327.[Abstract]
  14. Leung T, Manser E, Tan L, Lim L. A novel serine/threonine kinase binding the Ras-related RhoA GTPase which translocates the kinase to peripheral membranes. J Biol Chem. 1995; 270: 29051–29054.[Abstract/Free Full Text]
  15. Nakagawa O, Fujisawa K, Ishizaki T, Saito Y, Nakao K, Narumiya S. ROCK-I and ROCK-II, two isoforms of Rho-associated coiled-coil forming protein serine/threonine kinase in mice. FEBS Lett. 1996; 392: 189–193.[CrossRef][Medline] [Order article via Infotrieve]
  16. Ishizaki T, Uehata M, Tamechika I, Keel J, Nonomura K, Maekawa M, Narumiya S. Pharmacological properties of Y-27632, a specific inhibitor of rho-associated kinases. Mol Pharmacol. 2000; 57: 976–983.[Abstract/Free Full Text]
  17. Rikitake Y, Kim HH, Huang Z, Seto M, Yano K, Asano T, Moskowitz MA, Liao JK. Inhibition of Rho kinase (ROCK) leads to increased cerebral blood flow and stroke protection. Stroke. 2005; 36: 2251–2257.[Abstract/Free Full Text]
  18. Noma K, Oyama N, Liao JK. Physiological role of ROCKs in the cardiovascular system. Am J Physiol Cell Physiol. 2006; 290: C661–C668.[Abstract/Free Full Text]
  19. Rikitake Y, Liao JK. Rho GTPases, statins, and nitric oxide. Circ Res. 2005; 97: 1232–1235.[Abstract/Free Full Text]
  20. Sato M, Tani E, Fujikawa H, Kaibuchi K. Involvement of Rho-kinase-mediated phosphorylation of myosin light chain in enhancement of cerebral vasospasm. Circ Res. 2000; 87: 195–200.[Abstract/Free Full Text]
  21. Masumoto A, Mohri M, Shimokawa H, Urakami L, Usui M, Takeshita A. Suppression of coronary artery spasm by the Rho-kinase inhibitor fasudil in patients with vasospastic angina. Circulation. 2002; 105: 1545–1547.[Abstract/Free Full Text]
  22. Masumoto A, Hirooka Y, Shimokawa H, Hironaga K, Setoguchi S, Takeshita A. Possible involvement of Rho-kinase in the pathogenesis of hypertension in humans. Hypertension. 2001; 38: 1307–1310.[Abstract/Free Full Text]
  23. Uehata M, Ishizaki T, Satoh H, Ono T, Kawahara T, Morishita T, Tamakawa H, Yamagami K, Inui J, Maekawa M, Narumiya S. Calcium sensitization of smooth muscle mediated by a Rho-associated protein kinase in hypertension. Nature. 1997; 389: 990–994.[CrossRef][Medline] [Order article via Infotrieve]
  24. Mallat Z, Gojova A, Sauzeau V, Brun V, Silvestre JS, Esposito B, Merval R, Groux H, Loirand G, Tedgui A. Rho-associated protein kinase contributes to early atherosclerotic lesion formation in mice. Circ Res. 2003; 93: 884–888.[Abstract/Free Full Text]
  25. Matsui T, Amano M, Yamamoto T, Chihara K, Nakafuku M, Ito M, Nakano T, Okawa K, Iwamatsu A, Kaibuchi K. Rho-associated kinase, a novel serine/threonine kinase, as a putative target for small GTP binding protein Rho. Embo J. 1996; 15: 2208–2216.[Medline] [Order article via Infotrieve]
  26. Kimura K, Ito M, Amano M, Chihara K, Fukata Y, Nakafuku M, Yamamori B, Feng J, Nakano T, Okawa K, Iwamatsu A, Kaibuchi K. Regulation of myosin phosphatase by Rho and Rho-associated kinase (Rho-kinase). Science. 1996; 273: 245–248.[Abstract]

Related Article:

Cholesterol Primes Vascular Smooth Muscle to Induce Ca2 Sensitization Mediated by a Sphingosylphosphorylcholine–Rho-Kinase Pathway: Possible Role for Membrane Raft
Noriyasu Morikage, Hiroko Kishi, Masafumi Sato, Fengling Guo, Satoshi Shirao, Takashi Yano, Masaaki Soma, Kimikazu Hamano, Kensuke Esato, and Sei Kobayashi
Circ. Res. 2006 99: 299-306. [Abstract] [Full Text] [PDF]



This article has been cited by other articles:


Home page
 StrokeHome page
M. A. Moskowitz
The 2006 Thomas Willis Lecture: The Adventures of a Translational Researcher in Stroke and Migraine
Stroke, May 1, 2007; 38(5): 1645 - 1651.
[Full Text] [PDF]

This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Liao, J. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Liao, J. K.
Related Collections
Right arrowRelated Article

Circulation Research Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search
Copyright © 2006 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited.