G ProteinCoupled Receptor Kinasesin Cardiovascular Disease: WhyWhere MattersFadia A. Kamal, Joshua G. Travers, and Burns C. Blaxall*Cardiacfunctionis mainlycontrolledby -adrenergicreceptors (-ARs), members of the Gproteincoupled receptor (GPCR) family.GPCRsignalingandexpressionaretightlycontrolledbyGproteincoupled receptor kinases (GRKs), which induce GPCR internalizationandsignalterminationthroughphosphorylation.Reduced-ARden-sity and activity associated with elevated cardiac GRK expression andactivity have been described in various cardiovascular diseases. More-over, alterationsinextracardiacGRKshavebeenobservedinbloodvessels, adrenal glands, kidneys, and fat cells. The broad tissue distri-butionof GPCRs and GRKs suggests that a keenappreciationofintegrativephysiologymaydrivefuturetherapeuticdevelopment. Inthis review, we provide a brief summary of GRK isoforms, subcellularlocalization, and interacting partners that impinge directly or indirectlyon the cardiovascular system. We also discuss GRK/GPCR interactionsand their implications incardiovascular pathophysiology. (TrendsCardiovasc Med 2012;22:213219) 2012 Published by Elsevier Inc.IntroductionG-proteincoupled receptor kinases(GRKs) are found in nearly all mamma-lian cells but possess broad and diverseeffects ranging from G proteincoupledreceptor (GPCR) signal terminationtotranscriptional regulation. Hyper/hypo-activity of GRKs has been correlatedwithvarious humanpathophysiologies,including cardiovascular disease. As theirname implies, GRKs are dened by theirroleinGPCRphosphorylation, receptorinternalization, and signal termination.Excessive GRK-mediated GPCR phos-phorylationleadstoreceptordesensi-tization and alternative (GPCR-inde-pendent) signaling. As major players inGPCR-dependent and -independentsignalingpathways, GRKsarebecom-ing attractive therapeutic targets. Inparticular, modulatingtheexpressionand/or activity of specic GRKs andtheir interacting partners has beensuggestedasanoveltherapeuticstrat-egyincardiovasculardisease.GRK Isoforms, SubcellularLocalization, and InteractionsGRKsareclassiedintothreesubfami-liesGRK1, GRK2, andGRK4basedonsequencehomology, genestructure,andtissueexpression. TheGRK1sub-family includes GRKs 1 and 7, which aregenerally restrictedto the retina. TheGRK2 subfamily includes GRKs 2 and 3,which are ubiquitously expressed, al-though to varying degrees depending onthe tissue. The GRK4 subfamily in-cludes GRKs 4-6, where GRK4 is foundmainly inthe testes andrenal tissueand GRKs 5 and 6 are ubiquitouslyexpressed. Within the heart, GRKs 2, 3,and5areknowntobeexpressed, withGRKs 2 and 5 representing the main func-tional GRKs in the myocardium(Bel-monte and Blaxall 2011).With regard to protein structure, theGRKs containthree general domains.An 25amino acid N-terminal tailunique to the GRK family, a regulator ofG protein signaling (RGS) homology do-main, and a catalytic region containing aSer/Thr protein kinase domain (Sid-erovski et al. 1996) are common betweenall GRKs. The remaining C-terminal do-mainis characterizedby subtype-spe-cic structural elements that dictatemembrane targeting and subcellular lo-calization of different GRKs. Briey,GRKs1and7haveaC-terminusCaaxmotif for prenylation and subsequentmembrane recruitment. Membrane lo-calizationof GRKs4and6isaresultof C-terminus palmitoylation, whereasGRKs5and6C-terminuslipid-bindingdomain facilitates their membrane bind-ing (Pitcher et al. 1996, Stoffel et al.1994). GRKs 2 and 3 are generallycytoplasmicandareuniquelytargetedtothemembranefromthecytoplasminasignaling-dependentmanner: Up-onagonist stimulation, the activatedG subunits recruit these GRKs totheagonist-boundGPCR, culminatingin phosphorylation of the receptor(Pitcheretal.1992).Finally,sequenceanalysisof GRK5hasidentiedanu-clear localizationdomain, suggestingthat it may act as an epigenetic regula-tor; furthermore, accumulation ofGRK5 in cardiac myocyte nuclei pro-motes cardiac hypertrophy due to its func-tionasahistonedeacetylase(HDAC)ki-nase (Dorn 2009, Huang et al. 2012,Martini et al. 2008).Activationof GRKs, initiallydiscov-eredtofunctionasGPCRkinases,gen-erally requires N-terminusmediated al-losteric activation by the agonist-boundGPCR (Huang and Tesmer 2011), a fea-ture distinguishing them from other ser-ine-threonine protein kinases (Lodowskiet al. 2006). Subsequently, GRK-medi-ated GPCR phosphorylation, in combina-tion with recruitment of-arrestin to thereceptor, leads to functional repression ofFadia A. Kamal, Joshua G. Travers, andBurnsC. Blaxall areat TheHeart Institute,Molecular Cardiovascular Biology, Cincin-nati Childrens Hospital Medical Center, Cin-cinnati, OH 45229, USA.*Address correspondence to: Burns C.Blaxall, PhD, FAHA, The Heart Institute, Mo-lecular Cardiovascular Biology, CincinnatiChildrensHospital Medical Center, Cincin-nati, OH45229, USA. Tel.: (1) 513-803-4005; fax: (1)513-636-5958; e-mail: burns.blaxall@cchmc.org.Published online 10 October, 2012. 2012 Published by Elsevier Inc.1050-1738/$-see front matterTCM Vol. 22, No. 8, 2012 213Gproteinmediated signaling. GRK-mediated phosphorylation of diverseserine and threonine GPCRresiduescreates a specic pattern (or bar-code) that controls differential activa-tionof downstreamsignalingafea-turerecentlytermedbiasedsignaling(Patel et al. 2010). This occurs viamodulating-arrestin scaffolding withdivergentinteractingpartners(Kimetal. 2005, Patwardhan and Miller 2007).For example, phosphorylationof theangiotensinII receptor byGRK2and3 mediated receptor internalization,whereas phosphorylation by GRK5promotedactivationoftheextracellu-lar signal-related kinase (ERK) (Kim etal.2005).Recently, GRKshavebeenfoundtophosphorylate a variety of non-GPCRproteins, including transcription factorsand tyrosine kinases, further broadeningtheirfunctionalrolesinprocessessuchas proliferation, development, andim-munity. These alternative roles for GRKsmay result from the innate basal activityofGRKsorperhapsthroughphosphor-ylation of proteins located near activatedGPCRs (Usui et al. 2005). Sofar, theplatelet-derivedgrowthfactor receptor(PDGFR)istheonlynon-GPCRreceptorwhose desensitization is initiated by GRK2-dependent phosphorylation, wherephos-phorylation of the epidermal growthfactor receptor by GRK2 remains withunknown functional consequences(Freedman et al. 2002). Targets of GRKshavealsoexpandedtoincludecytoskel-etal proteins such as tubulin. Phosphor-ylationoftubulinbyGRK2inresponsetoGprovidesevidencethatGRK2isresponsible for transmitting signalsfromGPCRstothecytoskeleton(Hagaet al. 1998, Perrino et al. 2006).A summary of GRK interacting part-nersandtheresultant downstreamef-fects incardiovascular signalingpath-ways is provided in Table 1.GRKs in Cardiovascular Disease:Friends or Foes?HeartCardiac contractility is mainly con-trolled by catecholamines (CAs) that arelocally released into cardiac tissue fromsympathetic neurons or bycirculatingCAsthatarereleasedfromtheadrenalgland. CA levels are increased in re-sponsetoelevatedloadorstressontheheart,whereacutephysiologicstimula-tionof cardiac -adrenergic receptors(-ARs)resultsinanadaptiveincreasein cardiac output, which ultimately acti-vatesanegativefeedbacklooptosup-pressfurthercatecholaminerelease. Atthe cellular level, agonist-receptor inter-Table 1. Partial list of GRK interacting partners relevant to cardiovascular diseaseGRK subtype Interacting partner Tissue/cells Effect ReferenceGPCRGRK2 -AR Vascular smoothmuscle cellsPhosphorylation induces receptordesensitization; overexpression in VSMCsreduces the response to adrenergicstimulation.Eckhart et al.(2002)Angiotensin IIreceptorHEK 293 cells Phosphorylation by GRK2 mediatesreceptor internalization.Kim et al. (2005)GRK3 1-AR Isolated cardiomyocytes Cardiac-specic GRK3 inhibition elevatesblood pressure due to increasedsensitivity of the1-AR to stimulation.Vinge et al.(2008)GRK4 Dopamine 1 receptor(D1-R)Human renal proximaltubules CHO cellsPhosphorylation induces receptordesensitization; increased activity ofGRK4 splice variant is associated withhypertension.Felder et al.(2002)GRK5 -AR Transgenic mice in vivo GRK5 overexpression reduces cardiacresponsiveness to adrenergic stimulation.Rockman et al.(1996)Angiotensin IIreceptorHEK 293 cells Phosphorylation by GRK5 promotesactivation of ERK.Kim et al. (2005)Non-GPCRGRK2 PDGFR HEK 293 cells Smoothmuscle cellsPhosphorylation by GRK2 promotesreceptor desensitization.Freedman et al.(2002)Tubulin Porcine brain extracts GRK2 phoshporylates tubulin inresponse to G, linking GPCR activationto cytoskeletal remodeling.Haga et al.(1998)Glucose transporter 4 3T3-L1 adipocytes The GRK2 RGS domain sequesters Gq/11, thus inhibiting this insulin-responsivetransporter.Usui et al. (2004)IRS-1 3T3-L1 adipocytesIsolated cardiomyocytesPhosphorylation results in receptordegradation that impairs insulinsignaling.Usui et al. (2005)Ciccarelli et al.(2011)GRK5 Class II HDAC Neonatal rat ventricularmyocytesAdult cardiomyocytesGRK5 accumulation in cardiac myocytenuclei promotes cardiac hypertrophy.Martini et al.(2008)214 TCM Vol. 22, No. 8, 2012actions initiate GRK-mediated-AR de-sensitization and signal cessation. Clini-cal and experimental studies suggestthat this GRK-mediated receptor desen-sitization is initially an adaptive/protec-tivemechanismbecausechronic -ARstimulation can be deleterious to theheart. Inthefailingheart, diminishingcardiac output triggers a vicious cycle ofpersistent sympathetic activation, re-sultinginfurther -ARdesensitizationandmaladaptivesignalingdueinlargepart to GRK-mediated receptor phos-phorylationandlossof responsivenessto sympathetic stimulation.Desensitization of the-AR has beenassociatedwithupregulationof GRK2bothatthemRNAlevelandatthepro-tein level. To explore the role of GRK2 inthe heart, many labs have utilized the tech-nique of genetic manipulation. Interest-ingly, whereas homozygous knockout ofGRK2wasshowntobeembryoniclethal(Jaber et al. 1996), micehemizygousforGRK2(GRK2/) showincreased-ARmediated cardiac contractility (Rockman etal. 1998b). Furthermore, overexpression ofGRK2 following ischemia-reperfusionreduced adrenergic-mediated cardiaccontractilityandcardiacfunctioncon-comitant with increased apoptosis(Brinksetal. 2010). Conversely, condi-tional ablationof cardiacGRK2eitherbefore or 10 days postinfarction reducedmortality and enhanced cardiac contrac-tility as well as -AR responsiveness(Raakeet al. 2008). OverexpressionofGRK3 had no effect on cardiac sensitiv-ity to -AR stimulation in vivo; however,cardiac-specicinhibitionof GRK3re-sulted in elevated systolic blood pressureduetoincreasedcardiacoutput, afea-ture attributed to increased sensitivity ofthe 1-ARtostimulation(Vinge et al.2008).CardiacoverexpressionofGRK5resultedinreducedcardiacresponsive-ness to adrenergic stimulation (Rock-manet al. 1996) alongwithworsenedcardiac function (Chen et al. 2001), sug-gesting that GRK5 may impair-adren-ergic signaling in heart failure (HF)(Pinget al. 1997, Takagi et al. 1999).AlthoughGRK5upregulationhasbeenreported in experimental models of HF,thereis currentlynoevidenceof suchupregulation in human HF. In addition,whenGRK5is excludedfromthenu-cleus, a loss of the myocardial patholog-ical phenotypeensues, suggestingthatGRK5 subcellular localization plays acritical role in its function (Martini et al.2008). A recent study highlighted an ad-ditional roleforGRK5intheheart, inwhich the L41Qpolymorphism, mostabundant in African Americans, wascorrelatedwithreducedmortalityfromHF in human patients and was alsoshowntobeprotectiveagainst experi-mentalcardiomyopathyinamouseHFmodel (Liggett et al. 2008).To demonstrate a key role for GRK2 intheonsetandprogressionofHF,severalstrategies have been adopted to suppresstheexpressionand/oractivityof GRK2.OnesuchstrategyemploysARKct, theC-terminal peptide of GRK2, which com-petes for binding to G with endogenousGRK2, thus inhibiting its membrane re-cruitment and resultant receptor desen-sitization. ARKct, delivered to the heartvia transgenesis or viral transduction, isgenerally effective in preventing cardio-myopathy (Freeman et al. 2001, Hardinget al. 2001, Rengo et al. 2009, Rockmanet al. 1998a, Shah et al. 2001, White et al.2000) and limiting ischemic injury(Brinks et al. 2010), as well as normaliz-ing-ARsignaling(Eckhart andKoch2002, Rockman et al. 1998a, Shah et al.2001, Whiteet al. 2000). Forexample,whenARKctisexpressedinGRK2/mice, theydemonstrate increasedcar-diac contractility inresponse to -ARstimulation (Rockman et al. 1998b). Re-cently, a possible alternative mechanismfor the salutary cardiac effects ofARKct was reported, in which viraldeliverytoculturedcardiomyocytesse-questered G and prevented its inhibi-tory action on the L-type calcium chan-nel (Vlkers et al. 2011). This resulted inenhanced cardiac contractile respon-siveness to-AR agonists with no effecton -ARmediated cAMP signaling. In asimilar manner, when GRK5 is inhibitedby intracardiac adenoviral expression ofadGRK5-NT, theN-terminal peptideofGRK5, there is amelioration of HF in thespontaneously hypertensive rat (SHR)(Sorriento et al. 2010).To overcome the various challenges oflarge peptide therapeutics, we recently in-vestigated whether small molecules couldbe found with efcacy similar toARKctandthepossibleadvantageofsystemicdelivery. We recently reported the prom-ising effects of small molecule G inhi-bition in alleviating cardiac dysfunctionin two models of murine HF. ThesecompoundsbindtoGandallosteri-callyinhibit itsinteractionwithGRK2(andasmallgroupofotherinteractingpartners), thus disruptingdownstreamsignaling. Improved cardiac functionand reduced hypertrophy were ob-served, attributedmainly toenhanced-ARsignalingandreducedGRK2ex-pression and membrane recruitment(Casey et al. 2010).VasculatureImpairedGPCRsignalinginthevascu-lature has a dramatic impact on overallcardiovascular health. Disruption of2-ARmediated vasodilation, accompa-nied by vascular GRK2 upregulation,hasbeenimplicatedinhypertensioninboth human patients and animal models(Cohn et al. 2008, Cohn et al. 2009,Eckhart et al. 2002, Feldman 1990, Feld-manandGros 1998, Gros et al. 2000,Izzo et al. 2008). Interestingly, the prop-ertiesof -ARsinhumanlymphocytesmirror thechanges observedin-ARsfrom less accessible tissues, allowing cli-nicianstoutilizelymphocytesasvalu-able tools for the assessment of -ARfunction both in hypertension and in HF(Bonita et al. 2010, Hata et al. 2006,Oyama et al. 2006). Selective disparity ofGRK2is observedinhypertensive pa-tientsinwhomelevatedGRK2activityand protein expression are not accompa-nied by variations inGRKs 5 and 6,proteinkinaseA,or-arrestins1and2(Gros et al. 1997).TargetedoverexpressionofGRK2invascularsmoothmusclecells(VSMCs)led to a dampened vasodilation, in addi-tion to hypertension, vascular wall thick-ening, and myocardial hypertrophy(Eckhart et al. 2002). Thisoverexpres-sion also showed an unexpected attenu-ation in blood pressure rise in responsetovasoconstrictingangiotensinIIchal-lenge (Rockman et al. 1996). On thecontrary, the inhibition of GRK2 activityin the VSM by ARKct or genetic knock-down failed to reduce blood pressure inarenalstenosismodelofhypertension,despite increased2-ARmediated vaso-dilation. This was due to increased1D-adrenoreceptormediated vasoconstric-tion that is facilitated by GRK2inhibition (Cohn et al. 2008). GRK2 hasalso been implicated in the disruption ofnonadrenergic endothelial cell nitric ox-TCM Vol. 22, No. 8, 2012 215idesynthasemediatedvasodilationviaAKTinhibition in portal hypertensiverats,inwhichGRK2knockoutrestorednitricoxideproductionandnormalizedportalpressure(Liuetal.2005).Inad-dition, inhibition of GRK2 (but notGRKs 3, 5, or 6) resultedinreduceddesensitization of endothelin-inducedCa2and IP3 signaling in rat mesentericarterysmoothmuscle cells (resistancearteries) (Morris et al. 2010).ThesecondGRKisoformexpressedinVSMCs is GRK5. Vascular-targetedGRK5 overexpression in mice increasedblood pressure via a Gi-dependentpathway in a gender-dependent manner(malesmorethanfemales). IncontrasttoGRK2, overexpressionof GRK5didnotcausevascularorcardiachypertro-phy (Keys et al. 2005). Beyond theireffect on GPCRs, GRK5 has been foundto inhibit vascular endothelial growthfactor receptor signaling, anon-GPCRinteractingpartner, incoronaryarteryendothelial cells (Zhou et al. 2009). Therole of GRK3, another subtype ex-pressed within the VSM, in hypertensionremains essentially unexplored.Adrenal GlandAn alternative target for HF therapy is theelevatedlevel of catecholamines withincirculation. Prominent sympatheticner-vous system(SNS) hyperactivitystimu-latestheadrenalglandstosecreteexces-sive amounts of catecholamines fromtheir medullarychromafncells, apro-cesstightlycontrolledbynegativefeed-back inhibition through adrenal 2-ARs.Animal models of HFexhibit adrenalhypertrophy, downregulation of adrenal2-ARs, andGRK2upregulation. Adre-nalARKcttreatmentisabletorestoretheinhibitoryeffectof2-ARsonadre-nal catecholamine release, thus breakingthepathological cycleof persistent ad-renergic stimulation of the heart, result-ing in improved cardiac function inthese models (Lymperopoulos et al.2007). Moreover, recent ndings havecorrelatedthebenecialeffectsofexer-cise training in chronic HF to the reduc-tion in adrenal GRK2 expression (Rengoet al. 2010). Recently, -blocker treat-ment was foundtonormalize adrenal2-AR density and GRK2 expression in amyocardial infarction rat model (Rengoet al. 2012). Importantly, central inhibi-tionof thesympatheticoverdrivewithsympatholytic agents suchas moxoni-dine(animidazolereceptorand2-ARagonist) increasedmorbidityandmor-tality in cardiovascular disease (Clarkand Cleland 2000). This may be partiallyduetodesensitizationofadrenal 2-ARreceptorsandtheconsequentcatechol-amine hypersecretion.Aldosterone, a hormone released fromthe adrenal cortex and regulated by ang-iotensinII,isanothercontributortoHFpathology. Recently, inhibition of adrenalGRK2/arr1 biased signaling was showntobeeffectiveinamelioratingelevatedaldosterone levels and associated car-diac dysfunction in experimental modelsof HF (Lymperopoulos et al. 2011).KidneyThekidneysplayamajorroleinmain-tainingnormalbloodpressurebyregu-lating water and electrolyte transport inrenal proximal tubules via the dopamine1receptor(D1-R).Normally,dopaminestimulation of D1-R invokes a natri-ureticresponse.However,thisfunctionis lost in both animal (Nishi et al. 1993)andhumanhypertension(OConnell etal. 1997) due to D1-R desensitization byGRK4inrenal proximal tubules (Wa-tanabeet al. 2002); further, GRK4ex-pression is noted to increase in SHR rats(Sanadaet al. 2006). Singlenucleotidepolymorphismsleadingtoincreasedki-nase activity of the GRK4 splice varianthavebeencorrelatedwithhypertensionbothinhumanpatientsandinanimalmodels (Felder and Jose 2006, Felder etal. 2002). However, further studies mustbeperformedtoelucidatethestructureand function of GRK4 and its splicevariantstodrawaclearerimageof itsrole in hypertension.Impairedrenal D1-Rs inobesity-in-duced insulin resistance and the role ofGRKs inthat process present anotherpathological contributor to HF. Upregu-AdrenalAdrenalFigure 1. GRKs in cardiovascular disease. (A) Persistent sympathetic stimulation of the cardiomyocyte triggersGRK2 upregulation that aggravates -AR desensitization and impairs adrenergic signaling. GRK2 upregulationdue to sympathetic nervous system overdrive has also been shown to be involved in the development of insulinresistance. In the nucleus, GRK5 mediates cardiac hypertrophy by phosphorylating HDAC. (B) The adrenal glandwas recently recognized as an attractive target for HF therapy because adrenal medullary chromafn cells are thesites of catecholamine synthesis. GRK2 upregulation has been correlated with elevated catecholamine synthesisandsecretion, primarilyduetodesensitizationoftheinhibitory2-ARreceptors. (C)Intheadrenal cortex,angiotensin regulates aldosterone synthesis, where GRK2--arrestin 1mediated signaling interferes with thisregulatory pathway and elevated aldosterone secretion. (D) In the kidneys, dopamine 1-Rmediated natriuresisisdampenedbyGRK4;waterandsodiumretentionarekeyfactorsofhypertension.(E)Inthevasculature,2-ARmediated vasodilation is impaired by GRK2, leading to hypertension and cardiac and vascular hypertro-phy. GRK5 hyperactivity in the vasculature precipitates hypertension.216 TCM Vol. 22, No. 8, 2012lationofGRK4and, toalesserextent,GRK2 is observed in the renal proximaltubulesofobeseanimalsleadingtohy-perphosphorylationofD1-Randitsun-coupling from Gs, provoking impairedD1-Rmediated natriuresis and hyper-tension. The pathological processeswere ameliorated by treatment with theinsulin-sensitizing drug rosiglitazone(Trivedi and Lokhandwala 2005, Umranietal.2002).AlthoughGRK2maybeoflessimportanceforrenalD1-Rdesensi-tization, inhibiting GRK2 membrane re-cruitment or protein expression in insu-lin-treated kidney cells can normalizeD1-R phosphorylation and function(Banday et al. 2007).Insulin ResistanceDiseases such as diabetes, obesity, hyper-tension, and HF are often associated withinsulinresistance, wherereducedtissuesensitivity toinsulinis associatedwithmetabolic abnormalities. Enhanced SNSsignalingplaysaroleinthepathogen-esis of insulin resistance because-ARstimulationimpairsinsulin signaling inboth adipocytes and cardiac myocytes(Morisco et al. 2006). This occursthroughthesequesteringofGq/11viathe GRK2 RGS domain, thus inhibitingthe insulin-responsive glucose trans-porter 4 (Usui et al. 2004). Alternatively,GRK2canphosphorylateanddesensi-tize the insulin receptor substrate-1(IRS-1)inresponsetochronicstimula-tion of GPCRs such as the endothelin-Areceptor(Usuietal.2005).Invitroandin vivo data have indicated that reducedGRK2 levels induce enhanced insulinsensitivity and a lean phenotype and alsoprotect against tumor necrosis factor-,ahigh-fatdiet,andaging-inducedinsu-lin resistance (Garcia-Guerra et al.2010), as well as postischemic defects inmyocardial insulin signaling and cardiacmetabolism (Ciccarelli et al. 2011).These data demonstrate the importanceof GRK2 in the pathology of insulinresistance.ConclusionsThe vast physiological effects of GRKsmakethemanattractivetherapeutictar-get for cardiovascular as well as otherdiseases(Figure1). GRKinhibitionhasbeen shown to directly ameliorate cardio-vascular disease by inhibiting pathologi-cal signaling cascades and/or promotingsurvival signals. However, detailed infor-mationregarding their branching sig-naling pathways and interacting part-ners mayenablethetransitionof thispromising therapeutic strategy to theclinic. Discovery of GRKand/or Ginhibitory agents with a convenientroute of administration and limited sideeffectsmaybeakeystepinthistransi-tion. Considering the pleiotropic andmultiorgan effects of GRK signaling,systemic GRK inhibition may provide asuperior therapeutic strategy for cardio-vascular diseaseanditscomorbidities.Ourdata(Caseyetal.2010),aswellasothers, suggest that it is possible thatsystemicdeliveryofsmall moleculein-hibitorsmayameliorateGRK(orG-GRK)mediatedpathological signalingin multiple organs, thus treating cardio-vasculardiseasefromseveraltherapeu-tic angles.ReferencesBandayAA, Fazili FR, &LokhandwalaMF:2007. 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Thechallenge facing researchers and clinicians alike is to decipher the biolog-ical and clinical signicance of these variants and harness the informationforthepracticeofmedicine. ThecommonDSVstypicallyexertmodesteffect sizes, as evidenced by the results of genome-wide association studies,and hence have modest or negligible clinical implications. The focus is onthe rare variants with large effect sizes, which are expected to have strongerclinical implications, as in single gene disorders with Mendelian patternsof inheritance. However, the clinical implications of the rare variants forcommon complex cardiovascular diseases remain to be established. Themost important contribution of WES or WGS is in delineation of the novelmolecular pathways involved in the pathogenesis of the phenotype, whichwould be expected to provide for preventive and therapeutic opportunities.(Trends CardiovascMed2012;22:219223) 2012Elsevier Inc. Allrights reserved.IntroductionThe advent of massively parallel nucleicacidsequencingor next-generationse-quencing (NGS) technologies has had anenablingimpact indelineatingthege-neticmakeupof eachindividual. NGShasraisedconsiderableinterest inpo-tential applications of theinformationembedded in the DNA sequence of eachgenome in the practice of medicine. TheNGS platforms have afforded the oppor-tunity to sequence the entire genome ofanindividual (wholegenomesequenc-ing[WGS]), whichiscomposedof 3.2billion nucleotides, within a week. Like-wise, it hasenabledsequencingof theentire protein-coding region, referred toas exome, which is composed of approx-imately 180,000 exons in approximately23,500 genes and 30 million nucleotides,indozens of individuals withina fewdays(wholeexomesequencing[WES]).The enormity of this progress is remark-AliJ.MarianisattheCenterforCardiovas-cularGenetics, BrownFoundationInstituteof Molecular Medicine, The University ofTexas Health Science Center and Texas HeartInstitute, Houston, TX 77030, USA.*Address correspondence to: Ali J. Marian,MD, Center for Cardiovascular Genetics,Brown Foundation Institute of MolecularMedicine, The University of Texas HealthSciencesCenter,TexasHeartInstitute,6770Bertner St, Suite C900A, Houston, TX 77030,USA. Tel.: (1)7135002350; fax: (1)713500 2320; e-mail: Ali.J.Marian@uth.tmc.edu.Published online 24 August, 2012. 2012 Elsevier Inc. All rights reserved.1050-1738/$-see front matterTCM Vol. 22, No. 8, 2012 219