PI3K(p110α) as a determinant and gene therapy for atrial enlargement in atrial fibrillation.

Atrial fibrillation (AF) is an irregular heart rhythm, characterised by chaotic atrial activation, which is promoted by remodelling. Once initiated, AF can also propagate the progression of itself in the so-called ''AF begets AF''. Several lines of investigation have shown that signalling molecules, including reactive oxygen species, angiotensin II, and phosphoinositide 3-kinases (PI3Ks), in presence or absence of cardiovascular disease risk factors, stabilise and promote AF maintenance. In particular, reduced cardiac-specific PI3K activity that is not associated with oncology is cardiotoxic and increases susceptibility to AF. Atrial-specific PI3K(p110α) transgene can cause pathological atrial enlargement. Highlighting the crucial importance of the p110α protein in a clinical problem that currently challenges the professional health care practice, in over forty (40) transgenic mouse models of AF (Table1), currently existing, of which some of the models are models of human genetic disorders, including PI3K(p110α) transgenic mouse model, over 70% of them reporting atrial size showed enlarged, greater atrial size. Individuals with minimal to severely dilated atria develop AF more likely. Left atrial diameter and volume stratification are an assessment for follow-up surveillance to detect AF. Gene therapy to reduce atrial size will be associated with a reduction in AF burden. In this overview, PI3K(p110α), a master regulator of organ size, was investigated in atrial enlargement and in physiological determinants that promote AF. Table 1 Transgenic and Knockout Mouse Models of AF Gene Alteration Atrial enlargement Fibrosis Thrombus Ventricular dysfunction based on echo and/or catheter Conduction abnormalities by ECG APD Alteration AF pattern/other major cellular and molecular mechanisms References Rho GDIα TG Cardiac-specific overexpression of Rho GDP dissociation inhibitor (GDI)α with α-myosin heavy chain (α-MHC) promoter Atrial weight 0.6-fold increase vs NTg at 4 months but no changes at 4 weeks ✔ no significant increase in atrial and ventricle Not reported  ↔  Sinus bradycardia, varying degrees of AV block, prolongation of P-wave duration, and PR interval at 7 months Not reported Spontaneous Other mechanisms oreduced Connexin 40 expression oincreased expression of RhoA, Rac1, and Cdc42 [58] RhoA Cardiac-specific overexpression of RhoA with α-MHC promoter Atrial weight threefold increase vs NTg ✔ in ventricle Not reported ✔ Bradycardia and AV block Not reported Spontaneous Other mechanisms oincreased expression of hypertrophic genes oInflammation [59] Junction TG Cardiac-specific overexpression of junctin protein with α-MHC promoter Atrial weight, more than tenfold increase vs WT for right atrium ✔ in atrial and ventricle ✔ in left and right atria ✔ Bradycardia Atrial and ventricle APD 70, phase 3 ↑ Spontaneous Other mechanisms oreduced triadin, RYR2, diastolic Ca 2+ , and Ca 2+ transient amplitude [60] Junctate 1 TG Cardiac-specific SR-located Ca 2+ -binding protein junctate 1 overexpression with α-MHC promoter Atrial weight, fourfold increase for left atrium and about fivefold increase for right atrium vs WT ↑ in atria and ventricle ✔ Intra-atrial thrombi ✔ Ventricular bigeminy, sinus pause, and bradycardia APD 90, phase 4 ↑ Spontaneous Other mechanisms oreduced phospholamban phosphorylation, troponin I phosphorylation, Calreticulin, and RyR2 channel oreduced SR Ca 2+ content, Ca 2+ transient amplitude oincreased I Ca,L [61] AMPK TG N488I Cardiac-specific PRKAG2 (AMPK γ2 subunit) overexpression with missense mutation Not reported Not reported Not reported ✔ Reduced PR interval, persistent sinus bradycardia without AV block Not reported Spontaneous and paroxysmal Other mechanisms ocardiac glycogen accumulation [62] A 1 AR TG Cardiac-specific overexpression of A 1 adenosine receptor (A 1 AR) with α-MHC No difference No fibrosis Not reported ✔ Slow AV conduction APD 90, phase 4 ↔  APD 50, phase 2 ↔  APD 70, phase 2 ↔  Spontaneous [63] A 3 tg TG Cardiac-specific overexpression of A 3 adenosine receptor (A 3 AR) with α-MHC promoter Atrial size onefold and twofold increase at 12 weeks and 21 weeks, respectively, vs NTg Not present in atria and ventricle Not reported ✔ Absence of normal sinus rhythm, bradycardia, and intermittently complete Not reported Spontaneous Other mechanisms oreduced SERCA mRNA levels [64] RTEF1 TG Cardiac-specific overexpression of Transcription enhancer factor-1-related factor (RTEF1) with α-MHC promoter Atrial weight 4-sixfold increase vs control Not present in atria and ventricle ✔ Organised Not reported Slow conduction in working myocardium, prolonged PR interval, and QRS duration Not reported Spontaneous Mechanisms oincreased PP1β phosphatase ochronic dephosphorylation of cardiac connexin [65] ACE 8/8 TG Cardiac-restricted angiotensin-converting enzyme (ACE) Overexpression with α-MHC Ang II concentration was 4.3-fold higher in ACE mice compared to WT Atrial weight, about threefold increase vs WT ✔ in atria but not in ventricle Not reported ✔ AV block Not reported Spontaneous [66] K ir 2.1 TG K ir 2.1 I K1 channel subunit cardiac-specific overexpression with α-MHC promoter Atrial weight, left and right atrial to body weight 65% and 141% increase, respectively, vs control Not reported Not reported ✔ Absence of T wave and reduced QT interval APD 90, phase 4 ↓ APD 50, phase 2 ↔  APD 75, phase 3 ↔  MAP90 Phase 4 ↓ MAP75 phase 3 ↓ MAP50 , phase 2 ↔  Spontaneous [67] Kcne1 -/- K + -channel KCNE1 subunit global protein deletion in mouse Normal atrial size Not present in atria and ventricle Not reported  ↔  AV block APD 50, phase 2 ↓ APD 90, phase 4 ↓ Spontaneous [68] hKCNE1-hKCNQ1 TG Human (h)KCNE1-hKCNQ1 Cardiac-specific overexpression with α-MHC promoter in mouse Not reported Not reported Not reported Not reported Complex atrial and irregular ventricular excitation β-AR mediated APD 50, phase 2 ↑ APD 90, phase 4 ↓ Spontaneous Other mechanisms oIncreased I Ks density [69] Des -/- Desmin global knockout Not reported Not reported Not reported Not reported Supraventricular premature beats, spontaneous ventricular premature beats, and Wenckebach periodicity Not reported Spontaneous Other mechanisms oHypokalemia, oReduced refractory period [70] CREM-IbΔC-X Human cAMP-response element modulator (CREM) heart-directed overexpression with α-MHC promoter Atrial weight, about 5-sevenfold increase vs NTg at 12-16 weeks Not present in left atrium and ventricle ✔ Organised thrombi in left and right atria ✔ Not reported Not reported Spontaneous Other mechanisms oReduced phosphorylation of CREB and of PLB oIncreased phosphorylation of SERCA2, PP1, and mRNA levels of ANP [71] CREM-IbΔC-X Human cAMP-CREM heart-directed Overexpression with α-MHC promoter Left atrial size, twofold increase vs WT at 13-17 weeks ↑ in atria Not reported Not reported Ectopic beats APD 25, phase 1 ↑ APD 50, phase 2 ↑ APD 90 phase 4 ↑ Spontaneous and persistent Other mechanisms oLeaky SR Ca 2+ stores oDownregulation of connexin 40 [72] CREM-IbΔC-X Human cAMP- CREM and reduced RyR 2 -S2814A phosphorylation heart-directed overexpression with germline transmission and Meox2-Cre crossing Atrial weight, sixfold increase vs WT at 3 months ↑ in atria and ventricle Not reported  ↔  Spontaneous atrial ectopy APD 80, phase 4 ↑ Spontaneous at 3-month paroxysmal and persistent at 4-5 months Other mechanisms oincreased SR Ca 2+ leak and CaMKII activity oreduced connexin 40 [73] JDP TG Heart-restricted c-Jun dimerization protein 2 overexpression with α-MHC promoter Atrial cell diameter 1.4-fold increase vs WT Not present in the atrial and ventricle Not reported  ↔  Increased PR interval, AV block and Wenckebach periodicity Not reported Spontaneous Other mechanisms oreduced expression of connexin 40 and 43 oAng II signalling [74] RacET Heart-restricted constitutively active Rac1 Rho GTPase overexpression with α-MHC promoter Atrial weight, fourfold increase vs WT ↑ in atria and ventricle Not reported ✔ No observable conduction defects except AF Not reported Spontaneous and persistent Other mechanisms oincreased NADPH oxidase activity [75] Anxa7 -/- Annexin global knockout Not reported Not reported Not reported  ↔ at basal AV block, ventricular tachyarrhythmia, shorter P-wave and QRS duration, and abnormal conduction velocity Not reported Spontaneous Other mechanisms oreduced protein expression of SERCA2a oincrease expression of NCX protein oβ 1 -adrenergic signalling [76] TNF1.6 TG Heart-directed overexpression of tumour necrosis factor-α with α-MHC promoter Isolated atrial area 3.6-fold increase from 6 to 9 months in female vs NTg ✔ in atria ✔ Organised thrombi in atria Not reported Episodes of second degree AV block, premature beats, and Ventricular ectopy APD 75 Phase 4 ↔  Spontaneous Other mechanisms oimpaired Ca 2+ loading oreduced intracellular Ca 2+ transients [77] MHCsTNF TG Cardiac-specific overexpression of tumour necrotic factor with α-MHC promoter Not reported Not reported Not reported ✔ AV junctional rhythm, short PR interval and wide QRS complex Not reported Spontaneous Other mechanisms oreduced connexion 40 expression oinflammation [78] MURCTG Cardiac-specific overexpression of muscle-related coiled-coil protein with α-MHC promoter Enlarged atrial compared to NTg ↑ in atria and ventricle Thrombus in the left atrial ✔ Complete AV block and prolongation of the PR interval Not reported Spontaneous Other mechanisms oreduced SERCA2, increased ANP, BNP, βMHC, TGF-β1, TGF-β2, and TGF-β3 [79] Nup155 ± Reduced nuclear envelope permeability by nucleoporin (NUP) 155 gene missense mutation on R391H Not reported Not reported Not reported Not reported Irregular RR intervals APD 90, phase 4 ↓ Spontaneous Other mechanisms oreduced HSP70 nuclear localization [80] a1D -/- L-type Ca 2+ channel (Ca v 1.3) subunit global knockout Not reported Not reported Not reported Not reported SA and AV nodes conduction defects Not reported Spontaneous Other mechanisms olack of Ca v 1.3, and reduced I Ca,L [81] LTCC (α1D -/- ) L-type Ca 2+ channel α1D subunit global knockout Smaller compared with WT Not reported Not reported Not reported Sinus bradycardia and AV block Not reported Spontaneous Other mechanisms oreduced I Ca,L , Ca 2+ transient amplitude, and SR Ca 2+ content [82] dnPI3K-DCM Cardiac-specific dominant negative phosphoinositide 3-kinase p110α (dnPI3K) DCM due to overexpression of mammalian sterile 20-like kinase 1 expression with α-MHC promoter Atrial size 3.45-fold increase vs NTg ↑ in atria and ventricle ✔ Chronic thrombi in the left atrium ✔ Prolonged PR intervals, double peak P-wave, and second and third degree AV block Not reported Spontaneous Other mechanisms oaltered expression of metabolic genes and K + channels oreduced HSP70 [16] Dct -/- Melanin synthesis enzyme dopachrome tautomerase global knockout Not reported No Not reported  ↔  No observable conduction defects except for AF APD 50 , phase 2 ↔  APD 90 , phase 4 ↔  Spontaneous Other mechanisms oplasma membrane caveolae accumulation oenlargement of mitochondria [83] RyR2 R176Q/+ R176Q mutation in RYR2 gene through germline transmission and Meox2-Cre crossing Normal atrial size No fibrosis in atrial and ventricle Not reported Not reported RR interval variability, absence of P-wave APD 50 phase 2 ↔  APD 80 phase 4 ↔  Spontaneous Other mechanisms oincreased CaMKII-dependent phosphorylation of RyR2 oelevated SR Ca 2+ leak [84] Gα q TG Overexpression of activated Gαq cardiac protein with α-MHC promoter Left atrial size, 2.5-fold increase vs WT ↑ in atria but not in ventricle ✔ Left atrial, unorganised thrombus Not reported Premature atrial contraction and irregular RR interval APD 80 , phase 4 ↑ Spontaneous [85] NppaCre + Pitx2 - / - Atrial and ventricular-restricted loss of function of paired-like homeodomain transcription factor 2 (PITX2) Atrial length about 1.6-fold increase for left atrium and 1.2-fold increase for right atrium vs WT ↑ in ventricle but not in atria Not reported Not reported AV block APD 20 phase 1, ↔  APD 50 phase 2, ↔  APD 90 phase 4, ↔  Spontaneous Other mechanisms oreduced expression of Pitx2, oreduced expression of Nav1.5 oreduced expression of Kir2.1 [86] AnkB ± Ankyrin-B (ANK2) heterologous null mutation Not reported Not reported Not reported ✔ Spontaneous bradycardia and abnormal ventricular response APD 90 phase 4, ↓ Spontaneous Other mechanisms oreduced I Ca,L oreduced Cav1.3 expression, osignalling interaction between ankyrin-B and Cav1.2 [87] D1275N-Na v 1.5 Human sodium channel Na v 1.5 global missense mutation Not reported No Not reported ✔ prolongation of P-wave and QRS duration PR interval and AV block APD 50 , phase 2 ↑ APD 90 , phase 4 ↑ Spontaneous Other mechanisms oreduced peak I Na oincreased late I Na [88] SLN -/- Sarcolipin global knockout No difference ↑ in atria but not in ventricle Not reported Not reported Small oscillatory waves APD 50 , phase 2 ↔  APD 90 , phase 4 ↑ Spontaneous Other mechanisms oSR Ca 2+ overload oDADs oincreased phosphorylation of RyR 2 [89] FKBP12.6 -/- FK506-binding protein deficiency with reduced RYR2 phosphorylation at S2814 Not reported Not reported Not reported Not reported Absence of P-waves and irregular RR intervals APD 30 , phase 2 ↔  APD 50 , phase 2 ↔  Spontaneous Other mechanisms oLack of FK506-binding protein 12.6 oDADs oSR Ca 2+ leak oincreased I NCX oCaMKII phosphorylation of RYR 2 and PLB [90] MHC-TGFcys 33 ser Cardiac-restricted constitutively active TGFβ1 overexpression with αMHC promoter Not reported ↑ in atria Not reported Not reported Activation wavefront APD 80 , phase 4 ↓ for both left and right atria Spontaneous Other mechanisms oincreased Ca 2+ transient [91] DN-MSTN TG13 TG Heart-directed overexpression of the N-terminal pro-peptide with α-MHC promoter Atrial weight 3.7-fold increase vs NTg ↑ in atria Appears present  ↔  AV block, Bradycardia Increased P-waves and QRS duration Not reported Spontaneous Other mechanisms oreduced connexin 40 expression [92] Casq2 -/- Calsequestrin 2 global knockout Atria tissue area, about 1.8-2.0-fold increase vs WT No differences Not reported ✔ Atrial ectopic activity, bradycardia APD 80, phase 4↑ Spontaneous [93] LKB1 knockout Cardiac-specific AMPK-activating liver kinase B1 (LKB1) knockout with α-MHC promoter Atria size, about twofold increase for paroxysmal at 4-6 weeks and threefold increase for persistent AF over 6 weeks vs WT ↑ in atria ✔ Intra-atrial thrombi  ↔  Increased PR interval and QRS duration in paroxysmal AF Not reported Paroxysmal and persistent Other mechanisms oreduced expression of AMPK oincreased in connexin 40 and 43 expression oROS and inflammation [94] F1759A-Na v 1.5-dTG Human sodium channel Na v 1.5 cardiac-specific expression with α-MHC promoter Right and left atria area increase by 52% and 54%, respectively, vs control ↑ in atria and ventricle Not reported ✔ Premature ventricular complexes and non-sustained polymorphic VT APD 80, phase 4 ↑ for both right and left atria Spontaneous Other mechanisms oincreased late I Na oincreased glycogen accumulation omyofibril disorganisation omitochondria injury oNCX regulation of Na + entry [95] LKB1/CTR LKB1/CT atrial-specific knockdown Not reported ↑ in atria Not reported  ↔  Irregularly irregular R-R intervals Not reported Spontaneous Other mechanisms oAtrial cardiomyocyte produces calcitonin oCalcitonin receptor and its ligand signalling governs fibroblast roles oParacrine signalling between atrial cardiomyocyte released calcitonin and fibroblast [96] PLK2 deficiency PLK2 Knockout Greater left atrial area ↑ in atria Not reported  ↔  ventricular tachycardia APD ↔  ERP ↔  Spontaneous Other mechanisms oPLK2/ERK/OPN is a dominant structural remodelling axis for AF generation [97] Mouse models that have been used to study the pathophysiology of AF, including atrial enlargement, electrophysiological alterations, apoptosis, functional and molecular underpinnings, and anatomical, transgenic; RYR2, ryanodine receptor 2; SR, sarcoplasmic reticulum; APD, action potential; SERCA mRNA, sarco/endoplasmic reticulum Ca 2+ -ATPase messenger ribonucleic acid; CTR, calcitonin receptor; KCNE1, potassium voltage-gated channel subfamily E member 1; AV, Atrioventricular block; MAP, monophasic action potential; PLB, phospholamban; ANP, atrial natriuretic peptide; β-AR, beta adrenergic receptor; PPβ1, protein phosphatase type 1β; NADPH, nicotinamide adenine dinucleotide phosphate; CaMKII, Ca 2+ /calmodulin-dependent protein kinase II; NCX, sodium-calcium exchanger; SERCA2a, Sarco/endoplasmic reticulum calcium (Ca 2+ ) ATPase gene; TGF- β, Transforming growth factor beta; BNP, brain natriuretic peptide; HSP70, heat shock protein 70; DCM, dilated cardiomyopathy; AMPK, 5' adenosine monophosphate-activated protein kinase; PLK2, polo-like kinase 2; OPN, osteopontin; ERK1/2, extracellular signal-regulated kinase ½. ↔ unchanged in that condition; ✔ present in that condition; ↑ increased in that condition; ↓ reduced in that condition.