Hypoplastic left heart syndrome in context.

Hypoplastic left heart syndrome is a rare condition requiring major cardiac surgery during the neonatal period to sustain life, with subsequent procedures culminating in completion of the Fontan circulation - the common pathway for all 'single ventricle' conditions. Algorithms for care of these children are now well defined with predictable medium-term outcomes with the majority achieving a Fontan circulation. Hypoplastic left heart syndrome is one of a group of conditions that require complex surgery as a neonate and require a similar perioperative approach. Antenatal diagnosis is common in this patient subgroup, and there is a significant body of work that can be drawn on to inform parental choice.

Increased connective tissue growth factor associated with cardiac fibrosis in the mdx mouse model of dystrophic cardiomyopathy.

Cardiomyopathy contributes to morbidity and mortality in Duchenne muscular dystrophy (DMD), a progressive muscle-wasting disorder. A major feature of the hearts of DMD patients and the mdx mouse model of the disease is cardiac fibrosis. Connective tissue growth factor (CTGF) is involved in the fibrotic process in many organs. This study utilized the mdx mouse model to assess the role of CTGF and other extracellular matrix components during the development of fibrosis in the dystrophic heart. Left ventricular function of mdx and control mice at 6, 29 and 43 weeks was measured by echocardiography. Young (6 weeks old) mdx hearts had normal function and histology. At 29 weeks of age, mdx mice developed cardiac fibrosis and increased collagen expression. The onset of fibrosis was associated with increased CTGF transcript and protein expression. Increased intensity of CTGF immunostaining was localized to fibrotic areas in mdx hearts. The upregulation of CTGF was also concurrent with increased expression of tissue inhibitor of matrix metalloproteinases (TIMP-1). These changes persisted in 43 week old mdx hearts and were combined with impaired cardiac function and increased gene expression of transforming growth factor (TGF)-ß1 and matrix metalloproteinases (MMP-2, MMP-9). In summary, an association was observed between cardiac fibrosis and increased CTGF expression in the mdx mouse heart. CTGF may be a key mediator of early and persistent fibrosis in dystrophic cardiomyopathy.

Emergency Ross Procedure for Pediatric Aortic Valve Myxofibrosarcoma.

Primary cardiac tumors in children are uncommon and rarely demand surgical intervention. We report a malignant tumor arising from the aortic root in a 5-year-old boy presenting with left ventricular outflow tract obstruction and tumor embolism, its surgical management using the Ross procedure, and the unique histopathological aspects of the tumor.

Class IA phosphoinositide 3-kinase regulates heart size and physiological cardiac hypertrophy.

Class I(A) phosphoinositide 3-kinases (PI3Ks) are activated by growth factor receptors, and they regulate, among other processes, cell growth and organ size. Studies using transgenic mice overexpressing constitutively active and dominant negative forms of the p110alpha catalytic subunit of class I(A) PI3K have implicated the role of this enzyme in regulating heart size and physiological cardiac hypertrophy. To further understand the role of class I(A) PI3K in controlling heart growth and to circumvent potential complications from the overexpression of dominant negative and constitutively active proteins, we generated mice with muscle-specific deletion of the p85alpha regulatory subunit and germ line deletion of the p85beta regulatory subunit of class I(A) PI3K. Here we show that mice with cardiac deletion of both p85 subunits exhibit attenuated Akt signaling in the heart, reduced heart size, and altered cardiac gene expression. Furthermore, exercise-induced cardiac hypertrophy is also attenuated in the p85 knockout hearts. Despite such defects in postnatal developmental growth and physiological hypertrophy, the p85 knockout hearts exhibit normal contractility and myocardial histology. Our results therefore provide strong genetic evidence that class I(A) PI3Ks are critical regulators for the developmental growth and physiological hypertrophy of the heart.

Deletion of ribosomal S6 kinases does not attenuate pathological, physiological, or insulin-like growth factor 1 receptor-phosphoinositide 3-kinase-induced cardiac hypertrophy.

Ribosomal S6 kinases (S6Ks) have been depicted as critical effectors downstream of growth factor pathways, which play an important role in the regulation of protein synthesis by phosphorylating the ribosomal protein, S6. The goal of this study was to determine whether S6Ks regulate heart size, are critical for the induction of cardiac hypertrophy in response to a pathological or physiological stimulus, and whether S6Ks are critical downstream effectors of the insulin-like growth factor 1 (IGF1)-phosphoinositide 3-kinase (PI3K) pathway. For this purpose, we generated and characterized cardiac-specific S6K1 and S6K2 transgenic mice and subjected S6K1(-/-), S6K2(-/-), and S6K1(-/-) S6K2(-/-) mice to a pathological stress (aortic banding) or a physiological stress (exercise training). To determine the genetic relationship between S6Ks and the IGF1-PI3K pathway, S6K transgenic and knockout mice were crossed with cardiac-specific transgenic mice overexpressing the IGF1 receptor (IGF1R) or PI3K mutants. Here we show that overexpression of S6K1 induced a modest degree of hypertrophy, whereas overexpression of S6K2 resulted in no obvious cardiac phenotype. Unexpectedly, deletion of S6K1 and S6K2 had no impact on the development of pathological, physiological, or IGF1R-PI3K-induced cardiac hypertrophy. These studies suggest that S6Ks alone are not essential for the development of cardiac hypertrophy.

Current management of severe congenital mitral stenosis: outcomes of transcatheter and surgical therapy in 108 infants and children.

BACKGROUND: Severe congenital mitral stenosis (MS) is a rare anomaly that is frequently associated with additional left heart obstructions. Anatomic treatments for congenital MS include balloon mitral valvuloplasty (BMVP), surgical mitral valvuloplasty (SMVP), and mitral valve replacement (MVR), although the optimal therapeutic strategy is unclear. METHODS AND RESULTS: Between 1985 and 2003, 108 patients with severe congenital MS underwent BMVP or surgical intervention at a median age of 18 months (range 1 month to 17.9 years). Anatomic subtypes of MS were "typical" congenital MS in 78 patients, supravalvar mitral ring in 46, parachute mitral valve in 28, and double-orifice mitral valve in 11, with multiple types in approximately 50% of patients. Additional left heart anomalies were present in 82 patients (76%). The first MS intervention was BMVP in 64 patients, SMVP in 33, and MVR in 11. BMVP decreased peak and mean MS gradients by a median of 33% and 38%, respectively (P<0.001), but was complicated by significant mitral regurgitation in 28%. Cross-sectional follow-up was obtained at 4.8+/-4.2 years. Overall, Kaplan-Meier survival was 92% at 1 month, 84% at 1 year, and 77% at 5 years, with 69% 5-year survival during the first decade of our experience and 87% since (P=0.09). Initial MVR and younger age were associated with worse survival. Survival free from failure of biventricular repair or mitral valve reintervention was 55% at 1 year among patients who underwent BMVP and 69% among patients who underwent supravalvar mitral ring resection initially. Among patients who underwent BMVP, survival free from failure of biventricular repair or MVR was 79% at 1 month and 55% at 5 years, with worse outcome in younger patients and those who developed significant postdilation mitral regurgitation. CONCLUSIONS: BMVP effectively relieves left ventricular inflow obstruction in most infants and children with severe congenital MS who require intervention. However, surgical resection is preferable in patients with MS due to a supravalvar mitral ring. Five-year survival is relatively poor in patients with severe congenital MS, with worse outcomes in infants and patients undergoing MVR, but has improved in our more recent experience. Many patients have undergone second procedures for either recurrent/residual MS or mitral regurgitation resulting from dilation-related disruption of the mitral valve apparatus.

From stem cells to viable autologous semilunar heart valve.

BACKGROUND: An estimated 275,000 patients undergo heart valve replacement each year. However, existing solutions for valve replacement are complicated by the morbidity associated with lifelong anticoagulation of mechanical valves and the limited durability of bioprostheses. Recent advances in tissue engineering and our understanding of stem cell biology may provide a lifelong solution to these problems. METHODS AND RESULTS: Mesenchymal stem cells were isolated from ovine bone marrow and characterized by their morphology and antigen expression through immunocytochemistry, flow cytometry, and capacity to differentiate into multiple cell lineages. A biodegradable scaffold was developed and characterized by its tensile strength and stiffness as a function of time in cell-conditioned medium. Autologous semilunar heart valves were then created in vitro using mesenchymal stem cells and the biodegradable scaffold and were implanted into the pulmonary position of sheep on cardiopulmonary bypass. The valves were evaluated by echocardiography at implantation and after 4 months in vivo. Valves were explanted at 4 and 8 months and examined by histology and immunohistochemistry. Valves displayed a maximum instantaneous gradient of 17.2+/-1.33 mm Hg, a mean gradient of 9.7+/-1.3 mm Hg, an effective orifice area of 1.35+/-0.17 cm2, and trivial or mild regurgitation at implantation. Gradients changed little over 4 months of follow-up. Histology showed disposition of extracellular matrix and distribution of cell phenotypes in the engineered valves reminiscent of that in native pulmonary valves. CONCLUSIONS: Stem-cell tissue-engineered heart valves can be created from mesenchymal stem cells in combination with a biodegradable scaffold and function satisfactorily in vivo for periods of >4 months. Furthermore, such valves undergo extensive remodeling in vivo to resemble native heart valves.

Dilated cardiomyopathy resulting from high-level myocardial expression of Cre-recombinase.

BACKGROUND: Conditional gene inactivation in mice using the bacteriophage P1 Cre-loxP recombination system requires transgenic expression of Cre-recombinase driven by a tissue-specific or inducible promoter. METHODS AND RESULTS: Using the cardiac alpha-myosin-heavy-chain promoter, the most commonly used myocardial-specific transgenic promoter, we created transgenic mice expressing Cre-recombinase in the heart. Seven transgenic lines developed dilated cardiomyopathy and premature death from congestive heart failure. One founder line that survived long enough to propagate had extremely high-level Cre recombinase expression. Transgenic lines that expressed low levels remained healthy. The high-expressing strain developed heart failure over a very predictable and reproducible time course. Detailed examination of the high-expressing strain revealed important molecular, cellular, and pharmacologic hallmarks of cardiomyopathy. First, "fetal genes" such as atrial natriuretic factor and brain natriuretic protein were expressed, a marker of pathologic cardiac hypertrophy and heart failure. Second, an increased incidence of cardiac myocyte apoptosis was present. Third, treatment of mice with captopril or metoprolol, drugs that delay the progression of heart failure, improved survival. CONCLUSION: Cre-recombinase when expressed at high levels may cause organ dysfunction, which could be mistaken for an effect of conditional gene inactivation. In addition, the stereotypic cardiomyopathy and disease progression in the characterized, high-expressing transgenic strain suggests its utility as a model to study the effects of pharmacologic or genetic manipulations in heart failure.

Haploinsufficiency of the cardiac transcription factor Nkx2-5 variably affects the expression of putative target genes.

Heterozygous mutations of the cardiac transcription factor Nkx2-5 cause congenital heart disease. To elucidate the molecular pathways of transcription factor mutant phenotypes or diseases, direct targets are commonly sought in studies of homozygous null mutant animals and by heterologous promoter-reporter gene transactivation assays. The expression of putative target genes in a physiologic range of transcription factor concentration, however, is often not examined. Heterozygous Nkx2-5 knockout (Nkx2-5+/-) mice have no more than half-normal levels of Nkx2-5 protein. We therefore measured the mRNA expression of four putative targets of the cardiac transcription factor Nkx2-5 in wild-type and Nkx2-5+/- animals in a variety of developmental and pathologic states. Wild-type and Nkx2-5+/- embryonic hearts expressed similar levels of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), the RNA helicase Csm, and homeodomain only protein HOP. In the failing adult ventricle, ANF and BNP were up-regulated to the same extent in wild-type and Nkx2-5+/- myocardium. Csm and HOP were down-regulated in heart failure, and Nkx2-5+/- hearts expressed about half-normal levels in healthy and failing states. No consistent relationship existed between the expression of putative transcriptional targets and Nkx2-5 gene dosage in the physiologically relevant range. Any dependence of gene expression on Nkx2-5 gene dosage is affected by factors specific to the individual gene and the physiologic context.

Rapamycin attenuates load-induced cardiac hypertrophy in mice.

BACKGROUND: Cardiac hypertrophy, or an increase in heart size, is an important risk factor for cardiac morbidity and mortality. The mammalian target of rapamycin (mTOR) is a component of the insulin-phosphoinositide 3-kinase pathway, which is known to play a critical role in the determination of cell, organ, and body size. METHODS AND RESULTS: To examine the role of mTOR in load-induced cardiac hypertrophy, we administered rapamycin, a specific inhibitor of mTOR, to mice with ascending aortic constriction. Activity of p70 ribosomal S6 kinase 1 (S6K1), an effector of mTOR, was increased by 3.8-fold in the aortic-constricted heart. Pretreatment of mice with 2 mg. kg-1. d-1 of rapamycin completely suppressed S6K1 activation and S6 phosphorylation in response to pressure overload. The heart weight/tibial length ratio of vehicle-treated aortic-banded mice was increased by 34.4+/-3.6% compared with vehicle-treated sham-operated mice. Rapamycin suppressed the load-induced increase in heart weight by 67%. Attenuation of cardiac hypertrophy by rapamycin was associated with attenuation of the increase in myocyte cell size induced by aortic constriction. Rapamycin did not cause loss of body weight, lethality, or left ventricular dysfunction. CONCLUSIONS: mTOR or its target(s) seems to play an important role in load-induced cardiac hypertrophy. Because systemic administration of rapamycin has been used successfully for the treatment of transplant rejection in clinical practice, it may be a useful therapeutic modality to suppress cardiac hypertrophy in patients.

Inhibition of mTOR signaling with rapamycin regresses established cardiac hypertrophy induced by pressure overload.

BACKGROUND: Rapamycin is a specific inhibitor of the mammalian target of rapamycin (mTOR). We recently reported that administration of rapamycin before exposure to ascending aortic constriction significantly attenuated the load-induced increase in heart weight by approximately 70%. METHODS AND RESULTS: To examine whether rapamycin can regress established cardiac hypertrophy, mice were subjected to pressure overload (ascending aortic constriction) for 1 week, echocardiography was performed to verify an increase in ventricular wall thickness, and mice were given rapamycin (2 mg x kg(-1) x d(-1)) for 1 week. After 1 week of pressure overload (before treatment), 2 distinct groups of animals became apparent: (1) mice with compensated cardiac hypertrophy (normal function) and (2) mice with decompensated hypertrophy (dilated with depressed function). Rapamycin regressed the pressure overload-induced increase in heart weight/body weight (HW/BW) ratio by 68% in mice with compensated hypertrophy and 41% in mice with decompensated hypertrophy. Rapamycin improved left ventricular end-systolic dimensions, fractional shortening, and ejection fraction in mice with decompensated cardiac hypertrophy. Rapamycin also altered the expression of some fetal genes, reversing, in part, changes in alpha-myosin heavy chain and sarcoplasmic reticulum Ca2+ ATPase. CONCLUSIONS: Rapamycin may be a therapeutic tool to regress established cardiac hypertrophy and improve cardiac function.

Aortico-left ventricular tunnel: 35-year experience.

OBJECTIVES: The purpose of this study was to review our 35 years of experience with aortico-left ventricular tunnel (ALVT), with emphasis on diagnosis, surgical details, and follow-up. BACKGROUND: Aortico-left ventricular tunnel is a rare congenital anomaly. Neonatal surgery has been advocated in all due to long-term concern of valvar aortic regurgitation (AR). METHODS: We identified 11 patients from 1963 to August 2002. Clinical, echocardiographic, catheterization, and surgical details were reviewed. RESULTS: Eight of 11 patients presented at less than six months old (six with congestive heart failure) and three later with a murmur, all with clinical evidence of AR. Associated lesions, most commonly aortic valve and coronary artery anomalies, were present in 45%. Catheter occlusion was considered but not performed in five. Spontaneous occlusion was documented in one. Ten had surgery (nine in our institution), seven with direct suture and two by patch closure of the aortic end of the AVLT. At follow-up (median, 5 years; 1 month to 35 years), all were asymptomatic; three had residual ALVT (one moderate, two small/trivial), with at most mild AR. CONCLUSIONS: Aortico-left ventricular tunnel is a rare cardiac malformation with a good post-operative long-term outcome. Associated lesions occurred in 45%. Catheterization should be reserved for patients with unclear non-invasive findings or transcatheter closure. We recommend surgery for most patients. We report spontaneous closure in one patient, prompting consideration of conservative follow-up in rare small, asymptomatic AVLT.

Management of coronary artery fistulae. Patient selection and results of transcatheter closure.

OBJECTIVES: We report short-term findings in 33 patients after transcatheter closure (TCC) of coronary artery fistulae (CAF) and compare our results with those reported in the recent transcatheter and surgical literature. BACKGROUND: Transcatheter closure of CAF has been advocated as a minimally invasive alternative to surgery. METHODS: We reviewed all patients presenting with significant CAF between January 1988 and August 2000. Those with additional complex cardiac disease requiring surgical management were excluded. RESULTS: Of 39 patients considered for TCC, occlusion devices were placed in 33 patients (85%) at 35 procedures and included coils in 28, umbrella devices in 6 and a Grifka vascular occlusion device in 1. Post-deployment angiograms demonstrated complete occlusion in 19, trace in 11, or small residual flow in 5. Follow-up echocardiograms (median, 2.8 years) in 27 patients showed no flow in 22 or small residual flow in 5. Of the 6 patients without follow-up imaging, immediate post-deployment angiograms showed complete occlusion in 5 or small residual flow in 1. Thus, complete occlusion was accomplished in 27 patients (82%). Early complications included transient ST-T wave changes in 5, transient arrhythmias in 4 and single instances of distal coronary artery spasm, fistula dissection and unretrieved coil embolization. There were no deaths or long-term morbidity. Device placement was not attempted in 6 patients (15%), because of multiple fistula drainage sites in 4, extreme vessel tortuosity in 1 and an intracardiac hemangioma in 1. CONCLUSIONS: A comparison of our results with those in the recent transcatheter and surgical literature shows similar early effectiveness, morbidity and mortality. From data available, TCC of CAF is an acceptable alternative to surgery in most patients.

Intermediate outcomes of atrioventricular valvuloplasty in lateral tunnel Fontan patients.

BACKGROUND AND AIM OF THE STUDY: Lateral tunnel Fontan operation patients with atrioventricular valve (AVV) regurgitation have an increased incidence of Fontan failure (death, take-down or transplant). The outcomes of patients undergoing AVV repair during Fontan palliation were reviewed to determine the optimal technique and timing of repair. METHODS: Hospital records for all patients with AVV regurgitation at the time of their Fontan procedure were reviewed retrospectively. Patients with staged single-ventricle palliation culminating in a lateral tunnel Fontan operation who had their first AVV repair at the Children's Hospital, Boston, were included. AVV regurgitation was graded by semi-quantitative color Doppler echocardiography on a scale of 1 to 4, as was ventricular dysfunction. RESULTS: Among 859 lateral tunnel Fontan patients, 27 (3%) had a total of 30 AVV repairs (18 tricuspid, six mitral, six common AVV). Of the 27 first-time AVV repairs (16 TV, six MV, five CAVV), six were performed pre-Fontan, and 21 at or after Fontan. The median age at the first AVV repair was 3 years (range: 0.6-9.4 years). Preoperatively, the median echocardiographic severity of AVV regurgitation was grade 3 (range: 2-4). At median follow up of 1.2 years (range: 0-9.5 years) the severity of AVV regurgitation was reduced significantly to median grade 2 (range: 0-4; p <0.001). No patient with initial AVV repair at the time of Fontan underwent reoperation for AVV regurgitation. In all cases, ventricular function was maintained or improved, with preoperative median systemic ventricular function grade 1.5 (range: 1 to 4) versus postoperative grade 1 (range: 1-4; p = NS). There were no Fontan failures in the intermediate term. CONCLUSION: AVV regurgitation and ventricular systolic function can be maintained or improved in the intermediate term following AVV repair in single-ventricle patients.

Characterization of cardiac conduction system abnormalities in mice with targeted disruption of Six5 gene.

Myotonic dystrophy (DM) is an autosomal dominant multisystem disorder, caused by expansion of a CTG trinucleotide repeat in the 3' untranslated region of the myotonic dystrophy protein kinase gene (DMPK) on chromosome 19q13. Cardiac involvement in DM includes conduction abnormalities and functional deficits. Three hypotheses of molecular mechanisms for DM pathophysiology are; first, partial loss of myotonic dystrophy protein kinase (DMPK); second, decreased transcription of a neighboring homeodomain-encoding gene, Six5 (or DMAHP), and third, transdominant effects of the RNA and regulation of splicing associated with expression of expanded CUG repeats. However, the precise pathogenetic mechanism remains unresolved. We previously reported that dosage of Dm15, the mouse homologue of DMPK, strongly associates with the cardiac conduction abnormalities. For further distinction of the molecular mechanisms underlying the cardiac phenotype of DM, in the present study, we characterized the cardiac conduction findings of mice with targeted disruption of Six5 gene. Six5 heterozygous mice (adult and young) and their age matched wild type littermates were studied using in vivo electrophysiologic techniques, echocardiography, heart rate variability and exercise tolerance testing. No PR prolongation was detected, however, prolonged QRS duration and delayed infraHisian conduction were significant in adult Six5 heterozygous mice. By echocardiography, left ventricular (LV) end-diastolic dimension was enlarged in adult Six5 heterozygous mice, although neither fractioning shortening nor LV wall thickness showed significant differences. Six5 loss may partly contribute to conduction abnormalities in myotonic dystrophy, particularly infraHisian conduction delay, one of the initial phenotypes of adult-onset cardiac conduction abnormalities in DM patients.

Cytoplasmic CUG RNA foci are insufficient to elicit key DM1 features.

The genetic basis of myotonic dystrophy type I (DM1) is the expansion of a CTG tract located in the 3' untranslated region of DMPK. Expression of mutant RNAs encoding expanded CUG repeats plays a central role in the development of cardiac disease in DM1. Expanded CUG tracts form both nuclear and cytoplasmic aggregates, yet the relative significance of such aggregates in eliciting DM1 pathology is unclear. To test the pathophysiology of CUG repeat encoding RNAs, we developed and analyzed mice with cardiac-specific expression of a beta-galactosidase cassette in which a (CTG)(400) repeat tract was positioned 3' of the termination codon and 5' of the bovine growth hormone polyadenylation signal. In these animals CUG aggregates form exclusively in the cytoplasm of cardiac cells. A key pathological consequence of expanded CUG repeat RNA expression in DM1 is aberrant RNA splicing. Abnormal splicing results from the functional inactivation of MBNL1, which is hypothesized to occur due to MBNL1 sequestration in CUG foci or from elevated levels of CUG-BP1. We therefore tested the ability of cytoplasmic CUG foci to elicit these changes. Aggregation of CUG RNAs within the cytoplasm results both in Mbnl1 sequestration and in approximately a two fold increase in both nuclear and cytoplasmic Cug-bp1 levels. Significantly, despite these changes RNA splice defects were not observed and functional analysis revealed only subtle cardiac dysfunction, characterized by conduction defects that primarily manifest under anesthesia. Using a human myoblast culture system we show that this transgene, when expressed at similar levels to a second transgene, which encodes expanded CTG tracts and facilitates both nuclear focus formation and aberrant splicing, does not elicit aberrant splicing. Thus the lack of toxicity of cytoplasmic CUG foci does not appear to be a consequence of low expression levels. Our results therefore demonstrate that the cellular location of CUG RNA aggregates is an important variable that influences toxicity and support the hypothesis that small molecules that increase the rate of transport of the mutant DMPK RNA from the nucleus into the cytoplasm may significantly improve DM1 pathology.

A mouse model of cardiac rhabdomyoma generated by loss of Tsc1 in ventricular myocytes.

Tuberous sclerosis is a hamartoma syndrome due to mutations in TSC1 or TSC2 in which cardiac rhabdomyomas are seen in approximately 60% of patients. These lesions have an unusual natural history as they are usually most prominent immediately after birth and spontaneously resolve in most cases. To develop a mouse model of this lesion, we used a conditional, floxed allele of Tsc1 and a modified myosin light chain 2v allele in which cre recombinase expression occurs in ventricular myocytes. Mice with ventricular loss of Tsc1 had a median survival of 6 months and developed a dilated cardiomyopathy with the occurrence of scattered foci of enlarged ventricular myocytes. The enlarged cells were periodic acid-Schiff positive indicating the presence of excess glycogen and expressed elevated levels of phospho-S6, similar to findings in patient rhabdomyoma cells. The observations confirm that rhabdomyomas occur through a two hit mechanism of pathogenesis. However, the mice showed no evidence of fetal/neonatal demise, and there was no evidence of proliferation in the lesions. We propose that these differences are due to the timing of loss of Tsc1 in the ventricular myocytes and/or the truncated gestational period in the mouse compared with humans, during which progestational hormones may accentuate the growth of patient rhabdomyomas.

Phosphoinositide 3-kinase(p110alpha) plays a critical role for the induction of physiological, but not pathological, cardiac hypertrophy.

An unresolved question in cardiac biology is whether distinct signaling pathways are responsible for the development of pathological and physiological cardiac hypertrophy in the adult. Physiological hypertrophy is characterized by a normal organization of cardiac structure and normal or enhanced cardiac function, whereas pathological hypertrophy is associated with an altered pattern of cardiac gene expression, fibrosis, cardiac dysfunction, and increased morbidity and mortality. The elucidation of signaling cascades that play distinct roles in these two forms of hypertrophy will be critical for the development of more effective strategies to treat heart failure. We examined the role of the p110alpha isoform of phosphoinositide 3-kinase (PI3K) for the induction of pathological hypertrophy (pressure overload-induced) and physiological hypertrophy (exercise-induced) by using transgenic mice expressing a dominant negative (dn) PI3K(p110alpha) mutant specifically in the heart. dnPI3K transgenic mice displayed significant hypertrophy in response to pressure overload but not exercise training. dnPI3K transgenic mice also showed significant dilation and cardiac dysfunction in response to pressure overload. Thus, PI3K(p110alpha) appears to play a critical role for the induction of physiological cardiac growth but not pathological growth. PI3K(p110alpha) also appears essential for maintaining contractile function in response to pathological stimuli.