Cortical Bone Stem Cell Therapy Preserves Cardiac Structure and Function After Myocardial Infarction.

RATIONALE: Cortical bone stem cells (CBSCs) have been shown to reduce ventricular remodeling and improve cardiac function in a murine myocardial infarction (MI) model. These effects were superior to other stem cell types that have been used in recent early-stage clinical trials. However, CBSC efficacy has not been tested in a preclinical large animal model using approaches that could be applied to patients. OBJECTIVE: To determine whether post-MI transendocardial injection of allogeneic CBSCs reduces pathological structural and functional remodeling and prevents the development of heart failure in a swine MI model. METHODS AND RESULTS: Female Göttingen swine underwent left anterior descending coronary artery occlusion, followed by reperfusion (ischemia-reperfusion MI). Animals received, in a randomized, blinded manner, 1:1 ratio, CBSCs (n=9; 2×107 cells total) or placebo (vehicle; n=9) through NOGA-guided transendocardial injections. 5-ethynyl-2'deoxyuridine (EdU)-a thymidine analog-containing minipumps were inserted at the time of MI induction. At 72 hours (n=8), initial injury and cell retention were assessed. At 3 months post-MI, cardiac structure and function were evaluated by serial echocardiography and terminal invasive hemodynamics. CBSCs were present in the MI border zone and proliferating at 72 hours post-MI but had no effect on initial cardiac injury or structure. At 3 months, CBSC-treated hearts had significantly reduced scar size, smaller myocytes, and increased myocyte nuclear density. Noninvasive echocardiographic measurements showed that left ventricular volumes and ejection fraction were significantly more preserved in CBSC-treated hearts, and invasive hemodynamic measurements documented improved cardiac structure and functional reserve. The number of EdU+ cardiac myocytes was increased in CBSC- versus vehicle- treated animals. CONCLUSIONS: CBSC administration into the MI border zone reduces pathological cardiac structural and functional remodeling and improves left ventricular functional reserve. These effects reduce those processes that can lead to heart failure with reduced ejection fraction.

Interleukin-10 Inhibits Bone Marrow Fibroblast Progenitor Cell-Mediated Cardiac Fibrosis in Pressure-Overloaded Myocardium.

BACKGROUND: Activated fibroblasts (myofibroblasts) play a critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear, warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPCs) in pressure overload-induced cardiac fibrosis. We have previously shown that interleukin-10 (IL10) suppresses pressure overload-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits pressure overload-induced homing of BM-FPCs to the heart and their transdifferentiation to myofibroblasts and thus attenuates cardiac fibrosis. METHODS: Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction. To determine the bone marrow origin, chimeric mice were created with enhanced green fluorescent protein WT mice marrow to the IL10KO mice. For mechanistic studies, FPCs were isolated from mouse bone marrow. RESULTS: Pressure overload enhanced BM-FPC mobilization and homing in IL10KO mice compared with WT mice. Furthermore, WT bone marrow (from enhanced green fluorescent protein mice) transplantation in bone marrow-depleted IL10KO mice (IL10KO chimeric mice) reduced transverse aortic constriction-induced BM-FPC mobilization compared with IL10KO mice. Green fluorescent protein costaining with α-smooth muscle actin or collagen 1α in left ventricular tissue sections of IL10KO chimeric mice suggests that myofibroblasts were derived from bone marrow after transverse aortic constriction. Finally, WT bone marrow transplantation in IL10KO mice inhibited transverse aortic constriction-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited transforming growth factor-ß-induced transdifferentiation and fibrotic signaling in WT BM-FPCs in vitro. Furthermore, fibrosis-associated microRNA (miRNA) expression was highly upregulated in IL10KO-FPCs compared with WT-FPCs. Polymerase chain reaction-based selective miRNA analysis revealed that transforming growth factor-ß-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145, and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on transforming growth factor-ß-induced fibrotic signaling in BM-FPCs. CONCLUSIONS: Our findings suggest that IL10 inhibits BM-FPC homing and transdifferentiation to myofibroblasts in pressure-overloaded myocardium. Mechanistically, we show for the first time that IL10 suppresses Smad-miRNA-21-mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

Restoration of Hydrogen Sulfide Production in Diabetic Mice Improves Reparative Function of Bone Marrow Cells.

BACKGROUND: Bone marrow cell (BMC)-based treatment for critical limb ischemia in diabetic patients yielded a modest therapeutic effect resulting from cell dysfunction. Therefore, approaches that improve diabetic stem/progenitor cell functions may provide therapeutic benefits. Here, we tested the hypothesis that restoration of hydrogen sulfide (H2S) production in diabetic BMCs improves their reparative capacities. METHODS: Mouse BMCs were isolated by density-gradient centrifugation. Unilateral hind limb ischemia was conducted in 12- to 14-week-old db/+ and db/db mice by ligation of the left femoral artery. The H2S level was measured by either gas chromatography or staining with florescent dye sulfidefluor 7 AM. RESULTS: Both H2S production and cystathionine γ-lyase (CSE), an H2S enzyme, levels were significantly decreased in BMCs from diabetic db/db mice. Administration of H2S donor diallyl trisulfide (DATS) or overexpression of CSE restored H2S production and enhanced cell survival and migratory capacity in high glucose (HG)-treated BMCs. Immediately after hind limb ischemia surgery, the db/+ and db/db mice were administered DATS orally and/or given a local intramuscular injection of green fluorescent protein-labeled BMCs or red fluorescent protein-CSE-overexpressing BMCs (CSE-BMCs). Mice with hind limb ischemia were divided into 6 groups: db/+, db/db, db/db+BMCs, db/db+DATS, db/db+DATS+BMCs, and db/db+CSE-BMCs. DATS and CSE overexpression greatly enhanced diabetic BMC retention in ischemic hind limbs followed by improved blood perfusion, capillary/arteriole density, skeletal muscle architecture, and cell survival and decreased perivascular CD68+ cell infiltration in the ischemic hind limbs of diabetic mice. It is interesting to note that DATS or CSE overexpression rescued high glucose-impaired migration, tube formation, and survival of BMCs or mature human cardiac microvascular endothelial cells. Moreover, DATS restored nitric oxide production and decreased endothelial nitric oxide synthase phosphorylation at threonine 495 levels in human cardiac microvascular endothelial cells and improved BMC angiogenic activity under high glucose condition. Last, silencing CSE by siRNA significantly increased endothelial nitric oxide synthase phosphorylation at threonine 495 levels in human cardiac microvascular endothelial cells. CONCLUSIONS: Decreased CSE-mediated H2S bioavailability is an underlying source of BMC dysfunction in diabetes mellitus. Our data indicate that H2S and overexpression of CSE in diabetic BMCs may rescue their dysfunction and open novel avenues for cell-based therapeutics of critical limb ischemia in diabetic patients.

Leukocyte-Expressed ß2-Adrenergic Receptors Are Essential for Survival After Acute Myocardial Injury.

BACKGROUND: Immune cell-mediated inflammation is an essential process for mounting a repair response after myocardial infarction (MI). The sympathetic nervous system is known to regulate immune system function through ß-adrenergic receptors (ßARs); however, their role in regulating immune cell responses to acute cardiac injury is unknown. METHODS: Wild-type (WT) mice were irradiated followed by isoform-specific ßAR knockout (ßARKO) or WT bone-marrow transplantation (BMT) and after full reconstitution underwent MI surgery. Survival was monitored over time, and alterations in immune cell infiltration after MI were examined through immunohistochemistry. Alterations in splenic function were identified through the investigation of altered adhesion receptor expression. RESULTS: ß2ARKO BMT mice displayed 100% mortality resulting from cardiac rupture within 12 days after MI compared with ≈20% mortality in WT BMT mice. ß2ARKO BMT mice displayed severely reduced post-MI cardiac infiltration of leukocytes with reciprocally enhanced splenic retention of the same immune cell populations. Splenic retention of the leukocytes was associated with an increase in vascular cell adhesion molecule-1 expression, which itself was regulated via ß-arrestin-dependent ß2AR signaling. Furthermore, vascular cell adhesion molecule-1 expression in both mouse and human macrophages was sensitive to ß2AR activity, and spleens from human tissue donors treated with ß-blocker showed enhanced vascular cell adhesion molecule-1 expression. The impairments in splenic retention and cardiac infiltration of leukocytes after MI were restored to WT levels via lentiviral-mediated re-expression of ß2AR in ß2ARKO bone marrow before transplantation, which also resulted in post-MI survival rates comparable to those in WT BMT mice. CONCLUSIONS: Immune cell-expressed ß2AR plays an essential role in regulating the early inflammatory repair response to acute myocardial injury by facilitating cardiac leukocyte infiltration.

Induction of SENP1 in myocardium contributes to abnormities of mitochondria and cardiomyopathy.

Defect in mitochondrial biogenesis and cardiac energy metabolism is a critical contributing factor to cardiac hypertrophy and heart failure. Sentrin/SUMO specific protease 1 (SENP1) mediated regulation of PGC-1α transcriptional activity plays an essential role in mitochondrial biogenesis and mitochondrial function. However, whether SENP1 plays a role in cardiac hypertrophy and failure is unknown. We investigated whether alteration in SENP1 expression affects cardiomyopathy and the underlying mechanism. In our present study, we found that the expression of SENP1 was induced in mouse and human failing hearts associated with induced expression of mitochondrial genes. SENP1 expression in cardiomyocytes was induced by hypertrophic stimuli through calcium/calcineurin-NFAT3. SENP1 regulated mitochondrial gene expression by de-SUMOylation of MEF-2C, which enhanced MEF-2C-mediated PGC-1α transcription. Genetic induction of SENP1 led to mitochondrial dysregulation and cardiac dysfunction in vivo. Our data showed that pathogenesis of cardiomyopathy is attributed by SENP1 mediated regulation of mitochondrial abnormities. SENP1 up-regulation in diseased heart is mediated via calcineurin-NFAT/MEF2C-PGC-1α pathway.

Direct evidence of intracrine angiotensin II signaling in neurons.

The existence of a local renin-angiotensin system (RAS) in neurons was first postulated 40 years ago. Further studies indicated intraneuronal generation of ANG II. However, the function and signaling mechanisms of intraneuronal ANG II remained elusive. Since ANG II type 1 receptor (AT1R) is the major type of receptor mediating the effects of ANG II, we used intracellular microinjection and concurrent Ca(2+) and voltage imaging to examine the functionality of intracellular AT1R in neurons. We show that intracellular administration of ANG II produces a dose-dependent elevation of cytosolic Ca(2+) concentration ([Ca(2+)]i) in hypothalamic neurons that is sensitive to AT1R antagonism. Endolysosomal, but not Golgi apparatus, disruption prevents the effect of microinjected ANG II on [Ca(2+)]i. Additionally, the ANG II-induced Ca(2+) response is dependent on microautophagy and sensitive to inhibition of PLC or antagonism of inositol 1,4,5-trisphosphate receptors. Furthermore, intracellular application of ANG II produces AT1R-mediated depolarization of hypothalamic neurons, which is dependent on [Ca(2+)]i increase and on cation influx via transient receptor potential canonical channels. In summary, we provide evidence that intracellular ANG II activates endolysosomal AT1Rs in hypothalamic neurons. Our results point to the functionality of a novel intraneuronal angiotensinergic pathway, extending the current understanding of intracrine ANG II signaling.

ß1-adrenergic receptor and sphingosine-1-phosphate receptor 1 (S1PR1) reciprocal downregulation influences cardiac hypertrophic response and progression to heart failure: protective role of S1PR1 cardiac gene therapy.

BACKGROUND: The sphingosine-1-phosphate receptor 1 (S1PR1) and ß1-adrenergic receptor (ß1AR) are G-protein-coupled receptors expressed in the heart. These 2 receptors have opposing actions on adenylyl cyclase because of differential G-protein coupling. Importantly, both of these receptors can be regulated by the actions of G-protein-coupled receptor kinase-2, which triggers desensitization and downregulation processes. Although classic signaling paradigms suggest that simultaneous activation of ß1ARs and S1PR1s in a myocyte would simply result in opposing action on cAMP production, in this report we have uncovered a direct interaction between these 2 receptors, with regulatory involvement of G-protein-coupled receptor kinase-2. METHODS AND RESULTS: In HEK (human embryonic kidney) 293 cells overexpressing both ß1AR and S1PR1, we demonstrated that ß1AR downregulation can occur after stimulation with sphingosine-1-phosphate (an S1PR1 agonist), whereas S1PR1 downregulation can be triggered by isoproterenol (a ß-adrenergic receptor agonist) treatment. This cross talk between these 2 distinct G-protein-coupled receptors appears to have physiological significance, because they interact and show reciprocal regulation in mouse hearts undergoing chronic ß-adrenergic receptor stimulation and in a rat model of postischemic heart failure. CONCLUSIONS: We demonstrate that restoration of cardiac plasma membrane levels of S1PR1 produces beneficial effects that counterbalance the deleterious ß1AR overstimulation in heart failure.

Urotensin II promotes vagal-mediated bradycardia by activating cardiac-projecting parasympathetic neurons of nucleus ambiguus.

Urotensin II (U-II) is a cyclic undecapeptide that regulates cardiovascular function at central and peripheral sites. The functional role of U-II nucleus ambiguus, a key site controlling cardiac tone, has not been established, despite the identification of U-II and its receptor at this level. We report here that U-II produces an increase in cytosolic Ca(2+) concentration in retrogradely labeled cardiac vagal neurons of nucleus ambiguus via two pathways: (i) Ca(2+) release from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptor; and (ii) Ca(2+) influx through P/Q-type Ca(2+) channels. In addition, U-II depolarizes cultured cardiac parasympathetic neurons. Microinjection of increasing concentrations of U-II into nucleus ambiguus elicits dose-dependent bradycardia in conscious rats, indicating the in vivo activation of the cholinergic pathway controlling the heart rate. Both the in vitro and in vivo effects were abolished by the urotensin receptor antagonist, urantide. Our findings suggest that, in addition, to the previously reported increase in sympathetic outflow, U-II activates cardiac vagal neurons of nucleus ambiguus, which may contribute to cardioprotection.

Synaptic imbalance and increased inhibition impair motor function in SMA.

Movement is executed through the balanced action of excitatory and inhibitory neurotransmission in motor circuits of the spinal cord. Short-term perturbations in one of the two types of transmission are counteracted by homeostatic changes of the opposing type. Prolonged failure to balance excitatory and inhibitory drive results in dysfunction at the single neuron, as well as neuronal network levels. However, whether dysfunction in one or both types of neurotransmission leads to pathogenicity in neurodegenerative diseases characterized by select synaptic deficits is not known. Here, we used mouse genetics, functional assays, morphological methods, and viral-mediated approaches to uncover the pathogenic contribution of unbalanced excitation-inhibition neurotransmission in a mouse model of spinal muscular atrophy (SMA). We show that vulnerable motor circuits in the SMA spinal cord fail to respond homeostatically to the reduction of excitatory drive and instead increase inhibition. This imposes an excessive burden on motor neurons and further restricts their recruitment to activate muscle contraction. Importantly, genetic or pharmacological reduction of inhibitory synaptic drive improves neuronal function and provides behavioural benefit in SMA mice. Our findings identify the lack of excitation-inhibition homeostasis as a major maladaptive mechanism in SMA, by which the combined effects of reduced excitation and increased inhibition diminish the capacity of premotor commands to recruit motor neurons and elicit muscle contractions.

Aldosterone increases cardiac vagal tone via G protein-coupled oestrogen receptor activation.

In addition to acting on mineralocorticoid receptors, aldosterone has been recently shown to activate the G protein-coupled oestrogen receptor (GPER) in vascular cells. In light of the newly identified role for GPER in vagal cardiac control, we examined whether or not aldosterone activates GPER in rat nucleus ambiguus. Aldosterone produced a dose-dependent increase in cytosolic Ca(2+) concentration in retrogradely labelled cardiac vagal neurons of nucleus ambiguus; the response was abolished by pretreatment with the GPER antagonist G-36, but was not affected by the mineralocorticoid receptor antagonists, spironolactone and eplerenone. In Ca(2+)-free saline, the response to aldosterone was insensitive to blockade of the Ca(2+) release from lysosomes, while it was reduced by blocking the Ca(2+) release via ryanodine receptors and abolished by blocking the IP3 receptors. Aldosterone induced Ca(2+) influx via P/Q-type Ca(2+) channels, but not via L-type and N-type Ca(2+) channels. Aldosterone induced depolarization of cardiac vagal neurons of nucleus ambiguus that was sensitive to antagonism of GPER but not of mineralocorticoid receptor. in vivo studies, using telemetric measurement of heart rate, indicate that microinjection of aldosterone into the nucleus ambiguus produced a dose-dependent bradycardia in conscious, freely moving rats. Aldosterone-induced bradycardia was blocked by the GPER antagonist, but not by the mineralocorticoid receptor antagonists. In summary, we report for the first time that aldosterone decreases heart rate by activating GPER in cardiac vagal neurons of nucleus ambiguus.

Nesfatin-1 activates cardiac vagal neurons of nucleus ambiguus and elicits bradycardia in conscious rats.

Nesfatin-1, a peptide whose receptor is yet to be identified, has been involved in the modulation of feeding, stress, and metabolic responses. More recently, increasing evidence supports a modulatory role for nesfatin-1 in autonomic and cardiovascular activity. This study was undertaken to test if the expression of nesfatin-1 in the nucleus ambiguus, a key site for parasympathetic cardiac control, may be correlated with a functional role. As we have previously demonstrated that nesfatin-1 elicits Ca²âº signaling in hypothalamic neurons, we first assessed the effect of this peptide on cytosolic Ca²âº in cardiac pre-ganglionic neurons of nucleus ambiguus. We provide evidence that nesfatin-1 increases cytosolic Ca²âº concentration via a Gi/o-coupled mechanism. The nesfatin-1-induced Ca²âº rise is critically dependent on Ca²âº influx via P/Q-type voltage-activated Ca²âº channels. Repeated administration of nesfatin-1 leads to tachyphylaxis. Furthermore, nesfatin-1 produces a dose-dependent depolarization of cardiac vagal neurons via a Gi/o-coupled mechanism. In vivo studies, using telemetric and tail-cuff monitoring of heart rate and blood pressure, indicate that microinjection of nesfatin-1 into the nucleus ambiguus produces bradycardia not accompanied by a change in blood pressure in conscious rats. Taken together, our results identify for the first time that nesfatin-1 decreases heart rate by activating cardiac vagal neurons of nucleus ambiguus. Our results indicate that nesfatin-1, one of the most potent feeding peptides, increases cytosolic Ca²âº by promoting Ca²âº influx via P/Q channels and depolarizes nucleus ambiguus neurons; both effects are Gi/o-mediated. In vivo studies indicate that microinjection of nesfatin-1 into nucleus ambiguus produces bradycardia in conscious rats. This is the first report that nesfatin-1 increases the parasympathetic cardiac tone.

The inotropic peptide ßARKct improves ßAR responsiveness in normal and failing cardiomyocytes through G(ßγ)-mediated L-type calcium current disinhibition.

RATIONALE: The G(ßγ)-sequestering peptide ß-adrenergic receptor kinase (ßARK)ct derived from the G-protein-coupled receptor kinase (GRK)2 carboxyl terminus has emerged as a promising target for gene-based heart failure therapy. Enhanced downstream cAMP signaling has been proposed as the underlying mechanism for increased ß-adrenergic receptor (ßAR) responsiveness. However, molecular targets mediating improved cardiac contractile performance by ßARKct and its impact on G(ßγ)-mediated signaling have yet to be fully elucidated. OBJECTIVE: We sought to identify G(ßγ)-regulated targets and signaling mechanisms conveying ßARKct-mediated enhanced ßAR responsiveness in normal (NC) and failing (FC) adult rat ventricular cardiomyocytes. METHODS AND RESULTS: Assessing viral-based ßARKct gene delivery with electrophysiological techniques, analysis of contractile performance, subcellular Ca²(+) handling, and site-specific protein phosphorylation, we demonstrate that ßARKct enhances the cardiac L-type Ca²(+) channel (LCC) current (I(Ca)) both in NCs and FCs on ßAR stimulation. Mechanistically, ßARKct augments I(Ca) by preventing enhanced inhibitory interaction between the α1-LCC subunit (Cav1.2α) and liberated G(ßγ) subunits downstream of activated ßARs. Despite improved ßAR contractile responsiveness, ßARKct neither increased nor restored cAMP-dependent protein kinase (PKA) and calmodulin-dependent kinase II signaling including unchanged protein kinase (PK)Cε, extracellular signal-regulated kinase (ERK)1/2, Akt, ERK5, and p38 activation both in NCs and FCs. Accordingly, although ßARKct significantly increases I(Ca) and Ca²(+) transients, being susceptible to suppression by recombinant G(ßγ) protein and use-dependent LCC blocker, ßARKct-expressing cardiomyocytes exhibit equal basal and ßAR-stimulated sarcoplasmic reticulum Ca²(+) load, spontaneous diastolic Ca²(+) leakage, and survival rates and were less susceptible to field-stimulated Ca²(+) waves compared with controls. CONCLUSION: Our study identifies a G(ßγ)-dependent signaling pathway attenuating cardiomyocyte I(Ca) on ßAR as molecular target for the G(ßγ)-sequestering peptide ßARKct. Targeted interruption of this inhibitory signaling pathway by ßARKct confers improved ßAR contractile responsiveness through increased I(Ca) without enhancing regular or restoring abnormal cAMP-signaling. ßARKct-mediated improvement of I(Ca) rendered cardiomyocytes neither susceptible to ßAR-induced damage nor arrhythmogenic sarcoplasmic reticulum Ca²(+) leakage.

Phase 1 gene therapy for Duchenne muscular dystrophy using a translational optimized AAV vector.

Efficient and widespread gene transfer is required for successful treatment of Duchenne muscular dystrophy (DMD). Here, we performed the first clinical trial using a chimeric adeno-associated virus (AAV) capsid variant (designated AAV2.5) derived from a rational design strategy. AAV2.5 was generated from the AAV2 capsid with five mutations from AAV1. The novel chimeric vector combines the improved muscle transduction capacity of AAV1 with reduced antigenic crossreactivity against both parental serotypes, while keeping the AAV2 receptor binding. In a randomized double-blind placebo-controlled phase I clinical study in DMD boys, AAV2.5 vector was injected into the bicep muscle in one arm, with saline control in the contralateral arm. A subset of patients received AAV empty capsid instead of saline in an effort to distinguish an immune response to vector versus minidystrophin transgene. Recombinant AAV genomes were detected in all patients with up to 2.56 vector copies per diploid genome. There was no cellular immune response to AAV2.5 capsid. This trial established that rationally designed AAV2.5 vector was safe and well tolerated, lays the foundation of customizing AAV vectors that best suit the clinical objective (e.g., limb infusion gene delivery) and should usher in the next generation of viral delivery systems for human gene transfer.

Coordinated regulation of cardiac Na(+)/Ca (2+) exchanger and Na (+)-K (+)-ATPase by phospholemman (FXYD1).

Phospholemman (PLM) is the founding member of the FXYD family of regulators of ion transport. PLM is a 72-amino acid protein consisting of the signature PFXYD motif in the extracellular N terminus, a single transmembrane (TM) domain, and a C-terminal cytoplasmic tail containing three phosphorylation sites. In the heart, PLM co-localizes and co-immunoprecipitates with Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and L-type Ca(2+) channel. The TM domain of PLM interacts with TM9 of the α-subunit of Na(+)-K(+)-ATPase, while its cytoplasmic tail interacts with two small regions (spanning residues 248-252 and 300-304) of the proximal intracellular loop of Na(+)/Ca(2+) exchanger. Under stress, catecholamine stimulation phosphorylates PLM at serine(68), resulting in relief of inhibition of Na(+)-K(+)-ATPase by decreasing K(m) for Na(+) and increasing V(max), and simultaneous inhibition of Na(+)/Ca(2+) exchanger. Enhanced Na(+)-K(+)-ATPase activity lowers intracellular Na(+), thereby minimizing Ca(2+) overload and risks of arrhythmias. Inhibition of Na(+)/Ca(2+) exchanger reduces Ca(2+) efflux, thereby preserving contractility. Thus, the coordinated actions of PLM during stress serve to minimize arrhythmogenesis and maintain inotropy. In acute cardiac ischemia and chronic heart failure, either expression or phosphorylation of PLM or both are altered. PLM regulates important ion transporters in the heart and offers a tempting target for development of drugs to treat heart failure.

The next step in gene delivery: molecular engineering of adeno-associated virus serotypes.

Delivery is at the heart of gene therapy. Viral DNA delivery systems are asked to avoid the immune system, transduce specific target cell types while avoiding other cell types, infect dividing and non-dividing cells, insert their cargo within the host genome without mutagenesis or to remain episomal, and efficiently express transgenes for a substantial portion of a lifespan. These sought-after features cannot be associated with a single delivery system, or can they? The Adeno-associated virus family of gene delivery vehicles has proven to be highly malleable. Pseudotyping, using AAV serotype 2 terminal repeats to generate designer shells capable of transducing selected cell types, enables the packaging of common genomes into multiple serotypes virions to directly compare gene expression and tropism. In this review the ability to manipulate this virus will be examined from the inside out. The influence of host cell factors and organism biology including the immune response on the molecular fate of the viral genome will be discussed as well as differences in cellular trafficking patterns and uncoating properties that influence serotype transduction. Re-engineering the prototype vector AAV2 using epitope insertion, chemical modification, and molecular evolution not only demonstrated the flexibility of the best-studied serotype, but now also expanded the tool kit for molecular modification of all AAV serotypes. Current AAV research has changed its focus from examination of wild-type AAV biology to the feedback of host cell/organism on the design and development of a new generation of recombinant AAV delivery vehicles. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Myocardial adeno-associated virus serotype 6-betaARKct gene therapy improves cardiac function and normalizes the neurohormonal axis in chronic heart failure.

BACKGROUND: The upregulation of G protein-coupled receptor kinase 2 in failing myocardium appears to contribute to dysfunctional beta-adrenergic receptor (betaAR) signaling and cardiac function. The peptide betaARKct, which can inhibit the activation of G protein-coupled receptor kinase 2 and improve betaAR signaling, has been shown in transgenic models and short-term gene transfer experiments to rescue heart failure (HF). This study was designed to evaluate long-term betaARKct expression in HF with the use of stable myocardial gene delivery with adeno-associated virus serotype 6 (AAV6). METHODS AND RESULTS: In HF rats, we delivered betaARKct or green fluorescent protein as a control via AAV6-mediated direct intramyocardial injection. We also treated groups with concurrent administration of the beta-blocker metoprolol. We found robust and long-term transgene expression in the left ventricle at least 12 weeks after delivery. betaARKct significantly improved cardiac contractility and reversed left ventricular remodeling, which was accompanied by a normalization of the neurohormonal (catecholamines and aldosterone) status of the chronic HF animals, including normalization of cardiac betaAR signaling. Addition of metoprolol neither enhanced nor decreased betaARKct-mediated beneficial effects, although metoprolol alone, despite not improving contractility, prevented further deterioration of the left ventricle. CONCLUSIONS: Long-term cardiac AAV6-betaARKct gene therapy in HF results in sustained improvement of global cardiac function and reversal of remodeling at least in part as a result of a normalization of the neurohormonal signaling axis. In addition, betaARKct alone improves outcomes more than a beta-blocker alone, whereas both treatments are compatible. These findings show that betaARKct gene therapy can be of long-term therapeutic value in HF.

Analysis of AAV serotypes 1-9 mediated gene expression and tropism in mice after systemic injection.

This study examines transgene expression and biodistribution of adeno-associated virus (AAV) pseudotyped 1-9 after tail vein (TV) injection in male mice. Using a cytomegalovirus (CMV)-luciferase transgene, the time-course of expression in each animal was tracked throughout the experiment. The animals were imaged at 7, 14, 29, 56, and 100 days after the TV injection. The total number of photons emitted from each animal was recorded, allowing examination of expression level and kinetics for each pseudotyped virus. The bioluminescence imaging revealed three expression levels (i) low-expression group, AAV2, 3, 4, and 5; (ii) moderate-expression group, AAV1, 6, and 8; and (iii) high-expression group, AAV7 and 9. In addition, imaging revealed two classes of kinetics (i) rapid-onset, for AAV1, 6, 7, 8, and 9; and (ii) slow-onset, for AAV2, 3, 4, and 5. We next evaluated protein expression and viral genome copy numbers in dissected tissues. AAV9 had the best viral genome distribution and highest protein levels. The AAV7 protein and genome copy numbers were comparable to those of AAV9 in the liver. Most surprisingly, AAV4 showed the greatest number of genome copies in lung and kidney, and a high copy number in the heart. AAV6 expression was observed in the heart, liver, and skeletal muscle, and the genome distribution corroborated these observations.

Stable myocardial-specific AAV6-S100A1 gene therapy results in chronic functional heart failure rescue.

BACKGROUND: The incidence of heart failure is ever-growing, and it is urgent to develop improved treatments. An attractive approach is gene therapy; however, the clinical barrier has yet to be broken because of several issues, including the lack of an ideal vector supporting safe and long-term myocardial transgene expression. METHODS AND RESULTS: Here, we show that the use of a recombinant adeno-associated viral (rAAV6) vector containing a novel cardiac-selective enhancer/promoter element can direct stable cardiac expression of a therapeutic transgene, the calcium (Ca2+)-sensing S100A1, in a rat model of heart failure. The chronic heart failure-rescuing properties of myocardial S100A1 expression, the result of improved sarcoplasmic reticulum Ca2+ handling, included improved contractile function and left ventricular remodeling. Adding to the clinical relevance, long-term S100A1 therapy had unique and additive beneficial effects over beta-adrenergic receptor blockade, a current pharmacological heart failure treatment. CONCLUSIONS: These findings demonstrate that stable increased expression of S100A1 in the failing heart can be used for long-term reversal of LV dysfunction and remodeling. Thus, long-term, cardiac-targeted rAAV6-S100A1 gene therapy may be of potential clinical utility in human heart failure.

Converging Mechanisms of p53 Activation Drive Motor Neuron Degeneration in Spinal Muscular Atrophy.

The hallmark of spinal muscular atrophy (SMA), an inherited disease caused by ubiquitous deficiency in the SMN protein, is the selective degeneration of subsets of spinal motor neurons. Here, we show that cell-autonomous activation of p53 occurs in vulnerable but not resistant motor neurons of SMA mice at pre-symptomatic stages. Moreover, pharmacological or genetic inhibition of p53 prevents motor neuron death, demonstrating that induction of p53 signaling drives neurodegeneration. At late disease stages, however, nuclear accumulation of p53 extends to resistant motor neurons and spinal interneurons but is not associated with cell death. Importantly, we identify phosphorylation of serine 18 as a specific post-translational modification of p53 that exclusively marks vulnerable SMA motor neurons and provide evidence that amino-terminal phosphorylation of p53 is required for the neurodegenerative process. Our findings indicate that distinct events induced by SMN deficiency converge on p53 to trigger selective death of vulnerable SMA motor neurons.

Thrombospondin expression in myofibers stabilizes muscle membranes.

Skeletal muscle is highly sensitive to mutations in genes that participate in membrane stability and cellular attachment, which often leads to muscular dystrophy. Here we show that Thrombospondin-4 (Thbs4) regulates skeletal muscle integrity and its susceptibility to muscular dystrophy through organization of membrane attachment complexes. Loss of the Thbs4 gene causes spontaneous dystrophic changes with aging and accelerates disease in 2 mouse models of muscular dystrophy, while overexpression of mouse Thbs4 is protective and mitigates dystrophic disease. In the myofiber, Thbs4 selectively enhances vesicular trafficking of dystrophin-glycoprotein and integrin attachment complexes to stabilize the sarcolemma. In agreement, muscle-specific overexpression of Drosophila Tsp or mouse Thbs4 rescues a Drosophila model of muscular dystrophy with augmented membrane residence of ßPS integrin. This functional conservation emphasizes the fundamental importance of Thbs' as regulators of cellular attachment and membrane stability and identifies Thbs4 as a potential therapeutic target for muscular dystrophy.