In failing rat hearts, post-transcriptonal inhibition of phospholamban (PLB) expression by AAV9 vector-mediated cardiac delivery of short hairpin RNAs directed against PLB (shPLBr) improves both impaired SERCA2a controlled Ca2+ cycling and contractile dysfunction. Cardiac delivery of shPLB, however, was reported to cause cardiac toxicity in canines. Thus we developed a new AAV vector, scAAV6-amiR155-PLBr, expressing a novel engineered artificial microRNA (amiR155-PLBr) directed against PLB under control of a heart-specific hybrid promoter. Its PLB silencing efficiency and safety were compared with those of an AAV vector expressing shPLBr (scAAV6-shPLBr) from an ubiquitously active U6 promoter. Investigations were carried out in cultured neonatal rat cardiomyocytes (CM) over a period of 14 days. Compared to shPLBr, amiR155-PLBr was expressed at a significantly lower level, resulting in delayed and less pronounced PLB silencing. Despite decreased knockdown efficiency of scAAV6-amiR155-PLBr, a similar increase of the SERCA2a-catalyzed Ca2+ uptake into sarcoplasmic reticulum (SR) vesicles was observed for both the shPLBr and amiR155-PLBr vectors. Proteomic analysis confirmed PLB silencing of both therapeutic vectors and revealed that shPLBr, but not the amiR155-PLBr vector, increased the proinflammatory proteins STAT3, STAT1 and activated STAT1 phosphorylation at the key amino acid residue Tyr701. Quantitative RT-PCR analysis detected alterations in the expression of several cardiac microRNAs after treatment of CM with scAAV6-shPLBr and scAAV6-amiR155-PLBr, as well as after treatment with its related amiR155- and shRNAs-expressing control AAV vectors. The results demonstrate that scAAV6-amiR155-PLBr is capable of enhancing the Ca2+ transport function of the cardiac SR PLB/SERCA2a system as efficiently as scAAV6-shPLBr while offering a superior safety profile.
RNA interference (RNAi) has the potential to be a novel therapeutic strategy in diverse areas of medicine. We report on targeted RNAi for the treatment of heart failure (HF), an important disorder in humans resulting from multiple etiologies. Successful treatment of HF is demonstrated in a rat model of transaortic banding by RNAi targeting of phospholamban (PLB), a key regulator of cardiac Ca2+ homeostasis. Whereas gene therapy rests on recombinant protein expression as its basic principle, RNAi therapy employs regulatory RNAs to achieve its effect.
Methods and Results
We describe structural requirements to obtain high RNAi activity from adenoviral (AdV) and adeno-associated virus (AAV9) vectors and show that an AdV short hairpin RNA vector (AdV-shRNA) silenced PLB in cardiomyocytes (NRCMs) and improved hemodynamics in HF rats 1 month after aortic root injection. For simplified long-term therapy we developed a dimeric cardiotropic AAV vector (rAAV9-shPLB) delivering RNAi activity to the heart via intravenous injection. Cardiac PLB protein was reduced to 25% and SERCA2a suppression in the HF groups was rescued. In contrast to traditional vectors rAAV9 shows high affinity for myocardium, but low affinity for liver and other organs. rAAV9-shPLB therapy restored diastolic (LVEDP, dp/dtmin, Tau) and systolic (fractional shortening) functional parameters to normal range. The massive cardiac dilation was normalized and the cardiac hypertrophy, cardiomyocyte diameter and cardiac fibrosis significantly reduced. Importantly, there was no evidence of microRNA deregulation or hepatotoxicity during these RNAi therapies.
Our data show, for the first time, high efficacy of an RNAi therapeutic strategy in a cardiac disease.
Heart Failure; RNA Interference; Gene Therapy; Adeno-Associated Virus; Phospholamban
Adeno-associated virus (AAV)–mediated RNA interference shows promise as a therapy for chronic hepatitis B virus (HBV) infection, but its low efficacy and hepatotoxicity pose major challenges. We have generated AAV vectors containing different promoters and a panel of HBV-specific short hairpin RNAs (shRNAs) to investigate factors that contribute to the efficacy and pathogenesis of AAV-mediated RNA interference. HBV transgenic mice injected with high doses of AAV vectors containing the U6 promoter produced abundant shRNAs, transiently inhibited HBV, but induced severe hepatotoxicity. Sustained HBV suppression without liver toxicity can be achieved by lowering the dose of AAV-U6 vectors. AAVs containing the weaker H1 promoter did not cause liver injury, but their therapeutic efficacy was highly dependent on the sequence of the shRNA. Mice treated with the toxic U6-promoter-driven shRNA showed little change in hepatic microRNA levels, but a dramatic increase in hepatic leukocytes and inflammatory cytokines and chemokines. Hepatotoxicity was completely absent in immunodeficient mice and significantly alleviated in wild-type mice depleted of macrophages and granulocytes, suggesting that host inflammatory responses are the major cause of liver injury induced by the overexpressed shRNAs from AAV-U6 vectors. Our results demonstrate that selection of a highly potent shRNA and control its expression level is critical to achieve sustained HBV suppression without inducing inflammatory side effects.
Sun and colleagues generate a panel of AAV vectors containing various promoters and hepatitis B virus (HBV)-specific short hairpin RNAs (shRNAs) to investigate factors that contribute to the efficacy and pathogenesis of AAV-mediated RNA interference. They show that injecting HBV transgenic mice with high doses of AAV vectors containing the U6 promoter produce abundant shRNAs, transiently inhibit HBV, but induce severe hepatotoxicity. By contrast, AAVs containing the weaker H1 promoter do not cause liver injury, but their therapeutic efficacy is highly dependent on the sequence of the shRNA.
Adeno-associated viral (AAV) vectors show great promise because of their excellent safety profile; however, pre-existing immune responses have necessitated the administration of high titer AAV, posing a significant challenge to the advancement of gene therapy involving AAV vectors. Recombinant AAV vectors contain minimum viral proteins necessary for their assembly and gene delivery functions. During the process of AAV assembly and production, AAV vectors acquire, inherently and submissively, various cellular proteins, but the identity of these proteins is poorly characterized. We reason that by identifying host cell proteins inherently associated with AAV vectors we may better understand the contribution of cellular components to AAV vector assembly and, ultimately, may improve the production of AAV vectors for gene therapy. In this study, three serotypes of recombinant AAV, namely AAV2, AAV5, and AAV8, were investigated. We used liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) methods to identify protein composition in purified AAV vectors, confirmed protein identities using western blotting, and explored the potential function of selected proteins in AAV vector production using small hairpin (shRNA) methods. Using LC-MS/MS, we identified 44 AAV-associated cellular proteins including Y-box binding protein (YB1). We showed for the first time that the establishment of a novel producer cell line by introducing an shRNA sequence down-regulating YB1 resulted in up to 45- and 9-fold increase in physical vector genome titers of AAV2 and AAV8, respectively, and up to 7-fold increase in AAV2 transduction vector genome titers. Our results revealed that YB1 gene knockdown promoted AAV2 rep expression and vector DNA production and reduced the number of empty particles in AAV2 products, suggesting that YB1 plays an important role in AAV vector assembly by competition with adenovirus E2A and AAV capsid proteins for binding to the inverted terminal repeat (ITR) sequence. The significance and implications of our findings in future improvement of AAV production are discussed.
The targeting of Ca2+ cycling has emerged as a potential therapy for the treatment of severe heart failure. These approaches include gene therapy directed at overexpressing sarcoplasmic reticulum (SR) Ca2+ ATPase, or ablation of phospholamban (PLN) and associated protein phosphatase 1 (PP1) protein complexes. We previously reported that PP1β, one of the PP1 catalytic subunits, predominantly suppresses Ca2+ uptake in the SR among the three PP1 isoforms, thereby contributing to Ca2+ downregulation in failing hearts. In the present study, we investigated whether heart-failure-inducible PP1β-inhibition by adeno-associated viral-9 (AAV9) vector mediated gene therapy is beneficial for preventing disease progression in genetic cardiomyopathic mice.
We created an adeno-associated virus 9 (AAV9) vector encoding PP1β short-hairpin RNA (shRNA) or negative control (NC) shRNA. A heart failure inducible gene expression system was employed using the B-type natriuretic protein (BNP) promoter conjugated to emerald-green fluorescence protein (EmGFP) and the shRNA sequence. AAV9 vectors (AAV9-BNP-EmGFP-PP1βshRNA and AAV9-BNP-EmGFP-NCshRNA) were injected into the tail vein (2×1011 GC/mouse) of muscle LIM protein deficient mice (MLPKO), followed by serial analysis of echocardiography, hemodynamic measurement, biochemical and histological analysis at 3 months.
In the MLPKO mice, BNP promoter activity was shown to be increased by detecting both EmGFP expression and the induced reduction of PP1β by 25% in the myocardium. Inducible PP1βshRNA delivery preferentially ameliorated left ventricular diastolic function and mitigated adverse ventricular remodeling. PLN phosphorylation was significantly augmented in the AAV9-BNP-EmGFP-PP1βshRNA injected hearts compared with the AAV9-BNP-EmGFP-NCshRNA group. Furthermore, BNP production was reduced, and cardiac interstitial fibrosis was abrogated at 3 months.
Heart failure-inducible molecular targeting of PP1β has potential as a novel therapeutic strategy for heart failure.
Phospholamban (PLB) or the sarcoplasmic reticulum Ca2+-ATPase (SERCA) were fused to cyan fluorescent protein (CFP) and coexpressed with PLB fused to yellow fluorescent protein (YFP). The expressed fluorescently tagged proteins were imaged using epifluorescence and total internal reflection fluorescence microscopy. YFP fluorescence was selectively bleached by a focused laser beam. CFP fluorescence at the targeted site increased after YFP photobleaching, indicating fluorescence resonance energy transfer between CFP-SERCA/CFP-PLB and YFP-PLB. The increased donor fluorescence relaxed back toward baseline as a result of donor diffusion and exchange of bleached YFP-PLB for unbleached YFP-PLB, which restored fluorescence resonance energy transfer. Requenching of CFP donors, termed Förster transfer recovery (FTR), was quantified as an index of the rate of PLB subunit exchange from the PLB:SERCA and PLB:PLB membrane complexes. PLB subunit exchange from the PLB:SERCA regulatory complex was rapid, showing diffusion-limited FTR (τ=1.4 second). Conversely, PLB:PLB oligomeric complexes were found to be stable on a much longer time scale. Despite free lateral diffusion in the membrane, they showed no FTR over 80 seconds. Mutation of PLB position 40 from isoleucine to alanine (I40A-PLB) did not abolish PLB:PLB energy transfer, but destabilization of the PLB:PLB complex was apparent from an increased FTR rate (τ=8.4 seconds). Oligomers of I40A-PLB were stabilized by oxidative crosslinking of transmembrane cysteines with diamide. We conclude that PLB exchanges rapidly from its regulatory complex with the SERCA pump, whereas subunit exchange from the PLB oligomeric complex is slow and does not occur on the time scale of the cardiac cycle.
phospholamban; SERCA; FRET; TIRF; crosslinking
After a spinal cord lesion, axon regeneration is inhibited by the presence of a diversity of inhibitory molecules in the lesion environment. At and around the lesion site myelin-associated inhibitors, chondroitin sulfate proteoglycans (CSPGs) and several axon guidance molecules, including all members of the secreted (class 3) Semaphorins, are expressed. Interfering with multiple inhibitory signals could potentially enhance the previously reported beneficial effects of blocking single molecules. RNA interference (RNAi) is a tool that can be used to simultaneously silence expression of multiple genes. In this study we aimed to employ adeno-associated virus (AAV) mediated expression of short hairpin RNAs (shRNAs) to target all Semaphorin class 3 signaling by knocking down its receptors, Neuropilin 1 (Npn-1) and Neuropilin 2 (Npn-2).
We have successfully generated shRNAs that knock down Npn-1 and Npn-2 in a neuronal cell line. We detected substantial knockdown of Npn-2 mRNA when AAV5 viral vector particles expressing Npn-2 specific shRNAs were injected in dorsal root ganglia (DRG) of the rat. Unexpectedly however, AAV1-mediated expression of Npn-2 shRNAs and a control shRNA in the red nucleus resulted in an adverse tissue response and neuronal degeneration. The observed toxicity was dose dependent and was not seen with control GFP expressing AAV vectors, implicating the shRNAs as the causative toxic agents.
RNAi is a powerful tool to knock down Semaphorin receptor expression in neuronal cells in vitro and in vivo. However, when shRNAs are expressed at high levels in CNS neurons, they trigger an adverse tissue response leading to neuronal degradation.
The calcium pump SERCA2a (sarcoplasmic reticulum calcium ATPase 2a), which plays a central role in cardiac contraction, shows decreased expression in heart failure (HF). Increasing SERCA2a expression in HF models improves cardiac function. We used direct cardiac delivery of adeno-associated virus encoding human SERCA2a (AAV6-hSERCA2a) in HF and normal canine models to study safety, efficacy, and the effects of immunosuppression. Tachycardic-paced dogs received left ventricle (LV) wall injection of AAV6-hSERCA2a or solvent. Pacing continued postinjection for 2 or 6 weeks, until euthanasia. Tissue/serum samples were analyzed for hSERCA2a expression (Western blot) and immune responses (histology and AAV6-neutralizing antibodies). Nonpaced dogs received AAV6-hSERCA2a and were analyzed at 12 weeks; a parallel cohort received AAV-hSERCA2a and immunosuppression. AAV-mediated cardiac expression of hSERCA2a peaked at 2 weeks and then declined (to ∼50%; p<0.03, 6 vs. 2 weeks). LV end diastolic and end systolic diameters decreased in 6-week dogs treated with AAV6-hSERCA2a (p<0.05) whereas LV diameters increased in control dogs. Dogs receiving AAV6-hSERCA2a developed neutralizing antibodies (titer ≥1:120) and cardiac cellular infiltration. Immunosuppression dramatically reduced immune responses (reduced inflammation and neutralizing antibody titers <1:20), and maintained hSERCA2a expression. Thus cardiac injection of AAV6-hSERCA2a promotes local hSERCA2a expression and improves cardiac function. However, the hSERCA2a protein level is reduced by host immune responses. Immunosuppression alleviates immune responses and sustains transgene expression, and may be an important adjuvant for clinical gene therapy trials.
Zhu and colleagues employ direct cardiac delivery of adeno-associated virus encoding the human calcium pump SERCA2a (AAV6-hSERCA2a) in heart failure and normal canine models in order to study the safety and efficacy of the approach as well as the effects of concomitant immunosuppressant treatment. Tachycardic-paced dogs injected with AAV6-hSERCA2a via the left ventricle wall displayed hSERCA2a expression and improved cardiac function, although hSERCA2a protein levels were reduced by host immune responses. Immunosuppression dramatically reduced inflammation and neutralizing antibody titers while maintaining hSERCA2a expression.
Histidine-rich calcium binding protein (HRC) is located in the lumen of sarcoplasmic reticulum (SR) that binds to both triadin (TRN) and SERCA affecting Ca2+ cycling in the SR. Chronic overexpression of HRC that may disrupt intracellular Ca2+ homeostasis is implicated in pathogenesis of cardiac hypertrophy. Ablation of HRC showed relatively normal phenotypes under basal condition, but exhibited a significantly increased susceptibility to isoproterenol-induced cardiac hypertrophy. In the present study, we characterized the functions of HRC related to Ca2+ cycling and pathogenesis of cardiac hypertrophy using the in vitro siRNA- and the in vivo adeno-associated virus (AAV)-mediated HRC knock-down (KD) systems, respectively.
AAV-mediated HRC-KD system was used with or without C57BL/6 mouse model of transverse aortic constriction-induced failing heart (TAC-FH) to examine whether HRC-KD could enhance cardiac function in failing heart (FH). Initially we expected that HRC-KD could elicit cardiac functional recovery in failing heart (FH), since predesigned siRNA-mediated HRC-KD enhanced Ca2+ cycling and increased activities of RyR2 and SERCA2 without change in SR Ca2+ load in neonatal rat ventricular cells (NRVCs) and HL-1 cells. However, AAV9-mediated HRC-KD in TAC-FH was associated with decreased fractional shortening and increased cardiac fibrosis compared with control. We found that phospho-RyR2, phospho-CaMKII, phospho-p38 MAPK, and phospho-PLB were significantly upregulated by HRC-KD in TAC-FH. A significantly increased level of cleaved caspase-3, a cardiac cell death marker was also found, consistent with the result of TUNEL assay.
Increased Ca2+ leak and cytosolic Ca2+ concentration due to a partial KD of HRC could enhance activity of CaMKII and phosphorylation of p38 MAPK, causing the mitochondrial death pathway observed in TAC-FH. Our results present evidence that down-regulation of HRC could deteriorate cardiac function in TAC-FH through perturbed SR-mediated Ca2+ cycling.
Calcium (Ca2+) handling proteins are known to play a pivotal role in the pathophysiology of cardiomyopathy. However little is known about early changes in the diabetic heart and the impact of insulin treatment (Ins).
Zucker Diabetic Fatty rats treated with or without insulin (ZDF ± Ins, n = 13) and lean littermates (controls, n = 7) were sacrificed at the age of 19 weeks. ZDF + Ins (n = 6) were treated with insulin for the last 6 weeks of life. Gene expression of Ca2+ ATPase in the cardiac sarcoplasmatic reticulum (SERCA2a, further abbreviated as SERCA) and phospholamban (PLB) were determined by northern blotting. Ca2+ transport of the sarcoplasmatic reticulum (SR) was assessed by oxalate-facilitated 45Ca-uptake in left ventricular homogenates. In addition, isolated neonatal cardiomyocytes were stimulated in cell culture with insulin, glucose or triiodthyronine (T3, positive control). mRNA expression of SERCA and PLB were measured by Taqman PCR. Furthermore, effects of insulin treatment on force of contraction and relaxation were evaluated by cardiomyocytes grown in a three-dimensional collagen matrix (engineered heart tissue, EHT) stimulated for 5 days by insulin. By western blot phosphorylations status of Akt was determed and the influence of wortmannin.
SERCA levels increased in both ZDF and ZDF + Ins compared to control (control 100 ± 6.2 vs. ZDF 152 ± 26.6* vs. ZDF + Ins 212 ± 18.5*# % of control, *p < 0.05 vs. control, #p < 0.05 vs. ZDF) whereas PLB was significantly decreased in ZDF and ZDF + Ins (control 100 ± 2.8 vs. ZDF 76.3 ± 13.5* vs. ZDF + Ins 79.4 ± 12.9* % of control, *p < 0.05 vs control). The increase in the SERCA/PLB ratio in ZDF and ZDF ± Ins was accompanied by enhanced Ca2+ uptake to the SR (control 1.58 ± 0.1 vs. ZDF 1.85 ± 0.06* vs. ZDF + Ins 2.03 ± 0.1* μg/mg/min, *p < 0.05 vs. control). Interestingly, there was a significant correlation between Ca2+ uptake and SERCA2a expression. As shown by in-vitro experiments, the effect of insulin on SERCA2a mRNA expression seemed to have a direct effect on cardiomyocytes. Furthermore, long-term treatment of engineered heart tissue with insulin increased the SERCA/PLB ratio and accelerated relaxation time. Akt was significantly phosphorylated by insulin. This effect could be abolished by wortmannin.
The current data demonstrate that early type 2 diabetes is associated with an increase in the SERCA/PLB ratio and that insulin directly stimulates SERCA expression and relaxation velocity. These results underline the important role of insulin and calcium handling proteins in the cardiac adaptation process of type 2 diabetes mellitus contributing to cardiac remodeling and show the important role of PI3-kinase-Akt-SERCA2a signaling cascade.
Diabetic heart; Insulin; SERCA expression; Relaxation velocity
Molecular intervention using noninvasive myocardial gene transfer holds great promise for treating heart diseases. Robust cardiac transduction from peripheral vein injection has been achieved in rodents using adeno-associated virus (AAV) serotype-9 (AAV-9). However, a similar approach has failed to transduce the heart in dogs, a commonly used large animal model for heart diseases. To develop an effective noninvasive method to deliver exogenous genes to the dog heart, we employed an AAV-8 vector that expresses human placental alkaline phosphatase reporter gene under the transcriptional regulation of the Rous sarcoma virus promoter. Vectors were delivered to three neonatal dogs at the doses of 1.35×1014, 7.14×1014, and 9.06×1014 viral genome particles/kg body weight via the jugular vein. Transduction efficiency and overall safety were evaluated at 1.5, 2.5, and 12 months postinjection. AAV delivery was well tolerated and dog growth was normal. Blood chemistry and internal organ histology were unremarkable. Widespread skeletal muscle transduction was observed in all dogs without T-cell infiltration. Encouragingly, whole heart myocardial transduction was achieved in two dogs that received higher doses and cardiac expression lasted for at least 1 year. In summary, peripheral vein AAV-8 injection may represent a simple heart gene transfer method in large mammals. Further optimization of this gene delivery strategy may open the door for a readily applicable gene therapy method to treat many heart diseases.
Pan and colleagues administer, via the jugular vein, adeno-associated virus serotype 8 (AAV8) vector expressing a human placental alkaline phosphatase reporter gene under the control of the Rous sarcoma virus promoter to three neonatal dogs at doses of 1.35 × 1014, 7.14 × 1014, and 9.06 × 1014 viral genome particles/kg body weight. Using this approach, they observe widespread skeletal muscle transduction in all dogs without T cell infiltration. Interestingly, whole heart myocardial transduction was achieved in the two dogs that received the highest doses, and this expression lasted for at least 1 year.
Constitutive expression of short hairpin RNAs (shRNAs) may cause cellular toxicity in vivo and using microRNA (miRNA) scaffolds can circumvent this problem. Previously, we have shown that embedding small interfering RNA sequences targeting apolipoprotein B100 (ApoB) in shRNA (shApoB) or miRNA (miApoB) scaffolds resulted in differential processing and long-term efficacy in vivo. Here we show that adeno-associated virus (AAV)-shApoB- or AAV-miApoB-mediated ApoB knockdown induced differential liver morphology and transcriptome expression changes. Our analyses indicate that ApoB knockdown with both shApoB and miApoB resulted in alterations of genes involved in lipid metabolism. In addition, in AAV-shApoB-injected animals, genes involved in immune system activation or cell growth and death were affected, which was associated with increased hepatocyte proliferation. Subsequently, in AAV-miApoB-injected animals, changes of genes involved in oxidoreductase activity, oxidative phosphorylation and nucleic bases biosynthetic processes were observed. Our results demonstrate that long-term knockdown of ApoB in vivo by shApoB or miApoB induces several transcriptome changes in murine liver. The increased hepatocyte profileration by AAV-shRNA may have severe long-term effects indicating that AAV-mediated RNA interference therapy using artificial miRNA may be a safer approach for familial hypercholesterolemia therapy.
AAV; liver; shRNA; miRNA; ApoB; familial hypercholesterolemia
Anthrax lethal toxin (LT), secreted by Bacillus anthracis, causes severe cardiac dysfunction by unknown mechanisms. LT specifically cleaves the docking domains of MAPKK (MEKs); thus, we hypothesized that LT directly impairs cardiac function through dysregulation of MAPK signaling mechanisms.
Methods and Results
In a time-course study of LT toxicity, echocardiography revealed acute diastolic heart failure accompanied by pulmonary regurgitation and left atrial dilation in adult Sprague-Dawley rats at time points corresponding to dysregulated JNK, phospholamban (PLB) and protein phosphatase 2A (PP2A) myocardial signaling. Using isolated rat ventricular myocytes, we identified the MEK7-JNK1-PP2A-PLB signaling axis to be important for regulation of intracellular calcium (Ca2+i) handling, PP2A activation and targeting of PP2A-B56α to Ca2+i handling proteins, such as PLB. Through a combination of gain-of-function and loss-of-function studies, we demonstrated that over-expression of MEK7 protects against LT-induced PP2A activation and Ca2+i dysregulation through activation of JNK1. Moreover, targeted phosphorylation of PLB-Thr17 by Akt improved sarcoplasmic reticulum Ca2+i release and reuptake during LT toxicity. Co-immunoprecipitation experiments further revealed the pivotal role of MEK7-JNK-Akt complex formation for phosphorylation of PLB-Thr17 during acute LT toxicity.
Our findings support a cardiogenic mechanism of LT-induced diastolic dysfunction, by which LT disrupts JNK1 signaling and results in Ca2+i dysregulation through diminished phosphorylation of PLB by Akt and increased dephosphorylation of PLB by PP2A. Integration of the MEK7-JNK1 signaling module with Akt represents an important stress-activated signalosome that may confer protection to sustain cardiac contractility and maintain normal levels of Ca2+i through PLB-T17 phosphorylation.
Diastolic dysfunction; Anthrax lethal toxin; JNK1/2; Akt; Phospholamban
AAV9 is a powerful gene delivery vehicle capable of providing long-term gene expression in a variety of cell types, particularly cardiomyocytes. The use of AAV-delivery for RNA interference is an intense area of research, but a comprehensive analysis of knockdown in cardiac and liver tissues after systemic delivery of AAV9 has yet to be reported. We sought to address this question by using AAV9 to deliver a short-hairpin RNA targeting the enhanced green fluorescent protein (GFP) in transgenic mice that constitutively overexpress GFP in all tissues. The expression cassette was initially tested in vitro and we demonstrated a 61% reduction in mRNA and a 90% reduction in GFP protein in dual-transfected 293 cells. Next, the expression cassette was packaged as single-stranded genomes in AAV9 capsids to test cardiac GFP knockdown with several doses ranging from 1.8×1010 to 1.8×1011 viral genomes per mouse and a dose-dependent response was obtained. We then analyzed GFP expression in both heart and liver after delivery of 4.4×1011 viral genomes per mouse. We found that while cardiac knockdown was highly efficient, with a 77% reduction in GFP mRNA and a 71% reduction in protein versus control-treated mice, there was no change in liver expression. This was despite a 4.5-fold greater number of viral genomes in the liver than in the heart. This study demonstrates that single-stranded AAV9 vectors expressing shRNA can be used to achieve highly efficient cardiac-selective knockdown of GFP expression that is sustained for at least 7 weeks after the systemic injection of 8 day old mice, with no change in liver expression and no evidence of liver damage despite high viral genome presence in the liver.
Clinical observations and epidemiological surveys indicated that the prevalence of hypertension and heart diseases is increased in cold regions or during winter. Cold exposure increased NADPH oxidase gp91phox protein expression in heart, kidneys, and aorta in rats. The aim of this study was to investigate if RNA interference (RNAi) silencing of gp91phox would attenuate cold-induced hypertension and cardiovascular and renal damage. The recombinant adeno-associated virus serotype 2 (AAV-2) vector carrying gp91phox-shRNA (gp91-shRNA) was constructed for inhibiting gp91phox protein expression in cold-exposed rats. Blood pressure (BP) was monitored using a telemetry system. BP was increased in the Control-shRNA and PBS groups within 1 week of exposure to moderate cold (5°C) and reached a plateau after 7 weeks. The cold-induced increase in BP was attenuated significantly by intravenous delivery of gp91-shRNA (1.25×1010 particles/rat, 0.5 mL). One single dose of gp91-shRNA controlled hypertension for up to 10 weeks. In addition, gp91-shRNA reversed cold-induced vascular dysfunction. gp91-shRNA abolished the cold-induced up-regulation of gp91phox protein expression in heart, kidneys, and aorta, confirming effective silencing of gp91phox. The cold-induced increases in NADPH oxidase activity and superoxide production were eliminated by silencing of gp91phox, suggesting that the cold-induced up-regulation of NADPH oxidase activity may be attributed to the increased gp91phox protein expression. RNAi silencing of gp91phox abolished cold-induced cardiac and renal hypertrophy and attenuated aortic, coronary, and renal remodeling. The up-regulation of gp91phox may play a critical role in cold-induced cardiovascular dysfunction and organ damage. AAV delivery of gp91-shRNA may be a new and effective therapeutic approach for cold-related cardiovascular disorders.
Wang and colleagues investigate silencing of gp91phox as a potential way to attenuate cold-induced hypertension and cardiovascular and renal damage. Recombinant adeno-associated virus serotype 2 (AAV2) carrying gp91phox–short hairpin RNA was constructed and delivered to cold-exposed rats. A single dose of vector controlled hypertension for up to 10 weeks and reversed cold-induced vascular dysfunction as well as renal hypertrophy.
RNAi has potential for therapeutically downregulating the expression of dominantly inherited genes in a variety of human genetic disorders. Here we used the ROSA26 mouse, which constitutively expresses the bacterial lacZ gene in tissues body wide, as a model to test the ability to downregulate gene expression in striated muscles. Recombinant adeno-associated viral vectors (rAAVs) were generated that express short hairpin RNAs (shRNAs) able to target the lacZ mRNA. Systemic delivery of these rAAV6 vectors led to a decrease of β-galactosidase expression of 30–50-fold in the striated muscles of ROSA26 mice. However, high doses of vectors expressing 21 nucleotide shRNA sequences were associated with significant toxicity in both liver and cardiac muscle. This toxicity was reduced in cardiac muscle using lower vector doses. Furthermore, improved knockdown in the absence of toxicity was obtained by using a shorter (19 nucleotide) shRNA guide sequence. These results support the possibility of using rAAV vectors to deliver RNAi sequences systemically to treat dominantly inherited disorders of striated muscle.
We previously reported that self-complementary adeno-associated virus (scAAV) type 2 genomes of up to 3.3 kb can be successfully encapsidated into AAV2 serotype capsids. Here we report that such oversized AAV2 genomes fail to undergo packaging in other AAV serotype capsids, such as AAV1, AAV3, AAV6, and AAV8, as determined by Southern blot analyses of the vector genomes, although hybridization signals on quantitative DNA slot-blots could still be obtained. Recently, it has been reported that quantitative real-time PCR assays may result in substantial differences in determining titers of scAAV vectors depending on the distance between the primer sets and the terminal hairpin structure in the scAAV genomes. We also observed that the vector titers determined by the standard DNA slot-blot assays were highly dependent on the specific probe being used, with probes hybridizing to the ends of viral genomes being significantly overrepresented compared with the probes hybridizing close to the middle of the viral genomes. These differences among various probes were not observed using Southern blot assays. This overestimation of titer is a systemic error during scAAV genome quantification, regardless of viral genome sequences and capsid serotypes. Furthermore, different serotypes capsid and modification of capsid sequence may affect the ability of packaging intact, full-length AAV genomes. Although the discrepancy is modest with wild-type serotype capsid and short viral genomes, the measured titer could be as much as fivefold different with capsid mutant vectors and large genomes. Thus, based on our data, we suggest that Southern blot analyses should be performed routinely to more accurately determine the titers of recombinant AAV vectors. At the very least, the use of probes/primers hybridizing close to the mutant inverted terminal repeat in scAAV genomes is recommended to avoid possible overestimation of vector titers.
Wang and colleagues report that 3.3 kb self-complementary (sc) AAV2 genomes fail to undergo packaging into AAV serotype capsids other than AAV2. Serotypes tested include AAV1, AAV3, AAV6, and AAV8. The authors also address the issue of qPCR titering assays leading to overestimation of scAAV vector titers and suggest Southern blot analyses as a more accurate and reliable titering method.
In humans, overproduction of apolipoprotein B (apoB) is positively associated with premature coronary artery diseases. To reduce the levels of apoB mRNA, we have designed an apoB mRNA-specific hammerhead ribozyme targeted at nucleotide sequences GUA6679 (RB15) mediated by adenovirus, which efficiently cleaves and decreases apoB mRNA by 80% in mouse liver and attenuates the hyperlipidemic condition. In the current study, we used an adeno-associated virus vector, serotype 2 (AAV2) and a self-complementary AAV2 vector (scAAV2) to demonstrate the effect of long-term tissue-specific gene expression of RB15 on the regulation apoB mRNA in vivo.
We constructed a hammerhead ribozyme RB15 driven by a liver-specific transthyretin (TTR) promoter using an AAV2 vector (rAAV2-TTR-RB15). HepG2 cells and hyperlipidemic mice deficient in both the low density lipoprotein receptor and the apoB mRNA editing enzyme genes (LDLR-/-Apobec1-/-; LDb) were transduced with rAAV2-TTR-RB15 and a control vector rAAV-TTR-RB15-mutant (inactive ribozyme). The effects of ribozyme RB15 on apoB metabolism and atherosclerosis development were determined in LDb mice at 5-month after transduction. A self-complementary AAV2 vector expressing ribozyme RB15 (scAAV2-TTR-RB15) was also engineered and used to transduce HepG2 cells. Studies were designed to compare the gene expression efficiency between rAAV2-TTR-RB15 and scAAV2-TTR-RB15.
The effect of ribozyme RB15 RNA on reducing apoB mRNA levels in HepG2 cells was observed only on day-7 after rAAV2-TTR-RB15 transduction. And, at 5-month after rAAV2-TTR-RB15 treatment, the apoB mRNA levels in LDb mice were significantly decreased by 43%, compared to LDb mice treated with control vector rAAV2-TTR-RB15-mutant. Moreover, both the rAAV2-TTR-RB15 viral DNA and ribozyme RB15 RNA were still detectable in mice livers at 5-month after treatment. However, this rAAV2-TTR-RB15 vector mediated a prolonged but low level of ribozyme RB15 gene expression in the mice livers, which did not produce the therapeutic effects on alteration the lipid levels or the inhibition of atherosclerosis development. In contrast, the ribozyme RB15 RNA mediated by scAAV2-TTR-RB15 vector was expressed immediately at day-1 after transduction in HepG2 cells. The apoB mRNA levels were decreased 47% (p = 0.001), compared to the control vector scAAV2-TTR-RB15-mutant.
This study provided evidence that the rAAV2 single-strand vector mediated a prolonged but not efficient transduction in mouse liver. However, the scAAV2 double-strand vector mediated a rapid and efficient gene expression in liver cells. This strategy using scAAV2 vectors represents a better approach to express small molecules such as ribozyme.
gene therapy; adeno-associated virus vector; self-complementary AAV vector; hammerhead ribozyme; apolipoprotein B; liver-specific gene expression
α- and β-Adrenergic receptor agonists induce an inotropic response in the adult heart by promoting the phosphorylation of several regulatory proteins, including myosin-binding protein C (MyBP-C), cardiac troponin I (cTnI), and phospholamban (PLB). However, the adrenergic-induced phosphorylation of these proteins has not been characterized in the developing heart. Accordingly, we evaluated MyBP-C, cTnI, and PLB phosphorylation in cultured neonatal rat cardiomyocytes (NRCMs) after α- and β-receptor activation with phenylephrine and isoproterenol. α-Receptor stimulation increased, whereas β-receptor activation reduced MyBP-C phosphorylation. Isoelectric-focusing experiments indicated that the amount of monophosphorylated MyBP-C was sensitive to α-adrenergic activation, but diphosphorylated and triphosphorylated MyBP-C levels were largely unaffected. The phosphorylation of cTnI and PLB was consistent with the mechanism observed in adult hearts: α-and β-Receptor stimulation phosphorylated both proteins. For cTnI, the greatest difference associated with β-receptor activation was observed in the diphosphorylated state, whereas α-receptor activation was associated with a marked increase in the tetraphosphorylated protein and absence of the unphosphorylated state. Despite these apparent changes in cTnI and PLB phosphorylation, β-receptor activation failed to alter calcium transients in NRCMs. Collectively, these findings suggest that, unlike cTnI and PLB, MyBP-C and inotropy are not coupled to β-adrenergic stimulation in NRCMs. Therefore, cTnI and PLB probably play a more central role in modulating contractile function in NRCMs in response to catecholamines than does MyBP-C, and MyBP-C may have a structural role in stabilizing thick filament assembly rather than influencing cross-bridge formation in developing hearts.
The unfolded protein response (UPR) is a stress-induced cyto-protective mechanism elicited towards an influx of large amount of proteins in the endoplasmic reticulum (ER). In the present study, we evaluated if AAV manipulates the UPR pathways during its infection. We first examined the role of the three major UPR axes, namely, endoribonuclease inositol-requiring enzyme-1 (IRE1α), activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) in AAV infected cells. Total RNA from mock or AAV infected HeLa cells were used to determine the levels of 8 different ER-stress responsive transcripts from these pathways. We observed a significant up-regulation of IRE1α (up to 11 fold) and PERK (up to 8 fold) genes 12–48 hours after infection with self-complementary (sc)AAV2 but less prominent with single-stranded (ss)AAV2 vectors. Further studies demonstrated that scAAV1 and scAAV6 also induce cellular UPR in vitro, with AAV1 vectors activating the PERK pathway (3 fold) while AAV6 vectors induced a significant increase on all the three major UPR pathways [6–16 fold]. These data suggest that the type and strength of UPR activation is dependent on the viral capsid. We then examined if transient inhibition of UPR pathways by RNA interference has an effect on AAV transduction. siRNA mediated silencing of PERK and IRE1α had a modest effect on AAV2 and AAV6 mediated gene expression (∼1.5–2 fold) in vitro. Furthermore, hepatic gene transfer of scAAV2 vectors in vivo, strongly elevated IRE1α and PERK pathways (2 and 3.5 fold, respectively). However, when animals were pre-treated with a pharmacological UPR inhibitor (metformin) during scAAV2 gene transfer, the UPR signalling and its subsequent inflammatory response was attenuated concomitant to a modest 2.8 fold increase in transgene expression. Collectively, these data suggest that AAV vectors activate the cellular UPR pathways and their selective inhibition may be beneficial during AAV mediated gene transfer.
Adeno-associated virus (AAV) has shown great promise as a gene transfer vector. However, the incubation time needed to attain significant levels of gene expression is often too long for some clinical applications. Self-complementary AAV (scAAV) enters the cell as double stranded DNA, eliminating the step of second-strand synthesis, proven to be the rate-limiting step for gene expression of single-stranded AAV (ssAAV). The aim of this study was to compare the efficiency of these two types of AAV vectors in the murine myocardium. Four day old CD-1 mice were injected with either of the two AAV constructs, both expressing GFP and packaged into the AAV1 capsid. The animals were held for 4, 6, 11 or 21 days, after which they were euthanized and their hearts were excised. Serial sections of the myocardial tissue were used for real-time PCR quantification of AAV genome copies and for confocal microscopy. Although we observed similar numbers of AAV genomes at each of the different time points present in both the scAAV and the ssAAV infected hearts, microscopic analysis showed expression of GFP as early as 4 days in animals injected with the scAAV, while little or no expression was observed with the ssAAV constructs until day 11. AAV transduction of murine myocardium is therefore significantly enhanced using scAAV constructs.
We have developed a quantitative immunoblot method to measure the mole fraction of phospholamban (PLB) phosphorylated at Ser16 (Xp) in biological samples. In cardiomyocytes, PLB phosphorylation activates the sarcoplasmic reticulum calcium ATPase (SERCA), which reduces cytoplasmic Ca++ to relax the heart during diastole. Unphosphorylated PLB (uPLB) inhibits SERCA at low [Ca++] and phosphorylated PLB (pPLB) is less inhibitory, so myocardial physiology and pathology depend critically on Xp. Current methods of Xp determination by immunoblot provide moderate precision but poor accuracy. We have solved this problem using purified uPLB and pPLB standards, produced by solid-phase peptide synthesis. In each assay, a pair of blots is performed with identical standards and unknowns, using antibodies partially selective for uPLB and pPLB, respectively. When performed on mixtures of uPLB and pPLB, the assay measures both total PLB (tPLB) and Xp with accuracy of 96% or better. We assayed pig cardiac SR and found that Xp varied widely among four animals, from 0.08 to 0.38, but there was remarkably little variation in the ratios of Xp/tPLB and uPLB/SERCA, suggesting that PLB phosphorylation is tuned to maintain homeostasis in SERCA regulation.
Phospholamban; phosphorylation; SERCA; heart failure; western blot; XpPhospholamban phosphorylation and heart disease
The capsid protein synthesis in targeted tissues resulting from residual contaminating replication-competent adeno-associated virus particles (rcAAV) remains a concern for hazardous immune responses that shut down the factor IX expression in the hemophilia B clinical trial. To systematically reduce/eliminate the effects of potential contaminating rcAAV particles, we designed a novel adeno-associated virus (AAV) helper (pH22mir) with a microRNA binding cassette containing multiple copies of liver-specific (hsa-mir-122) and hematopoietic-specific (has-mir-142-3p) sequences to specifically control cap gene expression. In 293 cells, the rep and cap gene from pH22mir functioned similarly to that of conventional helper pH22. The vector yields and compositions from pH22mir and pH22 were indistinguishable. The performance of vector produced in this new system was comparable to that of similar vectors produced by conventional methods. In the human hepatic cell line, the capsid expression was reduced significantly from cap-mir cassette driven by a cytomegalovirus promoter. In the liver, 99.9% of capsid expression could be suppressed and no cap expression could be detected by western blot. In summary, we demonstrated a new concept in reducing de novo capsid synthesis in the targeted tissue. This strategy may not only help AAV vectors in controlling undesirable capsid gene expression, but can also be adopted for lentiviral or adenoviral vector production.
Replication-competent adeno-associated viral particles (rcAAV) are an undesirable contaminant of vector preparations that may affect transgene expression or elicit a hazardous immune response. In this study, Yuan and colleagues have designed a recombinant AAV (rAAV) vector production system to tightly control AAV rep and capsid activity from rcAAV particles. According to the authors, this new method does not have any effects on rAAV yield or affect rAAV vector performance and is compatible with all current rAAV production systems.
Recombinant adeno-associated virus vectors based on serotype 8 (AAV8) have shown significant promise for liver-directed gene therapy. However, to overcome the vector dose dependent immunotoxicity seen with AAV8 vectors, it is important to develop better AAV8 vectors that provide enhanced gene expression at significantly low vector doses. Since it is known that AAV vectors during intracellular trafficking are targeted for destruction in the cytoplasm by the host–cellular kinase/ubiquitination/proteasomal machinery, we modified specific serine/threonine kinase or ubiquitination targets on the AAV8 capsid to augment its transduction efficiency. Point mutations at specific serine (S)/threonine (T)/lysine (K) residues were introduced in the AAV8 capsid at the positions equivalent to that of the effective AAV2 mutants, generated successfully earlier. Extensive structure analysis was carried out subsequently to evaluate the structural equivalence between the two serotypes. scAAV8 vectors with the wild-type (WT) and each one of the S/T→Alanine (A) or K-Arginine (R) mutant capsids were evaluated for their liver transduction efficiency in C57BL/6 mice in vivo. Two of the AAV8-S→A mutants (S279A and S671A), and a K137R mutant vector, demonstrated significantly higher enhanced green fluorescent protein (EGFP) transcript levels (∼9- to 46-fold) in the liver compared to animals that received WT-AAV8 vectors alone. The best performing AAV8 mutant (K137R) vector also had significantly reduced ubiquitination of the viral capsid, reduced activation of markers of innate immune response, and a concomitant two-fold reduction in the levels of neutralizing antibody formation in comparison to WT-AAV8 vectors. Vector biodistribution studies revealed that the K137R mutant had a significantly higher and preferential transduction of the liver (106 vs. 7.7 vector copies/mouse diploid genome) when compared to WT-AAV8 vectors. To further study the utility of the K137R-AAV8 mutant in therapeutic gene transfer, we delivered human coagulation factor IX (h.FIX) under the control of liver-specific promoters (LP1 or hAAT) into C57BL/6 mice. The circulating levels of h.FIX:Ag were higher in all the K137R-AAV8 treated groups up to 8 weeks post-hepatic gene transfer. These studies demonstrate the feasibility of the use of this novel AAV8 vectors for potential gene therapy of hemophilia B.
Sen and colleagues generated AAV8 capsid point mutants by replacing specific serine/threonine kinase or ubiquitination target residues. Two of the mutants yielded significantly higher transgene expression over AAV8 when injected into mice, and the best performing vector also exhibited significantly reduced capsid ubiquitination, innate immune response activation, and neutralizing antibody formation.
Retinitis pigmentosa (RP) is the leading cause of inherited blindness in the developed world, affecting approximately 1 in 3,000 individuals. While there is currently no cure for RP, the genetic pathology has been well established. In this study we developed a novel mouse model of RP (huRhoP347S) expressing a pathogenic human rhodopsin gene with a Pro347Ser mutation on a rhodopsin knockout background. These mice undergo severe retinal degeneration at one month of age. In contrast to prior studies, this model was administered a gene therapy treatment at 19 days post natal. We evaluated several self-complementary adeno-associated virus serotypes for photoreceptor tropism including scAAV2/2, scAAV2/5, scAAV2/6.2 and scAAV2/9, and found that scAAV2/9 transduced photoreceptors with greater efficiency and expression than other vectors. We engineered a scAAV2/9 vector to contain a microRNA sequence specifically targeting the human rhodopsin gene and demonstrated its ability to silence rhodopsin by 60.2 ± 8.2% in vitro. In addition, we constructed a scAAV2/9 vector to contain a replacement “codon-modified” rhodopsin transgene (RhoR2) that was resistant to degradation by the microRNA. We found that delivery of the RhoR2 by scAAV2/9 is capable of restoring vision to rhodopsin knockout mice, and rescuing our novel transgenic huRhoP347S mouse model of dominant RP. Average a-wave responses of RhoR2-injected eyes were 1.8-fold higher than those of control-injected eyes. We found that delivery of the microRNA and replacement rhodopsin in a 1:2 ratio produced an average ERG a-wave response of 17.4 ± 2.9 μV compared to 6.5 ± 2.8 μV for eyes injected with negative control virus.
microRNA; P347S; gene therapy; RNAi; rhodopsin (Rho); retinitis pigmentosa (RP); AAV; AAV2/9