An acidic oligopeptide displayed on AAV2 improves axial muscle tropism after systemic delivery
© Lee et al.; licensee Biomed Central Ltd. 2012
Received: 29 April 2012
Accepted: 18 June 2012
Published: 18 June 2012
The appropriate tropism of adeno-associated virus (AAV) vectors that are systemically injected is crucial for successful gene therapy when local injection is not practical. Acidic oligopeptides have been shown to enhance drug delivery to bones.
In this study six-L aspartic acids (D6) were inserted into the AAV2 capsid protein sequence between amino acid residues 587 and 588. 129SVE mice were injected with double-stranded wild-type- (WT-) or D6-AAV2 mCherry expression vectors (3.24 x 1010 vg per animal) via the superficial temporal vein within 24 hours of birth.
Fluorescence microscopy and quantitative polymerase chain reaction confirmed higher levels of mCherry expression in the paraspinal and gluteus muscles in the D6-AAV2 injected mice. The results revealed that although D6-AAV2 was less efficient in the transduction of immortalized cells stronger mCherry signals were detected over the spine and pelvis by live imaging in the D6-AAV2-injected mice than were detected in the WT-AAV2-injected mice. In addition, D6-AAV2 lost the liver tropism observed for WT-AAV2.
An acidic oligopeptide displayed on AAV2 improves axial muscle tropism and decreases liver tropism after systemic delivery. This modification should be useful in creating AAV vectors that are suitable for gene therapy for diseases involving the proximal muscles.
KeywordsAdeno-associated virus Tropism L-aspartic acid Acidic oligopeptide
Adeno-associated virus serotype 2 (AAV2) is a non-pathogenic parvovirus that is commonly used in human gene therapy . The advantages of AAV2 vectors include the ability to infect non-dividing cells, sustained gene expression, and low immune responses [2, 3], but excessive liver tropism of these vectors and inefficient transduction of other organs after systemic injection is problematic. Other AAV serotypes have altered tissue tropism and higher infectivity than AAV2 [4, 5]. However, specific targeting is still a problem; for example, the transduction of the liver can induce innate immune responses and toxicity [6, 7]. Currently, studies focused on either genetic  or biochemical modifications  of the AAV capsid protein are ongoing.
Membrane-associated heparan sulfate proteoglycan (HSPG) is a receptor for the AAV2 virus . The HSPG-binding motif is composed of the amino acid residues R484, R487, K532, R585, and R588 of the capsid protein (according to the numbering for VP1) . The insertion of an oligopeptide between residues 587 and 588 disrupts the HSPG-binding motif  and has been shown to retarget AAV2 vectors to the angiogenic vasculature, diaphragm, heart, or endothelial cells [13–15].
The limited delivery of drugs to bones has been a barrier in the treatment of diseases of the skeletal system. Kasugai et al. demonstrated that proteins conjugated with an oligopeptide composed of six or more acidic amino acids (L-aspartate or L-glutamate) bound strongly to hydroxyapatite, a major component of bones . Oligopeptide-conjugated enzymes were later developed to treat diseases including hypophosphatasia  and mucopolysaccharidosis type IV . An AAV8 vector expressing deca-aspartate-tagged tissue-nonspecific alkaline phosphatase has also been used to treat hypophosphatasia .
In this study, we inserted six L-aspartic acids (D6) between residues 587 and 588 of the AAV2 capsid protein. We demonstrate that D6-AAV2 exhibits improved axial muscle tropism and decreased liver tropism after systemic delivery.
Plasmids and cell cultures
A nucleotide sequence (5'-GACGATGACGATGACGAT) encoding six L-aspartic acids (D6) was inserted between amino acid residues 587 and 588 of the AAV2 cap gene in the pAAV-RC plasmid (Agilent, Santa Clara, CA) using the QuikChange Lightning Site-Directed Mutagenesis Kit (Agilent). Double-stranded WT- and D6-AAV2 mCherry expression vectors were produced at the Powell Gene Therapy Center using methods previously reported . HEK293 cells were harvested and purified using a discontinuous iodixanol gradient and concentrated in an Apollo® concentrator with a final volume of 500 μl. Viral genome (vg) titers were determined using quantitative real-time PCR (qPCR) with primers directed against the CMV promoter region . The capsid proteins were analyzed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and silver staining. The heparan binding capability was measured by loading a known amount of WT- (4.95 × 1011 vg/ml) or D6-AAV2 (3.90 × 1011) into a heparin agarose column for chromatography . The flowthrough and eluate were collected, and qPCR was performed to determine the viral genome titer. HT1080 cells, HEK293 cells, C2C12 cells, and human chondrocytes were seeded in 96-well plates and reached 80% confluence 24 hours later. Cells were infected with the WT- or D6-AAV2 vector at a multiplicity of infection (MOI) of 1,000 for HEK293 cells, 10,000 for C2C12 cells, and 20,000 for HT1080 cells and human chondrocytes. HEK293 and C2C12 cells were infected in the presence of a helper adenovirus according to the infectivity assay protocol for HEK293 cells . Forty-eight hours after infection, the numbers of mCherry-positive cells were counted by fluorescence microscopy.
Neonatal 129SVE mice were injected with the WT- or D6-AAV2 vector (n = 7 each group with 3.24 × 1010 vg per animal in 30μL) within 24 hours of birth via the superficial temporal vein using a 29 G needle. Live imaging was performed on anesthetized mice (n = 3 each group, monthly up to 4 months after injection, under 2% isoflurane in 100% O2) using the Xenogen IVIS® Spectrum in vivo Bioluminescence and Fluorescent Imager (Caliper Life Sciences, Hopkinton, MA), and mCherry signals were obtained with excitation/emission wavelengths of 570/620 nm. Mice were euthanized under isoflurane anesthesia prior to tissue collection via thoracotomy and removal of the heart. For direct fluorescence microscopy, mouse tissue was fixed in 4% paraformaldehyde after direct dissection of the tissue, embedded in OCT and cut into 6–12 μm sections (Leica CM1850 cryotome, Houston, TX, USA). A Chroma 51006 FITC/Texas Red dual-band filter was used to eliminate autofluorescence (Chroma, Bellows Falls, VT). The tissues were also stained with 4’,6-diamidino-2-phenylindole (DAPI). Tissue samples from another 4 mice in each group were also harvested for DNA extraction using the DNeasy Blood & Tissue kit (QIAGEN, Valencia, CA, USA) 4 weeks after injection. The total vg copy numbers in the tissues were determined by qPCR and expressed as vg per μg DNA. All animal studies were approved and performed in accordance with guidelines of the University of Florida Institutional Animal Care and Use Committee (IACUC No. 201004974) and the National Taiwan University College of Medicine and College of Public Health Institutional Animal Care and Use Committee (IACUC No. 20110265).
Data are presented as the mean ± SD in each figure. Statistical analyses were performed using the SPSS (Statistical Package for the Social Sciences) statistical package, version 11.5. The Mann–Whitney Rank Test was used for comparisons of different groups. A p value less than 0.05 was considered statistically significant.
Results and discussion
Production of the D6-AAV2 vector and its infectivity in cells
Tropism of D6-AAV2
Proposed mechanisms for the altered tropism
The insertion of six L-aspartic acids into the capsid protein enhances AAV2 axial and hind limb muscle tropism and decreases liver tropism. It is known that the insertion of oligopeptides after amino acid residue 587 disrupts the HSPG-binding motif of AAV2 , leading to liver detargeting. However, acidic oligopeptides should bind to hydroxyapatite and lead to bone targeting . It is possible that the binding between the acidic oligopeptides and hydroxyapatite in large bones including the vertebrae and pelvis only temporarily retains the virus. Because D6-AAV2 does not readily infect the bone marrow cellular components, the viruses ultimately leave the bones and infect the nearby muscles.
Many hereditary myopathies, including Duchenne muscular dystrophy, limb girdle muscular dystrophy, and adult-onset Pompe disease, preferentially involve the proximal and trunk muscles . Therefore, the D6 modification would be helpful in designing viral vectors to treat those diseases. Because of the low yield of the AAV2 vector, we were not able to test D6-AAV2 in adult mice at the same dose per body weight as we used in the neonatal mice. There are already new AAV serotypes that have much higher transduction efficiencies than AAV2, such that addition of the D6 modification to those AAV vectors may further increase their relative muscle tropism and allow these vectors to be used in a safer manner in the treatment of hereditary myopathies.
In this study, we demonstrated that an acidic oligopeptide displayed on AAV2 improves axial muscle tropism and decreases liver tropism after systemic delivery. This modification should be useful in creating AAV vectors suitable for gene therapy for diseases involving the proximal muscles. Future studies of the targeting effects of different acidic oligopeptides in conjunction with different AAV serotypes may be helpful to expand the applications of AAVs.
Adeno-associated virus serotype 2
Six L-aspartic acids
Heparan sulfate proteoglycan
Quantitative real-time PCR
Multiplicity of infection.
We thank Mr. Michael Rule of the Cell and Tissue Analysis Core of the University of Florida for the help in the performing the in vivo live imaging on mice. We also thank Ms. Denise A Cloutier and Dr. Sushrusha Nayak in Dr. Byrne’s lab for their suggestions and support with the experiments. This work was partially supported by grants from the National Taiwan University Hospital (NTUH- 101-M1955).
- Mueller C, Flotte TR: Clinical gene therapy using recombinant adeno-associated virus vectors. Gene Ther. 2008, 15: 858-863. 10.1038/gt.2008.68.View ArticlePubMedGoogle Scholar
- Xiao X, Li J, Samulski RJ: Efficient long-term gene transfer into muscle tissue of immunocompetent mice by adeno-associated virus vector. J Virol. 1996, 70: 8098-8108.PubMed CentralPubMedGoogle Scholar
- Chirmule N, Propert K, Magosin S, Qian Y, Qian R, Wilson J: Immune responses to adenovirus and adeno-associated virus in humans. Gene Ther. 1999, 6: 1574-1583. 10.1038/sj.gt.3300994.View ArticlePubMedGoogle Scholar
- Hu C, Busuttil RW, Lipshutz GS: RH10 provides superior transgene expression in mice when compared with natural AAV serotypes for neonatal gene therapy. J Gene Med. 2010, 12: 766-778. 10.1002/jgm.1496.PubMed CentralView ArticlePubMedGoogle Scholar
- Zincarelli C, Soltys S, Rengo G, Rabinowitz JE: Analysis of AAV serotypes 1–9 mediated gene expression and tropism in mice after systemic injection. Mol Ther. 2008, 16: 1073-1080. 10.1038/mt.2008.76.View ArticlePubMedGoogle Scholar
- Martino AT, Suzuki M, Markusic DM, Zolotukhin I, Ryals RC, Moghimi B, Ertl HC, Muruve DA, Lee B, Herzog RW: The genome of self-complementary adeno-associated viral vectors increases Toll-like receptor 9-dependent innate immune responses in the liver. Blood. 2011, 117: 6459-6468. 10.1182/blood-2010-10-314518.PubMed CentralView ArticlePubMedGoogle Scholar
- Hasbrouck NC, High KA: AAV-mediated gene transfer for the treatment of hemophilia B: problems and prospects. Gene Ther. 2008, 15: 870-875. 10.1038/gt.2008.71.View ArticlePubMedGoogle Scholar
- White AF, Mazur M, Sorscher EJ, Zinn KR, Ponnazhagan S: Genetic modification of adeno-associated viral vector type 2 capsid enhances gene transfer efficiency in polarized human airway epithelial cells. Hum Gene Ther. 2008, 19: 1407-1414. 10.1089/hum.2008.117.View ArticlePubMedGoogle Scholar
- Bell CL, Vandenberghe LH, Bell P, Limberis MP, Gao GP, Van Vliet K, Agbandje-McKenna M, Wilson JM: The AAV9 receptor and its modification to improve in vivo lung gene transfer in mice. J Clin Invest. 2011, 121: 2427-2435. 10.1172/JCI57367.PubMed CentralView ArticlePubMedGoogle Scholar
- Summerford C, Samulski RJ: Membrane-associated heparan sulfate proteoglycan is a receptor for adeno-associated virus type 2 virions. J Virol. 1998, 72: 1438-1445.PubMed CentralPubMedGoogle Scholar
- Opie SR, Warrington KH, Agbandje-McKenna M, Zolotukhin S, Muzyczka N: Identification of amino acid residues in the capsid proteins of adeno-associated virus type 2 that contribute to heparan sulfate proteoglycan binding. J Virol. 2003, 77: 6995-7006. 10.1128/JVI.77.12.6995-7006.2003.PubMed CentralView ArticlePubMedGoogle Scholar
- Wu P, Xiao W, Conlon T, Hughes J, Agbandje-McKenna M, Ferkol T, Flotte T, Muzyczka N: Mutational analysis of the adeno-associated virus type 2 (AAV2) capsid gene and construction of AAV2 vectors with altered tropism. J Virol. 2000, 74: 8635-8647. 10.1128/JVI.74.18.8635-8647.2000.PubMed CentralView ArticlePubMedGoogle Scholar
- Yu CY, Yuan Z, Cao Z, Wang B, Qiao C, Li J, Xiao X: A muscle-targeting peptide displayed on AAV2 improves muscle tropism on systemic delivery. Gene Ther. 2009, 16: 953-962. 10.1038/gt.2009.59.PubMed CentralView ArticlePubMedGoogle Scholar
- Nicklin SA, Buening H, Dishart KL, de Alwis M, Girod A, Hacker U, Thrasher AJ, Ali RR, Hallek M, Baker AH: Efficient and selective AAV2-mediated gene transfer directed to human vascular endothelial cells. Mol Ther. 2001, 4: 174-181. 10.1006/mthe.2001.0424.View ArticlePubMedGoogle Scholar
- Grifman M, Trepel M, Speece P, Gilbert LB, Arap W, Pasqualini R, Weitzman MD: Incorporation of tumor-targeting peptides into recombinant adeno-associated virus capsids. Mol Ther. 2001, 3: 964-975. 10.1006/mthe.2001.0345.View ArticlePubMedGoogle Scholar
- Kasugai S, Fujisawa R, Waki Y, Miyamoto K, Ohya K: Selective drug delivery system to bone: small peptide (Asp)6 conjugation. J Bone Miner Res. 2000, 15: 936-943.View ArticlePubMedGoogle Scholar
- Nishioka T, Tomatsu S, Gutierrez MA, Miyamoto K, Trandafirescu GG, Lopez PL, Grubb JH, Kanai R, Kobayashi H, Yamaguchi S, et al: Enhancement of drug delivery to bone: characterization of human tissue-nonspecific alkaline phosphatase tagged with an acidic oligopeptide. Mol Genet Metab. 2006, 88: 244-255. 10.1016/j.ymgme.2006.02.012.PubMed CentralView ArticlePubMedGoogle Scholar
- Tomatsu S, Montano AM, Dung VC, Ohashi A, Oikawa H, Oguma T, Orii T, Barrera L, Sly WS: Enhancement of drug delivery: enzyme-replacement therapy for murine Morquio A syndrome. Mol Ther. 2010, 18: 1094-1102. 10.1038/mt.2010.32.PubMed CentralView ArticlePubMedGoogle Scholar
- Matsumoto T, Miyake K, Yamamoto S, Orimo H, Miyake N, Odagaki Y, Adachi K, Iijima O, Narisawa S, Millan JL, et al: Rescue of severe infantile hypophosphatasia mice by AAV-mediated sustained expression of soluble alkaline phosphatase. Hum Gene Ther. 2011, 22 (11): 1355-1364. 10.1089/hum.2010.210.PubMed CentralView ArticlePubMedGoogle Scholar
- Zolotukhin S, Potter M, Zolotukhin I, Sakai Y, Loiler S, Fraites TJ, Chiodo VA, Phillipsberg T, Muzyczka N, Hauswirth WW, et al: Production and purification of serotype 1, 2, and 5 recombinant adeno-associated viral vectors. Methods. 2002, 28: 158-167. 10.1016/S1046-2023(02)00220-7.View ArticlePubMedGoogle Scholar
- Lock M, McGorray S, Auricchio A, Ayuso E, Beecham EJ, Blouin-Tavel V, Bosch F, Bose M, Byrne BJ, Caton T, et al: Characterization of a recombinant adeno-associated virus type 2 Reference Standard Material. Hum Gene Ther. 2010, 21: 1273-1285. 10.1089/hum.2009.223.PubMed CentralView ArticlePubMedGoogle Scholar
- Saguil A: Evaluation of the patient with muscle weakness. Am Fam Physician. 2005, 71: 1327-1336.PubMedGoogle Scholar
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