Effects of Altering Heparan Sulfate Proteoglycan Binding and Capsid Hydrophilicity on Retinal Transduction by Adeno-associated Virus

ABSTRACT Adeno-associated viruses (AAVs) have recently emerged as the leading vector for retinal gene therapy. However, AAV vectors that are capable of achieving clinically relevant levels of transgene expression and widespread retinal transduction are still an unmet need. Using rationally designed AAV2-based capsid variants, we investigate the role of capsid hydrophilicity and hydrophobicity as it relates to retinal transduction. We show that hydrophilic, single-amino-acid mutations (V387R, W502H, E530K, L583R) in AAV2 negatively impact retinal transduction when heparan sulfate proteoglycan (HSPG) binding remains intact. Conversely, addition of hydrophobic point mutations to an HSPG binding-deficient capsid (AAV2ΔHS) leads to increased retinal transduction in both mouse and macaque. Our top performing vector, AAV2(4pMut)ΔHS, achieved robust rod and cone photoreceptor (PR) transduction in macaque, especially in the fovea, and demonstrates the ability to spread laterally beyond the borders of the subretinal injection (SRI) bleb. This study both evaluates biophysical properties of AAV capsids that influence retinal transduction and assesses the transduction and tropism of a novel capsid variant in a clinically relevant animal model. IMPORTANCE Rationally guided engineering of AAV capsids aims to create new generations of vectors with enhanced potential for human gene therapy. By applying rational design principles to AAV2-based capsids, we evaluated the influence of hydrophilic and hydrophobic amino acid mutations on retinal transduction as it relates to vector administration route. Through this approach, we identified a largely deleterious relationship between hydrophilic amino acid mutations and canonical HSPG binding by AAV2-based capsids. Conversely, the inclusion of hydrophobic amino acid substitutions on an HSPG binding-deficient capsid (AAV2ΔHS) generated a vector capable of robust rod and cone photoreceptor (PR) transduction. This vector AAV2(4pMut)ΔHS also demonstrates a remarkable ability to spread laterally beyond the initial subretinal injection (SRI) bleb, making it an ideal candidate for the treatment of retinal diseases that require a large area of transduction.

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Membrane-Associated Heparan Sulfate Proteoglycan Is a Receptor for Adeno-Associated Virus Type 2 Virions

Journal of Virology ◽

10.1128/jvi.72.2.1438-1445.1998 ◽

1998 ◽

Vol 72 (2) ◽

pp. 1438-1445 ◽

Cited By ~ 899

Author(s):

Candace Summerford ◽

Richard Jude Samulski

Keyword(s):

Gene Therapy ◽

Heparan Sulfate ◽

Cell Lines ◽

Heparan Sulfate Proteoglycan ◽

Heparan Sulfate Proteoglycans ◽

Target Cells ◽

Sulfate Proteoglycan ◽

Viral Receptor ◽

Adeno Associated Virus

ABSTRACT The human parvovirus adeno-associated virus (AAV) infects a broad range of cell types, including human, nonhuman primate, canine, murine, and avian. Although little is known about the initial events of virus infection, AAV is currently being developed as a vector for human gene therapy. Using defined mutant CHO cell lines and standard biochemical assays, we demonstrate that heparan sulfate proteoglycans mediate both AAV attachment to and infection of target cells. Competition experiments using heparin, a soluble receptor analog, demonstrated dose-dependent inhibition of AAV attachment and infection. Enzymatic removal of heparan but not chondroitin sulfate moieties from the cell surface greatly reduced AAV attachment and infectivity. Finally, mutant cell lines that do not produce heparan sulfate proteoglycans were significantly impaired for both AAV binding and infection. This is the first report that proteoglycan has a role in cellular attachment of a parvovirus. Together, these results demonstrate that membrane-associated heparan sulfate proteoglycan serves as the viral receptor for AAV type 2, and provide an explanation for the broad host range of AAV. Identification of heparan sulfate proteoglycan as a viral receptor should facilitate development of new reagents for virus purification and provide critical information on the use of AAV as a gene therapy vector.

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Molecular cloning and characterization of N-syndecan, a novel transmembrane heparan sulfate proteoglycan

The Journal of Cell Biology ◽

10.1083/jcb.117.1.191 ◽

1992 ◽

Vol 117 (1) ◽

pp. 191-201 ◽

Cited By ~ 130

Author(s):

DJ Carey ◽

DM Evans ◽

RC Stahl ◽

VK Asundi ◽

KJ Conner ◽

...

Keyword(s):

Amino Acid ◽

Heparan Sulfate ◽

Rat Brain ◽

Schwann Cells ◽

Core Protein ◽

Heparan Sulfate Proteoglycan ◽

Neonatal Rat ◽

Sulfate Proteoglycan ◽

The Core ◽

Neonatal Rat Brain

A cDNA clone coding for a membrane proteoglycan core protein was isolated from a neonatal rat Schwann cell cDNA library by screening with an oligonucleotide based on a conserved sequence in cDNAs coding for previously described proteoglycan core proteins. Primer extension and polymerase chain reaction amplification were used to obtain additional 5' protein coding sequences. The deduced amino acid sequence predicted a 353 amino acid polypeptide with a single membrane spanning segment and a 34 amino acid hydrophilic COOH-terminal cytoplasmic domain. The putative extracellular domain contains three potential glycosaminoglycan attachment sites, as well as a domain rich in Thr and Pro residues. Analysis of the cDNA and deduced amino acid sequences revealed a high degree of identity with the transmembrane and cytoplasmic domains of previously described proteoglycans but a unique extracellular domain sequence. On Northern blots the cDNA hybridized to a single 5.6-kb mRNA that was present in Schwann cells, neonatal rat brain, rat heart, and rat smooth muscle cells. A 16-kD protein fragment encoded by the cDNA was expressed in bacteria and used to immunize rabbits. The resulting antibodies reacted on immunoblots with the core protein of a detergent extracted heparan sulfate proteoglycan. The core protein had an apparent mass of 120 kD. When the anti-core protein antibodies were used to stain tissue sections immunoreactivity was present in peripheral nerve, newborn rat brain, heart, aorta, and other neonatal tissues. A ribonuclease protection assay was used to quantitate levels of the core protein mRNA. High levels were found in neonatal rat brain, heart, and Schwann cells. The mRNA was barely detectable in neonatal or adult liver, or adult brain.

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