Sergei Zolotukhin | PubMed Health

PubMed2022

Identification of Novel Retinal Pericyte-Targeting rAAV Vectors Through Directed Evolution.

PURPOSE: Retinal pericytes play a vital role in maintaining retinal homeostasis, and their dysfunction underlies pathogenesis in such vascular eye diseases as diabetic retinopathy and wet age-related macular degeneration. Consequently, retinal pericytes are attractive therapeutic targets for gene therapy, but effectively targeting pericytes with recombinant adeno-associated virus (rAAV) vectors remains a challenge. METHODS: We introduced genetic modifications into the surface-exposed variable regions of the rAAV2/2 capsid to generate a complex library (>1 × 107) of capsid mutants that were then screened for preferential tropism toward retinal pericytes. Using the Tg(Cspg4-DsRed.T1)1Akik/J reporter mouse model, which has red fluorescent pericytes that can be isolated via flow cytometry in order to recover vector genomes, we performed three rounds of screening and identified seven putative mutants capable of transducing retinal pericytes. RESULTS: Following intravitreal administration of mutant vectors packaging ubiquitously expressing green fluorescent protein reporters and postmortem flow cytometry of enzymatically digested retinae, two mutants in particular, Peri-E and Peri-G, demonstrated significantly greater transduction of retinal pericytes than unmodified rAAV2/2 (1.4-fold and 2.8-fold, respectively). CONCLUSIONS: Although difficult to characterize the effect of each point mutation in the context of multiple amino acid variations from the wild-type AAV2 sequence, we identified several point mutations that may play critical roles in limiting HSPG binding, evading neutralization by murine A20 monoclonal antibodies, modulating antigenicity, and evading ubiquitination to ultimately improve transduction efficiency of retinal pericytes. TRANSLATIONAL RELEVANCE: Identification of novel retinal pericyte targeting rAAV vectors enables the development of new, long-lasting gene therapies for retinal diseases such as diabetic retinopathy and wet age-related macular degeneration.

Animals↗

PubMed2013

Structural insights into adeno-associated virus serotype 5.

The adeno-associated viruses (AAVs) display differential cell binding, transduction, and antigenic characteristics specified by their capsid viral protein (VP) composition. Toward structure-function annotation, the crystal structure of AAV5, one of the most sequence diverse AAV serotypes, was determined to 3.45-Å resolution. The AAV5 VP and capsid conserve topological features previously described for other AAVs but uniquely differ in the surface-exposed HI loop between βH and βI of the core β-barrel motif and have pronounced conformational differences in two of the AAV surface variable regions (VRs), VR-IV and VR-VII. The HI loop is structurally conserved in other AAVs despite amino acid differences but is smaller in AAV5 due to an amino acid deletion. This HI loop is adjacent to VR-VII, which is largest in AAV5. The VR-IV, which forms the larger outermost finger-like loop contributing to the protrusions surrounding the icosahedral 3-fold axes of the AAVs, is shorter in AAV5, creating a smoother capsid surface topology. The HI loop plays a role in AAV capsid assembly and genome packaging, and VR-IV and VR-VII are associated with transduction and antigenic differences, respectively, between the AAVs. A comparison of interior capsid surface charge and volume of AAV5 to AAV2 and AAV4 showed a higher propensity of acidic residues but similar volumes, consistent with comparable DNA packaging capacities. This structure provided a three-dimensional (3D) template for functional annotation of the AAV5 capsid with respect to regions that confer assembly efficiency, dictate cellular transduction phenotypes, and control antigenicity.

Capsid Proteins↗