A Rapid, Cost-Effective Method to Prepare Recombinant Adeno-Associated Virus for Efficient Gene Transfer to the Developing Mouse Inner Ear

The oligodendrocyte-enriched orphan G protein-coupled receptor Gpr62 is dispensable for central nervous system myelination

BACKGROUND

Myelination is a highly regulated process in the vertebrate central nervous system (CNS) whereby oligodendrocytes wrap axons with multiple layers of insulating myelin in order to allow rapid electrical conduction. Establishing the proper pattern of myelin in neural circuits requires communicative axo-glial interactions, however, the molecular interactions that occur between oligodendrocytes and axons during developmental myelination and myelin maintenance remain to be fully elucidated. Our previous work identified G protein-coupled receptor 62 (Gpr62), an uncharacterized orphan g-protein coupled receptor, as being selectively expressed by mature oligodendrocytes within the CNS, suggesting a potential role in myelination or axoglial interactions. However, no studies to date have assessed the functional requirement for Gpr62 in oligodendrocyte development or CNS myelination.

METHODS

To address this, we generated a knockout mouse strain lacking the Gpr62 gene. We assessed CNS myelination during both postnatal development and adulthood using immunohistochemistry, electron microscopy and western blot. In addition, we utilized AAV-mediated expression of a tagged Gpr62 in oligodendrocytes to determine the subcellular localization of the protein in vivo.

RESULTS

We find that virally expressed Gpr62 protein is selectively expressed on the adaxonal myelin layer, suggestive of a potential role for Gpr62 in axo-myelinic signaling. Nevertheless, Gpr62 knockout mice display normal oligodendrocyte numbers and apparently normal myelination within the CNS during both postnatal development and adulthood.

CONCLUSIONS

We conclude that in spite of being well-placed to mediate neuronal-oligodendrocyte communications, Gpr62 is overall dispensable for CNS myelination.

Induced Liver Regeneration Enhances CRISPR/Cas9-Mediated Gene Repair in Tyrosinemia Type 1

The efficiency of gene repair by homologous recombination in the liver is enhanced by CRISP/Cas9 incision near the mutation. In this study, we explored interventions designed to further enhance in vivo hepatocyte gene repair in a model of hereditary tyrosinemia. A two-AAV system was employed: one virus carried a Staphylococcus pyogenes Cas9 (SpCas9) expression cassette and the other harbored a U6 promoter-driven sgRNA and a fragment of fumarylacetoacetate hydrolase (Fah) genomic DNA as the homologous recombination donor. In neonatal mice, a gene correction frequency of ∼10.8% of hepatocytes was achieved. The efficiency in adult mice was significantly lower at ∼1.6%. To determine whether hepatocyte replication could enhance the targeting frequency, cell division was induced with thyroid hormone T3. This more than doubled the gene correction efficiency to 3.5% (p < 0.005). To determine whether SpCas9 delivery was rate limiting, the gene repair AAV was administered to SpCas9 transgenic mice. However, this did not significantly enhance gene repair. Finally, we tested whether the Fanconi anemia (FA) DNA repair pathway was important in hepatocyte gene repair. Gene correction frequencies were significantly lower in neonatal mice lacking the FA complementation group A (Fanca) gene. Taken together, we conclude that pharmacological induction of hepatocyte replication along with manipulation of DNA repair pathways could be a useful strategy for enhancing in vivo gene correction.

Ultrafiltered recombinant AAV8 vector can be safely administered in vivo and efficiently transduces liver

Viral vectors are extensively purified for use in biomedical research, in order to separate biologically active virus particles and to eliminate production related impurities that are assumed to be detrimental to the host. For recombinant adeno-associated virus (rAAV) vectors this is typically accomplished using density gradient-based methods, which are tedious and require specialized ultracentrifugation equipment. In order to streamline the preparation of rAAV vectors for pilot and small animal studies, we recently devised a simple ultrafiltration approach that permits rapid virus concentration and partial removal of production-related impurities. Here we show that systemic administration of such rapidly prepared (RP) rAAV8 vectors in mice is safe and efficiently transduces the liver. Across a range of doses, delivery of RP rAAV8-CMV-eGFP vector induced enhanced green fluorescent protein (eGFP) expression in liver that was comparable to that obtained from a conventional iodixanol gradient-purified (IP) vector. Surprisingly, no liver inflammation or systemic cytokine induction was detected in RP rAAV injected animals, revealing that residual impurities in the viral vector preparation are not deleterious to the host. Together, these data demonstrate that partially purified rAAV vector can be safely and effectively administered in vivo. The speed and versatility of the RP method and lack of need for cumbersome density gradients or expensive ultracentrifuge equipment will enable more widespread use of RP prepared rAAV vectors, such as for pilot liver gene transfer studies.

Recent Advancements in the Regeneration of Auditory Hair Cells and Hearing Restoration

Neurosensory responses of hearing and balance are mediated by receptors in specialized neuroepithelial sensory cells. Any disruption of the biochemical and molecular pathways that facilitate these responses can result in severe deficits, including hearing loss and vestibular dysfunction. Hearing is affected by both environmental and genetic factors, with impairment of auditory function being the most common neurosensory disorder affecting 1 in 500 newborns, as well as having an impact on the majority of elderly population. Damage to auditory sensory cells is not reversible, and if sufficient damage and cell death have taken place, the resultant deficit may lead to permanent deafness. Cochlear implants are considered to be one of the most successful and consistent treatments for deaf patients, but only offer limited recovery at the expense of loss of residual hearing. Recently there has been an increased interest in the auditory research community to explore the regeneration of mammalian auditory hair cells and restoration of their function. In this review article, we examine a variety of recent therapies, including genetic, stem cell and molecular therapies as well as discussing progress being made in genome editing strategies as applied to the restoration of hearing function.