As a genus, the dependoviruses use a diverse group of cell surface carbohydrates for attachment and entry. Despite the fact that a majority of adeno-associated viruses (AAVs) utilize sialic acid (SIA) for binding and transduction, this virus-carbohydrate interaction is poorly understood. Utilizing X-ray crystallography, two SIA binding regions were mapped for AAV5 (Afione et al 2015). The first site mapped to the depression in the center of the 3-fold axis of symmetry, while the second site was located under the _HI loop close to the 5-fold axis. Mutagenesis of amino acids 569 and 585 or 587 within the 3-fold depression resulted in elimination or alteration in SIA-dependent transduction, respectively. This change in SIA binding was confirmed using glycan microarrays. Mutagenesis of the second site identified a role in transduction that was SIA independent. Further studies of the mutants at the 3-fold site demonstrated a change in transduction activity and cell tropism in vivo as well as resistance to neutralization by a polyclonal antibody raised against the wild-type virus. Application of these vectors for disease with unmet clinical need are ongoing. We have previously shown that in vitro transduction with bovine adeno-associated viral (BAAV) vectors restores connexin expression and rescues gap junction coupling in cochlear organotypic cultures from connexin-deficient mice that are models DFNB1 nonsyndromic hearing loss and deafness. In collaboration with Dr. Mammano we have reported that by manipulating inner ear connexin expression in vivo using BAAV vectors, and identifying the optimal route of vector delivery we have tested the use of gene therapy to restore hearing and identified limitations to this approach (Crispino et al 2017). Primary Sjgrens syndrome (pSS) is an autoimmune disease, characterized by lymphoid cell infiltration into the salivary and lacrimal glands, and affects 0.5% of the population in the United States of which 90% are women. The consequence of chronic immune cell activation in these exocrine glands is diminished secretory function, which leads to symptoms of dry mouth and dry eyes. In order to understand the environment of the salivary gland that might contribute to the gender bias associated with pSS we compared the transcriptome of male and female salivary glands from healthy individuals (Michael et al. 2012). Comparison of the transcriptome of minor salivary glands from normal male and female volunteers with that of salivary glands and other secretory epithelia identified a number of gender and tissue-specific gene expression patterns. These differences include, but are not limited to, a diverse set of genes involved in immune modulation, chemotactic control, inhibition of complement, metabolism, and neurogenesis. Analysis of these changes provides insight into the protective and predisposing molecular factors that may be involved in the development of pSS. To identify epithelial changes in gene expression within female patients associated with the loss of gland function, custom microarrays were probed with complementary RNA (cRNA) isolated from minor salivary glands (MSGs) of female patients with pSS who had low focus scores and low salivary flow rates, and the results were compared with those obtained using cRNA from the MSGs of sex-matched healthy volunteers. A significant increase in expression of BMP-6 was observed in RNA isolated from pSS patients compared with healthy volunteers. Overexpression of BMP-6 locally in the salivary or lacrimal glands of mice resulted in the loss of fluid secretion as well as changes in the connective tissue of the salivary gland. Assessment of the fluid movement in either isolated acinar cells from mice overexpressing BMP-6 or a human salivary gland cell line cultured with BMP-6 revealed a loss in volume regulation in these cells. Lymphocytic infiltration in the submandibular gland of BMP-6 vector-treated mice was increased. No significant changes in the production of proinflammatory cytokines or autoantibodies associated with pSS (anti-Ro/SSA and anti-La/SSB) were found after BMP-6 overexpression. In addition to identifying BMP-6 expression in association with xerostomia and xerophthalmia in pSS, the present results suggest that BMP-6-induced salivary and lacrimal gland dysfunction in pSS may not be the direct effect of autoantibodies or immune activation associated with the disease but a down stream change in epithelial gland function triggered by BMP-6 expression. Our findings show that changes in the epithelia of pSS patients has an effect on salivary gland function. Recently, we identified a connection between expression of aquaporin 5, a water channel critical for salivary gland fluid secretion, and BMP-6. Increased expression of this cytokine is strongly associated with the most common symptom of primary Sjgren's syndrome, the loss of salivary gland function. Using mathematical modeling we have proposed several mechanism by which over expression of a generic water channel could increase the salivary gland flow (Fong et al 2017). This finding led us to develop a therapy for the treatment of Sjgren's syndrome by increasing the water permeability of the gland. Our study demonstrates that the targeted increase of gland permeability not only resulted in the restoration of secretory gland function but also resolved the hallmark salivary gland inflammation and systemic inflammation associated with disease. Secretory function also increased in the lacrimal gland, suggesting this local therapy could treat the systemic symptoms associated with primary Sjgren's syndrome (Lai et al 2016). One potential setback to the use of gene therapy for the treatment of Sjgren's syndrome is the presence of neutralizing antibodies (nAb) against adeno-associated virus (AAV) serotypes. In order to evaluate the efficacy of this treatment option, nAb titers were measured in both healthy individuals and Sjgren's patients. Several serotypes with known transduction activity in mouse salivary glands were tested and only AAV5 showed a statistically significant change in the prevalence of nAbs between Sjgren's and healthy participants. Both groups showed a higher rate of nAbs for AAV2 compared with most of the other serotypes tested, except for bovine AAV (BAAV). Although a similar rate of seropositivity was seen against BAAV and AAV2, the percentage of samples with high titer was significantly lower with BAAV. Furthermore, the majority of positive samples exhibited low nAb titers in the primary Sjgren's syndrome (pSS) group for all serotypes except for AAV2. AAV5 was the only serotype that showed a statistically significant shift in the percentage of medium or high neutralizing titer. Based on these results, many serotypes are viable vectors in a gene therapy approach and pSS patients do not have a statistically significant higher rate of seropositivity or titer compared with healthy donors (Corden et al 2017). In summary, the future directions for the AAV Biology Section will be to continue examination and development of gene transfer vectors for use in treating disease as well as refine our tools for studying interactions necessary for cellular transduction.
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