Membrane-associated heparan sulfate is not required for rAAV-2 infection of human respiratory epithelia

Molecular Mechanisms in Pathophysiology of Mucopolysaccharidosis and Prospects for Innovative Therapy

Mucopolysaccharidoses (MPSs) are a group of inborn errors of the metabolism caused by a deficiency in the lysosomal enzymes required to break down molecules called glycosaminoglycans (GAGs). These GAGs accumulate over time in various tissues and disrupt multiple biological systems, including catabolism of other substances, autophagy, and mitochondrial function. These pathological changes ultimately increase oxidative stress and activate innate immunity and inflammation. We have described the pathophysiology of MPS and activated inflammation in this paper, starting with accumulating the primary storage materials, GAGs. At the initial stage of GAG accumulation, affected tissues/cells are reversibly affected but progress irreversibly to: (1) disruption of substrate degradation with pathogenic changes in lysosomal function, (2) cellular dysfunction, secondary/tertiary accumulation (toxins such as GM2 or GM3 ganglioside, etc.), and inflammatory process, and (3) progressive tissue/organ damage and cell death (e.g., skeletal dysplasia, CNS impairment, etc.). For current and future treatment, several potential treatments for MPS that can penetrate the blood-brain barrier and bone have been proposed and/or are in clinical trials, including targeting peptides and molecular Trojan horses such as monoclonal antibodies attached to enzymes via receptor-mediated transport. Gene therapy trials with AAV, ex vivo LV, and Sleeping Beauty transposon system for MPS are proposed and/or underway as innovative therapeutic options. In addition, possible immunomodulatory reagents that can suppress MPS symptoms have been summarized in this review.

Expansion of B4GALT7 linkeropathy phenotype to include perinatal lethal skeletal dysplasia

Proteoglycans have a core polypeptide connected to glycosaminoglycans (GAGs) via a common tetrasaccharide linker region. Defects in enzymes that synthesize the linker result in a group of autosomal recessive conditions called "linkeropathies". Disease manifests with skeletal and connective tissue features, including short stature, hyperextensible skin, and joint hypermobility. We report a family with three affected pregnancies showing short limbs, cystic hygroma, and perinatal death. Two spontaneously aborted; one survived 1 day after term delivery, and had short limbs, bell-shaped thorax, 11 ribs, absent thumbs, and cleft palate. Exome sequencing of the proband and one affected fetus identified compound heterozygous missense variants, NM_007255.3: c.808C>T (p.(Arg270Cys)) and NM_007255.3: c.398A>G (p.(Gln133Arg)), in B4GALT7, a gene required for GAG linker biosynthesis. Homozygosity for p.(Arg270Cys), associated with partial loss of B4GALT7 function, causes Larsen of Reunion Island syndrome (LRS), however no previous studies have linked p.(Gln133Arg) to disease. The p.(Gln133Arg) and p.(Arg270Cys) variants were transfected into CHO pgsB-618 cells. High protein expression of p.(Gln133Arg) was found, with mislocalization, compared to p.(Arg270Cys) that had a normal Golgi-like pattern. The p.(Gln133Arg) had almost no enzyme activity and little production of heparan sulfate GAGs, while p.(Arg270Cys) only had 17% of wild-type activity. These findings expand the phenotype of B4GALT7-related linkeropathies to include lethal skeletal dysplasia due to more severe loss of function.

Polarized AAVR expression determines infectivity by AAV gene therapy vectors

Adeno-associated virus (AAV) has been investigated to transfer the cystic fibrosis transmembrane conductance regulator (CFTR) to airways. Inhaled AAV2-CFTR in people with cystic fibrosis (CF) is safe, but inefficient. In vitro, AAV2 transduction of human airway epithelia on the apical (luminal) side is inefficient, but efficient basolaterally. We previously selected AAV2.5T, a novel capsid that apically transduces CF human airway epithelia and efficiently restores CFTR function. We hypothesize the AAV receptor (AAVR) is basolaterally localized, and that AAV2.5T utilizes an alternative apical receptor. We found AAVR in human airway epithelia by western blot and RNA-Seq analyses. Using immunocytochemistry we did not find endogenous AAVR at membranes but overexpression localized AAVR to the basolateral membrane, where it preferentially increased transduction. Anti-AAVR antibodies blocked transduction by AAV2 from the basolateral side but not AAV2.5T from the apical side, suggesting a unique apical receptor. Finally, we found infection by AAV2 but not AAV2.5T was blocked by CRISPR knockout of AAVR in cell lines. Our data suggest the absence of apical AAVR is rate limiting for AAV2, and efficient transduction by AAV2.5T is accomplished using an AAVR independent pathway. Our findings inform the development of gene therapy for CF, and AAV vectors in general.

Adeno-associated viral vectors show serotype specific transduction of equine joint tissue explants and cultured monolayers

Adeno-associated virus (AAV) receptors range from heparan sulfate proteoglycan to sialic acid moieties present on cell surfaces. Abundance of the glycan profiles is greatly influenced by animal species, cell type, and culture conditions. The objective of this study was to determine whether AAV serotypes' transduction efficiencies specifically in the equine monolayer culture model are an accurate representation of transduction efficiencies in tissue explants, a model more closely related to in vivo transduction. It was found that AAV 2 and 2.5 transduced cells more efficiently in explants than in monolayers. Through experiments involving assessing enzyme degradation of cell surface proteoglycans, this change could not be attributed to differences in the extra cellular matrix (ECM), but a similar change in AAV 5 transduction efficiency could be readily explained by differences in cell surface sialylated glycan. Unexpectedly it was found that in a small but diverse sample of horses evidence for serum neutralizing antibodies was only found to AAV 5. This suggests a unique relationship between this capsid and the equine host or an unresolved relationship between similar bovine AAV and the AAV 5 capsid immune response.

Overcoming the cystic fibrosis sputum barrier to leading adeno-associated virus gene therapy vectors

Gene therapy has not yet improved cystic fibrosis (CF) patient lung function in human trials, despite promising preclinical studies. In the human CF lung, inhaled gene vectors must penetrate the viscoelastic secretions coating the airways to reach target cells in the underlying epithelium. We investigated whether CF sputum acts as a barrier to leading adeno-associated virus (AAV) gene vectors, including AAV2, the only serotype tested in CF clinical trials, and AAV1, a leading candidate for future trials. Using multiple particle tracking, we found that sputum strongly impeded diffusion of AAV, regardless of serotype, by adhesive interactions and steric obstruction. Approximately 50% of AAV vectors diffused >1,000-fold more slowly in sputum than in water, with large patient-to-patient variation. We thus tested two strategies to improve AAV diffusion in sputum. We showed that an AAV2 mutant engineered to have reduced heparin binding diffused twice as fast as AAV2 on average, presumably because of reduced adhesion to sputum. We also discovered that the mucolytic N-acetylcysteine could markedly enhance AAV diffusion by altering the sputum microstructure. These studies underscore that sputum is a major barrier to CF gene delivery, and offer strategies for increasing AAV penetration through sputum to improve clinical outcomes.

Glycosidic enzymes enhance retinal transduction following intravitreal delivery of AAV2

PURPOSE

To determine whether the co-injection of extracellular matrix degrading enzymes improves retinal transduction following intravitreal delivery of adeno-associated virus-2 (AAV2).

METHODS

AAV2 containing cDNA encoding enhanced green fluorescent protein (GFP), under the control of a chicken β-actin promoter, was delivered by intravitreal injection to adult mice in conjunction with enzymes including collagenase, hyaluronan lyase, heparinase III, or chondroitin ABC lyase. Two weeks later, retinal flatmounts were examined for GFP expression using confocal microscopy.

RESULTS

Without the addition of enzymes, transduction was limited to occasional cells in the retinal ganglion cell layer. The addition of heparinase III or chondroitin ABC lyase greatly enhanced transduction of the retinal ganglion cell layer and increased the depth of transduction into the outer retina. Hyaluronan lyase had a limited effect and collagenase was ineffective. Electroretinograms survived with higher concentrations of heparinase III and chondroitin ABC lyase than were required for optimal retinal transduction.

CONCLUSIONS

AAV2-mediated retinal transduction is improved by co-injection of heparinase III or chondroitin ABC lyase. Improved transduction efficiency may allow intravitreal injection to become the preferred route for delivering gene therapy to both the inner and outer retina.

Requirements for receptor engagement during infection by adenovirus complexed with blood coagulation factor X

Human adenoviruses from multiple species bind to coagulation factor X (FX), yet the importance of this interaction in adenovirus dissemination is unknown. Upon contact with blood, vectors based on adenovirus serotype 5 (Ad5) binds to FX via the hexon protein with nanomolar affinity, leading to selective uptake of the complex into the liver and spleen. The Ad5:FX complex putatively targets heparan sulfate proteoglycans (HSPGs). The aim of this study was to elucidate the specific requirements for Ad5:FX-mediated cellular uptake in this high-affinity pathway, specifically the HSPG receptor requirements as well as the role of penton base-mediated integrin engagement in subsequent internalisation. Removal of HS sidechains by enzymatic digestion or competition with highly-sulfated heparins/heparan sulfates significantly decreased FX-mediated Ad5 cell binding in vitro and ex vivo. Removal of N-linked and, in particular, O-linked sulfate groups significantly attenuated the inhibitory capabilities of heparin, while the chemical inhibition of endogenous HSPG sulfation dose-dependently reduced FX-mediated Ad5 cellular uptake. Unlike native heparin, modified heparins lacking O- or N-linked sulfate groups were unable to inhibit Ad5 accumulation in the liver 1h after intravascular administration of adenovirus. Similar results were observed in vitro using Ad5 vectors possessing mutations ablating CAR- and/or α(v) integrin binding, demonstrating that attachment of the Ad5:FX complex to the cell surface involves HSPG sulfation. Interestingly, Ad5 vectors ablated for α(v) integrin binding showed markedly delayed cell entry, highlighting the need for an efficient post-attachment internalisation signal for optimal Ad5 uptake and transport following surface binding mediated through FX. This study therefore integrates the established model of α(v) integrin-dependent adenoviral infection with the high-affinity FX-mediated pathway. This has important implications for mechanisms that define organ targeting following contact of human adenoviruses with blood.

Impact of lentiviral vector-mediated transduction on the tightness of a polarized model of airway epithelium and effect of cationic polymer polyethylenimine

Lentiviral (LV) vectors are promising agents for efficient and long-lasting gene transfer into the lung and for gene therapy of genetically determined pulmonary diseases, such as cystic fibrosis, however, they have not been evaluated for cytotoxicity and impact on the tightness of the airway epithelium. In this study, we evaluated the transduction efficiency of a last-generation LV vector bearing Green Fluorescent Protein (GFP) gene as well as cytotoxicity and tight junction (TJ) integrity in a polarized model of airway epithelial cells. High multiplicities of infection (MOI) showed to be cytotoxic, as assessed by increase in propidium iodide staining and decrease in cell viability, and harmful for the epithelial tightness, as demonstrated by the decrease of transepithelial resistance (TER) and delocalization of occludin from the TJs. To increase LV efficiency at low LV:cell ratio, we employed noncovalent association with the polycation branched 25 kDa polyethylenimine (PEI). Transduction of cells with PEI/LV particles resulted in 2.5–3.6-fold increase of percentage of GFP-positive cells only at the highest PEI:LV ratios (1×10⁷ PEI molecules/transducing units with 50 MOI LV) as compared to plain LV. At this dose PEI/LV transduction resulted in 6.5 ± 2.4% of propidium iodide-positive cells. On the other hand, PEI/LV particles did not determine any alteration of TER and occludin localization. We conclude that PEI may be useful for improving the efficiency of gene transfer mediated by LV vectors in airway epithelial cells, in the absence of high acute cytotoxicity and alteration in epithelial tightness.