Xuan Liu

University of Florida, Gainesville, FL, United States

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Publications (7)31.58 Total impact

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    ABSTRACT: [This corrects the article on p. e35250 in vol. 7.].
    PLoS ONE 01/2014; 9(1). · 3.53 Impact Factor
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    ABSTRACT: Phosphodiesterase-6 (PDE6) is the key effector enzyme of the vertebrate phototransduction pathway in rods and cones. Rod PDE6 catalytic core is composed of two distinct subunits, PDE6α and PDE6β, whereas two identical PDE6α' subunits form the cone PDE6 catalytic core. It is not known whether this difference in PDE6 catalytic subunit identity contributes to the functional differences between rods and cones. To address this question, we expressed cone PDE6α' in the photoreceptor cells of the retinal degeneration 10 (rd10) mouse that carries a mutation in rod PDEβ subunit. We show that adeno-associated virus-mediated subretinal delivery of PDE6α' rescues rod electroretinogram responses and preserves retinal structure, indicating that cone PDE6α' can couple effectively to the rod phototransduction pathway. We also show that restoration of light sensitivity in rd10 rods is attributable to assembly of PDE6α' with rod PDE6γ. Single-cell recordings revealed that, surprisingly, rods expressing cone PDE6α' are twofold more sensitive to light than wild-type rods, most likely because of the slower shutoff of their light responses. Unlike in wild-type rods, the response kinetics in PDE6α'-treated rd10 rods accelerated with increasing flash intensity, indicating a possible direct feedback modulation of cone PDE6α' activity. Together, these results demonstrate that cone PDE6α' can functionally substitute for rod PDEαβ in vivo, conferring treated rods with distinct physiological properties.
    Journal of Neuroscience 07/2013; 33(29):11745-53. · 6.91 Impact Factor
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    ABSTRACT: Mutations in GUCY2D are associated with recessive Leber congenital amaurosis-1 (LCA1). GUCY2D encodes photoreceptor-specific, retinal guanylate cyclase-1 (RetGC1). Reports of retinal degeneration in LCA1 are conflicting; some describe no obvious degeneration and others report loss of both rods and cones. Proof of concept studies in models representing the spectrum of phenotypes is warranted. We have previously demonstrated AAV-mediated RetGC1 is therapeutic in GC1ko mice, a model exhibiting loss of cones only. The purpose of this study was to characterize AAV-mediated gene therapy in the RetGC1/RetGC2 double knockout (GCdko) mouse, a model lacking rod and cone function and exhibiting progressive loss of both photoreceptor subclasses. Use of this model also allowed for the evaluation of the functional efficiency of transgenic RetGC1 isozyme. Subretinal delivery of AAV8(Y733F) vector containing the human rhodopsin kinase (hGRK1) promoter driving murine Gucy2e was performed in GCdko mice at various postnatal time points. Treatment resulted in restoration of rod and cone function at all treatment ages and preservation of retinal structure in GCdko mice treated as late as 7 weeks of age. Functional gains and structural preservation were stable for at least 1 year. Treatment also conferred cortical- and subcortical-based visually- guided behavior. Functional efficiency of transgenic RetGC1 was indistinguishable from that of endogenous isozyme in congenic WT mice. This study clearly demonstrates AAV-mediated RetGC1 expression restores function to and preserves structure of rod and cone photoreceptors in a degenerative model of retinal guanylate cyclase deficiency, further supporting development of an AAV-based vector for treatment of LCA1.
    Human gene therapy 12/2012; · 4.20 Impact Factor
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    ABSTRACT: Achromatopsia is a rare autosomal recessive disorder which shows color blindness, severely impaired visual acuity, and extreme sensitivity to bright light. Mutations in the alpha subunits of the cone cyclic nucleotide-gated channels (CNGA3) are responsible for about 1/4 of achromatopsia in the U.S. and Europe. Here, we test whether gene replacement therapy using an AAV5 vector could restore cone-mediated function and arrest cone degeneration in the cpfl5 mouse, a naturally occurring mouse model of achromatopsia with a CNGA3 mutation. We show that gene therapy leads to significant rescue of cone-mediated ERGs, normal visual acuities and contrast sensitivities. Normal expression and outer segment localization of both M- and S-opsins were maintained in treated retinas. The therapeutic effect of treatment lasted for at least 5 months post-injection. This study is the first demonstration of substantial, relatively long-term restoration of cone-mediated light responsiveness and visual behavior in a naturally occurring mouse model of CNGA3 achromatopsia. The results provide the foundation for development of an AAV5-based gene therapy trial for human CNGA3 achromatopsia.
    PLoS ONE 01/2012; 7(4):e35250. · 3.53 Impact Factor
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    ABSTRACT: Autosomal recessive retinitis pigmentosa (RP), a heterogeneous group of degenerations of the retina, can be due to mutations in the MFRP (membrane-type frizzled-related protein) gene. A patient with RP with MFRP mutations, one of which is novel and the first splice site mutation reported, was characterized by noninvasive retinal and visual studies. The phenotype, albeit complex, suggested that this retinal degeneration may be a candidate for gene-based therapy. Proof-of-concept studies were performed in the rd6 Mfrp mutant mouse model. The fast-acting tyrosine-capsid mutant AAV8 (Y733F) vector containing the small chicken β-actin promoter driving the wild-type mouse Mfrp gene was used. Subretinal vector delivery on postnatal day 14 prevented retinal degeneration. Treatment rescued rod and cone photoreceptors, as assessed by electroretinography and retinal histology at 2 months of age. This AAV-mediated gene delivery also resulted in robust MFRP expression predominantly in its normal location within the retinal pigment epithelium apical membrane and its microvilli. The clinical features of MFRP-RP and our preliminary data indicating a response to gene therapy in the rd6 mouse suggest that this form of RP is a potential target for gene-based therapy.
    Human gene therapy 12/2011; 23(4):367-76. · 4.20 Impact Factor
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    ABSTRACT: Despite evidence that hyperactivity of the vasodeleterious axis (ACE/angiotensin II (Ang II)/AT1 receptor) of the renin-angiotensin system (RAS) is associated with the pathogenesis of diabetic retinopathy (DR) use of the inhibitors of this axis has met with limited success in the control of this pathophysiology. We investigated the hypothesis that enhancing the local activity of the recently established protective axis of the RAS, ACE2/Ang-(1-7), using adeno-associated virus (AAV)-mediated gene delivery of ACE2 or Ang-(1-7) would confer protection against diabetes-induced retinopathy. Genes expressing ACE2 and Ang-(1-7) were cloned in AAV vector. The effects of ocular AAV-ACE2/Ang-(1-7) gene transfer on DR in diabetic eNOS(-/-) mice and Sprague-Dawley (SD) rats were examined. Diabetes was associated with approximately tenfold and greater than threefold increases in the ratios of ACE/ACE2 and AT1R/Mas mRNA levels in the retina respectively. Intraocular administration of AAV-ACE2/Ang-(1-7) resulted in significant reduction in diabetes-induced retinal vascular leakage, acellular capillaries, infiltrating inflammatory cells and oxidative damage in both diabetic mice and rats. Our results demonstrate that DR is associated with impaired balance of retinal RAS. Increased expression of ACE2/Ang-(1-7) overcomes this imbalance and confers protection against DR. Thus, strategies enhancing the protective ACE2/Ang-(1-7) axis of RAS in the eye could serve as a novel therapeutic target for DR.
    Molecular Therapy 07/2011; 20(1):28-36. · 7.04 Impact Factor
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    ABSTRACT: Cardiac gene transfer may serve as a novel therapeutic approach for heart disease. Numerous serotypes of recombinant adeno-associated virus (rAAV) have been identified with variable tropisms to cardiac tissue. Both in vitro and in vivo experiments were undertaken to compare cardiac tropisms of rAAV-2, 5, 7, 8 and 9. For the in vitro studies, 10(7) vector genome (vg) of rAAV-2, 5, 7, 8 or 9 were used to transduce both rat neonatal cardiac myocytes (RNCM) and fibroblasts (RNCF). For the in vivo studies, 4 x 10(10) vg of rAAV-2, 5, 7, 8 or 9, and 4 x 10(11) vg of rAAV8 or 9 were administered in 5-day-old rats via a relatively non-invasive intracardiac injection. One and two months post-administration, green fluorescent protein (GFP) expression in tissues was visualized and GFP mRNA was quantified by the real-time polymerase chain reaction. At 3 days post-viral transduction, rAAV9 and rAAV2 produced the highest transducing efficiency in RNCM. Only rAAV2 elicited any transduction in the RNCF. The results obtained in vivo indicated that the order for transduction efficiency in the heart was: rAAV9 > rAAV8 > rAAV7 > rAAV2 = rAAV5. The transduction efficiency order in the liver was: rAAV2 > rAAV5 > rAAV7 > rAAV8 > rAAV9. Injection of a higher dose (4 x 10(11) vg) of rAAV9 provided more widespread and highly cardiac-selective GFP expression in the heart than rAAV8. Zero to minimal expression of GFP was found in the lung and kidney for both doses of all rAAV serotypes utilized. Collectively, the results obtained in the present study suggest that rAAV9 provides the most selective and stable transduction efficiency in cardiac tissue, and this expression was primarily exhibited in cardiac myocytes.
    The Journal of Gene Medicine 10/2009; 12(1):22-34. · 2.16 Impact Factor