Zika virus induces neuronal and vascular degeneration in developing mouse retina

Zika virus (ZIKV), a mosquito-borne flavivirus, can cause severe eye disease and even blindness in newborns. However, ZIKV-induced retinal lesions have not been studied in a comprehensive way, mechanisms of ZIKV-induced retinal abnormalities are unknown, and no therapeutic intervention is available to treat or minimize the degree of vision loss in patients. Here, we developed a novel mouse model of ZIKV infection to evaluate its impact on retinal structure. ZIKV (20 plaque-forming units) was inoculated into neonatal wild type C57BL/6J mice at postnatal day (P) 0 subcutaneously. Retinas of infected mice and age-matched controls were collected at various ages, and retinal structural alterations were analyzed. We found that ZIKV induced progressive neuronal and vascular damage and retinal inflammation starting from P8. ZIKV-infected retina exhibited dramatically decreased thickness with loss of neurons, initial neovascular tufts followed by vessel dilation and degeneration, increased microglia and leukocyte recruitment and activation, degeneration of astrocyte network and gliosis. The above changes may involve inflammation and endoplasmic reticulum stress-mediated cell apoptosis and necroptosis. Moreover, we evaluated the efficacy of preclinical drugs and the safety of ZIKV vaccine candidate in this mouse model. We found that ZIKV-induced retinal abnormalities could be blocked by a selective flavivirus inhibitor NITD008 and a live-attenuated ZIKV vaccine candidate could potentially induce retinal abnormalities. Overall, we established a novel mouse model and provide a direct causative link between ZIKV and retinal lesion in vivo, which warrants further investigation of the underlying mechanisms of ZIKV-induced retinopathy and the development of effective therapeutics.

Retinal degeneration in experimental coronavirus retinopathy (ECOR) is associated with increased TNF-alpha, soluble TNFR2 and altered TNF-alpha signaling

Experimental coronavirus retinopathy (ECOR) is a virally triggered model of retinal degeneration composed of both genetic and autoimmune components. Since TNF-alpha plays a role in immune-mediated processes we evaluated the levels of TNF-alpha/TNF-alpha receptors and the downstream signaling molecule nitric oxide (NO) during disease in both retinal degeneration susceptible BALB/c and degeneration resistant CD-1 mice. Following coronavirus injection, TNF-alpha mRNA was detected at higher levels within the retinas, and concentrations of TNF-alpha (p<0.005) and sTNFR1 (p<0.0005) proteins were increased within the sera of BALB/c but not CD-1 mice. While concentrations of sTNFR2 proteins were elevated in both BALB/c (p<0.00005) and CD-1 (p<0.005) mice compared to controls, concentrations were higher in BALB/c mice (p<0.0005). Gene expression of iNOS while initially high in BALB/c mice decreased during the acute phase of infection, while it increased in CD-1 mice. These trends are attributable to differences in monocyte TNFR2 release (p<0.0005) between the strains since sTNFR2 decreased (p<0.01) levels of NO production. These studies demonstrate that retinal degeneration following viral infection is associated with increased release of TNF-alpha/TNF receptors combined with a down-regulation of NO. Furthermore they suggest that these molecules are involved in alterations in immune response leading to autoimmune reactivity.

Combined effect of cyclosporine and sirolimus on improving the longevity of recombinant adenovirus-mediated transgene expression in the retina

OBJECTIVES

To reevaluate the longevity and intraocular safety of recombinant adenovirus (rAd)-mediated gene delivery after subretinal injection, and to prolong transgene expression through the combination of 2 synergistic immunosuppressants.

METHODS

An rAd vector carrying green fluorescent protein (GFP) gene was delivered subretinally in the rat eye. The GFP expression was monitored in real time by fundus fluorescent photography. Intraocular safety was examined by observation of changes of retinal pigmentation, cell infiltration in virus-contacted area, immunophenotyping for CD4(+) and CD8(+) cytotoxic T lymphocytes, and CD68(+) macrophages, histologic findings, and dark-adapted electroretinography. Two synergistic immunosuppressants, cyclosporine and sirolimus, were used alone or in combination to prolong transgene expression by temporary immunosuppression.

RESULTS

The GFP expression peaked on day 4, dramatically decreased on day 10, and was not detectable on day 14. The decreased GFP expression was coincident with cell infiltration in virus-contacted area. Immunostaining showed that the infiltrating cells were CD4(+) and CD8(+) cytotoxic T lymphocytes and CD68(+) macrophages. Clumped retinal pigmentation and decreased b wave of dark-adapted electroretinogram were observed at 3 to 4 weeks after injection. Histologic examination confirmed rAd-induced retinal degeneration. Transient immunosuppression by cyclosporine and sirolimus, either alone or in combination, improved transgene expression, with the combination being the most efficient. The combined immunosuppression attenuated but did not retard the rAd-induced retinal damage.

CONCLUSIONS

Transgene expression mediated by rAd after subretinal delivery is short-term and toxic to the retina. Combination of cyclosporine and sirolimus may act as an immunosuppressive adjunct to prolong rAd-mediated gene transfer.

CLINICAL RELEVANCE

The intraocular safety of rAd should be carefully considered before clinical trials are performed.

Epitope-tagged recombinant AAV vectors for expressing neurturin and its receptor in retinal cells

PURPOSE

Neurturin (NTN) is a potent neuronal survival factor in the central and peripheral nervous systems. We previously described altered expression of mRNAs for NTN and one of its receptor components, GFRa-2 in degenerative retinas of rd/rd mice. Towards assessing the potential for transfer of these genes to counteract retinal degeneration, we examined recombinant adeno-associated virus (rAAV) constructs for expression of NTN and GFRa-2 transgenes in retinal cells in vitro and for the effect of transgene expression on retinal function following intraocular delivery in rd/rd mice.

METHODS

The rAAV constructs incorporated epitope tags to facilitate discrimination between transgenic and endogenous expression. Expression of murine NTN was driven by a CMV promoter and a partial murine opsin promoter was used to drive expression of human GFRa-2. rAAV preparations were used to infect mouse retinal cell cultures and for intraocular injection of predegenerative rd/rd mice. Endogenous and transgene expression was analyzed by immunofluorescence. Photoreceptor function in treated mice was assessed by electroretinography.

RESULTS

Both vectors delivered and expressed their transgenes in vitro and in vivo. Differential targeting was achieved in vivo through the use of alternative promoters. Under the conditions examined, no functional rescue of rd photoreceptors was observed.

CONCLUSIONS

Therapeutic treatment of the rd model of retinal degeneration does not appear to be effected by simple modulation of the expression of NTN or GFRa-2, and may therefore depend on additional synergistic factors. Our AAV constructs will facilitate the development of combinatorial approaches to the treatment of central and peripheral neurodegenerations.

The use of adenovirus-mediated gene transfer to develop a rat model for photoreceptor degeneration

PURPOSE

To investigate the effects of recombinant adenovirus-mediated downregulation of cathepsin S (CatS) on the retinal pigment epithelium and/or neural retina in vivo.

METHODS

The expression of green fluorescent protein (gfp) after subretinal injection of a recombinant adenovirus, Ad.gfp, into rat eyes was first established by in vivo fundus fluorescence photography and fluorescence microscopy. The autofluorescent debris accumulation in Ad.CatSAS (recombinant adenovirus carrying the antisense CatS gene)injected rat eyes was monitored by fluorescence microscopy, and the antisense CatS RNA expression was demonstrated by in situ hybridization. Changes in the retinal morphology were assessed by light microscopy. ResuLTS. The gfp expression was present in 30% to 90% of the injection area at 3 days and was absent 9 days after Ad.gfp injection. In Ad.CatSAS-injected eyes, the expression of antisense CatS RNA was demonstrated by in situ hybridization. Autofluorescent debris accumulation was significantly higher in Ad.CatSAS-injected eyes than in control eyes. The shortening of photoreceptor outer segments in Ad.CatSAS-injected eyes coincided with intense autofluorescent debris accumulation. The number of layers of photoreceptor cells decreased with time and were 11, 9, and 8 at 7, 14, and 28 days after Ad.CatSAS injection, respectively. In control eyes, the number of layers of photoreceptor cells (14) remained unchanged.

CONCLUSIONS

These results demonstrate that recombinant adenovirus-mediated transient modulation of gene expression in retinal pigment epithelial (RPE) cells could induce changes in the retina, and, in spite of the low expression of endogenous CatS in RPE cells, this enzyme plays an important role in maintenance of normal retinal function.

Episcleritis associated with pigmentary retinal degeneration in an HTLV-I carrier

Human T-cell lymphotropic virus type I (HTLV-I) has been reported as the cause of a kind of endogenous uveitis (HTLV-I associated uveitis; HAU). We observed a case of episcleritis in a HTLV-I carrier with pigmentary retinal degeneration. HTLV-I infection might be associated with the development of episcleritis and pigmentary retinal degeneration. Patients with episcleritis or pigmentary retinal degeneration should be examined for HTLV-I infection.

Genetic predisposition to coronavirus-induced retinal disease

PURPOSE

Retinal inflammatory and degenerative processes in humans and animals frequently are associated with genetic factors. The murine coronavirus, mouse hepatitis virus (MHV), JHM strain, induces a biphasic retinal disease in adult BALB/c mice. The genetic constitution of the host and the virus serotype can be critical factors in determining the outcome of a virus infection. The purpose of this study was to evaluate the possible role of host genetics in murine coronavirus-induced retinal disease.

METHODS

JHM virus was inoculated by the intravitreal route into BALB/c, CD-1, and A/J mice. At varying times after inoculation, eye tissues were evaluated histologically. Antibody responses to the virus were evaluated by neutralization assays.

RESULTS

JHM virus induces a biphasic retinal disease in BALB/c mice. In the early phase, 1 to 7 days after inoculation, retinal vasculitis is observed. The second phase, characterized by retinal degeneration in the absence of inflammation, is seen by day 10 and progresses for several months. There is a similar biphasic disease process in JHM virus-infected A/J mice. However, retinal changes are less severe than those seen in BALB/c mice. Retinal tissue damage induced by JHM virus in CD-1 mice is different. Only the early phase of the disease, consisting of retinal vasculitis, was observed. These CD-1 mice do not develop the retinal degenerative disease. In fact, after day 10, the retina has a normal appearance. These differences in retinal tissue damage are seen over a wide range of infectivity of the virus inocula. Virus concentrations ranging from 10(1.4) to 10(4.4) TCID50/5 microliters were capable of inducing both inflammation and degeneration in BALB/c mice, whereas, the highest concentration of virus (10(4.4) TCID50/5 microliters) in CD-1 mice resulted in only the early inflammatory changes.

CONCLUSIONS

The authors show that the genetics of the host can profoundly affect the nature of retinal tissue damage. These studies substantiate the concept that a virus can indeed trigger retinal degenerative processes in genetically susceptible hosts.