Inhibition of mTOR via an AAV-Delivered shRNA Tested in a Rat OIR Model as a Potential Antiangiogenic Gene Therapy

Crocetin inhibits choroidal neovascularization in both in vitro and in vivo models

Choroidal neovascularization (CNV) is the primary pathogenic process underlying wet age-related macular degeneration, leading to severe vision loss. Despite current anti-vascular endothelial growth factor (VEGF) therapies, several limitations persist. Crocetin, a major bioactive constituent of saffron, exhibits multiple pharmacological activities, yet its role and mechanism in CNV remain unclear. Here, we investigated the potential effects of crocetin on CNV using in vitro and in vivo models. In human umbilical vein endothelial cells, crocetin demonstrated inhibition of VEGF-induced cell proliferation, migration, and tube formation in vitro, as assessed by CCK-8 and EdU assays, transwell and scratch assays, and tube formation analysis. Additionally, crocetin suppressed choroidal sprouting in ex vivo experiments. In the human retinal pigment epithelium (RPE) cell line ARPE-19, crocetin attenuated cobalt chloride-induced hypoxic cell injury, as evidenced by CCK-8 assay. As evaluated by quantitative PCR and Western blot assay, it also reduced hypoxia-induced expression of VEGF and hypoxia-inducible factor 1α (HIF-1α), while enhancing zonula occludens-1 expression. In a laser-induced CNV mouse model, intravitreal administration of crocetin significantly reduced CNV size and suppressed elevated expressions of VEGF, HIF-1α, TNFα, IL-1β, and IL-6. Moreover, crocetin treatment attenuated the elevation of phospho-S6 in laser-induced CNV and hypoxia-induced RPE cells, suggesting its potential anti-angiogenic effects through antagonizing the mechanistic target of rapamycin complex 1 (mTORC1) signaling. Our findings indicate that crocetin may hold promise as an effective drug for the prevention and treatment of CNV.

Down-regulation of HuR inhibits pathological angiogenesis in oxygen-induced retinopathy

HuR (also known as ELAV1), a ubiquitous RNA-binding protein, is implicated in the pathogenesis of diverse diseases via the mechanism of post-transcriptional regulation. Whether it is involved in pathological angiogenesis in oxygen-induced retinopathy is not clear. In this study, we detected HuR expression was increased in the retina of mouse model of oxygen-induced retinopathy (OIR) as well as in vascular endothelial cells exposed to hypoxia. With gain-of-function and loss-of-function studies using adenovirus infection, we found HuR over-expression promoted while HuR knockdown inhibited the migration, proliferation and tube formation of vascular endothelial cells. Moreover, HuR regulated the expression of VEGFA in vascular endothelial cells. We also found the retinal pathological angiogenesis in mouse OIR model was greatly reduced with HuR knockdown using recombinant AAV expressing HuR specific shRNA which was administered by intravitreal injection. The results of this study suggest HuR is involved in pathological angiogenesis via regulating angiogenic behaviors of endothelial cells, providing a potential target for the treatment of retinopathy of prematurity.

mTOR inhibition as a novel gene therapeutic strategy for diabetic retinopathy

In addition to laser photocoagulation, therapeutic interventions for diabetic retinopathy (DR) have heretofore consisted of anti-VEGF drugs, which, besides drawbacks inherent to the treatments themselves, are limited in scope and may not fully address the condition’s complex pathophysiology. This is because DR is a multifactorial condition, meaning a gene therapy focused on a target with broader effects, such as the mechanistic target of rapamycin (mTOR), may prove to be the solution in overcoming these concerns. Having previously demonstrated the potential of a mTOR-inhibiting shRNA packaged in a recombinant adeno-associated virus to address a variety of angiogenic retinal diseases, here we explore the effects of rAAV2-shmTOR-SD in a streptozotocin-induced diabetic mouse model. Delivered via intravitreal injection, the therapeutic efficacy of the virus vector upon early DR processes was examined. rAAV2-shmTOR-SD effectively transduced mouse retinas and therein downregulated mTOR expression, which was elevated in sham-treated and control shRNA-injected (rAAV2-shCon-SD) control groups. mTOR inhibition additionally led to marked reductions in pericyte loss, acellular capillary formation, vascular permeability, and retinal cell layer thinning, processes that contribute to DR progression. Immunohistochemistry showed that rAAV2-shmTOR-SD decreased ganglion cell loss and pathogenic Müller cell activation and proliferation, while also having anti-apoptotic activity, with these effects suggesting the therapeutic virus vector may be neuroprotective. Taken together, these results build upon our previous work to demonstrate the broad ability of rAAV2-shmTOR-SD to address aspects of DR pathophysiology further evidencing its potential as a human gene therapeutic strategy for DR.

Tortuosity of branch retinal artery is more associated with the genesis and progress of diabetic retinopathy

OBJECTIVE

The purpose of this study is to investigate the potential of using the tortuosity of branch retinal artery as a more promising indicator for early detection and accurate assessment of diabetic retinopathy (DR).

DESIGN AND METHOD

The diagnoses, consisting of whether DR or not as well as DR severity, were given by ophthalmologists upon the assessment of those fundus images from 495 diabetic patients. Meanwhile, benefiting from those good contrast and high optical resolution fundus images taken by confocal scanning laser ophthalmoscope, the branch arteries, branch veins, main arteries and main veins in retina can be segmented independently, and the tortuosity values of them were further extracted to investigate their potential correlations with DR genesis and progress based on one-way ANOVA test.

RESULTS

For both two comparisons, i.e., between non-DR group and DR group as well as among groups with different DR severity levels, larger tortuosity increments were always observed in retinal arteries and the increments in branch retinal vessels were even larger. Furthermore, it was newly found that branch arterial tortuosity was significantly associated with both DR genesis (p=0.030) and DR progress (p<0.001).

CONCLUSION

Based on this cohort study of 495 diabetic patients without DR and with different DR severity, the branch arterial tortuosity has been found to be more closely associated with DR genesis as well as DR progress. Therefore, the branch arterial tortuosity is expected to be a more direct and specific indicator for early detection of DR as well as accurate assessment of DR severity, which can further guide timely and rational management of DR to prevent from visual impairment or even blindness resulting from DR.

AAV expressing an mTOR-inhibiting siRNA exhibits therapeutic potential in retinal vascular disorders by preserving endothelial integrity

Expanding on previous demonstrations of the therapeutic effects of adeno‐associated virus (AAV) carrying small‐hairpin RNA (shRNA) in downregulating the mechanistic target of rapamycin (mTOR) in in vivo retinal vascular disorders, vascular endothelial growth factor (VEGF)‐stimulated endothelial cells were treated with AAV2‐shmTOR to examine the role of mTOR inhibition in retinal angiogenesis. AAV2‐shmTOR exposure significantly reduced mTOR expression in human umbilical vein endothelial cells (HUVECs) and decreased downstream signaling cascades of mTOR complex 1 (mTORC1) and mTORC2 under VEGF treatment. Moreover, the angiogenic potential of VEGF was significantly inhibited by AAV2‐shmTOR, which preserved endothelial integrity by maintaining tight junctions between HUVECs. These data thus support previous in vivo studies and provide evidence that AAV2‐shmTOR induces therapeutic effects by inhibiting the neovascularization of endothelial cells.

Viral-Vector-Delivered Anti-Angiogenic Therapies to the Eye

Pathological vessel growth harms vision and may finally lead to vision loss. Anti-angiogenic gene therapy with viral vectors for ocular neovascularization has shown great promise in preclinical studies. Most of the studies have been conducted with different adeno-associated serotype vectors. In addition, adeno- and lentivirus vectors have been used. Therapy has been targeted towards blocking vascular endothelial growth factors or other pro-angiogenic factors. Clinical trials of intraocular gene therapy for neovascularization have shown the treatment to be safe without severe adverse events or systemic effects. Nevertheless, clinical studies have not proceeded further than Phase 2 trials.