Academic Background

Age-related macular degeneration (AMD) is a major cause of central vision loss among the elderly, particularly in its neovascular (NV) form, where choroidal neovascularization (CNV) leads to rapid and severe vision loss. Current AMD treatments primarily rely on intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs, which, while significantly improving the condition, may lead to side effects such as reduced blood flow and exacerbation of geographic atrophy (GA) with long-term repeated injections. Therefore, exploring new therapeutic approaches to address the limitations of current treatments is crucial.

Early studies have shown that interactions between neurons/glia and blood vessels in the retina play a key role in regulating angiogenesis and the release of neurotrophic factors. Glial cells (such as Müller glia, astrocytes, and microglia) are commonly activated in retinal injury and disease, releasing pro-angiogenic factors like VEGF, which are major contributors to neovascularization in ischemic retinas. Thus, investigating how to modulate glial cell activation to suppress pathological angiogenesis is of significant clinical importance.

Botulinum neurotoxin type A (BoNT/A) is a drug widely used to treat various neurological disorders, inhibiting neurotransmitter release by cleaving synaptosomal-associated protein 25 (SNAP-25). Although the angiogenic effects of BoNT/A in non-ocular tissues have been studied, its role in retinal angiogenesis remains unclear. This study aims to explore whether BoNT/A modulates pathological angiogenesis by regulating glial cell activation and to uncover the underlying molecular mechanisms.

Source of the Paper

This paper was authored by a research team from Boston Children’s Hospital and Harvard Medical School, with primary authors including Austin T. Gregg, Tianxi Wang, Lois E. H. Smith, and Ye Sun. The paper was published online on June 26, 2024, in the journal Angiogenesis, titled Botulinum neurotoxin serotype A inhibited ocular angiogenesis through modulating glial activation via SOCS3.

Research Process

1. Animal Models and Experimental Design

The study employed a laser-induced choroidal neovascularization (CNV) mouse model, commonly used to mimic the angiogenic aspects of human neovascular AMD. Experimental mice were divided into two groups: control and treatment. The treatment group received intravitreal injections of BoNT/A immediately after laser injury, while the control group received saline. The efficacy of BoNT/A in inhibiting CNV and its molecular mechanisms were assessed using fundus fluorescein angiography (FFA), immunohistochemistry, and real-time quantitative PCR.

2. BoNT/A Cleavage of SNAP-25

The researchers first analyzed the expression of BoNT/A receptors and SNARE proteins in the mouse retina using a single-cell RNA sequencing (scRNA-seq) dataset, finding that SNAP-25 is widely expressed in retinal neurons. Subsequently, immunostaining confirmed BoNT/A’s ability to cleave SNAP-25 in the mouse retina, indicating its activity in the retina.

3. BoNT/A Inhibition of Pathological CNV

In the laser-induced CNV mouse model, BoNT/A significantly reduced the area of CNV lesions, suppressed vascular leakage, and inhibited retinal glial cell activation. Through FFA and immunohistochemical analysis, the researchers found that the area of CNV lesions in BoNT/A-treated mice decreased by approximately 32%, and vascular leakage was also significantly reduced.

4. BoNT/A Suppression of Glial Cell Activation

The study further explored the effects of BoNT/A on retinal glial cell activation. Through immunostaining, the researchers found that BoNT/A significantly reduced the activation of microglia and Müller glial cells, suggesting that BoNT/A exerts its anti-angiogenic effects by inhibiting glial cell activation.

5. BoNT/A Induction of SOCS3 Expression

The researchers found that BoNT/A treatment significantly induced SOCS3 mRNA expression while suppressing VEGFA mRNA expression. SOCS3, a suppressor of cytokine signaling, plays an important role in regulating inflammatory responses and angiogenesis. Using neuron/glia-specific SOCS3-deficient mice, the researchers further confirmed the critical role of SOCS3 in the anti-angiogenic effects of BoNT/A.

Main Results

1. BoNT/A Cleaves SNAP-25: BoNT/A cleaved SNAP-25 in the mouse retina, indicating its activity in the retina.
2. BoNT/A Inhibits CNV: In the laser-induced CNV mouse model, BoNT/A significantly reduced the area of CNV lesions and vascular leakage.
3. BoNT/A Suppresses Glial Cell Activation: BoNT/A significantly reduced the activation of microglia and Müller glial cells.
4. BoNT/A Induces SOCS3 Expression: BoNT/A treatment significantly induced SOCS3 mRNA expression while suppressing VEGFA mRNA expression.
5. Critical Role of SOCS3 in BoNT/A’s Effects: In neuron/glia-specific SOCS3-deficient mice, the anti-angiogenic effects of BoNT/A were significantly diminished.

Conclusion

This study demonstrates that BoNT/A suppresses pathological angiogenesis by inducing SOCS3 expression in neurons/glia, thereby inhibiting glial cell activation and reducing the release of pro-angiogenic factors such as VEGFA. These findings provide a new theoretical basis for BoNT/A as a potential therapeutic agent for neovascular retinal diseases.

Research Highlights

1. Novel Therapeutic Target: This study is the first to reveal the mechanism by which BoNT/A suppresses pathological angiogenesis by modulating glial cell activation.
2. Critical Role of SOCS3: The study confirms the critical role of SOCS3 in the anti-angiogenic effects of BoNT/A, providing a new direction for future drug development.
3. Potential Clinical Applications: As a drug already widely used in clinical practice, the discovery of BoNT/A’s anti-angiogenic effects offers new possibilities for its application in treating AMD and other retinal diseases.

Research Significance

This study not only uncovers a new mechanism by which BoNT/A suppresses pathological angiogenesis but also provides important theoretical foundations for developing new AMD treatments. By modulating glial cell activation, BoNT/A has the potential to become an effective treatment, reducing patients’ reliance on repeated intravitreal injections and improving long-term therapeutic outcomes.