Astaxanthin protects retinal ganglion cells from acute glaucoma via the Nrf2/HO-1 pathway
Introduction
Glaucoma has become the second major cause of irreversible blindness and around 61 million people worldwide were suffering from the disease in 2010 (Cook and Foster, 2012; Mudumbai, 2013). As one of the most prevalent types of glaucoma, acute glaucoma is characterized by rapid increase in the intraocular pressure and neuro-retinal destruction induced by retinal ischemia and reperfusion (I/R) (Baden et al., 2016; Bonomi et al., 1999). Diabetes is one of the leading causes of acute glaucoma in clinic, which induces the apoptosis and necrosis of retinal ganglion cells (RGCs) (Kimura et al., 2017). Although the detailed mechanism of the diabetic retinopathy remains unclear, accumulating evidence has indicated the crucial role that oxidative stress and reactive oxygen species (ROS) play in the complications induced by diabetes (Ghirlanda et al., 1997). Due to the high oxygen consumption and active energy metabolism, the retina is rather sensitive to anoxemia and ROS attack (Cui et al., 2006; Madsen-Bouterse and Kowluru, 2008). Therefore, it is urgent for us to identify new strategies to relieve the oxidative stress on the retina and treat acute glaucoma more efficiently.
Astaxanthin (AST) is a type of xanthophyll carotenoids and a red-orange color pigment which can be naturally synthesized in algae, yeast, shrimp, lobster, quail retina and salmon (Ambati et al., 2014; Laslett et al., 2012; Visioli and Artaria, 2017). Accumulating evidence has revealed the anti-oxidize effect of AST. For instance, the anti-oxidative effect of AST on salivary gland in an irradiation-induced mouse model has been reported (Yamada et al., 2010). In addition, research has also demonstrated the effect of AST on the apoptosis and autophagy signaling pathways including AMPK, PI3K/Akt and JNK signaling. Thus, AST may alleviate the neuro-retinal degeneration induced by the apoptosis of RGCs in diabetic patients (Hong-Brown et al., 2017; Lee et al., 2010). Considering the anti-oxidative, anti-inflammatory and anti-diabetic effects of AST, its applications in the prevention and treatment of acute glaucoma are potentially valuable.
The transcription factor nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) or NF-E2 related factor 2 (Nrf2) responds to endogenous and exogenous stress such as anoxemia and chemical insults, which induces multiple signaling modulations for cell defense (Krajka-Kuzniak et al., 2017). Nrf2 and its downstream transcription regulator heme oxygenase-1 (Ho-1) have been reported to participate in the maintenance of tissue homeostasis in the retina under stress or trauma (Cameron et al., 2018).
In this research, we aimed to identify the alleviating effect of AST on acute glaucoma and reveal the detailed mechanism. We hereby reported that AST protected the RGCs from apoptosis and alleviated the retinopathy symptoms in acute glaucoma mice through the Nrf2/Ho-1 pathway.
Section snippets
Animals
All experiments and procedures performed in animals in this research were examined and approved by the Animal Use Committee in Shandong University. The adult Nrf2−/− C57BL/6 mice and corresponding wild type C57BL/6 mice were purchased from Biocytogen (Beijing, China). CRISPR/Cas9 technology was used to knock out the Nrf2 gene in C57BL/6 mice. Briefly, sgRNA targeting Nrf2 gene and Cas9 mRNA were co-injected into fertilized eggs. Cas9 nuclease combined with genomic target sequence guiding by
AST protected the retinal tissues and RGCs
To verify the effects of AST on the retina of mice treated with I/R, H&E staining was performed. As shown in Fig. 1A, the retinal ganglion cell layer (GCL) and inner nuclear layer (INL) disappeared after the treatment of I/R, and the thickness of outer nuclear layer (ONL) also decreased dramatically. The oral administration of AST alleviated the damage caused by I/R treatment compared to the second group. Interestingly, knock-down of Nrf2 repressed the protective function of AST on the damaged
Discussion
Acute glaucoma includes a series of heterogenous diseases with diversiform symptoms and unoptimistic prognosis (Ban et al., 2017). Although the detailed mechanism and pathogenesis of acute glaucoma remain unclear, accumulating evidence has demonstrated that high intraocular pressure, increased oxidative stress, neuro-inflammation and irreversible apoptosis of RGCs promote the development of acute glaucoma and contribute to the final vision loss, thus seriously impacting the life quality of
Conclusion
In conclusion, we hereby verify the protective function of AST on the retina and RGCs in a mouse model with acute glaucoma. AST inhibits the oxidative stress by activating Nrf2 and Ho-1 and thus suppresses the apoptosis of RGCs and protects the integrity of retina in acute glaucoma. Although AST alone cannot completely cure acute glaucoma, we believe that AST can be used as an auxiliary agent to participate in the treatment of acute glaucoma and significantly relieve the symptoms of patients.
Author statement
Yan Li, Cuiying Chu and Shu Liu conducted the experiments and analyzed the data. Qiang Wang conceived and supervised this study. Yan Li and Qiang Wang wrote the manuscript.
Research involving human participants and/or animals
All experiments and procedures performed in animals in this research were examined and approved by the Animal Use Committee in Shandong University.
Informed consent
Not applicable.
Declaration of Competing Interest
The authors declare that they have no conflict of interest.
Acknowledgment
None.
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