Chaga mushroom (Inonotus obliquus) polysaccharides exhibit genoprotective effects in UVB-exposed embryonic zebrafish (Danio rerio) through coordinated expression of DNA repair genes

Chaga mushroom is one of the promising beneficial mushrooms thriving in the colder parts of Northern hemisphere. Chaga polysaccharides (IOP) have been reported to enhance immune response and alleviate oxidative stress during development. However, the effects of IOP on the genotoxicity in model organisms are yet to be clarified. In this study, IOP was extracted using hot water extraction method, followed by GC analysis. Zebrafish embryos (12 h post fertilization, hpf) were exposed to transient UVB (12 J/m²/s, 305-310nm) for 10 s using a UV hybridisation chamber, followed by IOP treatment (2.5 mg/mL) at 24 hpf for up to 7 days post fertilization (dpf). The genotoxic effects were assessed using acridine orange staining, alkaline comet assay, and qRT-PCR for screening DNA repair genes. Significant reduction in DNA damage and amelioration of the deformed structures in the IOP-treated zebrafish exposed to UVB (p < 0.05) was observed at 5 dpf and thereafter. The relative mRNA expressions of XRCC-5, XRCC-6, RAD51, and GADD45 were significantly upregulated, whereas p53 and BAX were downregulated in IOP-treated UVB-exposed zebrafish compared to UVB-exposed zebrafish. ELISA analysis revealed significantly decreased expression of XRCC5 and RAD51 in UVB-exposed compared to IOP-treated UVB-exposed and control zebrafish (7 dpf). However, p53 and BAX levels were high in UVB-exposed zebrafish, indicating higher apoptosis. Pathway analysis demonstrated coordinated regulation of DNA repair genes; p53 playing a pivotal role in regulating the expression of BAX, thereby promoting apoptosis in UVB-exposed zebrafish. Overall, IOP treatment ameliorated the genotoxic effects in UVB-exposed zebrafish by enhanced expression of DNA repair genes, which assisted in normal development. The study delineated the efficacy of IOP in mitigating UV-induced DNA damage in zebrafish.