Alterations of retinal autophagy after a blast simulated microgravity in rats

Emerging research has confirmed the crucial role of autophagy, an endogenous repair mechanism, in various blast injuries. However, its role in explosive ocular injury (EOI) under microgravity (MG) and normal gravity (NG) environments remains poorly understood. Therefore, this study aimed to investigate the changes in retinal lesions and retinal autophagy over time following EOI under both NG and MG environments. This study employed the hind-limb unloading model in Sprague-Dawley (SD) rats to simulate MG conditions and used self-made device with compressed gas to induce EOI. SD rats were randomly divided into six groups as follows: normal gravity control group (NG + non-EOI group), normal gravity model group at 1 day post-EOI injury (NG + EOI 1dpi group, n = 20), normal gravity model group at 7 days post-EOI injury (NG + EOI 7dpi group, n = 20), microgravity control group (MG + non-EOI group), microgravity model group at 1 day post-EOI injury (MG + EOI 1dpi group, n = 20), and microgravity model group at 7 days post-EOI injury (MG + EOI 7dpi group, n = 20). Evaluations of ocular health (gross pathology and histology), and retinal autophagy (histology and WB) were conducted before EOI, as well as at 1 and 7 days following EOI. Compared to the NG + non-EOI group, the NG + EOI group rats exhibited significant increases in autophagy-related proteins and genes in the retina, including Beclin1, LC3Ⅱ/LC3Ⅰ, ATF4, GRP78, CHOP, ATG5, and ATG7, along with a decrease in p62, indicating an elevation in retinal autophagy and ER-phagy levels. Retinal lesions, disintegration, and autophagosomes in the ganglion cell layer (GCL) and photoreceptor inner/outer segment layers (PISL/POSL) diminished over time in the NG + EOI group rats. Meanwhile, the MG + EOI group rats exhibited more severe retinal lesions and disintegration, along with an increased number of autophagosomes in the GCL and PISL/POSL, with these symptoms worsening over time compared to the MG + non-EOI group. Compared to the MG + non-EOI group, the MG + EOI group rats exhibited significant decreases in autophagy-related proteins and genes in the retina, including Beclin1, LC3Ⅱ/LC3Ⅰ, ATF4, GRP78, CHOP, ATG5, and ATG7, along with an increase in p62, suggesting a reduction in retinal autophagy levels. Taken together, retinal autophagy and ER-phagy may serve as a self-protective mechanism following EOI under NG conditions. However, under MG conditions, EOI may disrupt this protective mechanism, potentially causing irreversible retinal damage and increasing the risk of blindness in astronauts.