Simulated microgravity activates autophagy expression in the rat retina

Abstract

Objective

This study aims to investigate the expression and possible role of autophagy in the retina of rats under microgravity.

Methods

Adult Sprague-Dawley (SD) rats were randomly allocated to either the tail suspension group (TS) or the control group (CTRL). To simulate microgravity-induced redistribution of cephalad fluid observed in space, the rats in the TS group underwent tail suspension for a duration of 4 weeks. Optical coherence tomography angiography (OCTA) was applied to assess the ocular blood flow and thickness of the retina. Hematoxylin and eosin (H&E) staining, along with transmission electron microscopy (TEM), were used to investigate morphological changes and autophagosomes in the retina. Endoplasmic reticulum autophagy (ER-phagy) related proteins (ATF4, CHOP, and GRP78) in the rat retina were detected using an immunofluorescence assay (IFA). The levels of autophagy-related proteins (Beclin1, P62, LC3B, ATF4, CHOP, and GRP78) were quantified by Western blot (WB). The expression of ATG5 and ATG7 genes was examined via real-time quantitative PCR (qPCR).

Results

In fundus imaging signs, microgravity increases retinal thickness and the retinal vascular perfusion area. Moreover, microgravity also upregulates Beclin1, LC3B, ATF4, CHOP, and GRP78 while downregulating P62 in retina. It elevates the number of autophagosomes and activates autophagy and ER-phagy signaling pathways in retina.

Conclusion

Simulated microgravity can trigger the organism's intrinsic protective mechanisms, inducing the activation of autophagy (ER-phagy) in the retina, which may represent a self-defense mechanism against adverse conditions of microgravity-related stressors.