Rapamycin relieves the cataract caused by ablation of Gja8b through stimulating autophagy in zebrafish

Macroautophagy/Autophagy is known to be important for intracellular quality control in the lens. GJA8 is a major Gap Junction Protein in vertebrate lenses. Mutations in GJA8 cause cataracts in humans. The well-known cataractogenesis mechanism is that mutated GJA8 leads to abnormal assembly of gap junctions, resulting in defects in intercellular communication among lens cells. In this study, we observed that ablation of Gja8b (a homolog of mammalian GJA8) in zebrafish led to severe defects in organelle degradation, an important cause of cataractogenesis in developing lens. The role of Autophagy in organelle degradation in lens remains disputable. Intriguingly, we also observed that ablation of Gja8b induced deficient Autophagy in the lens. More importantly, in vivo treatment of zebrafish with rapamycin, an Autophagy activator that inhibits MAPK/JNK and mTORC1 signaling, stimulated Autophagy in the lens and relieved the defects in organelle degradation, resulting in the mitigation of cataracts in gja8b mutant zebrafish. Conversely, inhibition of Autophagy by treatment with the chemical reagent 3-MA blocked these recovery effects, suggesting the important roles of Autophagy in organelle degradation in the lens in gja8b mutant zebrafish. Further studies in HLE cells revealed that GJA8 interacted with ATG proteins. Overexpression of GJA8 stimulated Autophagy in HLE cells. These data suggest an unrecognized cataractogenesis mechanism caused by ablation of Gja8b and a potential treatment for cataracts by stimulating Autophagy in the lens.Abbreviations: 3-MA: 3-methyladenine; ATG: Autophagy related; AV: autophagic vacuoles; Dpf: days post fertilization; GJA1: Gap Junction Protein alpha 1; GJA3: Gap Junction Protein alpha 3; GJA8: Gap Junction Protein alpha 8; Hpf: hours post fertilization; MAP1LC3/LC3: microtubule associated protein 1 LIGHT chain 3; MTOR: mechanistic target of rapamycin kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; WT: wild type.