Cadmium impairs zebrafish swim bladder development via ROS mediated inhibition of the Wnt / Hedgehog pathway

The posterior swim bladder is an important organ in teleost fishes, that primarily maintains buoyancy and motility for swimming and survival. In this study, we examined the molecular mechanisms of the toxicity of cadmium (Cd) on the early development of the swim bladder in zebrafish. Embryonic Cd exposure resulted in the non-inflation of the swim bladder when the ambient Cd concentration was greater than or equal to 0.25 mg/L. Cd disturbed surfactant lipid distribution and inhibited the formation of all three tissue layers in the swim bladder. Additionally, excessive Cd down-regulated Wnt (fzd3, nkd1, fzd7 and axin2) and Hedgehog (ihh, shh, ptc1 and ptc2) signaling pathways. Conversely, Wnt signaling activation partially neutralized Cd-induced swim bladder developmental defects. Moreover, ROS scavenger reduced Glutathione (GSH) effectively recovered Cd induced defects in swim bladder and Wnt/Hedgehog signaling. Taken together, our results first revealed that Cd caused swim bladder developmental defects via ROS-mediated inhibition of the Wnt and Hedgehog pathways. These results herein provide important data for future toxicological studies and risk assessments of Cd.