Antagonistic effects of lycopene on cadmium-induced hippocampal dysfunctions in autophagy, calcium homeostatis and redox

Abstract

Cadmium (Cd), a widely existed environmental contaminant, was shown to trigger neurotoxicity by regulating autophagy, ion homeostasis and redox. Lycopene (LYC) is a natural substance with potent antioxidant capacity. Nevertheless, little is known about i) the relationship of Cd-induced neurotoxicity and autophagy, ion homeostasis as well as redox in the hippocampus; ii) the role of LYC in the regulation of hippocampal autophagy, ionic balance and antioxidant capacity during Cd exposure. Therefore, this study sought to investigate the Cd exposure-induced hippocampal dysfunctions for neurotoxicity, and the preventive potential of LYC on the hippocampus impairment by reversing the dysfunctions during the exposure. In vivo study with mice model demonstrated that Cd exposure increased gene expression of a wide spectrum of autophagy-related gene (ATG) and gene regulating autophagy in hippocampus. This suggests the activation of hippocampal autophagy mediated by Cd. Cd exposure also decreased Ca2+-ATPase activity, thus increasing intracellular Ca2+ concentration in hippocampus, indicating the possibility that Cd-induced autophagy requires the Ca2+ signaling. Moreover, Cd exposure triggered redox stress in hippocampus cells, as antioxidant enzyme activities were decreased while oxidative productions were promoted. Cd exposure led to severe cytotoxicity in hippocampus cells. Of important note, all the hippocampal dysfunctions upon Cd exposure were reversed by LYC treatment to normal situations, and exposure-induced neurotoxicity was abrogated. The in vivo findings were recapitulated relevantly in the mouse hippocampal neuronal cell line, TH22. In all, the above data imply that LYC could be a potent therapeutic agent in treating Cd-triggered hippocampal dysfunctions and subsequent cell damage.

Keywords: autophagy; cadmium; ion-ATPases; lycopene; redox.

Figure 1. LYC abrogates cadmium exposure-induced hippocampal autophagy activation

(a-i) ATG mRNAs, (j) beclin1, (k) Akt1, (l) MAPK1, (m) PRKAA2, (n) PRKAB1, (o) PRKAG2, (p) heatmap analysis. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 2. LYC abrogates cadmium exposure-induced autophagy activation in TH22

(a-j) ATG mRNAs, (k) Beclin1, (l) Akt1, (m) MAPK1, (n) PRKAA2, (o) PRKAB1, (p) PRKAG2, (q) heatmap analysis, (r-u) protein expression levels of beclin1, Akt1 and MAPK1. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 3. LYC inhibits Cd-induced dysfunction in hippocampal Ca2+ homeostasis

(a) Ca²⁺-ATPase, (b) Ca²⁺-Mg²⁺-ATPase, (c) Ca²⁺ content intracellular, (d) Mg²⁺ content intracellular, (e-l) ATG mRNAs, (m) heatmap analysis. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 4. LYC inhibits Cd-induced dysfunction in Ca2+ homeostasis in TH22

(a) Ca²⁺-ATPase, (b) Ca²⁺-Mg²⁺-ATPase, (c) Ca²⁺ content, (d) Mg²⁺ content. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 5. LYC blocks Cd-triggered redox enhancement in hippocampus

(a) GSH-Px, (b) SOD, (c) T-AOC, (d) CAT, (e) GSH, (f) GSH-ST, (g) H₂O₂, (h) MDA. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 6. LYC blocks Cd-triggered redox enhancement in TH22

(a) GSH-Px, (b) SOD, (c) T-AOC, (d) CAT, (e) GSH, (f) GSH-ST, (g) H₂O₂, (h) MDA. Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).

Figure 7. Cell viability in TH22

Bars represent mean ± S.D. (n=3). * represent LYC and Cd group compared to C group (P < 0.05); # represent LYC+Cd group compared to Cd group (P < 0.05).