TSSP3 - Transcriptomic analysis in zebrafish larvae identifies iron-dependent mitochondrial dysfunction as a key event of NAFLD progression induced by benzo[a]pyrene/ethanol co-exposure

Description : Among etiological factors of non-alcoholic fatty liver disease (NAFLD), a worldwide epidemic, environmental contaminants have gained importance. Among them, benzo[a]pyrene (B[a]P), a potent environmental carcinogen, in combination with ethanol, was shown to induce the transition of steatosis toward a steatohepatitis—like state both in vitro and in vivo. However, underlying mechanisms involved in the exacerbation of toxicant-induced NAFLD remain to decipher in vivo. In this context, we used high fat diet zebrafish model, in which we observed pathological progression of steatosis following a 7 days-co-exposure to 43 mM ethanol and 25 nM B[a]P. Transcriptomic analysis followed by functional analysis highlighted mitochondrial dysfunction, alterations in heme and iron homeostasis, involvement of AhR signaling and oxidative stress. Most of these mRNA dysregulations were validated by RT-qPCR. Furthermore, similar changes were also reproduced in a human in vitro hepatocyte model, HepaRG cells. Focusing on mitochondria, structural and functional disruptions were confirmed by transmission electronic microscopy and seahorse technology, respectively. Involvement of AhR signaling in these toxicological events, i.e. mitochondrial dysfunction, alterations in heme and iron homeostasis, was evidenced by using an AhR antagonist, CH223191. AhR-associated disruptions were further validated by analyzing respective mRNA expressions obtained from AhR-knock-out HepaRG cells. Furthermore, as co-exposure was found to increase the levels of both heme and hemin, we investigated mitochondrial iron as possibly underlying the induction of oxidative stress detected by an increased lipid peroxidation. We found that mitochondrial labile iron content was raised in toxicant-exposed larvae. This increase was prevented by the iron chelator, deferoxamine, which also inhibited liver co-exposure toxicity as evaluated by histology and RT-qPCR and histology. In conclusion, these results suggest that the increase in mitochondrial iron content induced by B[a]P/ethanol co-exposure is responsible for the mitochondrial dysfunction thus promoting pathological progression of NAFLD.

Created : May 4, 2021, 10:45 a.m.

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