ACSL4-mediated ZIP7-VDAC3 interaction regulates endoplasmic reticulum-mitochondria iron transfer in hepatocytes under PFOS exposure.

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant with adverse health consequences. Our previous studies showed that PFOS caused an increase in mitochondrial iron and accelerated the expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), one classic executor in the ferroptosis pathway. As ACSL4 is located in the mitochondria-associated endoplasmic reticulum (ER) membranes, here, we intended to further explore the role of ACSL4 in the inter-organelle iron crosstalk between ER and mitochondria under PFOS exposure. We found that PFOS caused ER iron accumulation in mice liver and human hepatocytes L-02. Inhibition of solute carrier family 39 member 7 (SLC39A7/ZIP7), a potential ER iron efflux channel supposed by us, alleviated PFOS-induced mitochondrial iron overload and further elevated ER iron level. Knockdown of voltage-dependent anion channel 3 (VDAC3) or mitochondrial calcium uniporter (MCU), the respective potential mitochondrial iron influx channels in outer/inner mitochondrial membrane, reversed the mitochondrial iron overload and aggravated ER iron accumulation in the cells under PFOS treatment. ACSL4 interacted with both ZIP7 and VDAC3 in mice liver and L-02 cells after treatment with PFOS. Upon inhibition of ACSL4, the ZIP7-VDAC3 interaction was reduced, mitigating mitochondrial iron overload and exacerbating iron accumulation in ER. Inhibiting VDAC3 or ZIP7 reversed the overloaded cytosolic iron under PFOS treatment, however, we found no further decrease in cytosolic iron after simultaneous inhibiting VDAC3 and ZIP7 compared with respectively inhibiting VDAC3 or ZIP7 alone. Our study provides evidence and reveals the molecular mechanism underneath the ER-mitochondria iron crosstalk under PFOS exposure, providing new insights into and enriches the understanding of the iron network-regulating function of the ferroptosis executor ACSL4 and highlighting its role in PFOS toxicity.