Slc22a4, also known as OCTN1, is an organic cation transporter. It plays a crucial role in transporting ergothioneine (ERGO), a food-derived antioxidant, into various cells, including those in the brain. This transport is significant as ERGO may have roles in brain function, such as promoting neurogenesis, neuronal maturation, and protecting against oxidative stress [1,4,5,6]. It is also involved in the renal reabsorption of ergothioneine [5]. Additionally, it has been associated with pathways related to rheumatoid arthritis, though its physiological function in this context is unclear [2,3].

In Octn1 gene knockout mice, ERGO is absent from the brain due to the lack of OCTN1 in neurons, neural stem cells, and microglia. This indicates that OCTN1 is essential for ERGO uptake into the brain parenchymal cells, suggesting that Slc22a4 plays a pivotal role in brain function, such as in promoting memory function and protecting against stress-induced sleep disturbance and neuronal injury [1,6].

In conclusion, Slc22a4 is crucial for the transport of ergothioneine, which has implications for brain function and protection against oxidative stress. Gene knockout mouse models have been instrumental in revealing its role in maintaining ERGO levels in the brain. Although its role in rheumatoid arthritis is not fully understood, research on Slc22a4 contributes to our understanding of its functions in both normal physiological processes and disease conditions.