SLC41A1 is essential for magnesium homeostasis in vivo

Solute carrier family 41 member A1 (SLC41A1) has been suggested to mediate magnesium (Mg²⁺) transport by several in vitro studies. However, the physiological function of SLC41A1 remains to be elucidated. In this study, cellular Mg²⁺ transport assays combined with zebrafish slc41a1 knockdown experiments were performed to disclose SLC41A1 function and its physiological relevance. The gene slc41a1 is ubiquitously expressed in zebrafish tissues and is regulated by water and dietary Mg²⁺ availability. Knockdown of slc41a1 in zebrafish larvae grown in a Mg²⁺-free medium resulted in a unique phenotype characterized by a decrease in zebrafish Mg content. This decrease shows that SLC41A1 is required to maintain Mg²⁺ balance and its dysfunction results in renal Mg²⁺ wasting in zebrafish larvae. Importantly, the Mg content of the larvae is rescued when mouse SLC41A1 is expressed in slc41a1-knockdown zebrafish. Conversely, expression of mammalian SLC41A1-p.Asp262Ala, harboring a mutation in the ion-conducting SLC41A1 pore, did not reverse the renal Mg²⁺ wasting. ²⁵Mg²⁺ transport assays in human embryonic kidney 293 (HEK293) cells overexpressing SLC41A1 demonstrated that SLC41A1 mediates cellular Mg²⁺ extrusion independently of sodium (Na⁺). In contrast, SLC41A1-p.Asp262Ala expressing HEK293 cells displayed similar Mg²⁺ extrusion activities than control (mock) cells. In polarized Madin-Darby canine kidney cells, SLC41A1 localized to the basolateral cell membrane. Our results demonstrate that SLC41A1 facilitates renal Mg²⁺ reabsorption in the zebrafish model. Furthermore, our data suggest that SLC41A1 mediates both Mg²⁺ uptake and extrusion.