Identifying and exploiting SLC39A14 regulatory mechanisms for the future development of therapeutics

Objective

"Solute carriers (SLCs) are membrane proteins that mediate the transport of biological and inorganic molecules. SLC39A14 regulates the transport of manganese (Mn) into primarily liver and intestinal cells from the blood. Bi-allelic loss of function (LOF) variants in SLC39A14 lead to an accumulation of blood Mn, which travels to the brain, causes significant deficits in motor function, eventually leads to the patients being non-ambulatory. Accordingly, these patients are diagnosed with Hypermanganesaemia with dystonia 2 (HMNDYT2) and are treated with Mn chelating agents. This treatment removes excess Mn from the blood; however, the five to eight day every four week treatment regime is impractical, and the treatment fails to alleviate clinical phenotypes in many cases. For this reason, new therapies must be developed. Many LOF variants lead to mislocalization of SLC39A14 away from the plasma membrane, similar to how CFTR mutations induce loss of function. Interestingly, the recently FDA-approved drug ""Trikafta"" restores CFTR function by relocalizing it LOF variants to the plasma membrane. This method of action could serve as the basis for future HMNDYT2 therapies, but the regulatory landscape surrounding SLC39A14 gene expression, proteostasis, and trafficking is currently unknown. To address this significant gap in knowledge, we will identify genes that regulate SLC39A14 and could be future targets for HMNDYT2 therapies. To do this, we will first characterize the mislocalization of all 15 known SLC39A14 LOF variants in the population using microscopy and flow cytometry. We will then engineer HepaRG liver cells to express WT- and mutant-SLC39A14-EGFP at the endogenous SLC39A14 locus and perform a FACS-based whole genome CRISPR KO screen to identify genes that, when mutated, restore mutant-SLC39A14 levels at the plasma membrane. Lastly, we will validate our findings in other liver and intestine model systems, setting the stage for future therapeutics."