SLC15A4 (Solute Carrier 15 member A4): integrated in vitro-in vivo analysis and functional characterization

The project provides an integrated in vitro and in vivo characterization of Solute Carrier 15 member A4 (SLC15A4/PHT1). SLC15A4 is a proton‑coupled transporter located in endo-lysosomal membranes, regulating immune and metabolic homeostasis. To bridge critical gaps in its transport properties, a multi‑level strategy combined heterologous expression systems (Xenopus oocytes, proteoliposomes), pancreatic cells, and zebrafish models. The project aimed to define substrate selectivity and pH‑dependent transport mechanics, clarify trafficking to endo‑lysosomal compartments in pancreatic β‑cells; investigate its contribution to vesicular signaling and metabolic homeostasis; establish in vivo knockout models to analyze inflammatory phenotypes.The consortium generated a coherent set of outcomes across three levels: Transport Mechanisms: Electrophysiological recordings demonstrated robust transport currents for L-histidine and selected peptides, showing maximum translocation at pH 5. Regulatory Discovery: The project uncovered an unexpected, nitrate-dependent L-histidine uptake mechanism, revealing a structural resemblance to the plant nitrate transporter NRT1.1. Cellular Homeostasis: Studies in pancreatic β‑cells confirmed SLC15A4 relevance for lysosomal pH regulation, mTORC1 signaling, and autophagic flux. In Vivo Phenotyping: Generation of slc15a4 knockout zebrafish lines revealed heightened inflammatory susceptibility under stress, validating its involvement in innate immune pathways. The research provides a coherent physiological framework. These insights advance the understanding of SLC15A4 as a conserved regulator of lysosomal flux, opening new translational avenues for therapeutic interventions in inflammatory bowel diseases (IBD), lupus, and type 2 diabetes.