The study, published in Proceedings of the National Academy of Sciences (PNAS), shows that TPC1 — a channel located predominantly in early endosomes, the intracellular compartments involved in sorting material taken up by cells — helps regulate both transferrin-mediated iron uptake and the acidity of these compartments.
Using complementary mouse models, the researchers found strikingly opposite effects when TPC1 activity was removed or increased. Mice lacking TPC1 showed reduced iron in the liver and spleen, consistent with iron deficiency. By contrast, mice carrying the gain-of-function TPC1^I486T mutation accumulated substantially more iron in these tissues.
At the cellular level, the team traced this effect to two interconnected processes. Loss of TPC1 reduced uptake of iron-carrying transferrin and made early endosomes less acidic, whereas the gain-of-function mutation increased transferrin uptake and produced more acidic endosomes. Because endosomal acidity helps drive the DMT1 transporter that releases iron into the cytosol, these changes provide a mechanism through which TPC1 activity can shift cells towards iron deficiency or iron overload. Importantly, experiments showed that TPC1 does not transport iron through its own channel pore, meaning its influence on iron is indirect.
A broad experimental approach allowed the researchers to connect ion-channel behaviour with whole-animal physiology. Endolysosomal patch-clamp electrophysiology showed that the corresponding human TPC1^I485T and mouse TPC1^I486T variants have enhanced channel activity when stimulated by the early-endosomal lipid PI3P. Single-channel measurements further showed that the mouse mutant was active even under basal conditions and became still more active following PI3P stimulation.
The team then used targeted base editing to generate the TPC1 gain-of-function mouse model and combined it with an existing TPC1 knockout model. Iron levels were examined using Prussian Blue and ferritin staining, ICP–MS tissue analysis and fluorescent probes measuring cytosolic and endolysosomal iron. High-content imaging of fluorescent transferrin and pH-sensitive transferrin probes was used to investigate transferrin trafficking and early-endosomal acidity.
The findings could have implications for understanding human iron disorders. The equivalent gain-of-function variant occurs in human TPC1, leading the authors to propose TPCN1 as a potential risk gene for iron-metabolism disorders. Excessive TPC1 activity could potentially predispose individuals to iron overload conditions such as hemosiderosis or hemochromatosis, while reduced activity could increase susceptibility to iron deficiency.
Together, the findings position TPC1 as an important link between endosomal ion-channel activity and one of the body's most fundamental metabolic processes, providing a new molecular framework for understanding how cells maintain the delicate balance between too little and too much iron.
- Find a copy of the paper here: https://www.pnas.org/doi/10.1073/pnas.2602941123
- See more linked research recently published by the Galione Group: https://www.pharm.ox.ac.uk/news/galione-group-research-identifies-endosomes-as-a-new-calcium-store-that-controls-iron-uptake