Rini H Pek, Xiaojing Yuan, Nicole Rietzschel, Jianbing Zhang, Laurie Jackson, Eiji Nishibori, Ana Ribeiro, William Simmons, Jaya Jagadeesh, Hiroshi Sugimoto, Md Zahidul Alam, Lisa Garrett, Malay Haldar, Martina Ralle, John D Phillips, David M Bodine, Iqbal Hamza
eLife. 2019; 8: e49503. Published online 2019 Oct 1. doi: 10.7554/eLife.49503 PMCID:PMC6773446
Free heme is cytotoxic as exemplified by hemolytic diseases and genetic deficiencies in heme recycling and detoxifying pathways. Thus, intracellular accumulation of heme has not been observed in mammalian cells to date. Here we show that mice deficient for the heme transporter SLC48A1 (also known as HRG1) accumulate over ten-fold excess heme in reticuloendothelial macrophage lysosomes that are 10 to 100 times larger than normal. Macrophages tolerate these high concentrations of heme by crystallizing them into hemozoin, which heretofore has only been found in blood-feeding organisms. SLC48A1 deficiency results in impaired erythroid maturation and an inability to systemically respond to iron deficiency. Complete heme tolerance requires a fully-operational heme degradation pathway as haplo insufficiency of HMOX1 combined with SLC48A1 inactivation causes perinatal lethality demonstrating synthetic lethal interactions between heme transport and degradation. Our studies establish the formation of hemozoin by mammals as a previously unsuspected heme tolerance pathway.
Porphyrins and metals were quantified at the NIDDK U54 supported CIHD University of Utah School of Medicine Iron and Heme Core.
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