Facilitative lysosomal transport of bile acids alleviates ER stress in mouse hematopoietic precursors

Abstract

Mutations in human equilibrative nucleoside transporter 3 (ENT3) encoded by SLC29A3 results in anemia and erythroid hypoplasia, suggesting that ENT3 may regulate erythropoiesis. Here, we demonstrate that lysosomal ENT3 transport of taurine-conjugated bile acids (TBA) facilitates TBA chemical chaperone function and alleviates endoplasmic reticulum (ER) stress in expanding mouse hematopoietic stem and progenitor cells (HSPCs). Slc29a3−/− HSPCs accumulate less TBA despite elevated levels of TBA in Slc29a3−/− mouse plasma and have elevated basal ER stress, reactive oxygen species (ROS), and radiation-induced apoptosis. Reintroduction of ENT3 allows for increased accumulation of TBA into HSPCs, which results in TBA-mediated alleviation of ER stress and erythroid apoptosis. Transplanting TBA-preconditioned HSPCs expressing ENT3 into Slc29a3−/− mice increase bone marrow repopulation capacity and erythroid pool size and prevent early mortalities. Together, these findings suggest a putative role for a facilitative lysosomal transporter in the bile acid regulation of ER stress in mouse HSPCs which may have implications in erythroid biology, the treatment of anemia observed in ENT3-mutated human genetic disorders, and nucleoside analog drug therapy.

Solute Carrier Nucleoside Transporters in Hematopoiesis and Hematological Drug Toxicities: A Perspective

“…Because of this, organelle nucleoside transport (i.e., ENT3) may have profound roles in cellular homeostasis. Consistently, ENT3 is widely expressed in many tissues including bone marrow, liver, placenta, pancreas, skin, heart, GIT, brain, fat, and skeletal muscle, mirroring the pattern of dysfunction observed in SLC29A3-mutated genetic disorders [37,190,191]. Interestingly, when ENT3 transport was examined for cargo selectivity, it was found to transport nucleosides, nucleobases, and monoamines at an obligatory acidic pH relevant to lysosomal and inner mitochondrial subdomains [37].…”

“…These studies indicate that ENT3 intricately regulates autophagy and lysosomal functions in hematopoietic and mesenchymal stem cells, which partially involve adenosine-dependent AMP-activated protein kinase (AMPK)/ mammalian target of rapamycin (mTOR) signaling. The mouse phenotypes recapitulate the disease symptoms observed in human ENT3 disorders, including anemia, suggesting that Slc29a3-deleted mice are a suitable model for further evaluating ENT3 hematopoietic disease pathologies [190].…”

“…The involvement of both ENT3 and ENT1 in human hematopoietic development sets a stage for future studies in this direction, particularly in understanding the involvement of these transporters in hematological toxicities of anticancer nucleoside analogs. Thus far, studies suggest ENT3 s role as an organelle transporter that can sense the lysosomal contents in adult hematopoietic stem cells, progenitors, and precursors, relaying the information to core cellular machineries including autophagy signaling, ER stress signaling, and nutrient sensing to ensure normal hematopoietic development [190,191]. These findings also suggest that the lysosomal retrograde transport of cargos is critical for the regulation of ER stress during mouse hematopoiesis.…”

“…Using homologous recombination to disrupt nearly 500 genes encoding secretion and membrane proteins, it was discovered that the third member in the ENT family (i.e., ENT3) is a crucial player in the development of RBCs in mice (Figure 1; top) [189]. Subsequent studies identified mice deficient for ENT3 that spontaneously developed anemia beginning at approximately 8 weeks, reaching severe mortality rates at approximately 18-20 weeks due to bone marrow failure [190,191]. Interestingly, an increasing number of human genetic disorders are being attributed to mutations in the human SLC29A3 gene (encodes ENT3) with anemia, bone marrow failure, and hepatosplenomegaly as common accompanying features.…”

“…Despite significant advances in ENT3 regulation of adult stem cell and blood tissue homeostasis, unfortunately, the loss of ENT3 transport of nucleosides alone could not fully explain the hematological pathologies in Slc29a3 KO mice. Moreover, HSC transplantation in Slc29a3-null mice increased survivability with notable improvement in health, whereas treatment with synthetic adenosine analogs (e.g., AICAR) resulted in only a partial recovery of ENT3 dysfunctions, including anemia, in Slc29a3 KO mice [190]. Transplantation of HSCs may be useful for treating ENT3 disorders; however, further studies are warranted to precisely understand the role of ENT3 in hematological toxicities and the molecular basis of dysfunctions in ENT3 spectrum disorders.…”