Identification of a novel putative mitochondrial protein FAM210B associated with erythroid differentiation

FAM210B regulates iron homeostasis and sex-specific responses in stress erythropoiesis

Iron is required for redox homeostasis but poses toxicity risks due to its redox activity. Erythropoiesis hence requires tight regulation of iron utilization for hemoglobin synthesis. The requirement for iron in erythropoiesis has necessitated the evolution of mechanisms to handle the iron required for hemoglobinization. FAM210B was identified as a regulator of mitochondrial iron import and heme synthesis in erythroid cell culture and zebrafish models. Here, we demonstrate that although FAM210B is required for erythroid differentiation and heme synthesis under standard cell culture conditions, holotransferrin supplementation was sufficient to chemically complement the iron-deficient phenotype. To investigate the role of FAM210B in erythropoiesis, we used knockout mice. Although Fam210b-/- mice were viable and did not exhibit overt erythropoietic defects in the bone marrow, the male mice exhibited an increase in serum transferrin, suggesting sex-specific alterations in systemic iron sensing. On phlebotomy-induced stress erythropoiesis, Fam210b-/- mice exhibited differences in serum transferrin levels, and more starkly, had markedly smaller spleens, indicating defects in stress response. Fam210b-/- males had defects in neutrophil and monocyte numbers, as well as decreased erythroid progenitor numbers during erythropoietic stress. Together, our findings show that Fam210b plays a key role in the splenic response to erythropoietic stress. Our findings reveal a critical role for FAM210B in mediating splenic stress erythropoiesis and suggest it may act as a sex-specific regulator, potentially linked to androgen signaling.

Research on iron regulatory erythroid factors in children with β-thalassemia

To investigate the differences in relative mRNA expression levels of the novel iron regulatory erythroid factors FAM210B, CCDC115, HO-1, PCBP1, PCBP2, NCOA4, and Nrf2 in children with β-thalassemia major (β-TM) before and after transfusion therapy. A total of 98 children with transfusion-dependent β-thalassemia were recruited from the First Affiliated Hospital of Guangxi Medical University between October 2022 and May 2023. The children were classified based on their hemoglobin (Hb) levels: 57 cases with Hb ≤ 90 g/L and 41 cases with Hb > 90 g/L. Real-time fluorescence quantitative PCR was employed to assess the relative mRNA expression between the groups. The mRNA expression levels of FAM210B, HO-1, and NCOA4 were significantly higher in the Hb ≤ 90 g/L group compared to the Hb > 90 g/L group (p < 0.05). Moreover, higher relative expression levels of FAM210B and NCOA4 correlated with an increased likelihood of requiring blood transfusions in β-TM children. The differences in the remaining factors did not reach statistical significance. FAM210B and NCOA4 may serve as indicators of erythropoiesis and the degree of anemia in children with β-TM. Further research is warranted to explore their potential as therapeutic targets for β-thalassemia and other erythropoietic disorders.

FAM210B activates STAT1/IRF9/IFIT3 axis by upregulating IFN-α/β expression to impede the progression of lung adenocarcinoma

FAM210B (family with sequence similarity 210 member B) is a novel protein that has been linked to tumor development. However, its role and underlying mechanisms in lung adenocarcinoma (LUAD) progression remain largely unexplored. In this study, FAM210B was observed to be down-regulated in LUAD cells. Analyses of public datasets revealed that decreased expression of FAM210B predicts poor survival. Accordingly, in vitro and in vivo studies have confirmed the inhibitory role of FAM210B on the growth and tumor metastasis of LUAD cells. RNA-seq analysis further indicated that FAM210B plays a role in regulating innate immune-related signaling pathways in LUAD cells, particularly involving the production of type I interferon (IFN-α/β). Specifically, FAM210B activates STAT1/IRF9/IFIT3 axis by upregulating IFN-α/β expression, leading to the inhibition of proliferation and migration of LUAD cells. Furthermore, TOM70 (Translocase of outer mitochondrial membrane 70, also named as TOMM70) has been identified as a functional interacting partner of FAM210B in its modulation on the expression of IFN-α/β, as well as the proliferative and metastatic phenotypes of LUAD cells. In conclusion, our study indicates that FAM210B is an important suppressor of cellular viability and mobility during lung cancer progression.

Deletion of the Mitochondrial Membrane Protein Fam210b Is Associated with the Development of Systemic Lupus Erythematosus

Mitochondrial dysfunction has been increasingly recognized as a trigger for systemic lupus erythematosus (SLE). Recent bioinformatics studies have suggested Fam210b as a significant candidate for the classification and therapeutic targeting of SLE. To experimentally prove the role of Fam210b in SLE, we constructed Fam210b knockout (Fam210b-/-) mice using the CRISPR-Cas9 method. We found that approximately 15.68% of Fam210b-/- mice spontaneously developed lupus-like autoimmunity, which was characterized by skin ulcerations, splenomegaly, and an increase in anti-double-stranded DNA (anti-dsDNA) IgG antibodies and anti-nuclear antibodies(ANA). Single-cell sequencing showed that Fam210b was mainly expressed in erythroid cells. Critically, the knockout of Fam210b resulted in abnormal erythrocyte differentiation and development in the spleens of mice. Concurrently, the spleens exhibited an increased number of CD71+ erythroid cells, along with elevated levels of reactive oxygen species (ROS) in the erythrocytes. The co-culture of CD71+ erythroid cells and lymphocytes resulted in lymphocyte activation and promoted dsDNA and IgG production. In summary, Fam210b knockout leads to a low probability of lupus-like symptoms in mice through the overproduction of ROS in CD71+ erythroid cells. Thus, Fam210b reduction may serve as a novel key marker that triggers the development of SLE.

Mendelian randomization study on causal association of FAM210B with drug-induced lupus

OBJECTIVE

Due to the complexity of drug-induced lupus (DIL) pathogenesis, more susceptibility factors need to be discovered. FAM210B is a new mitochondrial protein whose function has not been fully elucidated. This study will explore whether there is a correlation between FAM210B and the risk of DIL.

METHODS

At first, we extracted three FAM210B genetic variants from the GTEx database (n = 948), and extracted their corresponding genome-wide association study (GWAS) summary statistics from DIL (101 DIL cases and 218691 controls). Then, we performed a Mendelian randomization (MR) study to evaluate the causal association of the expression of FAM210B with DIL using inverse-variance weighted (IVW), the weighted median, MR-Egger, and MR-PRESSO test.

RESULTS

We successfully extracted three FAM210B single-nucleotide polymorphisms (SNPs) (rs116032784, rs34361943 and rs33923703) from the GTEx_Analysis_v8_eQTL data that can reduce FAM210B expression. The results of the MR analysis showed that genetically reduced expression of FAM210B was significantly associated with increased risk of DIL in European ancestry based on the IVW method (β = 1.037, p = 0.001, odds ratio [OR] = 2.821, 95% confidence interval [CI]:1.495-5.322).

CONCLUSION

MR analysis showed a causal relationship between FAM210B expression and the risk of DIL disease. Our results suggested that FAM210B may be a marker that can mark susceptibility of DIL in the future. It provides evidence for the study of DIL, but its specific mechanism of action in DIL needs to be further studied. Key Points •This is the first MR analysis to examine the association between FAM210B and DIL. •The findings of this study suggested that reduced FAM210B expression is associated with the increased risk of DIL. •FAM210B may be a marker that can mark susceptibility of DIL in the future.

Maternal PM2.5 exposure is associated with preterm birth and gestational diabetes mellitus, and mitochondrial OXPHOS dysfunction in cord blood

Maternal exposure to fine particulate matter (PM2.5) is associated with adverse pregnancy and neonatal health outcomes. To explore the mechanism, we performed mRNA sequencing of neonatal cord blood. From an ongoing prospective cohort, Air Pollution on Pregnancy Outcome (APPO) study, 454 pregnant women from six centers between January 2021 and June 2022 were recruited. Individual PM2.5 exposure was calculated using a time-weighted average model. In the APPO study, age-matched cord blood samples from the High PM2.5 (˃15 ug/m3; n = 10) and Low PM2.5 (≤ 15 ug/m3; n = 30) groups were randomly selected for mRNA sequencing. After selecting genes with differential expression in the two groups (p-value < 0.05 and log2 fold change > 1.5), pathway enrichment analysis was performed, and the mitochondrial pathway was analyzed using MitoCarta3.0. The risk of preterm birth (PTB) increased with every 5 µg/m3 increase of PM2.5 in the second trimester (odds ratio 1.391, p = 0.019) after adjusting for confounding variables. The risk of gestational diabetes mellitus (GDM) increased in the second (odds ratio 1.238, p = 0.041) and third trimester (odds ratio 1.290, p = 0.029), and entire pregnancy (odds ratio 1.295, p = 0.029). The mRNA-sequencing of cord blood showed that genes related to mitochondrial activity (FAM210B, KRT1, FOXO4, TRIM58, and FBXO7) and PTB-related genes (ADIPOR1, YBX1, OPTN, NFkB1, HBG2) were upregulated in the High PM2.5 group. In addition, exposure to high PM2.5 affected mitochondrial oxidative phosphorylation (OXPHOS) and proteins in the electron transport chain, a subunit of OXPHOS. These results suggest that exposure to high PM2.5 during pregnancy may increase the risk of PTB and GDM, and dysregulate PTB-related genes. Alterations in mitochondrial OXPHOS by high PM2.5 exposure may occur not only in preterm infants but also in normal newborns. Further studies with larger sample sizes are required.

Targeting Aggressive B-cell Lymphomas through Pharmacological Activation of the Mitochondrial Protease OMA1

DLBCL are aggressive, rapidly proliferating tumors that critically depend on the ATF4-mediated integrated stress response (ISR) to adapt to stress caused by uncontrolled growth, such as hypoxia, amino acid deprivation, and accumulation of misfolded proteins. Here, we show that ISR hyperactivation is a targetable liability in DLBCL. We describe a novel class of compounds represented by BTM-3528 and BTM-3566, which activate the ISR through the mitochondrial protease OMA1. Treatment of tumor cells with compound leads to OMA1-dependent cleavage of DELE1 and OPA1, mitochondrial fragmentation, activation of the eIF2α-kinase HRI, cell growth arrest, and apoptosis. Activation of OMA1 by BTM-3528 and BTM-3566 is mechanistically distinct from inhibitors of mitochondrial electron transport, as the compounds induce OMA1 activity in the absence of acute changes in respiration. We further identify the mitochondrial protein FAM210B as a negative regulator of BTM-3528 and BTM-3566 activity. Overexpression of FAM210B prevents both OMA1 activation and apoptosis. Notably, FAM210B expression is nearly absent in healthy germinal center B-lymphocytes and in derived B-cell malignancies, revealing a fundamental molecular vulnerability which is targeted by BTM compounds. Both compounds induce rapid apoptosis across diverse DLBCL lines derived from activated B-cell, germinal center B-cell, and MYC-rearranged lymphomas. Once-daily oral dosing of BTM-3566 resulted in complete regression of xenografted human DLBCL SU-DHL-10 cells and complete regression in 6 of 9 DLBCL patient-derived xenografts. BTM-3566 represents a first-of-its kind approach of selectively hyperactivating the mitochondrial ISR for treating DLBCL.

FAM210B is dispensable for erythroid differentiation in adult mice

Iron plays a central role in cellular redox processes, but its ability to adopt multiple oxidation states also enables it to catalyze deleterious reactions. The requirement for iron in erythropoiesis has necessitated the evolution of mechanisms with which to handle the iron required for hemoglobinization. FAM210B was identified as a regulator of mitochondrial iron import and heme synthesis in erythroid cell culture and zebrafish models. In this manuscript, we demonstrate that while FAM210B is required for erythroid differentiation and heme synthesis under standard cell culture conditions, holotransferrin supplementation was sufficient to chemically complement the iron-deficient phenotype. As the biology of FAM210B is complex and context specific, and whole-organism studies on FAM210 proteins have been limited, we sought to unravel the role of FAM210B in erythropoiesis using knockout mice. We were surprised to discover that Fam210b -/- mice were viable and the adults did not have erythropoietic defects in the bone marrow. In contrast to studies in C. elegans, Fam210b -/- mice were also fertile. There were some modest phenotypes, such as a slight increase in lymphocytes and white cell count in Fam210b -/- females, as well as an increase in body weight in Fam210b -/- males. However, our findings suggest that FAM210B may play a more important role in cellular iron homeostasis under iron deficient conditions. Here, we will discuss the cell culture conditions used in iron metabolism studies that can account for the disparate finding on FAM210B function. Moving forward, resolving these discrepancies will be important in identifying novel iron homeostasis genes.

Loss of the Novel Mitochondrial Membrane Protein FAM210B Is Associated with Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is an aggressive and challenging disease to treat. Due to the lack of effective early diagnosis and therapy for the illness, it is crucial to identify novel biomarkers that can predict tumor behavior in HCC. In such cases, family with sequence similarity 210 member B (FAM210B) is abundant in various human tissues, but its regulatory mechanisms and role in various tissues remain unclear. In this study, we analyzed the expression pattern of FAM210B in HCC using public gene expression databases and clinical tissue samples. Our results confirmed that FAM210B was dysregulated in both HCC cell lines and HCC paraffin section samples. FAM210B depletion significantly increased the capacity of cells to grow, migrate, and invade in vitro, while overexpression of FAM210B suppressed tumor growth in a xenograft tumor model. Furthermore, we identified FAM210B's involvement in MAPK signaling and p-AKT signaling pathways, both of which are known oncogenic signaling pathways. In summary, our study provides a rational basis for the further investigation of FAM210B as a valuable biological marker for diagnosing and predicting the prognosis of HCC patients.

Elucidation of the Role of FAM210B in Mitochondrial Metabolism and Erythropoiesis

Mitochondria play essential and specific roles during erythroid differentiation. Recently, FAM210B, encoding a mitochondrial inner membrane protein, has been identified as a novel target of GATA-1, as well as an erythropoietin-inducible gene. While FAM210B protein is involved in regulate mitochondrial metabolism and heme biosynthesis, its detailed function remains unknown. Here, we generated both knockout and knockdown of endogenous FAM210B in human induced pluripotent stem-derived erythroid progenitor (HiDEP) cells using CRISPR/Cas9 methodology. Intriguingly, erythroid differentiation was more pronounced in the FAM210B-depleted cells, and this resulted in increased frequency of orthochromatic erythroblasts and decreased frequencies of basophilic/polychromatic erythroblasts. Comprehensive metabolite analysis and functional analysis indicated that oxygen consumption rates and the NAD (NAD⁺)/NADH ratio were significantly decreased, while lactate production was significantly increased in FAM210B deletion HiDEP cells, indicating involvement of FAM210B in mitochondrial energy metabolism in erythroblasts. Finally, we purified FAM210B-interacting protein from K562 cells that stably expressed His/biotin-tagged FAM210B. Mass spectrometry analysis of the His/biotin-purified material indicated interactions with multiple subunits of mitochondrial ATP synthases, such as subunit alpha (ATP5A) and beta (ATP5B). Our results suggested that FAM210B contributes prominently to erythroid differentiation by regulating mitochondrial energy metabolism. Our results provide insights into the pathophysiology of dysregulated hematopoiesis.

Regulation of Heme Synthesis by Mitochondrial Homeostasis Proteins

Heme plays a central role in diverse, life-essential processes that range from ubiquitous, housekeeping pathways such as respiration, to highly cell-specific ones such as oxygen transport by hemoglobin. The regulation of heme synthesis and its utilization is highly regulated and cell-specific. In this review, we have attempted to describe how the heme synthesis machinery is regulated by mitochondrial homeostasis as a means of coupling heme synthesis to its utilization and to the metabolic requirements of the cell. We have focused on discussing the regulation of mitochondrial heme synthesis enzymes by housekeeping proteins, transport of heme intermediates, and regulation of heme synthesis by macromolecular complex formation and mitochondrial metabolism. Recently discovered mechanisms are discussed in the context of the model organisms in which they were identified, while more established work is discussed in light of technological advancements.

Coordinated changes in gene expression kinetics underlie both mouse and human erythroid maturation

BACKGROUND

Single-cell technologies are transforming biomedical research, including the recent demonstration that unspliced pre-mRNA present in single-cell RNA-Seq permits prediction of future expression states. Here we apply this RNA velocity concept to an extended timecourse dataset covering mouse gastrulation and early organogenesis.

RESULTS

Intriguingly, RNA velocity correctly identifies epiblast cells as the starting point, but several trajectory predictions at later stages are inconsistent with both real-time ordering and existing knowledge. The most striking discrepancy concerns red blood cell maturation, with velocity-inferred trajectories opposing the true differentiation path. Investigating the underlying causes reveals a group of genes with a coordinated step-change in transcription, thus violating the assumptions behind current velocity analysis suites, which do not accommodate time-dependent changes in expression dynamics. Using scRNA-Seq analysis of chimeric mouse embryos lacking the major erythroid regulator Gata1, we show that genes with the step-changes in expression dynamics during erythroid differentiation fail to be upregulated in the mutant cells, thus underscoring the coordination of modulating transcription rate along a differentiation trajectory. In addition to the expected block in erythroid maturation, the Gata1-chimera dataset reveals induction of PU.1 and expansion of megakaryocyte progenitors. Finally, we show that erythropoiesis in human fetal liver is similarly characterized by a coordinated step-change in gene expression.

CONCLUSIONS

By identifying a limitation of the current velocity framework coupled with in vivo analysis of mutant cells, we reveal a coordinated step-change in gene expression kinetics during erythropoiesis, with likely implications for many other differentiation processes.

Caenorhabditis elegans homologue of Fam210 is required for oogenesis and reproduction

Mitochondria are the central hub for many metabolic processes, including the citric acid cycle, oxidative phosphorylation, and fatty acid oxidation. Recent studies have identified a new mitochondrial protein family, Fam210, that regulates bone metabolism and red cell development in vertebrates. The model organism Caenorhabditis elegans has a Fam210 gene, y56a3a.22, but it lacks both bones and red blood cells. In this study, we report that Y56A3A.22 plays a crucial role in regulating mitochondrial protein homeostasis and reproduction. The nematode y56a3a.22 is expressed in various tissues, including the intestine, muscle, hypodermis, and germline, and its encoded protein is predominantly localized in mitochondria. y56a3a.22 deletion mutants are sterile owing to impaired oogenesis. Loss of Y56A3A.22 induced mitochondrial unfolded protein response (UPR^mt), which is mediated through the ATFS-1-dependent pathway, in tissues such as the intestine, germline, hypodermis, and vulval muscle. We further show that infertility and UPR^mt induces by Y56A3A.22 deficiency are not attributed to systemic iron deficiency. Together, our study reveals an important role of Y56A3A.22 in regulating mitochondrial protein homeostasis and oogenesis and provides a new genetic tool for exploring the mechanisms regulating mitochondrial metabolism and reproduction as well as the fundamental role of the Fam210 family.

Generation and Molecular Characterization of Human Ring Sideroblasts: a Key Role of Ferrous Iron in Terminal Erythroid Differentiation and Ring Sideroblast Formation

Ring sideroblasts are a hallmark of sideroblastic anemia, although little is known about their characteristics. Here, we first generated mutant mice by disrupting the GATA-1 binding motif at the intron 1 enhancer of the ALAS2 gene, a gene responsible for X-linked sideroblastic anemia (XLSA). Although heterozygous female mice showed an anemic phenotype, ring sideroblasts were not observed in their bone marrow. We next established human induced pluripotent stem cell-derived proerythroblast clones harboring the same ALAS2 gene mutation. Through coculture with sodium ferrous citrate, mutant clones differentiated into mature erythroblasts and became ring sideroblasts with upregulation of metal transporters (MFRN1, ZIP8, and DMT1), suggesting a key role for ferrous iron in erythroid differentiation. Interestingly, holo-transferrin (holo-Tf) did not induce erythroid differentiation as well as ring sideroblast formation, and mutant cells underwent apoptosis. Despite massive iron granule content, ring sideroblasts were less apoptotic than holo-Tf-treated undifferentiated cells. Microarray analysis revealed upregulation of antiapoptotic genes in ring sideroblasts, a profile partly shared with erythroblasts from a patient with XLSA. These results suggest that ring sideroblasts exert a reaction to avoid cell death by activating antiapoptotic programs. Our model may become an important tool to clarify the pathophysiology of sideroblastic anemia.

FAM210B is an erythropoietin target and regulates erythroid heme synthesis by controlling mitochondrial iron import and ferrochelatase activity

Erythropoietin (EPO) signaling is critical to many processes essential to terminal erythropoiesis. Despite the centrality of iron metabolism to erythropoiesis, the mechanisms by which EPO regulates iron status are not well-understood. To this end, here we profiled gene expression in EPO-treated 32D pro-B cells and developing fetal liver erythroid cells to identify additional iron regulatory genes. We determined that FAM210B, a mitochondrial inner-membrane protein, is essential for hemoglobinization, proliferation, and enucleation during terminal erythroid maturation. Fam210b deficiency led to defects in mitochondrial iron uptake, heme synthesis, and iron-sulfur cluster formation. These defects were corrected with a lipid-soluble, small-molecule iron transporter, hinokitiol, in Fam210b-deficient murine erythroid cells and zebrafish morphants. Genetic complementation experiments revealed that FAM210B is not a mitochondrial iron transporter but is required for adequate mitochondrial iron import to sustain heme synthesis and iron-sulfur cluster formation during erythroid differentiation. FAM210B was also required for maximal ferrochelatase activity in differentiating erythroid cells. We propose that FAM210B functions as an adaptor protein that facilitates the formation of an oligomeric mitochondrial iron transport complex, required for the increase in iron acquisition for heme synthesis during terminal erythropoiesis. Collectively, our results reveal a critical mechanism by which EPO signaling regulates terminal erythropoiesis and iron metabolism.

Effects of in vivo deletion of GATA2 in bone marrow stromal cells

The bone marrow (BM) microenvironment comprises multiple stem cell niches derived from BM mesenchymal stem cells (MSCs). Previous in vitro analyses have suggested that transcription factor GATA2 plays an important role in adipocyte differentiation of BM-MSCs and in hematopoietic support, but the role of GATA2 in vivo remains unknown. We evaluated GATA2 effects in BM-MSCs in vivo. Expression profiling analysis of Gata2-knockout Ter119^-CD45^- mesenchymal stromal cells obtained from compact bone from tamoxifen-treated Gata2 conditional knockout mice (Gata2^f/f/ER-Cre mice) revealed upregulation of 110 genes and downregulation of 141 genes by a factor of 2. Moreover, gene ontology analysis revealed significant enrichment of genes involved in cell adhesion and chemotaxis. We did not find any phenotypic changes when Gata2 was deleted with BM-MSC-related gene promoters, such as Nestin, Prx1, and Lepr, except for a significant decrease in the colony number of Gata2^f/f/Prx1-Cre mice. There was a significant decrease in the percentage of the common myeloid progenitor fraction when Gata2 was deleted in all BM cells, except hematopoietic cells after normal BM cells were transplanted into irradiated Gata2^f/f/ER-Cre mice with Gata2 subsequently knocked out by tamoxifen administration. In conclusion, GATA2 could affect the function of BM-MSCs in vivo, presumably by regulating the expression of extracellular signals.

Loss of the novel mitochondrial protein FAM210B promotes metastasis via PDK4-dependent metabolic reprogramming

Recent advances in tumor metabolism have revealed that metabolic reprogramming could dramatically promote caner metastasis. However, the relation and mechanism between metastasis and metabolic reprogramming are not thoroughly explored. Cell proliferation, colony formation, and invasion analysis were performed to evaluate the role of FAM210B in human cancer cells. Human ovarian cancer xenograft model was used to determine the effects of inhibiting FAM210B by shRNA on tumor metastasis. Microarray analysis was used to determine the target genes of FAM210B. FAM210B cellular localization was performed by mitochondria isolation and mitochondria protein extraction. To detect FAM210B-mediated metabolic reprogramming, oxygen consumption rate and extracellular acidification rate were measured. Our previous study screened a novel cancer progression-suppressor gene, FAM210B, which encodes an outer mitochondrial membrane protein, by the suppression of mortality by antisense rescue technique (SMART). Here we demonstrated that FAM210B loss was significantly associated with cancer metastasis and decreased survival in a clinical setting. Additionally, it was found that low expression of FAM210B was significantly correlated with decreased survival and enhanced metastasis in vivo and in vitro, and the loss of FAM210B led to an increased mitochondrial respiratory capacity and reduced glycolysis through the downregulation of pyruvate dehydrogenase kinase 4 (PDK4), which activated the EMT program and enhanced migratory and invasive properties. Collectively, our data unveil a potential metabolic target and mechanism of cancer metastasis.