Mutations in the iron-sulfur cluster biogenesis protein HSCB cause congenital sideroblastic anemia

Murine models of erythroid 5ALA synthesis disorders and their conditional synthetic lethal dependency on pyridoxine

ABSTRACT

X-linked sideroblastic anemia (XLSA) and X-linked protoporphyria (XLPP) are uncommon diseases caused by loss-of-function and gain-of-function mutations, respectively, in the erythroid form of 5-aminolevulinic acid synthetase (ALAS), ALAS2, which encodes the first enzyme in heme biosynthesis. A related congenital sideroblastic anemia (CSA) is due to mutations in SLC25A38 (solute carrier family 25 member A38), which supplies mitochondrial glycine for ALAS2 (SLC25A38-CSA). The lack of viable animal models has limited the studies on pathophysiology and development of therapies for these conditions. Here, using CRISPR-CAS9 gene editing technology, we have generated knockin mouse models that recapitulate the main features of XLSA and XLPP; and using conventional conditional gene targeting in embryonic stem cells, we also developed a faithful model of the SLC25A38-CSA. In addition to examining the phenotypes and natural history of each disease, we determine the effect of restriction or supplementation of dietary pyridoxine (vitamin B6), the essential cofactor of ALAS2, on the anemia and porphyria. In addition to the well-documented response of XLSA mutations to pyridoxine supplementation, we also demonstrate the relative insensitivity of the XLPP/EPP protoporphyrias, severe sensitivity of the XLSA models, and an extreme hypersensitivity of the SLC25A38-CSA model to pyridoxine deficiency, a phenotype that is not shared with another mouse hereditary anemia model, Hbbth3/+ β-thalassemia intermedia. Thus, in addition to generating animal models useful for examining the pathophysiology and treatment of these diseases, we have uncovered an unsuspected conditional synthetic lethality between the heme synthesis-related CSAs and pyridoxine deficiency. These findings have the potential to inform novel therapeutic paradigms for the treatment of these diseases.

Differentiation and Growth-Arrest-Related lncRNA (DAGAR): Initial Characterization in Human Smooth Muscle and Fibroblast Cells

Vascular smooth muscle cells (SMCs) can transition between a quiescent contractile or "differentiated" phenotype and a "proliferative-dedifferentiated" phenotype in response to environmental cues, similar to what in occurs in the wound healing process observed in fibroblasts. When dysregulated, these processes contribute to the development of various lung and cardiovascular diseases such as Chronic Obstructive Pulmonary Disease (COPD). Long non-coding RNAs (lncRNAs) have emerged as key modulators of SMC differentiation and phenotypic changes. In this study, we examined the expression of lncRNAs in primary human pulmonary artery SMCs (hPASMCs) during cell-to-cell contact-induced SMC differentiation. We discovered a novel lncRNA, which we named Differentiation And Growth Arrest-Related lncRNA (DAGAR) that was significantly upregulated in the quiescent phenotype with respect to proliferative SMCs and in cell-cycle-arrested MRC5 lung fibroblasts. We demonstrated that DAGAR expression is essential for SMC quiescence and its knockdown hinders SMC differentiation. The treatment of quiescent SMCs with the pro-inflammatory cytokine Tumor Necrosis Factor (TNF), a known inducer of SMC dedifferentiation and proliferation, elicited DAGAR downregulation. Consistent with this, we observed diminished DAGAR expression in pulmonary arteries from COPD patients compared to non-smoker controls. Through pulldown experiments followed by mass spectrometry analysis, we identified several proteins that interact with DAGAR that are related to cell differentiation, the cell cycle, cytoskeleton organization, iron metabolism, and the N-6-Methyladenosine (m6A) machinery. In conclusion, our findings highlight DAGAR as a novel lncRNA that plays a crucial role in the regulation of cell proliferation and SMC differentiation. This paper underscores the potential significance of DAGAR in SMC and fibroblast physiology in health and disease.

PI3K/HSCB axis facilitates FOG1 nuclear translocation to promote erythropoiesis and megakaryopoiesis

Erythropoiesis and megakaryopoiesis are stringently regulated by signaling pathways. However, the precise molecular mechanisms through which signaling pathways regulate key transcription factors controlling erythropoiesis and megakaryopoiesis remain partially understood. Herein, we identified heat shock cognate B (HSCB), which is well known for its iron-sulfur cluster delivery function, as an indispensable protein for friend of GATA 1 (FOG1) nuclear translocation during erythropoiesis of K562 human erythroleukemia cells and cord-blood-derived human CD34+CD90+hematopoietic stem cells (HSCs), as well as during megakaryopoiesis of the CD34+CD90+HSCs. Mechanistically, HSCB could be phosphorylated by phosphoinositol-3-kinase (PI3K) to bind with and mediate the proteasomal degradation of transforming acidic coiled-coil containing protein 3 (TACC3), which otherwise detained FOG1 in the cytoplasm, thereby facilitating FOG1 nuclear translocation. Given that PI3K is activated during both erythropoiesis and megakaryopoiesis, and that FOG1 is a key transcription factor for these processes, our findings elucidate an important, previously unrecognized iron-sulfur cluster delivery independent function of HSCB in erythropoiesis and megakaryopoiesis.

Comprehensive Genomic Analysis Identifies a Diverse Landscape of Sideroblastic and Nonsideroblastic Iron-Related Anemias with Novel and Pathogenic Variants in an Iron-Deficient Endemic Setting

Inherited iron metabolism defects are possibly missed or underdiagnosed in iron-deficient endemic settings because of a lack of awareness or a methodical screening approach. Hence, we systematically evaluated anemia cases (2019 to 2021) based on clinical phenotype, normal screening tests (high-performance liquid chromatography, α gene sequencing, erythrocyte sedimentation rate, C-reactive protein, and tissue transglutaminase), and abnormal iron profile by targeted next-generation sequencing (26-gene panel) supplemented with whole-exome sequencing, multiplex ligation probe amplification/mitochondrial DNA sequencing, and chromosomal microarray. Novel variants in ALAS2, STEAP3, and HSPA9 genes were functionally validated. A total of 290 anemia cases were screened, and 41 (14%) enrolled for genomic testing as per inclusion criteria. Comprehensive genomic testing revealed pathogenic variants in 23 of 41 cases (56%). Congenital sideroblastic anemia was the most common diagnosis (14/23; 61%), with pathogenic variations in ALAS2 (n = 6), SLC25A38 (n = 3), HSPA9 (n = 2) and HSCB, SLC19A2, and mitochondrial DNA deletion (n = 1 each). Nonsideroblastic iron defects included STEAP3-related microcytic anemia (2/23; 8.7%) and hypotransferrenemia (1/23; 4.3%). A total of 6 of 22 cases (27%) revealed a non-iron metabolism gene defect on whole-exome sequencing. Eleven novel variants (including variants of uncertain significance) were noted in 13 cases. Genotype-phenotype correlation revealed a significant association of frameshift/nonsense/splice variants with lower presentation age (0.8 months versus 9 years; P < 0.01) compared with missense variants. The systematic evaluation helped uncover an inherited iron defect in 41% (17/41) of cases, suggesting the need for active screening and awareness for these rare diseases in an iron-deficient endemic population.

Environmental cadmium exposure perturbs systemic iron homeostasis via hemolysis and inflammation, leading to hepatic ferroptosis in common carp (Cyprinus carpio L.)

Cadmium (Cd) pollution is considered a pressing challenge to eco-environment and public health worldwide. Although it has been well-documented that Cd exhibits various adverse effects on aquatic animals, it is still largely unknown whether and how Cd at environmentally relevant concentrations affects iron metabolism. Here, we studied the effects of environmental Cd exposure (5 and 50 μg/L) on iron homeostasis and possible mechanisms in common carp. The data revealed that Cd elevated serum iron, transferrin saturation and iron deposition in livers and spleens, leading to the disruption of systemic iron homeostasis. Mechanistic investigations substantiated that Cd drove hemolysis by compromising the osmotic fragility and inducing defective morphology of erythrocytes. Cd concurrently exacerbated hepatic inflammatory responses, resulting in the activation of IL6-Stat3 signaling and subsequent hepcidin transcription. Notably, Cd elicited ferroptosis through increased iron burden and oxidative stress in livers. Taken together, our findings provide evidence and mechanistic insight that environmental Cd exposure could undermine iron homeostasis via erythrotoxicity and hepatotoxicity. Further investigation and ecological risk assessment of Cd and other pollutants on metabolism-related effects is warranted, especially under the realistic exposure scenarios.

Plasma proteomic signature predicts who will get persistent symptoms following SARS-CoV-2 infection

BACKGROUND

The majority of those infected by ancestral Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) during the UK first wave (starting March 2020) did not require hospitalisation. Most had a short-lived mild or asymptomatic infection, while others had symptoms that persisted for weeks or months. We hypothesized that the plasma proteome at the time of first infection would reflect differences in the inflammatory response that linked to symptom severity and duration.

METHODS

We performed a nested longitudinal case-control study and targeted analysis of the plasma proteome of 156 healthcare workers (HCW) with and without lab confirmed SARS-CoV-2 infection. Targeted proteomic multiple-reaction monitoring analysis of 91 pre-selected proteins was undertaken in uninfected healthcare workers at baseline, and in infected healthcare workers serially, from 1 week prior to 6 weeks after their first confirmed SARS-CoV-2 infection. Symptom severity and antibody responses were also tracked. Questionnaires at 6 and 12 months collected data on persistent symptoms.

FINDINGS

Within this cohort (median age 39 years, interquartile range 30-47 years), 54 healthcare workers (44% male) had PCR or antibody confirmed infection, with the remaining 102 (38% male) serving as uninfected controls. Following the first confirmed SARS-CoV-2 infection, perturbation of the plasma proteome persisted for up to 6 weeks, tracking symptom severity and antibody responses. Differentially abundant proteins were mostly coordinated around lipid, atherosclerosis and cholesterol metabolism pathways, complement and coagulation cascades, autophagy, and lysosomal function. The proteomic profile at the time of seroconversion associated with persistent symptoms out to 12 months. Data are available via ProteomeXchange with identifier PXD036590.

INTERPRETATION

Our findings show that non-severe SARS-CoV-2 infection perturbs the plasma proteome for at least 6 weeks. The plasma proteomic signature at the time of seroconversion has the potential to identify which individuals are more likely to suffer from persistent symptoms related to SARS-CoV-2 infection.

FUNDING INFORMATION

The COVIDsortium is supported by funding donated by individuals, charitable Trusts, and corporations including Goldman Sachs, Citadel and Citadel Securities, The Guy Foundation, GW Pharmaceuticals, Kusuma Trust, and Jagclif Charitable Trust, and enabled by Barts Charity with support from University College London Hospitals (UCLH) Charity. This work was additionally supported by the Translational Mass Spectrometry Research Group and the Biomedical Research Center (BRC) at Great Ormond Street Hospital.

Iron Metabolism in the Disorders of Heme Biosynthesis

Given its remarkable property to easily switch between different oxidative states, iron is essential in countless cellular functions which involve redox reactions. At the same time, uncontrolled interactions between iron and its surrounding milieu may be damaging to cells and tissues. Heme—the iron-chelated form of protoporphyrin IX—is a macrocyclic tetrapyrrole and a coordination complex for diatomic gases, accurately engineered by evolution to exploit the catalytic, oxygen-binding, and oxidoreductive properties of iron while minimizing its damaging effects on tissues. The majority of the body production of heme is ultimately incorporated into hemoglobin within mature erythrocytes; thus, regulation of heme biosynthesis by iron is central in erythropoiesis. Additionally, heme is a cofactor in several metabolic pathways, which can be modulated by iron-dependent signals as well. Impairment in some steps of the pathway of heme biosynthesis is the main pathogenetic mechanism of two groups of diseases collectively known as porphyrias and congenital sideroblastic anemias. In porphyrias, according to the specific enzyme involved, heme precursors accumulate up to the enzyme stop in disease-specific patterns and organs. Therefore, different porphyrias manifest themselves under strikingly different clinical pictures. In congenital sideroblastic anemias, instead, an altered utilization of mitochondrial iron by erythroid precursors leads to mitochondrial iron overload and an accumulation of ring sideroblasts in the bone marrow. In line with the complexity of the processes involved, the role of iron in these conditions is then multifarious. This review aims to summarise the most important lines of evidence concerning the interplay between iron and heme metabolism, as well as the clinical and experimental aspects of the role of iron in inherited conditions of altered heme biosynthesis.

Molecular Mechanisms of Iron and Heme Metabolism

An abundant metal in the human body, iron is essential for key biological pathways including oxygen transport, DNA metabolism, and mitochondrial function. Most iron is bound to heme but it can also be incorporated into iron-sulfur clusters or bind directly to proteins. Iron's capacity to cycle between Fe²⁺ and Fe³⁺ contributes to its biological utility but also renders it toxic in excess. Heme is an iron-containing tetrapyrrole essential for diverse biological functions including gas transport and sensing, oxidative metabolism, and xenobiotic detoxification. Like iron, heme is essential yet toxic in excess. As such, both iron and heme homeostasis are tightly regulated. Here we discuss molecular and physiologic aspects of iron and heme metabolism. We focus on dietary absorption; cellular import; utilization; and export, recycling, and elimination, emphasizing studies published in recent years. We end with a discussion on current challenges and needs in the field of iron and heme biology.

When Ring Sideroblasts on Bone Marrow Smears Are Inconsistent with the Diagnosis of Myelodysplastic Neoplasms

Ring sideroblasts are commonly seen in myelodysplastic neoplasms and are a key condition for identifying distinct entities of myelodysplastic neoplasms according to the WHO classification. However, the presence of ring sideroblasts is not exclusive to myelodysplastic neoplasms. Ring sideroblasts are as well either encountered in non-clonal secondary acquired disorders, such as exposure to toxic substances, drug/medicine, copper deficiency, zinc overload, lead poison, or hereditary sideroblastic anemias related to X-linked, autosomal, or mitochondrial mutations. This review article will discuss diseases associated with ring sideroblasts outside the context of myelodysplastic neoplasms. Knowledge of the differential diagnoses characterized by the presence of ring sideroblasts in bone marrow is essential to prevent any misdiagnosis, which leads to delayed diagnosis and subsequent management of patients that differ in the different forms of sideroblastic anemia.

Using the Zebrafish as a Genetic Model to Study Erythropoiesis

Vertebrates generate mature red blood cells (RBCs) via a highly regulated, multistep process called erythropoiesis. Erythropoiesis involves synthesis of heme and hemoglobin, clearance of the nuclei and other organelles, and remodeling of the plasma membrane, and these processes are exquisitely coordinated by specific regulatory factors including transcriptional factors and signaling molecules. Defects in erythropoiesis can lead to blood disorders such as congenital dyserythropoietic anemias, Diamond–Blackfan anemias, sideroblastic anemias, myelodysplastic syndrome, and porphyria. The molecular mechanisms of erythropoiesis are highly conserved between fish and mammals, and the zebrafish (Danio rerio) has provided a powerful genetic model for studying erythropoiesis. Studies in zebrafish have yielded important insights into RBC development and established a number of models for human blood diseases. Here, we focus on latest discoveries of the molecular processes and mechanisms regulating zebrafish erythropoiesis and summarize newly established zebrafish models of human anemias.

Mitochondrial HSP70 Chaperone System-The Influence of Post-Translational Modifications and Involvement in Human Diseases

Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.

Mechanisms of cellular iron sensing, regulation of erythropoiesis and mitochondrial iron utilization

To maintain an adequate iron supply for hemoglobin synthesis and essential metabolic functions while counteracting iron toxicity, humans and other vertebrates have evolved effective mechanisms to conserve and finely regulate iron concentration, storage, and distribution to tissues. At the systemic level, the iron-regulatory hormone hepcidin is secreted by the liver in response to serum iron levels and inflammation. Hepcidin regulates the expression of the sole known mammalian iron exporter, ferroportin, to control dietary absorption, storage and tissue distribution of iron. At the cellular level, iron regulatory proteins 1 and 2 (IRP1 and IRP2) register cytosolic iron concentrations and post-transcriptionally regulate the expression of iron metabolism genes to optimize iron availability for essential cellular processes, including heme biosynthesis and iron-sulfur cluster biogenesis. Genetic malfunctions affecting the iron sensing mechanisms or the main pathways that utilize iron in the cell cause a broad range of human diseases, some of which are characterized by mitochondrial iron accumulation. This review will discuss the mechanisms of systemic and cellular iron sensing with a focus on the main iron utilization pathways in the cell, and on human conditions that arise from compromised function of the regulatory axes that control iron homeostasis.

Mendelian inheritance of anemia due to disturbed iron homeostasis

Genetic disorders that affect proteins involved in maintaining iron balance may lead to Mendelian anemias. They may be classified as defects of intestinal iron absorption, iron transport in the circulation, iron uptake and utilization by maturing erythroid cells, iron recycling by macrophages and systemic regulation of iron homeostasis. All these Mendelian anemias are rare disorders, prevalently recessive, characterized by microcytic and hypochromic red blood cells. Advances in our knowledge of iron metabolism and its systemic regulation on one side have facilitated the identification of novel iron related anemias, while on the other the study of the affected patients and of the corresponding animal models have contributed to our understanding of iron trafficking and regulation.

Myelodysplastic syndromes with ring sideroblasts (MDS-RS) and MDS/myeloproliferative neoplasm with RS and thrombocytosis (MDS/MPN-RS-T) - "2021 update on diagnosis, risk-stratification, and management"

DISEASE OVERVIEW

Ring sideroblasts (RS) are erythroid precursors with abnormal perinuclear mitochondrial iron accumulation. Two myeloid neoplasms defined by the presence of RS, include myelodysplastic syndromes with RS (MDS-RS) and MDS/myeloproliferative neoplasm with RS and thrombocytosis (MDS/MPN-RS-T).

DIAGNOSIS

MDS-RS is a lower risk MDS, with single or multilineage dysplasia (MDS-RS-SLD/MLD), <5% bone marrow (BM) blasts, <1% peripheral blood blasts and ≥15% BM RS (≥5% in the presence of SF3B1 mutations). MDS/MPN-RS-T, now a formal entity in the MDS/MPN overlap syndromes, has diagnostic features of MDS-RS-SLD, along with a platelet count ≥450 × 10⁹ /L and large atypical megakaryocytes.

MUTATIONS AND KARYOTYPE

Mutations in SF3B1 are seen in ≥80% of patients with MDS-RS-SLD and MDS/MPN-RS-T, and strongly correlate with the presence of BM RS; MDS/MPN-RS-T patients also demonstrate JAK2V617F (50%), DNMT3A, TET2 and ASXL1 mutations. Cytogenetic abnormalities are uncommon in both.

RISK STRATIFICATION

Most patients with MDS-RS-SLD are stratified into lower risk groups by the revised-IPSS. Disease outcome in MDS/MPN-RS-T is better than that of MDS-RS-SLD, but worse than that of essential thrombocythemia (MPN). Both diseases are associated with a low risk of leukemic transformation.

TREATMENT

Anemia and iron overload are complications seen in both and are managed similar to lower risk MDS and MPN. Luspatercept, a first-in-class erythroid maturation agent is now approved for the management of anemia in patients with MDS-RS and MDS/MPN-RS-T. Aspirin therapy is reasonable in MDS/MPN-RS-T, especially in the presence of JAK2V617F, but the value of platelet-lowering drugs remains to be defined.