Mysm1 is required for interferon regulatory factor expression in maintaining HSC quiescence and thymocyte development

Deubiquitinase MYSM1 promotes doxorubicin-induced cardiotoxicity by mediating TRIM21-ferroptosis axis in cardiomyocytes

Anthracycline antitumor drug doxorubicin (DOX) induces severe cardiotoxicity. Deubiquitinating enzymes (DUBs) are crucial for protein stability and function and play a significant role in cardiac pathophysiology. By comparing RNA sequencing datasets and conducting functional screening, we determined that Myb-like, SWIRM, and MPN domains 1 (MYSM1) is a key regulator of DOX-induced cardiotoxicity. In this study, we aimed to explore the function and regulatory mechanisms of MYSM1 in DOX-induced cardiotoxicity. Genetic knockdown of MYSM1 significantly mitigated DOX-induced cardiomyopathy. Correspondingly, cardiomyocyte-specific knockdown of MYSM1 by AAV9 protected the heart from DOX-induced cardiotoxicity. Gain- and loss-of-function analysis verified that MYSM1 mediated DOX-induced cardiomyocyte injury in vitro. Through a Co-IP combined with LC-MS/MS analysis, we discovered that MYSM1 directly interacted with tripartite motif-containing protein 21 (TRIM21). Mechanistic investigations revealed that MYSM1 regulates the deubiquitination and the stability of TRIM21 via its MPN domain. Furthermore, MYSM1 exacerbated DOX-induced cardiotoxicity by enhancing ferroptosis. This study identified MYSM1 as a potential therapeutic target for DOX-induced cardiotoxicity and illustrated a MYSM1-TRIM21-ferroptosis axis in regulating DOX-induced cardiotoxicity.

Deubiquitinase MYSM1: An Important Tissue Development and Function Regulator

MYSM1, a deubiquitinating enzyme, plays a pivotal role in diverse biological processes. Both MYSM1 knockout mice and patients with Mysm1 gene mutations exhibit developmental abnormalities across multiple tissues and organs. Serving as a crucial regulator, MYSM1 influences stem cell function, immune responses, and the pathogenesis of diverse diseases. This review comprehensively details MYSM1's deubiquitinating activities in both the nucleus and cytoplasmic compartments, its effects on stem cell proliferation, differentiation, and immune cell function, and its involvement in cancer, aging, and depression. The high sequence homology between murine and human MYSM1, along with similar phenotypes observed in Mysm1-deficient models, provides valuable insights into the etiology of human Mysm1-deficiency syndromes. This review aims to offer a foundation for future comprehensive research on MYSM1.

Deubiquitinase Mysm1 regulates neural stem cell proliferation and differentiation by controlling Id4 expression

Neural stem cells (NSCs) are critical for brain development and maintenance of neurogenesis. However, the molecular mechanisms that regulate NSC proliferation and differentiation remain unclear. Mysm1 is a deubiquitinase and is essential for the self-renewal and differentiation of several stem cells. It is unknown whether Mysm1 plays an important role in NSCs. Here, we found that Mysm1 was expressed in NSCs and its expression was increased with age in mice. Mice with Mysm1 knockdown by crossing Mysm1 floxed mice with Nestin-Cre mice exhibited abnormal brain development with microcephaly. Mysm1 deletion promoted NSC proliferation and apoptosis, resulting in depletion of the stem cell pool. In addition, Mysm1-deficient NSCs skewed toward neurogenesis instead of astrogliogenesis. Mechanistic investigations with RNA sequencing and genome-wide CUT&Tag analysis revealed that Mysm1 epigenetically regulated Id4 transcription by regulating histone modification at the promoter region. After rescuing the expression of Id4, the hyperproliferation and imbalance differentiation of Mysm1-deficient NSCs was reversed. Additionally, knockdown Mysm1 in aged mice could promote NSC proliferation. Collectively, the present study identified a new factor Mysm1 which is essential for NSC homeostasis and Mysm1-Id4 axis may be an ideal target for proper NSC proliferation and differentiation.

Late fetal hematopoietic failure results from ZBTB11 deficiency despite abundant HSC specification

Hematopoiesis produces diverse blood cell lineages to meet the basal needs and sudden demands of injury or infection. A rapid response to such challenges requires the expansion of specific lineages and a prompt return to balanced steady-state levels, necessitating tightly coordinated regulation. Previously we identified a requirement for the zinc finger and broad complex, tramtrak, bric-a-brac domain-containing 11 (ZBTB11) transcription factor in definitive hematopoiesis using a forward genetic screen for zebrafish myeloid mutants. To understand its relevance to mammalian systems, we extended these studies to mice. When Zbtb11 was deleted in the hematopoietic compartment, embryos died at embryonic day (E) 18.5 with hematopoietic failure. Zbtb11 hematopoietic knockout (Zbtb11hKO) hematopoietic stem cells (HSCs) were overabundantly specified from E14.5 to E17.5 compared with those in controls. Overspecification was accompanied by loss of stemness, inability to differentiate into committed progenitors and mature lineages in the fetal liver, failure to seed fetal bone marrow, and total hematopoietic failure. The Zbtb11hKO HSCs did not proliferate in vitro and were constrained in cell cycle progression, demonstrating the cell-intrinsic role of Zbtb11 in proliferation and cell cycle regulation in mammalian HSCs. Single-cell RNA sequencing analysis identified that Zbtb11-deficient HSCs were underrepresented in an erythroid-primed subpopulation and showed downregulation of oxidative phosphorylation pathways and dysregulation of genes associated with the hematopoietic niche. We identified a cell-intrinsic requirement for Zbtb11-mediated gene regulatory networks in sustaining a pool of maturation-capable HSCs and progenitor cells.

Familial immune-mediated aplastic anaemia in six different families

We studied the pathophysiology of aplastic anaemia (AA) in six different pairs of relatives without a family history of hematologic disorders or congenital AA. Five and four of the six pairs shared the HLA-DRB1*15:01 and B*40:02 alleles, respectively. Glycosylphosphatidylinositol-anchored protein-deficient blood cells were detected in eight of the 10 patients evaluated. In a mother-daughter pair from one family, flow cytometry detected leukocytes lacking HLA-A2 due to loss of heterogeneity in chromosome 6p. Whole-exome sequencing of the family pair revealed a missense mutation in MYSM1. These results suggest that genetic inheritance of immune traits might underlie familial AA in some patients.

Human hematopoietic stem cell vulnerability to ferroptosis

Hematopoietic stem cells (HSCs) have a number of unique physiologic adaptations that enable lifelong maintenance of blood cell production, including a highly regulated rate of protein synthesis. Yet, the precise vulnerabilities that arise from such adaptations have not been fully characterized. Here, inspired by a bone marrow failure disorder due to the loss of the histone deubiquitinase MYSM1, characterized by selectively disadvantaged HSCs, we show how reduced protein synthesis in HSCs results in increased ferroptosis. HSC maintenance can be fully rescued by blocking ferroptosis, despite no alteration in protein synthesis rates. Importantly, this selective vulnerability to ferroptosis not only underlies HSC loss in MYSM1 deficiency but also characterizes a broader liability of human HSCs. Increasing protein synthesis rates via MYSM1 overexpression makes HSCs less susceptible to ferroptosis, more broadly illustrating the selective vulnerabilities that arise in somatic stem cell populations as a result of physiologic adaptations.

Deubiquitinase catalytic activity of MYSM1 is essential in vivo for hematopoiesis and immune cell development

Myb-like SWIRM and MPN domains 1 (MYSM1) is a chromatin binding protein with deubiquitinase (DUB) catalytic activity. Rare MYSM1 mutations in human patients result in an inherited bone marrow failure syndrome, highlighting the biomedical significance of MYSM1 in the hematopoietic system. We and others characterized Mysm1-knockout mice as a model of this disorder and established that MYSM1 regulates hematopoietic function and leukocyte development in such models through different mechanisms. It is, however, unknown whether the DUB catalytic activity of MYSM1 is universally required for its many functions and for the maintenance of hematopoiesis in vivo. To test this, here we generated a new mouse strain carrying a Mysm1^D660N point mutation (Mysm1^DN) and demonstrated that the mutation renders MYSM1 protein catalytically inactive. We characterized Mysm1^DN/DN and Mysm1^fl/DN Cre^ERT2 mice, against appropriate controls, for constitutive and inducible loss of MYSM1 catalytic function. We report a profound similarity in the developmental, hematopoietic, and immune phenotypes resulting from the loss of MYSM1 catalytic function and the full loss of MYSM1 protein. Overall, our work for the first time establishes the critical role of MYSM1 DUB catalytic activity in vivo in hematopoiesis, leukocyte development, and other aspects of mammalian physiology.

Cell-intrinsic factors governing quiescence vis-à-vis activation of adult hematopoietic stem cells

Hematopoiesis is a highly complex process, regulated by both intrinsic and extrinsic factors. Often, these two regulatory arms work in tandem to maintain the steady-state condition of hematopoiesis. However, at times, certain intrinsic attributes of hematopoietic stem cells (HSCs) override the external stimuli and dominate the outcome. These could be genetic events like mutations or environmentally induced epigenetic or transcriptomic changes. Since leukemic stem cells (LSCs) share molecular pathways that also regulate normal HSCs, identifying specific, dominantly acting intrinsic factors could help in the development of novel therapeutic approaches. Here we have reviewed such dominantly acting intrinsic factors governing quiescence vis-à-vis activation of the HSCs in the face of external forces acting on them. For brevity, we have restricted our review to the articles dealing with adult HSCs of human and mouse origin that have been published in the last 10 years. Hematopoietic stem cells (HSCs) are closely associated with various stromal cells in their microenvironment and, thus, constantly receive signaling cues from them. The illustration depicts some dominantly acting intrinsic or cell-autonomous factors operative in the HSCs. These fall into various categories, such as epigenetic regulators, transcription factors, cell cycle regulators, tumor suppressor genes, signaling pathways, and metabolic regulators, which counteract the outcome of extrinsic signaling exerted by the HSC niche.

The Route of Early T Cell Development: Crosstalk between Epigenetic and Transcription Factors

Hematopoietic multipotent progenitors seed the thymus and then follow consecutive developmental stages until the formation of mature T cells. During this process, phenotypic changes of T cells entail stage-specific transcriptional programs that underlie the dynamic progression towards mature lymphocytes. Lineage-specific transcription factors are key drivers of T cell specification and act in conjunction with epigenetic regulators that have also been elucidated as crucial players in the establishment of regulatory networks necessary for proper T cell development. In this review, we summarize the activity of transcription factors and epigenetic regulators that together orchestrate the intricacies of early T cell development with a focus on regulation of T cell lineage commitment.

CD74 is a regulator of hematopoietic stem cell maintenance

Hematopoietic stem and progenitor cells (HSPCs) are a small population of undifferentiated cells that have the capacity for self-renewal and differentiate into all blood cell lineages. These cells are the most useful cells for clinical transplantations and for regenerative medicine. So far, it has not been possible to expand adult hematopoietic stem cells (HSCs) without losing their self-renewal properties. CD74 is a cell surface receptor for the cytokine macrophage migration inhibitory factor (MIF), and its mRNA is known to be expressed in HSCs. Here, we demonstrate that mice lacking CD74 exhibit an accumulation of HSCs in the bone marrow (BM) due to their increased potential to repopulate and compete for BM niches. Our results suggest that CD74 regulates the maintenance of the HSCs and CD18 expression. Its absence leads to induced survival of these cells and accumulation of quiescent and proliferating cells. Furthermore, in in vitro experiments, blocking of CD74 elevated the numbers of HSPCs. Thus, we suggest that blocking CD74 could lead to improved clinical insight into BM transplant protocols, enabling improved engraftment.

Hematopoietic stem and progenitor cells (HSPCs) can self-renew and differentiate into all blood cell lineages, making them useful for clinical transplantations and regenerative medicine. This study shows that blocking the MIF receptor CD74 increases the accumulation of HSPCs and could improve the efficacy of bone marrow transplantation protocols.

MYSM1 maintains ribosomal protein gene expression in hematopoietic stem cells to prevent hematopoietic dysfunction

Ribosomopathies are congenital disorders caused by mutations in the genes encoding ribosomal and other functionally related proteins. They are characterized by anemia, other hematopoietic and developmental abnormalities, and p53 activation. Ribosome assembly requires coordinated expression of many ribosomal protein (RP) genes; however, the regulation of RP gene expression, especially in hematopoietic stem cells (HSCs), remains poorly understood. MYSM1 is a transcriptional regulator essential for HSC function and hematopoiesis. We established that HSC dysfunction in Mysm1 deficiency is driven by p53; however, the mechanisms of p53 activation remained unclear. Here, we describe the transcriptome of Mysm1-deficient mouse HSCs and identify MYSM1 genome-wide DNA binding sites. We establish a direct role for MYSM1 in RP gene expression and show a reduction in protein synthesis in Mysm1-/- HSCs. Loss of p53 in mice fully rescues Mysm1-/- anemia phenotype but not RP gene expression, indicating that RP gene dysregulation is a direct outcome of Mysm1 deficiency and an upstream mediator of Mysm1-/- phenotypes through p53 activation. We characterize a patient with a homozygous nonsense MYSM1 gene variant, and we demonstrate reduced protein synthesis and increased p53 levels in patient hematopoietic cells. Our work provides insights into the specialized mechanisms regulating RP gene expression in HSCs and establishes a common etiology of MYSM1 deficiency and ribosomopathy syndromes.

Deubiquitinase MYSM1 in the Hematopoietic System and beyond: A Current Review

MYSM1 has emerged as an important regulator of hematopoietic stem cell function, blood cell production, immune response, and other aspects of mammalian physiology. It is a metalloprotease family protein with deubiquitinase catalytic activity, as well as SANT and SWIRM domains. MYSM1 normally localizes to the nucleus, where it can interact with chromatin and regulate gene expression, through deubiquitination of histone H2A and non-catalytic contacts with other transcriptional regulators. A cytosolic form of MYSM1 protein was also recently described and demonstrated to regulate signal transduction pathways of innate immunity, by promoting the deubiquitination of TRAF3, TRAF6, and RIP2. In this work we review the current knowledge on the molecular mechanisms of action of MYSM1 protein in transcriptional regulation, signal transduction, and potentially other cellular processes. The functions of MYSM1 in different cell types and aspects of mammalian physiology are also reviewed, highlighting the key checkpoints in hematopoiesis, immunity, and beyond regulated by MYSM1. Importantly, mutations in MYSM1 in human were recently linked to a rare hereditary disorder characterized by leukopenia, anemia, and other hematopoietic and developmental abnormalities. Our growing knowledge of MYSM1 functions and mechanisms of actions sheds important insights into its role in mammalian physiology and the etiology of the MYSM1-deficiency disorder in human.

Chromatin-Modifying Enzymes in T Cell Development

T cell development involves stepwise progression through defined stages that give rise to multiple T cell subtypes, and this is accompanied by the establishment of stage-specific gene expression. Changes in chromatin accessibility and chromatin modifications accompany changes in gene expression during T cell development. Chromatin-modifying enzymes that add or reverse covalent modifications to DNA and histones have a critical role in the dynamic regulation of gene expression throughout T cell development. As each chromatin-modifying enzyme has multiple family members that are typically all coexpressed during T cell development, their function is sometimes revealed only when two related enzymes are concurrently deleted. This work has also revealed that the biological effects of these enzymes often involve regulation of a limited set of targets. The growing diversity in the types and sites of modification, as well as the potential for a single enzyme to catalyze multiple modifications, is also highlighted.

Deubiquitinase Mysm1 regulates macrophage survival and polarization

Macrophages play pivotal roles in innate and adaptive immune response, tissue homeostasis and cancer development. Their development and heterogeneity are tightly controlled by epigenetic program and transcription factors. Deubiquitinase Mysm1 plays crucial roles in regulating stem cell maintenance and immune cell development. Here we show that Mysm1 expression is up regulated during bone marrow macrophage development. Mysm1 deficient cells exhibit accelerating proliferation with more cells going to S phase and higher cyclin D1, cyclin D2 and c-Myc expression. However, compared to WT counterparts, more cell death is also detected in Mysm1 deficient cells no matter M-CSF deprived or not. In LPS-condition medium, Mysm1^-/- macrophages show more pro-inflammatory factors IL-1β, TNFα and iNOS production. In addition, much higher expression of surface marker CD86 is detected in Mysm1^-/- macrophages. In vivo tumor model data demonstrate that in contrast to WT macrophages promoting tumor growth, Mysm1^-/- macrophages inhibit tumor growth, showing the properties of M1 macrophages. Collectively, these data indicate that Mysm1 is essential for macrophage survival and plays an important role in macrophage polarization and might be a target for cell therapy.

A role for the histone H2A deubiquitinase MYSM1 in maintenance of CD8+ T cells

Several previous studies outlined the importance of the histone H2A deubiquitinase MYSM1 in the regulation of stem cell quiescence and haematopoiesis. In this study we investigated the role of MYSM1 in T-cell development. Using mouse models that allow conditional Mysm1 ablation at late stages of thymic development, we found that MYSM1 is intricately involved in the maintenance, activation and survival of CD8⁺ T cells. Mysm1 ablation resulted in a twofold reduction in CD8⁺ T-cell numbers, and also led to a hyperactivated CD8⁺ T-cell state accompanied by impaired proliferation and increased pro-inflammatory cytokine production after ex vivo stimulation. These phenotypes coincided with an increased apoptosis and preferential up-regulation of p53 tumour suppressor protein in CD8⁺ T cells. Lastly, we examined a model of experimental cerebral malaria, in which pathology is critically dependent on CD8⁺ T cells. In the mice conditionally deleted for Mysm1 in the T-cell compartment, CD8⁺ T-cell numbers remained reduced following infection, both in the periphery and in the brain, and the mice displayed improved survival after parasite challenge. Collectively, our data identify MYSM1 as a novel factor for CD8⁺ T cells in the immune system, increasing our understanding of the role of histone H2A deubiquitinases in cytotoxic T-cell biology.

Myb-like, SWIRM, and MPN domains 1 (MYSM1) deficiency: Genotoxic stress-associated bone marrow failure and developmental aberrations

BACKGROUND

Myb-like, SWIRM, and MPN domains 1 (MYSM1) is a transcriptional regulator mediating histone deubiquitination. Its role in human immunity and hematopoiesis is poorly understood.

OBJECTIVES

We sought to investigate the clinical, cellular, and molecular features in 2 siblings presenting with progressive bone marrow failure (BMF), immunodeficiency, and developmental aberrations.

METHODS

We performed genome-wide homozygosity mapping, whole-exome and Sanger sequencing, immunophenotyping studies, and analysis of genotoxic stress responses. p38 activation, reactive oxygen species levels, rate of apoptosis and clonogenic survival, and growth in immune and nonimmune cells were assessed. The outcome of allogeneic hematopoietic stem cell transplantation (HSCT) was monitored.

RESULTS

We report 2 patients with progressive BMF associated with myelodysplastic features, immunodeficiency affecting B cells and neutrophil granulocytes, and complex developmental aberrations, including mild skeletal anomalies, neurocognitive developmental delay, and cataracts. Whole-exome sequencing revealed a homozygous premature stop codon mutation in the gene encoding MYSM1. MYSM1-deficient cells are characterized by increased sensitivity to genotoxic stress associated with sustained induction of phosphorylated p38 protein, increased reactive oxygen species production, and decreased survival following UV light-induced DNA damage. Both patients were successfully treated with allogeneic HSCT with sustained reconstitution of hematopoietic defects.

CONCLUSIONS

Here we show that MYSM1 deficiency is associated with developmental aberrations, progressive BMF with myelodysplastic features, and increased susceptibility to genotoxic stress. HSCT represents a curative therapy for patients with MYSM1 deficiency.