Loss of p53 compensates osteopenia in murine Mysm1 deficiency

PI3K/AKT signaling pathway as a critical regulator of epithelial-mesenchymal transition in colorectal tumor cells

Colorectal cancer (CRC) is one of the most frequent gastrointestinal malignancies that are considered as a global health challenge. Despite many progresses in therapeutic methods, there is still a high rate of mortality rate among CRC patients that is associated with poor prognosis and distant metastasis. Therefore, investigating the molecular mechanisms involved in CRC metastasis can improve the prognosis. Epithelial-mesenchymal transition (EMT) process is considered as one of the main molecular mechanisms involved in CRC metastasis, which can be regulated by various signaling pathways. PI3K/AKT signaling pathway has a key role in CRC cell proliferation and migration. In the present review, we discussed the role of PI3K/AKT pathway CRC metastasis through the regulation of the EMT process. It has been shown that PI3K/AKT pathway can induce the EMT process by down regulation of epithelial markers, while up regulation of mesenchymal markers and EMT-specific transcription factors that promote CRC metastasis. This review can be an effective step toward introducing the PI3K/AKT/EMT axis to predict prognosis as well as a therapeutic target among CRC patients. Video Abstract.

Changes in N6-methyladenosine RNA methylomes of human periodontal ligament cells in response to inflammatory conditions

OBJECTIVE

To investigate the changes in the m6A methylation modification profile of human periodontal ligament cells (hPDLCs) in response to inflammatory conditions.

BACKGROUND

Periodontitis is an infectious disease of the periodontal support tissue that leads to the loss of alveolar bone. HPDLCs are primary cells that can repair periodontal tissue defects caused by periodontitis. However, the inflammatory conditions induce inflammatory damage and decrease ossification of hPDLCs. This inflammatory response depends on genetic and epigenetic mechanisms, including m6A methylation.

METHODS

HPDLCs were cultured with osteogenic induction medium (NC group), while TNF-α (10 ng/mL) and IL-1β (5 ng/mL) were added to simulate inflammatory conditions (Inflam group). Then RNA-seq and MeRIP-seq analyses were performed to identify m6A methylation modification in the transcriptome range of hPDLCs.

RESULTS

The results showed that the osteogenic differentiation of hPDLCs was inhibited under inflammatory conditions. RNA-seq analysis also revealed that the decreased genes in response to inflammatory conditions were primarily annotated in processes associated with ossification. Compared with the NC group, differentially m6A-methylated genes were primarily enriched in histone modification processes. Among 145 histone modification genes, 25 genes have been reported to be involved in the regulation of osteogenic differentiation, and they include KAT6B, EP300, BMI1, and KDMs (KDM1A, KDM2A, KDM3A, KDM4B, and KDM5A).

CONCLUSION

This study demonstrated that the m6A landscape of hPDLCs was changed in response to inflammation. M6A methylation differences among histone modification genes may act on the osteogenic differentiation of hPDLCs.

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.

Ubiquitin modification in osteogenic differentiation and bone formation: From mechanisms to clinical significance

The ubiquitin-proteasome system is an important pathway for mediating posttranslational modification and protein homeostasis and exerts a wide range of functions in diverse biological processes, including stem cell differentiation, DNA repair, and cell cycle regulation. Many studies have shown that ubiquitination modification plays a critical role in regulating the osteogenic differentiation of stem cells and bone formation through various mechanisms. This review summarizes current progress on the effects and mechanisms of ubiquitin modification on transcription factors and signaling pathways involved in osteogenic differentiation. Moreover, the review highlights the latest advances in the clinical application of drugs in bone tissue engineering. A thorough understanding of ubiquitin modifications may provide promising therapeutic targets for stem cell-based bone tissue engineering.

Complement receptor C5aR1 on osteoblasts regulates osteoclastogenesis in experimental postmenopausal osteoporosis

In recent years, evidence has accumulated that the complement system, an integral part of innate immunity, may be involved in the regulation of bone homeostasis as well as inflammatory bone loss, for example, in rheumatoid arthritis and periodontitis. Complement may also contribute to osteoporosis development, but investigation of the mechanism is limited. Using mice with a conditional deletion of the complement anaphylatoxin receptor C5aR1, we here demonstrated that C5aR1 in osteoblasts (C5aR1 ^Runx2-Cre mice) or osteoclasts (C5aR1 ^LysM-Cre mice) did not affect physiological bone turnover or age-related bone loss in either sex, as confirmed by micro-computed tomography, histomorphometry, and biomechanical analyses of the bone and by the measurement of bone turnover markers in the blood serum. When female mice were subjected to ovariectomy (OVX), a common model for postmenopausal osteoporosis, significant bone loss was induced in C5aR1 ^fl/fl and C5aR1 ^LysM-Cre mice, as demonstrated by a significantly reduced bone volume fraction, trabecular number and thickness as well as an increased trabecular separation in the trabecular bone compartment. Confirming this, the osteoclast number and the receptor activator of nuclear factor k-B (RANK) ligand (RANKL) serum level were significantly elevated in these mouse lines. By contrast, C5aR1 ^Runx2-Cre mice were protected from bone loss after OVX and the serum RANKL concentration was not increased after OVX. These data suggested that bone cell-specific C5aR1 may be redundant in bone homeostasis regulation under physiological conditions. However, C5aR1 on osteoblasts was crucial for the induction of bone resorption under osteoporotic conditions by stimulating RANKL release, whereas C5aR1 on osteoclasts did not regulate OVX-induced bone loss. Therefore, our results implicate C5aR1 on osteoblasts as a potential target for treating postmenopausal osteoporosis.

Role of histone modification in the occurrence and development of osteoporosis

Osteoporosis is a systemic degenerative bone disease characterized by low bone mass and damage to bone microarchitecture, which increases bone fragility and susceptibility to fracture. The risk of osteoporosis increases with age; with the aging of the global population, osteoporosis is becoming more prevalent, adding to the societal healthcare burden. Histone modifications such as methylation, acetylation, ubiquitination, and ADP-ribosylation are closely related to the occurrence and development of osteoporosis. This article reviews recent studies on the role of histone modifications in osteoporosis. The existing evidence indicates that therapeutic targeting of these modifications to promote osteogenic differentiation and bone formation may be an effective treatment for this disease.

MYSM1 inhibits human colorectal cancer tumorigenesis by activating miR-200 family members/CDH1 and blocking PI3K/AKT signaling

Background

Histone epigenetic modification disorder is an important predisposing factor for the occurrence and development of many cancers, including colorectal cancer (CRC). The role of MYSM1, a metalloprotease that deubiquitinates monoubiquitinated histone H2A, in colorectal cancer was identified to evaluate its potential clinical application value.

Methods

MYSM1 expression levels in CRC cell lines and tumor tissues were detected, and their associations with patient survival rate and clinical stage were analyzed using databases and tissue microarrays. Gain- and loss-of-function studies were performed to identify the roles of MYSM1 in CRC cell proliferation, apoptosis, cell cycle progression, epithelial-mesenchymal transition (EMT) and metastasis in vitro and in vivo. ChIP, rescue assays and signal pathway verification were conducted for mechanistic study. Immunohistochemistry (IHC) was used to further assess the relationship of MYSM1 with CRC diagnosis and prognosis.

Results

MYSM1 was significantly downregulated and was related to the overall survival (OS) of CRC patients. MYSM1 served as a CRC suppressor by inducing apoptosis and inhibiting cell proliferation, EMT, tumorigenic potential and metastasis. Mechanistically, MYSM1 directly bound to the promoter region of miR-200/CDH1, impaired the enrichment of repressive H2AK119ub1 modification and epigenetically enhanced miR-200/CDH1 expression. Testing of paired CRC patient samples confirmed the positive regulatory relationship between MYSM1 and miR-200/CDH1. Furthermore, silencing MYSM1 stimulated PI3K/AKT signaling and promoted EMT in CRC cells. More importantly, a positive association existed between MYSM1 expression and a favorable CRC prognosis.

Conclusions

MYSM1 plays essential suppressive roles in CRC tumorigenesis and is a potential target for reducing CRC progression and distant metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02106-2.

Increased Presence of Complement Factors and Mast Cells in Alveolar Bone and Tooth Resorption

Periodontitis is the inflammatory destruction of the tooth-surrounding and -supporting tissue, resulting at worst in tooth loss. Another locally aggressive disease of the oral cavity is tooth resorption (TR). This is associated with the destruction of the dental mineralized tissue. However, the underlying pathomechanisms remain unknown. The complement system, as well as mast cells (MCs), are known to be involved in osteoclastogenesis and bone loss. The complement factors C3 and C5 were previously identified as key players in periodontal disease. Therefore, we hypothesize that complement factors and MCs might play a role in alveolar bone and tooth resorption. To investigate this, we used the cat as a model because of the naturally occurring high prevalence of both these disorders in this species. Teeth, gingiva samples and serum were collected from domestic cats, which had an appointment for dental treatment under anesthesia, as well as from healthy cats. Histological analyses, immunohistochemical staining and the CH-50 and AH-50 assays revealed increased numbers of osteoclasts and MCs, as well as complement activity in cats with TR. Calcifications score in the gingiva was highest in animals that suffer from TR. This indicates that MCs and the complement system are involved in the destruction of the mineralized tissue in this condition.

Aberrantly Expressed lncRNAs and mRNAs of Osteogenically Differentiated Mesenchymal Stem Cells in Ossification of the Posterior Longitudinal Ligament

Ectopic bone formation is the chief characteristic of ossification of the posterior longitudinal ligament (OPLL). Emerging evidence has revealed that long non-coding RNAs (lncRNAs) can regulate the osteogenic differentiation of mesenchymal stem cells (MSCs), which are the main cells responsible for bone formation. However, the role of lncRNAs in the pathogenesis of OPLL remains unclear. In this study, 725 aberrantly expressed lncRNAs and 664 mRNAs in osteogenically differentiated MSCs from OPLL patients (OPLL MSCs) were identified by microarrays and confirmed by qRT-PCR assays. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the most enriched pathways included the p53, JAK-STAT, and PI3K-Akt signaling pathways. The co-expression network showed the interactions between the aberrantly expressed lncRNAs and mRNAs in OPLL MSCs, and the potential targets and transcription factors of the lncRNAs were predicted. Our research demonstrated the aberrantly expressed lncRNA and mRNA and the potential regulatory networks involved in the ectopic bone formation of OPLL. These findings imply that lncRNAs may play a vital role in OPLL, which provides a new perspective on the pathogenesis of OPLL.

Interaction of Deubiquitinase 2A-DUB/MYSM1 with DNA Repair and Replication Factors

The deubiquitination of histone H2A on lysine 119 by 2A-DUB/MYSM1, BAP1, USP16, and other enzymes is required for key cellular processes, including transcriptional activation, apoptosis, and cell cycle control, during normal hematopoiesis and tissue development, and in tumor cells. Based on our finding that MYSM1 colocalizes with γH2AX foci in human peripheral blood mononuclear cells, leukemia cells, and melanoma cells upon induction of DNA double-strand breaks with topoisomerase inhibitor etoposide, we applied a mass spectrometry-based proteomics approach to identify novel 2A-DUB/MYSM1 interaction partners in DNA-damage responses. Differential display of MYSM1 binding proteins significantly enriched after exposure of 293T cells to etoposide revealed an interacting network of proteins involved in DNA damage and replication, including factors associated with poor melanoma outcome. In the context of increased DNA-damage in a variety of cell types in Mysm1-deficient mice, in bone marrow cells upon aging and in UV-exposed Mysm1-deficient skin, our current mass spectrometry data provide additional evidence for an interaction between MYSM1 and key DNA replication and repair factors, and indicate a potential function of 2A-DUB/MYSM1 in DNA repair processes.

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.

Influence of Menopause on Inflammatory Cytokines during Murine and Human Bone Fracture Healing

Postmenopausal females display a chronic inflammatory phenotype with higher levels of circulating pro-inflammatory cytokines. Furthermore, the inflammatory response to injury may be altered under estrogen-deficiency, because it was shown previously that estrogen-deficient mice displayed increased levels of the inflammatory cytokines Midkine (Mdk) and Interleukin-6 (IL-6) in the early fracture hematoma. Because a balanced immune response to fracture is required for successful bone regeneration, this might contribute to the delayed fracture healing frequently observed in osteoporotic, postmenopausal fracture patients. In this study, we aimed to investigate whether further cytokines in addition to Mdk and IL-6 might be affected by estrogen-deficiency after fracture in mice and whether these cytokines are also relevant during human fracture healing. Additionally, we aimed to investigate whether serum from male vs. female fracture patients affects osteogenic differentiation of human mesenchymal stem cells (MSCs). To address these questions, female mice were either sham-operated or ovariectomized (OVX) and subjected to standardized femur osteotomy. A broad panel of pro- and anti-inflammatory cytokines was determined systemically and locally in the fracture hematoma. In a translational approach, serum was collected from healthy controls and patients with an isolated fracture. Mdk and IL-6 serum levels were determined at day 0, day 14 and day 42 after fracture. Subgroup analysis was performed to investigate differences between male and female fracture patients after menopause. In an in vitro approach, human MSCs were cultured with the collected patient serum and osteogenic differentiation was assessed by qPCR and alkaline-phosphatase staining. Our results suggest an important role for the pro-inflammatory cytokines Mdk and IL-6 in the response to fracture in estrogen-deficient mice among all of the measured inflammatory mediators. Notably, both cytokines were also significantly increased in the serum of patients after fracture. However, only Mdk serum levels differed significantly between male and female fracture patients after menopause. MSCs cultivated with serum from female fracture patients displayed significantly reduced osteogenic differentiation, which was attenuated by Mdk-antibody treatment. In conclusion, our study demonstrated increased Mdk levels after fracture in OVX mice and female fracture patients after menopause. Because Mdk is a negative regulator of bone formation, this might contribute to impaired osteoporotic fracture healing.

Deubiquitinating Enzymes and Bone Remodeling

Bone remodeling, which is essential for bone homeostasis, is controlled by multiple factors and mechanisms. In the past few years, studies have emphasized the role of the ubiquitin-dependent proteolysis system in regulating bone remodeling. Deubiquitinases, which are grouped into five families, remove ubiquitin from target proteins and are involved in several cell functions. Importantly, a number of deubiquitinases mediate bone remodeling through regulating differentiation and/or function of osteoblast and osteoclasts. In this review, we review the functions and mechanisms of deubiquitinases in mediating bone remodeling.

2A-DUB/Mysm1 Regulates Epidermal Development in Part by Suppressing p53-Mediated Programs

Development and homeostasis of the epidermis are governed by a complex network of sequence-specific transcription factors and epigenetic modifiers cooperatively regulating the subtle balance of progenitor cell self-renewal and terminal differentiation. To investigate the role of histone H2A deubiquitinase 2A-DUB/Mysm1 in the skin, we systematically analyzed expression, developmental functions, and potential interactions of this epigenetic regulator using Mysm1-deficient mice and skin-derived epidermal cells. Morphologically, skin of newborn and young adult Mysm1-deficient mice was atrophic with reduced thickness and cellularity of epidermis, dermis, and subcutis, in context with altered barrier function. Skin atrophy correlated with reduced proliferation rates in Mysm1^-/- epidermis and hair follicles, and increased apoptosis compared with wild-type controls, along with increases in DNA-damage marker γH2AX. In accordance with diminished α6-Integrin^high+CD34⁺ epidermal stem cells, reduced colony formation of Mysm1^-/- epidermal progenitors was detectable in vitro. On the molecular level, we identified p53 as potential mediator of the defective Mysm1-deficient epidermal compartment, resulting in increased pro-apoptotic and anti-proliferative gene expression. In Mysm1^-/-p53^-/- double-deficient mice, significant recovery of skin atrophy was observed. Functional properties of Mysm1^-/- developing epidermis were assessed by quantifying the transepidermal water loss. In summary, this investigation uncovers a role for 2A-DUB/Mysm1 in suppression of p53-mediated inhibitory programs during epidermal development.