Interactions of HMGB Proteins with the Genome and the Impact on Disease

HMG-B transcription factors of unicellular opisthokonts and their relatedness to the Sox-Tcf/Lef-Mata proteins of Metazoa and fungi

A phylogenetic analysis of transcription factors of the Sox-Tcf/Lef-Mata (STM) family of the HMG-B superfamily was carried out in order to clarify the evolutionary roots of the Wnt signaling pathway in unicellular organisms. The data set for analysis included protein sequences of metazoans, fungi, unicellular opisthokonts, apusomonads and amoebozoans. The topology of the phylogenetic tree suggests that STM-related proteins arose in the common ancestor of Opisthokonta and Amoebozoa, two of amoebozoan STM proteins are sister-related to opisthokont ones and the three known lineages of STM transcription factors (STM family in narrow sence) are found in Opisthokonta only. Of these, the holozoan Sox protein branch is the result of either the first or second branching, that originated in the common ancestor of Opisthokonta. The lineage containing Tcf/Lef proteins (holozoan) and the lineage containing Mata proteins (holomycotan) are sister. They derived either at the time of the Holozoa and Holomycota divergence or originate from two paralogs of the common ancestor of Opisthokonta, which arose after the separation of the Sox lineage. Interaction with Armadillo-like proteins may be an original feature of the STM protein family and existed in the unicellular ancestors of multicellular animals; a connection is possible between the presence of Mata-related proteins in Aphelidium protococcorum and specific genome feature of this species.

An i-motif-regulated enhancer, eRNA and adjacent lncRNA affect Lhb expression through distinct mechanisms in a sex-specific context

Genome-wide studies have demonstrated regulatory roles for diverse non-coding elements, but their precise and interrelated functions have often remained enigmatic. Addressing the need for mechanistic insight, we studied their roles in expression of Lhb which encodes the pituitary gonadotropic hormone that controls reproduction. We identified a bi-directional enhancer in gonadotrope-specific open chromatin, whose functional eRNA (eRNA2) supports permissive chromatin at the Lhb locus. The central untranscribed region of the enhancer contains an iMotif (iM), and is bound by Hmgb2 which stabilizes the iM and directs transcription specifically towards the functional eRNA2. A distinct downstream lncRNA, associated with an inducible G-quadruplex (G4) and iM, also facilitates Lhb expression, following its splicing in situ. GnRH activates Lhb transcription and increased levels of all three RNAs, eRNA2 showing the highest response, while estradiol, which inhibits Lhb, repressed levels of eRNA2 and the lncRNA. The levels of these regulatory RNAs and Lhb mRNA correlate highly in female mice, though strikingly not in males, suggesting a female-specific function. Our findings, which shed new light on the workings of non-coding elements and non-canonical DNA structures, reveal novel mechanisms regulating transcription which have implications not only in the central control of reproduction but also for other inducible genes.

Oncoproteins E6 and E7 upregulate topoisomerase I to activate the cGAS-PD-L1 pathway in cervical cancer development

Background: Cervical cancer (CC) stands as a significant health threat to women globally, with high-risk human papillomaviruses as major etiologic agents. The DNA damage repair (DDR) protein topoisomerase I (TOP1) has been linked to various cancers, yet its distinct roles and mechanisms in CC are not fully elucidated. Methods: We investigated TOP1 expression in cervical intraepithelial neoplasia (CIN) and CC tissues utilizing qRT-PCR and IHC, correlating findings with patient prognosis. Subsequent knockdown studies were performed in vitro and in vivo to evaluate the influence of TOP1 on tumor growth, DNA repair, and inflammatory responses. Results: TOP1 was highly expressed in CIN and CC, negatively correlating with patient prognosis. Inhibition of TOP1 impeded CC cell growth and disrupted DNA repair. TOP1 was shown to regulate tumor-promoting inflammation and programmed death-ligand 1 (PD-L1) production in a cGAS-dependent manner. HPV oncoproteins E6 and E7 upregulated TOP1 and activated the cGAS-PD-L1 pathway. Conclusions: TOP1 acts as a DNA repair mediator, promoting CC development and immune evasion. Targeting the TOP1-cGAS-PD-L1 axis could be a potential therapeutic strategy for CC.

HMGB1/RAGE axis in tumor development: unraveling its significance

High mobility group protein 1 (HMGB1) plays a complex role in tumor biology. When released into the extracellular space, it binds to the receptor for advanced glycation end products (RAGE) located on the cell membrane, playing an important role in tumor development by regulating a number of biological processes and signal pathways. In this review, we outline the multifaceted functions of the HMGB1/RAGE axis, which encompasses tumor cell proliferation, apoptosis, autophagy, metastasis, and angiogenesis. This axis is instrumental in tumor progression, promoting tumor cell proliferation, autophagy, metastasis, and angiogenesis while inhibiting apoptosis, through pivotal signaling pathways, including MAPK, NF-κB, PI3K/AKT, ERK, and STAT3. Notably, small molecules, such as miRNA-218, ethyl pyruvate (EP), and glycyrrhizin exhibit the ability to inhibit the HMGB1/RAGE axis, restraining tumor development. Therefore, a deeper understanding of the mechanisms of the HMGB1/RAGE axis in tumors is of great importance, and the development of inhibitors targeting this axis warrants further exploration.

The Association Between Serum Levels of Glial Biomarkers, Clinical Severity and Electro-encephalography Features in Idiopathic West and Lennox-Gastaut Syndromes

Introduction

Although the contribution of enhanced glial activity in seizure induction is increasingly recognized, the role of glia-induced neuroinflammation in the physiopathology of epileptic encephalopathy (EE) has been scarcely investigated.

Methods

To delineate the contribution of glial activity in EE, we measured levels of glia-derived mediators with previously described biomarker value, including glial fibrillary acidic protein (GFAP), high mobility group box 1 (HMGB1), chitinase-3-like protein 1 (CHI3L1), soluble CD163 (sCD163) and triggering receptor expressed on myeloid cells 2 (TREM2) by ELISA in sera of patients with idiopathic West syndrome (WS, n=18), idiopathic Lennox-Gastaut syndrome (LGS, n=13) and healthy controls (n=31).

Results

Patients with EE showed significantly higher CHI3L1 levels compared to healthy controls. Levels of HMGB1, CHI3L1, sCD163 and TREM2 were higher in LGS patients than WS patients and/or healthy controls. One or more of the investigated mediators were associated with treatment responsiveness, disease severity and presence of pathological features on electroencephalography (EEG).

Conclusions

To our knowledge, our findings provide the initial patient-based evidence that astrocyte- and microglia-mediated neuroinflammation might be involved in the pathogenesis of LGS and WS. Moreover, glial mediators may serve as prognostic biomarkers in patients with idiopathic EE.

Mutual promotion of co-condensation of KRAS G-quadruplex and a well-folded protein HMGB1

Liquid-liquid phase separation (LLPS) of G-quadruplex (GQ) is involved in many crucial cellular processes, while the quadruplex-folding and their functions are typically modulated by specific DNA-binding proteins. However, the regulatory mechanism of binding proteins, particularly the well-folded proteins, on the LLPS of GQs is largely unknown. Here, we investigated the effect of HMGB1 on the condensation of a G-quadruplex of KRAS promoter (GQKRAS). The results show that these two rigid macro-biomolecules undergo co-condensation through a mutual promotion manner, while neither of them can form LLPS alone. Fluidity measurements confirm that the liquid-like droplets are highly dynamic. HMGB1 facilitates and stabilizes the quadruplex folding of GQKRAS, and this process enhances their co-condensation. The KRAS promoter DNA retains quadruplex folding in the droplets; interference with the GQ-folding disrupts the co-condensation of GQKRAS/HMGB1. Mechanistic studies reveal that electrostatic interaction is a key driving force of the interaction and co-condensation of GQKRAS/HMGB1; meanwhile, the recognition of two macro-biomolecules plays a crucial role in this process. This result indicates that the phase separation of GQs can be modulated by DNA binding proteins, and this process could also be an efficient way to recruit specific DNA binding proteins.

Identification of aging-related genes in diagnosing osteoarthritis via integrating bioinformatics analysis and machine learning

BACKGROUND

Osteoarthritis (OA) is one of the main causes of pain and disability in the world, it may be caused by many factors. Aging plays a significant role in the onset and progression of OA. However, the mechanisms underlying it remain unknown. Our research aimed to uncover the role of aging-related genes in the progression of OA.

METHODS

In Human OA datasets and aging-related genes were obtained from the GEO database and the HAGR website, respectively. Bioinformatics methods including Gene Ontology (GO), Kyoto Encyclopedia of Genes Genomes (KEGG) pathway enrichment, and Protein-protein interaction (PPI) network analysis were used to analyze differentially expressed aging-related genes (DEARGs) in the normal control group and the OA group. And then weighted gene coexpression network analysis (WGCNA), the least absolute shrinkage and selection operator (LASSO) regression, and the Random Forest (RF) machine learning algorithms were used to find the hub genes.

RESULTS

Four overlapping hub genes: HMGB2, CDKN1A, JUN, and DDIT3 were identified. According to the nomogram model and receiver operating characteristic (ROC) curve analysis, four hub DEARGs had good diagnostic value in distinguishing normal from OA. Furthermore, the qRT-PCR test demonstrated that HMGB2, CDKN1A, JUN, and DDIT3 mRNA expression levels were lower in OA group than in normal group.

CONCLUSION

Finally, these four-hub aging-related genes may help us understand the underlying mechanism of aging in osteoarthritis and could be used as possible diagnostic and therapeutic targets.

Circ_0001589/miR-1248/HMGB1 axis enhances EMT-mediated metastasis and cisplatin resistance in cervical cancer

Cervical cancer is the fourth most common malignant tumors in female worldwide. Cirular RNAs (circRNA) represent a new class of regulatory RNA and play a pivotal role in the carcinogenesis and development of tumors. However, their functions have not been fully elucidated in cervical cancer. In this study, we identified an upregulated circRNA, circ_0001589, both in fresh clinical samples and tissue microarray of cervical cancer. Transwell assay and cell apoptosis assay by flow cytometry demonstrated circ_0001589 promotes epithelial-mesenchymal transition (EMT)-mediated cell migration and invasion, and enhanced cisplatin resistance in vitro. In addition, in nude mice model, circ_0001589 increased the number of lung metastases and recovered xenograft growth from cisplatin treatment in vivo. Mechanistically, RNA pull-down assay, RNA immunoprecipitation, and dual-luciferase reporter assay disclosed that circ_0001589 function as an competing endogenous RNA to sponge miR-1248, which directly target the 3' untranslated region of high mobility group box-B1 (HMGB1). Thereby, circ_0001589 upregulated HMGB1 protein expression and accelerate cervical cancer progression. The rescue experiments also revealed that miR-1248 overexpression or HMGB1 knockdown partially reversed the regulatory functions of circ_0001589 on cell migration, invasion, and cisplatin resistance. In summary, our findings suggest the upregulation of circ_0001589 promoted EMT-mediated cell migration and invasion, and enhanced cisplatin resistance via regulating miR-1248/HMGB1 axis in cervical cancer. These results provided new evidence for understanding the carcinogenesis mechanism and finding new therapeutic target for cervical cancer.

Correlation of serum HMGB1 and HMGB2 levels with clinical symptoms in allergic rhinitis children

This research aimed to explore the serum high-mobility group box 1 (HMGB1) and high-mobility group box 2 (HMGB2) levels in allergic rhinitis (AR) children and its correlation with clinical results. This present prospective observational study enrolled 179 AR children and 100 healthy children who came to our hospital during October 2020 to August 2022. The serum HMGB1, HMGB2, interleukin (IL)-6, IL-1β, interferon-γ, and C-reactive protein (CRP) levels were measured by enzyme-linked immunosorbent assay. Demographic and clinical statistics including age, body mass index (BMI), sex, diastolic blood pressure, SBP, family history of allergy, Visual Analogue Score (VAS) and Rhinoconjunctivitis Quality of Life Questionnaire were collected. All data used SPSS 18.0 to statistical analyses. The proportion of family history of allergy was obviously higher in the AR group than that in the healthy group. The serum levels of HMGB1, HMGB2 and cytokines were remarkably enhanced in the AR patients. Spearman analysis supported that positive correlation existed among the HMGB1, HMGB2, CRP, IL-6 and IL-1β levels. Serum IL-6, CRP, HMGB2, IL-1β, VAS score and Rhinoconjunctivitis Quality of Life Questionnaire score levels were significantly higher and serum interferon-γ levels were significantly lower in the HMGB1 high expression group. Similar results were found in in the HMGB2 high group compared to the HMGB2 low group. In addition, HMGB1 and HMGB2 could be potential diagnostic biomarkers of AR patients. Finally, we found that HMGB1, HMGB2, IL-6, IL-1β, and family history of allergy were the risk factors for AR. This study showed that the serum HMGB1 and HMGB2 levels was remarkably enhanced in AR patients and closely associated with cytokines. This study may provide new targets and a comprehensive approach for the treatment of AR patients.

Epigenetic Regulation and Chromatin Remodeling in Malaria Parasites

Plasmodium falciparum, the human malaria parasite, infects two hosts and various cell types, inducing distinct morphological and physiological changes in the parasite in response to different environmental conditions. These variations required the parasite to adapt and develop elaborate molecular mechanisms to ensure its spread and transmission. Recent findings have significantly improved our understanding of the regulation of gene expression in P. falciparum. Here, we provide an up-to-date overview of technologies used to highlight the transcriptomic adjustments occurring in the parasite throughout its life cycle. We also emphasize the complementary and complex epigenetic mechanisms regulating gene expression in malaria parasites. This review concludes with an outlook on the chromatin architecture, the remodeling systems, and how this 3D genome organization is critical in various biological processes.

HMGB family proteins: Potential biomarkers and mechanistic factors in cardiovascular diseases

Cardiovascular disease (CVD) is the most fatal disease that causes sudden death, and inflammation contributes substantially to its occurrence and progression. The prevalence of CVD increases as the population ages, and the pathophysiology is complex. Anti-inflammatory and immunological modulation are the potential methods for CVD prevention and treatment. High-Mobility Group (HMG) chromosomal proteins are one of the most abundant nuclear nonhistone proteins which act as inflammatory mediators in DNA replication, transcription, and repair by producing cytokines and serving as damage-associated molecular patterns in inflammatory responses. The most common and well-studied HMG proteins are those with an HMGB domain, which participate in a variety of biological processes. HMGB1 and HMGB2 were the first members of the HMGB family to be identified and are present in all investigated eukaryotes. Our review is primarily concerned with the involvement of HMGB1 and HMGB2 in CVD. The purpose of this review is to provide a theoretical framework for diagnosing and treating CVD by discussing the structure and function of HMGB1 and HMGB2.

The DNA binding high mobility group box protein family functionally binds RNA

Nucleic acid binding proteins regulate transcription, splicing, RNA stability, RNA localization, and translation, together tailoring gene expression in response to stimuli. Upon discovery, these proteins are typically classified as either DNA or RNA binding as defined by their in vivo functions; however, recent evidence suggests dual DNA and RNA binding by many of these proteins. High mobility group box (HMGB) proteins have a DNA binding HMGB domain, act as transcription factors and chromatin remodeling proteins, and are increasingly understood to interact with RNA as means to regulate gene expression. Herein, multiple layers of evidence that the HMGB family are dual DNA and RNA binding proteins is comprehensively reviewed. For example, HMGB proteins directly interact with RNA in vitro and in vivo, are localized to RNP granules involved in RNA processing, and their protein interactors are enriched in RNA binding proteins involved in RNA metabolism. Importantly, in cell-based systems, HMGB-RNA interactions facilitate protein-protein interactions, impact splicing outcomes, and modify HMGB protein genomic or cellular localization. Misregulation of these HMGB-RNA interactions are also likely involved in human disease. This review brings to light that as a family, HMGB proteins are likely to bind RNA which is essential to HMGB protein biology. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

HmbC, a Protein of the HMG Family, Participates in the Regulation of Carotenoid Biosynthesis in Fusarium fujikuroi

In the fungus Fusarium fujikuroi, carotenoid production is up-regulated by light and down-regulated by the CarS RING finger protein, which modulates the mRNA levels of carotenoid pathway genes (car genes). To identify new potential regulators of car genes, we used a biotin-mediated pull-down procedure to detect proteins capable of binding to their promoters. We focused our attention on one of the proteins found in the screening, belonging to the High-Mobility Group (HMG) family that was named HmbC. The deletion of the hmbC gene resulted in increased carotenoid production due to higher mRNA levels of car biosynthetic genes. In addition, the deletion resulted in reduced carS mRNA levels, which could also explain the partial deregulation of the carotenoid pathway. The mutants exhibited other phenotypic traits, such as alterations in development under certain stress conditions, or reduced sensitivity to cell wall degrading enzymes, revealed by less efficient protoplast formation, indicating that HmbC is also involved in other cellular processes. In conclusion, we identified a protein of the HMG family that participates in the regulation of carotenoid biosynthesis. This is probably achieved through an epigenetic mechanism related to chromatin structure, as is frequent in this class of proteins.

Relationship between circulating senescence-associated secretory phenotype levels and severity of type 2 diabetes-associated periodontitis: A cross-sectional study

BACKGROUND

Senescence-associated secretory phenotype (SASP) has recently been found to drive comorbid diabetes and periodontitis by inducing a chronic, low-degree inflammatory state. Here, we sought to explore the relationship between circulating SASP and the severity of type 2 diabetes-associated periodontitis (DP).

METHODS

Eighty patients (middle-aged periodontitis, M-P group; aged periodontitis, A-P group; M-DP group; and A-DP group; n = 20) provided gingival epithelium, serum, and periodontal clinical parameters. Circulating levels of 12 DP-related SASP factors were analyzed by immunoassay. Correlation between periodontal clinical parameters and circulating SASP levels was analyzed by Spearman's rank correlation coefficient and back propagation artificial neural network (BPNN). Senescence markers (p16, p21, and HMGB1) in gingiva were determined by immunofluorescence assay.

RESULTS

M-DP group had increased serum levels of twelve SASP factors compared with the M-P group (p < 0.5). Serum levels of IL-6, IL-4, and RAGE were higher in the A-DP group than the A-P group (p < 0.5). The circulating concentrations of certain SASP proteins, including IL-1β, IL-4, MMP-8, OPG, RANKL, and RAGE were correlated with the clinical parameters of DP. BPNN showed that serum SASP levels had considerable predictive value for CAL of DP. Additionally, the DP group had higher expressions of p16, p21, and cytoplasmic-HMGB1 in the gingiva than the P group (p < 0.5).

CONCLUSIONS

Significantly enhanced circulating SASP levels and aggravated periodontal destruction were observed in patients with DP. Importantly, a non-negligible association between serum SASP levels and the severity of DP was found.

Polycomb Recruiters Inside and Outside of the Repressed Domains

The establishment and stable inheritance of individual patterns of gene expression in different cell types are required for the development of multicellular organisms. The important epigenetic regulators are the Polycomb group (PcG) and Trithorax group (TrxG) proteins, which control the silenced and active states of genes, respectively. In Drosophila, the PcG/TrxG group proteins are recruited to the DNA regulatory sequences termed the Polycomb response elements (PREs). The PREs are composed of the binding sites for different DNA-binding proteins, the so-called PcG recruiters. Currently, the role of the PcG recruiters in the targeting of the PcG proteins to PREs is well documented. However, there are examples where the PcG recruiters are also implicated in the active transcription and in the TrxG function. In addition, there is increasing evidence that the genome-wide PcG recruiters interact with the chromatin outside of the PREs and overlap with the proteins of differing regulatory classes. Recent studies of the interactomes of the PcG recruiters significantly expanded our understanding that they have numerous interactors besides the PcG proteins and that their functions extend beyond the regulation of the PRE repressive activity. Here, we summarize current data about the functions of the PcG recruiters.

Structure and Functions of HMGB2 Protein

High-Mobility Group (HMG) chromosomal proteins are the most numerous nuclear non-histone proteins. HMGB domain proteins are the most abundant and well-studied HMG proteins. They are involved in variety of biological processes. HMGB1 and HMGB2 were the first members of HMGB-family to be discovered and are found in all studied eukaryotes. Despite the high degree of homology, HMGB1 and HMGB2 proteins differ from each other both in structure and functions. In contrast to HMGB2, there is a large pool of works devoted to the HMGB1 protein whose structure-function properties have been described in detail in our previous review in 2020. In this review, we attempted to bring together diverse data about the structure and functions of the HMGB2 protein. The review also describes post-translational modifications of the HMGB2 protein and its role in the development of a number of diseases. Particular attention is paid to its interaction with various targets, including DNA and protein partners. The influence of the level of HMGB2 expression on various processes associated with cell differentiation and aging and its ability to mediate the differentiation of embryonic and adult stem cells are also discussed.

Thanksgiving to Yeast, the HMGB Proteins History from Yeast to Cancer

Yeasts have been a part of human life since ancient times in the fermentation of many natural products used for food. In addition, in the 20th century, they became powerful tools to elucidate the functions of eukaryotic cells as soon as the techniques of molecular biology developed. Our molecular understandings of metabolism, cellular transport, DNA repair, gene expression and regulation, and the cell division cycle have all been obtained through biochemistry and genetic analysis using different yeasts. In this review, we summarize the role that yeasts have had in biological discoveries, the use of yeasts as biological tools, as well as past and on-going research projects on HMGB proteins along the way from yeast to cancer.

The role of high mobility group box 1 in neuroinflammatory related diseases

High mobility group box 1 (HMGB1) is a ubiquitous and highly conserved non-histone DNA-binding protein with different biological functions according to its subcellular localization. It is widely believed that HMGB1, which is released into the extracellular space, plays a key role in the inflammatory response. In recent years, numerous studies have shown that the development of various neurological diseases such as epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), cerebrovascular disease and traumatic brain injury (TBI) are inextricably linked to inflammation. We will review the mechanisms of HMGB1 and its receptors in nervous system inflammation to provide a basis for further development of new HMGB1-based therapies.

Vanguard is a Glucose Deprivation-Responsive Long Non-Coding RNA Essential for Chromatin Remodeling-Reliant DNA Repair

Glucose metabolism contributes to DNA damage response pathways by regulating chromatin remodeling, double-strand break (DSB) repair, and redox homeostasis, although the underlying mechanisms are not fully established. Here, a previously uncharacterized long non-coding RNA is revealed that is call Vanguard which acts to promote HMGB1-dependent DNA repair in association with changes in global chromatin accessibility. Vanguard expression is maintained in cancer cells by SP1-dependent transcription according to glucose availability and cellular adenosine triphosphate (ATP) levels. Vanguard promotes complex formation between HMGB1 and HDAC1, with the resulting deacetylation of HMGB1 serving to maintain its nuclear localization and DSB repair function. However, Vanguard downregulation under glucose limiting conditions promotes HMGB1 translocation from the nucleus, increasing DNA damage, and compromising cancer cell growth and viability. Moreover, Vanguard silencing increases the effectiveness of poly (ADP-ribose) polymerase inhibitors against breast cancer cells with wild-type breast cancer gene-1 status, suggesting Vanguard as a potential therapeutic target.

HMGB1 is a mediator of cuproptosis-related sterile inflammation

Cuproptosis is a recently recognized modality of cell death driven by intracellular copper-dependent mitochondrial stress. However, the mediators of the sterile inflammatory response to cuproptotic death are undetermined. Here, we report that high-mobility group box 1 (HMGB1), a damage-associated molecular pattern, is released by cuproptotic cells to initiate inflammation. Mechanically, copper accumulation-induced adenosine triphosphate (ATP) depletion activates AMP-activated protein kinase (AMPK) to promote HMGB1 phosphorylation, resulting in increased extracellular release. In contrast, genetic (using RNAi) or pharmacologic (using dorsomorphin) inhibition of AMPK activation limits cuproptosis and HMGB1 release. Functionally, the ability of HMGB1-deficient cuproptotic cells to promote advanced glycosylation end product-specific receptor (AGER, also known as RAGE)-dependent inflammatory cytokine production is greatly reduced. Thus, HMGB1 is a key immune mediator of cuproptosis-initiated sterile inflammation.

Induction of senescence upon loss of the Ash2l core subunit of H3K4 methyltransferase complexes

Gene expression is controlled in part by post-translational modifications of core histones. Methylation of lysine 4 of histone H3 (H3K4), associated with open chromatin and gene transcription, is catalyzed by type 2 lysine methyltransferase complexes that require WDR5, RBBP5, ASH2L and DPY30 as core subunits. Ash2l is essential during embryogenesis and for maintaining adult tissues. To expand on the mechanistic understanding of Ash2l, we generated mouse embryo fibroblasts (MEFs) with conditional Ash2l alleles. Upon loss of Ash2l, methylation of H3K4 and gene expression were downregulated, which correlated with inhibition of proliferation and cell cycle progression. Moreover, we observed induction of senescence concomitant with a set of downregulated signature genes but independent of SASP. Many of the signature genes are FoxM1 responsive. Indeed, exogenous FOXM1 was sufficient to delay senescence. Thus, although the loss of Ash2l in MEFs has broad and complex consequences, a distinct set of downregulated genes promotes senescence.

Epigenetic Regulation of Cellular Senescence

Senescence is a complex cellular stress response that abolishes proliferative capacity and generates a unique secretory pattern that is implicated in organismal aging and age-related disease. How a cell transitions to a senescent state is multifactorial and often requires transcriptional regulation of multiple genes. Epigenetic alterations to DNA and chromatin are powerful regulators of genome architecture and gene expression, and they play a crucial role in mediating the induction and maintenance of senescence. This review will highlight the changes in chromatin, DNA methylation, and histone alterations that establish and maintain cellular senescence, alongside the specific epigenetic regulation of the senescence-associated secretory phenotype (SASP).

MicroRNA-Mediated Downregulation of HMGB2 Contributes to Cellular Senescence in Microvascular Endothelial Cells

High mobility group box 2 (HMGB2) is a non-histone chromosomal protein involved in various biological processes, including cellular senescence. However, its role in cellular senescence has not been evaluated extensively. To determine the regulatory role and mechanism of HMGB2 in cellular senescence, we performed gene expression analysis, senescence staining, and tube formation assays using young and senescent microvascular endothelial cells (MVECs) after small RNA treatment or HMGB2 overexpression. HMGB2 expression decreased with age and was regulated at the transcriptional level. siRNA-mediated downregulation inhibited cell proliferation and accelerated cellular senescence. In contrast, ectopic overexpression delayed senescence and maintained relatively higher tube-forming activity. To determine the HMGB2 downregulation mechanism, we screened miRNAs that were significantly upregulated in senescent MVECs and selected HMGB2-targeting miRNAs. Six miRNAs, miR-23a-3p, 23b-3p, -181a-5p, -181b-5p, -221-3p, and -222-3p, were overexpressed in senescent MVECs. Ectopic introduction of miR-23a-3p, -23b-3p, -181a-5p, -181b-5p, and -221-3p, with the exception of miR-222-3p, led to the downregulation of HMGB2, upregulation of senescence-associated markers, and decreased tube formation activity. Inhibition of miR-23a-3p, -181a-5p, -181b-5p, and -221-3p delayed cellular senescence. Restoration of HMGB2 expression using miRNA inhibitors represents a potential strategy to overcome the detrimental effects of cellular senescence in endothelial cells.