[Pathogenic role of insufficiency of polycomb repressive complex in primary myelofibrosis].

Primary myelofibrosis (PMF) is characterized by the clonal expansion of megakaryocytes and myeloid cells from stem cells with abnormal cytokine expression, resulting in bone marrow fibrosis, angiogenesis, and osteosclerosis. The use of next-generation sequencing revealed that both genetic and epigenetic changes are important in the pathogenesis of PMF. Several epigenetic regulator genes, including TET2, the polycomb-related gene ASXL1, and the polycomb-group gene EZH2, have been found to be targeted by somatic gene mutations in PMF patients. Among these, loss of Ezh2 has been demonstrated to disrupt the function of the polycomb repressive complex 2, promoting the development of JAK2V617F-induced myelofibrosis in mice. In this analysis, we highlight the role of PRC dysfunction in the pathogenesis of PMF.

Polycomb repressive complex 1.1 coordinates homeostatic and emergency myelopoiesis.

Polycomb repressive complex (PRC) 1 regulates stem cell fate by mediating mono-ubiquitination of histone H2A at lysine 119. While canonical PRC1 is critical for hematopoietic stem and progenitor cell (HSPC) maintenance, the role of non-canonical PRC1 in hematopoiesis remains elusive. PRC1.1, a non-canonical PRC1, consists of PCGF1, RING1B, KDM2B, and BCOR. We recently showed that PRC1.1 insufficiency induced by the loss of PCGF1 or BCOR causes myeloid-biased hematopoiesis and promotes transformation of hematopoietic cells in mice. Here we show that PRC1.1 serves as an epigenetic switch that coordinates homeostatic and emergency hematopoiesis. PRC1.1 maintains balanced output of steady-state hematopoiesis by restricting C/EBPα-dependent precocious myeloid differentiation of HSPCs and the HOXA9- and ß-catenin-driven self-renewing network in myeloid progenitors. Upon regeneration, PRC1.1 is transiently inhibited to facilitate formation of granulocyte-macrophage progenitor (GMP) clusters, thereby promoting emergency myelopoiesis. Moreover, constitutive inactivation of PRC1.1 results in unchecked expansion of GMPs and eventual transformation. Collectively, our results define PRC1.1 as a novel critical regulator of emergency myelopoiesis, dysregulation of which leads to myeloid transformation.

A Nosocomial Outbreak Caused by Human Rhinovirus Species A Type 61 in a Welfare Facility in Gunma Prefecture, Japan.

Human rhinovirus (HRV) infections are generally referred to as the common cold, and are the main cause of mild symptoms. HRV is less frequently implicated in the development of severe respiratory infections. This study reports a nosocomial outbreak of bronchitis and pneumonia caused by HRV in a hospital during the COVID-19 epidemic in September 2022 in Gunma Prefecture, Japan. The patient continued to be symptomatic for nine days. During this outbreak, all 15 residents displayed respiratory symptoms. HRV-A was detected in 12 of the 12 samples, and phylogenetic analysis classified the strain as HRV-A type 61. HRV, COVID-19, and other respiratory infections cannot be differentiated based solely on clinical symptoms. A surveillance system to monitor them is thus needed.

Detection of Respiratory Viruses during the Early Phase of the Coronavirus Disease 2019 Pandemic in Ibaraki and Gunma Prefectures, Japan.

Respiratory infections are common, and the most common causative agent is a virus. Therefore, routine surveillance of respiratory viruses is useful in the case of novel viral diseases such as coronavirus disease 2019 (COVID-19). In this study, to clarify the kind of virus involved in suspected cases of COVID-19 in the early stages of the pandemic, we attempted to detect various respiratory viruses in 613 specimens that tested negative for severe acute respiratory syndrome coronavirus 2 using reverse transcription polymerase chain reaction. As a result, viruses were detected in 59 (9.6%) patients. In addition, human rhinovirus (HRV), human metapneumovirus (HMPV), human respiratory syncytial virus, and human parechovirus were detected in 29, 25, 3, and 2 patients, respectively. Although this study was conducted over a short period of time and not all specimens were tested, these results indicate that various respiratory viruses, especially HRV and HMPV, can be detected even during the early stages of the COVID-19 pandemic. Because various respiratory viruses maintain a constant effect during the outbreak of the newly emerged pandemic, systematic surveillance of respiratory viruses is needed during the normal period to make good use for clinical and public health.

Insufficiency of non-canonical PRC1 synergizes with JAK2V617F in the development of myelofibrosis.

Insufficiency of polycomb repressive complex 2 (PRC2), which trimethylates histone H3 at lysine 27, is frequently found in primary myelofibrosis and promotes the development of JAK2V617F-induced myelofibrosis in mice by enhancing the production of dysplastic megakaryocytes. Polycomb group ring finger protein 1 (Pcgf1) is a component of PRC1.1, a non-canonical PRC1 that monoubiquitylates H2A at lysine 119 (H2AK119ub1). We herein investigated the impact of PRC1.1 insufficiency on myelofibrosis. The deletion of Pcgf1 in JAK2V617F mice strongly promoted the development of lethal myelofibrosis accompanied by a block in erythroid differentiation. Transcriptome and chromatin immunoprecipitation sequence analyses showed the de-repression of PRC1.1 target genes in Pcgf1-deficient JAK2V617F hematopoietic progenitors and revealed Hoxa cluster genes as direct targets. The deletion of Pcgf1 in JAK2V617F hematopoietic stem and progenitor cells (HSPCs), as well as the overexpression of Hoxa9, restored the attenuated proliferation of JAK2V617F progenitors. The overexpression of Hoxa9 also enhanced JAK2V617F-mediated myelofibrosis. The expression of PRC2 target genes identified in PRC2-insufficient JAK2V617F HSPCs was not largely altered in Pcgf1-deleted JAK2V617F HSPCs. The present results revealed a tumor suppressor function for PRC1.1 in myelofibrosis and suggest that PRC1.1 insufficiency has a different impact from that of PRC2 insufficiency on the pathogenesis of myelofibrosis.

Relationships between Viral Load and the Clinical Course of COVID-19.

To predict the clinical outcome of coronavirus disease-2019 (COVID-19), we examined relationships among epidemiological data, viral load, and disease severity. We examined viral loads of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) in fatal (15 cases), symptomatic/survived (133 cases), and asymptomatic cases (138 cases) using reverse transcription quantitative real-time PCR (RT-qPCR). We examined 5768 nasopharyngeal swabs (NPS) and attempted to detect the SARS-CoV-2 genome using RT-qPCR. Among them, the viral genome was detected using the method for the 370 NPS samples with a positive rate of 6.4%. A comparison of each age showed that the fatal case was higher than the survived case and asymptomatic patients. Survived cases were older than asymptomatic patients. Notably, the viral load in the fatal cases was significantly higher than in symptomatic or asymptomatic cases (p < 0.05). These results suggested that a high viral load of the SARS-CoV-2 in elderly patients at an early stage of the disease results in a poor outcome. We should, therefore, intervene early to prevent a severe stage of the disease in such cases.

DHODH inhibition synergizes with DNA-demethylating agents in the treatment of myelodysplastic syndromes.

Dihydroorotate dehydrogenase (DHODH) catalyzes a rate-limiting step in de novo pyrimidine nucleotide synthesis. DHODH inhibition has recently been recognized as a potential new approach for treating acute myeloid leukemia (AML) by inducing differentiation. We investigated the efficacy of PTC299, a novel DHODH inhibitor, for myelodysplastic syndrome (MDS). PTC299 inhibited the proliferation of MDS cell lines, and this was rescued by exogenous uridine, which bypasses de novo pyrimidine synthesis. In contrast to AML cells, PTC299 was inefficient at inhibiting growth and inducing the differentiation of MDS cells, but synergized with hypomethylating agents, such as decitabine, to inhibit the growth of MDS cells. This synergistic effect was confirmed in primary MDS samples. As a single agent, PTC299 prolonged the survival of mice in xenograft models using MDS cell lines, and was more potent in combination with decitabine. Mechanistically, a treatment with PTC299 induced intra-S-phase arrest followed by apoptotic cell death. Of interest, PTC299 enhanced the incorporation of decitabine, an analog of cytidine, into DNA by inhibiting pyrimidine production, thereby enhancing the cytotoxic effects of decitabine. RNA-seq data revealed the marked downregulation of MYC target gene sets with PTC299 exposure. Transfection of MDS cell lines with MYC largely attenuated the growth inhibitory effects of PTC299, suggesting MYC as one of the major targets of PTC299. Our results indicate that the DHODH inhibitor PTC299 suppresses the growth of MDS cells and acts in a synergistic manner with decitabine. This combination therapy may be a new therapeutic option for the treatment of MDS.

PRC2 insufficiency causes p53-dependent dyserythropoiesis in myelodysplastic syndrome.

EZH1 and EZH2 are enzymatic components of polycomb repressive complex (PRC) 2, which catalyzes histone H3K27 tri-methylation (H3K27me3) to repress the transcription of PRC2 target genes. We previously reported that the hematopoietic cell-specific Ezh2 deletion (Ezh2Δ/Δ) induced a myelodysplastic syndrome (MDS)-like disease in mice. We herein demonstrated that severe PRC2 insufficiency induced by the deletion of one allele Ezh1 in Ezh2-deficient mice (Ezh1+/-Ezh2Δ/Δ) caused advanced dyserythropoiesis accompanied by a differentiation block and enhanced apoptosis in erythroblasts. p53, which is activated by impaired ribosome biogenesis in del(5q) MDS, was specifically activated in erythroblasts, but not in hematopoietic stem or progenitor cells in Ezh1+/-Ezh2Δ/Δ mice. Cdkn2a, a major PRC2 target encoding p19Arf, which activates p53 by inhibiting MDM2 E3 ubiquitin ligase, was de-repressed in Ezh1+/-Ezh2Δ/Δ erythroblasts. The deletion of Cdkn2a as well as p53 rescued dyserythropoiesis in Ezh1+/-Ezh2Δ/Δ mice, indicating that PRC2 insufficiency caused p53-dependent dyserythropoiesis via the de-repression of Cdkn2a. Since PRC2 insufficiency is often involved in the pathogenesis of MDS, the present results suggest that p53-dependent dyserythropoiesis manifests in MDS in the setting of PRC2 insufficiency.

Efficacy of the novel tubulin polymerization inhibitor PTC-028 for myelodysplastic syndrome.

Monomer tubulin polymerize into microtubules, which are highly dynamic and play a critical role in mitosis. Therefore, microtubule dynamics are an important target for anticancer drugs. The inhibition of tubulin polymerization or depolymerization was previously targeted and exhibited efficacy against solid tumors. The novel small molecule PTC596 directly binds tubulin, inhibits microtubule polymerization, downregulates MCL-1, and induces p53-independent apoptosis in acute myeloid leukemia cells. We herein investigated the efficacy of PTC-028, a structural analog of PTC596, for myelodysplastic syndrome (MDS). PTC-028 suppressed growth and induced apoptosis in MDS cell lines. The efficacy of PTC028 in primary MDS samples was confirmed using cell proliferation assays. PTC-028 synergized with hypomethylating agents, such as decitabine and azacitidine, to inhibit growth and induce apoptosis in MDS cells. Mechanistically, a treatment with PTC-028 induced G2/M arrest followed by apoptotic cell death. We also assessed the efficacy of PTC-028 in a xenograft mouse model of MDS using the MDS cell line, MDS-L, and the AkaBLI bioluminescence imaging system, which is composed of AkaLumine-HCl and Akaluc. PTC-028 prolonged the survival of mice in xenograft models. The present results suggest a chemotherapeutic strategy for MDS through the disruption of microtubule dynamics in combination with DNA hypomethylating agents.

Bmi1 restricts the adipogenic differentiation of bone marrow stromal cells to maintain the integrity of the hematopoietic stem cell niche.

The polycomb group protein Bmi1 maintains hematopoietic stem cell (HSC) functions. We previously reported that Bmi1-deficient mice exhibited progressive fatty changes in bone marrow (BM). A large portion of HSCs reside in the perivascular niche created partly by endothelial cells and leptin receptor+ (LepR+) BM stromal cells. To clarify how Bmi1 regulates the HSC niche, we specifically deleted Bmi1 in LepR+ cells in mice. The Bmi1 deletion promoted the adipogenic differentiation of LepR+ stromal cells and caused progressive fatty changes in the BM of limb bones with age, resulting in reductions in the numbers of HSCs and progenitors in BM and enhanced extramedullary hematopoiesis. This adipogenic change was also evident during BM regeneration after irradiation. Several adipogenic regulator genes appeared to be regulated by Bmi1. Our results indicate that Bmi1 keeps the adipogenic differentiation program repressed in BM stromal cells to maintain the integrity of the HSC niche.

Ezh1 Targets Bivalent Genes to Maintain Self-Renewing Stem Cells in Ezh2-Insufficient Myelodysplastic Syndrome.

Polycomb repressive complex (PRC) 2 represses transcription through histone H3K27 trimethylation (H3K27me3). We previously reported that the hematopoietic-cell-specific deletion of Ezh2, encoding a PRC2 enzyme, induced myelodysplastic syndrome (MDS) in mice, whereas the concurrent Ezh1 deletion depleted hematopoietic stem and progenitor cells (HSPCs). We herein demonstrated that mice with only one Ezh1 allele (Ezh1+/-Ezh2Δ/Δ) maintained HSPCs. A chromatin immunopreciptation sequence analysis revealed that residual PRC2 preferentially targeted genes with high levels of H3K27me3 and H2AK119 monoubiquitination (H2AK119ub1) in HSPCs (designated as Ezh1 core target genes), which were mostly developmental regulators, and maintained H3K27me3 levels in Ezh1+/-Ezh2Δ/Δ HSPCs. Even upon the complete depletion of Ezh1 and Ezh2, H2AK119ub1 levels were largely retained, and only a minimal number of Ezh1 core targets were de-repressed. These results indicate that genes marked with high levels of H3K27me3 and H2AK119ub1 are the core targets of polycomb complexes in HSPCs as well as MDS stem cells.

Bcor insufficiency promotes initiation and progression of myelodysplastic syndrome.

BCOR, encoding BCL-6 corepressor (BCOR), is X-linked and targeted by somatic mutations in various hematological malignancies including myelodysplastic syndrome (MDS). We previously reported that mice lacking Bcor exon 4 (Bcor ΔE4/y ) in the hematopoietic compartment developed NOTCH-dependent acute T-cell lymphoblastic leukemia (T-ALL). Here, we analyzed mice lacking Bcor exons 9 and 10 (Bcor ΔE9-10/y ), which express a carboxyl-terminal truncated BCOR that fails to interact with core effector components of polycomb repressive complex 1.1. Bcor ΔE9-10/y mice developed lethal T-ALL in a similar manner to Bcor ΔE4/y mice, whereas Bcor ΔE9-10/y hematopoietic cells showed a growth advantage in the myeloid compartment that was further enhanced by the concurrent deletion of Tet2 Tet2 Δ/Δ Bcor ΔE9-10/y mice developed lethal MDS with progressive anemia and leukocytopenia, inefficient hematopoiesis, and the morphological dysplasia of blood cells. Tet2 Δ/Δ Bcor ΔE9-10/y MDS cells reproduced MDS or evolved into lethal MDS/myeloproliferative neoplasms in secondary recipients. Transcriptional profiling revealed the derepression of myeloid regulator genes of the Cebp family and Hoxa cluster genes in Bcor ΔE9-10/y progenitor cells and the activation of p53 target genes specifically in MDS erythroblasts where massive apoptosis occurred. Our results reveal a tumor suppressor function of BCOR in myeloid malignancies and highlight the impact of Bcor insufficiency on the initiation and progression of MDS.

Steroidal Glycosides from Convallaria majalis Whole Plants and Their Cytotoxic Activity.

Phytochemical examination of Convallaria majalis (Liliaceae) whole plants yielded 15 steroidal glycosides (1-15), including nine new compounds (4-6, 10-15) with a lycotetrose unit. The structures of the new compounds were determined using two-dimensional Nuclear magnetic resonance (NMR) analyses and chemical methods. The isolated compounds were evaluated for cytotoxicity against HL-60 human promyelocytic leukemia cells, A549 human lung adenocarcinoma cells, and HSC-4 and HSC-2 human oral squamous cell carcinoma cell lines. Of these, (25S)-spirost-5-en-3ß-yl O-ß-d-glucopyranosyl-(1→2)-O-[ß-d-xylopyranosyl-(1→3)]-O-ß-d-glucopyranosyl-(1→4)-ß-d-galactopyranoside (1) exhibited cytotoxic activity against HL-60, A549, HSC-4, and HSC-2 cells with IC50 values ranging from 0.96 to 3.15 µM. The corresponding furostanol glycoside of 1, (25S)-26-[(ß-d-glucopyranosyl)oxy]-22α-hydroxyfurost-5-en-3ß-yl O-ß-d-glucopyranosyl-(1→2)-O-[ß-d-xylopyranosyl-(1→3)]-O-ß-d-glucopyranosyl-(1→4)-ß-d-galactopyranoside (8), was cytotoxic to the adherent cell lines of A549, HSC-4, and HSC-2 cells with IC50 values of 2.97, 11.04, and 8.25 µM, respectively. The spirostanol lycotetroside (1) caused necrotic cell death in A549 cells in a dose-dependent manner. Alternatively, the furostanol lycotetroside (8) induced apoptotic cell death in A549 cells in a time-dependent manner, as was evident by morphological observations and flow cytometry analyses.

Steroidal glycosides from the bulbs of Fritillaria meleagris and their cytotoxic activities.

Steroidal glycosides (1-18), including 10 new compounds (1-10), were isolated from the bulbs of Fritillaria meleagris (Liliaceae). The structures of the new compounds were determined by two-dimensional (2D) NMR analysis, and by hydrolytic cleavage followed by spectroscopic and chromatographic analysis. The isolated compounds and their aglycones were evaluated for cytotoxic activity against HL-60 human promyelocytic leukemia cells and A549 human lung adenocarcinoma cells. Morphological observation and flow cytometry analysis showed that 5ß-spirostanol glycoside (2) and a cholestane derivative (17a) induced apoptotic cell death in HL-60 cells through different mechanisms of action. Furthermore, the (22R)-spirosolanol glycoside (11) selectively induced apoptosis in A549 cells without affecting the caspase-3 activity level.

Novel synthetic collagen fibers, poly(PHG), stimulate platelet aggregation through glycoprotein VI.

Novel synthetic collagen fibers, poly(PHG) made by polycondensation of Pro-Hyp-Gly, spontaneously assume polymeric structure with molecular weights greater than 10(5). Its application for biomaterials has been explored, but that for a platelet agonist has not been investigated. Poly(PHG)-induced platelet aggregation independently of thromboxane A(2) and integrin alpha2beta1. Poly(PHG)-induced tyrosine phosphorylation of glycoprotein VI (GPVI)-related molecules and failed to activate GPVI/FcRgamma-deficient platelets. Binding of GPVI to poly(PHG) was confirmed by a surface plasmon resonance spectroscopy, suggesting that poly(PHG) activates platelets through GPVI. Poly(PHG) is an useful research tool to investigate GPVI-mediated signals and a substitute for collagen in platelet functional assays.

A novel RUNX1 mutation in familial platelet disorder with propensity to develop myeloid malignancies.

We describe a Japanese family with familial platelet disorder with propensity to develop myeloid malignancies (FPD/MM). Among the three affected individuals, two members developed myeloid malignancies. Sequence studies demonstrate that all affected individuals of the pedigree display a heterozygous single nucleotide deletion in exon 8 of the RUNX1 gene.