Protein phosphatase, Mg2+/Mn2+-dependent 1D (PPM1D) mutations in haematological cancer.

Until recently, the protein phosphatase, Mg2+/Mn2+-dependent 1D (PPM1D) gene had not been examined in haematological cancer, but several studies have now explored the functional role of this gene and its aberrations. It is often mutated in the context of clonal haemopoiesis (including in patients with lymphoma, myeloproliferative neoplasms and myelodysplastic syndrome) and mutations have been associated with exposure to cytotoxic and radiation therapy, development of therapy-related neoplasms and inferior survival. The vast majority of PPM1D mutations found in haematopoietic cells are of the nonsense or frameshift type and located within terminal exon 6. These genetic defects are rarely found in the blood of healthy individuals. PPM1D encodes the PPM1D phosphatase [also named wild-type p53-induced phosphatase 1 (WIP1)], which negatively regulates signalling molecules within the DNA damage response pathway, including tumour suppressor p53. Clonal expansion of PPM1D mutant haematopoietic cells can potentially be prevented with inhibitors; however, human trials are awaited. In the present review, we provide a review of the literature regarding PPM1D and its role in haematological cancer.

The role of mTOR-mediated signals during haemopoiesis and lineage commitment.

The serine/threonine protein kinase mechanistic target of rapamycin (mTOR) has been implicated in the regulation of an array of cellular functions including protein and lipid synthesis, proliferation, cell size and survival. Here, we describe the role of mTOR during haemopoiesis within the context of mTORC1 and mTORC2, the distinct complexes in which it functions. The use of conditional transgenic mouse models specifically targeting individual mTOR signalling components, together with selective inhibitors, have generated a significant body of research emphasising the critical roles played by mTOR, and individual mTOR complexes, in haemopoietic lineage commitment and development. This review will describe the profound role of mTOR in embryogenesis and haemopoiesis, underscoring the importance of mTORC1 at the early stages of haemopoietic cell development, through modulation of stem cell potentiation and self-renewal, and erythroid and B cell lineage commitment. Furthermore, the relatively discrete role of mTORC2 in haemopoiesis will be explored during T cell development and B cell maturation. Collectively, this review aims to highlight the functional diversity of mTOR signalling and underline the importance of this pathway in haemopoiesis.

Role of the bone morphogenic protein pathway in developmental haemopoiesis and leukaemogenesis.

Myeloid leukaemias share the common characteristics of being stem cell-derived clonal diseases, characterised by excessive proliferation of one or more myeloid lineage. Chronic myeloid leukaemia (CML) arises from a genetic alteration in a normal haemopoietic stem cell (HSC) giving rise to a leukaemic stem cell (LSC) within the bone marrow (BM) 'niche'. CML is characterised by the presence of the oncogenic tyrosine kinase fusion protein breakpoint cluster region-abelson murine leukaemia viral oncogene homolog 1 (BCR-ABL), which is responsible for driving the disease through activation of downstream signal transduction pathways. Recent evidence from our group and others indicates that important regulatory networks involved in establishing primitive and definitive haemopoiesis during development are reactivated in myeloid leukaemia, giving rise to an LSC population with altered self-renewal and differentiation properties. In this review, we explore the role the bone morphogenic protein (BMP) signalling plays in stem cell pluripotency, developmental haemopoiesis, HSC maintenance and the implication of altered BMP signalling on LSC persistence in the BM niche. Overall, we emphasise how the BMP and Wnt pathways converge to alter the Cdx-Hox axis and the implications of this in the pathogenesis of myeloid malignancies.

Complete recovery from paraparesis in spinal cord compression due to extramedullary haemopoiesis in beta-thalassaemia by emergency radiation therapy.

Extramedullary haemopoiesis (EMH) is a complication commonly associated with beta-thalassaemia intermedia; it is frequently asymptomatic but can sometimes lead to symptomatic tumour-like masses. No guidelines or common consensus are available in literature regarding the different treatment strategies and only single cases have been reported. We describe a case of spinal cord compression due to intrathoracic EMH masses treated with combined radiotherapy and hydroxyurea.

Current Trends on Hemopoietic Stem Cells.

Advances in single-cell technology and genetic mouse models have resulted in the identification of new types of hemopoietic stem cells (HSC), resulting in baffling observations, suggesting a reconsideration of the long-held notion that all hematopoietic cells in the adult are derived from HSCs. The existence of long-lived HSC-independent hematopoiesis has led to the conclusion that despite the single hierarchical differentiation route that generates functional blood types, other differentiation routes exist in-vivo. Heterogeneity in the HSC population and the evolving knowledge around HSC has translated to it's improved application as a therapeutic tool for various blood disorders. The reprogramming of non-hematopoietic somatic and mature blood cells to pluripotency with their subsequent differentiation into hematopoietic stem cells/progenitor cells and the introduction of new generation sequencing holds the potential for the resolution of ambiguities involved in HSC bone marrow transplantation. There is a change in the paradigm for HSC transplantation donor selection. Donor choice favors haploidentical HCT than cord blood. This review provides a general overview of the current events around hemopoietic stem cells, with emphasis on the rising trend of HSC transplantation, especially haploidentical stem cell transplantation.

RPL27A is a target of miR-595 and may contribute to the myelodysplastic phenotype through ribosomal dysgenesis.

We investigated the functional consequences following deletion of a microRNA (miR) termed miR-595 which resides on chromosome 7q and is localised within one of the commonly deleted regions identified for Myelodysplasia (MDS) with monosomy 7 (-7)/isolated loss of 7q (7q-). We identified several targets for miR-595, including a large ribosomal subunit protein RPL27A. RPL27A downregulation induced p53 activation, apoptosis and inhibited proliferation. Moreover, p53-independent effects were additionally identified secondary to a reduction in the ribosome subunit 60s. We confirmed that RPL27A plays a pivotal role in the maintenance of nucleolar integrity and ribosomal synthesis/maturation. Of note, RPL27A overexpression, despite showing no significant effects on p53 mRNA levels, did in fact enhance cellular proliferation. In normal CD34+ cells, RPL27A knockdown preferentially blocked erythroid proliferation and differentiation. Lastly, we show that miR-595 expression appears significantly downregulated in the majority of primary samples derived from MDS patients with (-7)/(7q-), in association with RPL27A upregulation. This significant downregulation of miR-595 is also apparent when higher risk MDS cases are compared to lower risk cases. The potential clinical importance of these findings requires further validation.

Clinical significance of acquired somatic mutations in aplastic anaemia.

Aplastic anaemia (AA) is frequently associated with other disorders of clonal haemopoiesis such as paroxysmal nocturnal haemoglobinuria (PNH), myelodysplastic syndrome (MDS) and T-large granular lymphocytosis. Certain clones may escape the immune attack within the bone marrow environment and proliferate and attain a survival advantage over normal haemopoietic stem cells, such as trisomy 8, loss of heterozygosity of short arm of chromosome 6 and del13q clones. Recently acquired somatic mutations (SM), excluding PNH clones, have been reported in around 20-25 % of patients with AA, which predispose to a higher risk of later malignant transformation to MDS/acute myeloid leukaemia. Furthermore, certain SM, such as ASXL1 and DNMT3A are associated with poor survival following immunosuppressive therapy, whereas PIGA, BCOR/BCORL1 predict for good response and survival. Further detailed and serial analysis of the immune signature in AA is needed to understand the pathogenetic basis for the presence of clones with SM in a significant proportion of patients.

Automated analysis of bone marrow aspirates from dogs with haematological disorders.

Automated analysis of bone marrow (BM) aspirates is a useful 'pre-microscopical' screen to identify hypocellular samples and those with potentially abnormal cells. In order to determine whether automated analysis could also be used to identify haemopoietic abnormalities, EDTA-anticoagulated BM aspirates from 43 dogs were analysed using the Advia 2120 instrument. Corresponding Wright-stained BM smears were evaluated microscopically to determine smear quality, cell composition and 500-cell differential counts, and correlation to automated analysis parameters was computed. Leucocyte cytograms generated by the automated analyzer were scrutinized and compared with those of 'normal' BM. Twenty-three neoplastic and 20 non-neoplastic samples were analysed, including samples from 10 cases of acute myeloid leukaemia, four cases of acute lymphocytic leukaemia, four cases of chronic lymphocytic leukaemia, one case of chronic neutrophilic leukaemia, three cases of multiple myeloma, one case of myelodysplastic syndrome, five cases of non-regenerative immune-mediated haemolytic anaemia, one case of immune-mediated neutropenia, three cases of immune-mediated thrombocytopenia, six cases of inflammatory disease, three samples with myelotoxicity and two samples analysed for staging of neoplasia. Automated white blood cell (WBC) counts correlated significantly with smear cellularity, particle cellularity and particle number. There was a significant difference in WBC counts of samples with insufficient versus sufficient particles. Significant correlations between Advia percent neutrophils and microscopical determination of marrow segmented neutrophils/neutrophilic granulocyte reserve, Advia percent lymphocytes and microscopical determination of lymphocytes/rubricytes, Advia percent large unstained cells and microscopical determination of myeloblasts/promyelocytes and between Advia percent eosinophils and manual determination of eosinophils were identified. This suggested that Advia WBC counts may be used to approximate BM sample quality and that Advia differential counts may predict marrow granulocyte reserve and lymphocyte/rubricyte stores. Distinct and consistent alterations in cytogram patterns were observed in cases of acute leukaemia, but were less obvious in chronic leukaemia. Complete automated BM analysis was performed in approximately 2 min, while staining and coverslipping of BM slides required approximately 30 min. Hence, although automated analysis should not supplant microscopical evaluation of BM, it can provide useful ancillary information in a short time and flag potentially inadequate or abnormal samples.

Morphological study of bone marrow to assess the effects of lead acetate on haemopoiesis and aplasia and the ameliorating role of Carica papaya extract.

Lead causes damage to the body by inducing oxidative stress. The sites of damage include the bone marrow, where marrow hypoplasia and osteosclerosis may be observed. Leaves of Carica papaya, which have antioxidant and haemopoietic properties, were tested against the effect of lead acetate in experimental rats. The rats were divided into 8 groups; control, lead acetate only, Carica papaya (50 mg and 200 mg), post-treatment with Carica papaya (50 mg and 200 mg) following lead acetate administration and pre-treatment with Carica papaya (50 mg and 200 mg) followed by lead acetate administration. The substances were administered for 14 days. The effects were evaluated by measuring protein carbonyl content (PCC) and glutathione content (GC) in the bone marrow. Histological changes in the bone marrow were also observed. The results showed that Carica papaya induced a significant reduction in the PCC activity and significantly increased the GC in the bone marrow. Carica papaya also improved the histology of the bone marrow compared with that of the lead acetate-treated group. In summary, Carica papaya was effective against the oxidative damage caused by lead acetate in the bone marrow and had a stimulatory effect on haemopoiesis.