On the pathogenesis of preleukemic myelodysplastic syndromes: development of a dysplastic hemopoietic proliferation in the rat after a single pulse dose of dimethylbenz(a)anthracene (DMBA)

A research review of experimental animal models with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) consists of a group of hematologic tumors that are derived from the clonal proliferation of hematopoietic stem cells, featuring abnormal hematopoietic cell development and ineffective hematopoiesis. Animal models are an important scientific research platform that has been widely applied in the research of human diseases, especially tumors. Animal models with MDS can simulate characteristic human genetic variations and tumor phenotypes. They also provide a reliable platform for the exploration of the pathogenesis and diagnostic markers of MDS as well as for a drug efficacy evaluation. This paper reviews the research status of three animal models and a new spontaneous mouse model with MDS.

Novel spontaneous myelodysplastic syndrome mouse model

Background

Myelodysplastic syndrome (MDS) is a group of disorders involving hemopoietic dysfunction leading to leukemia. Although recently progress has been made in identifying underlying genetic mutations, many questions still remain. Animal models of MDS have been produced by introduction of specific mutations. However, there is no spontaneous mouse model of MDS, and an animal model to simulate natural MDS pathogenesis is urgently needed.

Methods

In characterizing the genetically diverse mouse strains of the Collaborative Cross (CC) we observed that one, designated JUN, had abnormal hematological traits. This strain was thus further analyzed for phenotypic and pathological identification, comparing the changes in each cell population in peripheral blood and in bone marrow.

Results

In a specific-pathogen free environment, mice of the JUN strain are relatively thin, with healthy appearance. However, in a conventional environment, they become lethargic, develop wrinkled yellow hair, have loose and light stools, and are prone to infections. We found that the mice were cytopenic, which was due to abnormal differentiation of multipotent bone marrow progenitor cells. These are common characteristics of MDS.

Conclusions

A mouse strain, JUN, was found displaying spontaneous myelodysplastic syndrome. This strain has the advantage over existing models in that it develops MDS spontaneously and is more similar to human MDS than genetically modified mouse models. JUN mice will be an important tool for pathogenesis research of MDS and for evaluation of new drugs and treatments.

Summary of animal models of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a malignant tumor of the hematological system characterized by long-term, progressive refractory hemocytopenia. In addition, the risk of leukemia is high, and once it develops, the course of acute leukemia is short with poor curative effect. Animal models are powerful tools for studying human diseases and are highly effective preclinical platforms. Animal models of MDS can accurately show genetic aberrations and hematopoietic clone phenotypes with similar cellular features (such as impaired differentiation and increased apoptosis), and symptoms can be used to assess existing treatments. Animal models are also helpful for understanding the pathogenesis of MDS and its relationship with acute leukemia, which helps with the identification of candidate genes related to the MDS phenotype. This review summarizes the current status of animal models used to research myelodysplastic syndrome (MDS).

Downregulation of microRNA-144 inhibits proliferation and promotes the apoptosis of myelodysplastic syndrome cells through the activation of the AKAP12-dependent ERK1/2 signaling pathway

BACKGROUND

Myelodysplastic syndromes (MDS) represent a family of hematopoietic stem cell disorders characterized by ineffective hematopoiesis. While the functions of many microRNAs have been identified in MDS, microRNA-144 (miR-144) remains poorly understood. Thus, the aim of the present study was to determine the effects of miR-144 on cell proliferation and apoptosis in MDS cells and mechanism thereof.

METHODS

MDS-related microarrays were used for screening differentially expressed genes in MDS. The relationship between miR-144 and A-kinase anchoring protein 12 (AKAP12) was determined by a dual luciferase reporter gene assay. Subsequently, gain- and loss-function approaches were used to assess the effects of miR-144 and AKAP12 on cell proliferation, cell cycle and cell apoptosis by MTT assay and flow cytometry. Following the induction of a mouse model with MDS, the tumor tissues were extract for evaluation of apoptosis and the expression of miR-144, AKAP12, and the relevant genes associated with extracellular-regulated protein kinases 1/2 (ERK1/2) signaling pathway and apoptosis.

RESULTS

We observed significantly diminished expression of AKAP12 in MDS samples. miR-144 directly bound to AKAP12 3'UTR and reduced its expression in hematopoietic cells. Downregulation of miR-144 or upregulation of AKAP12 was observed to prolong cell cycle, inhibit cell proliferation, and induce apoptosis, accompanied by increased expression of AKAP12, p-ERK1/2, caspase-3, caspase-9, Bax, and p53, as well as decreased expression of Bcl-2. The transplanted tumors in mice with down-regulated miR-144 exhibited a lower mean tumor diameter and weight, and increased apoptosis index and expression of AKAP12 and ERK1/2.

CONCLUSION

Taken together, these studies demonstrate the stimulative role of miR-144 in MDS progression by regulating AKAP12-dependent ERK1/2 signaling pathway.

Proceedings of the 2011 National Toxicology Program Satellite Symposium

The 2011 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was held in Denver, Colorado in advance of the Society of Toxicologic Pathology's 30th Annual Meeting. The goal of the NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting or discussion. Some lesions and topics covered during the symposium include: proliferative lesions from various fish species including ameloblastoma, gas gland hyperplasia, nodular regenerative hepatocellular hyperplasia, and malignant granulosa cell tumor; spontaneous cystic hyperplasia in the stomach of CD1 mice and histiocytic aggregates in the duodenal villous tips of treated mice; an olfactory neuroblastoma in a cynomolgus monkey; various rodent skin lesions, including follicular parakeratotic hyperkeratosis, adnexal degeneration, and epithelial intracytoplasmic accumulations; oligodendroglioma and microgliomas in rats; a diagnostically challenging microcytic, hypochromic, responsive anemia in rats; a review of microcytes and microcytosis; nasal lesions associated with green tea extract and Ginkgo biloba in rats; corneal dystrophy in Dutch belted rabbits; valvulopathy in rats; and lymphoproliferative disease in a cynomolgus monkey.

Systemic toxicity from subchronic dermal exposure, chemical characterization, and dermal penetration of catalytically cracked clarified slurry oil

Clarified slurry oil (CSO), the heavy residual fraction from the fluidized catalytic cracker, was applied to the shaven backs of groups of 10 male and 10 female Sprague-Dawley rats 5 days/week for 13 weeks at doses of 8, 30, 125, or 500 mg/kg/day, and to another group for 2 weeks at doses of 2000 mg/kg/day. The rats were fitted with cardboard Elizabethan collars to minimize the ingestion of the test material, which was applied undiluted and remained uncovered on the skin. A similar group of rats served as controls; they were treated in the same manner except that no CSO was applied to their skin. There was a dose-related mortality and depression of body weight gain in the rats treated with CSO at doses of 30 mg/kg/day or greater; none of the rats dosed at 2000 mg/kg/day survived more than 2 weeks. The primary target organs of CSO toxicity were the liver, thymus, and bone marrow. The effects on the liver included increased weight (250% at 500 mg/kg/day), cholangiolitis, diffuse liver cell degeneration and hypertrophy, necrosis, fibrosis, decreased serum glucose, increased levels of alkaline phosphatase, aspartate aminotransferase, alanine amino transferase, bilirubin, and triglycerides. The thymus was found to be small and upon microscopic examination to be atrophic or hypoplastic. Erythroid hypoplasia was found in the bone marrow of some of the rats dosed at 30 mg/kg/day and increased in severity with increasing dose. The erythroid hypoplasia was accompanied by a dose-related anemia. Even in the rats dosed at 8 mg/kg/day, very slight abnormalities in the bile ducts were observed upon microscopic examination of the liver. Chromatographic separation and analyses demonstrated that CSO contains about 58% 3- to 5-ring polycyclic aromatic hydrocarbons (PAHs) and approximately 8-10% carbazole derivatives. In vitro and in vivo skin penetration studies demonstrated that the carbazole materials penetrate through the skin to a considerable extent (about 44%); less penetration was observed with 2- or 3-ring (8-13%) or 5-ring PAHs (3%).

Recovery patterns of rat hemopoietic stem cells between pulse doses of 7,12-dimethylbenz(a)anthracene (DMBA) applied in a leukemogenic regimen

Male Wistar rats received repeated pulse doses of 7,12-dimethylbenz(a)anthracene (DMBA), known to elicit myelodysplasia followed by acute, mostly erythroblastic, leukemia at 10-day intervals. The recovery of spleen colony forming hemopoietic stem cells (CFU-s) surviving the cytocidal action of DMBA was examined between pulses. Recovery after a pulse of 35 mg/kg body weight varied with the organ source of the CFU-s (femoral bone marrow or spleen) and the number of preceding DMBA pulses. After a single DMBA pulse bone marrow CFU-s initially recovered faster than reported for normal bone marrow CFU-s transplanted into chemically conditioned rats. But recovery was followed by regeneration arrest. Population doubling times of marrow CFU-s increased with the number of DMBA pulses. Recovery of splenic CFU-s was slower after a single DMBA pulse than reported for normal spleen CFU-s transplanted into chemically conditioned rats. The CFU-s population doubling times were not significantly different after a single or five DMBA pulses. After three pulses, however, recovery of splenic CFU-s was exceedingly slow until day 5 and subsequently accelerated, but was still slower than after one or five pulses. In the spleen CFU-s recovery was always accompanied by regeneration of total cell numbers with a preference for erythroid regeneration. In the bone marrow this was the case after three DMBA pulses only.

The concept of preleukemia: clinical and laboratory studies

Thirty-five years ago, a handful of astute clinical hematologists began to notice that some of their patients with acute nonlymphocytic leukemia had a history of a preceding ill-defined hemopathy. This "preleukemic" hemopathy was increasingly reported anecdotally and through careful retrospective analyses. In more recent prospective studies, this syndrome has been relatively well defined. Indeed, it is widely accepted that there exists a hematopoietic abnormality not recognizable as classical, overt, acute nonlymphocytic leukemia, which, nonetheless, can represent an early phase of leukemia. In this manuscript, the author reviews the original case reports, the initial retrospective studies, and the prospective studies which have clarified some of the clinical and laboratory features of the preleukemic syndrome. The notion that the preleukemic syndrome represents an established neoplastic process will be reviewed with special attention to assessment of clonal hematopoiesis, cytogenetic studies, and clonal evolution. Studies on induced leukemia and preleukemia in experimental animals and humans will be reviewed as will be the semantic issues which have complicated our ability to compare interinstitutional studies. A simple classification scheme of the myelodysplastic syndromes will be presented as will be a framework agenda for future studies on the pathophysiology of these syndromes.

Myelodysplastic syndromes: pathogenesis, functional abnormalities, and clinical implications

The myelodysplastic syndromes represent a preleukaemic state in which a clonal abnormality of haemopoietic stem cell is characterised by a variety of phenotypic manifestations with varying degrees of ineffective haemopoiesis. This state probably develops as a sequence of events in which the earliest stages may be difficult to detect by conventional pathological techniques. The process is characterised by genetic changes leading to abnormal control of cell proliferation and differentiation. Expansion of an abnormal clone may be related to independence from normal growth factors, insensitivity to normal inhibitory factors, suppression of normal clonal growth, or changes in the immunological or nutritional condition of the host. The haematological picture is of peripheral blood cytopenias: a cellular bone marrow, and functional abnormalities of erythroid, myeloid, and megakaryocytic cells. In most cases marrow cells have an abnormal DNA content, often with disturbances of the cell cycle: an abnormal karyotype is common in premalignant clones. Growth abnormalities of erythroid or granulocyte-macrophage progenitors are common in marrow cultures, and lineage specific surface membrane markers indicate aberrations of differentiation. Progression of the disorder may occur through clonal expansion or through clonal evolution with a greater degree of malignancy. Current attempts to influence abnormal growth and differentiation have had only limited success. Clinical recognition of the syndrome depends on an acute awareness of the signs combined with the identification of clonal and functional abnormalities.