Modeling PDGF-driven gliomagenesis in the mouse

Gliomas are the most common form of brain tumors, with glioblastoma being the most aggressive form. Glioblastoma is characterized by a number of genetic aberrations, among them amplification and overexpression of platelet-derived growth factor receptor alpha (PDGFRA) that sometimes occurs together with inactivating mutations or loss of the tumor suppressor p53 (TP53). The infiltrative nature and rapid growth of glioblastoma make it incurable despite extensive treatment. A better understanding of the molecular genetic defects underlying brain tumor development is necessary in order to design novel and more efficient therapies. In the present study we investigated how the combination of increased growth factor signaling and p53 loss induces brain tumors. We generated two transgenic mouse models overexpressing PDGF-B or the long isoform of PDGF-A under the glial fibrillary acidic protein (GFAP) promoter. Thus, the transgene is active in neural stem cells and astrocytes, cells that normally express GFAP. We demonstrate that overexpression of PDGF-B on its own did not trigger brain tumor development. However, when the PDGF-B transgenic mice were crossed onto a Trp53 null background, malignant tumors resembling human glioblastoma appeared at the age of 2-6 months. These tumors displayed histopathological features of human glioblastoma with integrated vascular proliferations expressing PDGFR-β, glial tumor cells expressing PDGFR-α, pseudopalisading necrosis and abnormal cell nuclei. The changes in the brains of PDGF-B/Trp53 null mice were evident long before tumors formed. We found increased numbers of PDGFR-α expressing cells, distorted vasculature, with prominent PDGFR-β expression in areas where brain tumors later occurred. In addition, neurosphere-forming cells were situated in more widespread locations compared to wild type (wt) mice. In contrast to PDGF-B transgenic mice the overexpression of PDGF-AL led to an early lethality of the mice. We detected increased numbers of undifferentiated glial cells and in a few mice neoplastic glioma-like lesions. In summary, these studies provide new insights into the role of excessive PDGF exposure during brain tumor development

Novel Perspectives on p53 Function in Neural Stem Cells and Brain Tumors

Malignant glioma is the most common brain tumor in adults and is associated with a very poor prognosis. Mutations in the p53 tumor suppressor gene are frequently detected in gliomas. p53 is well-known for its ability to induce cell cycle arrest, apoptosis, senescence, or differentiation following cellular stress. That the guardian of the genome also controls stem cell self-renewal and suppresses pluripotency adds a novel level of complexity to p53. Exactly how p53 works in order to prevent malignant transformation of cells in the central nervous system remains unclear, and despite being one of the most studied proteins, there is a need to acquire further knowledge about p53 in neural stem cells. Importantly, the characterization of glioma cells with stem-like properties, also known as brain tumor stem cells, has opened up for the development of novel targeted therapies. Here, we give an overview of what is currently known about p53 in brain tumors and neural stem cells. Specifically, we review the literature regarding transformation of adult neural stem cells and, we discuss how the loss of p53 and deregulation of growth factor signaling pathways, such as increased PDGF signaling, lead to brain tumor development. Reactivation of p53 in brain tumor stem cell populations in combination with current treatments for glioma should be further explored and may become a viable future therapeutic approach

Brain Abnormalities and Glioma-Like Lesions in Mice Overexpressing the Long Isoform of PDGF-A in Astrocytic Cells

BACKGROUND: Deregulation of platelet-derived growth factor (PDGF) signaling is a hallmark of malignant glioma. Two alternatively spliced PDGF-A mRNAs have been described, corresponding to a long (L) and a short (S) isoform of PDGF-A. In contrast to PDGF-A(S), the PDGF-A(L) isoform has a lysine and arginine rich carboxy-terminal extension that acts as an extracellular matrix retention motif. However, the exact role of PDGF-A(L) and how it functionally differs from the shorter isoform is not well understood.\ud \ud METHODOLOGY/PRINCIPAL FINDINGS: We overexpressed PDGF-A(L) as a transgene under control of the glial fibrillary acidic protein (GFAP) promoter in the mouse brain. This directs expression of the transgene to astrocytic cells and GFAP expressing neural stem cells throughout the developing and adult central nervous system. Transgenic mice exhibited a phenotype with enlarged skull at approximately 6-16 weeks of age and they died between 1.5 months and 2 years of age. We detected an increased number of undifferentiated cells in all areas of transgene expression, such as in the subependymal zone around the lateral ventricle and in the cerebellar medulla. The cells stained positive for Pdgfr-α, Olig2 and NG2 but this population did only partially overlap with cells positive for Gfap and the transgene reporter. Interestingly, a few mice presented with overt neoplastic glioma-like lesions composed of both Olig2 and Gfap positive cell populations and with microvascular proliferation, in a wild-type p53 background.\ud \ud CONCLUSIONS: Our findings show that PDGF-A(L) can induce accumulation of immature cells in the mouse brain. The strong expression of NG2, Pdgfr-α and Olig2 in PDGF-A(L) brains suggests that a fraction of these cells are oligodendrocyte progenitors. In addition, accumulation of fluid in the subarachnoid space and skull enlargement indicate that an increased intracranial pressure contributed to the observed lethality.\ud \u

PDGF and PDGF receptors in glioma

The family of platelet-derived growth factors (PDGFs) plays a number of critical roles in normal embryonic development, cellular differentiation, and response to tissue damage. Not surprisingly, as it is a multi-faceted regulatory system, numerous pathological conditions are associated with aberrant activity of the PDGFs and their receptors. As we and others have shown, human gliomas, especially glioblastoma, express all PDGF ligands and both the two cell surface receptors, PDGFR-α and -β. The cellular distribution of these proteins in tumors indicates that glial tumor cells are stimulated via PDGF/PDGFR-α autocrine and paracrine loops, while tumor vessels are stimulated via the PDGFR-β. Here we summarize the initial discoveries on the role of PDGF and PDGF receptors in gliomas and provide a brief overview of what is known in this field

GFAP promoter driven transgenic expression of PDGFB in the mouse brain leads to glioblastoma in a Trp53 null background

Glioblastomas are the most common and malignant astrocytic brain tumors in human adults. The tumor suppressor gene TP53 is commonly mutated and/or lost in astrocytic brain tumors and the TP53 alterations are often found in combination with excessive growth factor signaling via PDGF/PDGFRalpha. Here, we have generated transgenic mice over-expressing human PDGFB in brain, under control of the human GFAP promoter. These mice showed no phenotype, but on a Trp53 null background a majority of them developed brain tumors. This occurred at 2-6 months of age and tumors displayed human glioblastoma-like features with integrated development of Pdgfralpha+ tumor cells and Pdgfrbeta+/Nestin+ vasculature. The transgene was expressed in subependymal astrocytic cells, in glia limitans, and in astrocytes throughout the brain substance, and subsequently, microscopic tumor lesions were initiated equally in all these areas. With tumor size, there was an increase in Nestin positivity and variability in lineage markers. These results indicate an unexpected plasticity of all astrocytic cells in the adult brain, not only of SVZ cells. The results also indicate a contribution of widely distributed Pdgfralpha+ precursor cells in the tumorigenic proces

Мышечная дистрофия Дюшенна: современные подходы к ведению и лечению пациентов

Duchenne muscular dystrophy is one of the most common forms of childhood muscular dystrophies. Its incidence is 1 in 3.5–6 thousand newborn boys according to various sources. The disease is caused by the mutation in the DMD gene coding the dystrophin protein, it leads to the dystrophin absence or malfunction. The disease is characterized by proximal muscle weakness and gastrocnemius muscles pseudohypertrophy. In average, patients lose the ability to walk by themselves by the age of 11 and become nonambulatory. The authors have present modern epidemiological data and etiopathogenesis features of Duchenne muscular dystrophy, and have described clinical signs of different disease stages. The algorithm and key points of differential diagnosis are indicated. Special attention was given to the patients’ management: pathogenetic treatment and rehabilitation of pediatric patients.Мышечная дистрофия Дюшенна — одна из наиболее частых форм мышечных дистрофий детского возраста. По разным источникам, заболеваемость миодистрофией Дюшенна оценивается как 1 на 3,5–6 тыс. новорожденных мальчиков. В основе заболевания лежит мутация гена DMD, кодирующего белок дистрофин, приводящая к отсутствию или недостаточной функции дистрофина. Заболевание характеризуется слабостью проксимальных и псевдогипертрофией икроножных мышц, и в среднем к 11 годам пациенты теряют возможность самостоятельно передвигаться и становятся неамбулаторными больными. Авторами представлены современные эпидемиологические данные и особенности этиопатогенеза мышечной дистрофии Дюшенна, описаны клинические характеристики разных стадий болезни. Подробно представлен алгоритм и указаны ключевые этапы дифференциально-диагностического поиска. Особое внимание уделено вопросам лечения пациентов, в том числе патогенетическому лечению, реабилитации пациентов детского возраста