Macrophages in brain tumours induced transplacentally by N-ethyl-N-nitrosourea in rats: an electron-microscope study

Lipid Droplets in Cancer: Guardians of Fat in a Stressful World

Cancer cells possess remarkable abilities to adapt to adverse environmental conditions. Their survival during severe nutrient and oxidative stress depends on their capacity to acquire extracellular lipids and the plasticity of their mechanisms for intracellular lipid synthesis, mobilisation, and recycling. Lipid droplets, cytosolic fat storage organelles present in most cells from yeast to men, are emerging as major regulators of lipid metabolism, trafficking, and signalling in various cells and tissues exposed to stress. Their biogenesis is induced by nutrient and oxidative stress and they accumulate in various cancers. Lipid droplets act as switches that coordinate lipid trafficking and consumption for different purposes in the cell, such as energy production, protection against oxidative stress or membrane biogenesis during rapid cell growth. They sequester toxic lipids, such as fatty acids, cholesterol and ceramides, thereby preventing lipotoxic cell damage and engage in a complex relationship with autophagy. Here, we focus on the emerging mechanisms of stress-induced lipid droplet biogenesis; their roles during nutrient, lipotoxic, and oxidative stress; and the relationship between lipid droplets and autophagy. The recently discovered principles of lipid droplet biology can improve our understanding of the mechanisms that govern cancer cell adaptability and resilience to stress.

End-stage dying glioma cells are engulfed by mouse microglia with a strain-dependent efficacy

Microglia phagocytic activity for apoptotic glioma cells is hardly analysed inspite of its relevance to tissue damage prevention. We provide evidence for a phosphatidylserine-independent clearance of mouse glioma cells at an advanced stage of death, suggesting microglia recognition of late apoptotic markers. Dying cells were immediately cleared or stayed for hours in that stage before engulfment occurred. This phagocytic activity was restricted to a microglia subset representing 30 to 70% of the population according to the used strain. Expression of receptors involved in late apoptotic markers recognition therefore seems confined to a subpopulation of microglia and to be strain-dependent.

A sequential ultrastructural and histoautoradiographic study of early neoplastic lesions in ethylnitrosourea-induced rat glioma

A sequential study of the early stage of development of ethylnitrosourea (ENU)-induced glioma in the rat was performed by electron microscopy and [3H]thymidine histoautoradiography. Hyperplasia, the earliest neoplastic change that was detectable morphologically, consisted of a few or several immature oligodendroglia-like cells which were connected with one another or with preexisting neural tissue by junctional apparatus, and showed no reactive changes in the astrocytes or microglia. The labelling index of hyperplastic cells was 2.6%. Foci of early neoplastic proliferation (ENP) showed mild destructive changes in the neighboring neural tissue, and their major constituent cells had characteristics of immature oligodendroglias. The labelling index of cells showing ENP was 3.3%. The intercellular spaces exhibited slight enlargement with accumulation of extracellular matrix and a decrease in the number of junctional apparatus on the neoplastic cells. Microtumors showed apparent destruction of the preexisting neural tissue to form a tumor mass with an increase in the extracellular matrix. Constituent cells of the microtumors were similar to those of the ENP, although reactive astrocytes and microglias occurred more frequently. The labelling index was 9.6% in the central area of microtumors and 5.3% in the peripheral area. These findings suggest that in the initial or very early stages of glial cell neoplastic proliferation, it is necessary for the neoplastic cells to maintain contact with the neurons for metabolic purposes, and that after losing contact, these cells can proliferate autonomously with the accumulation of extracellular matrix.

Lymphoreticular cells in human brain tumours and in normal brain

The present investigation, using various rosetting assays of cell suspensions prepared by mechanical disaggregation or collagenase digestion, demonstrated lymphoreticular cells in human normal brain (cerebral cortex and cerebellum) and in malignant brain tumours. The study revealed T and B lymphocytes and their subsets (bearing receptors for Fc(IgG) and C3) in 5/14 glioma suspensions, comprising less than 15% of the cell population. Between 20-60% of cells in tumour suspensions morphologically resembled macrophages and less than or equal to 75% of these cells formed strong rosettes. Lymphocytes were not found in cancer-free (putatively normal) brain. Macrophages and the smaller "microglial cells" (both phagocytic, staining with sudan black, and expressing Fc(IgG) and C3 receptors) were found in normal brain in numbers similar to those in tumour suspensions, but with less rosetting avidity. These cells may be part of an immunological defence mechanism.

Neuronal changes in experimental gliomas

Gliomas were induced transplancentally by the administration of ethylnitrosourea to pregnant rats on the 15th day of gestation. The fine structure of neurones involved in these tumours was studied in order to assess the changes caused by neoplasia. The severity of the neuronal damage depended on their location, Those within the tumours being more affected than those in the neighbouring brain. The histological type and grade of malignancy also influenced the changes: periventricular pleomorphic gliomas and ependymomas of high-grade malignancy caused the most severe alterations. Neurones displayed a spectrum of appearances from apparent normality to complete necrosis. Both nucleus and cytoplasm were affected: of the cytoplasmic organelles the rough-surfaced endoplasmic reticulum and mitochondria showed the most striking changes. There were many lipofuscin granules and autophagic vacuoles. Axons underwent advanced degeneration: swollen mitochondria, disrupted vesicles and vacuoles, disintegrated microtubules, irregular filaments and unidentified debris were sometimes seen. Disintegration of myelin sheaths frequently occurred with consequent engulfing of their debris by macrophages and reacting astrocytes. The neuronal satellites--mainly oligodendrocytes--were often replaced by neoplastic glial cells. Hydrolytic 'marker' enzymes were demonstrated in neurones at various stages of degeneration. In all cases neurones displayed low acid phosphatase activity, while thiamine pyrophosphatase activity decreased with increasing neuronal degeneration.

Macrophages in experimental and human brain tumors. Part 1: Studies of the macrophage content of experimental rat brain tumors of varying immunogenicity

Although the presence of lymphoreticular cells within tumors has been recognized for over 100 years, it is only within the last decade that the concept has arisen that standard histological examination techniques may lead to an underestimation of the true extent of tumor infiltration by lymphoreticular cells, and particularly by macrophages. The macrophage content of certain systemic tumors has been correlated with their immunogenicity and growth characteristics. Since the central nervous system is to some extent an "immunologically privileged site" and contains within it specialized reticuloendothelial cells called microglia, the authors determined the macrophage content of three rodent brain-tumor cell lines, and attempted to correlate this macrophage content with their immunogenicity and growth characteristics. Their findings indicate a direct correlation between the immunogenicity and macrophage content of these three neural tumor cell lines.