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Abstract

The relationship of neuronal DNA damage to tangle-bearing neurons and nitrotyrosine (NT) expression, a neurochemical marker of oxidative damage mediated by peroxynitrite, was examined in visual cortex of AD patients. Many terminal deoxynucleotidyl transferase (TdT)-positive neurons were detected and the majority (93%) of these TdT-labeled neurons lacked evidence of tangle formation. NT expression was elevated in AD cases and most TdT-labeled nuclei also showed strong NT immunoreactivity. These data suggest the hypothesis that the neurons with DNA damage in the absence of tangle formation may degenerate by tangle-independent mechanisms and that oxidative damage may contribute to such mechanisms in AD.

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Identification of programmed cell death in situ via specific labeling of nuclear DNA fragmentation

SA Ben-Sasson, Y Sherman, Y Gavrieli (1992)

Programmed cell death (PCD) plays a key role in developmental biology and in maintenance of the steady state in continuously renewing tissues. Currently, its existence is inferred mainly from gel electrophoresis of a pooled DNA extract as PCD was shown to be associated with DNA fragmentation. Based on this observation, we describe here the development of a method for the in situ visualization of PCD at the single-cell level, while preserving tissue architecture. Conventional histological sections, pretreated with protease, were nick end labeled with biotinylated poly dU, introduced by terminal deoxy- transferase, and then stained using avidin-conjugated peroxidase. The reaction is specific, only nuclei located at positions where PCD is expected are stained. The initial screening includes: small and large intestine, epidermis, lymphoid tissues, ovary, and other organs. A detailed analysis revealed that the process is initiated at the nuclear periphery, it is relatively short (1-3 h from initiation to cell elimination) and that PCD appears in tissues in clusters. The extent of tissue-PCD revealed by this method is considerably greater than apoptosis detected by nuclear morphology, and thus opens the way for a variety of studies.

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Dose-dependent induction of apoptosis in human tumour cell lines by widely diverging stimuli.

Nancy Martin, T Cotter, S V Lennon (1991)

Cell death may occur by either of two mechanisms: apoptosis or necrosis. Necrosis, the first type of cell death to be recognized, is an uncontrolled degenerative phenomenon invariably caused by noxious stimuli and is the result of irreversible failure of membrane function. Apoptosis, on the other hand, is a death process which involves a series of well-organized events which require active cell participation, and is primarily caused by physiological stimuli. In the present study we show that cell death induced by a range of varied agents may take the form of either apoptosis or necrosis. Apoptotic cell death was found to occur at low levels of these agents, while at higher levels necrosis occurred. Hence, cells which are not killed directly, but merely injured by these agents, have the capacity to activate an internally programmed suicide death mechanism, whereas cells receiving greater injuries apparently do not. In addition, the presence of extracellular calcium was found to be necessary for the induction of apoptosis with all agents tested.