Bax and p53 are differentially involved in the regulation of caspase-3 expression and activation during neurodegeneration in Lurcher mice

Epoxyeicosatrienoic Acid Inhibits the Apoptosis of Cerebral Microvascular Smooth Muscle Cells by Oxygen Glucose Deprivation via Targeting the JNK/c-Jun and mTOR Signaling Pathways

As a component of the neurovascular unit, cerebral smooth muscle cells (CSMCs) are an important mediator in the development of cerebral vascular diseases such as stroke. Epoxyeicosatrienoic acids (EETs) are the products of arachidonic acid catalyzed by cytochrome P450 epoxygenase. EETs are shown to exert neuroprotective effects. In this article, the role of EET in the growth and apoptosis of CSMCs and the underlying mechanisms under oxygen glucose deprivation (OGD) conditions were addressed. The viability of CMSCs was decreased significantly in the OGD group, while different subtypes of EETs, especially 14,15-EET, could increase the viability of CSMCs under OGD conditions. RAPA (serine/threonine kinase Mammalian Target of Rapamycin), a specific mTOR inhibitor, could elevate the level of oxygen free radicals in CSMCs as well as the anti-apoptotic effects of 14,15-EET under OGD conditions. However, SP600125, a specific JNK (c-Jun N-terminal protein kinase) pathway inhibitor, could attenuate oxygen free radicals levels in CSMCs as well as the anti-apoptotic effects of 14,15-EET under OGD conditions. These results strongly suggest that EETs exert protective functions during the growth and apoptosis of CSMCs, via the JNK/c-Jun and mTOR signaling pathways in vitro. We are the first to disclose the beneficial roles and underlying mechanism of 14,15-EET in CSMC under OGD conditions.

Doppel induces degeneration of cerebellar Purkinje cells independently of Bax

Doppel (Dpl) is a prion protein paralog that causes neurodegeneration when expressed ectopically in the brain. To investigate the cellular mechanism underlying this effect, we analyzed Dpl-expressing transgenic mice in which the gene for the proapoptotic protein Bax had been deleted. We found that Bax deletion does not alter either clinical symptoms or Purkinje cell degeneration in Dpl transgenic mice. In addition, we observed that degenerating Purkinje cells in these animals do not display DNA fragmentation or caspase-3 activation. Our results suggest that non-Bax-dependent pathways mediate the toxic effects of Dpl in Purkinje cells, highlighting a possible role for nonapoptotic mechanisms in the death of these neurons.

Translocation of cytochrome c during cerebellar degeneration in Lurcher and weaver mutant mice

Cytochrome c translocation from the inner mitochondrial membrane into the cytosol is the initial step of the intrinsic apoptotic pathway. As no evidence was ever presented for cytochrome c translocation during cerebellar degeneration in Lurcher (Lc/+) and weaver (wv/wv) mutant mice, we searched for the presence of such a process in cerebellar homogenates of mutant and wild-type mice from postnatal day (P)1 to P56. Here we present the first documented time course of cytochrome c translocation spanning the entire period of neurodegeneration in both mutant types. We identified cytochrome c with Western blotting and monitored cell loss in the cerebellum with Calbindin D-28k immunohistochemistry, Nissl-staining and morphometry. No cytochrome c translocation was ever detected in wild-types at any age investigated. Translocated cytochrome c appeared between P13 and P21 in Lc/+ and between P5 and P6 in wv/wv. These two intervals precisely coincide with the respective periods of maximal neuronal death in the cerebellum. Secondary translocation was also observed at a later stage between P42 and P49 in Lc/+ and from P22 onwards in wv/wv. Since no substantial neuronal loss has ever been observed in Lc/+ and wv/wv mutants at these postnatal ages, the delayed translocation may correspond to cytochrome c of extraneuronal, presumably glial origin. Observations of an increased expression of glial fibrillary acidic protein and sustained remodeling of the astrocytic network in the cerebellum of both mutants, long after the cessation of neuronal death make this assumption rather plausible.

Apoptosis in the mammalian CNS: Lessons from animal models

It is generally assumed that about half of the neurons produced during neurogenesis die before completion of maturation of the central nervous system (CNS). Neural cell death is also relevant in aging and several neurodegenerative diseases. Among the modalities by which neurons die, apoptosis has very much attracted the interest of investigators because in this type of cell death neurons are actively responsible for their own demise by switching on a number of genes and activating a series of specific intracellular pathways. This review focuses on the cellular and molecular mechanisms of apoptosis in normal and transgenic animal models related to naturally occurring neuronal death within the CNS. We will also consider some examples of apoptotic cell death in canine neuropathologies. A thorough analysis of naturally occurring neuronal death in vivo will offer a basis for parallel and future studies involving secondary neuronal loss such as those in neurodegenerative disorders, trauma or ischaemia.

In vivo cellular and molecular mechanisms of neuronal apoptosis in the mammalian CNS

Apoptosis has been recognized to be an essential process during neural development. It is generally assumed that about half of the neurons produced during neurogenesis die before completion of the central nervous system (CNS) maturation, and this process affects nearly all classes of neurons. In this review, we discuss the experimental data in vivo on naturally occurring neuronal death in normal, transgenic and mutant animals, with special attention to the cerebellum as a study model. The emerging picture is that of a dual wave of apoptotic cell death affecting central neurons at different stages of their life. The first wave consists of an early neuronal death of proliferating precursors and young postmitotic neuroblasts, and appears to be closely linked to cell cycle regulation. The second wave affects postmitotic neurons at later stages, and is much better understood in functional terms, mainly on the basis of the neurotrophic concept in its broader definition. The molecular machinery of late apoptotic death of postmitotic neurons more commonly follows the mitochondrial pathway of intracellular signal transduction, but the death receptor pathway may also be involved.Undoubtedly, analysis of naturally occurring neuronal death (NOND) in vivo will offer a basis for parallel and future studies aiming to elucidate the mechanisms of pathologic neuronal loss occurring as the result of conditions such as neurodegenerative disorders, trauma or ischemia.

Implication of p53 and caspase-3 in kainic acid but not in N-methyl-D-aspartic acid-induced apoptosis in organotypic hippocampal mouse cultures

Apoptotic death is known to be an active process requiring the activation of several apoptotic proteins. Depending on the tissue studied and the stimulus used, these processes are distinct. In this work, we studied if there is a putative implication of the p53 and the caspase-3 proteins in kainic acid (KA) and N-methyl-D-aspartic acid (NMDA)-induced apoptosis in organotypic cultures and if there is any relationship between their respective expressions. We found that KA and NMDA both induce apoptosis but only KA-induced apoptosis is p53- and caspase-3-dependent. This demonstrates that KA and NMDA induce apoptosis following different intracellular pathways.

Cerebellar granule cells as a model to study mechanisms of neuronal apoptosis or survival in vivo and in vitro

Granule cells of the cerebellum constitute the largest homogeneous neuronal population of mammalian brain. Due to their postnatal generation and the feasibility of well characterized primary in vitro cultures, cerebellar granule cells are a model of election for the study of cellular and molecular correlates of mechanisms of survival/apoptosis and neurodegeneration/neuroprotection. The present review mainly deals with recent data on mechanisms and factors promoting survival or apoptotic elimination of cerebellar granule neurons, with a particular focus on the molecular correlates at the level of gene expression and induction of cellular signal pathways. The in vivo development is first analysed with particular reference to the role played by several neurotrophic factors and by the NMDA subtype of glutamate receptor. Then, mechanisms of survival/apoptosis are examined in the model of primary in vitro cultures, where the role of neurotrophins acting on cerebellar granule cells is followed by the large deal of data coming from the paradigm of potassium/serum withdrawal. The role of some key genes of the Bcl family, of some kinase systems and of transcriptional factors is primarily highlighted. Furthermore, the involvement of mitochondria, free radicals and proteases of the caspase family is considered. Finally, the use of cerebellar granule neurons in primary culture to experimentally address the issue of neurodegeneration and pharmacological neuroprotection is considered, with some comments on models at the borderline between necrosis and apoptosis, such as the excitotoxic neuronal damage. The overlapping of cellular signal pathways activated in granule neurons by apparently unrelated stimuli, such as neurotrophins and neurotransmitters/neuromodulators is stressed to put into light the special 'trophic' role played by activity in neurons. Finally, the advantage of designing and performing conceptually equivalent experiments on cerebellar granule neurons during development in vivo and in vitro, is stressed. On the basis of the reviewed material, it is concluded that cerebellar granule neurons have acquired a special position in modern neuroscience as one of the most reliable models for the study of neural development, function and pathology.