Active caspase-3 expression during postnatal development of rat cerebellum is not systematically or consistently associated with apoptosis

Proteome integral solubility alteration high-throughput proteomics assay identifies Collectin-12 as a non-apoptotic microglial caspase-3 substrate

Caspases are a family of proteins mostly known for their role in the activation of the apoptotic pathway leading to cell death. In the last decade, caspases have been found to fulfill other tasks regulating the cell phenotype independently to cell death. Microglia are the immune cells of the brain responsible for the maintenance of physiological brain functions but can also be involved in disease progression when overactivated. We have previously described non-apoptotic roles of caspase-3 (CASP3) in the regulation of the inflammatory phenotype of microglial cells or pro-tumoral activation in the context of brain tumors. CASP3 can regulate protein functions by cleavage of their target and therefore could have multiple substrates. So far, identification of CASP3 substrates has been performed mostly in apoptotic conditions where CASP3 activity is highly upregulated and these approaches do not have the capacity to uncover CASP3 substrates at the physiological level. In our study, we aim at discovering novel substrates of CASP3 involved in the normal regulation of the cell. We used an unconventional approach by chemically reducing the basal level CASP3-like activity (by DEVD-fmk treatment) coupled to a Mass Spectrometry screen (PISA) to identify proteins with different soluble amounts, and consequently, non-cleaved proteins in microglia cells. PISA assay identified several proteins with significant change in their solubility after DEVD-fmk treatment, including a few already known CASP3 substrates which validated our approach. Among them, we focused on the Collectin-12 (COLEC12 or CL-P1) transmembrane receptor and uncovered a potential role for CASP3 cleavage of COLEC12 in the regulation of the phagocytic capacity of microglial cells. Taken together, these findings suggest a new way to uncover non-apoptotic substrates of CASP3 important for the modulation of microglia cell physiology.

Making the head: Caspases in life and death

The term apoptosis, as a way of programmed cell death, was coined a half century ago and since its discovery the process has been extensively investigated. The anatomy and physiology of the head are complex and thus apoptosis has mostly been followed in separate structures, tissues or cell types. This review aims to provide a comprehensive overview of recent knowledge concerning apoptosis-related molecules involved in the development of structures of head with a particular focus on caspases, cysteine proteases having a key position in apoptotic pathways. Since many classical apoptosis-related molecules, including caspases, are emerging in several non-apoptotic processes, these were also considered. The largest organ of the head region is the brain and its development has been extensively investigated, including the roles of apoptosis and related molecules. Neurogenesis research also includes sensory organs such as the eye and ear, efferent nervous system and associated muscles and glands. Caspases have been also associated with normal function of the skin and hair follicles. Regarding mineralised tissues within craniofacial morphogenesis, apoptosis in bones has been of interest along with palate fusion and tooth development. Finally, the role of apoptosis and caspases in angiogenesis, necessary for any tissue/organ development and maintenance/homeostasis, are discussed. Additionally, this review points to abnormalities of development resulting from improper expression/activation of apoptosis-related molecules.

Nonapoptotic caspases in neural development and in anesthesia-induced neurotoxicity

Apoptosis, classically initiated by caspase pathway activation, plays a prominent role during normal brain development as well as in neurodegeneration. The noncanonical, nonlethal arm of the caspase pathway is evolutionarily conserved and has also been implicated in both processes, yet is relatively understudied. Dysregulated pathway activation during critical periods of neurodevelopment due to environmental neurotoxins or exposure to compounds such as anesthetics can have detrimental consequences for brain maturation and long-term effects on behavior. In this review, we discuss key molecular characteristics and roles of the noncanonical caspase pathway and how its dysregulation may adversely affect brain development. We highlight both genetic and environmental factors that regulate apoptotic and sublethal caspase responses and discuss potential interventions that target the noncanonical caspase pathway for developmental brain injuries.

Increased glutamate transporter-associated anion currents cause glial apoptosis in episodic ataxia 6

Episodic ataxia type 6 is an inherited neurological condition characterized by combined ataxia and epilepsy. A severe form of this disease with episodes combining ataxia, epilepsy and hemiplegia was recently associated with a proline to arginine substitution at position 290 of the excitatory amino acid transporter 1 in a heterozygous patient. The excitatory amino acid transporter 1 is the predominant glial glutamate transporter in the cerebellum. However, this glutamate transporter also functions as an anion channel and earlier work in heterologous expression systems demonstrated that the mutation impairs the glutamate transport rate, while increasing channel activity. To understand how these changes cause ataxia, we developed a constitutive transgenic mouse model. Transgenic mice display epilepsy, ataxia and cerebellar atrophy and, thus, closely resemble the human disease. We observed increased glutamate-activated chloride efflux in Bergmann glia that triggers the apoptosis of these cells during infancy. The loss of Bergmann glia results in reduced glutamate uptake and impaired neural network formation in the cerebellar cortex. This study shows how gain-of-function of glutamate transporter-associated anion channels causes ataxia through modifying cerebellar development.

Caspase-3 Mediated Cell Death in the Normal Development of the Mammalian Cerebellum

Caspase-3, onto which there is a convergence of the intrinsic and extrinsic apoptotic pathways, is the main executioner of apoptosis. We here review the current literature on the intervention of the protease in the execution of naturally occurring neuronal death (NOND) during cerebellar development. We will consider data on the most common altricial species (rat, mouse and rabbit), as well as humans. Among the different types of neurons and glia in cerebellum, there is ample evidence for an intervention of caspase-3 in the regulation of NOND of the post-mitotic cerebellar granule cells (CGCs) and Purkinje neurons, as a consequence of failure to establish proper synaptic contacts with target (secondary cell death). It seems possible that the GABAergic interneurons also undergo a similar type of secondary cell death, but the intervention of caspase-3 in this case still remains to be clarified in full. Remarkably, CGCs also undergo primary cell death at the precursor/pre-migratory stage of differentiation, in this instance without the intervention of caspase-3. Glial cells, as well, undergo a process of regulated cell death, but it seems possible that expression of caspase-3, at least in the Bergmann glia, is related to differentiation rather than death.

Non-apoptotic Caspase regulation of stem cell properties

The evolutionarily conserved family of proteins called caspases are the main factors mediating the orchestrated programme of cell suicide known as apoptosis. Since this protein family was associated with this essential biological function, the majority of scientific efforts were focused towards understanding their molecular activation and function during cell death. However, an emerging body of evidence has highlighted a repertoire of non-lethal roles within a large variety of cell types, including stem cells. Here we intend to provide a comprehensive overview of the key role of caspases as regulators of stem cell properties. Finally, we briefly discuss the possible pathological consequences of caspase malfunction in stem cells, and the therapeutic potential of caspase regulation applied to this context.

When dying is not the end: Apoptotic caspases as drivers of proliferation

Caspases are well known for their role as executioners of apoptosis. However, recent studies have revealed that these lethal enzymes also have important mitogenic functions. Caspases can promote proliferation through autonomous regulation of the cell cycle, as well as by induction of secreted signals, which have a profound impact in neighboring tissues. Here, I review the proliferative role of caspases during development and homeostasis, in addition to their key regenerative function during tissue repair upon injury. Furthermore, the emerging properties of apoptotic caspases as drivers of carcinogenesis are discussed, as well as their involvement in other diseases. Finally, I examine further effects of caspases regulating death and survival in a non-autonomous manner.

Exposure of neonatal rats to alcohol has differential effects on neuroinflammation and neuronal survival in the cerebellum and hippocampus

Background

Fetal alcohol exposure is a leading cause of preventable birth defects, yet drinking during pregnancy remains prevalent worldwide. Studies suggest that activation of the neuroimmune system plays a role in the effects of alcohol exposure during the rodent equivalent to the third trimester of human pregnancy (i.e., first week of neonatal life), particularly by contributing to neuronal loss. Here, we performed a comprehensive study investigating differences in the neuroimmune response in the cerebellum and hippocampus, which are important targets of third trimester-equivalent alcohol exposure.

Methods

To model heavy, binge-like alcohol exposure during this period, we exposed rats to alcohol vapor inhalation during postnatal days (P)3–5 (blood alcohol concentration = 0.5 g/dL). The cerebellar vermis and hippocampus of rat pups were analyzed for signs of glial cell activation and neuronal loss by immunohistochemistry at different developmental stages. Cytokine production was measured by reverse transcriptase polymerase chain reaction during peak blood alcohol concentration and withdrawal periods. Additionally, adolescent offspring were assessed for alterations in gait and spatial memory.

Results

We found that this paradigm causes Purkinje cell degeneration in the cerebellar vermis at P6 and P45; however, no signs of neuronal loss were found in the hippocampus. Significant increases in pro-inflammatory cytokines were observed in both brain regions during alcohol withdrawal periods. Although astrocyte activation occurred in both the hippocampus and cerebellar vermis, microglial activation was observed primarily in the latter.

Conclusions

These findings suggest that heavy, binge-like third trimester-equivalent alcohol exposure has time- and brain region-dependent effects on cytokine levels, morphological activation of microglia and astrocytes, and neuronal survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0382-9) contains supplementary material, which is available to authorized users.

Morphological and Phagocytic Profile of Microglia in the Developing Rat Cerebellum

Microglia are being increasingly recognized as playing important roles in neurodevelopment. The cerebellum matures postnatally, undergoing major growth, but the role of microglia in the developing cerebellum is not well understood. Using the laboratory rat we quantified and morphologically categorized microglia throughout the vermis and across development using a design-based unbiased stereology method. We found that microglial morphology changed from amoeboid to ramified during the first 3 postnatal weeks in a region specific manner. These morphological changes were accompanied by the sudden appearance of phagocytic cups during the third postnatal week from P17 to P19, with an approximately fourfold increase compared with the first week, followed by a prompt decline at the end of the third week. The microglial phagocytic cups were significantly higher in the granular layer (∼69%) than in the molecular layer (ML; ∼31%) during a 3 d window, and present on ∼67% of microglia with thick processes and ∼33% of microglia with thin processes. Similar proportions of phagocytic cups associated to microglia with either thick or thin processes were found in the ML. We observed cell nuclei fragmentation and cleaved caspase-3 expression within some microglial phagocytic cups, presumably from dying granule neurons. At P17 males showed an approximately twofold increase in microglia with thin processes compared with females. Our findings indicate a continuous process of microglial maturation and a nonuniform distribution of microglia in the cerebellar cortex that implicates microglia as an important cellular component of the developing cerebellum.

Sexual Differences in Cell Loss during the Post-Hatch Development of Song Control Nuclei in the Bengalese Finch

Birdsongs and the regions of their brain that control song exhibit obvious sexual differences. However, the mechanisms underlying these sexual dimorphisms remain unknown. To address this issue, we first examined apoptotic cells labeled with caspase-3 or TUNEL in Bengalese finch song control nuclei - the robust nucleus of the archopallium (RA), the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the high vocal center (HVC) and Area X from post-hatch day (P) 15 to 120. Next, we investigated the expression dynamics of pro-apoptotic (Bid, Bad and Bax) and anti-apoptotic (Bcl-2 and Bcl-xL) genes in the aforementioned nuclei. Our results revealed that the female RA at P45 exhibited marked cell apoptosis, confirmed by low densities of Bcl-xL and Bcl-2. Both the male and female LMAN exhibited apoptotic peaks at P35 and P45, respectively, and the observed cell loss was more extensive in males. A corresponding sharp decrease in the density of Bcl-2 after P35 was observed in both sexes, and a greater density of Bid was noted at P45 in males. In addition, we observed that RA volume and the total number of BDNF-expressing cells decreased significantly after unilateral lesion of the LMAN or HVC (two areas that innervate the RA) and that greater numbers of RA-projecting cells were immunoreactive for BDNF in the LMAN than in the HVC. We reasoned that a decrease in the amount of BDNF transported via HVC afferent fibers might result in an increase in cell apoptosis in the female RA. Our data indicate that cell apoptosis resulting from different pro- and anti-apoptotic agents is involved in generating the differences between male and female song control nuclei.

Cellular commitment in the developing cerebellum

The mammalian cerebellum is located in the posterior cranial fossa and is critical for motor coordination and non-motor functions including cognitive and emotional processes. The anatomical structure of cerebellum is distinct with a three-layered cortex. During development, neurogenesis and fate decisions of cerebellar primordium cells are orchestrated through tightly controlled molecular events involving multiple genetic pathways. In this review, we will highlight the anatomical structure of human and mouse cerebellum, the cellular composition of developing cerebellum, and the underlying gene expression programs involved in cell fate commitments in the cerebellum. A critical evaluation of the cell death literature suggests that apoptosis occurs in ~5% of cerebellar cells, most shortly after mitosis. Apoptosis and cellular autophagy likely play significant roles in cerebellar development, we provide a comprehensive discussion of their role in cerebellar development and organization. We also address the possible function of unfolded protein response in regulation of cerebellar neurogenesis. We discuss recent advancements in understanding the epigenetic signature of cerebellar compartments and possible connections between DNA methylation, microRNAs and cerebellar neurodegeneration. Finally, we discuss genetic diseases associated with cerebellar dysfunction and their role in the aging cerebellum.

Hypoxic preconditioning differentially affects GABAergic and glutamatergic neuronal cells in the injured cerebellum of the neonatal rat

In this study we examined cerebellar alterations in a neonatal rat model of hypoxic-ischemic brain injury with or without hypoxic preconditioning (Pc). Between postnatal days 7 and 15, the cerebellum is still undergoing intense cellular proliferation, differentiation and migration, dendritogenesis and synaptogenesis. The expression of glutamate decarboxylase 1 (GAD67) and the differentiation factor NeuroD1 were examined as markers of Purkinje and granule cells, respectively. We applied quantitative immunohistochemistry to sagittal cerebellar slices, and Western blot analysis of whole cerebella obtained from control (C) rats and rats submitted to Pc, hypoxia-ischemia (L) and a combination of both treatments (PcL). We found that either hypoxia-ischemia or Pc perturbed the granule cells in the posterior lobes, affecting their migration and final placement in the internal granular layer. These effects were partially attenuated when the Pc was delivered prior to the hypoxia-ischemia. Interestingly, whole nuclear NeuroD1 levels in Pc animals were comparable to those in the C rats. However, a subset of Purkinje cells that were severely affected by the hypoxic-ischemic insult—showing signs of neuronal distress at the levels of the nucleus, cytoplasm and dendritic arborization—were not protected by Pc. A monoclonal antibody specific for GAD67 revealed a three-band pattern in cytoplasmic extracts from whole P15 cerebella. A ∼110 kDa band, interpreted as a potential homodimer of a truncated form of GAD67, was reduced in Pc and L groups while its levels were close to the control animals in PcL rats. Additionally we demonstrated differential glial responses depending on the treatment, including astrogliosis in hypoxiated cerebella and a selective effect of hypoxia-ischemia on the vimentin-immunolabeled intermediate filaments of the Bergmann glia. Thus, while both glutamatergic and GABAergic cerebellar neurons are compromised by the hypoxic-ischemic insult, the former are protected by a preconditioning hypoxia while the latter are not.

Expression of autophagy and UPR genes in the developing brain during ethanol-sensitive and resistant periods

Fetal alcohol spectrum disorders (FASD) results from ethanol exposure to the developing fetus and is the leading cause of mental retardation. FASD is associated with a broad range of neurobehavioral deficits which may be mediated by ethanol-induced neurodegeneration in the developing brain. An immature brain is more susceptible to ethanol neurotoxicity. We hypothesize that the enhanced sensitivity of the immature brain to ethanol is due to a limited capacity to alleviate cellular stress. Using a third trimester equivalent mouse model of ethanol exposure, we demonstrated that subcutaneous injection of ethanol induced a wide-spread neuroapoptosis in postnatal day 4 (PD4) C57BL/6 mice, but had little effect on the brain of PD12 mice. We analyzed the expression profile of genes regulating apoptosis, and the pathways of ER stress response (also known as unfolded protein response, UPR) and autophagy during these ethanol-sensitive and resistant periods (PD4 versus PD12) using PCR microarray. The expression of pro-apoptotic genes, such as caspase-3, was much higher on PD4 than PD12; in contrast, the expression of genes that regulate UPR and autophagy, such as atf6, atg4, atg9, atg10, beclin1, bnip3, cebpb, ctsb, ctsd, ctss, grp78, ire1α, lamp, lc3 perk, pik3c3, and sqstm1 was significantly higher on PD12 than PD4. These results suggest that the vulnerability of the immature brain to ethanol could result from high expression of pro-apoptotic proteins and a deficiency in the stress responsive system, such as UPR and autophagy.

Differential changes in the cellular composition of the developing marsupial brain

Throughout development both the body and the brain change at remarkable rates. Specifically, the number of cells in the brain undergoes dramatic nonlinear changes, first exponentially increasing in cell number and then decreasing in cell number. Different cell types, such as neurons and glia, undergo these changes at different stages of development. The current investigation used the isotropic fractionator method to examine the changes in cellular composition at multiple developmental milestones in the short-tailed opossum, Monodelphis domestica. Here we report several novel findings concerning marsupial brain development and organization. First, during the later stages of neurogenesis (P18), neurons make up most of the cells in the neocortex, although the total number of neurons remains the same throughout the life span. In contrast, in the subcortical regions, the number of neurons decreases dramatically after P18, and a converse relationship is observed for nonneuronal cells. In the cerebellum, the total number of cells gradually increases until P180 and then remains constant, and then the number of neurons is consistent across the developmental ages examined. For the three major structures examined, neuronal density and the percentage of neurons within a structure are highest during neurogenesis and then decrease after this point. Finally, the total number of neurons in the opossum brain is relatively low compared with other small-brained mammals such as mice. The relatively low number of neurons and correspondingly high number of nonneurons suggests that in the marsupial brain nonneurons may play a significant role in signal processing.

Immunoreactivity of Ki-67/β-tubulin and immunocolocalization with active caspase-3 in rat dentate gyrus during postnatal development

This study was based on our previous report that the expression of active caspase-3 kept at a high level in dentate gyrus during postnatal development, which is not related to an apoptotic event. We addressed the hypothesis that the active caspase-3 expression may be related to a nonapoptotic role in the regulation of the cell cycle and differentiation or other physiological functions. To confirm this hypothesis, through a temporal investigation from postnatal day (P) 0, 4, 7, 10, 14, 21, 28, to 56, based on immunofluorescent method, we dual labeled active caspase-3 with Ki-67 or β-tubulin in the dentate gyrus. Our results showed a minority of active caspase-3 positive cells were colabeled with the proliferation marker Ki-67 in stratum moleculare (MOL), granular cell layer (GCL), subgranular zone (SGZ) and polymorphic stratum (POLY) from P0 to P14, and the colabeled cells decreased gradually with age. From P21 to P56, the colocalization of the two proteins was mainly focused on SGZ. There was a positive correlation between the positive cells of active caspase-3 with that of Ki-67. In addition, an extensive colocalization between active caspase-3 and β-tubulin was observed at all the age groups. There was a strong positive correlation between the intensity of active caspase-3 in GCL with that of β-tubulin in MOL, GCL and POLY of dentate gyrus and the stratum lucidum of CA3. Our data raised the possibility of a nonapoptotic role of active caspase-3 in dentate gyrus, which may be partly associated with cellular proliferation and differentiation, and also may be related to neurite outgrowth, axonal transport, or dendrite elongation of granular cells during postnatal development.

Antiapoptotic signaling via MCL1 confers resistance to caspase-3-mediated apoptotic cell death in the pregnant human uterine myocyte

Our group has previously identified elevated levels of nonapoptotic active caspase 3 (CASP3) accompanied by increased prosurvival, antiapoptotic signaling in the pregnant mouse uterus during late gestation. We speculated that increased antiapoptotic signaling desensitized the pregnant uterine myocyte to the apoptotic action of uterine CASP3. This current study examines the mechanism by which the pregnant myocyte gains resistance to the apoptotic effects of increased uterine CASP3. Using both primary human pregnant fundal myometrial cultures and the telomerase-immortalized human uterine myocyte cell line (hTERT) as our model systems, uterine myocytes were exposed to UV irradiation and Fas ligand to stimulate both the intrinsic and extrinsic apoptotic pathways. Stimulation of either the intrinsic or extrinsic apoptotic pathways resulted in elevated levels of uterine myocyte CASP3. However, apoptotic cell death was restricted to CASP3 activated by intrinsic stimulation via UV light. In contrast Fas ligand-mediated CASP3 activation was accompanied by increased antiapoptotic signaling mimicking our in vivo observations in the pregnant mouse uterus. Using small interfering RNA to inhibit antiapoptotic signaling, we determined the ability of the human uterine myocyte to resist apoptotic cell death in the absence of the prosurvival, antiapoptotic signaling. Accordingly, suppression of antiapoptotic signaling specifically mediated by myeloid cell leukemia sequence 1 was sufficient to sensitize the uterine myocyte to undergo apoptotic cell death. These data demonstrate that elevated myeloid cell leukemia sequence 1 levels are sufficient to confer apoptotic resistance on the human uterine myocyte despite highly elevated levels of active CASP3.

The executioners sing a new song: killer caspases activate microglia

Activation of microglia and inflammation-mediated neurotoxicity are suggested to have key roles in the pathogenesis of several neurodegenerative disorders. We recently published an article in Nature revealing an unexpected role for executioner caspases in the microglia activation process. We showed that caspases 8 and 3/7, commonly known to have executioner roles for apoptosis, can promote microglia activation in the absence of death. We found these caspases to be activated in microglia of PD and AD subjects. Inhibition of this signaling pathway hindered microglia activation and importantly reduced neurotoxicity in cell and animal models of disease. Here we review evidence suggesting that microglia can have a key role in the pathology of neurodegenerative disorders. We discuss possible underlying mechanisms regulating their activation and neurotoxic effect. We focus on the provocative hypothesis that caspase inhibition can be neuroprotective by targeting the microglia rather than the neurons themselves.

Strain differences in developmental vulnerability to alcohol exposure via embryo culture in mice

BACKGROUND

Prenatal alcohol exposure can result in varying degrees of neurodevelopmental deficits, growth retardation, and facial dysmorphology. Variation in these adverse outcomes not only depends on the dose and pattern of alcohol exposure but also on less well understood interactions among environmental, genetic, and maternal factors. The current study tested the hypothesis that fetal genotype is an important determinant of ethanol teratogenesis by evaluating effects of ethanol exposure via embryo culture in 3 inbred strains of mice known to differ in the vulnerability of prenatal alcohol exposure in vivo.

METHODS

Three strains of mice, C57BL/6N (B6), DBA/2 (D2), and 129S6/SvEvTac (129S6) were assessed in a whole embryo culture beginning on embryonic day 8.25, with or without alcohol administration at 88 mM for 6 hours followed by 42 hours culture in ethanol-free media.

RESULTS

Contrasting strain differences in susceptibility were observed for the brain, the face, and other organ systems using the Maele-Fabry and Picard scoring system. The forebrain, midbrain, hindbrain, heart, optic vesicle, caudal neural tube, and hindlimbs of the B6 mice were severely delayed in growth, whereas compared to the respective controls, only the forebrain and optic vesicle were delayed in the D2 mice, and no effects were found in the 129S6 mice. A large number of cleaved (c)-caspase 3 positive (+) cells were found in regions of the brain, optic vesicles, cranial nerve nuclei V, VII, VIII, and IX as well as the craniofacial primordial; only a few were found in corresponding regions of the B6 controls. In contrast, only a small number of c-caspase 3 immunostaining cells were found in either the alcohol treated or the controls of the D2 embryos and in 129S6 embryos. The independent apoptotic markers TUNEL and Nile blue staining further confirmed the strain differences in apoptotic responses in both the neural tube and craniofacial primordia.

CONCLUSIONS

Under embryo culture conditions, in which alcohol exposure factors and fetal developmental staging were controlled, and maternal and intrauterine factors were eliminated, the degree of growth retardation and the extent and type of neurodevelopmental teratogenesis varied significantly across strains. Notably, the 129S6 strain was remarkably resistant to alcohol-induced growth deficits, confirming a previous in vivo study, and the D2 strain was also significantly less affected than the B6 strain. These findings demonstrate that fetal genotype is an important factor that can contribute to the variation in fetal alcohol spectrum disorder.

Cleaved caspase-3 expression after experimental stroke exhibits different phenotypes and is predominantly non-apoptotic

Cleaved caspase-3 (CC3) is well known as an executioner protease of apoptosis following brain ischemia. However, an increasing body of evidence suggests several non-apoptotic functions of CC3. To improve our understanding of the relation between cell death-related and non-adverse effects of postischemic caspase-3 activation, we examined the spatiotemporal distribution and identity of CC3-positive cells at days 2, 3 and 4 after permanent middle cerebral artery occlusion in rats. The lacking colocalization of CC3 and TUNEL staining indicated, that CC3 expression was predominantly non-apoptotic. Nuclear CC3 expression was frequently found to be colocalized with GFAP-positive astrocytes within the tissue adjacent to the infarct, whereas cytoplasmatic CC3 expression occurred solely in the lesion. Multiple fluorescence labeling revealed costaining of cytoplasmatic CC3 with markers directed against astrocytes, macrophages/microglia and supposedly pericytes. Our findings suggest that CC3 expression was predominantly associated with cellular responses to stroke such as reactive astrogliosis and the infiltration of macrophages.

Effects of d-3-hydroxybutyrate treatment on hypoglycemic coma in rat pups

d-3-Hydroxybutyrate (3OHB) is an alternative energy substrate for the brain during hypoglycemia, especially in infancy. Knowledge of the capacity and limits of 3OHB to compensate for cerebral glucose depletion during hypoglycemia in developing brain is important for its potential clinical use, but is scarce. We studied the effect of 3OHB treatment during insulin-induced hypoglycemia in 13-day-old rat pups. 3OHB treatment resulted in increased 3OHB plasma levels in hypoglycemic animals (3-4mM vs. 0.5-1mM untreated), and delayed the onset of clinical coma by 70min and of burst-suppression coma by 90min. 3OHB treated animals did not survive after resuscitation with glucose, compared to 80% survival of untreated hypoglycemic pups. Cleaved-caspase-3 immunohistochemistry and double labeling studies demonstrated a 20-fold increase of apoptotic mature oligodendrocytes in white matter of 3OHB treated animals. 3OHB treatment delays the onset of clinical and burst-suppression coma during hypoglycemia, but the prolonged duration of hypoglycemia is associated with increased mortality after resuscitation and cellular white matter injury.

SCLM, total saponins extracted from Chaihu-jia-longgu-muli-tang, reduces chronic mild stress-induced apoptosis in the hippocampus in mice

Increasing evidence demonstrates that stress or depression can lead to atrophy and cell loss in the hippocampus. In contrast, antidepressant treatment significantly reduces apoptosis in the dentate granule cell layer and subgranular zone in animal models of depression. In the present study, we investigated the neuroprotective action of SCLM, the total saponins extracted from Chaihu-jia-longgu-muli-tang, a traditional Chinese medicinal formula which was prescribed 1000 years ago, in the reduction of apoptosis in hippocampal neurons using an experimental chronic mild stress (CMS) model. Mice were subjected to the CMS procedure for a period of 21 consecutive days. SCLM (100 mg/kg, p.o.) or fluoxetine (20 mg/ kg, p.o.) was administered during the stress periods. CMS mice showed a decreased sucrose intake over 21 days, and an increase in the number of TUNEL-positive neurons as well as up-regulation of the apoptotic-related factors, such as Bax and caspase-3 in the hippocampus, compared with control mice. On the other hand, the administration of SCLM (100 mg/kg) and fluoxetine (20 mg/kg) reversed these effects induced by CMS, showing a significant increase of sucrose intake and a dramatic reduction of TUNEL-positive neurons and decreased expression of Bax and caspase-3 proteins. The present results suggest that SCLM possesses a significant antidepressant-like property, and this effect may be through protection against stress-induced neuronal apoptosis by affecting the expression of Bax and caspase-3 proteins in the hippocampus. These findings provide important information that the anti-apoptotic effect of herbal medicine therapy may be beneficial for the treatment of depression.

Regional differences in the temporal expression of non-apoptotic caspase-3-positive bergmann glial cells in the developing rat cerebellum

Although caspases have been intimately linked to apoptotic events, some of the pro-apoptotic caspases also may regulate differentiation. We previously demonstrated that active caspase-3 is expressed and has an apparent non-apoptotic function during the development of cerebellar Bergmann glia. The current study seeks to further correlate active/cleaved caspase-3 expression with the developmental phenotype of Bergmann glia by examining regional differences in the temporal pattern of expression of cleaved caspase-3 immunoreactivity in lobules of the cerebellar vermis. In general, we found that the expression pattern of cleaved caspase-3 corresponds to the reported developmental temporal profile of the lobes and that its levels peak at 15 days and declines thereafter. Compared to intermediate or late maturing lobules, early maturing lobules had higher levels of active caspase-3 at earlier postnatal times. This period of postnatal development is precisely the time during which Bergmann glia initiate differentiation.

HIV-1 Tat and morphine have interactive effects on oligodendrocyte survival and morphology

Human immunodeficiency virus (HIV)-infected individuals who abuse opiates show faster progression to AIDS, and enhanced incidence of HIV-1 encephalitis. Most opiates with abuse liability are preferential agonists for mu-opioid receptors (MORs), and MORs are expressed on both neurons and glia, including oligodendrocytes (OLs). Tat, gp120, and other viral toxins, cause neurotoxicity in vitro and/or when injected into brain, and co-exposure to opiates can augment HIV-1 protein-induced insults to both glial and neuronal populations. We examined the effects of HIV-1 Tat +/- opiate exposure on OL survival and differentiation. In vivo studies utilized transgenic mice expressing Tat(1-86) regulated by an inducible glial fibrillary acidic protein promoter. Although MBP levels were unchanged on immunoblots, certain structural and apoptotic indices were abnormal. After only 2 days of Tat induction, OLs showed an upregulation of active caspase-3 that was enhanced by morphine exposure. Tat also upregulated TUNEL staining, but only in the presence of morphine. Tat significantly reduced the length of processes in Golgi-Kopsch impregnated OLs. A greater proportion of cells exhibited diminished or aberrant cytoplasmic processes, especially when mice expressing Tat were co-exposed to morphine. Collectively, our data show that OLs in situ are extremely sensitive to effects of Tat +/- morphine, although it is not clear if immature OLs as well as differentiated OLs are targeted equally. Significant elevations in caspase-3 activity and TUNEL labeling, and evidence of increased degeneration/regeneration of OLs exposed to Tat +/- morphine suggest that toxicity toward OLs may be accompanied by heightened OL turnover.

Morphine causes rapid increases in glial activation and neuronal injury in the striatum of inducible HIV-1 Tat transgenic mice

HIV encephalitis (HIVE) is accompanied by brain inflammation, leukocyte infiltration, and glial activation, and HIV patients who abuse opiates are more likely to develop HIVE. To better understand how opiates could alter HIV-related brain inflammation, the expression of astrocyte (GFAP immunoreactivity) and macrophage/microglial (F4/80 or Mac1 immunoreactivity) markers in the striatum, and the percentage of 3-nitrotyrosine (3-NT) positive macrophages/microglia, was determined following a 2-day exposure to morphine (5 mg/kg/day via time-release, subcutaneous implant) and doxycycline in GFAP-driven, doxycycline-inducible HIV-1 Tat transgenic mice. Data show that both morphine and Tat induction via doxycycline increased astrocyte activation, with significant additive increases achieved with combined morphine and doxycycline exposure. By contrast, combined Tat induction and morphine exposure, but neither manipulation alone, significantly increased the proportion of macrophages/microglia present in the striatum of transgenic mice, although morphine exposure was necessary to elevate 3-NT co-detection in Mac1-positive macrophages/microglia. Finally, Tat induction increased the percentage of neurons expressing active caspase-3, and this was even more significantly elevated by co-administration of morphine. In spite of elevations in caspase-3, neuronal TUNEL reactivity was unchanged in all groups, even after 10 days of Tat induction. Importantly, co-administration of naltrexone completely antagonized the effects of morphine. These findings indicate that morphine rapidly and significantly increases the activation of astrocytes and macrophages/microglia in the brains of inducible Tat transgenic mice, supporting the theory that early inflammatory changes in glia could underlie the development of HIVE in opiate-abusing AIDS patients.

Nerve growth factor neuroprotection of ethanol-induced neuronal death in rat cerebral cortex is age dependent

Organotypic cultures of rat cortex were used to test the hypotheses that nerve growth factor (NGF) is neuroprotective for immature cortical neurons and that ethanol abolishes this neuroprotection in a developmental stage-dependent manner. Samples were obtained on gestational day (G) 16 or postnatal day (P) 3 and cultured with ethanol (0 or 400 mg/dl) and NGF (0 or 30 ng/ml) for 72 h. Dying neurons were identified as exhibiting terminal nick-end labeling, immunoreactivity for activated caspase 3, or condensed nuclear chromatin. Two cortical compartments were examined in fetal tissue: a superficial, cell-sparse marginal zone (MZ) and a cell-dense cortical plate (CP). At P3, the CP was subdivided into a cell-dense upper cortical plate (UCP) and a less densely packed lower cortical plate (LCP). Neuronal death in the MZ was affected by neither NGF nor ethanol at both ages. In the fetal CP, NGF did not affect the incidence of cell death, but ethanol increased it. Treatment with NGF caused an upregulation of the expression of Neg, a gene known to be affected by NGF and ethanol. NGF did not ameliorate the ethanol-induced death. In pups, ethanol increased the amount of death in the LCP. NGF did protect against this death. Neither ethanol nor NGF altered the incidence of cell death in the UCP. The laminar-dependent neuroprotection did not correlate with expression of NGF receptors or Neg. Thus, NGF can be protective against the neurotoxic effect of ethanol in the neonatal brain. This effect is site selective and time dependent and it targets postmigratory, differentiating neurons.

Altered cerebellar development in mice lacking pituitary adenylate cyclase-activating polypeptide

Previous studies have demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic effects during neurodevelopment. In particular, the occurrence of PACAP and its receptors in the cerebellum during pre- and postnatal periods suggests that it could play a crucial role in ontogenesis of this structure. To test this hypothesis, we compared the histogenesis of cerebellar cortex in wild-type and PACAP-knockout (PACAP-/-) mice at postnatal days (P)4 and 7. Morphometric analysis of PACAP-/- mice revealed a significant reduction in the thickness of the external granule cell layer at P4 and of the internal granule cell layer at P7. Expression of nestin, a neural precursor marker, and synaptophysin, a mature neuronal marker, was quantified by real-time PCR and Western blot. No modification of nestin expression was noticed between wild-type and PACAP-/- mice, but a substantial decrease in synaptophysin expression was observed in PACAP-/- mice at P4 and P7. Immunohistochemistry revealed a reduction in synaptophysin labelling in the molecular and internal granule cell layers of PACAP-/- mice at P7. Caspase-3 activation was significantly increased in PACAP-/- mice at P4 and P7. Autoradiographic studies revealed no difference in PACAP binding site distributions and PACAP was effective at stimulating cAMP production in both wild-type and PACAP-/- cultured granule cells. This study demonstrates that disruption of the PACAP gene induces alteration of the immature cerebellum. Neuronal differentiation of granule cells was delayed whereas cell death that naturally occurs during ontogeny was increased in PACAP-/- mice. These data provide the first evidence of a physiological role for PACAP during cerebellar development.

Nine procaspases are expressed in normal human epidermis, but only caspase-14 is fully processed

BACKGROUND

During normal stratification of the epidermis, keratinocytes undergo a complex programme of terminal differentiation. This programmed cell death results in corneocyte accumulation to form the stratum corneum (SC). Terminal differentiation and apoptosis share numerous features such as elimination of nuclei and organelles, changes in cell shape, and activation of transglutaminases and proteases. Caspases are cysteine proteases that play a central role in apoptosis. Therefore they may also be involved in the terminal differentiation of keratinocytes.

OBJECTIVES

To identify the caspases expressed in normal human epidermis and to define their pattern of expression and activation.

METHODS

We analysed mRNAs from human epidermis by reverse transcription-polymerase chain reaction (RT-PCR), skin cryosections by immunohistological methods, and epidermal protein extracts by Western blotting.

RESULTS

The mRNAs encoding caspase-1, -2, -3, -4, -6, -7, -8, -9, -10 and -14 were detected by RT-PCR. Accordingly, the immunohistological analyses showed clear expression in the epidermis of the corresponding proteins except caspase-2 and caspase-8, with only a weak expression of caspase-9. Moreover, procaspase-1, -2, -3, -4, -6, -7, -9, -10 and -14, and the fully processed caspase-14, were immunodetected in total epidermis extracts. However, only procaspase-1 and the processed caspase-14 were detected in extracts of superficial SC. In addition to these two proteins, procaspase-4 was detected in extracts of superficial SC obtained from lesional psoriatic skin.

CONCLUSIONS

This study, the first exhaustive description of caspase expression and processing in normal human epidermis, indicates that in vivo granular keratinocytes express nine procaspases, and in addition the activated form of caspase-14. This confirms that only caspase-14 is involved in keratinocyte differentiation, and suggests that keratinocytes are ready to induce apoptosis in response to cutaneous damage.

A transgene-assisted genetic screen identifies essential regulators of vascular development in vertebrate embryos

Formation of a functional vasculature during mammalian development is essential for embryonic survival. In addition, imbalance in blood vessel growth contributes to the pathogenesis of numerous disorders. Most of our understanding of vascular development and blood vessel growth comes from investigating the Vegf signaling pathway as well as the recent observation that molecules involved in axon guidance also regulate vascular patterning. In order to take an unbiased, yet focused, approach to identify novel genes regulating vascular development, we performed a three-step ENU mutagenesis screen in zebrafish. We first screened live embryos visually, evaluating blood flow in the main trunk vessels, which form by vasculogenesis, and the intersomitic vessels, which form by angiogenesis. Embryos that displayed reduced or absent circulation were fixed and stained for endogenous alkaline phosphatase activity to reveal blood vessel morphology. All putative mutants were then crossed into the Tg(flk1:EGFP)(s843) transgenic background to facilitate detailed examination of endothelial cells in live and fixed embryos. We screened 4015 genomes and identified 30 mutations affecting various aspects of vascular development. Specifically, we identified 3 genes (or loci) that regulate the specification and/or differentiation of endothelial cells, 8 genes that regulate vascular tube and lumen formation, 8 genes that regulate vascular patterning, and 11 genes that regulate vascular remodeling, integrity and maintenance. Only 4 of these genes had previously been associated with vascular development in zebrafish illustrating the value of this focused screen. The analysis of the newly defined loci should lead to a greater understanding of vascular development and possibly provide new drug targets to treat the numerous pathologies associated with dysregulated blood vessel growth.

Caspase-3 activation in astrocytes following postnatal excitotoxic damage correlates with cytoskeletal remodeling but not with cell death or proliferation

Caspase-3 has classically been defined as the main executioner of programmed cell death. However, recent data supports the participation of this protease in non-apoptotic cellular events including cell proliferation, cell cycle regulation, and cellular differentiation. In this study, astroglial cleavage of caspase-3 was analyzed following excitotoxic damage in postnatal rats to determine if its presence is associated with apoptotic cell death, cell proliferation, or cytoskeletal remodeling. A well-characterized in vivo model of excitotoxicity was studied, where damage was induced by intracortical injection of N-methyl-D-asparate (NMDA) in postnatal day 9 rats. Our results demonstrate that cleaved caspase-3 was mainly observed in the nucleus of activated astrocytes in the lesioned hemisphere as early as 4 h postlesion and persisted until the glial scar was formed at 7-14 days, and it was not associated with TUNEL labeling. Caspase-3 enzymatic activity was detected at 10 h and 1 day postlesion in astrocytes, and co-localized with caspase-cleaved fragments of glial fibrillary acidic protein (CCP-GFAP). However, at longer survival times, when astroglial hypertrophy was observed, astroglial caspase-3 did not generally correlate with GFAP cleavage, but instead was associated with de novo expression of vimentin. Moreover, astroglial caspase-3 cleavage was not associated with BrdU incorporation. These results provide further evidence for a nontraditional role of caspases in cellular function that is independent of cell death and suggest that caspase activation is important for astroglial cytoskeleton remodeling following cellular injury.

Dynamic changes of apoptosis and expression of Bcl-2 family members in the posthatch hippocampus of Bengalese finches

The hippocampus of songbirds plays an important role in spatial memory, and probably in song learning. Although prolonged neuronal generation and apoptosis are thought to be closely correlated with memory function, natural changes of the number of neurons and in apoptosis in the hippocampus of songbirds have not been fully investigated during development and in the adult. In the current study, we examined developmental changes in the volume and the number of neurons and apoptotic cells in the hippocampus of songbirds (Lonchura striata) from posthatch day (P5) to adulthood. Apoptotic cells were determined by Nissl staining and immunohistochemistry for cleaved caspase-3, a key apoptotic caspase executioner. The expression levels of Bcl-2 family member mRNA and protein, including Bcl-2, Bcl-xL and Bax, were also investigated. Our results indicated that: (1) the hippocampus volume significantly increased from P5 to P60, although the number of neurons remained stable in all studied stages; (2) the number of apoptotic cells was highest at P45, based either on the Nissl staining or on the immunohistochemistry for caspase-3; (3) Bcl-2 mRNA expression was high from P5 to adulthood, while Bax mRNA declined abruptly from P5 to adulthood, and Bcl-x mRNA was high after P45. Bcl-2 protein was only detected at P5 and P15, while detection of Bcl-xL and Bax proteins paralleled levels of mRNA expression. Our study provides detailed changes of apoptosis in the posthatch songbird hippocampus, suggesting an important role for caspase-3 and Bcl-2 family members in hippocampus apoptosis.

Different types of neural cell death in the cerebellum of the ataxia and male sterility (AMS) mutant mouse

To investigate the mechanisms(s) of age-dependent atrophy of the cerebellum of the ataxia and male sterility (AMS) mouse at young age, the morphological changes were evaluated and the nature of neural cell death was examined. Dying Purkinje cells lacked characters of classical apoptosis except for light microscopic morphology, but their death was considered to be autonomous death triggered by the direct effect of ams mutation, because of the acute and near-complete disappearance and particular change of the cytoplasm. In contrast, in the granular layer, typical apoptotic bodies were recognized by electron microscopy, and substantial numbers of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end-labeling (TUNEL)-positive cells and activated caspase-3-positive cells were observed. Granule cell death was considered to be target-related apoptosis induced after post-synaptic Purkinje cell death, because the age-dependent changes in TUNEL-positive cell counts followed that of Purkinje cell loss and the peak value was still noted 1 week after total loss of Purkinje cells. These results indicate that both total and partial losses of Purkinje cells and granule cells, respectively, contributed to the atrophy of the AMS cerebellum. Furthermore, different types of neuronal death were recognized; the granule cell death was apoptotic while Purkinje cell death was different from that of classical apoptosis.

Calpain activation is required for glutamate-induced p27 down-regulation in cultured cortical neurons

Recent evidence suggests that cell cycle-related molecules play pivotal roles in multiple forms of cell death in post-mitotic neurons. Nevertheless, it remains unclear what molecular mechanisms are involved in the regulation of expression levels and activities of these molecules. We showed previously that treatment with extracellular glutamate decreases cyclin-dependent kinase inhibitor p27 before neuronal cell death. In this study, we demonstrate that reductions of both p27 and neuronal viability were dependent on activity of calpain, a Ca(2+)-dependent protease, but not on activity of caspase 3. Interestingly, the glutamate-induced reduction of p27 was not dependent on the ubiquitin-proteasome system. In fact, p27 was present only in the neuronal nucleus, whereas calpain 1, a ubiquitous calpain, was observed both in the neuronal nucleus and cytoplasm in control cultures. Glutamate treatment did not change the localization patterns of p27 and calpain 1. It reduced p27 expression level in the nucleus in a calpain-dependent manner. In vitro experiments using neuronal cell lysate and p27 recombinant protein revealed that p27 was degraded as a substrate of activated calpain 1. These results suggest that calpain(s), activated by glutamate treatment, degrade(s) p27 in the nucleus of neurons, which might promote aberrant cell cycle progression.

Neural-specific inactivation of ShcA results in increased embryonic neural progenitor apoptosis and microencephaly

Brain size is precisely regulated during development and involves coordination of neural progenitor cell proliferation, differentiation, and survival. The adapter protein ShcA transmits signals from receptor tyrosine kinases via MAPK (mitogen-activated protein kinase)/ERK (extracellular signal-regulated kinase) and PI3K (phosphatidylinositol 3-kinase)/Akt signaling pathways. In the CNS, ShcA expression is high during embryonic development but diminishes as cells differentiate and switches to ShcB/Sck/Sli and ShcC/N-Shc/Rai. To directly test ShcA function in brain development, we used Cre/lox technology to express a dominant-negative form of ShcA (ShcFFF) in nestin-expressing neural progenitors. ShcFFF-expressing mice display microencephaly with brain weights reduced to 50% of littermate controls throughout postnatal and adult life. The cerebrum appeared most severely affected, but the gross architecture of the brain is normal. Body weight was mildly affected with a delay in reaching mature weight. At a mechanistic level, the ShcFFF microencephaly phenotype appears to be primarily attributable to elevated apoptosis levels throughout the brain from embryonic day 10.5 (E10.5) to E12, which declined by E14.5. Apoptosis remained at normal basal levels throughout postnatal development. Proliferation indices were not significantly altered in the embryonic neuroepithelium or within the postnatal subventricular zone. In another approach with the same nestin-Cre transgene, conditional deletion of ShcA in mice with a homozygous floxed shc1 locus also showed a similar microencephaly phenotype. Together, these data suggest a critical role for ShcA in neural progenitor survival signaling and in regulating brain size.

Region-Specific Interrelations between Apoptotic Proteins Expression and DNA Fragmentation in the Neonatal Rat Brain

DNA fragmentation, mRNA and protein levels of Bcl-XL, Bax and caspase-3 were determined to characterize interrelations between expression of these apoptotic markers in the neonatal brain regions. High DNA fragmentation intensity in the cortex was in consonance with the lowest Bcl-XL/Bax expression ratio, the highest procaspase-3 and active caspase-3 levels. Low and intermediate DNA fragmentation levels in the cerebellum and hippocampus respectively were also in a good agreement with apoptotic proteins expression in these structures. In the cortex, hippocampus and cerebellum DNA fragmentation intensity was proportional to the active caspase-3 level. In contrast to these structures, in the brainstem, the lowest level of this protease was accompanied by the highest intensity of DNA fragmentation among the brain regions studied. The data suggest that cell death normally occurring during early postnatal life could be realized in the developing brainstem via caspase-3-independent pathways in animals that express this protease.

Bergmann glia utilize active caspase-3 for differentiation

Recently, functions associated with caspase have been modified from their well-established role in apoptosis. Although caspases are still regarded as mediators of apoptosis, some of the pro-apoptotic caspases, namely caspase-8, -14 and -3 also regulate differentiation in certain cell types, namely myelomonocytic cells, osteoblasts, skeletal muscle cells, keratinocytes, and T lymphocytes. In the central nervous system, non-apoptotic active caspase-3 expression has been located in proliferating and differentiating neuronal cells of the ventricular zone and external granular layer of the developing cerebellar cortex. We previously demonstrated that active caspase-3 expression was not limited to neuronal cells but also was located in the Bergmann glia of the postnatal cerebellum. In that study, active caspase-3 immunolabeling did not markedly colocalize with Ki67, a proliferation marker, but was present in differentiating Bergmann glia that expressed brain lipid binding protein (BLBP) and thus, by its localization, suggested a role in the differentiation of Bergmann glia. The current study addresses the function of caspase-3 in Bergmann glia development by utilizing a Bergmann glial culture preparation. Inhibition of caspase-3 activity by the peptide inhibitor, DMQD-FMK, increased the number of proliferating precursor glial cells and decreased the number of differentiating Bergmann glia, without significantly altering the non-glial active caspase-3 negative population. The transformation in the developmental state of Bergmann glia occurring after suppression of caspase-3 activity strongly suggests an involvement of this enzyme in promoting differentiation of Bergmann glia.

Loss of neurons from laminas I-III of the spinal dorsal horn is not required for development of tactile allodynia in the spared nerve injury model of neuropathic pain

It has been proposed that death of inhibitory interneurons in the dorsal horn contributes to the neuropathic pain that follows partial nerve injury. In this study, we have used two approaches to test whether there is neuronal death in the dorsal horn in the spared nerve injury (SNI) model. We performed a stereological analysis of the packing density of neurons in laminas I-III 4 weeks after operation and found no reduction on the ipsilateral side compared with that seen on the contralateral side or in sham-operated or naive rats. In addition, we used two markers of apoptosis, terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) staining and immunocytochemical detection of cleaved (activated) caspase-3. Neither of these methods demonstrated apoptotic neurons in the dorsal spinal cord 1 week after operation. Although TUNEL-positive cells were present throughout the gray and white matter at this stage, they were virtually all labeled with antibody against ionized calcium-binding adapter molecule 1, a marker for microglia. All animals that underwent SNI showed clear signs of tactile allodynia affecting the ipsilateral hindpaw. These results suggest that a significant loss of neurons from the dorsal horn is not necessary for the development of tactile allodynia in the SNI model.

Non-lethal active caspase-3 expression in Bergmann glia of postnatal rat cerebellum

Caspase-3, an apoptotic executor, has been shown in recent years to mediate non-lethal events like cellular proliferation and differentiation, primarily in studies related to non-neural tissue. In central nervous system development, the role of active caspase-3 is still unclear. We provide the first evidence for a potential new role of active (cleaved) caspase-3 in promoting differentiation of Bergmann glia. This study was predicated on the hypothesis that active caspase-3 is important for the differentiation of glia. We addressed the hypothesis through the following specific aims: (1) to establish the expression of active caspase-3 in glia; (2) to determine the developmental phenotype of the active caspase-3-expressing glia; and (3) to confirm that active caspase-3 expression is not mediating an apoptotic event. Through a temporal investigation from postnatal day 8 to 21, we observed that Bergmann glia express active caspase-3 without compromising their survival. Potential apoptotic fate of active caspase-3-positive Bergmann glia were ruled out based on immunohistochemical exclusion of phosphatidylserine exposure (Annexin V), DNA fragmentation (TUNEL), and DNA compaction (TOPRO-3). More than 90% of the active caspase-3-positive cells lacked colabeling for one of the apoptotic markers. Correlative studies using a proliferation marker Ki67 and a differentiation marker brain lipid-binding protein suggest that the expression of active caspase-3 was mostly associated with differentiating rather than proliferating Bergmann glia at all ages. Thus, this study supports the hypothesis that active caspase-3 may be regulating both differentiation of Bergmann glia by allowing the cells to exit the cell cycle and their morphogenesis.

Cellular and molecular analyses of vascular tube and lumen formation in zebrafish

Tube and lumen formation are essential steps in forming a functional vasculature. Despite their significance, our understanding of these processes remains limited, especially at the cellular and molecular levels. In this study, we analyze mechanisms of angioblast coalescence in the zebrafish embryonic midline and subsequent vascular tube formation. To facilitate these studies, we generated a transgenic line where EGFP expression is controlled by the zebrafish flk1 promoter. We find that angioblasts migrate as individual cells to form a vascular cord at the midline. This transient structure is stabilized by endothelial cell-cell junctions, and subsequently undergoes lumen formation to form a fully patent vessel. Downregulating the VEGF signaling pathway, while affecting the number of angioblasts, does not appear to affect their migratory behavior. Our studies also indicate that the endoderm, a tissue previously implicated in vascular development, provides a substratum for endothelial cell migration and is involved in regulating the timing of this process, but that it is not essential for the direction of migration. In addition, the endothelial cells in endodermless embryos form properly lumenized vessels, contrary to what has been previously reported in Xenopus and avian embryos. These studies provide the tools and a cellular framework for the investigation of mutations affecting vasculogenesis in zebrafish.

Fetal origin of adverse pregnancy outcome: the water disinfectant by-product chloroacetonitrile induces oxidative stress and apoptosis in mouse fetal brain

Epidemiological studies indicate a relationship between water disinfectant by-products (DBP) and adverse pregnancy outcomes (APO) including neural tube defects. These studies suggest that fetal brain may be vulnerable to DBP during early stages of development. Therefore, we examined several molecular markers commonly known to indicate chemical-induced neurotoxicity during fetal brain development following prenatal exposure to the DBP; chloroacetonitrile (CAN). Pregnant mice, at gestation day 6 (GD6), were treated with a daily oral dose of CAN (25 mg/kg). At GD12, two groups of animals were treated with an i.v. tracer dose of [2-14C]-CAN. These animals were sacrificed at 1 and 24 h after treatment and processed for quantitative in situ micro-whole-body autoradiography. The remaining groups of animals continued to receive CAN. At GD18, control and treated animals were weighed, anesthetized, and fetuses were obtained and their brains were removed for biochemical and immunohistochemical analyses. Whole-body autoradiography studies indicate a significant uptake and retention of [2-14C]-CAN/metabolites (M) in fetal brain (cerebral cortex, hippocampus, cerebellum) at 1 and 24 h. There was a 20% reduction in body weight and a 22% reduction in brain weight of fetuses exposed to CAN compared to controls. A significant increase in oxidative stress markers was observed in various fetal brain regions in animals exposed to CAN compared to controls. This was indicated by a 3- to 4-fold decrease in the ratio of the reduced to oxidized form of glutathione (GSH/GSSG), increased lipid peroxidation (1.3-fold), and increased 8-hydroxy-2-deoxyguanosine levels (1.4-fold). Cupric silver staining indicated a significant increase in the number of degenerating neurons in cortical regions in exposed animals. In animals exposed to CAN there was increase in nuclear DNA fragmentation (TUNEL staining) detected in the cerebral cortex and cerebellum (2-fold increase in apoptotic indices). Caspase-3 activity in cerebral cortex and cerebellum of treated animals were also increased (1.7- and 1.5-fold, respectively). In conclusion, this study indicates that CAN/M crossed the placenta and accumulated in fetal brain tissues where it caused oxidative stress and neuronal apoptosis. These events could predispose the fetus to altered brain development leading to APO as well as behavioral and learning and memory deficits.

Neural stem cell differentiation is dependent upon endogenous caspase 3 activity

Caspase proteases have become the focal point for the development and application of anti-apoptotic therapies in a variety of central nervous system diseases. However, this approach is based on the premise that caspase function is limited to invoking cell death signals. Here, we show that caspase-3 activity is elevated in nonapoptotic differentiating neuronal cell populations. Moreover, peptide inhibition of protease activity effectively inhibits the differentiation process in a cultured neurosphere model. These results implicate caspase-3 activation as a conserved feature of neuronal differentiation and suggest that targeted inhibition of this protease in neural cell populations may have unintended consequences.

Vital functions for lethal caspases

Caspases are a family of cysteine proteases expressed as inactive zymogens in virtually all animal cells. These enzymes play a central role in most cell death pathways leading to apoptosis but growing evidences implicate caspases also in nonapoptotic functions. Several of these enzymes, activated in molecular platforms referred to as inflammasomes, play a role in innate immune response by processing some of the cytokines involved in inflammatory response. Caspases are requested for terminal differentiation of specific cell types, whether this differentiation process leads to enucleation or not. These enzymes play also a role in T and B lymphocyte proliferation and, in some circumstances, appear to be cytoprotective rather than cytotoxic. These pleiotropic functions implicate caspases in the control of life and death but the fine regulation of their dual effect remains poorly understood. The nonapoptotic functions of caspases implicate that cells can restrict the proteolytic activity of these enzymes to selected substrates. Deregulation of the pathways in which caspases exert these nonapoptotic functions is suspected to play a role in the pathophysiology of several human diseases.

Early postnatal exposure to alcohol reduces the number of neurons in the occipital but not the parietal cortex of the rat

BACKGROUND

The rat brain undergoes a period of rapid growth in the early postnatal period. During this time, the neocortex seems to be vulnerable to ethanol injury. Subdivisions of the neocortex develop in a temporospatial gradient that is likely to determine their vulnerability to ethanol-induced damage and whether damage is permanent. Therefore, the authors investigated the effect of postnatal ethanol exposure on the neocortex and specific subregions at the cessation of exposure and in the mature brain.

METHODS

Four-day-old rat pups with intragastric cannulae were artificially reared from postnatal day (PN) 4 through PN9. Of 12 daily feeds, two consecutive feeds contained either ethanol (4.5 g/kg) or an isocaloric maltose/dextrin solution. On PN10 or PN115, animals were perfused intracardially, and the brains were removed. Stereological methods were used to determine the total number of neurons and glial cells in, and the volume of, the neocortex, the parietal cortex, and the occipital cortex.

RESULTS

Exposure to ethanol did not affect body or brain weight at PN10. In contrast, at PN115 forebrain weight was significantly lower in ethanol-exposed animals compared with control-treated animals. There was no effect of treatment on body weight at PN115. On PN10, neocortical volume was 15% smaller in the ethanol-exposed animals compared with controls, with no change in the total number of neurons or glial cells. Occipital cortical volume was reduced by 22% in the ethanol-exposed animals, with a significant deficit in the total number of neurons (ethanol-exposed, 2.62 x 10; gastrostomy control, 3.20 x 10). There was no effect of ethanol exposure on the total number of glial cells in the occipital cortex or on any parameter in the parietal cortex. There was also no significant effect of ethanol exposure on the occipital cortex on PN115.

CONCLUSIONS

These findings provide support for the hypothesis that a specific area or cell population might be differentially vulnerable to ethanol exposure during the brain growth spurt and that cell deficits evident on PN10 may not be permanent.