Dynamics of expression of apoptosis-regulatory proteins Bid, Bcl-2, Bcl-X, Bax and Bak during development of murine nervous system

Bcl-2 expression inversely correlates with tumour cell differentiation in medulloblastoma

Medulloblastoma (MB) is a cerebellar primitive neuroectodermal tumour that occurs predominantly in childhood. It can be mainly divided into classical and desmoplastic tumours, but differential diagnosis is often difficult. Patients' prognosis is poor and neuropathological markers that reliably predict outcome are still missing. In a series of 104 MBs including 80 tumours of the classical and 24 tumours of the desmoplastic variant we studied the number of apoptotic figures and the expression of the proto-oncogene bcl-2, an anti-apoptotic protein known to affect tumour cell proliferation. We observed a strong correlation between the expression of bcl-2 with patients' age (P < 0.001) as well as with the desmoplastic subtype (P < 0.001). Here, protein expression was found to be restricted to internodular, less differentiated, highly proliferative areas. In classical MB, bcl-2 was detected only in 23% of cases and was highly inversely correlated with the expression of synaptophysin (P < 0.001) indicating that bcl-2 is predominantly expressed by undifferentiated classical MB. With regard to prognosis the expression of bcl-2 tended to correlate with poor outcome in classical MB but not in desmoplastic MB, although not to a statistically significant extension (P = 0.06). On the other hand, a high number of apoptotic figures in the tumour tissue was found to indicate poor prognosis independent of the histological subtype (P < 0.05).

Enhanced in vitro midbrain dopamine neuron differentiation, dopaminergic function, neurite outgrowth, and 1-methyl-4-phenylpyridium resistance in mouse embryonic stem cells overexpressing Bcl-XL

Embryonic stem (ES) cells provide a potentially unlimited source of specialized cells for regenerative medicine. The ease of inducing stable genetic modifications in ES cells allows for in vitro manipulations to enhance differentiation into specific cell types and to optimize in vivo function of differentiated progeny in animal models of disease. We have generated mouse ES cells that constitutively express Bcl-XL, an antiapoptotic protein of Bcl-2 family. In vitro differentiation of Bcl-XL overexpressing ES (Bcl-ES) cells resulted in higher expression of genes related to midbrain dopamine (DA) neuron development and increased the number of ES-derived neurons expressing midbrain DA markers compared with differentiation of wild-type ES cells. Moreover, DA neurons derived from Bcl-ES cells were less susceptible to 1-methyl-4-phenylpyridium, a neurotoxin for DA neurons. On transplantation into parkinsonian rats, the Bcl-ES-derived DA neurons exhibited more extensive fiber outgrowth and led to a more pronounced reversal of behavioral symptoms than wild-type ES-derived DA neurons. These data suggest a role for Bcl-XL during in vitro midbrain DA neuron differentiation and provide an improved system for cell transplantation in a preclinical animal model of Parkinson's disease.

Olfactory neurons in bax knockout mice are protected from bulbectomy-induced apoptosis

Surgical ablation of the olfactory bulb (bulbectomy) triggers a massive wave of apoptosis in mature olfactory sensory neurons within the olfactory epithelium. The aim of the current study was to determine if this process is dependent on expression of the pro-apoptotic protein Bax. Immunohistochemical detection of caspase-3 activation and olfactory epithelial thickness was used to demonstrate and quantify neuronal apoptosis in bax knockout and wild type mice, following bulbectomy. Caspase-3 activation and epithelial thinning were both reduced in the bax knockout mouse compared to the wild type mouse, at least up to 9 days post-bulbectomy, indicating that apoptosis was inhibited not just delayed. This study demonstrates that Bax plays a major role in olfactory neuron apoptosis following surgical deafferentation.

Cycloheximide and actinomycin D delay death and affect bcl-2, bax, and Ice gene expression in astrocytes under in vitro ischemia

An in vitro ischemia model was established and the effect of the metabolic inhibitors cycloheximide (CHX) and actinomycin D (ActD) on apoptosis in astrocytes under ischemia studied. CHX decreased by 75% the number of cells dying after 6 hr of ischemia compared with control cultures. TdT-mediated dUTP nick end labelling (TUNEL) staining of comparable cultures was reduced by 40%. ActD decreased cell death by 60% compared with controls. The number of TUNEL-positive cells was reduced by 38%. The nuclear shrinkage in TUNEL-positive astrocytes in control cultures did not occur in ActD-treated astrocytes, indicating that nuclear shrinkage and DNA fragmentation during apoptosis are two unrelated processes. Expression of bcl-2 (alpha and beta), bax, and Ice in astrocytes under similar ischemic conditions, as measured by quantitative reverse transcription-polymerase chain reaction, indicated that ischemia down-regulated bcl-2 (alpha and beta) and bax. Ice was initially down-regulated from 0 to 4 hr, before returning to control levels after 8 hr of ischemia. ActD decreased the expression of these genes. CHX reduced the expression of bcl-2 (alpha and beta) but increased bax and Ice expression. It is hypothesized that the balance of proapoptotic (Bad, Bax) and antiapoptotic (Bcl-2, Bcl-Xl) proteins determines apoptosis. The data suggest that the ratio of Bcl-2/Bad in astrocytes following ActD and CHX treatment does not decrease as much in untreated cells during ischemia. Our data indicate that it is the ratio of Bcl-2 family members that plays a critical role in determining ischemia-induced apoptosis. It is also important to note that ischemia-induced apoptosis involves the regulation of RNA and protein synthesis.

The gene that encodes the herpes simplex virus type 1 latency-associated transcript influences the accumulation of transcripts (Bcl-x(L) and Bcl-x(S)) that encode apoptotic regulatory proteins

The herpes simplex virus type 1 latency-associated transcript (LAT) inhibits apoptosis. We demonstrate here that LAT influences the accumulation of the Bcl-x(L) transcript versus the Bcl-x(S) transcript in Neuro-2A cells. Bcl-x(L) encodes an antiapoptotic protein, whereas Bcl-x(S) encodes a proapoptotic protein. Promoting the accumulation of Bcl-x(L) in neurons may inhibit apoptosis, thus enhancing the latency-reactivation cycle.

Fluoro-jade identification of cerebellar granule cell and purkinje cell death in the alpha1A calcium ion channel mutant mouse, leaner

Cell death is a critical component of normal nervous system development; too little or too much results in abnormal development and function of the nervous system. The leaner mouse exhibits excessive, abnormal cerebellar granule cell and Purkinje cell death during postnatal development, which is a consequence of a mutated calcium ion channel subunit, alpha(1A). Previous studies have shown that leaner cerebellar Purkinje cells die in a specific pattern that appears to be influenced by functional and anatomical boundaries of the cerebellum. However, the mechanism of Purkinje cell death and the specific timing of the spatial pattern of cell death remain unclear. By double labeling both leaner and wild-type cerebella with Fluoro-Jade and terminal deoxynucleotide transferase-mediated, deoxyuridine triphosphate nick-end labeling or Fluoro-Jade and tyrosine hydroxylase immunohistochemistry we demonstrated that the relatively new stain, Fluoro-Jade, will label neurons that are dying secondary to a genetic mutation. Then, by staining leaner and wild-type cerebella between postnatal days 20 and 80 with Fluoro-Jade, we were able to show that Purkinje cell death begins at approximately postnatal day 25, peaks in the vermis about postnatal day 40 and in the hemispheres at postnatal day 50 and persists at a low level at postnatal day 80. In addition, we showed that there is a significant difference in the amount of cerebellar Purkinje cell death between rostral and caudal divisions of the leaner cerebellum, and that there is little to no Purkinje cell death in the wild type cerebellum at the ages we examined. This is the first report of the use of Fluoro-Jade to identify dying neurons in a genetic model for neuronal cell death. By using Fluoro-Jade, we have specifically defined the temporospatial pattern of postnatal Purkinje cell death in the leaner mouse. This information can be used to gain insight into the dynamic mechanisms controlling Purkinje cell death in the leaner cerebellum.

Interaction of 14-3-3 with Bid during seizure-induced neuronal death

Seizure-induced neuronal death may involve coordinated intracellular trafficking and protein-protein interactions of members of the Bcl-2 family. The 14-3-3 proteins are known to sequester certain pro-apoptotic members of this family. BH3-interacting domain death agonist (Bid) may contribute to seizure-induced neuronal death, although regulation by 14-3-3 has not been reported. In this study we examined whether 14-3-3 proteins interact with Bid during seizure-induced neuronal death. Brief seizures were evoked in rats by intraamygdala microinjection of kainic acid to elicit unilateral hippocampal CA3 neuronal death. Coimmunoprecipitation analysis demonstrated that although Bcl-2-associated death promoter (Bad) constitutively bound 14-3-3, there was no interaction between Bid and 14-3-3 in control brain. Seizures triggered Bid cleavage and a commensurate increase in binding of Bid to 14-3-3 within injured hippocampus. Casein kinases I and II, which can inactivate Bid by phosphoserine/threonine modification, did not coimmunoprecipitate with Bid. The largely uninjured contralateral hippocampus did not exhibit Bid cleavage or binding of 14-3-3 to Bid. In vitro experiments confirmed that 14-3-3beta is capable of binding truncated Bid, likely in the absence of phosphoserine/threonine modification. These data suggest 14-3-3 proteins may target active as well as inactive conformations of pro-apoptotic Bcl-2 death agonists, highlighting novel targets for intervention in seizure-induced neuronal death.

Seizure-like activity leads to the release of BAD from 14-3-3 protein and cell death in hippocampal neurons in vitro

Seizure-induced neuronal death may involve engagement of the BCL-2 family of apoptosis-regulating proteins. In the present study we examined the activation of proapoptotic BAD in cultured hippocampal neurons following seizures induced by removal of chronic glutamatergic transmission blockade. Kynurenic acid withdrawal elicited an increase in seizure-like electrical activity, which was inhibited by blockers of AMPA (CNQX) and NMDA (MK801 and AP5) receptor function. However, only NMDA receptor antagonists inhibited calcium entry as assessed by fura-2, and cell death of hippocampal neurons. Seizures increased proteolysis of caspase-3 and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) of cells. Seizure-like activity induced dephosphorylation of BAD and the disruption of its constitutive interaction with 14-3-3 proteins. In turn, BAD dimerized with antiapoptotic BCL-Xl after seizures. However, the absence of neuroprotective effects of pathway intervention suggests that BAD may perform a reinforcement rather than instigator role in cell death following seizures in vitro.

BAK alters neuronal excitability and can switch from anti- to pro-death function during postnatal development

BAK is a pro-apoptotic BCL-2 family protein that localizes to mitochondria. Here we evaluate the function of BAK in several mouse models of neuronal injury including neuronotropic Sindbis virus infection, Parkinson's disease, ischemia/stroke, and seizure. BAK promotes or inhibits neuronal death depending on the specific death stimulus, neuron subtype, and stage of postnatal development. BAK protects neurons from excitotoxicity and virus infection in the hippocampus. As mice mature, BAK is converted from anti- to pro-death function in virus-infected spinal cord neurons. In addition to regulating cell death, BAK also protects mice from kainate-induced seizures, suggesting a possible role in regulating synaptic activity. BAK can alter neurotransmitter release in a direction consistent with its protective effects on neurons and mice. These findings suggest that BAK inhibits cell death by modifying neuronal excitability.

Msx2 and p21(CIP1/WAF1) mediate the proapoptotic effects of bone morphogenetic protein-4 on ventricular zone progenitor cells

Treatment of cultured ventricular zone (VZ) progenitor cells with bone morphogenetic protein-4 (BMP4) promoted cell death in a dose-dependent manner. VZ progenitor cells became progressively more resistant to the proapoptotic effects of BMP4 between E10 and E16, and, by E18 and thereafter, BMP4 treatment no longer led to progenitor cell death. BMP4 treatment of E13 progenitor cells promoted expression of msx2 and p21(CIP1/WAF1) (p21) and inhibition of expression of either gene prevented BMP4-mediated apoptosis. Treatment of E18 cells with BMP4 failed to induce apoptosis but still induced expression of low levels of msx2 and p21. Knockout of bax significantly reduced but did not prevent BMP4-mediated death of E13 murine progenitor cells. These observations indicate that msx2 and p21 mediate the proapoptotic effects of BMP4 on VZ progenitor cells and that each gene is necessary but insufficient to promote apoptosis.

Temporal and spatial profile of Bid cleavage after experimental traumatic brain injury

Apoptosis plays an essential role in the cascade of CNS cell degeneration after traumatic brain injury. However, the underlying mechanisms are poorly understood. The authors examined the temporal profile and cell subtype distribution of the proapoptotic protein Bid from 6 hours to 7 days after cortical impact injury in the rat. Increased protein levels of tBid were seen in the cortex ipsilateral to the injury site from 6 hours to 3 days after trauma. Immunohistologic examinations revealed expression of tBid in neurons, astrocytes, and oligodendrocytes from 6 hours to 3 days after impact injury, and concurrent assessment of DNA damage using TUNEL identified tBid-immunopositive cells with apoptoticlike morphology in the traumatized cortex. Moreover, Bid cleavage and activation of caspase-8 and caspase-9 occurred at similar time points and in similar brain regions (i.e., cortical layers 2 to 5) after impact injury. In contrast, there was no evidence of caspase-8 or caspase-9 processing or Bid cleavage in the ipsilateral hippocampus, contralateral cortex, and hippocampus up to 7 days after the injury. The results provide the first evidence of Bid cleavage in the traumatized cortex after experimental traumatic brain injury in vivo, and demonstrate that tBid is expressed in neurons and glial cells. Further, findings indicate that cleavage of Bid may be associated with the activation of the initiator caspase-8 and caspase-9. Finally, these data support the hypothesis that cleavage of Bid contributes to the apoptotic degeneration of different CNS cells in the injured cortex.