Characterization of the cell death promoter, Bad, in the developing rat retina and forebrain

GM-CSF protects rat photoreceptors from death by activating the SRC-dependent signalling and elevating anti-apoptotic factors and neurotrophins

BACKGROUND

The term retinitis pigmentosa (RP) comprises a heterogeneous group of hereditary and sporadic human retinal degenerative diseases. The molecular and cellular events still remain obscure, thus hiding effective therapies. Granulocyte–macrophage colony-stimulating factor (GM-CSF) is a hematopoietic factor which plays a crucial role in protecting neuronal cells. Binding of GM-CSF to its receptor induces several intracellular signaling pathways and kinases. Here we examined whether GM-CSF has a neuroprotective effect on photoreceptor degeneration in Royal College of Surgeons (RCS) rats.

METHODS

GM-CSF was injected into the vitreous body of RCS rats either once at the onset of photoreceptor degeneration at day 21, or twice at day 21 and day 42. At day 84, when photoreceptor degeneration is completed, the rats were sacrificed, their eyes enucleated and processed for histological staining and counting the surviving photoreceptor nuclei. The expression of apoptosis-related factors, such as BAD, APAF1 and BCL-2 was examined by Western blot analysis. The expression of neurotrophins such as ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF), and glia-derived neurotrophic actor (GDNF), as well as glial fibrillary acidic protein (GFAP) was analysed by Western blots and immunohistochemistry. The expression of JAK/STAT, ERK1/2 and SRC pathway proteins was assessed by Western blot analysis.

RESULTS

GM-CSF protects significantly against photoreceptor degeneration in comparison to control group. After a single injection of GM-CSF at P21, a 4-fold increase of photoreceptors was observed, whereas eyes which received a repeated injection of GM-CSF at P42 showed a 10-fold increase of photoreceptors. Western blot analysis revealed a decreased BAD and an increased pBAD and BCL-2 expression, indicating changed expression profiles of apoptosis-related proteins. Neurotrophic factors examined are up-regulated, whereas GFAP was also modulated. At cell signalling levels, GM-CSF activates SRC-dependent STAT3 which is independent of JAK2, while proteins of the ERK1/2 pathway are not affected.

CONCLUSIONS

The data suggest that GM-CSF is a potent therapeutic agent in photoreceptor degeneration caused by mutation of the receptor tyrosine kinase gene (Mertk), and may be also effective in other photoreceptor degeneration.

Inflammation-inducing Th1 and Th17 cells differ in their expression patterns of apoptosis-related molecules

Th1 cells are remarkably more susceptible to activation induced cell death than Th17. Here, we compared cultures of these two cell subpopulations for their expression of apoptosis-related molecules when re-exposed to their specific antigen. We also compared the expression of apoptosis-related molecules in the mouse eye with inflammation induced by Th1 or Th17 cells. Using qPCR we found that the mRNA transcript levels of the majority of tested apoptosis-related molecules were higher in the Th1 cultures, and in eyes with Th1-induced inflammation. Apoptotic intrinsic pathway molecules played minor roles in the processes in vitro or in vivo, whereas extrinsic pathway molecules, as well as PD-1, its ligands and Tim3, were heavily involved.

WITHDRAWN: Reprint of: Variations in the rheostat model of apoptosis: What studies of retinal ganglion cell death tell us about the functions of the Bcl2 family proteins

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi:10.1016/j.exer.2010.03.004. The duplicate article has therefore been withdrawn.

Variations in the rheostat model of apoptosis: what studies of retinal ganglion cell death tell us about the functions of the Bcl2 family proteins

Studies of the functions of members of the Bcl2 gene family suggested that apoptosis was controlled by a rheostat in which anti-apoptotic proteins like BCL2 bound and sequestered pro-apoptotic proteins like BAX. Our current understanding of these proteins suggests that this is a simplistic model. The new rheostat model predicts that BH3-only peptides act as neutralizing ligands for the anti-apoptotic proteins, thus allowing molecules like BAX to become activated and initiate mitochondrial dysfunction - a critical step in the intrinsic apoptotic program. Studies of retinal ganglion cell apoptosis indicate that a threshold of BAX expression is required for its successful activation, which is independent of the overall concentration of anti-apoptotic proteins in these cells.

GM-CSF regulates the ERK1/2 pathways and protects injured retinal ganglion cells from induced death

Granulocyte-macrophage-colony-stimulating-factor (GM-CSF) is a potent hematopoietic cytokine. In the present study, we examined whether GM-CSF is neuroprotective in retinal ganglion cells (RGCs). First, we studied the expression of GM-CSF and the GM-CSF-alpha-receptor in rat and human retina and in RGC-5 cells. Then, RGC-5 cells were incubated with apoptosis-inducing agents (e.g., staurosporine, glutamate and NOR3). The cell death was assessed by Live-Death-Assays and apoptosis-related-proteins were examined by immunoblotting. In addition, the expression of phosphorylated ERK1/2-pathway-proteins after incubation with GM-CSF and after inhibiting MEK1/2 with U0126 was analyzed. To assess the in vivo-effect, first staurosporine or GM-CSF plus staurosporine was injected into the vitreous body of Sprague-Dawley rats. In a second axotomy model the optic nerve was cut and GM-CSF was injected into the vitreous body. In both models, the RGCs were labeled retrogradely with either Fluoro-Gold or 4-Di-10-Asp and counted. As a first result, we identified GM-CSF and the GM-CSF-alpha-receptor in rat and human retina as well as in RGC-5 cells. Then, in the RGC-5 cells GM-CSF counteracts induced cell death in a dose-and time-dependent manner. With respect to apoptosis, Western blot analysis revealed a decreased Bad-expression and an increased Bcl-2-expression after co-incubation with GM-CSF. Concerning signaling pathways, incubation with GM-CSF activates the ERK1/2 pathway, whereas inhibition of MEK1/2 with U0126 strongly decreased the phosphorylation downstream in the ERK1/2 pathway, and the antiapoptotic activity of GM-CSF in vitro. Like in vitro, GM-CSF counteracts the staurosporine-induced cell death in vivo and protects RGCs from axotomy-induced degeneration. Our data suggest that GM-CSF might be a novel therapeutic agent in neuropathic disease of the eye.

Localization and developmental ontogeny of the pro-apoptotic Bnip3 mRNA in the postnatal rat cortex and hippocampus

Naturally occurring cell death occurs during the first two postnatal weeks in the rat cortex and hippocampus. During this process, apoptosis is initiated by activating or altering expression of pro-apoptotic members of the Bcl-2 family. Bnip3 is a pro-apoptotic member of the Bcl-2 family that induces cell death by opening the mitochondrial permeability transition pore. To date, Bnip3 expression in the central nervous system has only been examined during hypoxia-mediated apoptosis in the adult rat brain. In this study, we investigated the localization and ontogeny of Bnip3 mRNA expression in the postnatal male and female rat brain. Bnip3 mRNA was localized by in situ hybridization in the neonatal cortex, hippocampus, habenula and thalamus. Using quantitative real-time RT-PCR, Bnip3 mRNA levels were found to be greatest at postnatal day 6.5 in the female anterior and posterior cingulate cortices and hippocampus. Bnip3 mRNA expression also increased in the male anterior cingulate cortex at postnatal day 6.5. However, a developmental change in Bnip3 levels did not occur in the male posterior cingulate cortex and hippocampus. In the anterior cingulate cortex on postnatal day 6.0 and adulthood, female rats had significantly greater levels of Bnip3 mRNA compared to that of males. Altering levels of testosterone in the neonatal rat did not alter the sex differences in Bnip3 mRNA levels. The transient increase in Bnip3 mRNA expression correlates with naturally occurring cell death in the neonatal rat cortex and hippocampus. Thus, Bnip3 may be a mediator of developmental apoptosis in the postnatal rat brain.

Expression of antiapoptotic and proapoptotic molecules in diabetic retinas

PURPOSE

To investigate the expression of the antiapoptotic and proapoptotic markers in diabetic retinas.

METHODS

In total, 12 donor eyes from six subjects with diabetes mellitus, and 10 eyes from five nondiabetic subjects without known ocular disease serving as control subjects were examined. Immunohistochemical techniques were used with antibodies directed against cyclooxygenase-2 (Cox-2), Akt (protein kinase B), Mcl-1, Bad, cytochrome c, apoptosis-inducing factor (AIF), tumour necrosis factor receptor-1-associated death domain protein (TRADD), and Fas-associated death domain protein (FADD).

RESULTS

In retinas from all subjects without diabetes, cytoplasmic immunoreactivity for the antiapoptotic molecules Cox-2, Akt, and Mcl-1 was noted in ganglion cells. Cytoplasmic immunostaining for Cox-2 was also noted in the retinal pigment epithelial cells. Weak immunoreactivity for the mitochondrial apoptogenic proteins cytochrome c, and AIF was noted in the inner segments of photoreceptors, in the inner one-third of the outer plexiform layer, in cells in the inner nuclear layer, in the inner plexiform layer, and in ganglion cells. There was no immunoreactivity for the other antibodies tested. All diabetic retinas showed de novocytoplasmic immunoreactivity for Bad in ganglion cells, and in occasional cells in the inner nuclear layer. Upregulation of cytochrome cand AIF immunoreactivity was noted. Cox-2, Akt, and Mcl-1 immunoreactivity was not altered in the diabetic retinas. There was no immunoreactivity for TRADD, and FADD.

CONCLUSIONS

Ganglion cells in diabetic and nondiabetic retinas express the antiapoptotic molecules Cox-2, Akt, and Mcl-1. Retinal ganglion cells express the proapoptotic molecule Bad in response to diabetes-induced neuronal injury. Diabetic retinas show upregulation of the mitochondrial proteins cytochrome c, and AIF.

Wild-type alpha-synuclein interacts with pro-apoptotic proteins PKCdelta and BAD to protect dopaminergic neuronal cells against MPP+-induced apoptotic cell death

Alpha-synuclein is a pre-synaptic protein of unknown function that has been implicated in the pathogenesis of Parkinson's disease (PD). Recently, we demonstrated that 1-methyl-4-phenylpyridinium (MPP+) induces caspase-3-dependent proteolytic activation of PKCdelta, which subsequently contributes to neuronal apoptotic cell death in mesencephalic dopaminergic neuronal cells. In the present study, we examined whether PKCdelta interacts with alpha-synuclein to modulate MPP+-induced dopaminergic degeneration. Over-expression of wild-type human alpha-synuclein in mesencephalic dopaminergic neuronal cells (N27 cells) attenuated MPP+-induced (300 microM) cytotoxicity, release of mitochondrial cytochrome c, and subsequent caspase-3 activation, without affecting reactive oxygen species (ROS) generation. Wild-type alpha-synuclein over-expression also dramatically reduced MPP+-induced caspase-3-mediated proteolytic cleavage of PKCdelta, whereas over-expression of the mutant human alpha-synucleinA53T did not alter the PKCdelta cleavage under similar conditions. Immunoprecipitation-kinase assay revealed reduced PKCdelta kinase activity in wild-type alpha-synuclein over-expressing cells in response to MPP+ treatment. Wild-type alpha-synuclein over-expression also rescued mesencephalic dopaminergic neuronal cells from MPP+-induced apoptotic cell death, while alpha-synucleinA53T exacerbated the MPP+-induced DNA fragmentation. Furthermore, co-immunoprecipitation studies revealed that alpha-synuclein interacts with the pro-apoptotic proteins PKCdelta and BAD, but not with the anti-apoptotic protein Bcl-2 following MPP+ treatment. We also observed that the interaction between PKCdelta and alpha-synuclein does not involve direct phosphorylation. Together, our results demonstrate that wild-type alpha-synuclein interacts with the pro-apoptotic molecules BAD and PKCdelta to protect dopaminergic neuronal cells against neurotoxic insults.

Survival and axonal regeneration of retinal ganglion cells in adult cats

Axotomized retinal ganglion cells (RGCs) in adult cats offer a good experimental model to understand mechanisms of RGC deteriorations in ophthalmic diseases such as glaucoma and optic neuritis. Alpha ganglion cells in the cat retina have higher ability to survive axotomy and regenerate their axons than beta and non-alpha or beta (NAB) ganglion cells. By contrast, beta cells suffer from rapid cell death by apoptosis between 3 and 7 days after axotomy. We introduced several methods to rescue the axotomized cat RGCs from apoptosis and regenerate their axons; transplantation of the peripheral nerve (PN), intraocular injections of neurotrophic factors, or an antiapoptotic drug. Apoptosis of beta cells can be prevented with intravitreal injections of BDNF+CNTF+forskolin or a caspase inhibitor. The injection of BDNF+CNTF+forskolin also increases the numbers of regenerated beta and NAB cells, but only slightly enhances axonal regeneration of alpha cells. Electrical stimulation to the cut end of optic nerve is effective for the survival of axotomized RGCs in cats as well as in rats. To recover function of impaired vision in cats, further studies should be directed to achieve the following goals: (1). substantial number of regenerating RGCs, (2). reconstruction of the retino-geniculo-cortical pathway, and (3). reconstruction of retinotopy in the target visual centers.

Regulation of thymocyte homeostasis by Fliz1

Fliz1 (fetal liver zinc finger protein 1) is a novel zinc finger protein preferentially expressed in fetal liver hematopoietic progenitors and in several adult organs, including the thymus. To investigate the in vivo function of Fliz1 in regulating the development of T cell lineage, we generated and studied transgenic mice overexpressing human Fliz1 in a T-cell specific and inducible manner. We found that overexpression of human Fliz1 in adult animals resulted in a substantial decrease in total number of thymocytes due to enhanced apoptosis, whereas maturation of thymocytes remained undisturbed. The Fliz1-induced apoptosis is dependent on the N-terminus of Fliz1, which contains an acidic and a serine-rich domains, and might be due to augmented expression of bad, a pro-apoptotic gene. Taken together, our data suggest that Fliz1 plays a role in regulating thymocyte homeostasis.

Perinatal asphyxia: timing and mechanisms of injury in neonatal encephalopathy

This article summarizes the recent medical literature regarding perinatal asphyxia with respect to timing and mechanisms of injury for neonates who were clinically diagnosed with an encephalopathy in the newborn period. Multiple mechanisms of injury are reviewed, including genetic vulnerability, acquired inflammatory responses, and clotting defects that can lead to ischemic-induced brain damage. Before effective treatments for fetal and neonatal brain disorders can be developed, accurate and timely diagnoses of fetal or neonatal brain injury must be achieved. Specific subsets of children can then benefit from neuroprotective strategies that can target the specific developmental aspects of brain adaptation or plasticity relative to the specific etiology and timing of injury after asphyxia.

Bcl-2 family gene products in cerebral ischemia and traumatic brain injury

The proto-oncogene bcl-2 plays a key role in regulating programmed cell death in neurons. The present review discusses the mechanisms by which bcl-2 family genes regulate programmed cell death, and their role in controlling cell death in cerebral ischemia and traumatic brain. Expression of several bcl-2 family members is altered in brain tissues after ischemia and trauma, suggesting that bcl-2 family genes could play a role in determining the fate of injured neurons. Furthermore, alteration of expression of bcl-2 family genes using transgenic approaches, viral vectors, or anti-sense oligonucleotides modifies neuronal cell death and neurological outcome after injury. These data suggest that the activity of bcl-2 family gene products participates in determining cellular and neurologic outcomes in ischemia and trauma. Strategies that either mimic the death-suppressor effects or inhibit the death-promoter effects of bcl-2 family gene products may improve outcome after ischemia and trauma.

Altruistic cell suicide and the specialized case of the virus-infected nervous system

Depending on their differentiation state, vertebrate neurones can commit suicide after neurotropic virus infection. Such suicide might be an evolved strategy in multicellular organisms for limiting virus expansion. Regulation of suicide in this context operates by a programme similar to that activated during embryogenesis or in response to nervous-system injury and disease. In contrast to immature neurones that can readily initiate apoptosis following infection, mature neurones are generally highly resistant and can survive for long periods if they remain functional. Mature, infected neurones might gain competence to die owing to the attuned activation of pathways that sensitize the cell to subsequent stress. The consequence of either perturbation of function as a result of viral persistence or a chronic but progressive loss of infected neurones might be a failure of key neural functions.