Bim expression indicates the pathway to retinal cell death in development and degeneration

Targeting circular RNA-Glra2 alleviates retinal neurodegeneration induced by ocular hypertension

Glaucoma is a leading cause of irreversible vision loss characterized by retinal neurodegeneration. Circular RNAs (circRNAs) have emerged as the potential biomarkers and therapeutic targets for neurodegenerative diseases. However, the expression profiling of circRNAs in glaucomatous neurodegeneration has not been fully understood. In this study, we built a glaucomatous neurodegeneration model via the injection of microbeads into anterior chamber. circRNA expression profile and bioinformatics analysis revealed that compared with normal retinas, 171 circRNAs were dysregulated in the glaucomatous retinas, including 101 up-regulated circRNAs and 70 down-regulated circRNAs. Detecting the level of circular RNA-glycine receptor α2 subunit gene (cGlra2) in aqueous humor made it possible to distinguish glaucoma patients from cataract patients. Silencing of cGlra2 protected against oxidative stress- or hydrostatic pressure-induced retinal ganglion cell (RGC) injury in vitro. Moreover, silencing of cGlra2 retarded ocular hypertension-induced retinal neurodegeneration in vivo as shown by increased TUJ1 staining, reduced reactive gliosis, decreased retinal cell apoptosis, enhanced visual acuity, and improved retinal function. cGlra2 acted as a miRNA sponge to regulate RGC function through cGlra2/miR-144/BCL2L11 signaling axis. Collectively, this study provides novel insights into the underlying mechanism of retinal neurodegeneration and highlights the potential of cGlra2 as a target for the diagnosis and treatment of glaucoma.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Bim Expression Modulates Branching Morphogenesis of the Epithelium and Endothelium

Branching morphogenesis is a key developmental process during organogenesis, such that its disruption frequently leads to long-term consequences. The kidney and eye share many etiologies, perhaps, due to similar use of developmental branching morphogenesis and signaling pathways including cell death. Tipping the apoptotic balance towards apoptosis imparts a ureteric bud and retinal vascular branching phenotype similar to one that occurs in papillorenal syndrome. Here, to compare ureteric bud and retinal vascular branching in the context of decreased apoptosis, we investigated the impact of Bim, Bcl-2's rival force. In the metanephros, lack of Bim expression enhanced ureteric bud branching with increases in ureteric bud length, branch points, and branch end points. Unfortunately, enhanced ureteric bud branching also came with increased branching defects and other undesirable consequences. Although we did see increased nephron number and renal mass, we observed glomeruli collapse. Retinal vascular branching in the absence of Bim expression had similarities with the ureteric bud including increased vascular length, branching length, segment length, and branching interval. Thus, our studies emphasize the impact appropriate Bim expression has on the overall length and branching in both the ureteric bud and retinal vasculature.

All-Trans Retinoic Acid Attenuates Blue Light-Induced Apoptosis of Retinal Photoreceptors by Upregulating MKP-1 Expression

The study investigated the antiapoptotic effects of all-trans retinoic acid (RA) on retinal degeneration caused by exposure to blue light. Sprague-Dawley rats received intraperitoneal injections of RA and, if necessary, the mitogen-activated protein kinase phosphotase-1(MKP-1) inhibitor, (E)-2-benzylidene-3-(cyclohexylamino)-2, 3-dihydro-1H-inden-1-one (BCI), or the retinoic acid receptor (RAR) antagonist, AGN 193109. Retinal damage was induced by 24 h of continuous exposure to blue light. Haematoxylin and eosin staining and electroretinography were performed to measure retinal thickness and retinal function before and at 3 days and 7 days after light exposure. The retinal protein expression levels of phosphorylated c-Jun N-terminal kinase (JNK), phosphorylated nuclear factor-κB, MKP-1, Bim, Bax, and cleaved caspase-3 were also measured. Terminal-deoxynucleotidyl-transferase-mediated deoxyuridine triphosphate-biotin nick end labelling (TUNEL) staining and immunofluorescent staining of cleaved caspase-3 were also performed to evaluate photoreceptor apoptosis. The administration of RA significantly mitigated retinal dysfunction and the decrease in the outer nuclear layer (ONL) thickness at 3 days and 7 days after light exposure. RA also reduced the percentage of TUNEL-positive nuclei in the ONL and cleaved caspase-3 immunofluorescence intensity at 3 days after light exposure. Light exposure increased the retinal expression of proapoptotic proteins (Bim, Bax, and cleaved caspase-3), which was attenuated by RA. Moreover, RA enhanced the expression of MKP-1 and inhibited the phosphorylation of JNK, which were attenuated by the inhibition of RAR. The inhibitory effects of RA on blue light-induced photoreceptor apoptosis were abrogated by the MKP-1inhibitor. Our results indicate that RA alleviates photoreceptor loss following blue light exposure, at least partly, by the MKP-1/JNK pathway, which may serve as a therapeutic target for relieving retinal degeneration.

Mouse Retinal Organoid Growth and Maintenance in Longer-Term Culture

Using retinal organoid systems, organ-like 3D tissues, relies implicitly on their robustness. However, essential key parameters, particularly retinal growth and longer-term culture, are still insufficiently defined. Here, we hypothesize that a previously optimized protocol for high yield of evenly-sized mouse retinal organoids with low variability facilitates assessment of such parameters. We demonstrate that these organoids reliably complete retinogenesis, and can be maintained at least up to 60 days in culture. During this time, the organoids continue to mature on a molecular and (ultra)structural level: They develop photoreceptor outer segments and synapses, transiently maintain its cell composition for about 5-10 days after completing retinogenesis, and subsequently develop pathologic changes - mainly of the inner but also outer retina and reactive gliosis. To test whether this organoid system provides experimental access to the retina during and upon completion of development, we defined and stimulated organoid growth by activating sonic hedgehog signaling, which in patients and mice in vivo with a congenital defect leads to enlarged eyes. Here, a sonic hedgehog signaling activator increased retinal epithelia length in the organoid system when applied during but not after completion of development. This experimentally supports organoid maturation, stability, and experimental reproducibility in this organoid system, and provides a potential enlarged retina pathology model, as well as a protocol for producing larger organoids. Together, our study advances the understanding of retinal growth, maturation, and maintenance, and further optimizes the organoid system for future utilization.

IER3IP1 deficiency leads to increased β-cell death and decreased β-cell proliferation

Mutations in the gene for Immediate Early Response 3 Interacting Protein 1 (IER3IP1) cause permanent neonatal diabetes mellitus in human. The mechanisms involved have not been determined and the role of IER3IP1 in β-cell survival has not been characterized. In order to determine if there is a molecular link between IER3IP1 deficiency and β-cell survival and proliferation, we knocked down Ier3ip1 gene expression in mouse MIN6 insulinoma cells. IER3IP1 suppression induced apoptotic cell death which was associated with an increase in Bim and a decrease in Bcl-xL. Knockdown of Bim reduced apoptotic cell death in MIN6 cells induced by IER3IP1 suppression. Overexpression of the anti-apoptotic molecule Bcl-xL prevents cell death induced by IER3IP1 suppression. Moreover, IER3IP1 also regulates activation of the unfolded protein response (UPR). IER3IP1 suppression impairs the Inositol Requiring 1 (IRE1) and PKR-like ER kinase (PERK) arms of UPR. The cell proliferation of MIN6 cells was also decreased in IER3IP1 deficient cells. These results suggest that IER3IP1 suppression induces an increase in cell death and a decrease in cell proliferation in MIN6 cells, which may be the mechanism that mutations in IER3IP1 lead to diabetes.

Tgfbi/Bigh3 silencing activates ERK in mouse retina

BIGH3 is a secreted protein, part of the extracellular matrix where it interacts with collagen and integrins on the cell surface. BIGH3 can play opposing roles in cancer, acting as either tumor suppressor or promoter, and its mutations lead to different forms of corneal dystrophy. Although many studies have been carried out, little is known about the physiological role of BIGH3. Using the cre-loxP system, we generated a mouse model with disruption of the Bigh3 genomic locus. Bigh3 silencing did not result in any apparent phenotype modifications, the mice remained viable and fertile. We were able to determine the presence of BIGH3 in the retinal pigment epithelium (RPE). In the absence of BIGH3, a transient decrease in the apoptotic process involved in retina maturation was observed, leading to a transient increase in the INL thickness at P15. This phenomenon was accompanied by an increased activity of the pro-survival ERK pathway.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Human retinal transmitochondrial cybrids with J or H mtDNA haplogroups respond differently to ultraviolet radiation: implications for retinal diseases

Background

It has been recognized that cells do not respond equally to ultraviolet (UV) radiation but it is not clear whether this is due to genetic, biochemical or structural differences of the cells. We have a novel cybrid (cytoplasmic hybrids) model that allows us to analyze the contribution of mitochondrial DNA (mtDNA) to cellular response after exposure to sub-lethal dose of UV. mtDNA can be classified into haplogroups as defined by accumulations of specific single nucleotide polymorphisms (SNPs). Recent studies have shown that J haplogroup is high risk for age-related macular degeneration while the H haplogroup is protective. This study investigates gene expression responses in J cybrids versus H cybrids after exposure to sub-lethal doses of UV-radiation.

Methodology/Principal Findings

Cybrids were created by fusing platelets isolated from subjects with either H (n = 3) or J (n = 3) haplogroups with mitochondria-free (Rho⁰) ARPE-19 cells. The H and J cybrids were cultured for 24 hours, treated with 10 mJ of UV-radiation and cultured for an additional 120 hours. Untreated and treated cybrids were analyzed for growth rates and gene expression profiles. The UV-treated and untreated J cybrids had higher growth rates compared to H cybrids. Before treatment, J cybrids showed lower expression levels for CFH, CD55, IL-33, TGF-A, EFEMP-1, RARA, BCL2L13 and BBC3. At 120 hours after UV-treatment, the J cybrids had decreased CFH, RARA and BBC3 levels but increased CD55, IL-33 and EFEMP-1 compared to UV-treated H cybrids.

Conclusion/Significance

In cells with identical nuclei, the cellular response to sub-lethal UV-radiation is mediated in part by the mtDNA haplogroup. This supports the hypothesis that differences in growth rates and expression levels of complement, inflammation and apoptosis genes may result from population-specific, hereditary SNP variations in mtDNA. Therefore, when analyzing UV-induced damage in tissues, the mtDNA haplogroup background may be important to consider.

General pathophysiology in retinal degeneration

Retinal degeneration, including that seen in age-related macular degeneration and retinitis pigmentosa (RP), is the most common form of neural degenerative disease in the world. There is great genetic and allelic heterogeneity of the various retinal dystrophies. Classifications of these diseases can be ambiguous, as there are similar clinical presentations in retinal degenerations arising from different genetic mechanisms. As would be expected, alterations in the activity of the phototransduction cascade, such as changes affecting the renewal and shedding of the photoreceptor OS, visual transduction, and/or retinol metabolism have a great impact on the health of the retina. Mutations within any of the molecules responsible for these visual processes cause several types of retinal and retinal pigment epithelium degenerative diseases. Apoptosis has been implicated in the rod cell loss seen in a mouse model of RP, but the precise mechanisms that connect the activation of these pathways to the loss of phosphodiesterase (PDE6β) function has yet to be defined. Additionally, the activation of apoptosis by CCAAT/-enhancer-binding protein homologous protein (CHOP), after activation of the unfolded protein response pathway, may be responsible for cell death, although the mechanism remains unknown. However, the mechanisms of cell death after loss of function of PDE6, which is a commonly studied mammalian model in research, may be generalizable to loss of function of different key proteins involved in the phototransduction cascade.

Photoreceptor cell death and rescue in retinal detachment and degenerations

Photoreceptor cell death is the ultimate cause of vision loss in various retinal disorders, including retinal detachment (RD). Photoreceptor cell death has been thought to occur mainly through apoptosis, which is the most characterized form of programmed cell death. The caspase family of cysteine proteases plays a central role for inducing apoptosis, and in experimental models of RD, dying photoreceptor cells exhibit caspase activation; however, there is a paradox that caspase inhibition alone does not provide a sufficient protection against photoreceptor cell loss, suggesting that other mechanisms of cell death are involved. Recent accumulating evidence demonstrates that non-apoptotic forms of cell death, such as autophagy and necrosis, are also regulated by specific molecular machinery, such as those mediated by autophagy-related proteins and receptor-interacting protein kinases, respectively. Here we summarize the current knowledge of cell death signaling and its roles in photoreceptor cell death after RD and other retinal degenerative diseases. A body of studies indicate that not only apoptotic but also autophagic and necrotic signaling are involved in photoreceptor cell death, and that combined targeting of these pathways may be an effective neuroprotective strategy for retinal diseases associated with photoreceptor cell loss.

Detection of DNA fragmentation in retinal apoptosis by TUNEL

Terminal dUTP nick end labeling (TUNEL) is an invaluable technique used in the study of late-stage apoptosis. The technique is based upon detection of fragmented DNA, a well-recognized characteristic of apoptosis, usually with fluorescent markers. Here, we describe the TUNEL technique (1) employing two different detection techniques, fluorescence microscopy and fluorescence-activated cell sorting (2) which can be applied to the analysis of apoptosis in retinal tissues or retinal cell cultures, respectively.

Gene networks: dissecting pathways in retinal development and disease

During retinal neurogenesis, diverse cellular subtypes originate from multipotent neural progenitors in a spatiotemporal order leading to a highly specialized laminar structure combined with a distinct mosaic architecture. This is driven by the combinatorial action of transcription factors and signaling molecules which specify cell fate and differentiation. The emerging approach of gene network analysis has allowed a better understanding of the functional relationships between genes expressed in the developing retina. For instance, these gene networks have identified transcriptional hubs that have revealed potential targets and pathways for the development of therapeutic options for retinal diseases. Much of the current knowledge has been informed by targeted gene deletion experiments and gain-of-functional analysis. In this review we will provide an update on retinal development gene networks and address the wider implications for future disease therapeutics.

The Bcl-2 family member BIM has multiple glaucoma-relevant functions in DBA/2J mice

Axonal insult induces retinal ganglion cell (RGC) death through a BAX-dependent process. The pro-apoptotic Bcl-2 family member BIM is known to induce BAX activation. BIM expression increased in RGCs after axonal injury and its induction was dependent on JUN. Partial and complete Bim deficiency delayed RGC death after mechanical optic nerve injury. However, in a mouse model of glaucoma, DBA/2J mice, Bim deficiency did not prevent RGC death in eyes with severe optic nerve degeneration. In a subset of DBA/2J mice, Bim deficiency altered disease progression resulting in less severe nerve damage. Bim deficient mice exhibited altered optic nerve head morphology and significantly lessened intraocular pressure elevation. Thus, a decrease in axonal degeneration in Bim deficient DBA/2J mice may not be caused by a direct role of Bim in RGCs. These data suggest that BIM has multiple roles in glaucoma pathophysiology, potentially affecting susceptibility to glaucoma through several mechanisms.

The Bcl-2 proteins Noxa and Bcl-xL co-ordinately regulate oxidative stress-induced apoptosis

Because the detailed molecular mechanisms by which oxidative stress induces apoptosis are not completely known, we investigated how the complex Bcl-2 protein network might regulate oxidative stress-induced apoptosis. Using MEFs (mouse embryonic fibroblasts), we found that the endogenous anti-apoptotic Bcl-2 protein Bcl-xL prevented apoptosis initiated by H(2)O(2). The BH3 (Bcl-2 homology 3)-only Bcl-2 protein Noxa was required for H(2)O(2)-induced cell death and was the single BH3-only Bcl-2 protein whose pro-apoptotic activity was completely antagonized by endogenous Bcl-xL. Upon H(2)O(2) treatment, Noxa mRNA displayed the greatest increase among BH3-only Bcl-2 proteins. Expression levels of the anti-apoptotic Bcl-2 protein Mcl-1 (myeloid cell leukaemia sequence 1), the primary binding target of Noxa, were reduced in H(2)O(2)-treated cells in a Noxa-dependent manner, and Mcl-1 overexpression was able to prevent H(2)O(2)-induced cell death in Bcl-xL-deficient MEF cells. Importantly, reduction of the expression of both Mcl-1 and Bcl-xL caused spontaneous cell death. These studies reveal a signalling pathway in which H(2)O(2) activates Noxa, leading to a decrease in Mcl-1 and subsequent cell death in the absence of Bcl-xL expression. The results of the present study indicate that both anti- and pro-apoptotic Bcl-2 proteins co-operate to regulate oxidative stress-induced apoptosis.

Prolonged expression of Puma in cholinergic amacrine cells during the development of rat retina

During development of the nervous system, large numbers of neurons are overproduced and then eliminated by programmed cell death. Puma is a BH3-only protein that is reported to be involved in the initiation of developmental programmed cell death in rodent retinal neurons. The expression and cellular localization of Puma in retinal tissues during development are not, however, well known. Here the authors report the expression pattern of Puma during retinal development in the rat. During the period of programmed cell death in the retina, Puma was expressed in some members of each retinal neuron, including retinal ganglion cells, amacrine cells, bipolar cells, horizontal cells, and photoreceptor cells. Although the developmental programmed cell death of cholinergic amacrine cells is known to be independent of Puma, this protein was expressed in almost all their dendrites and somata of cholinergic amacrine cells at postnatal age 2 to 3 weeks, and it continued to be detected in cholinergic dendrites in the inner plexiform layer for up to 8 weeks after birth. These results suggest that Puma has some significant roles in retinal neurons after eye opening, especially that of cholinergic amacrine cells, in addition to programmed cell death of retinal neurons before eye opening.

N-cadherin mediates neuronal cell survival through Bim down-regulation

N-cadherin is a major adhesion molecule involved in the development and plasticity of the nervous system. N-cadherin-mediated cell adhesion regulates neuroepithelial cell polarity, neuronal precursor migration, growth cone migration and synaptic plasticity. In vitro, it has been involved in signaling events regulating processes such as cell mobility, proliferation and differentiation. N-cadherin has also been implicated in adhesion-dependent protection against apoptosis in non-neuronal cells. In this study, we investigated if the engagement of N-cadherin participates to the control of neuronal cells survival/death balance. We observed that plating either primary mouse spinal cord neurons or primary rat hippocampal neurons on N-cadherin recombinant substrate greatly enhances their survival compared to non-specific adhesion on poly-L-lysine. We show that N-cadherin engagement, in the absence of other survival factors (cell-matrix interactions and serum), protects GT1-7 neuronal cells against apoptosis. Using this cell line, we then searched for the signaling pathways involved in the survival effect of N-cadherin engagement. The PI3-kinase/Akt survival pathway and its downstream effector Bad are not involved, as no phosphorylation of Akt or Bad proteins in response to N-cadherin engagement was observed. In contrast, N-cadherin engagement activated the Erk1/2 MAP kinase pathway. Moreover, N-cadherin ligation mediated a 2-fold decrease in the level of the pro-apoptotic protein Bim-EL whereas the level of the anti-apoptotic protein Bcl-2 was unchanged. Inhibition of Mek1/2 kinases with U0126, and the resulting inhibition of Erk1/2 phosphorylation, induced the increase of both the level of Bim-EL and apoptosis of cells seeded on the N-cadherin substrate, suggesting that Erk phosphorylation is necessary for cell survival. Finally, the overexpression of a phosphorylation defective form of Bim-EL prevented N-cadherin-engagement induced cell survival. In conclusion, our results show that N-cadherin engagement mediates neuronal cell survival by enhancing the MAP kinase pathway and down-regulating the pro-apoptotic protein Bim-EL.

BBC3 (PUMA) regulates developmental apoptosis but not axonal injury induced death in the retina

BACKGROUND

Naturally occurring apoptosis is a developmental process that shapes the retina by eliminating overproduced neurons. In the absence of the proapoptotic Bcl-2 family member BAX, developmental apoptosis in the retina is disrupted and extra neurons survive. It is unknown how BAX is activated or if this regulation varies between neuronal types and subtypes. Since the Bcl-2 family members BIM, BID, and BBC3 (PUMA) are powerful direct activators of BAX, we used mice deficient for each of these genes to investigate their importance in developmental apoptosis.

RESULTS

Bax deficient mice have an increase in retinal ganglion cells (RGCs), bipolar cells and dopaminergic amacrine cells, but not photoreceptors, horizontal cells or cholinergic amacrine cells. The retinas of adult Bim and Bid deficient mice appeared to have no increase in any retinal cell type. Bbc3 deficient mice, either homozygous or heterozygous for a null allele of Bbc3, had an increase in the same cell types as Bax deficient mice. An analogous result may occur in the brain where, similar to Bax deficient mice, Bbc3 deficient mice have a larger gross brain weight compared to wild type mice. In contrast to its developmental role, BBC3 did not appear to be a primary factor in BAX-dependent axonal injury induced neurodegeneration in adult RGCs.

CONCLUSION

The regulation of BAX activation in the retina appears to be complex, dependent on the developmental stage of the animal, the nature of the insult and even the type of neuron.

Bim is responsible for the inherent sensitivity of the developing retinal vasculature to hyperoxia

Apoptosis plays an important role in development and remodeling of vasculature during organogenesis. Coordinated branching and remodeling of the retinal vascular tree is essential for normal retinal function. Bcl-2 family members, such as bim not only influence apoptosis, but also cell adhesive and migratory properties essential during vascular development. Here we examined the impact of bim deficiency on postnatal retinal vascularization, as well as retinal neovascularization during oxygen-induced ischemic retinopathy (OIR) and laser-induced choroidal neovascularization. Loss of bim expression was associated with increased retinal vascular density in mature animals. This was mainly attributed to increased numbers of pericytes and endothelial cells. However, the initial spread of the superficial layer of retinal vasculature and, the appearance and density of the tip cells were similar in bim+/+ and bim-/- mice. In addition, hyaloid vessel regression was attenuated in the absence of bim. Furthermore, in the absence of bim retinal vessel obliteration and neovascularization did not occur during OIR. Instead, normal inner retinal vascularization proceeded independent of changes in oxygen levels. In contrast, choroidal neovascularization occurred equally well in bim+/+ and bim-/- mice. Together our data suggest bim expression may be responsible for the inherent sensitivity of the developing retinal vasculature to changes in oxygen levels, and promotes vessel obliteration in response to hyperoxia.

Noncanonical functions of BCL-2 proteins in the nervous system

BCL-2 family proteins form heterodimers or homo-oligomers to inhibit or induce apoptotic cell death, respectively. They often relocalize from the cytoplasm to mitochondria to carry out these functions. The traditional model is that in healthy cells, anti-death family members hold pro-death BCL-2 family members in check. Upon receiving a death stimulus, another set of proteins (BH3-only proteins) inactivate the protective BCL-2 proteins, forcing them to release their pro-death partners that are subsequently triggered to oligomerize and porate the mitochondrial outer membrane leading to cell death. In support of this traditional view, there is a preponderance of supporting evidence derived from the study of events that occur following treatment of cells with a death stimulus. Knockout and mutant mice also exhibit many developmental and treatment-induced phenotypes consistent with this model of antagonism between BCL-2 family proteins. Emphasis is logically placed on those phenotypes that support the model. However, this working model of BCL-2 family interactions has become so engrained that alternative, potentially valid interpretations are sometimes dismissed. Therefore, it is useful to consider the evidence that seems contrary to accepted models. In particular, the analysis of BCL-2 family functions in the nervous system has revealed unexpected outcomes that can serve to further stimulate critical probing of the yet unknown biochemical functions of BCL-2 proteins.

The Bcl-2 family in autoimmune and degenerative disorders

Members of the Bcl-2 family are essential regulators of programmed cell death and thus play a major role in the development and function of many tissues. The balance between pro-survival and pro-apoptotic members of the family decides whether a cell will live or die. This mechanism allows organisms to get rid of cells that are no longer needed or have become dangerous. Deregulation of apoptosis is a major contributing factor in the development of many diseases. A deeper understanding of how the Bcl-2 family proteins orchestrate death in normal and pathologic conditions is thus relevant not only for disease etiology, but also to try to prevent these various disorders. Experiments with transgenic and gene-ablated mice have helped elucidate the function of the different members of the Bcl-2 family and their physiological roles. The present review highlights the role of Bcl-2 family members in autoimmune and degenerative disorders, with a particular focus on the mouse models that have been used to study their function.

Histone deacetylase activity in conjunction with E2F-1 and p53 regulates Apaf-1 expression in 661W cells and the retina

Apaf-1 and the cysteine proteases known as caspases are genes central to the intrinsic apoptotic pathway in the retina. Previously, we have shown that histone deacetylase (HDAC) activity regulates Apaf-1 expression in the retina. In this study, we unravel the detailed molecular mechanism of HDAC-mediated regulation of Apaf-1 initially by use of a cell line (661W), which expresses some cone-specific genes and then by means of an ex vivo retinal explant system. Inhibition of HDAC activity by trichostatin A (TSA) up-regulates Apaf-1 expression, which precedes the induction of apoptosis. Furthermore, by a bioinformatics approach, we identify E2F-1 and p53 binding sites on the mouse Apaf-1 promoter and show by chromatin immunoprecipitation assays that these sites are occupied in vitro and that treatment with TSA results in increased binding of E2F-1 and p53 to the Apaf-1 promoter. By performing siRNA to these transcription factors, we illustrate that they govern Apaf-1 expression levels in vitro. Finally, in a retinal explant system, we show that similar to our 661W results, E2F-1 and p53 are up-regulated after inhibition of HDAC activity in the retina. This correlates with our previous observation in the explant system that Apaf-1 expression increases significantly and leads to an induction of apoptosis after inhibition of HDAC activity. Overall, we propose a role for HDAC activity, E2F-1, and p53 in the regulation of Apaf-1 expression in 661W cells; initial data also indicate a regulatory role in the retina.

Rosiglitazone acts as a neuroprotectant in retinal cells via up-regulation of sestrin-1 and SOD-2

Rosiglitazone is a member of the thiazolidinedione family of synthetic peroxisome proliferator-activated receptor (PPAR) agonists. It is a selective ligand of the PPARgamma subtype and functions by regulating the transcription of insulin-responsive genes. A screen of FDA-approved compounds identified rosiglitazone as a novel anti-apoptotic agent in retinal cells both in vitro and in vivo, functioning as a neuroprotectant in response to oxidative and calcium stress. We have found that the likely mechanism of action is via increased protein expression of the antioxidant enzymes superoxide dismutase 2 (SOD-2) and sestrin-1, boosting antioxidant defences. Transcription of both genes appears to be mediated by PPARgamma as their up-regulation is reversed by the PPARgamma antagonist GW9662 and proliferator hormone response elements were found in the putative promoter regions of mouse SOD-2 and sestrin-1. However, further investigation revealed that p53 expression was also induced in response to rosiglitazone and chromatin immunoprecipitation assays confirm that it is a bona fide target of PPARgamma. Furthermore, inhibition of p53 partially blocks the observed increase in SOD-2 and sestrin-1 expression indicating that p53 expression is upstream of both antioxidants. We conclude that rosiglitazone may increase cell survival in retinal diseases and potentially other neuronal diseases in which oxidative stress is a key factor.

The protein kinase DYRK1A regulates caspase-9-mediated apoptosis during retina development

The precise regulation of programmed cell death is critical for the normal development of the nervous system. We show here that DYRK1A (minibrain), a protein kinase essential for normal growth, is a negative regulator of the intrinsic apoptotic pathway in the developing retina. We provide evidence that changes in Dyrk1A gene dosage in the mouse strongly alter the cellularity of inner retina layers and result in severe functional alterations. We show that DYRK1A does not affect the proliferation or specification of retina progenitor cells, but rather regulates the number of cells that die by apoptosis. We demonstrate that DYRK1A phosphorylates caspase-9 on threonine residue 125, and that this phosphorylation event is crucial to protect retina cells from apoptotic cell death. Our data suggest a model in which dysregulation of the apoptotic response in differentiating neurons participates in the neuropathology of diseases that display DYRK1A gene-dosage imbalance effects, such as Down's syndrome.

Ionic dysregulatory phenotyping of pathologic retinal thinning with manganese-enhanced MRI

PURPOSE

To test the hypothesis that manganese-enhanced MRI (MEMRI) provides a sensitive and robust measure of an important retinal ionic dysregulatory phenotype in pathologic retinal thinning.

METHODS

Four hours after intraperitoneal MnCl(2) injection, high-resolution MEMRI data were collected from overnight dark-adapted male control Sprague-Dawley and albino Royal College of Surgeons rats before (at development stage postnatal day [P] 17) and during photoreceptor degeneration (P36 and P57). In separate experiments, control rats, with and without repetitive hypoxic preconditioning, were subjected to high IOP (100 mm Hg) for 60 minutes followed by 24 hours or 7 days of reperfusion (e.g., ischemia/reperfusion). Central retinal thickness and intraretinal ion activity were measured from the MEMRI data. Histology examination was also performed to confirm retinal damage.

RESULTS

In two different neurodegenerative models, MEMRI revealed first-time evidence for changes (P < 0.05) in intraretinal ion regulation before and during pathologic, but not (P > 0.05) developmental, retinal thinning. This phenotype was significantly altered by a neuroprotective repetitive hypoxic preconditioning protocol.

CONCLUSIONS

MEMRI and a nontoxic systemic dose of MnCl(2) provided an objective, noninvasive measure of an ionic deregulatory phenotype that appears useful for improved early diagnosis and treatment prognosis in a range of neurodegenerative diseases and their treatment.