Function of BID - a molecule of the bcl-2 family - in ischemic cell death in the brain

Mitochondrial mechanisms, particularly the release of cytochrome c, play a role in the death of nerve and glial cells in cerebral ischemia. We have currently investigated whether BID, a proapoptotic molecule of the bcl-2 family and promoter of the release of cytochrome c is expressed in the brain, activated by cerebral ischemia in vivo, and contributes to ischemic cell death. We found BID in the cytosol of mouse brain and of primary cultured mouse neurons and showed that neuronal BID is a substrate for caspase 8. BID was cleaved in vivo 4 h after transitory occlusion of the middle cerebral artery. Further, BID-/- mice had a significant attenuation of infarction (-67%) and significantly lower release of cytochrome c (-41 %). The findings indicate that the proapoptotic molecule BID may contribute to the demise of nerve cells from cerebral ischemia by release of cytochrome c and activation of caspase. Copyright (C) 2002 S. Karger AG, Basel

BCL-2 Protein Expression is Widespread in the Developing Nervous-System and Retained in the Adult PNS

Cell death is a common feature of neural development in all vertebrates. The bcl-2 proto-oncogene has been shown to protect a variety of cell types from programmed cell death. We have examined the distribution of bcl-2 protein in the developing and adult nervous systems. bcl-2 protein is widespread during embryonic development. Proliferating neuroepithelial cells of ventricular zones as well as the postmitotic cells of the cortical plate, cerebellum, hippocampus and spinal cord express bcl-2. Postnatally, bcl-2 is principally retained in the granule cells of the cerebellum and dentate gyrus of the hippocampus. bcl-2 expression in the CNS declines with aging. In the peripheral nervous system, neurons and supporting cells of sympathetic and sensory ganglia retain substantial bcl-2 protein throughout life. The widespread expression of bcl-2 in CNS and PNS neurons during embryonic development and its selective retention in the adult PNS is consistent with a role for bcl-2 in regulating neuronal survival. In addition, the expression of bcl-2 in some neuronal populations beyond the recognized period of cell death is suggestive of a role for bcl-2 beyond simply protecting neurons from developmental cell death

The κ-Deleting Element: Germline and Rearranged, Duplicated and Dispersed Forms

Human light chain genes are used in a κ before λ order. Accompanying this hierarchy is the rearrangement of a κ-deleting element (Kde) which eliminates the kappa locus before λ gene rearrangement. In approximately 60% of rearrangements the Kde recombines at a conserved heptamer within the Jκ-Cκ intron. We demonstrated that aberrant V/J rearrangements possessing apparent N nucleotides existed 5\u27 to the Jκ-Kde rearrangements. This suggests that the Kde may selectively eliminate nonfunctional V/J alleles. A κ-producing cell that displayed the unusual finding of λ gene rearrangement demonstrated a rearranged Kde. This rearrangement was a Vκ/Kde recombination and the heptamer-11 bp spacer-nonamer flanking the Vκ is the target site of the Kde 40% of the time. The mouse possesses a counterpart to the Kde (recombining sequence [RS]) and the highly conserved regions surround the heptamer-spacer-nonamer signals. No complete protein product was predicted from the germline Kde near its break-point and no consistent fusion product was predicted from either the V/Kde or V/J-Kde rearrangements. A distal portion of the Kde is duplicated and is present at 2q11 as well as 2p11. The evolutionary conservation of the kappa-elimination event, the duplication and maintenance of the Kde indicates that it has a function. A portion of the Kde may still prove to encode a trans-acting factor that directly affects λ rearrangement. A certain role for the Kde is its site-specific rearrangement, which destroys ineffective κ genes and sets the stage for λ gene utilization

A Role for Proapoptotic BID in the DNA-Damage Response

SummaryThe BCL-2 family of apoptotic proteins encompasses key regulators proximal to irreversible cell damage. The BH3-only members of this family act as sentinels, interconnecting specific death signals to the core apoptotic pathway. Our previous data demonstrated a role for BH3-only BID in maintaining myeloid homeostasis and suppressing leukemogenesis. In the absence of Bid, mice accumulate chromosomal aberrations and develop a fatal myeloproliferative disorder resembling chronic myelomonocytic leukemia. Here, we describe a role for BID in preserving genomic integrity that places BID at an early point in the path to determine the fate of a cell. We show that BID plays an unexpected role in the intra-S phase checkpoint downstream of DNA damage distinct from its proapoptotic function. We further demonstrate that this role is mediated through BID phosphorylation by the DNA-damage kinase ATM. These results establish a link between proapoptotic Bid and the DNA-damage response

BAX Is Required for Neuronal Death after Trophic Factor Deprivation and during Development

AbstractMembers of the BCL2-related family of proteins either promote or repress programmed cell death. BAX, a death-promoting member, heterodimerizes with multiple death-repressing molecules, suggesting that it could prove critical to cell death. We tested whether Bax is required for neuronal death by trophic factor deprivation and during development. Neonatal sympathetic neurons and facial motor neurons from Bax-deficient mice survived nerve growth factor deprivation and disconnection from their targets by axotomy, respectively. These salvaged neurons displayed remarkable soma atrophy and reduced elaboration of neurites; yet they responded to readdition of trophic factor with soma hypertrophy and enhanced neurite outgrowth. Bax-deficient superior cervical ganglia and facial nuclei possessed increased numbers of neurons. Our observations demonstrate that trophic factor deprivation–induced death of sympathetic and motor neurons depends on Bax

A Distinct Pathway Remodels Mitochondrial Cristae and Mobilizes Cytochrome c during Apoptosis

AbstractThe mechanism during apoptosis by which cytochrome c is rapidly and completely released in the absence of mitochondrial swelling is uncertain. Here, we show that two distinct pathways are involved. One mediates release of cytochrome c across the outer mitochondrial membrane, and another, characterized in this study, is responsible for the redistribution of cytochrome c stored in intramitochondrial cristae. We have found that the “BH3-only” molecule tBID induces a striking remodeling of mitochondrial structure with mobilization of the cytochrome c stores (∼85%) in cristae. This reorganization does not require tBID's BH3 domain and is independent of BAK, but is inhibited by CsA. During this process, individual cristae become fused and the junctions between the cristae and the intermembrane space are opened

Enforced Bcl-2 Expression Inhibits Antigen-mediated Clonal Elimination of Peripheral B Cells in an Antigen Dose–dependent Manner and Promotes Receptor Editing in Autoreactive, Immature B Cells

The mechanisms that establish immune tolerance in immature and mature B cells appear to be distinct. Membrane-bound autoantigen is thought to induce developmental arrest and receptor editing in immature B cells, whereas mature B cells have shortened lifespans when exposed to the same stimulus. In this study, we used Eμ–bcl-2-22 transgenic (Tg) mice to test the prediction that enforced expression of the Bcl-2 apoptotic inhibitor in B cells would rescue mature, but not immature, B cells from tolerance induction. To monitor tolerance to the natural membrane autoantigen H-2Kb, we bred 3–83μδ (anti-Kk,b) Ig Tg mice to H-2b mice or to mice expressing transgene-driven Kb in the periphery. In 3–83μδ/bcl-2 Tg mice, deletion of autoreactive B cells induced by peripheral Kb antigen expression in the liver (MT-Kb Tg) or epithelia (KerIV-Kb Tg), was partly or completely inhibited, respectively. Furthermore, Bcl-2 protected peritoneal B-2 B cells from deletion mediated by acute antigen exposure, but this protection could be overcome by higher antigen dose. In contrast to its ability to block peripheral self-tolerance, Bcl-2 overexpression failed to inhibit central tolerance induced by bone marrow antigen expression, but instead, enhanced the receptor editing process. These studies indicate that apoptosis plays distinct roles in central and peripheral B cell tolerance