Biomedical subjects

S Tonegawa

Publications and source records attributed to S Tonegawa.

At least 37 records · Page 2Linked to original sources

PubMed1998

Inhibition of intrathymic T cell development by expression of a transgenic antagonist peptide.

The mature T cell receptor (TCR) repertoire is shaped by positive- and negative-selection events taking place during T cell development. These events are regulated by interactions between the TCR and major histocompatibility complex molecules presenting self-peptides. It has been shown that many antagonist peptides are efficient at mediating positive selection. In this study we analyzed the effects of a transgene encoding an antagonist peptide (influenza NP34) that is presented by H-2Db in a Tap-1-independent fashion in mice expressing the influenza NP68-specific TCR F5. We find that the transgenic peptide does not mediate positive or negative selection in F5(+)Tap-1(-/-) mice, but inhibits maturation of CD8(+) single positive thymocytes in F5(+)Tap-1(+) mice without inducing signs of negative selection. We conclude that antagonism of antigen recognition occurs not only at the level of mature T cells but also in T cell development.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

CD4(+) T cells prevent spontaneous experimental autoimmune encephalomyelitis in anti-myelin basic protein T cell receptor transgenic mice.

Autoimmune diseases result from a failure of tolerance. Although many self-reactive T cells are present in animals and humans, their activation appears to be prevented normally by regulatory T cells. In this study, we show that regulatory CD4(+) T cells do protect mice against the spontaneous occurrence of experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis. Anti-myelin basic protein (MBP) TCR transgenic mice (T/R+) do not spontaneously develop EAE although many self-reactive T cells are present in their thymi and peripheral lymphoid organs. However, the disease develops in all crosses of T/R+ mice with recombination-activating gene (RAG)-1 knockout mice in which transgenic TCR-expressing cells are the only lymphocytes present (T/R- mice). In this study, crosses of T/R+ mice with mice deficient for B cells, CD8(+) T cells, NK1.1 CD4(+) T (NKT) cells, gamma/delta T cells, or alpha/beta T cells indicated that alpha/beta CD4(+) T cells were the only cell population capable of controlling the self-reactive T cells. To confirm the protective role of CD4(+) T cells, we performed adoptive transfer experiments. CD4(+) T cells purified from thymi or lymph nodes of normal mice prevented the occurrence of spontaneous EAE in T/R- mice. To achieve full protection, the cells had to be transferred before the recipient mice manifested any symptoms of the disease. Transfer of CD4(+) T cells after the appearance of symptoms of EAE had no protective effect. These results indicate that at least some CD4(+) T cells have a regulatory function that prevent the activation of self-reactive T cells.

Animals↗

PubMed1998

Differences in the level of expression of class I major histocompatibility complex proteins on thymic epithelial and dendritic cells influence the decision of immature thymocytes between positive and negative selection.

Both positive and negative selection of immature T cells rely on engagement of their antigen-specific receptors (TCR) by peptide in association with proteins encoded in the major histocompatibility complex (MHC) protein. The decision made between these two outcomes seems to be determined by the number of TCR engaged by peptide-MHC complexes. It has been unclear how such a mechanism can be reconciled with evidence that positive and negative selection occur in different thymic compartments and are mediated by different antigen-presenting cells (APCs). In this study we demonstrate that the level of class I MHC protein is 10-fold higher on thymic dendritic cells, which mediate the negative selection of immature T cells, than on thymic epithelial cells, which mediate for positive selection. We also demonstrate that as little as a 3-fold increase in the level of a particular cognate peptide-MHC ligand is sufficient to result in negative rather than positive selection. The results suggest that quantitative differences in the level of expression of class I MHC proteins on thymic epithelial and dendritic cells contribute to the opposing roles these cells play in forming the repertoire of mature class I MHC restricted (CD8+) T cells.

Animals↗

PubMed1998

Alterations in dopamine release but not dopamine autoreceptor function in dopamine D3 receptor mutant mice.

Dopamine (DA) autoreceptors expressed along the somatodendritic extent of midbrain DA neurons modulate impulse activity, whereas those expressed at DA nerve terminals regulate both DA synthesis and release. Considerable evidence has indicated that these DA autoreceptors are of the D2 subtype of DA receptors. However, many pharmacological studies have suggested an autoreceptor role for the DA D3 receptor. This possibility was tested with mice lacking the D3 receptor as a result of gene targeting. The basal firing rates of DA neurons within both the substantia nigra and ventral tegmental area were not different in D3 receptor mutant and wild-type mice. The putative D3 receptor-selective agonist R(+)-trans-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-(1)benzopyrano(4,3-b)-1,4-oxazin+ ++-9-ol (PD 128907) was equipotent at inhibiting the activity of both populations of midbrain DA neurons in the two groups of mice. In the gamma-butyrolactone (GBL) model of DA autoreceptor function, mutant and wild-type mice were identical with respect to striatal DA synthesis and its suppression by PD 128907. In vivo microdialysis studies of DA release in ventral striatum revealed higher basal levels of extracellular DA in mutant mice but similar inhibitory effects of PD 128907 in mutant and wild-type mice. These results suggest that the effects of PD 128907 on dopamine cell function reflect stimulation of D2 as opposed to D3 receptors. Although D3 receptors do not seem to be significantly involved in DA autoreceptor function, they may participate in postsynaptically activated short-loop feedback modulation of DA release.

Animals↗

PubMed1998

Ejaculatory abnormalities in mice with targeted disruption of the gene for heme oxygenase-2.

Nitric oxide (NO) is well established as a neurotransmitter in the central and peripheral nervous systems. More recently, another gas, carbon monoxide (CO) has also been implicated in neurotransmission. In the nervous system CO is formed by a subtype of heme oxygenase (HO) designated HO2. HO2 is localized to discrete neuronal populations in the brain resembling localizations of soluble guanylyl cyclase, which is activated by CO. CO may also function in the peripheral autonomic nervous system, in conjunction with NO. The majority of ganglia in the myenteric plexus possess both HO2 and neuronal NO synthase (NOS). Defects in myenteric plexus neurotransmission occur both in mice with targeted deletion of genes for HO2 and neuronal NOS. HO2 also occurs in other autonomic ganglia including the petrosal, superior cervical and nodose ganglia. Neuronal NOS is localized to neurons regulating male reproductive behavior, such as penile erection, and NOS inhibitors prevent erection. Because of the other parallels between NO and CO, we speculated that CO may play a role in male reproductive behavior. In the present study we describe HO2 localization in neuronal structures regulating copulatory reflexes. Reflex activity of the bulbospongiosus muscle, which mediates ejaculation and ejaculatory behavior, is markedly diminished in mice with targeted deletion of the gene for HO2 (HO2-).

Animals↗

PubMed1998

Why do mature CNS neurons of mammals fail to re-establish connections following injury--functions of bcl-2.

Factors inside and outside neurons control the process of axonal growth and regeneration. Recently, it has become apparent that neurons are determined intrinsically for their ability to grow axons. In the mammalian CNS, the intrinsic machinery of neurons that triggers the growth of axons during early embryonic stages is shut down at a certain point in development; as a consequence, axon elongation and regeneration cannot occur in postnatal life. The proto-oncogene Bcl-2 has been recognized to act as a key regulator for the program of axon elongation inside neurons. However, expressing the gene Bcl-2 in CNS neurons is not sufficient to induce nerve regeneration in the adult CNS, eliminating the inhibitory mechanism in the mature CNS environment is still required. Recently, the formation of glia scar has been reported to be the major limiting factor in the CNS environment that blocks nerve regeneration. These new discoveries challenge the classical view of nerve regeneration in the mammalian CNS. It opens up a new dimension in the study of the cellular and molecular mechanisms underlying neurodevelopmental and neurodegenerative diseases.

Aging↗

PubMed1997

Targeted gene deletion of heme oxygenase 2 reveals neural role for carbon monoxide.

Neuronal nitric oxide synthase (nNOS) generates NO in neurons, and heme-oxygenase-2 (HO-2) synthesizes carbon monoxide (CO). We have evaluated the roles of NO and CO in intestinal neurotransmission using mice with targeted deletions of nNOS or HO-2. Immunohistochemical analysis demonstrated colocalization of nNOS and HO-2 in myenteric ganglia. Nonadrenergic noncholinergic relaxation and cyclic guanosine 3',5' monophosphate elevations evoked by electrical field stimulation were diminished markedly in both nNOSDelta/Delta and HO-2(Delta)/Delta mice. In wild-type mice, NOS inhibitors and HO inhibitors partially inhibited nonadrenergic noncholinergic relaxation. In nNOSDelta/Delta animals, NOS inhibitors selectively lost their efficacy, and HO inhibitors were inactive in HO-2(Delta)/Delta animals.

Animals↗

PubMed1997

Preserved acute pain and reduced neuropathic pain in mice lacking PKCgamma.

In normal animals, peripheral nerve injury produces a persistent, neuropathic pain state in which pain is exaggerated and can be produced by nonpainful stimuli. Here, mice that lack protein kinase C gamma (PKCgamma) displayed normal responses to acute pain stimuli, but they almost completely failed to develop a neuropathic pain syndrome after partial sciatic nerve section, and the neurochemical changes that occurred in the spinal cord after nerve injury were blunted. Also, PKCgamma was shown to be restricted to a small subset of dorsal horn neurons, thus identifying a potential biochemical target for the prevention and therapy of persistent pain.

Animals↗

PubMed1997

Heme oxygenase 1 is required for mammalian iron reutilization.

The majority of iron for essential mammalian biological activities such as erythropoiesis is thought to be reutilized from cellular hemoproteins. Here, we generated mice lacking functional heme oxygenase 1 (Hmox1; EC 1.14.99.3), which catabolizes heme to biliverdin, carbon monoxide, and free iron, to assess its participation in iron homeostasis. Hmox1-deficient adult mice developed an anemia associated with abnormally low serum iron levels, yet accumulated hepatic and renal iron that contributed to macromolecular oxidative damage, tissue injury, and chronic inflammation. Our results indicate that Hmox1 has an important recycling role by facilitating the release of iron from hepatic and renal cells, and describe a mouse model of human iron metabolic disorders.

Anemia↗

PubMed1997

Reduced stress defense in heme oxygenase 1-deficient cells.

Stressed mammalian cells up-regulate heme oxygenase 1 (Hmox1; EC 1.14.99.3), which catabolizes heme to biliverdin, carbon monoxide, and free iron. To assess the potential role of Hmox1 in cellular antioxidant defense, we analyzed the responses of cells from mice lacking functional Hmox1 to oxidative challenges. Cultured Hmox1(-/-) embryonic fibroblasts demonstrated high oxygen free radical production when exposed to hemin, hydrogen peroxide, paraquat, or cadmium chloride, and they were hypersensitive to cytotoxicity caused by hemin and hydrogen peroxide. Furthermore, young adult Hmox1(-/-) mice were vulnerable to mortality and hepatic necrosis when challenged with endotoxin. Our in vitro and in vivo results provide genetic evidence that up-regulation of Hmox1 serves as an adaptive mechanism to protect cells from oxidative damage during stress.

Animals↗

PubMed1997

Tolerance induction and autoimmune encephalomyelitis amelioration after administration of myelin basic protein-derived peptide.

Experimental autoimmune encephalomyelitis (EAE), a demyelinating disease of the central nervous system, is an animal model of paralyzing human disease, multiple sclerosis. EAE is readily induced by immunization with myelin basic protein (MBP) in mice transgenic for an alphabeta T cell receptor (TCR) that is specific for MBP. Subcutaneous injection of p17 (a peptide consisting of 17 NH2-terminal aminoacids of MBP) in complete Freund's adjuvant (CFA) causes paralysis. Induction of paralysis is inhibited by prior intraperitoneal injection of the same peptide in incomplete Freund's adjuvant (IFA). In addition, ongoing paralysis is ameliorated by subsequent intraperitoneal injection of p17 in IFA. Tolerance induction is equally efficient in Fas-deficient and IL-4-deficient TCR-transgenic mice, suggesting that neither activation-induced cell death nor differentiation into Th2 type cells plays a role in the tolerance induction. Tolerance induction by p17 seems to be based on reduction in the responsiveness of anti-MBP T cells, as documented by lower overall antigen-induced lymphokine production and proliferation, as well as diminished upregulation of early activation marker CD69 by tolerized T cells. We propose that continuous encounters of MBP-specific T cells with p17 play a critical role in the induction and maintenance of tolerance.

Animals↗

PubMed1997

Myelin basic protein-specific T helper 2 (Th2) cells cause experimental autoimmune encephalomyelitis in immunodeficient hosts rather than protect them from the disease.

Chronic inflammatory autoimmune diseases such as multiple sclerosis, diabetes, and rheumatoid arthritis are caused by CD4(+) Th1 cells. Because Th2 cells antagonize Th1 cell functions in several ways, it is believed that immune deviation towards Th2 can prevent or cure autoimmune diseases. Experimental autoimmune encephalomyelitis (EAE) is a demyelinating disease used as a model for multiple sclerosis. Using an adoptive transfer system we assessed the role of Th1 and Th2 cells in EAE. In vitro generated Th1 and Th2 cells from myelin basic protein (MBP)-specific TCR transgenic mice were transferred into normal and immunodeficient mice. Th1 cells caused EAE in all recipients after a brief preclinical phase. Surprisingly, Th2 cells also caused EAE in RAG-1 KO mice and in alphabeta T cell-deficient mice, albeit after a longer preclinical phase. Normal or gammadelta T cell-deficient mice were resistant to EAE induced by Th2 cells. The histopathological features of this disease resembled those of an allergic process. In addition, disease induction by Th1 cells was not altered by coadmininstration of Th2 cells in any of the recipients. These findings indicate that MBP-specific Th2 cells have the potential to induce EAE and that the disease induced by previously activated Th1 cells cannot be prevented by normal lymphocytes nor by previously activated Th2 cells.

Animals↗

PubMed1997

The T cell receptor repertoire of intestinal intraepithelial gammadelta T lymphocytes is influenced by genes linked to the major histocompatibility complex and to the T cell receptor loci.

Most of the gammadelta T cells in the intestinal epithelium of normal mice use the Vgamma1 or the Vgamma7 gene segments. However, the relative proportions of gammadelta intraepithelial lymphocytes expressing either the Vgamma1 or the Vgamma7 chain vary among different strains of mice whereas they are quite constant between different individuals of the same strain, suggesting that genetic factors, rather than environmental factors, are responsible for the observed differences. To analyze the genetic factors influencing the representation of different gammadelta T cell subsets in the intestinal epithelium, we used available anti-T cell antigen receptor (TCR) V region-specific mAbs against Vgamma1, Vgamma4, Vgamma7, and Vdelta4 to examine the TCR repertoire of intraepithelial gammadelta lymphocytes in a set of (C57BL/6 x DBA/2) recombinant inbred strains. Our results show that the representation of different Vgamma and Vdelta gene products among gammadelta intestinal intraepithelial lymphocytes is under a complex genetic control with a marked influence by genes closely linked to the TCRgamma, TCRdelta, and major histocompatibility complex loci.

Animals↗

PubMed1997

Skeletal and CNS defects in Presenilin-1-deficient mice.

Presenilin-1 (PS1) is the major gene responsible for early-onset familial Alzheimer's disease (FAD). To understand the normal function of PS1, we have generated a targeted null mutation in the murine homolog of PS1. We report that PS1-/- mice die shortly after natural birth or Caesarean section. The skeleton of homozygous mutants is grossly deformed. Hemorrhages occur in the CNS of PS1 null mutants with varying location, severity, and time of onset. The ventricular zone of PS1-/- brains is markedly thinner by embryonic day 14.5, indicating an impairment in neurogenesis. Bilateral cerebral cavitation caused by massive neuronal loss in specific subregions of the mutant brain is prominent after embryonic day 16.5. These results show that PS1 is required for proper formation of the axial skeleton, normal neurogenesis, and neuronal survival.

Alzheimer Disease↗

PubMed1997

CD3 delta deficiency arrests development of the alpha beta but not the gamma delta T cell lineage.

The CD3 complex found associated with the T cell receptor (TCR) is essential for signal transduction following TCR engagement. During T cell development, TCR-mediated signalling promotes the transition from one developmental stage to the next and controls whether a thymocyte undergoes positive or negative selection. The roles of particular CD3 components in these events remain unclear. Indeed, it is unknown whether they have specialized or overlapping roles. However, the multiplicity of CD3 components and their evolutionary conservation suggest that they serve distinct functions. Here the developmental requirement for the CD3 delta chain is analyzed by generating a mouse line specifically lacking this component (delta-/- mice). Strikingly, CD3 delta is shown to be differentially required during development. In particular, CD3 delta is not needed for steps in development mediated by pre-TCR or gamma delta TCR, but is required for further development of thymocytes expressing alpha beta TCR. Absence of CD3 delta specifically blocks the thymic selection processes that mediate the transition from the double-positive to single-positive stages of development.

Animals↗

PubMed1997

Bcl-2 promotes regeneration of severed axons in mammalian CNS.

Most neurons of the mammalian central nervous system (CNS) lose the ability to regenerate severed axons in vivo after a certain point in development. At least part of this loss in regenerative potential is intrinsic to neurons. Although embryonic retinal ganglion cells (RGCs) can grow axons into tectum of any age, most RGCs from older animals fail to extend axons into CNS tissue derived from donors of any age, including the embryonic tectum. Here we report that the proto-oncogene bcl-2 plays a key role in this developmental change by promoting the growth and regeneration of retinal axons. This effect does not seem to be an indirect consequence of its well-known anti-apoptotic activity. Another anti-apoptotic drug, ZVAD, supported neuronal survival but did not promote axon regeneration in culture. This finding could lead to new strategies for the treatment of injuries to the CNS.

Animals↗

PubMed1997

Synaptic plasticity, place cells and spatial memory: study with second generation knockouts.

The use of genetically engineered mice has been a major development in neuroscience research. Genetic engineering is an undoubtedly powerful technique; however, the value of this approach has been debated, particularly in relation to its use to probe the underlying bases of complex behaviors, such as memory. A recent new development of the technique is the ability to target a specific gene knockout to a particular subregion or even to specific and limited cell types of the mouse brain. An example of this approach is the knockout of the NMDARI gene in only CAI-pyramidal cells of the hippocampus. The resulting animals can be tested by several methods, including in vivo multielectrode recording during behavioral tasks. The data provide strong evidence in favor of the notion that NMDA receptor-dependent synaptic plasticity at CAI synapses is required for both the acquisition of spatial memory and the formation of normal CAI place fields. This relationship suggests that robust place fields may be essential for spatial memory.

Animals↗

PubMed1997

NMDA receptor-dependent refinement of somatotopic maps.

We have examined the role of NMDA receptor-mediated neural activity in the formation of periphery-related somatosensory patterns, using genetically engineered mice. We demonstrate that ectopic expression of a transgene of an NMDAR1 splice variant rescues neonatally fatal NMDAR1 knockout (KO) mice, although the average life span varies depending on the level of the transgene expression. In NMDAR1 KO mice with "high" levels of the transgene expression, sensory periphery-related patterns were normal along both the trigeminal and dorsal column pathways. In the KO mice with "low" levels of the transgene expression, the patterns were absent in the trigeminal pathway. Our results indicate that NMDA receptor-mediated neural activity plays a critical role in pattern formation along the ascending somatosensory pathways.

Alternative Splicing↗