Autoimmune dilated cardiomyopathy in PD-1 receptor-deficient mice

Dilated cardiomyopathy is a severe pathology of the heart with poorly understood etiology. Disruption of the gene encoding the negative immunoregulatory receptor PD-1 in BALB/c mice, but not in BALB/c RAG-2-/- mice, caused dilated cardiomyopathy with severely impaired contraction and sudden death by congestive heart failure. Affected hearts showed diffuse deposition of immunoglobulin G (IgG) on the surface of cardiomyocytes. All of the affected PD-1-/- mice exhibited high-titer circulating IgG autoantibodies reactive to a 33-kilodalton protein expressed specifically on the surface of cardiomyocytes. These results indicate that PD-1 may be an important factor contributing to the prevention of autoimmune diseases.

A protein conjugation system essential for autophagy

Autophagy is a process for the bulk degradation of proteins, in which cytoplasmic components of the cell are enclosed by double-membrane structures known as autophagosomes for delivery to lysosomes or vacuoles for degradation. This process is crucial for survival during starvation and cell differentiation. No molecules have been identified that are involved in autophagy in higher eukaryotes. We have isolated 14 autophagy-defective (apg) mutants of the yeast Saccharomyces cerevisiae and examined the autophagic process at the molecular level. We show here that a unique covalent-modification system is essential for autophagy to occur. The carboxy-terminal glycine residue of Apg12, a 186-amino-acid protein, is conjugated to a lysine at residue 149 of Apg5, a 294-amino-acid protein. Of the apg mutants, we found that apg7 and apg10 were unable to form an Apg5/Apg12 conjugate. By cloning APG7, we discovered that Apg7 is a ubiquitin-E1-like enzyme. This conjugation can be reconstituted in vitro and depends on ATP. To our knowledge, this is the first report of a protein unrelated to ubiquitin that uses a ubiquitination-like conjugation system. Furthermore, Apg5 and Apg12 have mammalian homologues, suggesting that this new modification system is conserved from yeast to mammalian cells.

Randomization of left-right asymmetry due to loss of nodal cilia generating leftward flow of extraembryonic fluid in mice lacking KIF3B motor protein

Microtubule-dependent motor, murine KIF3B, was disrupted by gene targeting. The null mutants did not survive beyond midgestation, exhibiting growth retardation, pericardial sac ballooning, and neural tube disorganization. Prominently, the left-right asymmetry was randomized in the heart loop and the direction of embryonic turning. lefty-2 expression was either bilateral or absent. Furthermore, the node lacked monocilia while the basal bodies were present. Immunocytochemistry revealed KIF3B localization in wild-type nodal cilia. Video microscopy showed that these cilia were motile and generated a leftward flow. These data suggest that KIF3B is essential for the left-right determination through intraciliary transportation of materials for ciliogenesis of motile primary cilia that could produce a gradient of putative morphogen along the left-right axis in the node.

The genome of the social amoeba Dictyostelium discoideum

The social amoebae are exceptional in their ability to alternate between unicellular and multicellular forms. Here we describe the genome of the best-studied member of this group, Dictyostelium discoideum. The gene-dense chromosomes of this organism encode approximately 12,500 predicted proteins, a high proportion of which have long, repetitive amino acid tracts. There are many genes for polyketide synthases and ABC transporters, suggesting an extensive secondary metabolism for producing and exporting small molecules. The genome is rich in complex repeats, one class of which is clustered and may serve as centromeres. Partial copies of the extrachromosomal ribosomal DNA (rDNA) element are found at the ends of each chromosome, suggesting a novel telomere structure and the use of a common mechanism to maintain both the rDNA and chromosomal termini. A proteome-based phylogeny shows that the amoebozoa diverged from the animal-fungal lineage after the plant-animal split, but Dictyostelium seems to have retained more of the diversity of the ancestral genome than have plants, animals or fungi.

Natural and synthetic non-peptide antigens recognized by human gamma delta T cells

T lymphocytes express either alpha beta or gamma delta T-cell receptor heterodimers. Most alpha beta T cells recognize antigenic peptides bound to major histocompatibility complex molecules but the antigen recognition and biological function of gamma delta T cells is unknown. A major human gamma delta T-cell subset expressing V gamma 2 and V delta 2 germline genes, but having diverse junctional sequences, is found in human mycobacterial lesions and responds in vitro to antigens of bacteria and parasites. In addition, certain haematopoietic tumour cells are specifically recognized and lysed by these T cells. V gamma 2V delta 2-bearing T cells were shown to recognize mycobacterial antigens that are protease resistant and phosphatase sensitive. Because of the difficulty in isolating natural antigens from mycobacterial culture filtrates or extracts, we synthesized a series of monoalkyl phosphates, and found that some, particularly monoethyl phosphate, could mimic the activity of mycobacterial antigens in stimulating these gamma delta T cells. Here we report the identification of natural antigens produced by mycobacteria recognized by human V gamma 2V delta 2-bearing T cells as isopentenyl pyrophosphate and related prenyl pyrophosphate derivatives, compounds involved in the synthesis of complex polyisoprenoid compounds in microbial and mammalian cells. Substitution of phosphate for the pyrophosphate moiety, or elimination of the double bond, greatly reduced antigenic activity of these compounds. These results provide formal evidence that, in contrast to recognition of major histocompatibility complex-bound peptide antigens by alpha beta T cells, human gamma delta T cells can recognize naturally occurring small non-peptidic antigens.

Accumulation of autophagic vacuoles and cardiomyopathy in LAMP-2-deficient mice

Lysosome-associated membrane protein-2 (LAMP-2) is a highly glycosylated protein and an important constituent of the lysosomal membrane. Here we show that LAMP-2 deficiency in mice increases mortality between 20 and 40 days of age. The surviving mice are fertile and have an almost normal life span. Ultrastructurally, there is extensive accumulation of autophagic vacuoles in many tissues including liver, pancreas, spleen, kidney and skeletal and heart muscle. In hepatocytes, the autophagic degradation of long-lived proteins is severely impaired. Cardiac myocytes are ultrastructurally abnormal and heart contractility is severely reduced. These findings indicate that LAMP-2 is critical for autophagy. This theory is further substantiated by the finding that human LAMP-2 deficiency causing Danon's disease is associated with the accumulation of autophagic material in striated myocytes.

T-cell adhesion induced by proteoglycan-immobilized cytokine MIP-1 beta

Lymphocyte migration from blood into tissue depends on integrin-mediated adhesion to endothelium. Adhesion requires not only integrin ligands on the endothelium, but also activation signals because T-cell integrins cannot bind well until they are activated. The physiological 'triggers' for T-cell adhesion are unknown, but cytokines may be good candidates as they are released during inflammation and trigger adhesion in neutrophils and monocytes. We have identified a cytokine, macrophage inflammatory protein-1 beta (MIP-1 beta), that induces both chemotaxis and adhesion of T cells; MIP-1 beta is most effective at augmenting adhesion of CD8+ T cells to the vascular cell adhesion molecule VCAM-1. We reasoned that, as cytokines in vivo will be rapidly washed away, MIP-1 beta might be bound to endothelial surfaces and so induce adhesion in its immobilized form. Here we show that: (1) MIP-1 beta is present on lymph node endothelium; (2) immobilized MIP-1 beta induces binding of T cells to VCAM-1 in vitro. MIP-1 beta was immobilized by binding to proteoglycan: a conjugate of heparin with bovine serum albumin and cellular proteoglycan CD44 were both effective. We propose that MIP-1 beta and other cytokines with glycosaminoglycan-binding sites will bind to and be presented by endothelial proteoglycans to trigger adhesion selectively not only of lymphocyte subsets, but also of other cell types.

Direct derivation of conditionally immortal cell lines from an H-2Kb-tsA58 transgenic mouse

Studies on cell lines have greatly improved our understanding of many important biological questions. Generation of cell lines is facilitated by the introduction of immortalizing oncogenes into cell types of interest. One gene known to immortalize many different cell types in vitro encodes the simian virus 40 (SV40) large tumor (T) antigen (TAg). To circumvent the need for gene insertion in vitro to generate cell lines, we created transgenic mice harboring the SV40 TAg gene. Since previous studies have shown that TAg expression in transgenic mice is associated with tumorigenesis and aberrant development, we utilized a thermolabile TAg [from a SV40 strain, tsA58, temperature sensitive (ts) for transformation] to reduce the levels of functional TAg present in vivo. To direct expression to a broad range of tissues, we used the mouse major histocompatibility complex H-2Kb promoter, which is both widely active and can be further induced by interferons. tsA58 TAg mRNA was expressed in tissues of all animals harboring the hybrid construct. Development of all tissues was macroscopically normal except for thymus, which consistently showed hyperplasia. Fibroblast and cytokeratin+ thymic epithelial cultures from these mice were readily established without undergoing crisis and were conditionally immortal in their growth; the degree of conditionality was correlated with the levels of tsA58 TAg detected. One strain of H-2Kb-tsA58 mice has been bred through several generations to homozygosity and transmits a functional copy of the transgene.

Target cells for 1,25-dihydroxyvitamin D3 in intestinal tract, stomach, kidney, skin, pituitary, and parathyroid

After mature rats that had been fed on a vitamin D3-deficient diet were injected with tritium-labeled 1,25-dihydroxyvitamin D3, radioactivity became concentrated in nuclei of luminal and cryptal epithelium of the duodenum, jejunum, ileum, and colon; in nuclei of the epithelium of kidney distal tubules including the macula densa, and in podocytes of glomeruli; in nuclei of the epidermis including outer hairshafts and sebaceous glands; and in nuclei of certain cells of the stomach, anterior and posterior pituitary, and parathyroid. These results reveal cell types that contain receptors for 1,25-dihydroxyvitamin D3 or metabolites of this compound both in known or hypothesized target tissues and in tissues that were previously unknown to participate in vitamin D3 metabolism.

Parkin ubiquitinates the alpha-synuclein-interacting protein, synphilin-1: implications for Lewy-body formation in Parkinson disease

Parkinson disease is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic-ubiquitinated inclusions (Lewy bodies). Mutations in alpha-synuclein (A53T, A30P) and parkin cause familial Parkinson disease. Both these proteins are found in Lewy bodies. The absence of Lewy bodies in patients with parkin mutations suggests that parkin might be required for the formation of Lewy bodies. Here we show that parkin interacts with and ubiquitinates the alpha-synuclein-interacting protein, synphilin-1. Co-expression of alpha-synuclein, synphilin-1 and parkin result in the formation of Lewy-body-like ubiquitin-positive cytosolic inclusions. We further show that familial-linked mutations in parkin disrupt the ubiquitination of synphilin-1 and the formation of the ubiquitin-positive inclusions. These results provide a molecular basis for the ubiquitination of Lewy-body-associated proteins and link parkin and alpha-synuclein in a common pathogenic mechanism through their interaction with synphilin-1.

Charcot-Marie-Tooth disease type 2A caused by mutation in a microtubule motor KIF1Bbeta

The kinesin superfamily motor protein KIF1B has been shown to transport mitochondria. Here, we describe an isoform of KIF1B, KIF1Bbeta, that is distinct from KIF1B in its cargo binding domain. KIF1B knockout mice die at birth from apnea due to nervous system defects. Death of knockout neurons in culture can be rescued by expression of the beta isoform. The KIF1B heterozygotes have a defect in transporting synaptic vesicle precursors and suffer from progressive muscle weakness similar to human neuropathies. Charcot-Marie-Tooth disease type 2A was previously mapped to an interval containing KIF1B. We show that CMT2A patients contain a loss-of-function mutation in the motor domain of the KIF1B gene. This is clear indication that defects in axonal transport due to a mutated motor protein can underlie human peripheral neuropathy.

Targeted disruption of mouse conventional kinesin heavy chain, kif5B, results in abnormal perinuclear clustering of mitochondria

Mouse kif5B gene was disrupted by homologous recombination. kif5B-/- mice were embryonic lethal with a severe growth retardation at 9.5-11.5 days postcoitum. To analyze the significance of this conventional kinesin heavy chain in organelle transport, we studied the distribution of major organelles in the extraembryonic cells. The null mutant cells impaired lysosomal dispersion, while brefeldin A could normally induce the breakdown of their Golgi apparatus. More prominently, their mitochondria abnormally clustered in the perinuclear region. This mitochondrial phenotype was reversed by an exogenous expression of KIF5B, and a subcellular fractionation revealed that KIF5B is associated with mitochondria. These data collectively indicate that kinesin is essential for mitochondrial and lysosomal dispersion rather than for the Golgi-to-ER traffic in these cells.

Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans

Acute and long-term effects of resistance exercise combined with vascular occlusion on muscular function were investigated. Changes in integrated electromyogram with respect to time (iEMG), vascular resistive index, and plasma lactate concentration were measured in five men either during or after elbow flexion exercises with the proximal end of the arm occluded at 0-100 mmHg. The mean iEMG, postexercise hyperemia, and plasma lactate concentration were all elevated with the increase in occlusion pressure at a low-intensity exercise, whereas they were unchanged with the increase in occlusion pressure at high-intensity exercise. To investigate the long-term effects of low-intensity exercise with occlusion, older women (n = 24) were subjected to a 16-wk exercise training for elbow flexor muscles, in which low-intensity [ approximately 50-30% one repetition maximum (1 RM)] exercise with occlusion at approximately 110 mmHg (LIO), low-intensity exercise without occlusion (LI), and high- to medium-intensity ( approximately 80-50% 1 RM) exercise without occlusion (HI) were performed. Percent increases in both cross-sectional area and isokinetic strength of elbow flexor muscles after LIO were larger than those after LI (P < 0.05) and similar to those after HI. The results suggest that resistance exercise at an intensity even lower than 50% 1 RM is effective in inducing muscular hypertrophy and concomitant increase in strength when combined with vascular occlusion.

Lymphocyte interactions with endothelial cells

Adhesion of lymphocytes to endothelium is vital to lymphocyte migration into lymphoid tissue and into inflammatory sites. In this review, Yoji Shimizu and colleagues identify the molecules that mediate lymphocyte-endothelial cell adhesion, describe the underlying principles of lymphocyte migration, and discuss a model of the sequence of events that allow a lymphocyte to successfully attach to endothelium and migrate into the surrounding tissue.

Sonic Hedgehog-induced activation of the Gli1 promoter is mediated by GLI3

Drosophila transcription factor cubitus interruptus (Ci) and its co-activator CRE (cAMP response element)-binding protein (CBP) activate a group of target genes on the anterior-posterior border in response to hedgehog protein (Hh) signaling. In the anterior region, in contrast, the carboxyl-truncated form of Ci generated by protein processing represses Hh expression. In vertebrates, three Ci-related transcription factors (glioblastoma gene products (GLIs) 1, 2, and 3) were identified, but their functional difference in Hh signal transduction is unknown. Here, we report distinct roles for GLI1 and GLI3 in Sonic hedgehog (Shh) signaling. GLI3 containing both repression and activation domains acts both as an activator and a repressor, as does Ci, whereas GLI1 contains only the activation domain. Consistent with this, GLI3, but not GLI1, is processed to generate the repressor form. Transcriptional co-activator CBP binds to GLI3, but not to GLI1. The trans-activating capacity of GLI3 is positively and negatively regulated by Shh and cAMP-dependent protein kinase, respectively, through a specific region of GLI3, which contains the CBP-binding domain and the phosphorylation sites of cAMP-dependent protein kinase. GLI3 directly binds to the Gli1 promoter and induces Gli1 transcription in response to Shh. Thus, GLI3 may act as a mediator of Shh signaling in the activation of the target gene Gli1.

Angiotensin II type 2 receptor overexpression activates the vascular kinin system and causes vasodilation

Angiotensin II (Ang II) is a potent vasopressor peptide that interacts with 2 major receptor isoforms - AT1 and AT2. Although blood pressure is increased in AT2 knockout mice, the underlying mechanisms remain undefined because of the low levels of expression of AT2 in the vasculature. Here we overexpressed AT2 in vascular smooth muscle (VSM) cells in transgenic (TG) mice. Aortic AT1 was not affected by overexpression of AT2. Chronic infusion of Ang II into AT2-TG mice completely abolished the AT1-mediated pressor effect, which was blocked by inhibitors of bradykinin type 2 receptor (icatibant) and nitric oxide (NO) synthase (L-NAME). Aortic explants from TG mice showed greatly increased cGMP production and diminished Ang II-induced vascular constriction. Removal of endothelium or treatment with icatibant and L-NAME abolished these AT2-mediated effects. AT2 blocked the amiloride-sensitive Na(+)/H(+) exchanger, promoting intracellular acidosis in VSM cells and activating kininogenases. The resulting enhancement of aortic kinin formation in TG mice was not affected by removal of endothelium. Our results suggest that AT2 in aortic VSM cells stimulates the production of bradykinin, which stimulates the NO/cGMP system in a paracrine manner to promote vasodilation. Selective stimulation of AT2 in the presence of AT1 antagonists is predicted to have a beneficial clinical effect in controlling blood pressure.

Natural killer-like nonspecific tumor cell lysis mediated by specific ligand-activated Valpha14 NKT cells

We have recently identified alpha-galactosylceramide (alpha-GalCer) as a specific ligand for an invariant Valpha14/Vbeta8.2 T cell receptor exclusively expressed on the majority of Valpha14 NKT cells, a novel subset of lymphocytes. Here, we report that alpha-GalCer selectively activates Valpha14 NKT cells resulting in prevention of tumor metastasis. The effector mechanisms of the ligand-activated Valpha14 NKT cells seem to be mediated by natural killer (NK)-like nonspecific cytotoxicity. Indeed, the cytotoxic index obtained by alpha-GalCer-activated Valpha14 NKT cells was reduced by the addition of cold target tumor cells or by treatment with concanamycin A, which inhibits activation and secretion of perforin, but not by mAbs against molecules involved in the NKT cell recognition and conventional cytotoxicity, such as CD1d, Vbeta8, NK1. 1, Ly49C, Fas, or Fas ligand. These results suggest that the ligand-activated Valpha14 NKT cells kill tumor cells directly through a CD1d/Valpha14 T cell receptor-independent, NK-like mechanism.

Inducible expression of mutant alpha-synuclein decreases proteasome activity and increases sensitivity to mitochondria-dependent apoptosis

Parkinson's disease (PD) is a common progressive neurodegenerative disorder caused by the loss of dopaminergic neurons in the substantia nigra. Although mutations in alpha-synuclein have been identified in autosomal dominant PD, the mechanism by which dopaminergic neural cell death occurs remains unknown. Proteins encoded by two other genes in which mutations cause familial PD, parkin and UCH-L1, are involved in regulation of the ubiquitin-proteasome pathway, suggesting that dysregulation of the ubiquitin-proteasome pathway is involved in the mechanism by which these mutations cause PD. We established inducible PC12 cell lines in which wild-type or mutant alpha-synuclein can be de-repressed by removing doxycycline. Differentiated PC12 cell lines expressing mutant alpha-synuclein showed decreased activity of proteasomes without direct toxicity. Cells expressing mutant alpha-synuclein showed increased sensitivity to apoptotic cell death when treated with sub-toxic concentrations of an exogenous proteasome inhibitor. Apoptosis was accompanied by mitochondrial depolarization and elevation of caspase-3 and -9, and was blocked by cyclosporin A. These data suggest that expression of mutant alpha-synuclein results in sensitivity to impairment of proteasome activity, leading to mitochondrial abnormalities and neuronal cell death.

Direct presentation of nonpeptide prenyl pyrophosphate antigens to human gamma delta T cells

Human V gamma 2V delta 2+ T cells recognize mycobacterial nonpeptide antigens, such as isopentenyl pyrophosphate, and their synthetic analogs, such as monoethyl phosphate, through a TCR-dependent process. Here, we examine the presentation of these antigens. V gamma 2V delta 2+ T cells recognized secreted prenyl pyrophosphate antigens in the absence of other accessory cells but, under such conditions, required T cell-T cell contact. Recognition required neither the expression of classical MHC class I, MHC class II, or CD1a, CD1b, and CD1c molecules, nor MHC class I or class II peptide loading pathways. Fixed accessory cells also presented the prenyl pyrophosphate antigens to gamma delta T cells. Thus, in contrast with the presentation of conventional peptide antigens, protein antigens, and superantigens to alpha beta T cells, prenyl pyrophosphate antigens are presented to gamma delta T cells through a novel extracellular pathway that does not require antigen uptake, antigen processing, or MHC class I or class II expression. This pathway allows for the rapid recognition of bacteria by gamma delta T cells and suggests that gamma delta T cells play a role in the early response to bacterial infection.

High-affinity IgE receptor on eosinophils is involved in defence against parasites

Parasitic infections are often associated with eosinophilia and high levels of immunoglobulin E (IgE). This observation has led to speculation that eosinophils and IgE may act together in the immune response against parasites. In support of this hypothesis, IgE and eosinophils participate in cytotoxic reactions directed against Schistosoma mansoni larvae in vitro. Furthermore, epidemiological studies have shown an inverse correlation between levels of specific IgE and rates of infection with Schistosoma. The low-affinity IgE receptor (Fc epsilon RII/CD23) was first incriminated in eosinophil activation. The fact that the high-affinity IgE receptor (Fc epsilon RI) is not only expressed on mast cells and basophils but also on Langerhans cells led us to investigate the presence of Fc epsilon RI on eosinophils. Here we show that Fc epsilon RI is expressed on eosinophils from hypereosinophilic patients, is involved in eosinophil degranulation, and participates in eosinophil-mediated cytotoxicity against S. mansoni. Our results indicate that Fc epsilon RI may play a major part in immune defence against parasites.