Toll-like receptor 2-deficient mice are protected from insulin resistance and beta cell dysfunction induced by a high-fat diet.

AIMS/HYPOTHESIS: Inflammation contributes to both insulin resistance and pancreatic beta cell failure in human type 2 diabetes. Toll-like receptors (TLRs) are highly conserved pattern recognition receptors that coordinate the innate inflammatory response to numerous substances, including NEFAs. Here we investigated a potential contribution of TLR2 to the metabolic dysregulation induced by high-fat diet (HFD) feeding in mice. METHODS: Male and female littermate Tlr2(+/+) and Tlr2(-/-) mice were analysed with respect to glucose tolerance, insulin sensitivity, insulin secretion and energy metabolism on chow and HFD. Adipose, liver, muscle and islet pathology and inflammation were examined using molecular approaches. Macrophages and dendritic immune cells, in addition to pancreatic islets were investigated in vitro with respect to NEFA-induced cytokine production. RESULTS: While not showing any differences in glucose homeostasis on chow diet, both male and female Tlr2(-/-) mice were protected from the adverse effects of HFD compared with Tlr2(+/+) littermate controls. Female Tlr2(-/-) mice showed pronounced improvements in glucose tolerance, insulin sensitivity, and insulin secretion following 20 weeks of HFD feeding. These effects were associated with an increased capacity of Tlr2(-/-) mice to preferentially burn fat, combined with reduced tissue inflammation. Bone-marrow-derived dendritic cells and pancreatic islets from Tlr2(-/-) mice did not increase IL-1beta expression in response to a NEFA mixture, whereas Tlr2(+/+) control tissues did. CONCLUSION/INTERPRETATION: These data suggest that TLR2 is a molecular link between increased dietary lipid intake and the regulation of glucose homeostasis, via regulation of energy substrate utilisation and tissue inflammation.

Early onset of somatic mutation in immunoglobulin VH genes during the primary immune response.

The dynamics of somatic mutation in Ig variable genes was investigated in order to define a population of B cells undergoing mutation. BALB/cJ mice were injected with PC-KLH, and splenic RNA was prepared 5, 7, and 13 d later. The mRNA was annealed to gamma constant region primers to make cDNA transcripts encoding VH genes. 103 cDNA clones corresponding to 18 different genes from the VH7183, VH3660, and VHS107 subfamilies were sequenced to identify mutation. VH genes had a low level of mutation on day 5 after immunization and accumulated more mutation by day 7 at a rate of 10(-3) mutations per nucleotide per generation. However, by day 13, the number of mutations per gene did not increase, and most of the substitutions encoded replacement amino acid changes that were clustered in the hypervariable regions, indicating that the mutational process was less active during the second week and that antigen selection had occurred. The data are consistent with a developmentally regulated mechanism in which mutation is activated during the first week of the primary immune response for a limited time period, after which selection acts to preserve the beneficial mutants.

Protooncogene bcl-2 gene transfer abrogates Fas/APO-1 antibody-mediated apoptosis of human malignant glioma cells and confers resistance to chemotherapeutic drugs and therapeutic irradiation.

The majority of human malignant glioma cells express Fas/APO-1 and are susceptible to Fas/APO-1 antibody-mediated apoptosis in vitro. The sensitivity of Fas/APO-1-positive glioma cell lines to Fas/APO-1 antibody-mediated killing correlates inversely with the constitutive expression of the antiapoptotic protooncogene bcl-2. Here we report that BCL-2 protein expression of human glial tumors in vivo correlates with malignant transformation in that BCL-2 immunoreactive glioma cells were more abundant in WHO grade III/IV gliomas than in grade I/II gliomas. Fas/APO-1 antibody-sensitive human glioma cell lines stably transfected with a murine bcl-2 cDNA acquired resistance to Fas/APO-1 antibody-mediated apoptosis. Forced expression of bcl-2 also attenuated TNF alpha-mediated cytotoxicity of glioma cell lines in the presence of actinomycin D and cycloheximide and conferred partial protection from irradiation and the cancer chemotherapy drugs, cisplatin and BCNU. Preexposure of the glioma cell lines to the cytokines, IFN gamma and TNF alpha, which sensitize for Fas/APO-1-dependent killing, partially overcame bcl-2-mediated rescue from apoptosis, suggesting that multimodality immunotherapy involving cytokines and Fas/APO-1 targeting might eventually provide a promising approach to the treatment of human malignant gliomas.

Human small cell lung cancer expresses the octamer DNA-binding and nervous system-specific transcription factor N-Oct 3 (brain-2).

Small cell lung cancer (SCLC) cells express several characteristics of neuronal cells, including synthesis of neuropeptides and expression of the respective receptors. Establishment and maintenance of the neuronal phenotype of SCLC may depend on expression of gene transcription factors inherent to the central nervous system. The present study shows the nervous system-specific transcription factor N-Oct 3 (brain-2) to be expressed in all 13 SCLC cell lines investigated. Furthermore, N-Oct 3 (brain-2) was also found in SCLC-derived skin metastasis. In contrast, in extracts and RNA of non-SCLC cell lines and non-SCLC tumor tissues, such as lung squamous, large cell, and adenocarcinoma, expression of N-Oct 3 (brain-2) was not detectable. These data support the concept that SCLC cells derive from the neuroectodermal cell lineage since expression of N-Oct 3 (brain-2) protein is highly abundant at the neural tube stage and in the adult restricted to the neuroectodermal cell lineage.

Fas/APO-1 gene transfer for human malignant glioma.

Human malignant glioma cells are susceptible to apoptosis induced by antibodies to Fas/APO-1, a cytokine receptor protein of the nerve growth factor/tumor necrosis factor receptor superfamily. Here we show that a critical level of cell surface expression of Fas/APO-1 is a prerequisite for induction of glioma cell apoptosis via Fas/APO-1. Although Fas/APO-1 mRNA was expressed in three Fas/APO-1 antibody-resistant glioma cell lines, these cells expressed either little Fas/APO-1 protein (LN-319 and LN-405) or an abnormal Fas/APO-1 protein that was not translocated to the cell membrane and therefore functionally inactive (LN-308). Although all glioma cell lines expressed mRNA for Fas/APO-1-delta TM, a soluble form of Fas/APO-1 lacking the transmembrane domain, none of the cell lines released detectable amounts of soluble Fas/APO-1, a potential endogenous antagonist of Fas/APO-1-mediated glioma cell apoptosis. Stable transfection of three resistant glioma cell lines with a human Fas/APO-1 cDNA expression vector dramatically enhanced cell surface expression of Fas/APO-1 and induced susceptibility to Fas/APO-1 antibody-mediated apoptosis. These data indicate that malignant glioma cells, unlike other tumor cells, uniformly harbor the intracellular cascade required for Fas/APO-1-mediated apoptosis. Low level of Fas/APO-1 expression results from inefficient transcription and translation of the Fas/APO-1 gene or the synthesis of mutant Fas/APO-1 proteins. gamma-Interferon, tumor necrosis factor-alpha, and interleukin 1 beta augmented Fas/APO-1-mediated apoptosis of Fas/APO-1-transfected glioma cells by acting on the subcellular suicidal cascade triggered by Fas/APO-1 activation. Dexamethasone attenuated Fas/APO-1 antibody-induced apoptosis, not only of constitutively Fas/APO-1-positive glioma cells, but also of Fas/APO-1-transfected glioma cells. The antiapoptotic effect of dexamethasone could be overcome by preexposure of the glioma cells to gamma-interferon or by coexposure to Fas/APO-1 antibodies and cycloheximide. Thus, Fas/APO-1 gene transfer and combined immunotherapy using Fas/APO-1 antibodies and cytokines may overcome Fas/APO-1 antibody resistance of Fas/APO-1-negative human malignant glioma cells, which may represent subpopulations within single gliomas or form a separate subgroup of human malignant gliomas.

A new look at the role of p53 in leukemia cell sensitivity to chemotherapy.

A gene encoding the p53 val135 mutant, which assumes mutant conformation at 38.5 degrees C and wild-type conformation at 32.5 degrees C, was introduced into p53-deficient K562 myeloid leukemia cells. Forced expression of wild-type, but not mutant, p53 resulted in growth arrest, accumulation of p21 and Bax proteins, and delayed cell death. Wild-type p53 enhanced the cytotoxic effects of some drugs and attenuated those of others. Compared with wild-type p53, mutant p53 induced much stronger sensitization to drug cytotoxicity. This occurred in the absence of effects on cell cycle progression or activation of several p53 target genes. Although both mutant and wild-type p53 induced changes of immunophenotype, no specific pattern of differentiation was associated with enhanced chemosensitivity. Thus, (1) induction of growth arrest and activation of p53 target genes such as p21 and bax are linked to the wild-type conformation of p53; (2) p53 induces immunophenotypic changes of myeloid leukemia cells suggestive of multidirectional differentiation in a conformation-dependent manner; and (3) (so-called) mutant p53 induces chemosensitization in the absence of effects on cell cycle progression, activation of bax, p21, gadd45 and mdm-2, or a specific pattern of differentiation; and (4) chemosensitization mediated by wild-type p53 may be masked by transcription-dependent induction of growth arrest.

Treatment of experimental glioma by administration of adenoviral vectors expressing Fas ligand.

Fas ligand (FasL) is a cytokine, produced by activated T cells and NK cells, that triggers apoptosis of Fas-positive target cells including human glioma cells. As shown here, in vitro infection of rat F98 and human LN18 glioma cell lines with recombinant adenovirus (rAd) expressing FasL cDNA under control of the cytomegalovirus promoter (rAd-CMV-FasL) induced striking cytotoxicity in Fas-positive glioma cell lines but not in the Fas-negative F98 glioma subline F98/ZH. The extent of FasL-mediated cytotoxic effects outranged the expectations based on expression of beta-galactosidase (beta-Gal) by F98 cells infected with a control virus expressing the lacZ gene (rAd-CMV-lacZ). The detection of FasL bioactivity in supernatants of infected cells provides evidence of a bystander mechanism involving the cytotoxic action of FasL on uninfected cells. In F98 tumor-bearing rats, infection with rAd-CMV-FasL increased the mean survival time by 50% compared with infection with rAd-CMV-lacZ or untreated controls. These data suggest that viral vector transduction of the FasL gene could be part of a successful glioma gene therapy.

Production of macrophage colony-stimulating factor by astrocytes and brain macrophages.

Morphological hallmarks of inflammatory and degenerative diseases of the brain are hypertrophy of astrocytes and accumulation of macrophages recruited from circulating blood monocytes and/or from resident macrophages, the so-called microglial cells. Recently, production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by astrocytes has been suggested to contribute to the macrophage response. Here we report that in addition to GM-CSF, murine astrocytes also produce macrophage (M)-CSF upon stimulation with tumor necrosis factor alpha, interleukin-1 and lipopolysaccharides. The bioactivity detected in supernatant of astrocytes was characterized using the M-CSF-dependent cell line M-NFS-60 and neutralizing anti-M-CSF antibodies. RNase protection analysis showed M-CSF mRNA already in unstimulated astrocytes without striking up-regulation by the stimuli. Thus, in astrocytes the expression of the M-CSF gene is predominantly regulated at the posttranscriptional level.

Production of hemopoietic colony-stimulating factors by astrocytes.

Astrocytes may play a central role in regulation of immune mediated processes in the central nervous system. By their inducible expression of MHC class II Ag and secretion of cytokines they may propagate expansion and activation of T and B lymphocytes invading the brain tissue. Here we report that astrocytes may also contribute to the macrophage response observed in inflammatory and degenerative diseases of the brain. Murine astrocytes secrete granulocyte-macrophage CSF (GM-CSF) as evidenced by induction of colony formation in bone marrow cells and growth of FDC-P1 cells. Both effects are neutralized with anti-GM-CSF- but not with anti-IL-3-antibodies. Some residual activity detected in the bone marrow assay after antibody treatment can be explained by concomitant production of granulocyte CSF (G-CSF). The mRNA of both G- and GM-CSF are identified by Northern blots in astrocytes. Furthermore, mRNA for IL-1 alpha and IL-1 beta are detected in comparable amounts in astrocytes and brain macrophages, the latter, however, comprising much more potent sources of TNF-alpha.

Neurons and neuroblastoma as a source of macrophage colony-stimulating factor.

Accumulation of macrophages in brain tissue as observed in nervous system injury may be due to local production of hematopoietic colony-stimulating factors (CSF). The present work shows human neuroblastoma cells and murine neurons, namely granule cells of the cerebellum, to produce macrophage (M)-CSF which guides expansion and differentiation of macrophage lineage cells. The mRNA-encoding M-CSF but not the respective protein is present in mouse brain including cerebellum. Neither granulocyte M-CSF nor IL-3 is produced by cerebellar neurons or neuroblastoma. By their production of M-CSF, neurons may regulate the macrophage response and lead to local expansion and enhanced function of macrophages in inflammatory diseases of the central nervous system.

Transforming growth factor-beta (TGF-beta)-resistant helper T lymphocyte clones show a concomitant loss of all three types of TGF-beta receptors.

Three ovalbumin-specific T helper cell lines (OVA-7T cells) that differ in their susceptibility to the immunosuppressive effects of transforming growth factor-beta (TGF-beta) were cloned. The frequency of TGF-beta-resistant OVA-7T cell clones correlated with the decline of TGF-beta sensitivity in the original OVA-7T parental cell lines. In TGF-beta-resistant OVA-7T cell clones, TGF-beta inhibited neither the growth of the T cells nor their secretion of granulocyte macrophage CSF. TGF-beta suppressed the expression of c-myc mRNA in OVA-7T-responder but not in OVA-7T-nonresponder cells. TGF-beta resistance was found to be due to a loss of TGF-beta high-affinity binding sites, with an absence of expression of the distinct 54-, 70-, 110-, and 250-kDa surface proteins that bind TGF-beta on TGF-beta-susceptible T cells. Loss of TGF-beta R may enable T cells to escape the negative feedback control provided by TGF-beta secreted from activated T cells during an immune response.

T cell apoptosis induced by interleukin-2 deprivation or transforming growth factor-beta 2: modulation by the phosphatase inhibitors okadaic acid and calyculin A.

The phosphatase inhibitors okadaic acid and calyculin A were used to examine the role of phosphorylation processes in T cell apoptosis induced by interleukin-2 (IL-2) deprivation or transforming growth factor-beta 2 (TGF-beta 2). Okadaic acid and calyculin A inhibited IL-2-driven T cell proliferation and induced apoptosis at concentrations known to inhibit protein phosphatase 1. High concentrations of both agents caused toxic changes of prominent cellular swelling and dilatation of rough endoplasmic reticular profiles. When the T cells were induced to undergo apoptosis by IL-2 deprivation, okadaic acid and calyculin A delayed loss of membrane integrity, nucleosomal size DNA fragmentation, and loss of bcl-2 mRNA. However, T cells deprived of IL-2 in the presence of okadaic acid or calyculin A revealed DNA breaks by in situ DNA end labeling and apoptotic morphology by electron microscopy and failed to show enhanced survival after reexposure to IL-2. Although TGF-beta-mediated signaling is thought to involve the dephosphorylation of specific substrates, okadaic acid and calyculin A not only failed to inhibit, but actually augmented, TGF-beta 2-induced inhibition of T cell proliferation and induction of apoptosis. Exposure to either TGF-beta 2 or the phosphatase inhibitors prevented phosphorylation of the retinoblastoma protein RB. In summary, okadaic acid and calyculin A: (i) induce T cell apoptosis in the presence of IL-2, (ii) allow us to distinguish essential from epiphenomenal features of T cell apoptosis after IL-2 deprivation, and (iii) cooperate with TGF-beta 2 in inducing growth arrest and apoptosis of murine T cells via intracellular cascades that converge in the prevention of RB phosphorylation.

Transforming growth factor-beta 2 induces apoptosis of murine T cell clones without down-regulating bcl-2 mRNA expression.

Transforming growth factor-beta (TGF beta) is a potent immunosuppressive cytokine which inhibits the antigen (Ag)-dependent expansion of T cells both in vitro and in vivo by mechanisms not well defined yet. Here we report that exposure of interleukin (IL)-2-dependent T cell lines to TGF beta 2 results in apoptosis defined by morphology, nucleosomal size DNA fragmentation and in situ DNA end labeling. TGF beta 2-induced T cell apoptosis showed the following characteristics: (1) in contrast to the rapid evolution of apoptosis following IL-2 deprivation, apoptosis of T cells triggered by TGF beta 2 was delayed; (2) cycloheximide prevented TGF beta 2-induced apoptosis of CTLL-2 but not of OVA-7 T helper cells; (3) in contrast to apoptosis following IL-2 deprivation, TGF beta 2-mediated T cell apoptosis was not associated with decreased expression of the proto-oncogenes, bcl-2 or c-myc; (4) TGF beta 2-induced apoptosis was not restricted to IL-2-dependent T cell lines since the IL-4-dependent T cell line, CT.4S, as well as EL4 lymphoma cells, which grow independently of exogenous IL-2, were also susceptible to TGF beta 2-mediated apoptosis. Taken together, these data may present a novel mechanism of TGF beta 2-mediated suppression of T cell expansion in response to Ag and IL-2, the activation of the endogenous death program of apoptosis, which appears to operate independently of direct interactions of TGF beta 2 with the IL-2/IL-2 receptor system.

Cell type-specific regulation of expression of transcription factor AP-2 in neuroectodermal cells.

AP-2 is a cell type-specific DNA-binding transcription factor that regulates selected target genes in vertebrate organisms. Here we investigated cell type-specific expression and regulation of AP-2 in neuroectodermal cell lineages. During retinoic acid (RA)-mediated differentiation of P19 embryonal carcinoma cells into neuroectodermal cell types that include immunohistochemically defined neurons and astrocytes, we observed a strong induction of AP-2 transcripts and protein. In contrast, AP-2 mRNA was not induced in P19 cells which undergo mesoendodermal differentiation in response to 1% dimethylsulfoxide or low concentrations of RA, respectively. The potential of both neurons and astrocytes to express AP-2 was ascertained by using cerebellar neurons and astrocytes derived from newborn mice. Unlike these types of cells, microglial cells do not express AP-2. Dibutyryl cyclic AMP further enhanced levels of AP-2 transcripts in both P19 astrocytes and primary astrocytes which also respond to agents elevating intracellular cAMP (noradrenaline, isoproterenol, forskolin). The cAMP-dependent induction of AP-2 could be blocked by inhibitors of protein kinase A. In contrast to its action in P19 cells, RA had no effect on AP-2 mRNA levels in primary astrocytes. Our results indicate that AP-2 may play a role as a retinoic acid-sensitive regulator during differentiation of neurons and glia from an embryonic neural precursor. Furthermore, AP-2 may be involved in gene transcription in both mature neurons and astrocytes.

Sequence analysis of the promoter region of the glioblastoma derived T cell suppressor factor/transforming growth factor (TGF)-beta 2 gene reveals striking differences to the TGF-beta 1 and -beta 3 genes.

Human glioblastoma cells secrete a factor termed glioblastoma derived T cell suppressor factor (G-TsF) or transforming growth factor beta 2 (TGF-beta 2) which inhibits the response of T cells to mitogenic or antigenic stimulation. In the present study we isolated the promoter region of the G-TsF/TGF-beta 2 gene. The promoter region shares no homology to the promoter of the TGF-beta 1 or the 5' region of the TGF-beta 3 gene and harbours several familiar DNA motifs, including the cytokine-1 region, an octamer-like sequence, Sp1- and AP-2-like elements and a putative NF-kappa B site. In contrast to the TGF-beta 1 gene, the G-TsF/TGF-beta 2 gene contains three TATA-like sequences but lacks an AP-1 site. To understand the cell type specificity of expression of G-TsF/TGF-beta 2, the individual contribution of the DNA elements detected in the promoter has to be analysed in further studies.

Somatic mutation in anti-phosphorylcholine antibodies.

A detailed analysis of the genes and proteins that participate in the murine immune response to PC has provided key insights at the structural level into the phenomenon of somatic mutation in B cells. Most anti-PC antibodies are encoded by 1 VH gene of the S107 subfamily, and 3 VK genes, VKT15 of the VK22 subfamily, VKM3 from the VK8 subfamily, and VK167 from the VK24 subfamily. No mutation was detected in these genes until the 2nd wk after immunization, indicating that mutation is under developmental control. The protein sequences of 73 heavy and light chains derived from the secondary response support the concept of developmental activation of mutation after antigen stimulation. No mutation was found in the IgM antibodies, whereas half of the IgG and IgA antibodies had mutation. Most of the mutated antibodies had higher affinity for antigen than their germline counterparts, which suggests that the major role of somatic mutation is to increase affinity rather than to create new specificities. Nucleotide sequencing established two hallmarks of mutation in immunoglobulin genes: mutations are targeted to a 1 kilobase region surrounding and including the rearranged variable gene, and they occur at an extraordinary frequency of 10(-2) nucleotide substitutions. Mutation is probably caused by DNA repair, and may occur during error-prone repair of nicked DNA around the variable gene or during mismatch repair of misaligned structural intermediates. The elucidation of this remarkable mechanism clearly requires studies of a more dynamic character. Two major questions that need to be answered are: what targets mutation to the variable gene, and what enzymes are involved?