Abstract
HIV-1–specific cytotoxic T-lymphocyte (CTL) responses have been detected at a low frequency in many HIV-1–exposed, persistently seronegative (HEPS) subjects. However, it is unclear how CTLs could protect against HIV acquisition in HEPS subjects, when high levels of circulating CTL fail to prevent disease progression in most seropositive subjects. To address this issue we studied CD8+ lymphocyte responses to a panel of HIV-1 CTL epitopes in 91 HEPS and 87 HIV-1–infected Nairobi sex workers. HIV-specific responses in seropositive women focused strongly on epitopes rarely or never recognized in HEPS subjects, who targeted epitopes that were subdominant or unrecognized in infected women. These differences in epitope specificity were restricted by only those HLA class I alleles that are associated with a reduced risk of HIV-1 infection in this cohort. Late seroconversion in HEPS donors was associated with a switch in epitope specificity and/or immunodominance to those epitopes preferentially recognized by HIV-1–infected women. The likelihood of detecting HIV-1–specific responses in HEPS women increased with the duration of viral exposure, suggesting that HIV-1–specific CD8+ responses are acquired over time. The association between differential recognition of distinct CTL epitopes and protection from HIV-1 infection may have significant implications for vaccine design.
Authors
Rupert Kaul, Tao Dong, Francis A. Plummer, Joshua Kimani, Timothy Rostron, Peter Kiama, Ephantus Njagi, Erastus Irungu, Bashir Farah, Julius Oyugi, Rana Chakraborty, Kelly S. MacDonald, Job J. Bwayo, Andrew McMichael, Sarah L. Rowland-Jones
Abstract
To investigate the physiological function of syntaxin 4 in the regulation of GLUT4 vesicle trafficking, we used homologous recombination to generate syntaxin 4–knockout mice. Homozygotic disruption of the syntaxin 4 gene results in early embryonic lethality, whereas heterozygous knockout mice, Syn4+/–, had normal viability with no significant impairment in growth, development, or reproduction. However, the Syn4+/– mice manifested impaired glucose tolerance with a 50% reduction in whole-body glucose uptake. This defect was attributed to a 50% reduction in skeletal muscle glucose transport determined by 2-deoxyglucose uptake during hyperinsulinemic-euglycemic clamp procedures. In parallel, insulin-stimulated GLUT4 translocation in skeletal muscle was also significantly reduced in these mice. In contrast, Syn4+/– mice displayed normal insulin-stimulated glucose uptake and metabolism in adipose tissue and liver. Together, these data demonstrate that syntaxin 4 plays a critical physiological role in insulin-stimulated glucose uptake in skeletal muscle. Furthermore, reduction in syntaxin 4 protein levels in this tissue can account for the impairment in whole-body insulin-stimulated glucose metabolism in this animal model.
Authors
Chunmei Yang, Kenneth J. Coker, Jason K. Kim, Silvia Mora, Debbie C. Thurmond, Ann C. Davis, Baoli Yang, Roger A. Williamson, Gerald I. Shulman, Jeffrey E. Pessin
Abstract
Tight junctions regulate paracellular conductance and ionic selectivity. These properties vary among epithelia but the molecular basis of this variation remains unknown. To test whether members of the claudin family of tight junction proteins influence paracellular ionic selectivity, we expressed human claudin-4 in cultured MDCK cells using an inducible promoter. Overexpression increased the complexity of tight junction strands visible by freeze-fracture microscopy without affecting the levels of claudin-1, -2, or -3, occludin, or ZO-1. A decrease in conductance correlated directly with the kinetics of claudin-4 induction. Dilution potentials revealed that the decrease in paracellular conductance resulted from a selective decrease in Na+ permeability without a significant effect on Cl– permeability. Flux for an uncharged solute, mannitol, and the rank order of permeabilities for the alkali metal cations were unchanged. A paracellular site for these effects was supported by the lack of apical/basal directionality of the dilution potentials, the linearity of current-voltage relationships, and the lack of influence of inhibitors of major transcellular transporters. These results provide, to our knowledge, the first direct demonstration of the ability of a claudin to influence paracellular ion selectivity and support a role for the claudins in creating selective channels through the tight-junction barrier.
Authors
Christina Van Itallie, Christoph Rahner, James Melvin Anderson
Abstract
The pathogenetic basis for diabetic neuropathy has been enigmatic. Using two different animal models of diabetes, we have investigated the hypothesis that experimental diabetic neuropathy results from destruction of the vasa nervorum and can be reversed by administration of an angiogenic growth factor. Nerve blood flow, as measured by laser Doppler imaging or direct detection of a locally administered fluorescent lectin analogue, was markedly attenuated in rats with streptozotocin-induced diabetes, consistent with a profound reduction in the number of vessels observed. A severe peripheral neuropathy developed in parallel, characterized by significant slowing of motor and sensory nerve conduction velocities, compared with nondiabetic control animals. In contrast, 4 weeks after intramuscular gene transfer of plasmid DNA encoding VEGF-1 or VEGF-2, vascularity and blood flow in the nerves of treated animals were similar to those of nondiabetic control rats; constitutive overexpression of both transgenes resulted in restoration of large and small fiber peripheral nerve function. Similar experiments performed in a rabbit model of alloxan-induced diabetes produced comparable results. These findings support the notion that diabetic neuropathy results from microvascular ischemia involving the vasa nervorum and suggest the feasibility of a novel treatment strategy for patients in whom peripheral neuropathy constitutes a secondary complication of diabetes.
Authors
Peter Schratzberger, Dirk H. Walter, Kilian Rittig, Ferdinand H. Bahlmann, Roberto Pola, Cynthia Curry, Marcy Silver, Joseph G. Krainin, David H. Weinberg, Allan H. Ropper, Jeffrey M. Isner
Abstract
The relationship between abnormal cell proliferation and aberrant control of hormonal secretion is a fundamental and poorly understood issue in endocrine cell neoplasia. Transgenic mice with parathyroid-targeted overexpression of the cyclin D1 oncogene, modeling a gene rearrangement found in human tumors, were created to determine whether a primary defect in this cell-cycle regulator can cause an abnormal relationship between serum calcium and parathyroid hormone response, as is typical of human primary hyperparathyroidism. We also sought to develop an animal model of hyperparathyroidism and to examine directly cyclin D1’s role in parathyroid tumorigenesis. Parathyroid hormone gene regulatory region–cyclin D1 (PTH–cyclin D1) mice not only developed abnormal parathyroid cell proliferation, but also developed chronic biochemical hyperparathyroidism with characteristic abnormalities in bone and, notably, a shift in the relationship between serum calcium and PTH. Thus, this animal model of human primary hyperparathyroidism provides direct experimental evidence that overexpression of the cyclin D1 oncogene can drive excessive parathyroid cell proliferation and that this proliferative defect need not occur solely as a downstream consequence of a defect in parathyroid hormone secretory control by serum calcium, as had been hypothesized. Instead, primary deregulation of cell-growth pathways can cause both the hypercellularity and abnormal control of hormonal secretion that are almost inevitably linked together in this common disorder.
Authors
Yasuo Imanishi, Yoshitaka Hosokawa, Katsuhiko Yoshimoto, Ernestina Schipani, Sanjay Mallya, Alexandros Papanikolaou, Olga Kifor, Takehiko Tokura, Marilyn Sablosky, Felicia Ledgard, Gloria Gronowicz, Timothy C. Wang, Emmett V. Schmidt, Charles Hall, Edward M. Brown, Roderick Bronson, Andrew Arnold
Abstract
Elevated serum levels of uric acid have been associated with an increased risk for gout, hypertension, cardiovascular disease, and renal failure. The molecular mechanisms for the diminished excretion of urate in these disorders, however, remain poorly understood. Human galectin 9, which is highly homologous to the rat urate transporter rUAT, has been reported to be a secreted or cytosolic protein. We provide data that galectin 9 is hUAT, the first identified human urate transporter. hUAT is a highly selective urate ion channel when inserted in lipid bilayers. When expressed in renal epithelial cells it is an integral plasma membrane protein with at least two transmembrane domains. The gene for hUAT consists of 11 exons and is mapped to chromosome 17; a highly homologous gene, hUAT2, maps to a nearby region of chromosome 17 and is also likely to be a urate transporter. hUAT is expressed in a wide variety of tissues and is present in at least three isoforms; hUAT2 is less widely expressed at severalfold lower levels than hUAT. Further knowledge about the functions of hUAT, its isoforms, and hUAT2, as well as mutational analysis of hUAT1 and hUAT2 in individuals or families with hyperuricemia, should significantly improve our understanding of the molecular mechanisms of urate homeostasis.
Authors
Michael S. Lipkowitz, Edgar Leal-Pinto, Joshua Z. Rappoport, Vesna Najfeld, Ruth G. Abramson
Abstract
Degradation of ECM, particularly interstitial collagen, promotes plaque instability, rendering atheroma prone to rupture. Previous studies implicated matrix metalloproteinases (MMPs) in these processes, suggesting that dysregulated MMP activity, probably due to imbalance with endogenous inhibitors, promotes complications of atherosclerosis. We report here that the serine proteinase inhibitor tissue factor pathway inhibitor-2 (TFPI-2) can function as an MMP inhibitor. TFPI-2 diminished the ability of the interstitial collagenases MMP-1 and MMP-13 to degrade triple-helical collagen, the primary load-bearing molecule of the ECM within human atheroma. In addition, TFPI-2 also reduced the activity of the gelatinases MMP-2 and MMP-9. In contrast to the “classical” tissue inhibitors of MMPs (TIMPs), TFPI-2 expression in situ correlated inversely with MMP levels in human atheroma. TFPI-2 colocalized primarily with smooth muscle cells in the normal media as well as the plaque’s fibrous cap. Conversely, the macrophage-enriched shoulder region, the prototypical site of matrix degradation and plaque rupture, stained only weakly for TFPI-2 but intensely for gelatinases and interstitial collagenases. Evidently, human mononuclear phagocytes, an abundant source of MMPs within human atheroma, lost their ability to express this inhibitor during differentiation in vitro. These findings establish a new, anti-inflammatory function of TFPI-2 of potential pathophysiological significance for human diseases, including atherosclerosis.
Authors
Michael P. Herman, Galina K. Sukhova, Walter Kisiel, Don Foster, Marilyn R. Kehry, Peter Libby, Uwe Schönbeck
Abstract
To study the effects of IL-1α in arthritis, we generated human IL-1α (hIL-1α). Transgenic mice expressed hIL-1α mRNA in various organs, had high serum levels of hIL-1α, and developed a severe polyarthritic phenotype at 4 weeks of age. Not only bone marrow cells but also synoviocytes from knee joints produced biologically active hIL-1α. Synovitis started 2 weeks after birth, and 8-week-old mice showed hyperplasia of the synovial lining layer, the formation of hyperplastic synovium (pannus) and, ultimately, destruction of cartilage. Hyperplasia of the synovial lining was due to the accumulation of macrophage-like cells expressing F4/80 molecules. hIL-1α was widely distributed in macrophage- and fibroblast-like cells of the synovial lining cells, as well as synovial fluid monocytes. T and B cells were rare in the synovial fluid, and analysis of marker expression suggests that synoviocytes were directly histolytic and did not act as antigen-presenting cells. In the joints of these mice, we found elevated levels of cells of the monocyte/macrophage and granulocyte lineages and of polymorphonuclear neutrophils (PMNs), most of which expressed Gr-1, indicating that they were mature, tissue-degrading PMNs. Cultured synoviocytes and PMNs from these animals overexpress GM-CSF, suggesting that the hematopoietic changes induced by IL-1 and the consequent PMN activation and joint destruction are mediated by this cytokine.
Authors
Yasuo Niki, Harumoto Yamada, Shuhji Seki, Toshiyuki Kikuchi, Hironari Takaishi, Yoshiaki Toyama, Kyosuke Fujikawa, Norihiro Tada
Abstract
Osteoclastic bone resorption requires cell-matrix contact, an event mediated by the αvβ3 integrin. The structural components of the integrin that mediate osteoclast function are, however, not in hand. To address this issue, we generated mice lacking the β3 integrin gene, which have dysfunctional osteoclasts. Here, we show the full rescue of β3–/– osteoclast function following expression of a full-length β3 integrin. In contrast, truncated β3, lacking a cytoplasmic domain (hβ3Δc), is completely ineffective in restoring function to β3–/– osteoclasts. To identify the components of the β3 cytoplasmic domain regulating osteoclast function, we generated six point mutants known, in other circumstances, to mediate β integrin signaling. Of the six, only the S752P substitution, which also characterizes a form of the human bleeding disorder Glanzmann’s thrombasthenia, fails to rescue β3–/– osteoclasts or restore ligand-activated signaling in the form of c-src activation. Interestingly, the double mutation Y747F/Y759F, which disrupts platelet function, does not affect the osteoclast. Thus similarities and distinctions exist in the mechanisms by which the β3 integrin regulates platelets and osteoclasts.
Authors
Xu Feng, Deborah V. Novack, Roberta Faccio, Daniel S. Ory, Kunihiko Aya, Martin I. Boyer, Kevin P. McHugh, F. Patrick Ross, Steven L. Teitelbaum
Abstract
We sought to determine whether mice deficient in the proinflammatory caspase-1, which cleaves precursors of IL-1β and IL-18, were protected against ischemic acute renal failure (ARF). Caspase-1–/– mice developed less ischemic ARF as judged by renal function and renal histology. These animals had significantly reduced blood urea nitrogen and serum creatinine levels and a lower morphological tubular necrosis score than did wild-type mice with ischemic ARF. Since caspase-1 activates IL-18, lack of mature IL-18 might protect these caspase-1–/– mice from ARF. In wild-type animals, we found that ARF causes kidney IL-18 levels to more than double and induces the conversion of the IL-18 precursor to the mature form. This conversion is not observed in caspase-1–/– ARF mice or sham-operated controls. We then injected wild-type mice with IL-18–neutralizing antiserum before the ischemic insult and found a similar degree of protection from ARF as seen in caspase-1–/– mice. In addition, we observed a fivefold increase in myeloperoxidase activity in control mice with ARF, but no such increase in caspase-1–/– or IL-18 antiserum–treated mice. Finally, we confirmed histologically that caspase-1–/– mice show decreased neutrophil infiltration, indicating that the deleterious role of IL-18 in ischemic ARF may be due to increased neutrophil infiltration.
Authors
Vyacheslav Y. Melnikov, Tevfik Ecder, Giamila Fantuzzi, Britta Siegmund, M. Scott Lucia, Charles A. Dinarello, Robert W. Schrier, Charles L. Edelstein
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