Abstract
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.
Authors
Yoshiaki Tsutsumi, Hiroaki Matsubara, Hiroya Masaki, Hiroki Kurihara, Satoshi Murasawa, Shinji Takai, Mizuo Miyazaki, Yoshihisa Nozawa, Ryoji Ozono, Keigo Nakagawa, Takeshi Miwa, Noritaka Kawada, Yasukiyo Mori, Yasunobu Shibasaki, Yohko Tanaka, Soichiro Fujiyama, Yohko Koyama, Atsuko Fujiyama, Hakuo Takahashi, Toshiji Iwasaka
Abstract
Nitric oxide (NO) inhalation has been reported to increase the oxygen affinity of sickle cell erythrocytes. Also, proposed allosteric mechanisms for hemoglobin, based on S-nitrosation of β-chain cysteine 93, raise the possibilty of altering the pathophysiology of sickle cell disease by inhibiting polymerization or by increasing NO delivery to the tissue. We studied the effects of a 2-hour treatment, using varying concentrations of inhaled NO. Oxygen affinity, as measured by P50, did not respond to inhaled NO, either in controls or in individuals with sickle cell disease. At baseline, the arterial and venous levels of nitrosylated hemoglobin were not significantly different, but NO inhalation led to a dose-dependent increase in mean nitrosylated hemoglobin, and at the highest dosage, a significant arterial-venous difference emerged. The levels of nitrosylated hemoglobin are too low to affect overall hemoglobin oxygen affinity, but augmented NO transport to the microvasculature seems a promising strategy for improving microvascular perfusion.
Authors
Mark T. Gladwin, Alan N. Schechter, James H. Shelhamer, Lewis K. Pannell, Deirdre A. Conway, Borys W. Hrinczenko, James S. Nichols, Margaret E. Pease-Fye, Constance T. Noguchi, Griffin P. Rodgers, Frederick P. Ognibene
Abstract
We found that the plasma of patients with active systemic lupus erythematosus (SLE) could induce a human B-cell line (Ramos) to express high levels of immune accessory molecules that are commonly found on blood B cells of patients with active SLE. The ability of SLE plasma to induce such phenotypic changes could be abrogated by neutralizing antibodies specific for the CD40 ligand (CD154) but not by antibodies to TNF-α. Immunoprecipitation studies with anti-CD154 identified a 20-kDa protein in the plasma of SLE patients with active disease, but not in plasma of normal donors, indicating that such plasma contained soluble CD154 (sCD154). Using a quantitative ELISA method, we found that the plasma of patients with active disease had levels of sCD154 that were significantly higher than those found in plasma of normal donors. Levels of CD154 transcripts in SLE blood lymphocytes correlated with the relative concentrations of sCD154 found in SLE plasma. Furthermore, plasma levels of sCD154 correlated with the titers of anti–double-stranded DNA autoantibody and with clinical disease activity. These studies indicate that sCD154 of patients with SLE may act as a functional ligand for CD40 that is associated with SLE disease activity.
Authors
Kazunori Kato, Ernesto Santana-Sahagún, Laura Z. Rassenti, Michael H. Weisman, Naoto Tamura, Shigeto Kobayashi, Hiroshi Hashimoto, Thomas J. Kipps
Abstract
Human rhinoviruses (HRVs) are the predominant cause of the common cold. Although this disease is per se rather harmless, HRV infection is considered to set the stage for more dangerous pathogens in vivo. Here we demonstrate that HRV-14, a member of the major group HRV family, can efficiently inhibit antigen-induced T-cell proliferation and T-cell responses to allogeneic monocytes. HRV-14 triggered a significant downregulation of MHC class II molecules on monocytes. Moreover, supernatants from monocytes cultured in the presence of HRV-14 strongly reduced the allogeneic T-cell stimulatory property of untreated monocytes and monocyte-derived dendritic cells (md-DCs), whereas Epstein Barr virus–transformed B-lymphoblastoid cells were not sensitive. Analysis of the supernatant revealed that HRV-14 induced the production of significant amounts of the immunosuppressive cytokine IL-10. The important T-cell stimulatory cytokine IL-12 or the proinflammatory cytokines IL-1β or TNF-α were not detected or were only minimally detected. Finally, monocytes pretreated with HRV-14 were greatly inhibited in their production of IL-12 upon stimulation with IFN-γ/LPS. These observations suggest that altered cytokine production in mononuclear phagocytes upon interaction with HRV downmodulates appropriate immune responses during the viral infection.
Authors
Johannes Stöckl, Helga Vetr, Otto Majdic, Gerhard Zlabinger, Ernst Kuechler, Walter Knapp
Abstract
The autosomal recessive form of type I pseudohypoaldosteronism (PHA-I) is an inherited salt-losing syndrome resulting from diminution-of-function mutations in the 3 subunits of the epithelial Na+ channel (ENaC). A PHA-I stop mutation (αR508stop) of the ENaC α subunit is predicted to lack the second transmembrane domain and the intracellular COOH-terminus, regions of the protein involved in pore function. Nonetheless, we observed a measurable Na+ current in Xenopus laevis oocytes that coexpress the β and γ subunits with the truncated α subunit. The mutant α was coassembled with β and γ subunits and was present at the cell surface at a lower density, consistent with the lower Na+ current seen in oocytes with the truncated α subunit. The single-channel Na+ conductance for the mutant channel was only slightly decreased, and the appearance of the macroscopic currents was delayed by 48 hours with respect to wild-type. Our data suggest novel roles for the α subunit in the assembly and targeting of an active channel to the cell surface, and suggest that channel pores consisting of only the β and γ subunits can provide significant residual activity. This activity may be sufficient to explain the absence of a severe pulmonary phenotype in patients with PHA-I.
Authors
Olivier Bonny, Ahmed Chraibi, Jan Loffing, Nicole Fowler Jaeger, Stefan Gründer, Jean-Daniel Horisberger, Bernard C. Rossier
Abstract
Leptin administration inhibits diencephalic nitric oxide synthase (NOS) activity and increases brain serotonin (5-HT) metabolism in mice. We evaluated food intake, body-weight gain, diencephalic NOS activity, and diencephalic content of tryptophan (TRP), 5-HT, hydroxyindoleacetic acid (5-HIAA), and 5-HIAA/5-HT ratio after intracerebroventricular (ICV) or intraperitoneal (IP) leptin injection in mice. Five consecutive days of ICV or IP leptin injections induced a significant reduction in neuronal NOS (nNOS) activity, and caused a dose-dependent increase of 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio. Diencephalic 5-HT metabolism showed a significant increase in 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio 3 hours after a single leptin injection. This effect was maintained for 3 hours and had disappeared by 12 hours after injection. After a single IP leptin injection, the peak for 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio was achieved at 6 hours. Single injections of ICV or IP leptin significantly increased diencephalic 5-HT content. Leptin-induced 5-HT increase was antagonized by the coadministration of L-arginine only when the latter was ICV injected, whereas D-arginine did not influence leptin effects on brain 5-HT content. Finally, in nNOS-knockout mice, the appetite-suppressant activity of leptin was strongly reduced, and the leptin-induced increase in brain 5-HT metabolism was completely abolished. Our results indicate that the L-arginine/NO pathway is involved in mediating leptin effects on feeding behavior, and demonstrate that nNOS activity is required for the effects of leptin on brain 5-HT turnover.
Authors
Gioacchino Calapai, Francesco Corica, Andrea Corsonello, Lidia Sautebin, Massimo Di Rosa, Giuseppe M. Campo, Michele Buemi, Vittorio Nicita Mauro, Achille P. Caputi
Abstract
The renal Na+/phosphate (Pi) cotransporter Npt2 is expressed in the brush border membrane (BBM) of proximal tubular cells. We examined the effect of Npt2 gene knockout on age-dependent BBM Na+/Pi cotransport, expression of Na+/Pi cotransporter genes Npt1, Glvr-1, and Ram-1, and the adaptive response to chronic Pi deprivation. Na+/Pi cotransport declines with age in wild-type mice (Npt2+/+), but not in mice homozygous for the disrupted Npt2 allele (Npt2–/–). At all ages, Na+/Pi cotransport in Npt2–/– mice is approximately 15% of that in Npt2+/+ littermates. Only Npt1 mRNA abundance increases with age in Npt2+/+ mice, whereas Npt1, Glvr-1, and Ram-1 mRNAs show an age-dependent increase in Npt2–/– mice. Pi deprivation significantly increases Na+/Pi cotransport, Npt2 protein, and mRNA in Npt2+/+ mice. In contrast, Pi-deprived Npt2–/– mice fail to show the adaptive increase in transport despite exhibiting a fall in serum Pi. We conclude that (a) Npt2 is a major determinant of BBM Na+/Pi cotransport; (b) the age-dependent increase in Npt1, Glvr-1, and Ram-1 mRNAs in Npt2–/– mice is insufficient to compensate for loss of Npt2; and (c) Npt2 is essential for the adaptive BBM Na+/Pi cotransport response to Pi deprivation.
Authors
Hannah M. Hoag, Josée Martel, Claude Gauthier, Harriet S. Tenenhouse
Abstract
Tuberous sclerosis (TSC) is an autosomal dominant genetic disorder in which benign hamartomas develop in multiple organs, caused by mutations in either TSC1 or TSC2. We developed a murine model of Tsc2 disease using a gene targeting approach. Tsc2-null embryos die at embryonic days 9.5–12.5 from hepatic hypoplasia. Tsc2 heterozygotes display 100% incidence of multiple bilateral renal cystadenomas, 50% incidence of liver hemangiomas, and 32% incidence of lung adenomas by 15 months of age. Progression to renal carcinoma, fatal bleeding from the liver hemangiomas, and extremity angiosarcomas all occur at a rate of less than 10%. The renal cystadenomas develop from intercalated cells of the cortical collecting duct and uniformly express gelsolin at high levels, enabling detection of early neoplastic lesions. The tumor expression pattern of the mice is influenced by genetic background, with fewer large renal cystadenomas in the outbred Black Swiss background and more angiosarcomas in 129/SvJae chimeric mice. The slow growth of the tumors in the heterozygote mice matches the limited growth potential of the great majority of TSC hamartomas, and the influence of genetic background on phenotype correlates with the marked variability in expression of TSC seen in patients.
Authors
Hiroaki Onda, Andreas Lueck, Peter W. Marks, Henry B. Warren, David J. Kwiatkowski
Abstract
Guillain-Barré syndrome and its variant, Miller-Fisher syndrome, are acute, postinfectious, autoimmune neuropathies that frequently follow Campylobacter jejuni enteritis. The pathogenesis is believed to involve molecular mimicry between sialylated epitopes on C. jejuni LPSs and neural gangliosides. More than 90% of Miller-Fisher syndrome cases have serum anti-GQ1b and anti-GT1a ganglioside antibodies that may also react with other disialylated gangliosides including GD3 and GD1b. Structural studies on LPS from neuropathy-associated C. jejuni strains have revealed GT1a-like and GD3-like core oligosaccharides. To determine whether this structural mimicry results in pathogenic autoantibodies, we immunized mice with GT1a/GD3-like C. jejuni LPS and then cloned mAb’s that reacted with both the immunizing LPS and GQ1b/GT1a/GD3 gangliosides. Immunohistology demonstrated antibody binding to ganglioside-rich sites including motor nerve terminals. In ex vivo electrophysiological studies of nerve terminal function, application of antibodies either ex vivo or in vivo via passive immunization induced massive quantal release of acetylcholine, followed by neurotransmission block. This effect was complement-dependent and associated with extensive deposits of IgM and C3c at nerve terminals. These data provide strong support for the molecular mimicry hypothesis as a mechanism for the induction of cross-reactive pathogenic anti-ganglioside/LPS antibodies in postinfectious neuropathies.
Authors
Carl S. Goodyear, Graham M. O’Hanlon, Jaap J. Plomp, Eric R. Wagner, Ian Morrison, Jean Veitch, Lynne Cochrane, Roland W. M. Bullens, Peter C. Molenaar, Joe Conner, Hugh J. Willison
Abstract
In vitro, fibroblast growth factor-2 (FGF2) has been implicated in cardiomyocyte growth and reexpression of fetal contractile genes, both markers of hypertrophy. However, its in vivo role in cardiac hypertrophy during pressure overload is not well characterized. Mice with or without FGF2 (Fgf2+/+ and Fgf2–/–, respectively) were subjected to transverse aortic coarctation (AC). Left ventricular (LV) mass and wall thickness were assessed by echocardiography preoperatively and once a week postoperatively for 10 weeks. In vivo LV function during dobutamine stimulation, cardiomyocyte cross-sectional area, and recapitulation of fetal cardiac genes were also measured. AC Fgf2–/– mice develop significantly less hypertrophy (4–24% increase) compared with AC Fgf2+/+ mice (41–52% increase). Cardiomyocyte cross-sectional area is significantly reduced in AC Fgf2–/– mice. Noncoarcted (NC) and AC Fgf2–/– mice have similar β-adrenergic responses, but those of AC Fgf2+/+ mice are blunted. A lack of mitotic growth in both AC Fgf2+/+ and Fgf2–/– hearts indicates a hypertrophic response of cardiomyocytes. Consequently, FGF2 plays a major role in cardiac hypertrophy. Comparison of α- and β-cardiac myosin heavy chain mRNA and protein levels in NC and AC Fgf2+/+ and Fgf2–/– mice indicates that myosin heavy chain composition depends on hemodynamic stress rather than on FGF2 or hypertrophy, and that isoform switching is transcriptionally, not posttranscriptionally, regulated.
Authors
Jo El J. Schultz, Sandra A. Witt, Michelle L. Nieman, Peter J. Reiser, Sandra J. Engle, Ming Zhou, Sharon A. Pawlowski, John N. Lorenz, Thomas R. Kimball, Thomas Doetschman
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