Nathan O'Connor

Weill Cornell Medical College, New York City, NY, United States

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Publications (7)33.16 Total impact

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    ABSTRACT: Pulmonary fibrosis is characterized by an inflammatory response that includes macrophages, neutrophils, lymphocytes, and mast cells. The purpose of this study was to evaluate whether mast cells play a role in initiating pulmonary fibrosis. Pulmonary fibrosis was induced with bleomycin in mast-cell-deficient WBB6F1-W/W(v) (MCD) mice and their congenic controls (WBB6F1-(+)/(+)). Mast cell deficiency protected against bleomycin-induced pulmonary fibrosis, but protection was reversed with the re-introduction of mast cells to the lungs of MCD mice. Two mast cell mediators were identified as fibrogenic: histamine and renin, via angiotensin (ANG II). Both human and rat lung fibroblasts express the histamine H1 and ANG II AT1 receptor subtypes and when activated, they promote proliferation, transforming growth factor β1 secretion, and collagen synthesis. Mast cells appear to be critical to pulmonary fibrosis. Therapeutic blockade of mast cell degranulation and/or histamine and ANG II receptors should attenuate pulmonary fibrosis.
    DNA and cell biology 04/2013; 32(4):206-18. · 2.28 Impact Factor
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    ABSTRACT: Mast cells are associated with inflammation and fibrosis. Whether they protect against or contribute to renal fibrosis is unclear. Based on our previous findings that mast cells can express and secrete active renin, and that angiotensin (ANG II) is profibrotic, we hypothesized that mast cells play a critical role in tubulointerstitial fibrosis. We tested this hypothesis in the 14-day unilateral ureteral obstruction (UUO) model in rats and mast cell-deficient (MCD) mice (WBB6F1-W/Wv) and their congenic controls (CC). In the 14-day UUO rat kidney, mast cell number is increased and they express active renin. Stabilizing mast cells in vivo with administration of cromolyn sodium attenuated the development of tubulointerstitial fibrosis, which was confirmed by measuring newly synthesized pepsin-soluble collagen and blind scoring of fixed trichrome-stained kidney sections accompanied by spectral analysis. Fibrosis was absent in UUO kidneys from MCD mice unlike that observed in the CC mice. Losartan treatment reduced the fibrosis in the CC UUO kidneys. The effects of mast cell degranulation and renin release were tested in the isolated, perfused kidney preparation. Mast cell degranulation led to renin-dependent protracted flow recovery. This demonstrates that mast cell renin is active in situ and the ensuing ANG II can modulate intrarenal vascular resistance in the UUO kidney. Collectively, the data demonstrate that mast cells are critical to the development of renal fibrosis in the 14-day UUO kidney. Since renin is present in human kidney mast cells, our work identifies potential targets in the treatment of renal fibrosis.
    AJP Renal Physiology 09/2011; 302(1):F192-204. · 4.42 Impact Factor
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    ABSTRACT: We previously reported that mast cells express renin, the rate-limiting enzyme in the renin-angiotensin cascade. We have now assessed whether mast cell renin release triggers angiotensin formation in the airway. In isolated rat bronchial rings, mast cell degranulation released enzyme with angiotensin I-forming activity blocked by the selective renin inhibitor BILA2157. Local generation of angiotensin (ANG II) from mast cell renin elicited bronchial smooth muscle contraction mediated by ANG II type 1 receptors (AT(1)R). In a guinea pig model of immediate type hypersensitivity, anaphylactic mast cell degranulation in bronchial rings resulted in ANG II-mediated constriction. As in rat bronchial rings, bronchoconstriction (BC) was inhibited by a renin inhibitor, an AT(1)R blocker, and a mast cell stabilizer. Anaphylactic release of renin, histamine, and beta-hexosaminidase from mast cells was confirmed in the effluent from isolated, perfused guinea pig lung. To relate the significance of this finding to humans, mast cells were isolated from macroscopically normal human lung waste tissue specimens. Sequence analysis of human lung mast cell RNA showed 100% homology between human lung mast cell renin and kidney renin between exons 1 and 10. Furthermore, the renin protein expressed in lung mast cells was enzymatically active. Our results demonstrate the existence of an airway renin-angiotensin system triggered by release of mast-cell renin. The data show that locally produced ANG II is a critical factor governing BC, opening the possibility for novel therapeutic targets in the management of airway disease.
    Proceedings of the National Academy of Sciences 02/2008; 105(4):1315-20. · 9.74 Impact Factor
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    ABSTRACT: High spatial and time resolution single-molecule fluorescence resonance energy transfer measurements have been used to probe the structural and kinetic parameters of transfer RNA (tRNA) movements within the aminoacyl (A) and peptidyl (P) sites of the ribosome. Our investigation of tRNA motions, quantified on wild-type, mutant, and L1-depleted ribosome complexes, reveals a dynamic exchange between three metastable tRNA configurations, one of which is a previously unidentified hybrid state in which only deacylated-tRNA adopts its hybrid (P/E) configuration. This new dynamic information suggests a framework in which the formation of intermediate states in the translocation process is achieved through global conformational rearrangements of the ribosome particle.
    Molecular Cell 03/2007; 25(4):505-17. · 15.28 Impact Factor
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    Nathan O'Connor, Randi B Silver
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    ABSTRACT: This chapter discusses the use of ratiometric fluorescent probes for measuring intracellular pH (pHi) and Cai(2+) concentration at the single cell level. The development of sensitive and stable probes for monitoring pHi and Cai(2+) in living cells has provided the scientists with invaluable tools for studying a multitude of cellular processes. These probes afford a noninvasive and semiquantitative assessment of pHi and Cai(2+), eliminating the need to impale cells with microelectrodes. The development and availability of membrane permeant Cai(2+)- and pH-specific fluorescent probes coupled to major advances in the technology and design of low-light-level charge-coupled devices geared toward biological applications, and improved microscope optics, have made it possible to visualize a two-dimensional fluorescence signal that is related to Cai(2+) and pHi. The chapter describes the basis for using dual excitation ratio imaging and tries to provide a framework for understanding and developing the technique for investigating the roles of Cai(2+) and pHi in cellular processes. The technique of quantitative ratio imaging for the measurement of pHi and Cai(2+) has revolutionized the field of cell physiology. Using the proper equipment and choosing the right dyes for the experimental needs should provide reliable and reproducible results. More importantly, the amount of data produced from each experiment, when analyzing pHi and Cai(2+) on an individual cell basis, yields valuable information on the heterogeneity of cellular responses.
    Methods in cell biology 02/2007; 81:415-33. · 1.44 Impact Factor
  • Nathan O'Connor, Randi B. Silver
    Methods in Cell Biology - METHOD CELL BIOL. 01/2007; 81:415-433.
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    ABSTRACT: τH2 fMet-Phe 59.5±1.7 18.6±1.2 21.9±1.3 Met-Phe 60.9±2.2 18.3±1.5 20.8±1.6 Phe 72.1±1.2 13.0±0.80 14.9±0.98 Laboratory Strains fMet-Phe2 52.9±1.6 21.6±1.1 25.5±1.3 ΔL13,4 73.4 ±1.6 11.6±0.97 15.0±1.3 G2252C2,4 17.4±1.2 28.0±1.2 54.7±1.6 G2553C2,4 19.8±1.4 43.1±1.7 37.1±1.7

Publication Stats

163 Citations
33.16 Total Impact Points


  • 2008–2013
    • Weill Cornell Medical College
      • Department of Physiology and Biophysics
      New York City, NY, United States
  • 2007
    • Cornell University
      • Department of Physiology and Biophysics
      Ithaca, NY, United States