title: The Multitarget Ligand 3-Iodothyronamine Modulates β-Adrenergic Receptor 2 Signaling.
abstract: BACKGROUND
  3-Iodothyronamine (3-T1AM), a signaling molecule with structural similarities to thyroid hormones, induces numerous physiological responses including reversible body temperature decline. One target of 3-T1AM is the trace amine-associated receptor 1 (TAAR1), which is a member of the rhodopsin-like family of G protein-coupled receptors (GPCRs). Interestingly, the effects of 3-T1AM remain detectable in TAAR1 knockout mice, suggesting further targets for 3-T1AM such as adrenergic receptors. Therefore, we evaluated whether β-adrenergic receptor 1 (ADRB1) and 2 (ADRB2) signaling is affected by 3-T1AM in HEK293 cells and in human conjunctival epithelial cells (IOBA-NHC), where these receptors are highly expressed endogenously.
  
  
  METHODS
  A label-free EPIC system for prescreening the 3-T1AM-induced effects on ADRB1 and ADRB2 in transfected HEK293 cells was used. In addition, ADRB1 and ADRB2 activation was analyzed using a cyclic AMP assay and a MAPK reporter gene assay. Finally, fluorescence Ca(2+) imaging was utilized to delineate 3-T1AM-induced Ca(2+) signaling.
  
  
  RESULTS
  3-T1AM (10(-5)-10(-10)M) enhanced isoprenaline-induced ADRB2-mediated Gs signaling but not that of ADRB1-mediated signaling. MAPK signaling remained unaffected for both receptors. In IOBA-NHC cells, norepinephrine-induced Ca(2+) influxes were blocked by the nonselective ADRB blocker timolol (10 µM), indicating that ADRBs are most likely linked with Ca(2+) channels. Notably, timolol was also found to block 3-T1AM (10(-5)M)-induced Ca(2+) influx.
  
  
  CONCLUSIONS
  The presented data support that 3-T1AM directly modulates β-adrenergic receptor signaling. The relationship between 3-T1AM and β-adrenergic signaling also reveals a potential therapeutic value for suppressing Ca(2+) channel-mediated inflammation processes, occurring in eye diseases such as conjunctivitis.
authors.affiliation: Institut für Experimentelle Pädiatrische Endokrinologie, Berlin, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Dinter
authors.affiliation: Department of Ophthalmology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Noushafarin
authors.initials: N
authors.lastname: Khajavi
authors.affiliation: Institut für Experimentelle Pädiatrische Endokrinologie, Berlin, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Mühlhaus
authors.affiliation: Institut für Experimentelle Pädiatrische Endokrinologie, Berlin, Germany.
authors.forename: Carolin Leonie
authors.initials: CL
authors.lastname: Wienchol
authors.affiliation: Institut für Biochemie, Molekulare Biochemie, Medizinische Fakultät, University of Leipzig, Leipzig, Germany.
authors.forename: Maxi
authors.initials: M
authors.lastname: Cöster
authors.affiliation: Institut für Biochemie, Molekulare Biochemie, Medizinische Fakultät, University of Leipzig, Leipzig, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hermsdorf
authors.affiliation: Institut für Biochemie, Molekulare Biochemie, Medizinische Fakultät, University of Leipzig, Leipzig, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Stäubert
authors.affiliation: Institut für Experimentelle Endokrinologie, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Josef
authors.initials: J
authors.lastname: Köhrle
authors.affiliation: Institut für Biochemie, Molekulare Biochemie, Medizinische Fakultät, University of Leipzig, Leipzig, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Schöneberg
authors.affiliation: Institut für Experimentelle Pädiatrische Endokrinologie, Berlin, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Kleinau
authors.affiliation: Department of Ophthalmology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mergler
authors.affiliation: Institut für Experimentelle Pädiatrische Endokrinologie, Berlin, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Biebermann
keywords: Calcium channel; Calcium homeostasis; Human conjunctiva; Signaling; Thyronamine; β-Adrenergic receptors