title: Type 2 iodothyronine deiodinase is expressed in human preadipocytes.
abstract: BACKGROUND
  Type 2 iodothyronine deiodinase (D2) is an enzyme that catalyzes the production of triiodothyronine (T3) from thyroxine (T4) and plays a critical role in providing the local intracellular T3. Although D2 is highly expressed in brown adipose tissue, it was thought that D2 is hardly expressed in white adipose tissue. In the present study, we examined whether D2 is expressed in human preadipocytes, using human mesenteric and subcutaneous preadipocytes (HMPA and HSCPA, respectively).
  
  
  METHODS
  HMPA and HSCPA were purchased and cultured in the preadipocyte medium containing 10% fetal bovine serum. We measured D2 activity and mRNA level in HMPA and HSCPA incubated with or without dibutyryl cyclic adenosine monophosphate [(Bu)₂cAMP].
  
  
  RESULTS
  D2 activity and mRNA were detectable in human HMPA and HSCPA. The apparent Michaelis-Menten constant (K(m)) value for T4 in HMPA was 2.1 ± 0.2 nM, and the maximum velocity (V(max)) value was 333.3 ± 28.0 femtomols of I⁻ released/mg protein/hour, respectively. On the other hand, the apparent K(m) value for T4 in HSCPA was 2.0 ± 0.2 nM and the V(max) value was 91.2 ± 8.7 femtomols of I⁻ released/mg protein/hour, respectively. D2 activities in HMPA and HSCPA incubated with 1 mM (Bu)₂cAMP for 24 hours were 7-fold (HMPA) and 3-fold (HSCPA) higher than those without (Bu)₂cAMP, respectively. D2 mRNA levels in HMPA and HSCPA incubated with 1 mM (Bu)₂cAMP for 3 hours were 10-fold (HMPA) and 5-fold (HSCPA) higher than those without (Bu)₂cAMP, respectively.
  
  
  CONCLUSIONS
  In the present study, we have clearly demonstrated that D2 activity and mRNA are present in the human preadipocytes from both mesenteric and subcutaneous adipose tissue. Our experiments are the first ones that identify human preadipocytes as one of the sources of T3 production.
authors.affiliation: Department of Internal Medicine II, Kansai Medical University, Osaka, Japan.
authors.forename: Emiko
authors.initials: E
authors.lastname: Nomura
authors.forename: Nagaoki
authors.initials: N
authors.lastname: Toyoda
authors.forename: Azusa
authors.initials: A
authors.lastname: Harada
authors.forename: Kumiko
authors.initials: K
authors.lastname: Nishimura
authors.forename: Chizuko
authors.initials: C
authors.lastname: Ukita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Morimoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kosaki
authors.forename: Toshiji
authors.initials: T
authors.lastname: Iwasaka
authors.forename: Mitsushige
authors.initials: M
authors.lastname: Nishikawa
mesh_terms: D017667:Adipocytes / Q000201:enzymology*; D002001:Adipose Tissue, Brown / Q000201:enzymology; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000235:genetics*; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D014284:Triiodothyronine / Q000096:biosynthesis
chemical_list: D014284:Triiodothyronine; D007453:Iodide Peroxidase