Type 2 Iodothyronine Deiodinase Is Expressed in Human Preadipocytes

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 (Km) value for T4 in HMPA was 2.1 ± 0.2 nM, and the maximum velocity (Vmax) value was 333.3 ± 28.0 femtomols of I− released/mg protein/hour, respectively. On the ...