LEPTIN AND UCP1 GENES ARE RECIPROCALLY REGULATED IN BROWN ADIPOSE-TISSUE

In a previous work we showed that only unilocular brown adipocytes exp ress leptin. In order to investigate the relationship between leptin g ene expression, brown adipocyte activity (UCP1) and morphology, we stu died brown adipose tissues of mice (C57BL, female, 7 weeks old) acclim ated at different temperatures (19 degrees C and 28 degrees C). Northe rn blot analysis revealed higher leptin and lower UCP1 mRNA levels in mice exposed to 28 degrees C than in the group acclimated at 19 degree s C. Also protein expression (immunohistochemistry) differed in the tw o groups: at 28 degrees C brown adipocytes were positive for leptin an d only weakly positive for UCP1, while at 19 degrees C they were lepti n-negative and UCP1-positive. In the former group the morphology was m ainly unilocular. Our data suggest that in brown adipocytes of warm-ac climated mice leptin expression is closely related to their hypoactive functional stage, as evidenced by their low level of UCP1 synthesis a nd the morphological rearrangement of the lipid content (unilocularity ).