Antioxidative defense and mitochondrial thermogenic response in brown adipose tissue
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Cold-exposure activates interscapular brown adipose tissue (IBAT) non-shivering thermogenesis that relies primarily on intensification of metabolic rate and uncoupling. During cold-acclimation, uncoupling in IBAT decreases superoxide (O(2) (center dot-)) production and as an adaptive response the activities of manganese and copper, zinc superoxide dismutase (Mn- and CuZn-SOD, respectively) are decreased, as well. However, molecular mechanisms governing this SODs adaptive response are still unsolved. Besides, knowing that NO reinforces IBAT uncoupling, we wondered whether nitric oxide (NO) is taking part in SODs regulation? Mn- and CuZn-SOD mRNA and protein expression, uncoupling protein 1 (UCP1), nitrotyrosine and nuclear factor-kappa B (NF-kappa B) immunolabeling, as well as total SOD (tSOD) activity in IBAT of rats subjected to cold (4 +/- A 1A degrees C) for 1, 3, 7, 12, 21 and 45 days and treated by l-arginine or N (omega)-nitro-l-arginine-methyl ester (l-NAME) were examined. Cold increased UCP1 immunopositivity and decreased tSOD activity during entire cold-acclimation and transiently, (day 3), activated NF-kappa B and increased Mn and CuZn-SOD mRNA expression and nitrotyrosine labeling, suggesting NO involvement in this signaling. However, SODs mRNA expression was decreasing from day 12 till the end of cold-acclimation. l-arginine augmented and prolonged cold-induced UCP1 and nitrotyrosine immunopositivity, NF-kappa B activation and SODs mRNA expression increase, while l-NAME expressed an opposite effect. Related to cold, l-arginine decreased, while l-NAME increased Mn-SOD protein expression. In contrast, neither low temperature nor both treatments applied affected CuZn-SOD protein expression. The results showed that adaptive decrease in SODs activity on uncoupling-decreased O(2) (center dot-) production was achieved already at the level of gene transcription and that NO takes part in the regulation of IBAT SOD isoforms.