Pref-1 (pre-adipocyte factor-1) is known to play a central role in regulating white adipocyte differentiation, but the role of Pref-1 in BAT (brown adipose tissue) has not been analysed. In the present study we found that Pref-1 expression is high in fetal BAT and declines progressively after birth. However, Pref-1-null mice showed unaltered fetal development of BAT, but exhibited signs of over-activation of BAT thermogenesis in the post-natal period. In C/EBP (CCAAT/enhancer-binding protein) α-null mice, a rodent model of impaired fetal BAT differentiation, Pref-1 was dramatically overexpressed, in association with reduced expression of the Ucp1 (uncoupling protein 1) gene, a BAT-specific marker of thermogenic differentiation. In brown adipocyte cell culture models, Pref-1 was mostly expressed in pre-adipocytes and declined with brown adipocyte differentiation. The transcription factor C/EBPδ activated the Pref-1 gene transcription in brown adipocytes, through binding to the proximal promoter region. Accordingly, siRNA (small interfering RNA)-induced C/EBPδ knockdown led to reduced Pref-1 gene expression. This effect is consistent with the observed overexpression of C/EBPδ in C/EBPα-null BAT and high expression of C/EBPδ in brown pre-adipocytes. Dexamethasone treatment of brown pre-adipocytes suppressed Pref-1 down-regulation occurring throughout the brown adipocyte differentiation process, increased the expression of C/EBPδ and strongly impaired expression of the thermogenic markers UCP1 and PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator-α]. However, it did not alter normal fat accumulation or expression of non-BAT-specific genes. Collectively, these results specifically implicate Pref-1 in controlling the thermogenic gene expression program in BAT, and identify C/EBPδ as a novel transcriptional regulator of Pref-1 gene expression that may be related to the specific role of glucocorticoids in BAT differentiation.
Background/Aims: Uncoupling protein-3 (UCP3) is expressed in liver only under conditions of high fatty acid catabolism. However, the specific role of UCP3 in liver mitochondria and overall hepatic function is still poorly known. Methods: A model of “in vivo” induction of UCP3 expression in mouse liver mitochondria via a tail-vein injection of a recombinant adenoviral vector was developed. The effects on liver mitochondrial bioenergetics and permeability transition, liver gene expression, and systemic metabolism were then determined. Results: UCP3 expression in liver did not cause basal, non-specific, uncoupling but led to a stimulation of palmitate-induced state 4 respiration. UCP3 expression in liver also caused an increase in the expression of certain genes involved in lipid catabolism and metabolic response to starvation (e.g. medium chain acyl-CoA-dehydrogenase or peroxisome proliferator-activated receptor-γ co-activator-1α). UCP3 also conferred to liver mitochondria an enhanced sensitivity to classical inducers of permeability transition, such as calcium and carboxyatractylate. Conclusion: UCP3 expression in liver exerts direct actions on mitochondrial activity, favoring fatty acid-induced uncoupling and sensitizing mitochondria to permeability transition, as well as causing retrograde signaling to nuclear gene expression consistent with favoring lipid catabolism and oxidative metabolism.
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