Valproic acid and CEBPalpha-mediated regulation of adipokine gene expression in hypothalamic neurons and 3T3-L1 adipocytes.
OBJECTIVE
Valproic acid (VPA) is the drug of choice for treating epilepsy, but has the unwanted effects of inducing weight gain and increasing the risk of developing insulin resistance. The mechanism through which these side effects occur is unknown. VPA inhibits histone deacetylase (HDAC), but also decreases the transcriptional activity of CCAAT enhancer binding protein alpha (CEBPalpha). Given the possible association between VPA, CEBPalpha and adipokine gene regulation, we hypothesized that they would alter the expression of resistin (rstn), fasting-induced adipose factor (fiaf) and suppressor of cytokine signaling-3 (socs-3), genes implicated in the development of leptin and insulin resistance.


METHODS
We investigated the effects of VPA (1 mM; 24 or 48 h) on gene expression using real-time RT-PCR in 3 distinct models: N-1 hypothalamic neurons, 3T3-L1 adipocytes and male CD-1 mice. Subsequently, cells were treated with 5 nM of the more specific HDAC inhibitor trichostatin A (TSA). CEBPalpha expression was also modified in N-1 neurons using either RNA interference (RNAi) or an overexpression vector to evaluate its effects on target gene expression.


RESULTS
In N-1 neurons, VPA induced significant increases in CEBPalpha and socs-3, but inhibited rstn and fiaf gene expression. In contrast, TSA induced rstn and socs-3, but inhibited fiaf. VPA also induced the expression of CEBPalphain 3T3-L1 adipocytes, but had no effect on other target genes, and TSA suppressed fiaf and socs-3.Subsequently, CEBPalpha was overexpressed (24 h) or silenced using RNAi (24 and 48 h) in N-1 neurons. The silencing of CEBPalpha led to significant decreases in rstn mRNA, but increased fiaf and socs-3 expression, whereas its overexpression had the opposite effect. When male CD-1 mice were treated with either a single (100 mg/kg; 24 h), or multiple (200 mg/kg; 72 h) daily injections of VPA, no changes in body weight or gene expression were detected in either hypothalamic or adipose tissues.


CONCLUSIONS
In summary, these experiments reveal a potentially important role for CEBPalpha in the regulation of hypothalamic gene expression in N-1 neurons and suggest that it might modulate central energy metabolism. Although VPA also modified hypothalamic gene expression in vitro, it remains to be determined whether it has similar effects in vivo.
Brown
Russell
R
Department of Obstetrics and Gynaecology, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada.
Imran
Syed A
SA
Ur
Ehud
E
Wilkinson
Michael
M
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000502:physiology; D054392:Adipokines / Q000096:biosynthesis* / Q000235:genetics*; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002461:Cell Line, Transformed; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D007031:Hypothalamus / Q000187:drug effects* / Q000502:physiology; D008297:Male; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D014635:Valproic Acid / Q000494:pharmacology*
D054392:Adipokines; D022763:CCAAT-Enhancer-Binding Protein-alpha; D014635:Valproic Acid