Valproic Acid and CEBPα-Mediated Regulation of Adipokine Gene Expression in Hypothalamic Neurons and 3T3-L1 Adipocytes

Abstract

Background/Aims: 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 α (CEBPα). Given the possible association between VPA, CEBPα 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). CEBPα 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 CEBPα 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 CEBPαin 3T3-L1 adipocytes, but had no effect on other target genes, and TSA suppressed fiaf and socs-3.Subsequently, CEBPα was overexpressed (24 h) or silenced using RNAi (24 and 48 h) in N-1 neurons. The silencing of CEBPα 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 CEBPα 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.

Tissue-specific effects of valsartan onrstnandfiafgene expression in theob/obmouse

“…36,49,50,52 In fact, there is now good evidence for a local RAS within adipose tissue that appears to regulate adipose tissue growth, metabolism and differentiation. 14,40 These observations are consistent with the identification of angiotensin II receptor expression in human and rodent adipocytes. 15,16 The RAS also appears to be a critical modulator of triglyceride metabolism and cellular differentiation in adipose tissue, 50 where it significantly impacts adipokine gene regulation.…”

Comment on: Kim et al. (2010) Hypothalamic Angptl4/Fiaf Is a Novel Regulator of Food Intake and Body Weight. Diabetes;59:2772–2780

“…(1) complements our own previously published studies where we quantified fiaf mRNA in cultured hypothalamic neurons (5,6). Moreover, we provided evidence for the CCAAT/enhancer binding protein ␣-dependent regulation of hypothalamic-derived fiaf (6), a transcription factor implicated in the regulation of proinflammmatory processes within the central nervous system.…”

Inactivation of Histone Deacetylase 1 (HDAC1) But Not HDAC2 Is Required for the Glucocorticoid-Dependent CCAAT/Enhancer-Binding Protein α (C/EBPα) Expression and Preadipocyte Differentiation

“…Further, the chronic use of VPA also results in visceral weight gain, because it is still used in patients suffering from epilepsy (36,42,43) or having manic episodes during bipolar disorders (44). We have shown that one of the mechanisms by which glucocorticoids mediate this effect is through the up-regulation of C/ebp␣ via direct transcriptional activation of the promoter and regulation of the transcriptional activity of C/EBP␤ (13)(14)(15).…”

“…On the other hand, several studies show the opposite, where TSA and the antiepileptic drug valproic acid (VPA) favor adipogenesis (13,36,and reviewed in Ref. 37).…”