Interrupting activator protein‐1 signaling in conscious rats can modify neuropeptide Y gene expression and feeding behavior of phenylpropanolamine

Abstract

Phenylpropanolamine (PPA), an amphetamine (AMPH)-like anorectic agent, is a sympathetic amine used in over-thecounter cold remedies and weight-control preparations worldwide. Although PPA has been withdrawn from market because of the risk of myocardial injury or hemorrhagic stroke (Mersfelder 2001;Pilsczek et al. 2003), some reappraisals for the use of PPA were still reported in USA because of the proposed conclusions that chance, bias, and confounding were plausible alternative explanations for the observed findings of PPA (Stier and Hennekens 2006). Pharmacological evidence reveals that the mechanism for the appetite-suppressing effect of PPA is linked to the central release of catecholamine that may act on a1-adrenoceptors and dopamine D1 receptors ( Address correspondence and reprint requests to Dr Dong-Yih Kuo, Department of Physiology, Chung Shan Medical University, Taichung City 40201, Taiwan. E-mail: dykuo@csmu.edu.twAbbreviation used: AMPH, amphetamine; AP-1, activator protein 1; CART, cocaine-and amphetamine-regulated transcript; EMSA, electromobility shift assay; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ICV, intracerebroventricle; NPY, neuropeptide Y; ODN, oligodeoxynucleotides; POMC, proopiomelanocortin; PPA, phenylpropanolamine; RT-PCR, reverse transcription-polymerase chain reaction; SOD, superoxide dismutase; S-ODN, phosphorothioate oligodeoxynucleotides. AbstractThe mechanism for phenylpropanolamine (PPA)-induced anorexia has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an orexigenic agent abundant in the brain. However, molecular mechanisms behind this effect are not well known. In this study, we investigated whether activator protein-1 (AP-1) signaling was involved. Rats were daily treated with PPA for 4 days. Changes in hypothalamic NPY, c-fos, c-jun, superoxide dismutase (SOD)-1, and SOD-2 mRNA contents were measured and compared. Results showed that c-fos and cjun mRNA levels were increased following PPA treatment, which were relevant to a reduction in NPY mRNA level. To further determine if c-fos/c-jun genes were involved in PPA anorexia, infusions of antisense oligonucleotide into cerebroventricle were performed before daily PPA treatment in freely moving rats. Results showed that either c-fos or c-jun knock down could block PPA anorexia and restore NPY mRNA content to normal level. It is suggested that AP-1 signaling may participate in the central regulation of PPAmediated appetite suppression via the modulation of NPY gene expression. Moreover, this modulation might be partly because of the neuroprotective effect of AP-1 since SOD gene was activated during PPA treatment.

Roles of protein kinase Cα isozyme in the regulation of oxidative stress and neuropeptide Y gene expression in phenylpropanolamine‐mediated appetite suppression

“…The increase in SOD induced by PKCa could reduce the oxidative stress in hypothalamus, which might mediate the restoration of NPY gene expression. Although the SOD-2 mRNA level on Day 4 reversed to normal level because of the development of tolerance to PPA (80 mg/kg) treatment, which was also observed in our previous report (Hsieh et al 2008a), the restoration of NPY gene expression was not affected. Thus, it is possible that PKCa, d, and k signaling were co-activated for the induction of antioxidative enzyme during PPA treatment, which in turn would favor the restoration of NPY gene expression and feeding behavior.…”

“…The increase in SOD induced by PKCα could reduce the oxidative stress in hypothalamus, which might mediate the restoration of NPY gene expression. Although the SOD‐2 mRNA level on Day 4 reversed to normal level because of the development of tolerance to PPA (80 mg/kg) treatment, which was also observed in our previous report (Hsieh et al. 2008a), the restoration of NPY gene expression was not affected.…”

“…Previously, we reported that cAMP response element binding protein and activator protein 1 were involved in the regulation of NPY‐mediated PPA anorexia (Hsieh et al. 2008a,b).…”

Long‐term changes in dopamine‐stimulated gene expression after single‐day methamphetamine exposure

“…The protein products of these gene families form a heterodimeric receptor complex, activator protein-1 (AP-1), which interacts with the AP-1 binding site regulatory element found in multiple target genes (Curran and Franza, 1988;Morgan and Curran, 1991). AP-1 has been found to regulate the CNS expression of such target genes as glutamate receptor subunits, dynorphin, neuropeptide Y, and corticotrophin releasing factor (Hsieh et al, 2008;Kelz et al, 1999;Qiang Fig. 4.…”

Measurement of Immediate‐Early Gene Activation‐ c‐fos and Beyond

“…One approach to identify genes that are directly linked to fos expression is the antisense-targeting technology. Downregulation of c-fos using antisense oligonucleotides (45)(46)(47)(48) or tissue-specific knockdown of fos-related antigen, FRA-2 (49) identified sets of genes that are directly under the control of AP-1 transcription factor.…”