Developmental Changes in Opioid Peptides and Their Receptors inCpefat/CpefatMice Lacking Peptide Processing Enzyme Carboxypeptidase E
- Dr. Yemiliya Berman, Department of Pharmacology, New York University School of Medicine, New York, NY 10016. E-mail: bermay01{at}med.nyu.edu
Abstract
Carboxypeptidase E (CPE) is involved in the biosynthesis of a number of neuropeptides including opioid peptides. A point mutation in this gene results in a loss of enzyme activity, decrease in mature neuroendocrine peptides, and development of late onset obesity as seen in Cpefat/Cpefatmice. In this study, we examined the processing of peptides derived from prodynorphin and proenkephalin in various brain regions of these mice during development. At 6 to 8 weeks, an age prior to the onset of obesity, levels of dynorphin peptides are decreased in all brain regions, whereas levels of ir-Met-enkephalin are differentially altered. There is an accumulation of C-terminally extended forms of all three opioid peptides inCpefat/Cpefatmice, consistent with a lack of CPE activity. Thus, it appears that there is no direct correlation between the level of mature opioid peptides and the development of obesity in these mice. Since altered levels of peptides can influence the opioid receptor system, we examined the functional activity of μ and κ opioid receptors using [35S]guanosine-5′-O-(γ-thio)-triphosphate binding assays. We find no differences in κ receptor activity inCpefat/Cpefatcompared with control littermate mice. In contrast, the μ receptor activity is differentially altered in select regions ofCpefat/Cpefatmice in response to a μ-specific ligand. Taken together, these results suggest that the lack of CPE activity leads to alterations in the level of opioid peptides during development and that changes in peptide levels differentially affect opioid receptor activity in vivo.
Footnotes
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↵1 Current address: Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, NE 68588.
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↵2 Current address: Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016.
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This work is supported in part by National Institute of Health Grants DA00342 (to Y.B.) and NS26880 and DA00458 (to L.A.D.).
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DOI: 10.1124/jpet.102.037663
- Abbreviations:
- CPE
- carboxypeptidase E
- ProDyn
- prodynorphin
- ProEnk
- proenkephalin
- [35S]GTPγS
- guanosine-5′-O-(γ-thio)-triphosphate
- DAMGO
- [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin
- ICI 199,441
- 2-(3,4-dichlorophenyl)-N-methyl-N-[(1S)-1-phenyl-2-(1-pyrrolidinyl)ethyl]acetamide
- RIA
- radioimmunoassay
- ir
- immunoreactive
- Dyn
- dynorphin
- Met-Enk
- Met-enkephalin
- E-64
- N-[N-(l-3-trans-carboxyoxiran-2-carbonyl)-l-leucyl]-agmatine
- CPB
- carboxypeptidase B
- ANOVA
- analysis of variance
- CCK
- cholecystokinin injections
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- Received April 18, 2002.
- Accepted September 6, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
