ABSTRACT
BACKGROUND: Substance use disorder is a neurobiological disease characterized by episodes of relapse despite periods of withdrawal. It is thought that neuroadaptations in discrete brain areas of the reward pathway, including the nucleus accumbens, underlie these aberrant behaviors. The ubiquitin-proteasome system degrades proteins and has been shown to be involved in cocaine-induced plasticity, but the role of E3 ubiquitin ligases, which conjugate ubiquitin to substrates, is unknown. Here, we examined E3 ubiquitin-protein ligase SMURF1 (SMURF1) in neuroadaptations and relapse behavior during withdrawal following cocaine self-administration. METHODS: SMURF1 and downstream targets ras homolog gene family, member A (RhoA), SMAD1/5, and Runt-related transcript factor 2 were examined using Western blotting (n = 9-11/group), quantitative polymerase chain reaction (n = 6-9/group), co-immunoprecipitation (n = 9-11/group), tandem ubiquitin binding entities affinity purification (n = 5-6/group), and quantitative chromatin immunoprecipitation (n = 3-6/group) (2 rats/sample). Viral-mediated gene transfer (n = 7-12/group) and intra-accumbal microinjections (n = 9-10/group) were used to examine causal roles of SMURF1 and substrate RhoA, respectively, in cue-induced cocaine seeking. RESULTS: SMURF1 protein expression was decreased, while SMURF1 substrates RhoA and SMAD1/5 were increased, in the nucleus accumbens on withdrawal day 7, but not on withdrawal day 1, following cocaine self-administration. Viral-mediated gene transfer of Smurf1 or constitutive activation of RhoA attenuated cue-induced cocaine seeking, while catalytically inactive Smurf1 enhanced cocaine seeking. Furthermore, SMURF1-regulated, SMAD1/5-associated transcription factor Runt-related transcript factor 2 displayed increased binding at promoter regions of genes previously associated with cocaine-induced plasticity. CONCLUSIONS: SMURF1 is a key mediator of neuroadaptations in the nucleus accumbens following cocaine exposure and mediates cue-induced cocaine seeking during withdrawal.
Subject(s)
Cocaine/administration & dosage , Drug-Seeking Behavior/physiology , Nucleus Accumbens/physiology , Smad1 Protein/physiology , Ubiquitin-Protein Ligases/physiology , Animals , Cocaine-Related Disorders/genetics , Cues , Male , Nucleus Accumbens/drug effects , Proteasome Endopeptidase Complex , Rats , Rats, Sprague-Dawley , Self Administration , Signal Transduction , Smad1 Protein/genetics , Ubiquitin-Protein Ligases/geneticsABSTRACT
Opiate abuse and addiction have become a worldwide epidemic with great societal and financial burdens, highlighting a critical need to understand the neurobiology of opiate addiction. Although several studies have focused on drug-dependent changes in neurons, the role of glia in opiate addiction remains largely unstudied. RNA sequencing pathway analysis from the prefrontal cortex (PFC) of male rats revealed changes in several genes associated with oligodendrocyte differentiation and maturation following heroin self-administration. Among these genes changed was Sox10, which is regulated, in part, by the chromatin remodeler BRG1/SMARCA4. To directly test the functional role of Sox10 in mediating heroin-induced behavioral plasticity, we selectively overexpressed Sox10 and BRG1 in the PFC. Overexpression of either Sox10 or BRG1 decreased the motivation to obtain heroin infusions in a progressive ratio test without altering the acquisition or maintenance of heroin self-administration. These data demonstrate a critical, and perhaps compensatory, role of Sox10 and BRG1 in oligodendrocytes in regulating the motivation for heroin.
