Impact of three-month morphine withdrawal on rat brain cortex, hippocampus, striatum and cerebellum: proteomic and phosphoproteomic studies

Incidence of alternative splicing associated with sex and opioid effects in the axon guidance pathway

The alternative splicing of a gene results in distinct transcript isoforms that can result in proteins that differ in function. Alternative splicing processes are prevalent in the brain, have varying incidence across brain regions, and can present sexual dimorphism. Exposure to opiates and other substances of abuse can also alter the type and incidence of the splicing process and the relative abundance of the isoforms produced. The disruption of alternative splicing patterns associated with sex differences and morphine exposure in the prefrontal cortex of a pig model was studied. The numbers of genes presenting one or more significant (FDR-adjusted p-value < 0.05) alternative splicing events were 933 and 1,368 genes when comparing females relative to males and morphine- relative to saline-treated animals, respectively. The sex-dependent opioid effect was most extreme in the contrast between morphine- versus saline-treated males with 1,934 significantly differentially spliced genes. The most frequent and significant alternative splicing type was skipped exon (∼56 % event), followed by retained intron (∼15 % events). The pathways encompassing a significant number of differentially spliced genes included axon guidance, glutamatergic synapses, circadian rhythm, and lysine degradation. Genes in these pathways included ROBO1, SEMA6C, GRIN3A, GRM2, ARNTL, CLOCK, HYKK, and DOT1L. Transcription factors ETV7 and DMAP1 presented a significant number of differentially spliced target genes. The distribution of the genes presenting differential alternative splicing in the axon guidance and circadian rhythm pathways indicates that this regulatory mechanism impacts hubs and peripheral genes. The identification of sexual dimorphism in the effect of morphine across multiple pathways confirms the necessity to explore the effects of drugs of abuse within sex. Altogether, our findings advance the understanding of the response to factors that can impact the activity of excitatory synapses by modulating transcriptional mechanisms that support the plasticity of the prefrontal cortex.

The impact of multifunctional enkephalin analogs and morphine on the protein changes in crude membrane fractions isolated from the rat brain cortex and hippocampus

Endogenous opioid peptides serve as potent analgesics through the opioid receptor (OR) activation. However, they often suffer from poor metabolic stability, low lipophilicity, and low blood-brain barrier permeability. Researchers have developed many strategies to overcome the drawbacks of current pain medications and unwanted biological effects produced by the interaction with opioid receptors. Here, we tested multifunctional enkephalin analogs LYS739 (MOR/DOR agonist and KOR partial antagonist) and LYS744 (MOR/DOR agonist and KOR full antagonist) under in vivo conditions in comparison with MOR agonist, morphine. We applied 2D electrophoretic resolution to investigate differences in proteome profiles of crude membrane (CM) fractions isolated from the rat brain cortex and hippocampus exposed to the drugs (10 mg/kg, seven days). Our results have shown that treatment with analog LYS739 induced the most protein changes in cortical and hippocampal samples. The identified proteins were mainly associated with energy metabolism, cell shape and movement, apoptosis, protein folding, regulation of redox homeostasis, and signal transduction. Among these, the isoform of mitochondrial ATP synthase subunit beta (ATP5F1B) was the only protein upregulation in the hippocampus but not in the brain cortex. Contrarily, the administration of analog LYS744 caused a small number of protein alterations in both brain parts. Our results indicate that the KOR full antagonism, together with MOR/DOR agonism of multifunctional opioid ligands, can be beneficial in treating chronic pain states by reducing changes in protein expression levels but retaining analgesic efficacy.

Functional modular networks identify the pivotal genes associated with morphine addiction and potential drug therapies

BACKGROUND

Chronic morphine usage induces lasting molecular and microcellular adaptations in distinct brain areas, resulting in addiction-related behavioural abnormalities, drug-seeking, and relapse. Nonetheless, the mechanisms of action of the genes responsible for morphine addiction have not been exhaustively studied.

METHODS

We obtained morphine addiction-related datasets from the Gene Expression Omnibus (GEO) database and screened for Differentially Expressed Genes (DEGs). Weighted Gene Co-expression Network Analysis (WGCNA) functional modularity constructs were analyzed for genes associated with clinical traits. Venn diagrams were filtered for intersecting common DEGs (CDEGs). Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis for functional annotation. Protein-protein interaction network (PPI) and CytoHubba were used to screen for hub genes. Potential treatments for morphine addiction were figured out with the help of an online database.

RESULTS

Sixty-five common differential genes linked to morphine addiction were identified, and functional enrichment analysis showed that they were primarily involved in ion channel activity, protein transport, the oxytocin signalling pathway, neuroactive ligand-receptor interactions, and other signalling pathways. Based on the PPI network, ten hub genes (CHN2, OLIG2, UGT8A, CACNB2, TIMP3, FKBP5, ZBTB16, TSC22D3, ISL1, and SLC2A1) were checked. In the data set GSE7762, all of the Area Under Curve (AUC) values for the hub gene Receiver Operating Characteristic (ROC) curves were greater than 0.8. We also used the DGIdb database to look for eight small-molecule drugs that might be useful for treating morphine addiction.

CONCLUSIONS

The hub genes are crucial genes associated with morphine addiction in the mouse striatum. The oxytocin signalling pathway may play a vital role in developing morphine addiction.

The Dose-Dependent Effects of Multifunctional Enkephalin Analogs on the Protein Composition of Rat Spleen Lymphocytes, Cortex, and Hippocampus; Comparison with Changes Induced by Morphine

This work aimed to test the effect of 7-day exposure of rats to multifunctional enkephalin analogs LYS739 and LYS744 at doses of 3 mg/kg and 10 mg/kg on the protein composition of rat spleen lymphocytes, brain cortex, and hippocampus. Alterations of proteome induced by LYS739 and LYS744 were compared with those elicited by morphine. The changes in rat proteome profiles were analyzed by label-free quantification (MaxLFQ). Proteomic analysis indicated that the treatment with 3 mg/kg of LYS744 caused significant alterations in protein expression levels in spleen lymphocytes (45), rat brain cortex (31), and hippocampus (42). The identified proteins were primarily involved in RNA processing and the regulation of cytoskeletal dynamics. In spleen lymphocytes, the administration of the higher 10 mg/kg dose of both enkephalin analogs caused major, extensive modifications in protein expression levels: LYS739 (119) and LYS744 (182). Among these changes, the number of proteins associated with immune responses and apoptotic processes was increased. LYS739 treatment resulted in the highest number of alterations in the rat brain cortex (152) and hippocampus (45). The altered proteins were functionally related to the regulation of transcription and cytoskeletal reorganization, which plays an essential role in neuronal plasticity. Administration with LYS744 did not increase the number of altered proteins in the brain cortex (26) and hippocampus (26). Our findings demonstrate that the effect of κ-OR full antagonism of LYS744 is opposite in the central nervous system and the peripheral region (spleen lymphocytes).

Alterations in the Proteome and Phosphoproteome Profiles of Rat Hippocampus after Six Months of Morphine Withdrawal: Comparison with the Forebrain Cortex

The knowledge about proteome changes proceeding during protracted opioid withdrawal is lacking. Therefore, the aim of this work was to analyze the spectrum of altered proteins in the rat hippocampus in comparison with the forebrain cortex after 6-month morphine withdrawal. We utilized 2D electrophoretic workflow (Pro-Q® Diamond staining and Colloidal Coomassie Blue staining) which was preceded by label-free quantification (MaxLFQ). The phosphoproteomic analysis revealed six significantly altered hippocampal (Calm1, Ywhaz, Tuba1b, Stip1, Pgk1, and Aldoa) and three cortical proteins (Tubb2a, Tuba1a, and Actb). The impact of 6-month morphine withdrawal on the changes in the proteomic profiles was higher in the hippocampus—14 proteins, only three proteins were detected in the forebrain cortex. Gene Ontology (GO) enrichment analysis of differentially expressed hippocampal proteins revealed the most enriched terms related to metabolic changes, cytoskeleton organization and response to oxidative stress. There is increasing evidence that energy metabolism plays an important role in opioid addiction. However, the way how morphine treatment and withdrawal alter energy metabolism is not fully understood. Our results indicate that the rat hippocampus is more susceptible to changes in proteome and phosphoproteome profiles induced by 6-month morphine withdrawal than is the forebrain cortex.

Proteomic Analysis Unveils Expressional Changes in Cytoskeleton- and Synaptic Plasticity-Associated Proteins in Rat Brain Six Months after Withdrawal from Morphine

Drug withdrawal is associated with abstinence symptoms including deficits in cognitive functions that may persist even after prolonged discontinuation of drug intake. Cognitive deficits are, at least partially, caused by alterations in synaptic plasticity but the precise molecular mechanisms have not yet been fully identified. In the present study, changes in proteomic and phosphoproteomic profiles of selected brain regions (cortex, hippocampus, striatum, and cerebellum) from rats abstaining for six months after cessation of chronic treatment with morphine were determined by label-free quantitative (LFQ) proteomic analysis. Interestingly, prolonged morphine withdrawal was found to be associated especially with alterations in protein phosphorylation and to a lesser extent in protein expression. Gene ontology (GO) term analysis revealed enrichment in biological processes related to synaptic plasticity, cytoskeleton organization, and GTPase activity. More specifically, significant changes were observed in proteins localized in synaptic vesicles (e.g., synapsin-1, SV2a, Rab3a), in the active zone of the presynaptic nerve terminal (e.g., Bassoon, Piccolo, Rims1), and in the postsynaptic density (e.g., cadherin 13, catenins, Arhgap35, Shank3, Arhgef7). Other differentially phosphorylated proteins were associated with microtubule dynamics (microtubule-associated proteins, Tppp, collapsin response mediator proteins) and the actin–spectrin network (e.g., spectrins, adducins, band 4.1-like protein 1). Taken together, a six-month morphine withdrawal was manifested by significant alterations in the phosphorylation of synaptic proteins. The altered phosphorylation patterns modulating the function of synaptic proteins may contribute to long-term neuroadaptations induced by drug use and withdrawal.