Mechanisms of Prodynorphin Gene Dysregulation in the Brain of Human Alcoholics

• Main Author: Taqi, Malik Mumtaz
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för farmaceutisk biovetenskap 2011
• Subjects: PHARMACY; FARMACI
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158235; http://nbn-resolving.de/urn:isbn:978-91-554-8149-0

The endogenous opioid system (EOS) including dynorphin opioid peptides and κ-opioid receptor (KOR) plays a critical role in alcohol dependence. Aims of the thesis were to evaluate whether the EOS undergoes molecular adaptations in brain areas involved in cognitive control of addiction in human alcohol dependent subjects, and to analyze the impact of genetic and epigenetic factors on these adaptive changes. The main findings were that (1) the dynorphin/KOR system including PDYN mRNA and dynorphins in the dorsolateral prefrontal cortex (dl-PFC), dynorphins in the hippocampus, and KOR mRNA in the orbitofrontal cortex (OFC), is upregulated in human alcoholics. No other significant changes in the EOS were found. (2) Three PDYN single nucleotide polymorphisms (SNPs), which show the most significant association with alcohol dependence, form CpG sites that are methylated in human brain at different levels. Methylation of the C, non-risk variant of the 3’-untranslated region (3’-UTR) SNP (rs2235749; C>T) was increased in dl-PFC and positively correlated with dynorphins. The DNA-binding factor that differentially targeted the T, risk allele and methylated and unmethylated C allele of this SNP was identified in human brain. We hypothesize that influences of the genetic, epigenetic and environmental factors may be integrated through alterations in methylation of the PDYN 3’jUTR CpG/SNP and, as a consequence, affect PDYN transcription and vulnerability to develop alcohol dependence. (3) The principal component analysis suggested that PDYN expression in the dl-PFC may be related to alcoholism, while in the hippocampus may depend on the genotype of the PDYN promoter SNP (rs1997794; T>C). The T, low risk allele of this SNP resides within non-canonical AP-1-binding element and may be targeted by JUND and FOSB proteins, the dominant AP-1 constituents in the human brain. The T to C transition abrogated AP-1 binding. The impact of genetic variations on PDYN transcription may be relevant for diverse adaptive responses of this gene to alcohol. (4) It was proposed that PDYN transcription may be regulated by intragenic DNA regulatory elements controlling the DNA-protein interactions through formation of non-canonical DNA secondary structures. The dynorphin-encoding sequence in PDYN was found to have potential to form such DNA structure in vitro, and this formation was affected by CpG methylation in this region. This methylation sensitive non-canonical DNA structure formation may be involved in regulation of initiation of PDYN transcription from alternative start sites located within this region, or in splicing of non-canonical mRNA. In conclusion, the dynorphin/KOR system has been identified as the site of robust adaptive changes associated with alcohol dependence in the areas of human brain involved in cognitive control of addiction. Regulation of PDYN was found to be brain area specific, apparently affected by the genetic and epigenetic factors, and possibly dependent on the internal properties of the gene such as its ability to form non-canonical DNA secondary structures.