Investigating the Potential Influence of Cause of Death and Cocaine Levels on the Differential Expression of Genes Associated with Cocaine Abuse

Abstract

The development of new therapeutic strategies for the treatment of complex brain disorders such as drug addiction is likely to be advanced by a more complete understanding of the underlying molecular pathophysiology. Although the study of postmortem human brain represents a unique resource in this regard, it can be challenging to disentangle the relative contribution of chronic pathological processes versus perimortem events to the observed changes in gene expression. To begin to unravel this issue, we analyzed by quantitative PCR the midbrain expression of numerous candidate genes previously associated with cocaine abuse. Data obtained from chronic cocaine abusers (and matched control subjects) dying of gunshot wounds were compared with a prior study of subjects with deaths directly attributable to cocaine abuse. Most of the genes studied (i.e., tyrosine hydroxylase, dopamine transporter, forkhead box A2, histone variant H3 family 3B, nuclear factor kappa B inhibitor alpha, growth arrest and DNA damage-inducible beta) were found to be differentially expressed in chronic cocaine abusers irrespective of immediate cause of death or perimortem levels of cocaine, suggesting that these may represent core pathophysiological changes arising with chronic drug abuse. On the other hand, chemokine C-C motif ligand 2 and jun proto-oncogene expression were unaffected in cocaine-abusing subjects dying of gunshot wounds, in contrast to the differential expression previously reported in cocaine-related fatalities. The possible influence of cause of death and other factors on the cocaine-responsiveness of these genes is discussed.

Transcriptomic profiling of the ventral tegmental area and nucleus accumbens in rhesus macaques following long-term cocaine self-administration

“…And while there is also a robust down-regulation of the dopamine transporter (SLC6A3; q < 0.01), there were no significant differences in expression of any of the dopamine receptors. These findings confirm previous studies in post-mortem human cocaine abusers (Bannon et al, 2014; Bannon et al, 2015; Little et al, 1998; Zhou et al, 2014a) as well as in rats following extended cocaine exposure (Cerruti et al, 1994; Letchworth et al, 1997; Letchworth et al, 1999). …”

“…We also see corresponding differences in the upstream regulators of these genes, notably FOXA2, that are similar to human post-mortem findings (Bannon et al, 2014; Bannon et al, 2015). FOXA1 and FOXA2 have previously been demonstrated to regulate midbrain dopaminergic development and function (Ferri et al, 2007; Kittappa et al, 2007; Lin et al, 2009; Metzakopian et al, 2015; Metzakopian et al, 2012; Stott et al, 2013).…”

“…These genes have previously been shown to specify midbrain dopaminergic fate (Ferri et al, 2007) and are direct regulators not only of DDC and TH in mature dopaminergic neurons, but also of engrailed 1 and 2 (EN1, EN2) and the nuclear receptor NR4A2 (also known as NURR1) in immature neurons. FOXA2 down regulation has likewise been observed in the midbrain of human cocaine abusers (Bannon et al, 2014; Bannon et al, 2015). In addition to developmental roles in specifying dopaminergic neuronal fate, FOXA1 and FOXA2 have also been demonstrated to regulate midbrain dopaminergic function and survival in the adult brain (Kittappa et al, 2007).…”

“…Indeed, in this work we also see a down-regulation of genes associated with dopaminergic neuron development and function, including the genes traditionally associated with dopamine synthesis (DDH and TH) and transport (SLC6A3), consistent with findings from human cocaine abusers. Previous studies have observed decreases in the dopamine transporter in post-mortem studies from human cocaine abusers (Bannon et al, 2014; Bannon et al, 2015; Little et al, 1998; Zhou et al, 2014a) as well as in rats following extended cocaine exposure (Cerruti et al, 1994; Letchworth et al, 1997; Letchworth et al, 1999; Zhang et al, 2012). The parallels between these studies and previous human studies extend to a reduced expression of tyrosine hydroxylase in the VTA (Bannon et al, 2014; Bannon et al, 2015), although rat studies have been more ambiguous (Freeman et al, 2000; Rodriguez-Espinosa and Fernandez-Espejo, 2015; Vrana et al, 1993).…”

Identification of long noncoding RNAs dysregulated in the midbrain of human cocaine abusers

“…Recent analysis of human postmortem midbrain has revealed a molecular signature of pathophysiological changes in gene expression that are diagnostic for chronic cocaine abuse (Bannon et al . , ), but our understanding of the mediators of these changes remains rudimentary.…”