Differential Expression of FosB Proteins and Potential Target Genes in Select Brain Regions of Addiction and Depression Patients

Chronic exposure to stress or drugs of abuse has been linked to altered gene expression throughout the body, and changes in gene expression in discrete brain regions are thought to underlie many psychiatric diseases, including major depressive disorder and drug addiction. Preclinical models of these disorders have provided evidence for mechanisms of this altered gene expression, including transcription factors, but evidence supporting a role for these factors in human patients has been slow to emerge. The transcription factor.FosB is induced in the prefrontal cortex (PFC) and hippocampus (HPC) of rodents in response to stress or cocaine, and its expression in these regions is thought to regulate their top down control of reward circuitry, including the nucleus accumbens (NAc). Here, we use biochemistry to examine the expression of the FosB family of transcription factors and their potential gene targets in PFC and HPC postmortem samples from depressed patients and cocaine addicts. We demonstrate that Delta FosB and other FosB isoforms are downregulated in the HPC but not the PFC in the brains of both depressed and addicted individuals. Further, we show that potential Delta FosB transcriptional targets, including GluA2, are also downregulated in the HPC but not PFC of cocaine addicts. Thus, we provide the first evidence of FosB gene expression in human HPC and PFC in these psychiatric disorders, and in light of recent findings demonstrating the critical role of HPC Delta FosB in rodent models of learning and memory, these data suggest that reduced Delta FosB in HPC could potentially underlie cognitive deficits accompanying chronic cocaine abuse or depression.