Phosphorylation of FADD (Fas-associated death domain protein) at serine 194 is increased in the prefrontal cortex of opiate abusers: Relation to mitogen activated protein kinase, phosphoprotein enriched in astrocytes of 15 kDa, and Akt signaling pathways involved in neuroplasticity

Abstract

Fas-associated protein with death domain (FADD) is a multifunctional protein that can induce both apoptotic and non-apoptotic actions. Recently, FADD was found downregulated in the prefrontal cortex of opiate abusers, which suggested an attenuation of Fas death signals in human addicts. Phosphorylation of FADD (Ser194) has been reported to regulate its non-apoptotic activity, which might include the induction of neuroplastic effects in the brain. This postmortem brain study examined the status of phosphorylated (p)-Ser194 FADD and signaling pathways involved in neuroplasticity in the prefrontal cortex (BA 9) of short-term (ST) and long-term (LT) heroin or methadone abusers. In these subjects, the content of monomeric p-FADD was significantly increased when compared with that in age-, gender-, and postmortem delay–matched controls (all addicts: 65%, n=26; ST abuse: 51%; n=11; LT abuse: 75%, n=15). Oligomeric p-FADD forms were modestly increased (11%–23%). At the subcellular level, opiate addiction upregulated the expression of monomeric p-FADD in the nucleus (110%) and that of p-oligomers in the cytosol (66%). In LT opiate addicts (but not ST abusers), a pronounced downregulation of p-extracellular signal-regulated kinase (ERK)1/2 (52%) and p-c-Jun NH 2-terminal protein kinase (JNK)1/2 (51%), but not p-p38 mitogen-activated protein kinase (MAPK), was quantified in the prefrontal cortex (total homogenate and subcellular compartments). Similarly, the signaling pathway mediated by p-phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) protein and its phosphorylating kinase p-Akt1 was also downregulated in cortical homogenate (43% and 41%, respectively) and cytosolic preparations of chronic opiate addicts. The results indicate that opiate addiction in humans is associated with an altered balance between p-Ser194 FADD (increased) and total FADD (decreased) in brain, which may favor its neuroplastic actions. The interaction between p-FADD (upregulated) and neuronal pathways (downregulated) could play a relevant role in mediating specific forms of structural and behavioral neuroplasticity.