Brain Region-Specific Decrease In the Activity of Protein Kinase C, and Increase In Activated MAP Kinases In Regressive Autism

Background:  Autism is a severe neurodevelopmental disorder that is characterized by impaired language, communication and social skills.  In regressive autism, children first show sign of normal social and language development but eventually lose these skills and develop autistic behavior. Calcium and phospholipid-dependent protein kinase C (PKC) and mitogen-activated protein (MAP)-kinases are involved in receptor-coupled signal transduction, and participate in neuronal functions, gene expression, memory, and cell differentiation.

Objectives:  The aim of this study was to compare the activity of PKC and the levels of activated MAP-kinases, namely c-jun N-terminal kinase (JNK), MAPK/extracellular signal-regulated kinase-1 (MEK 1) and P38 kinase in postmortem brain tissue samples from individuals with regressive autism, autistic subjects without clinical history of regression, and age-matched control subjects.

Methods:  The postmortem frozen brain regions, i.e., cerebellum, and cortices from frontal, temporal, parietal and occipital regions of brains from autism and control subjects were obtained from NICHD Brain and Tissue bank for Developmental Disorders at the University of Maryland.  The tissues were homogenized (10% w/v) in cold buffer containing 50 mM Tris-HCl (pH 7.4), 8.5% sucrose, 2 mM EDTA, 10 mM b-mercaptoethanol and protease inhibitor cocktail in a Downs homogenizer with 5 strokes at 4 ⁰C. The protein concentration was assayed by the Bradford method. Activity of PKC and the levels of MAP kinases (JNK, MEK 1 and P38) were measured by enzyme linked-immunosorbent assay kits. 

Results:  The activity of PKC was significantly decreased in the frontal cortex of individuals with regressive autism compared to developmentally normal subjects and autistic individuals without regression. Such changes were not observed in temporal cortex, parietal and occipital cortices and cerebellum in subjects with regressive autism.  Further studies in the frontal cortex showed that the levels of non-phosphorylated forms of MAP kinases (JNK, MEK 1 and P38) were not affected in individuals with regressive and non-regressive autism.  However, the levels of activated forms of these MAP kinases, i.e., their phosphorylated forms were increased in regressive autism.  It is known that activated MAP kinases are increased under oxidative stress conditions. 

Conclusions:  These results suggest that regression in autism may in part, be associated with oxidative stress and altered PKC-mediated phosphorylation of proteins involved in cell signaling.