Decreased levels of synaptosomal associated protein 25 in the brain of patients with Down Syndrome and Alzheimer's disease

Synaptosomal associated protein 25 kDa (snap-25) is a widely distributed me mbrane-associated protein in the brain, mainly localized in nerve terminals . In nerve terminals, snap-25 participates in docking and/or fusion of syna ptic vesicles with the plasmalemma, a process essential for synaptic vesicl e exocytosis. Recent work suggests a role in brain development, forming pre synaptic sites by regulating axonal outgrowth and nerve growth-induced neur ite elongation. In Down syndrome (DS) brain, it is abnormally developed fro m early life, and brain pathology becomes even more pronounced when Alzheim er's disease (AD) develops in the fourth decade. This information led us to examine snap-25 in the brain of patients with DS and AD. We studied snap-2 5 and glial fibrillary acidic protein (GFAP) brain levels in five individua l brain areas of 9 aged patients with DS, 9 patients with AD and 9 controls , applying two-dimensional gel electrophoresis. Decreased snap-25 levels we re found in the five brain regions of the patients with DS and AD. Increase d expression levels of GFAP were found in the frontal, parietal, temporal a nd occipital cortex regions of the DS and AD patients. Decreased snap-25 pr otein levels in the brain of DS and AD may reflect impaired synaptogenesis or represent neuronal loss. Findings of increased GFAP, a marker for neuron al loss, along with data from literature would support the notion of decrea sed snap-25 secondary to neuronal decay in both neurodegenerative disorders .