Search

Alpha-synuclein is an evolutionary highly conserved neuronal protein localized in presynaptic nerve terminals. The protein has been suggested to be involved in the pathogenesis of neurodegenerative diseases, but little is known about the physiological function of the protein. In the present study we used newborn, three, 14, 93 and 710-day-old rats to examine the expression of alpha-synuclein messenger RNA and protein during development of the hippocampus and cerebral cortex. Using in situ hybridization and an S1 nuclease protection assay, we found a high expression of alpha-synuclein messenger RNA during early postnatal development, followed by a marked decrease between postnatal days 14 and 93. In contrast, the amount of alpha-synuclein protein, as determined by immunoblotting, continued to increase throughout development and remained at a high level for at least two years. The persistent high expression of alpha-synuclein protein throughout development suggests that the protein is involved in maintaining synaptic function. Furthermore, the discrepancy between the levels of alpha-synuclein messenger RNA and protein after postnatal day 14 indicates that the amount of alpha-synuclein is determined by post-transcriptional regulation, and not by messenger RNA expression alone. To estimate the changes of alpha-synuclein expression per synapse, we compared the developmental expression of alpha-synuclein with synaptophysin, a well-established synaptic marker. The alpha-synuclein/synaptophysin messenger RNA and protein ratio was high during early development, but low in adult (postnatal day 93) and old (postnatal day 710) rats. This could indicate a higher expression of alpha-synuclein per synapse during early development.

Deposits in the brain of beta-amyloid and tau proteins constitute the two major characteristics of Alzheimer's disease. It is unknown how the deposits are formed, but several studies have suggested that proteases might play a crucial role. Consequently, the search for proteases responsible for processing tau and amyloid precursor protein has become relevant. Here, the ability of thrombin to process tau in vitro is examined. Thrombin, which is found in blood but presumably also in the nervous system, cleaves tau and generates a stable 25 kDa fragment. Immunoblot and amino acid sequencing reveals that the fragment is derived from the C-terminal of tau, and a microtubule assembly assay shows that it has a reduced capacity to promote microtubule assembly compared with full length tau.

The principal fibrous component of neurofibrillary pathology in Alzheimer's disease, the paired helical filament, is formed from hyperphosphorylated microtubule-associated protein tau. Here we show that recombinant tau protein either in a non-phosphorylated state or following phosphorylation with brain extract can be assembled in vitro into filaments resembling those seen in Alzheimer's disease.

The paired helical filament, which comprises the major fibrous element of the neurofibrillary tangle in Alzheimer's disease, contains abnormally phosphorylated microtubule-associated protein tau as its principal constituent. The repeat region of tau protein, which represents the microtubule binding domain, forms the core of the filament. Here we show that an expressed fragment of tau protein spanning the repeat region can assemble in vitro into filaments like those found in Alzheimer's disease