Wednesday, November 21, 2012

Neurofibrillary tangles, senile plaques, and neuronal death

       Alzheimer's disease is characterized by neurofibrillary tangles, senile plaques, and neuronal death. The neurofibrillary tangles contain paired helical filaments composed of hyperphosphorylated tau, while the senile plaques are comprised of an array of proteins deposited around a core of insoluble Ab peptide.

       The cause of neuronal death remains unknown, but considerable evidence suggests that it is secondary to an increase in the brain Ab load. The molecular events involved in the constitutive production of Ap are increasingly being understood.

     The first step appears to be cleavage of the amyloid precursor protein (APP) by (3-secretase (Vassar et al., 1999; Lin et al., 2000), yielding an extracellular fragment known as sAPP(3, which is shed into the extracellular space (Mills & Reiner, 1999). Cleavage of C99 within the membrane by an enzyme known as y-secretase, which appears to be identical to the presenilins (Wolfe et al., 1999; Lin et al., 2000), liberates intact A{3. Both the 40 and 42 amino acid versions of A(3 are amphipathic, consisting of 28 charged amino acids and either 12 or 14 hydrophobic amino acids (for A(3t_40 and A(3142, respectively).

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