EFFECT OF ALZHEIMERS BRAIN EXTRACTS ON DYNEIN IMMUNOREACTIVITY IN PC12 CELLS

The neurodegenerative process in Alzheimer's disease (AD) has been sug gested to occur as a consequence of microtubule disruption and subsequ ent loss of intracellular transport, Structural microtubule-associated proteins (MAPs) have been investigated for their role in the etiology of AD, but dynein, a force-producing MAP which mediates intracellular transport, has not been examined, In this report, dynein (MAP1C) immu noreactivity in AD brain tissue homogenates was observed increased 3.7 -fold compared with control brain homogenate preparations, Similarly, NGF-differentiated PC12 cells cultured in the presence of soluble extr acts prepared from AD brain tissue homogenates, exhibited an approxima te 15-fold increase in dynein immunoreactivity compared to that of con trol brain tissue extracts, In contrast, AD clarified extracts had lit tle effect upon ''kinesin-like'' protein immunoreactivity increased (a pproximately 2-fold); whereas, tau immunoreactivity was observed to be moderately increased (5-fold) over that of control brain extract trea ted PC12 cells, Chemical dephosphorylation and alkaline phosphatase tr eatment of AD extract-treated PC12 cell lysate prior to Western blotti ng resulted in complete loss of immunoreactivity, suggesting the dynei n being monitored is a phosphorylated isoform, Furthermore, treatment of clarified brain tissue extracts with trypsin and (NH4)(2)SO4 sugges ts the endogenous elements giving rise to increased PC12 cell dynein i ntermediate chain immunoreactivity to be proteinaceous in nature, The observed increase in dynein intermediate-chain dynein immunoreactivity following exposure of neuronal cells to endogenous elements of AD bra in may be reflective of dynein-microtubular array differences, Such an approach may be useful in assessing the effect of endogenous biomolec ules on retrograde axonal transport in neuronal culture models.