Immunochemical and biochemical characterization of τ proteins in normal and Alzheimer's disease brains with Alz 50 and Tau-1

Microtubule-associated protein τ was characterized in 5 Alzheimer and 5 control brains using two monoclonal antibodies, Alz 50 and Tau-1. Quantitative analysis of immunoblots with the antibodies showed that both homogenate and supernatant fractions (12,000 x g) from Alzheimer brains contained 38-65% less τ immunoreactivity compared to normal brains. The reduction was found in all brain regions studied (frontal and temporal lobes and thalamus) and in both gray and white matter. In partially purified τ preparations, the yield of protein was lower in Alzheimer (by 35%) than in control brain. Incubation of brain proteins, transferred onto nitrocellulose paper, with alkaline phosphatase had either no effect or slightly increased the antibody binding to τ proteins from both brain tissues. Immunoblots of τ-enriched preparations subjected to two-dimensional gel electrophoresis showed no major changes in the staining pattern of τ isoforms in Alzheimer samples except for a weaker reactivity of the basic isovariants as compared to non-Alzheimer samples. The elution volume of τ from Alzheimer brain supernatant on a Sepharose CL-6B column was similar to that from non-Alzheimer brain and equal to that of aldolase (M(r) = 158,000). Our data suggest that most of τ proteins from both types of brain have similar biochemical properties. The reduction in τ reactivity in Alzheimer tissue may be due to a reduction in neuronal cell population or incorporation of soluble τ into stable structures such as neurofibrillary tangles, since the tangles have been shown to react with anti-τ antibodies.