Fig. 4.
Accumulation of NFTs after transgenic tau suppression. (A) Semiquantitative grading of neurofibrillary pathology in tauP301L-positive mice. Tangles in three to five animals, at ages in months (M), evaluated with PG5, AT8, or Bielschowsky stain, in neocortical (ctx) and CA1 hippocampal (CA1) regions were graded using an adaptation of the CERAD (Consortium to Establish a Registry for AD) neuropsychological rating scales, by using area of most severe involvement, as follows: 0 (none), + (sparse, <5 NFTs/hpf), ++ (moderate, 5 to 25 NFTs/hpf), or +++ (severe, >25 NFTs/hpf). The neuropil scored 0 when AT8 staining was absent, + when only a mild granular background staining was noted, ++ when neuropil staining was moderate, and +++ when neuropil staining was severe and diffuse. (B) CA1 neurons staining with PHF1 antibody recognizing tau phosphoserines 396 and 404 did not diminish after transgene suppression for 6 weeks. (C) Concentrations of sarkosyl-insoluble tauP301L proteins were measured in extracts of forebrain homogenates by using immunoblots. With age, the predominant tau species shifted from a doublet of ~55-kD proteins to a 64-kD protein. Suppression of tauP301L reduced levels of the 55-kD species (gray symbols), but failed to halt the accumulation of the 64-kD species in mice ≥4 months of age (black symbols). (D) The number and length of fibrils in sarkosyl-insoluble fractions from extracts of forebrain homogenates increased with age. Suppressing transgenic tau in ≥4-month-old mice failed to prevent the increase in the amount or size of the fibrils.