Tau pathology in two Dutch families with mutations in the microtubule-binding region of tau

Abstract

Different mutations in the microtubule-associated tau protein gene have recently been identified in several families with hereditary frontotemporal dementia and Parkinsonism (FTDP-17) linked to chromosome 17q21-22. Some families show neuronal and glial deposits containing hyperphosphorylated tau in several brain regions. We have investigated the presence of tau deposits by using a panel of anti-tau antibodies in three brains of a family with the P301L mutation (HFTD1) and in another family with the G272V mutation (HFTD2) of the tau gene. Numerous intracytoplasmic tau deposits in neurons, glial cells, and neurites were found in hippocampal formation, neocortex, and substantia nigra. These deposits in three patients from HFTD1 consisted of slender twisted filaments 15 nm wide with variable periodicity and a few straight filaments. Tau extracted from these filaments appeared as two major bands of 64 and 68 kd and a minor band of 72 kd that, after alkaline phosphatase treatment, proved to consist mainly of 4-repeat tau isoforms and one of the 3-repeat isoforms. In three patients from HFTD2 numerous Pick-like bodies were present. The conclusion is that the type and distribution of tau deposits in HFTD1 and HFTD2, the physical structure of filaments, and tau isoform composition in HFTD1 differ from Alzheimer's disease and an FTDP-17 family with a V337M mutation in the tau gene.

Figure 1.

Tau immunostaining in hippocampal formation and neocortex from affected members from HFTD1 (A) and (B) and HFTD2 (C) and (D). Tau deposits are stained by antibody AT8 in the inner molecular layer, granule cells of the dentate gyrus (A) and temporal cortex (B) from an affected member from HFTD1. Numerous Pick-like bodies and granule cells with a perinuclear ring are stained by antibody AT8 in dentate gyrus (C) and temporal cortex (D) from an affected member from HFTD2. Scale bars: 100 μm in A, 66 μm in B, 50 μm in C, and 40 μm in D.

Figure 2.

Electron micrographs of sarkosyl-insoluble filaments from HFTD1. (A) and (B) show examples of twisted ribbons and (C) and (D) show examples of rope-like stranded filaments. (A) and (C) are unlabeled, whereas (B) and (D) have been labeled with phosphorylation-dependent anti-tau antibody AT8. Scale bar, 100 nm.

Figure 3.

Immunoblots of sarkosyl-insoluble tau from affected members from HFTD1. (A) Immunoblots of sarkosyl-insoluble tau extracted from hippocampus from an Alzheimer’s disease patient (lane 1) and hippocampus (lanes 2, 3) and frontal cortex (lanes 4–6) from three affected members of HFTD1 stained by antiserum BR134. Tau bands of 60, 64, 68, and 72 kd are indicated. (B) Immunoblots of sarkosyl-insoluble tau from brain of an affected HFTD1 member, before (lane 1) and after (lane 2) alkaline phosphatase treatment, using antiserum BR133. Note that before alkaline phosphatase treatment two major bands of 64 and 68 kd and a minor band of 72 kd are present; after alkaline phosphatase treatment, three major bands are visible which correspond to tau isoforms with 4 repeats and no amino-terminal amino acid insert (4R) and both 4 and 3 repeat tau isoforms with 29-amino acid amino-terminal insert (4R + 29aa and 3R + 29aa). These are isoforms D, E and B respectively in panel (C). (C) Schematic representation of the 6 tau isoforms present in adult human brain showing the position of G272V and P301L mutations. The P301L mutation is in the alternatively spliced exon 10 and is present only in tau isoforms with 4 repeats, whereas G272V is present in all isoforms.