Incidence and extent of TDP-43 accumulation in aging human brain

The demographics of the cases in this study are shown in Table 3. We selected 136 cases as control elderly (mean age at death?±?1 SD, 78.5?±?9.7 y).
For comparison, we selected 29 AD, 11 LBD, and 11 AGD cases from the series of autopsied
individuals. Compared with the control elderly group, the mean age at death was higher
for AD, LBD, and AGD groups (Table 3).

Table 3. Demographics of cases included in this study

Distribution of TDP-43 pathology in control elderly brains

TDP-43 immunoreactive structures were found in 55/136 (40.0 %) cases (Table 4). Most of these structures were DNs (53/136 cases, 39.0 %; Table 5); they were predominantly detected at the uncus of the anterior hippocampus (29/136
cases, 21.3 %; Table 5, Fig. 3a). In rare instances, DNs were present in other limbic areas such as the uncus of
the amygdala (5/134 cases, 3.7 %; two cases of amygdala were unavailable, Table 5). In control elderly brains, TDP-43 immunoreactive GCIs and NCIs were rare. In fact,
GCIs were observed only in a 94-year-old woman’s entorhinal cortex and NCIs only in
a 98-year-old woman’s subiculum and pyramidal layer (Table 5). No NIIs were present in control elderly brains. TDP-43 immunoreactive DNs were
also found in the inferior olivary complex (14/136 cases, 10.3 %), anterior horn (7/136
cases, 5.1 %), and white matter of the lumbar spinal cord (11/136 cases, 8.1 %), as
shown in Table 5. No NCIs or GCIs were found in the medulla oblongata or lumbar spinal cord.

Table 4. Presence of TDP-43 pathology

Table 5. TDP-43 distribution in this study

Fig. 3. TDP-43 immunoreactive structures in representative cases. a Dystrophic neurites in the uncus of the anterior hippocampus in the control elderly
brain. b Neuronal cytoplasmic inclusions (arrows) in the dentate gyrus in Alzheimer’s disease (AD). c Glial cytoplasmic inclusions (arrows) in the entorhinal cortex in AD. d Neuronal intranuclear inclusion (arrow) in the dentate gyrus in AD. Scale bar?=?20 ?m

Distribution of TDP-43 pathology in AD, LBD, and AGD brains

AD brains

TDP-43–positive structures were found in 21/29 (72.2 %) AD brains and were widely
distributed in the amygdala and hippocampus (Tables 4, 5). These structures were composed of NCIs (17/29 cases, 58.6 %) and GCIs (18/29 cases,
62.1 %) as well as DNs (19/29 cases, 65.5 %) (Fig. 3b, c). DNs were observed in the uncus of the anterior hippocampus (11/28 cases, 39.3 %;
in one case, the anterior hippocampus was unavailable) as well as in the amygdala
(14/29 cases, 48.3 %). In 7/29 cases (24.1 %), TDP-43 immunoreactive NIIs were also
present in the amygdala and hippocampus (Fig. 3d). To a lesser degree, TDP-43–positive DNs were found in the medulla oblongata (5/29
cases; 17.2 %) and lumbar spinal cord (3/29 cases; 10.3 %). There were neither NCIs
nor GCIs in any case of AD (Table 5).

LBD brains

TDP-43 immunoreactive structures were found in 8/11 (72.7 %) LBD brains and predominantly
observed in the uncus of the anterior hippocampus and amygdala (Tables 4, 5). To a lesser degree, they were also found in the amygdaloid nuclei, entorhinal cortex,
subiculum, and pyramidal cells of the hippocampus. TDP-43 immunoreactive structures
mainly took the form of DNs (8/11 cases, 72.7 %), and occasionally of NCIs or GCIs
in the hippocampus and amygdala (2/11 cases, 18.2 %). DNs were observed in the uncus
of the anterior hippocampus (5/11 cases, 45.5 %) and in the amygdala (3/11 cases,
27.3 %). TDP-43 immunoreactive NIIs were found in the entorhinal cortex of only one
case. In the medulla oblongata, TDP-43 immunoreactive DNs were present in the inferior
olivary complex (4/11 cases, 36.4 %; Table 5). There were no DNs in the spinal cord. No NCIs or GCIs were found in any case of
LBD.

AGD brains

TDP-43 immunoreactive structures were found in 6/11 (54.5 %) AGD brains and observed
in the uncus and amygdaloid nuclei (Tables 4, 5). These structures were DNs (6/11 cases, 54.5 %). TDP-43 immunoreactive NCIs or GCIs
were also found in the amygdaloid nuclei (3/11 cases, 27.3 %). DNs were observed in
the uncus of the anterior hippocampus (5/11 cases, 45.5 %) and amygdala (3/10 cases,
33.3 %; one case was unavailable). No TDP-43–positive NIIs were found in these brains.
In the medulla oblongata, we found TDP-43 immunoreactive DNs in the inferior olivary
complex in two cases (2/11 cases, 18.2 %; Table 5). In the lumbar spinal cord, we found TDP-43 immunoreactive DNs in the white matter
in an 85-year-old male. Neither NCIs nor GCIs were found in any of the AGD brains.

Age and frequencies of DNs in four groups

The mean age at death was significantly higher in cases with TDP-43 immunoreactive
structures than in those without TDP-43 immunoreactive structures in control elderly
and AGD (Table 4). However, there were no significant differences in the mean age at death in AD and
LBD (Table 4). Neither the brain weight nor sex ratio differed significantly among the four groups.

Because DNs were the predominant form of TDP-43 immunoreactive structure and observed
mostly in the uncus in control elderly, we analyzed the frequencies of DNs in the
uncus of the anterior hippocampus and amygdala in comparison with those of AD, LBD,
and AGD. There were no significant differences in the frequency of cases with DNs
in the uncus of the anterior hippocampus between control elderly and disease controls
(Fig. 4a). In contrast, the frequency of cases with DNs observed in the uncus of the amygdala
was higher in AD, LBD, and AGD compared with control elderly (Fig. 4b).

Fig. 4. Incidence of TDP-43 immunoreactive dystrophic neurites (DNs) in the uncus of the anterior
hippocampus and amygdala. a There were no significant differences in the number of cases with DNs in the uncus
of the anterior hippocampus between control elderly brains and brains with Alzheimer’s
disease (AD), Lewy body disease (LBD), and argyrophilic grain disease (AGD). b The incidence of DNs in the amygdala was significantly higher in the AD, LBD, and
AGD brains than in control elderly brains

In addition, we focused on the association between the percentage of cases carrying
DNs in the uncus of the anterior hippocampus and aging in control elderly. DNs were
observed from age 65 to 94. In these individuals, there was no statistical association
between the rate of DNs and aging (Fig. 5). However, the rate of DNs may increase beyond 90 years of age (Fig. 5).

Fig. 5. Correlation between age and incidence of TDP-43 immunoreactive structures in the uncus
of the anterior hippocampus in control elderly brains. The incidence of TDP-43 positive
brains ranged between 13 % and 27 % between ages 65 and 89 years. Although there were
no significant differences, the incidence of TDP-43–positive brains increased to 50 %
at ages 90 to 94 years

The relationship between TDP-43 immunoreactivity and cognitive function, cerebrovascular
disease in control elderly brains

In control elderly brains, the rates of cases with cognitive impairment (CDR???0.5)
among cases with and without TDP-43 immunoreactive structures were 38.3 % (18/47 cases,
CDR was unavailable in 8 cases) and 34.3 % (28/70 cases, CDR was unavailable in 11
cases), respectively.

In addition, we examined the influence of cerebrovascular pathology. The rates of
cases with cerebrovascular pathology among cases with and without TDP-43 immunoreactive
structures were 61.2 % (34/55 cases) and 67.9 % (55/81 cases), respectively. There
were no significant differences between cases with and without TDP-43 immunoreacrive
structures.

TDP-43 pathology in comorbid pathologies, other neurological disorders and intermediate
pathologies.

TDP-43 immunoreactive structures were also found in the following cases: AD plus LBD
(5/6 cases, 83.3 %); AD plus AGD (3/3 cases, 100 %); AD plus PSP (1/1 case, 100 %);
AD plus HS (1/1 case, 100 %); LBD plus AGD (1/1 case, 100 %); LBD plus PSP (0/1 case,
0 %); AGD plus HS (1/1 case, 100 %); NFTD (3/6 cases, 50 %); CJD (0/4 cases, 0 %);
ALS/ALS with dementia (4/4 cases, 100 %); MSA (2/3 cases, 66.7 %); SCA6 (2/2 cases,
100 %); SCA3 (0/1 case, 0 %); PSP (2/2 cases, 100 %); HS (2/2 cases, 100 %); DRPLA
(0/1 case, 0 %); CBD (1/1 case, 100 %); FTLD-TDP (1/1 case, 100 %); MELAS (0/1 case,
0 %); NFTC (13/27 cases, 48.1 %); ADC (9/18 cases, 50 %); and PSC (6/12 cases, 50 %).