TDP-43 proteinopathy and motor neuron disease in chronic traumatic encephalopathy

Abstract

Epidemiological evidence suggests that the incidence of amyotrophic lateral sclerosis is increased in association with head injury. Repetitive head injury is also associated with the development of chronic traumatic encephalopathy (CTE), a tauopathy characterized by neurofibrillary tangles throughout the brain in the relative absence of β-amyloid deposits. We examined 12 cases of CTE and, in 10, found a widespread TAR DNA-binding protein of approximately 43kd (TDP-43) proteinopathy affecting the frontal and temporal cortices, medial temporal lobe, basal ganglia, diencephalon, and brainstem. Three athletes with CTE also developed a progressive motor neuron disease with profound weakness, atrophy, spasticity, and fasciculations several years before death. In these 3 cases, there were abundant TDP-43-positive inclusions and neurites in the spinal cord in addition to tau neurofibrillary changes, motor neuron loss, and corticospinal tract degeneration. The TDP-43 proteinopathy associated with CTE is similar to that found in frontotemporal lobar degeneration with TDP-43 inclusions, in that widespread regions of the brain are affected. Akin to frontotemporal lobar degeneration with TDP-43 inclusions, in some individuals with CTE, the TDP-43 proteinopathy extends to involve the spinal cord and is associated with motor neuron disease. This is the first pathological evidence that repetitive head trauma experienced in collision sports might be associated with the development of a motor neuron disease.

FIGURE 1

Cases of chronic traumatic encephalopathy (CTE) with widespread TAR DNA-binding protein of approximately 43 kd (TDP-43) immunoreactivity and motor neuron disease (CTE + MND). (A–C) Tau-immunoreactive neurofibrillary degeneration in the frontal cortex of the 3 cases of CTE + MND (whole-mount 50-μm sections immunostained for CP13, original magnification: 1×). (D–I) Tau-positive neurofibrillary tangles, glial tangles, and neuropil neurites are particularly dense at the depth of the cortical sulci, CP13 immunostain, original magnification: (D–F) 50×; (G–I) 100×. (J) TDP-43 immunostaining reveals abundant TDP-positive pathology in all cortical layers in the frontal cortex of Case 1, original magnification: 50×. (K) Numerous TDP-43–positive ring-shaped neurites (RNs) and ring-shaped glial inclusions (RGIs) in the frontal cortex of Case 2, original magnification: 200×. (L) Double immunostaining shows that most TDP-43–positive RNs and RGIs (red) are not colocalized with tau-positive neurites (PHF-1 brown, arrows), original magnification: 400×. (M) TDP-43–positive filamentous neuronal inclusions, original magnification: 600×. (N) Double immunostaining shows a tau-positive pretangle (PHF-1 brown, arrow) that is not associated with TDP-43 immunoreactivity (red), original magnification: 400×. (O) Double immunostaining shows a tau-positive tangle (PHF-1, arrow) that is not associated with TDP-43 immunoreactivity (red), original magnification: 400×.

FIGURE 2

Spinal cord pathology in chronic traumatic encephalopathy (CTE) with TAR DNA-binding protein of approximately 43 kd (TDP-43) proteinopathy, tauopathy, and motor neuron disease (CTE + MND). (A, B) Whole-mount 50-μm sections of lumbar and thoracic spinal cord immunostained with antibody AT8 showing abundant tau immunostaining in the ventral horns. (C) Tau-positive astrocytic tangles in the ventral horn of Case 1 (AT8 immunostain, original magnification: 100×). (D) Whole-mount 10-μm section through high thoracic spinal cord showing marked myelin and axonal loss in the lateral and ventral corticospinal tracts. Atrophic ventral roots are not visible. Luxol fast blue hematoxylin and eosin stain, original magnification: 1×. (E) Whole-mount 50-μm section of high thoracic cord showing intense immunoreactivity for activated microglia and macrophages in lateral and corticospinal tracts (LN-3 immunostain, original magnification: 1×). (F) Tau-positive neurofibrillary tangles in ventral horn of Case 3, AT8 immunostain, original magnification: 600×. (G) TDP-43 immunoreactivity in ventral horn, original magnification: 50×. (H) TDP-43 immunoreactive filamentous neuronal inclusions (FNIs), ring-shaped glial inclusions (RGIs), and ring-shaped neurites (RNs) in the ventral horns of the lumbar spinal cord in Case 3, original magnification: 200×. (I) Tau-positive astrocytes and their processes surrounding degenerating anterior horn cells in the thoracic spinal cord (AT8 immunostain, original magnification: 350×). (J) TDP-43–positive FNIs, RGIs, and RNs in the ventral horns of the lumbar spinal cord in Case 2, original magnification: 200×. (K) TDP-43–positive FNI in the anterior horn, original magnification: 400×.(L) Double immunostained sections show tau-positive astrocytes (brown) and their processes surrounding anterior horn neurons containing TDP-43–positive filamentous inclusions (red), PHF-1 and TDP-43 immunostains, original magnification: 400×. (M) TDP-43–positive FNIs, RGIs, and RNs in the lumbar ventral horns in Case 1, original magnification: 200×. (N) TDP-43–positive FNIs in the anterior horn, original magnification: 400×. (O) Double immunostained sections showing tau-positive astrocytes (brown) and their processes surrounding anterior horn neurons containing TDP-43–positive FNIs (red), PHF-1 and TDP-43 immunostains, original magnification: 600×.

FIGURE 3

TAR DNA-binding protein of approximately 43 kd (TDP-43) immunoreactivity in chronic traumatic encephalopathy (CTE). TDP-43 immunoreactivity is found as glial cytoplasmic inclusions (GCIs) and neuropil neurites in multiple brainstem nuclei including hypoglossal nucleus (A), oculomotor nucleus (B), substantia nigra (C) (original magnification: 200×). TDP-43 immunoreactivity in the medial temporal lobe structures consists primarily of dotlike neurites. (D) Hippocampus, CA1 (original magnification: 200×). TDP-43–positive dystrophic neurites and GCIs are also found in white matter. (E) Subcortical frontal white matter (original magnification: 200×). No ubiquitinated or TDP-43–positive inclusions are found in the dentate gyrus of the hippocampus. (F) Dentate gyrus of the hippocampus (original magnification: 400×).

FIGURE 4

Limited colocalization of tau and TAR DNA-binding protein of approximately 43 kd (TDP-43). (A, B) Laser scanning confocal microscopy was carried out on sections from the frontal cortex of Case 1 (A) and Case 2 (B). Sections were double immunostained for TDP-43 (green) and PHF-1 (red). Areas of colocalization appear yellow. In (A), there are abundant tau-positive neurites around a small blood vessel; white arrowhead indicates a small cluster of tau-positive neurites that seem to be colocalized with TDP-43. (B) Many TDP-43–positive neurites (green) and a few tau-positive neurites (red). Most neurites do not seem to be colocalized, but arrowheads point to occasional colocalized intraneuronal inclusions and neurites. White bars = 200 μm.