Presence of tau pathology within foetal neural allografts in patients with Huntington's and Parkinson's disease

Abstract

Cell replacement has been explored as a therapeutic strategy to repair the brain in patients with Huntington's and Parkinson's disease. Post-mortem evaluations of healthy grafted tissue in such cases have revealed the development of Huntington- or Parkinson-like pathology including mutant huntingtin aggregates and Lewy bodies. An outstanding question remains if tau pathology can also be seen in patients with Huntington's and Parkinson's disease who had received foetal neural allografts. This was addressed by immunohistochemical/immunofluorescent stainings performed on grafted tissue of two Huntington's disease patients, who came to autopsy 9 and 12 years post-transplantation, and two patients with Parkinson's disease who came to autopsy 18 months and 16 years post-transplantation. We show that grafts also contain tau pathology in both types of transplanted patients. In two patients with Huntington's disease, the grafted tissue showed the presence of hyperphosphorylated tau [both AT8 (phospho-tau Ser202 and Thr205) and CP13 (pSer202) immunohistochemical stainings] pathological inclusions, neurofibrillary tangles and neuropil threads. In patients with Parkinson's disease, the grafted tissue was characterized by hyperphosphorylated tau (AT8; immunofluorescent staining) pathological inclusions, neurofibrillary tangles and neuropil threads but only in the patient who came to autopsy 16 years post-transplantation. Abundant tau-related pathology was observed in the cortex and striatum of all cases studied. While the striatum of the grafted Huntington's disease patient revealed an equal amount of 3-repeat and 4-repeat isoforms of tau, the grafted tissue showed elevated 4-repeat isoforms by western blot. This suggests that transplants may have acquired tau pathology from the host brain, although another possibility is that this was due to acceleration of ageing. This finding not only adds to the recent reports that tau pathology is a feature of these neurodegenerative diseases, but also that tau pathology can manifest in healthy neural tissue transplanted into the brains of patients with two distinct neurodegenerative disorders.

Keywords: foetal transplants; human brain samples; neurodegenerative disorders; prion-like spread; tau protein.

Figure 1

Presence of phosphorylated tau within neuronal foetal allografts in a 67-year-old patient with Huntington’s disease 9 years post-transplantation. (A–L) Double immunohistochemistry for distinct forms of phosphorylated tau (nickel-enhanced DAB) labelled with the antibody AT8 (phospho-tau Ser202 and Thr205) and CP13 (pSer202) as well as neuronal elements stained for NeuN (DAB; A–I’’) or MAP2 (J–L). Presence of AT8+ tau neurofibrillary tangles, neuropil threads and neuronal inclusions in the cortex (A–C) and striatum (D–F) of a patient with Huntington’s disease. (G) Macroscopic view of tissue grafted into the caudate nucleus highlighting the transplant architectural subdivisions (P-zones, dotted lines). (H and I) Higher power magnification showing two distinct P-zone and non P-zone areas of the graft where AT8+ inclusions and neuropil threads were found (insets; H’, H’’, I’, I’’). CP13+ fibrils detected in the P-zones and non P-zones of the grafted tissue (J–L). Scale bars: A = 150 µm; B and D = 60 µm; C, H’ and H’’ = 40 µm; E = 30 µm; F and H = 100 µm; G = 500 µm; I and J = 200 µm; I’, I’’, J’, J’’, K and L = 20 µm. NeuN = neuronal nuclei.

Figure 2

Presence of phosphorylated tau within neuronal foetal allografts in a 40-year-old patient with Huntington’s disease 12 years post-transplantation. (A–K’) Double immunohistochemistry for distinct forms of phosphorylated tau (nickel-enhanced DAB) labelled with the antibody CP13 (Tau-pSer202) or AT180 (phospho-PHF-tau pThr231) as well as neuronal elements stained for MAP2 showing the presence of CP13+ tau inclusions in the cortex (A) and striatum (B and C) of the Huntington’s disease patient. (D) Macroscopic view of the grafted tissue highlighting the transplant architectural subdivisions into P-zones (dotted lines) as observed in the putamen. (E–I’’) Higher power magnification showing the distinct P-zones and non P-zones of the graft and the presence of CP13+ inclusions (insets; E’, G’, H’, I’ and I’’). AT180+ inclusions were also detected in the P-zones and non P-zones of the grafts (J and K). Scale bars: A–C = 50 µm; D = 500 µm; E, G = 50 µm; E’, F, G’, H, I’, I’’, J’, J’’and J’’’ = 20 µm; I = 200 µm; J, K = 100 µm.

Figure 3

Stereological quantifications of tau-related pathological elements in Huntington’s disease and Parkinson’s disease transplanted cases. (A) Quantification of AT8+ (phospho-tau Ser202 and Thr205) tau staining in the Huntington’s disease patient who passed away 9 years post-transplantation. (B) Quantification of CP13+ (Tau-pSer202) tau staining in the Huntington’s disease patient who passed away 12 years post-transplantation. (C) Quantification of AT8+ tau staining in the Parkinson’s disease patient who passed away 16 years post-transplantation. (D) Quantification of AT8+ tau staining in the Parkinson’s disease patient who passed away 18 months post-transplantation. Neurofibrillary tangles, neuropil threads and inclusions were quantified using stereology and plotted as the number of events encountered per surface area expressed in mm² of tissue.

Figure 4

The presence of phosphorylated tau within neuronal foetal allografts in patients with Parkinson’s disease is time-dependent. (A–I) Triple immunofluorescence for phosphorylated tau (AT8; phospho-tau Ser202 and Thr205) and neuronal elements as detected with MAP2 and TH showing the presence of AT8+ tau inclusions in the cortex of a 74-year-old patient with Parkinson’s disease 16 years post-transplantation. (D) Macroscopic view of the grafted tissue as observed in the putamen and various examples of the phosphorylated tau staining patterns observed within the grafted tissue (E–I). (J–R’) Triple immunofluorescence for phosphorylated tau (AT8; phospho-tau Ser202 and Thr205) and neuronal elements stained for MAP2 or TH showing the presence of AT8+ tau inclusions in the cortex (J–L) and striatum (M–O) of a 59-year-old patient with Parkinson’s disease 18 months post-transplantation. (P) Macroscopic view of the grafted tissue as observed in the putamen. (Q–R’) Higher power magnification showing the absence of any type of phosphorylated tau staining within the transplanted tissue. Scale bars: A, B, E-H, K, L, O, Q, R = 50 µm; C, J, M, N = 25 µm; D = 155 µm; I = 100 µm; P = 310 µm.

Figure 5

Tau-related pathology in control brains and as a function of age. (A–I) Representative images of double immunohistochemistry for neuronal elements (NeuN or MAP2; DAB) and phosphorylated tau (AT8, CP13, AT180; nickel-intensified DAB) in control brains of 70, 41 and 12 years of age. (A–C) The brain of a healthy 70-year-old control, matching the age of the Huntington’s disease patient presented in Fig. 1 and the Parkinson’s disease patient presented in Fig. 4, display age-related tau pathology. (D–F) Only a small number of phosphorylated tau neuronal threads (black arrows) can be seen in the brain of a healthy 41-year-old control, age-matched with the Huntington’s disease patient presented in Fig. 2. (G–I) In contrast to aged controls, the brain from a 12-year-old control, corresponding to the age of the grafted tissue, is completely devoid of any tau inclusions. Scale bars: A = 30 µm; B, G, H = 120 µm; C, F, I = 100 µm; D = 50 µm; E = 60 µm. NeuN = neuronal nuclei.