Tetsuaki Arai

Phosphorylated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis.

TAR DNA‐binding protein of 43kDa (TDP‐43) is deposited as cytoplasmic and intranuclear inclusions in brains of patients with frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD‐U) and amyotrophic lateral sclerosis (ALS). Previous studies reported that abnormal phosphorylation takes place in deposited TDP‐43. The aim of this study was to identify the phosphorylation sites and responsible kinases, and to clarify the pathological significance of phosphorylation of TDP‐43.

Prion-like spreading of pathological α-synuclein in brain

α-Synuclein is the major component of filamentous inclusions that constitute the defining characteristic of neurodegenerative α-synucleinopathies. However, the molecular mechanisms underlying α-synuclein accumulation and spread are unclear. Here we show that intracerebral injections of sarkosyl-insoluble α-synuclein from brains of patients with dementia with Lewy bodies induced hyperphosphorylated α-synuclein pathology in wild-type mice. Furthermore, injection of fibrils of recombinant human and mouse α-synuclein efficiently induced similar α-synuclein pathologies in wild-type mice. C57BL/6J mice injected with α-synuclein fibrils developed abundant Lewy body/Lewy neurite-like pathology, whereas mice injected with soluble α-synuclein did not. Immunoblot analysis demonstrated that endogenous mouse α-synuclein started to accumulate 3 months after inoculation, while injected human α-synuclein fibrils disappeared in about a week. These results indicate that α-synuclein fibrils have prion-like properties and inoculation into wild-type brain induces α-synuclein pathology in vivo. This is a new mouse model of sporadic α-synucleinopathy and should be useful for elucidating progression mechanisms and evaluating disease-modifying therapy.

Phosphorylated TDP-43 in Alzheimer’s disease and dementia with Lewy bodies

Phosphorylated and proteolytically cleaved TDP-43 is a major component of the ubiquitin-positive inclusions in the most common pathological subtype of frontotemporal lobar degeneration (FTLD-U). Intracellular accumulation of TDP-43 is observed in a subpopulation of patients with other dementia disorders, including Alzheimer’s disease (AD) and dementia with Lewy bodies (DLB). However, the pathological significance of TDP-43 pathology in these disorders is unknown, since biochemical features of the TDP-43 accumulated in AD and DLB brains, especially its phosphorylation sites and pattern of fragmentation, are still unclear. To address these issues, we performed immunohistochemical and biochemical analyses of AD and DLB cases, using phosphorylation-dependent anti-TDP-43 antibodies. We found a higher frequency of pathological TDP-43 in AD (36–56%) and in DLB (53–60%) than previously reported. Of the TDP-43-positive cases, about 20–30% showed neocortical TDP-43 pathology resembling the FTLD-U subtype associated with progranulin gene (PGRN) mutations. Immunoblot analyses of the sarkosyl-insoluble fraction from cases with neocortical TDP-43 pathology showed intense staining of several low-molecular-weight bands, corresponding to C-terminal fragments of TDP-43. Interestingly, the band pattern of these C-terminal fragments in AD and DLB also corresponds to that previously observed in the FTLD-U subtype associated with PGRN mutations. These results suggest that the morphological and biochemical features of TDP-43 pathology are common between AD or DLB and a specific subtype of FTLD-U. There may be genetic factors, such as mutations or genetic variants of PGRN underlying the co-occurrence of abnormal deposition of TDP-43, tau and α-synuclein.

Truncation and pathogenic mutations facilitate the formation of intracellular aggregates of TDP-43

TAR DNA binding protein of 43 kDa (TDP-43) is a major component of the ubiquitin-positive inclusions found in the brain of patients with frontotemporal lobar degeneration (FTLD-U) and amyotrophic lateral sclerosis (ALS). Here, we report that expression of TDP-43 C-terminal fragments as green fluorescent protein (GFP) fusions in SH-SY5Y cells results in the formation of abnormally phosphorylated and ubiquitinated inclusions that are similar to those found in FTLD-U and ALS. Co-expression of DsRed-tagged full-length TDP-43 with GFP-tagged C-terminal fragments of TDP-43 causes formation of cytoplasmic inclusions positive for both GFP and DsRed. Cells with GFP and DsRed positive inclusions lack normal nuclear staining for endogenous TDP-43. These results suggest that GFP-tagged C-terminal fragments of TDP-43 are bound not only to transfected DsRed-full-length TDP-43 but also to endogenous TDP-43. Endogenous TDP-43 may be recruited to cytoplasmic aggregates of TDP-43 C-terminal fragments, which results in the failure of its nuclear localization and function. Interestingly, expression of GFP-tagged TDP-43 C-terminal fragments harboring pathogenic mutations that cause ALS significantly enhances the formation of inclusions. We also identified cleavage sites of TDP-43 C-terminal fragments deposited in the FTLD-U brains using mass spectrometric analyses. We propose that generation and aggregation of phosphorylated C-terminal fragments of TDP-43 play a primary role in the formation of inclusions and resultant loss of normal TDP-43 localization, leading to neuronal degeneration in TDP-43 proteinopathy.

Prion-like Properties of Pathological TDP-43 Aggregates from Diseased Brains

TDP-43 is the major component protein of ubiquitin-positive inclusions in brains of patients with frontotemporal lobar degeneration (FTLD-TDP) or amyotrophic lateral sclerosis (ALS). Here, we report the characterization of prion-like properties of aggregated TDP-43 prepared from diseased brains. When insoluble TDP-43 from ALS or FTLD-TDP brains was introduced as seeds into SH-SY5Y cells expressing TDP-43, phosphorylated and ubiquitinated TDP-43 was aggregated in a self-templating manner. Immunoblot analyses revealed that the C-terminal fragments of insoluble TDP-43 characteristic of each disease type acted as seeds, inducing seed-dependent aggregation of TDP-43 in these cells. The seeding ability of insoluble TDP-43 was unaffected by proteinase treatment but was abrogated by formic acid. One subtype of TDP-43 aggregate was resistant to boiling treatment. The insoluble fraction from cells harboring TDP-43 aggregates could also trigger intracellular TDP-43 aggregation. These results indicate that insoluble TDP-43 has prion-like properties that may play a role in the progression of TDP-43 proteinopathy.

Cell mediators of inflammation in the Alzheimer disease brain.

Lesions of Alzheimer disease are associated with low-grade but sustained inflammatory responses. Activated microglia agglomerate in the center of senile plaques. Reactive astrocytes marginate the amyloid beta-protein (A beta) deposits and extend their processes toward the center of plaques. Both microglia and astrocytes are known to secrete a wide variety of molecules involved in inflammation and are potential sources of proinflammatory elements in the brain. Dystrophic neurites occur in senile plaques with such glial reactions, suggesting the relevance of inflammatory responses to the neuronal degeneration in Alzheimer disease. Activated glial cells are, therefore, targets of anti-inflammatory therapy of Alzheimer disease. However, evidence also indicates that these cells eliminate A beta from the brain. A beta is produced continuously in both the normal and the AD brain. Under normal conditions, A beta is removed successfully before it accumulates as extracellular amyloid fibrils. Even in Alzheimer disease, a large portion of A beta may be cleared from the brain with a small portion being left and deposited as neurotoxic senile plaques. Both in vivo and in vitro studies showed the effective uptake of A beta by microglia. Before clinical application, it must be determined whether the treatment that suppresses glial activation and inflammatory responses inhibits A beta removal by glial cells.

Distinct isoforms of tau aggregated in neurons and glial cells in brains of patients with Pick's disease, corticobasal degeneration and progressive supranuclear palsy

Abstract. We investigated isoform composition of aggregated tau protein in brains with Picks disease (PiD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) by immunoblot analysis of sarkosyl-insoluble fractions of brain homogenates. We also examined the adjacent brain tissues immunohistochemically with a rabbit antibody, Ex10, which specifically recognizes exon 10 of tau. The Ex10 recognizes tau isoforms with four microtubule-binding repeats (4Rtau) but not those with three microtubule-binding repeats (3Rtau). Sarkosyl-insoluble tau from the brains of patients with CBD and PSP consisted of 4Rtau. Insoluble tau from the PiD brains contained both 3Rtau and 4Rtau, where 3Rtau predominated over 4Rtau. In brain tissues of CBD and PSP, Ex10 immunostained all neuronal and glial tau-positive structures. They included pre-tangles, astrocytic plaques, tuft-shaped astrocytes, and oligodendroglial coiled bodies. In PiD brains, astrocytic inclusions were also positive for 4Rtau. However, the majority of, if not all, Pick bodies and oligodendroglial tau inclusions were negative for 4Rtau. Such results suggest that, in neurons and oligodendroglia, tau isoforms involved in the pathological processes differ between CBD/PSP and PiD, and are thus disease specific. This contrasts with the astrocytic tau isoforms that accumulate similarly in all three disorders.

LRRK2 expression in normal and pathologic human brain and in human cell lines

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) have been recently identified in families with autosomal-dominant late-onset Parkinson disease. We report that by reverse transcriptase-polymerase chain reaction, the mRNA of LRRK2 is expressed in soluble extracts of human brain, liver, and heart and in cultured human astrocytes, microglia, and oligodendroglia as well as in human neuroblastoma cell lines. We find by Western blotting using a polyclonal antibody of the leucine-rich repeat kinase 2 protein (Lrrk2) specific for C-terminal residues 2511-2527 that an apparent full-length protein and several of its fractions are expressed in soluble extracts of normal human brain. By immunocytochemistry, the antibody recognizes neurons, and more weakly astrocytes and microglia, in normal brain tissue. It intensely labels Lewy bodies in Parkinson disease and related neurodegenerative disorders. It also labels a subset of neurofibrillary tangles in Alzheimer disease and the Parkinsonism dementia complex of Guam (PDCG). It labels thorn-shaped astrocytes and oligodendroglial coiled bodies in PDCG; oligodendroglial inclusions in multiple system atrophy; Pick bodies in Pick disease; nuclear and cytoplasmic inclusions in Huntington disease; and intraneuronal and glial inclusions in amyotrophic lateral sclerosis. In summary, LRRK2 is constitutively expressed in neurons and also in glial cells of human brain. It strongly associates with pathological inclusions in several neurodegenerative disorders.

Abnormal phosphorylation of Ser409/410 of TDP-43 in FTLD-U and ALS

A monoclonal antibody specific for phosphoserines 409 and 410 of TDP‐43 (mAb pS409/410) has been produced. It strongly stained TDP‐43‐positive inclusions in brain of patients with frontotemporal lobar degeneration and amyotrophic lateral sclerosis, but did not stain nuclei, in which normal TDP‐43 is localized. It did not recognize TDP‐43 rapidly extracted from brains of rats at various developmental stages, strongly suggesting that phosphorylation of Ser409/410 is an abnormal event. Analysis of postmortem changes of TDP‐43 revealed that the amounts of Sarkosyl‐insoluble, urea‐soluble full‐length TDP‐43 and a 35 kDa N‐terminal fragment increased time‐dependently.

Identification of amino‐terminally cleaved tau fragments that distinguish progressive supranuclear palsy from corticobasal degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative diseases that are characterized by intracytoplasmic aggregates of hyperphosphorylated tau with four microtubule‐binding repeats. Although PSP and CBD have distinctive pathological features, no biochemical difference in aggregated tau has been identified. In this study, we examined the brains of eight patients with PSP, six patients with CBD, and one atypical case with pathological features of both CBD and PSP. On immunoblots of sarkosyl‐insoluble brain extracts, a 33kDa band predominated in the low molecular weight tau fragments in PSP, whereas two closely related bands of approximately 37kDa predominated in CBD. Immunoblots of the atypical case showed both the 33kDa band and the 37kDa doublet. Protein sequencing and immunochemical analyses showed that the 33kDa band and the 37kDa doublet consisted of the carboxyl half of tau with different amino termini. These results suggest that, despite the identical composition of tau isoforms, different proteolytic processing of abnormal tau takes place in these two diseases. Such a biochemical divergence may be related to the neuropathological features of these diseases.