In addition to motor neurone degeneration, up to 50% of amyotrophic lateral sclerosis (ALS) patients present with cognitive decline. Understanding the neurobiological changes underlying these cognitive deficits is critical, as cognitively impaired patients exhibit a shorter survival time from symptom onset. Given the pathogenic role of synapse loss in other neurodegenerative diseases in which cognitive decline is apparent, such as Alzheimer’s disease, we aimed to assess synaptic integrity in the ALS brain. Here, we have applied a unique combination of high-resolution imaging of post-mortem tissue with neuropathology, genetic screening and cognitive profiling of ALS cases. Analyses of more than 1 million synapses using two complimentary high-resolution techniques (electron microscopy and array tomography) revealed a loss of synapses from the prefrontal cortex of ALS patients. Importantly, synapse loss was significantly greater in cognitively impaired cases and was not due to cortical atrophy, nor associated with dementia-associated neuropathology. Interestingly, we found a trend between pTDP-43 pathology and synapse loss in the frontal cortex and discovered pTDP-43 puncta at a subset of synapses in the ALS brains. From these data, we postulate that synapse loss in the prefrontal cortex represents an underlying neurobiological substrate of cognitive decline in ALS.Electronic supplementary materialThe online version of this article (10.1007/s00401-017-1797-4) contains supplementary material, which is available to authorized users.

Mitochondria play a key role in common neurodegenerative diseases and contain their own genome: mtDNA. Common inherited polymorphic variants of mtDNA have been associated with several neurodegenerative diseases, and somatic deletions of mtDNA have been found in affected brain regions. However, there are conflicting reports describing the role of rare inherited variants and somatic point mutations in neurodegenerative disorders, and recent evidence also implicates mtDNA levels. To address these issues we studied 1363 post mortem human brains with a histopathological diagnosis of Parkinson’s disease (PD), Alzheimer’s disease (AD), Frontotemporal dementia – Amyotrophic Lateral Sclerosis (FTD-ALS), Creutzfeldt Jacob disease (CJD), and healthy controls. We obtained high-depth whole mitochondrial genome sequences using off target reads from whole exome sequencing to determine the association of mtDNA variation with the development and progression of disease, and to better understand the development of mtDNA mutations and copy number in the aging brain. With this approach, we found a surprisingly high frequency of heteroplasmic mtDNA variants in 32.3% of subjects. However, we found no evidence of an association between rare inherited variants of mtDNA or mtDNA heteroplasmy and disease. In contrast, we observed a reduction in the amount of mtDNA copy in both AD and CJD. Based on these findings, single nucleotide variants of mtDNA are unlikely to play a major role in the pathogenesis of these neurodegenerative diseases, but mtDNA levels merit further investigation.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0404-6) contains supplementary material, which is available to authorized users.

Dementia with Lewy bodies is characterized by the accumulation of Lewy bodies and Lewy neurites in the CNS, both of which are composed mainly of aggregated α-synuclein phosphorylated at Ser129. Although phosphorylated α-synuclein is believed to exert toxic effects at the synapse in dementia with Lewy bodies and other α-synucleinopathies, direct evidence for the precise synaptic localization has been difficult to achieve due to the lack of adequate optical microscopic resolution to study human synapses. In the present study we applied array tomography, a microscopy technique that combines ultrathin sectioning of tissue with immunofluorescence allowing precise identification of small structures, to quantitatively investigate the synaptic phosphorylated α-synuclein pathology in dementia with Lewy bodies. We performed array tomography on human brain samples from five patients with dementia with Lewy bodies, five patients with Alzheimer's disease and five healthy control subjects to analyse the presence of phosphorylated α-synuclein immunoreactivity at the synapse and their relationship with synapse size. Main analyses were performed in blocks from cingulate cortex and confirmed in blocks from the striatum of cases with dementia with Lewy bodies. A total of 1 318 700 single pre- or postsynaptic terminals were analysed. We found that phosphorylated α-synuclein is present exclusively in dementia with Lewy bodies cases, where it can be identified in the form of Lewy bodies, Lewy neurites and small aggregates (<0.16 µm3). Between 19% and 25% of phosphorylated α-synuclein deposits were found in presynaptic terminals mainly in the form of small aggregates. Synaptic terminals that co-localized with small aggregates of phosphorylated α-synuclein were significantly larger than those that did not. Finally, a gradient of phosphorylated α-synuclein aggregation in synapses (pre > pre + post > postsynaptic) was observed. These results indicate that phosphorylated α-synuclein is found at the presynaptic terminals of dementia with Lewy bodies cases mainly in the form of small phosphorylated α-synuclein aggregates that are associated with changes in synaptic morphology. Overall, our data support the notion that pathological phosphorylated α-synuclein may disrupt the structure and function of the synapse in dementia with Lewy bodies.

Rationale: Myocardial infarction (MI) is one of the leading causes of death worldwide and inflammation is central to the tissue response and patient outcomes. The 18kDa translocator protein (TSPO) has been utilized in positron emission tomography (PET) as an inflammatory biomarker. The aims of this study were to: 1) screen novel, fluorinated, TSPO radiotracers for susceptibility to the rs6971 genetic polymorphism using in vitro competition binding assays in human brain and heart, 2) assess whether the in vivo characteristics of our lead radiotracer, 18 F-LW223, are suitable for clinical translation and 3) validate whether 18 F-LW223 can detect macrophage driven inflammation in a rat myocardial infarction model. Methods: Fifty-one human brain and twenty-nine human heart tissue samples were screened for the rs6971 polymorphism. Competition binding assays were conducted with 3 H-PK11195 and the following ligands: PK11195, PBR28 and our novel compounds (AB5186 and LW223). Naive rats and mice were used for in vivo PET kinetic studies, radiometabolite studies and dosimetry experiments. Rats underwent permanent coronary artery ligation and were scanned using PET/CT with invasive input function at 7 days following MI. For quantification of PET signal in the hypoperfused myocardium, K 1 was used as a surrogate marker of perfusion to correct the binding potential for impaired radiotracer transfer from plasma to tissue (BP TC). Results: LW223 binding to TSPO was not susceptible to the rs6971 genetic polymorphism in human brain and heart samples. In rodents, 18 F-LW223 displayed a specific uptake consistent with TSPO expression, a slow metabolism in blood (62% of parent at 120 min), a high plasma free fraction of 38.5% and a suitable dosimetry profile Brain Tissue for Binding Assays Heart Tissue for Binding Assays