Co-incidental C9orf72 expansion mutation-related frontotemporal lobar degeneration pathology and sporadic Creutzfeldt-Jakob disease

Detection of an Intermediate in the Unfolding Process of the N-Terminal Domain of TDP-43

TAR DNA-binding protein 43 (TDP-43) is a nuclear protein accumulating in intraneuronal cytoplasmic inclusions associated with amyotrophic lateral sclerosis, frontotemporal lobar degeneration with tau-negative/ubiquitin-positive inclusions, and limbic-predominant age-related TDP-43 encephalopathy. Oligomerization of full-length TDP-43, driven by its N-terminal domain (NTD), is essential for its function, but aberrant self-assembly also promotes liquid-liquid phase separation and formation of solid inclusions. Building on recent all-atom molecular dynamics simulations and using various biophysical approaches, we identified a partially unfolded state accumulating during unfolding of TDP-43 NTD, before the major energy barrier of unfolding is crossed. Intrinsic fluorescence spectroscopy coupled to a stopped-flow device at high urea concentration reveals that the intermediate state has a fluorescence emission distinct from those of the native and unfolded states and forms within the 14 ms dead time. Conventional fluorescence spectroscopy shows it still accumulates at moderate urea concentration. Circular dichroism and H/D exchange results show a species with an intermediate content of secondary structure and a distorted β-sheet, whereas SYPRO orange fluorescence indicates an open conformation with more exposed hydrophobic regions compared to the native state. Importantly, this intermediate is observed even at low protein concentration, when TDP-43 NTD is largely monomeric, indicating that its formation is independent of the initial TDP-43 NTD oligomeric state. Dynamic light scattering at high protein concentration shows that the intermediate is a partially folded dimer. The intermediate forms upon chemical denaturation and does not occur under thermal unfolding. Overall, the findings highlight the presence of one more partially folded state for TDP-43 NTD, underlining its high structural plasticity and suggesting that its distinct unfolding pathway may play a critical role in both its functional and pathological behaviors.

Metabolic Brain Changes Can Predict the Underlying Pathology in Neurodegenerative Brain Disorders: A Case Report of Sporadic Creutzfeldt-Jakob Disease with Concomitant Parkinson's Disease

The co-occurrence of multiple proteinopathies is being increasingly recognized in neurodegenerative disorders and poses a challenge in differential diagnosis and patient selection for clinical trials. Changes in brain metabolism captured by positron emission tomography (PET) with 18 F-fluorodeoxyglucose (FDG) allow us to differentiate between different neurodegenerative disorders either by visual exploration or by studying disease-specific metabolic networks in individual patients. However, the impact of multiple proteinopathies on brain metabolism and metabolic networks remains unknown due to the absence of pathological studies. In this case study, we present a 67-year-old patient with rapidly progressing dementia clinically diagnosed with probable sporadic Creutzfeldt-Jakob disease (sCJD). However, in addition to the expected pronounced cortical and subcortical hypometabolism characteristic of sCJD, the brain FDG PET revealed an intriguing finding of unexpected relative hypermetabolism in the bilateral putamina, raising suspicions of coexisting Parkinson's disease (PD). Additional investigation of disease-specific metabolic brain networks revealed elevated expression of both CJD-related pattern (CJDRP) and PD-related pattern (PDRP) networks. The patient eventually developed akinetic mutism and passed away seven weeks after symptom onset. Neuropathological examination confirmed neuropathological changes consistent with sCJD and the presence of Lewy bodies confirming PD pathology. Additionally, hyperphosphorylated tau and TDP-43 pathology were observed, a combination of four proteinopathies that had not been previously reported. Overall, this case provides valuable insights into the complex interplay of neurodegenerative pathologies and their impact on metabolic brain changes, emphasizing the role of metabolic brain imaging in evaluating potential presence of multiple proteinopathies.

Cerebrospinal Fluid Biomarker Profile in TDP-43-Related Genetic Frontotemporal Dementia

Cerebrospinal fluid (CSF) biomarkers, namely total tau, phospho-tau and amyloid beta peptides, have received much attention specifically regarding Alzheimer’s disease (AD), since they can detect the biochemical fingerprint of AD and serve as a diagnostic tool for accurate and early diagnosis during life. In the same way, biomarkers for other neurodegenerative disease pathologies are also needed. We present a case series of six patients with genetic frontotemporal dementia (FTD), with TDP-43 underlying proteinopathy, in an attempt to assess TDP-43 as a novel biomarker alone and in combination with established AD biomarkers for this specific patient group, based on the principles of personalized and precision medicine. Our results indicate that genetic TDP-43-FTD is characterized by increased CSF TPD-43 and increased TDP-43 × τΤ/τP-181 combination. Hence, TDP-43 combined with tau proteins could be a useful tool for the diagnosis of genetic FTD with TDP-43 underling histopathology, supplementing clinical, neuropsychological and imaging data.