Exclusive induction of tau2 epitope in microglia/macrophages in inflammatory lesions-tautwopathy distinct from degenerative tauopathies

Microglia: Friend and foe in tauopathy

Aggregation of misfolded microtubule associated protein tau into abnormal intracellular inclusions defines a class of neurodegenerative diseases known as tauopathies. The consistent spatiotemporal progression of tau pathology in Alzheimer's disease (AD) led to the hypothesis that tau aggregates spread in the brain via bioactive tau "seeds" underlying advancing disease course. Recent studies implicate microglia, the resident immune cells of the central nervous system, in both negative and positive regulation of tau pathology. Polymorphisms in genes that alter microglial function are associated with the development of AD and other tauopathies. Experimental manipulation of microglia function can alter tau pathology and microglia-mediated neuroinflammatory cascades can exacerbate tau pathology. Microglia also exert protective functions by mitigating tau spread: microglia internalize tau seeds and have the capacity to degrade them. However, when microglia fail to degrade these tau seeds there are deleterious consequences, including secretion of exosomes containing tau that can spread to neurons. This review explores the intersection of microglia and tau from the perspective of neuropathology, neuroimaging, genetics, transcriptomics, and molecular biology. As tau-targeted therapies such as anti-tau antibodies advance through clinical trials, it is critical to understand the interaction between tau and microglia.

Neuropathology of SCA34 showing widespread oligodendroglial pathology with vacuolar white matter degeneration: a case study

Spinocerebellar ataxia type 34 (SCA34) is an autosomal dominant inherited ataxia due to mutations in ELOVL4, which encodes one of the very long-chain fatty acid elongases. SCA38, another spinocerebellar ataxia, is caused by mutations in ELOVL5, a gene encoding another elongase. However, there have been no previous studies describing the neuropathology of either SCA34 or 38. This report describes the neuropathological findings of an 83-year-old man with SCA34 carrying a pathological ELOVL4 mutation (NM_022726, c.736T>G, p.W246G). Macroscopic findings include atrophies in the pontine base, cerebellum, and cerebral cortices. Microscopically, marked neuronal and pontocerebellar fiber loss was observed in the pontine base. In addition, in the pontine base, accumulation of CD68-positive macrophages laden with periodic acid-Schiff (PAS)-positive material was observed. Many vacuolar lesions were found in the white matter of the cerebral hemispheres and, to a lesser extent, in the brainstem and spinal cord white matter. Immunohistological examination and ultrastructural observations with an electron microscope suggest that these vacuolar lesions are remnants of degenerated oligodendrocytes. Electron microscopy also revealed myelin sheath destruction. Unexpectedly, aggregation of the four-repeat tau was observed in a spatial pattern reminiscent of progressive supranuclear palsy. The tau lesions included glial fibrillary tangles resembling tuft-shaped astrocytes and neurofibrillary tangles and pretangles. This is the first report to illustrate that a heterozygous missense mutation in ELOVL4 leads to neuronal loss accompanied by macrophages laden with PAS-positive material in the pontine base and oligodendroglial degeneration leading to widespread vacuoles in the white matter in SCA34.

Targeting higher levels of lactate in the post-injury period following traumatic brain injury

BACKGROUND

Secondary traumatic brain injury (TBI) consequences continue multiple cascades of biochemical reactions caused by initial neurotrauma and one of the important pathogenetic processes is mitochondrial dysfunction partly characterized by elevation of lactate/pyruvate ratio in brain following metabolic failure.

OBJECTIVE

To identify lactate, pyruvate, lactate dehydrogenase, tau protein, ceruloplasmin blood levels in the post-injury period following TBI in relation to its different forms.

PATIENTS AND METHODS

Ninety-six patients (mean age ± SD 38.8 ± 10.39 years) at 12 months post-injury follow-ups TBI (post-TBI) were investigated; plasma lactate and pyruvate levels were measured by the spectrophotometric method according to the manufacturer protocols; tau protein, ceruloplasmin and lactate dehydrogenase (LDH) were measured in sera by enzyme-linked immunosorbent assays. Group 1 was comprised of 54 participants who had a history of mild TBI, group 2 was comprised of 42 patients who had a history of moderate TBI.

RESULTS

In this work, we found the highest plasma lactate levels in the patients with the post-injury period following moderate TBI as compared to controls (p = 0.0047, t = 2.924, 95 % CI -0.2154 to -0.04071) where the median lactate level was 0.832 ± 0.033 and 0704 ± 0.021 mmol/L in controls. No significant differences were seen between mild and moderate post-TBI (p = 0.079; t = 1.772); significant difference was also seen between general post-TBI group versus controls (p = 0.0181; t = 2.396; 95 % CI -0.1627 to -0.01551) with the median total lactate level of 0.793 ± 0.019 mmol/L. Lactate data did not distinguish with the respect to gender or age. The results showed no significant differences in tau protein, pyruvate, LDH and ceruloplasmin levels.

CONCLUSION

This study shows higher lactate levels in the post-injury period following TBI that reflect post-injury oxidative dysmetabolism and are more expressed in the post-injury period following moderate TBI.

Targeting Higher Levels of Tau Protein in Ukrainian Patients with Wilson's Disease

INTRODUCTION

Wilson's disease (WD) is a rare genetic disorder of copper metabolism in which impaired copper homeostasis may enhance amyloid aggregation and trigger neurodegeneration. Tau protein is a highly soluble microtubule-associated phosphoprotein that plays a significant role in microtubule stabilization; it is also a critical component of neurotoxic degenerative mechanisms. Tau has been shown to be involved in neuronal degeneration and axonal damage, and impaired copper metabolism has been shown to be involved in copper intoxication and thus associated with the processes of neurodegeneration and cellular damage. We have therefore investigated tau protein as a potential marker of axonal impairment and neurodegeneration.

METHODS

Patients with WD (n = 47; mean age ± standard deviation [SD] 30.19 ± 7.87 years; mean disease duration : 10.06 ± 3.9 years) and healthy controls (HC; n = 30; mean age 29.6 ± 4.73 years) were tested for serum tau protein levels using an enzyme-linked immunosorbent assay method. All patients were receiving a stable penicillamine dose as ongoing therapy.

RESULTS

Patients with WD had a higher mean tau protein level than did the HC (221.7 ± 135.1 vs. 71.14 ± 20.56 pg/mL, p < 0.0001). Patients with WD also had abnormally high serum tau protein levels (t statistic 6.047, 95% confidence interval - 218.2 to - 95.86) in both the cerebral and hepatocerebral forms of WD, with patients having the cerebral form showing a tendency toward higher tau levels. We found that tau protein did not differ according to gender, disease duration, age at disease onset, ceruloplasmin serum level and copper serum level.

CONCLUSION

This study provides novel data revealing that high tau protein levels in WD patients could be a potential biomarker for axonal impairment and possible neuronal damage due to tau protein, leading to neurodegeneration in WD.

Toward biomarkers in multiple sclerosis: new advances

Multiple sclerosis is an autoimmune disease that commonly affects young adults. If initially characterized by acute relapses, it is later followed by only incomplete remission. Over years, progressive disability and irreversible deficit lead to chronic neurological deficits in the majority of patients. The clinical course is protracted and unpredictable, and no biological marker is useful in predicting the evolution of autoaggression and disability. It is difficult to diagnose and to monitor disease progression after the initial symptoms or even during the major clinical manifestations, and it is difficult to treat. In this review, the authors report recent advances in the field, focusing on the search of new antigens as a marker of the disease, in their relevance to the pathophysiology and diagnosis of the disease.

Truncation of tau at E391 promotes early pathologic changes in transgenic mice

Proteolytic cleavage of tau at glutamic acid 391 (E391) is linked to the pathogenesis of Alzheimer disease (AD). This C-terminal-truncated tau species exists in neurofibrillary tangles and abnormal neurites in the brains of AD patients and may potentiate tau polymerization. We generated a mouse model that expresses human tau truncated at E391 to begin to elucidate the role of this C-terminal-truncated tau species in the development of tau pathology. Our results show that truncated but otherwise wild-type human tau is sufficient to drive pretangle pathologic changes in tau, including accumulation of insoluble tau, somatodendritic redistribution, formation of pathologic conformations, and dual phosphorylation of tau at sites associated with AD pathology. In addition, these mice exhibit atypical neuritic tau immunoreactivity, including abnormal neuritic processes and dystrophic neurites. These results suggest that changes in tau proteolysis can initiate tauopathy.

Local delivery of recombinant human bone morphogenetic protein-2 increases axonal regeneration and the expression of tau protein after facial nerve injury

This study explored the function and possible mechanism of bone morphogenetic protein-2 (BMP-2) in the healing of injured peripheral nerves in vivo. Rabbit facial nerves were injured by clamping and then treated with recombinant human BMP-2 (rhBMP-2) or phosphate-buffered saline (control) by injecting once during surgery and twice a day post-injury for 7 days. Facial nerve fragments within 5 mm of the clamping point were examined at different times post-surgery. Axon structures visualized by Bielschowsky staining were similar in experimental and control nerves 2 and 6 weeks post-injury. At 4 weeks post-injury, cross-section images of facial nerves showed that axons treated with rhBMP-2 were denser and thicker, and levels of tau protein were increased. It is concluded from these data that rhBMP-2 may affect injured facial nerve regeneration by inducing more neurons to return to embryonic patterns of tau gene expression.

Microglial activation in brain lesions with tau deposits: comparison of human tauopathies and tau transgenic mice TgTauP301L

The aim of this study is to clarify the relationship of microglia to phosphorylated tau accumulation and the characteristics of microglial activation in brain lesions of human tauopathies in comparison to mutant tau transgenic (TG) mice. We performed immunocytochemical analyses of brains from six patients with tauopathies, and 24 mice (18 TG mice expressing mutant tau P301L and six non-TG control mice, 11 to 27 months of age) using anti-tau antibodies and various microglial markers. In the tau TG, both semiquantitative severity ratings of microglial activation and an ultrastructural study were performed. In human tauopathies, Iba1- and major histocompatibility complex (MHC) class II-positive activated microglia increased in regions of phosphorylated tau (AT8) accumulation. The immunoreactivity of scavenger receptor class A (SRA) was present in some activated microglia, including phagocytic microglia in Alzheimer's disease (AD). Double-immunofluorescent analysis under a confocal microscope showed activated microglia at the vicinity of AT8-positive cells. Semiquantitative data of the TG and control mice indicated that the immunopositivity of AT8 was closely associated with the number of Iba1-positive microglia in the cortical area. Tau-associated microglia showed rare immunoreactivity for MHC class II antigen and SRA in the TG mice. Ultrastructurally, activated microglia with enlarged cytoplasm were located near neurons containing abnormal cytoskeletons. This comparative study of human tauopathies and tau TG mice indicated that microglial activation was closely related to phosphorylated tau accumulation, and that activated microglia of the TG mice may have the low expression of MHC class II and SRA compared with those of human tauopathies.