Co-occurrence of chronic traumatic encephalopathy and prion disease

Chronic Traumatic Encephalopathy and Neuropathological Comorbidities

With age, the presence of multiple neuropathologies in a single individual becomes increasingly common. Given that traumatic brain injury and the repetitive head impacts (RHIs) that occur in contact sports have been associated with the development of many neurodegenerative diseases, including chronic traumatic encephalopathy (CTE), Alzheimer's disease, Lewy body disease, and amyotrophic lateral sclerosis, it is becoming critical to understand the relationship and interactions between these pathologies. In fact, comorbid pathology is common in CTE and likely influenced by both age and the severity and type of exposure to RHI as well as underlying genetic predisposition. Here, we review the major comorbid pathologies seen with CTE and in former contact sports athletes and discuss what is known about the associations between RHI, age, and the development of neuropathologies. In addition, we examine the distinction between CTE and age-related pathology including primary age-related tauopathy and age-related tau astrogliopathy.

Recent Preclinical Insights Into the Treatment of Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative condition associated with significant mortality and morbidity. The central pathophysiological mechanisms by which repetitive cranial injury results in the neurodegeneration of CTE are poorly understood. Current well-established working models emphasize a central role for trauma-induced excessive phosphorylation and accumulation of insoluble tangles of Tau protein. In this review, we summarize recent data from preclinical animal models of CTE where a series of candidate treatments have been carefully evaluated, including kinase inhibitors, antibody therapy, and anti-inflammatory therapies. We discuss the overall translational potential of these approaches and provide recommendations for future bench-to-bedside treatment strategies.

Chronic traumatic encephalopathy: understanding the facts and debate

PURPOSE OF REVIEW

Chronic traumatic encephalopathy (CTE) is hypothesized to be a progressive neurodegenerative disease leading to dementia after repetitive head impacts. This review summarizes the recent evidence on CTE to highlight the facts currently known and the areas that remain poorly understood.

RECENT FINDINGS

Increasing evidence suggests that many of the prior assertions about CTE in relation to repetitive head trauma are premature. First, CTE lesions have been observed in individuals with no history of head trauma/impacts. In addition, attempts to characterize possible clinical markers of CTE have had several shortcomings, notably an absence of detailed clinical assessments during life, vague/nonspecific symptom reports, and crude methodology. Moreover, recent studies demonstrate that current CTE pathological criteria have limitations and are in need of refinement/validation.

SUMMARY

CTE is still in the early stages of research as a neuropathological condition and no specific clinical criteria exist. Claims about CTE being a progressive disease entity and caused exclusively by head trauma/impacts are not well supported at present. Such assertions may have impeded our understanding of the frequency and significance of this disorder. Refining diagnostic criteria to reduce ambiguity in classifying cases will be essential before risk factors and/or possible clinical markers may be identified.

What is strain in neurodegenerative diseases?

Neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, are characterized by the aggregation of misfolded proteins, including Aβ, tau and α-synuclein. It is well recognized that these misfolded proteins are able to self-propagate and spread throughout the nervous system and cause neuronal injury in a way that resembles prion disease. These disease-specific misfolded proteins demonstrate unique features, including the seeding barrier, the conformational memory effect, strain selection and strain evolution, based on the presence of various strains. However, the accurate definition of the term strain remains to be clarified. Here, a clear interpretation is proposed by a retrospective of its history in prion research and the recent progress in neurodegeneration research. Furthermore, the causes contributing to the genesis of various strains are also summarized. Deeper insight into strains helps us to understand the phenomena we observe in this field and it also enlightens us on the elusive mechanisms and management of neurodegeneration.

Co-existence of PrPD types 1 and 2 in sporadic Creutzfeldt-Jakob disease of the VV subgroup: phenotypic and prion protein characteristics

We report a detailed study of a cohort of sporadic Creutzfeldt-Jakob disease (sCJD) VV1-2 type-mixed cases (valine homozygosity at codon 129 of the prion protein, PrP, gene harboring disease-related PrP, PrPD, types 1 and 2). Overall, sCJDVV1-2 subjects showed mixed clinical and histopathological features, which often correlated with the relative amounts of the corresponding PrPD type. However, type-specific phenotypic characteristics were only detected when the amount of the corresponding PrPD type exceeded 20-25%. Overall, original features of types 1 (T1) and 2 (T2) in sCJDVV1 and -VV2, including rostrocaudal relative distribution and conformational indicators, were maintained in sCJDVV1-2 except for one of the two components of T1 identified by electrophoretic mobility as T121. The T121 conformational characteristics shifted in the presence of T2, inferring a conformational effect of PrPD T2 on T121. The prevalence of sCJDVV1-2 was 23% or 57% of all sCJDVV cases, depending on whether standard or highly sensitive type-detecting procedures were adopted. This study, together with previous data from sCJDMM1-2 (methionine homozygosity at PrP gene codon 129) establishes the type-mixed sCJD variants as an important component of sCJD, which cannot be identified with current non-tissue based diagnostic tests of prion disease.

Altered distribution, aggregation, and protease resistance of cellular prion protein following intracranial inoculation

Prion protein (PrP^C) is a protease-sensitive and soluble cell surface glycoprotein expressed in almost all mammalian cell types. PrP^Sc, a protease-resistant and insoluble form of PrP^C, is the causative agent of prion diseases, fatal and transmissible neurogenerative diseases of mammals. Prion infection is initiated via either ingestion or inoculation of PrP^Sc or when host PrP^C stochastically refolds into PrP^Sc. In either instance, the early events that occur during prion infection remain poorly understood. We have used transgenic mice expressing mouse PrP^C tagged with a unique antibody epitope to monitor the response of host PrP^C to prion inoculation. Following intracranial inoculation of either prion-infected or uninfected brain homogenate, we show that host PrP^C can accumulate both intra-axonally and within the myelin membrane of axons suggesting that it may play a role in axonal loss following brain injury. Moreover, in response to the inoculation host PrP^C exhibits an increased insolubility and protease resistance similar to that of PrP^Sc, even in the absence of infectious prions. Thus, our results raise the possibility that damage to the brain may be one trigger by which PrP^C stochastically refolds into pathogenic PrP^Sc leading to productive prion infection.

Traumatic Brain Injury-related voiding dysfunction in mice is caused by damage to rostral pathways, altering inputs to the reflex pathways

Brain degeneration, including that caused by traumatic brain injury (TBI) often leads to severe bladder dysfunction, including incontinence and lower urinary tract symptoms; with the causes remaining unknown. Male C57BL/6J mice underwent repetitive moderate brain injury (rmdTBI) or sham injury, then mice received either cis P-tau monoclonal antibody (cis mAb), which prevents brain degeneration in TBI mice, or control (IgG). Void spot assays revealed age-dependent incontinence in IgG controls 8 months after injury, while cis mAb treated or sham mice showed no dysfunction. No obvious bladder pathology occurred in any group. Urodynamic cystometry in conscious mice revealed overactive bladder, reduced maximal voiding pressures and incontinence in IgG control, but not sham or cis mAb treated mice. Hyperphosphorylated tau deposition and neural tangle-like pathology occurred in cortical and hippocampal regions only of IgG control mice accompanied with post-traumatic neuroinflammation and was not seen in midbrain and hindbrain regions associated with bladder filling and voiding reflex arcs. In this model of brain degeneration bladder dysfunction results from rostral, and not hindbrain damage, indicating that rostral brain inputs are required for normal bladder functioning. Detailed analysis of the functioning of neural circuits controlling bladder function in TBI should lead to insights into how brain degeneration leads to bladder dysfunction, as well as novel strategies to treat these disorders.