Traumatic brain injury (TBI), considered as an event and/or a disease, initiates a complex pathophysiologic central nervous system cascade with acute effects and secondary insults that may lead to chronic functional, neurocognitive, and neuropsychiatric deficits.¹ Traumatic brain injury is classified according to its degree of severity (mild, moderate, and severe). In the United States, there are more than 3.5 million emergency department visits for TBI and more than 280 000 patients are hospitalized annually with TBI, with most of these classified as mild TBI (mTBI). There are also many more individuals with mTBI who never seek medical attention. More than 300 000 armed service members sustained TBI during combat and training from 2000 to 2014.² Approximately half of patients with TBI in the United States incur at least some short-term disability.³ Traumatic brain injury is associated with an increased risk of neurodegenerative disorders, such as Alzheimer disease, years or decades after injury.⁴ In addition, repetitive mTBI is a risk factor for a neurodegenerative condition called chronic traumatic encephalopathy (CTE).^5-7 Chronic traumatic encephalopathy, which can be confirmed only by postmortem neuropathologic examination, is defined by the abnormal accumulation of hyperphosphorylated tau protein (P-tau) in neurons, astroglia, and cell processes distributed around small blood vessels at the depth of cortical sulci in an irregular pattern.⁸

Traumatic brain injury (TBI) is a cause of death and disability and can lead to tauopathy-related dementia at an early age. Pathologically, TBI results in axonal injury that is coupled to tau hyperphosphorylation, leading to microtubule instability and tau-mediated neurodegeneration. This suggests that the forms of this protein might serve as neuroinjury-related biomarkers for diagnosis of injury severity and prognosis of the neurological damage prior to clinical expression. We initially determined whether we could detect tau in body fluids using a highly sensitive assay. We used a novel immunoassay, enhanced immunoassay using multi-arrayed fiberoptics (EIMAF) either alone or in combination with rolling circle amplification (a-EIMAF) for the detection of total (T) and phosphorylated (P) tau proteins from brains and biofluids (blood, CSF) of rodents following controlled cortical impact (CCI) and human patients post severe TBI (sTBI). This assay technology for tau is the most sensitive to date with a detection limit of approximately 100 ag/mL for either T-tau and P-tau. In the rodent models, T-tau and P-tau levels in brain and blood increased following CCI during the acute phase and remained high during the chronic phase (30 d). In human CSF samples, T-tau and P-tau increased during the sampling period (5–6 d). T-tau and P-tau in human serum rose during the acute phase and decreased during the chronic stage but was still detectable beyond six months post sTBI. Thus, EIMAF has the potential for assessing both the severity of the proximal injury and the prognosis using easily accessible samples.

Single and repeated sports-related mild traumatic brain injury (mTBI), also referred to as concussion, can result in chronic post-concussive syndrome (PCS), neuropsychological and cognitive deficits, or chronic traumatic encephalopathy (CTE). However PCS is often difficult to diagnose using routine clinical, neuroimaging or laboratory evaluations, while CTE currently only can be definitively diagnosed postmortem. We sought to develop an animal model to simulate human repetitive concussive head injury for systematic study. In this study, mice received single or multiple head impacts by a stereotaxic impact device with a custom-made rubber tip-fitted impactor. Dynamic changes in MRI, neurobiochemical markers (Tau hyperphosphorylation and glia activation in brain tissues) and neurobehavioral functions such as anxiety, depression, motor function and cognitive function at various acute/subacute (1-7 day post-injury) and chronic (14-60 days post-injury) time points were examined. To explore the potential biomarkers of rCHI, serum levels of total Tau (T-Tau) and phosphorylated Tau (P-Tau) were also monitored at various time points. Our results show temporal dynamics of MRI consistent with structural perturbation in the acute phase and neurobiochemical changes (P-Tau and GFAP induction) in the subacute and chronic phase as well as development of chronic neurobehavioral changes, which resemble those observed in mTBI patients.

Chronic wasting disease (CWD) of elk (Cervus elaphus nelsoni) and mule deer (Odocoileus hemionus) is one of three naturally occurring forms of prion disease, the others being Creutzfeldt–Jakob disease in humans and scrapie in sheep. In the last few decades, CWD has spread among captive and free-ranging cervids in 13 US states, two Canadian provinces and recently in Korea. The origin of the CWD agent(s) in cervids is not known. This study describes the development of a transgenic mouse line (TgElk) homozygous for a transgene array encoding the elk prion protein (PrP^C) and its use in propagating and simulating CWD in mice. Intracerebral injection of one mule deer and three elk CWD isolates into TgElk mice led to disease with incubation periods of 127 and 95 days, respectively. Upon secondary passage, the incubation time was reduced to 108 and 90 days, respectively. Upon passage into TgElk mice, CWD prions (PrP^Sc) maintained the characteristic Western blot profiles seen in CWD-affected mule deer and elk and produced histopathological modifications consistent with those observed in the natural disease. The short incubation time observed on passage from cervid to mouse with both mule deer and elk CWD brain homogenates and the demonstrated capacity of the animals to propagate (mouse to mouse) CWD agents make the TgElk line a valuable model to study CWD agents in cervid populations. In addition, these results with this new transgenic line suggest the intriguing hypothesis that there could be more than one strain of CWD agent in cervids.

Studies in vivo and in vitro have suggested that the mechanism underlying Alzheimer’s disease (AD) neuropathogenesis is initiated by an interaction between the cellular prion protein (PrPC) and amyloid-β oligomers (Aβo). This PrPC-Aβo complex activates Fyn kinase which, in turn, hyperphosphorylates tau (P-Tau) resulting in synaptic dysfunction, neuronal loss and cognitive deficits. AD transgenic mice lacking PrPC accumulate Aβ, but show normal survival and no loss of spatial learning and memory suggesting that PrPC functions downstream of Aβo production but upstream of intracellular toxicity within neurons. Since AD and traumatic brain injury (TBI)-linked chronic traumatic encephalopathy are tauopathies, we examined whether similar mechanistic pathways are responsible for both AD and TBI pathophysiologies. Using transgenic mice expressing different levels of PrPC, our studies investigated the influence and necessity of PrPC on biomarker (total-tau [T-Tau], P-Tau, GFAP) levels in brain and blood as measured biochemically following severe TBI in the form of severe closed head injury (sCHI). We found that following sCHI, increasing levels of T-Tau and P-Tau in the brain were associated with the PrPC expression levels. A similar relationship between PrPC expression and P-Tau levels following sCHI were found in blood in the absence of significant T-Tau changes. This effect was not seen with GFAP which increased within 24 h following sCHI and progressively decreased by the 7 day time point regardless of the PrPC expression levels. Changes in the levels of all biomarkers were independent of gender. We further enhanced and expanded the quantitation of brain biomarkers with correlative studies using immunohisochemistry. We also demonstrate that a TBI-induced calpain hyperactivation is not required for the generation of P-Tau. A relationship was demonstrated between the presence/absence of PrPC, the levels of P-Tau and cognitive dysfunction. Our studies suggest that PrPC is important in mediating TBI related pathology.

In this study, we demonstrate that a moderate amount of protein misfolding cyclic amplification (PMCA) coupled to a novel surround optical fibre immunoassay (SOFIA) detection scheme can be used to detect the disease-associated form of the prion protein (PrP^Sc) in protease-untreated plasma from preclinical and clinical scrapie sheep, and white-tailed deer with chronic wasting disease, following natural and experimental infection. PrP^Sc, resulting from a conformational change of the normal (cellular) form of prion protein (PrP^C), is considered central to neuropathogenesis and serves as the only reliable molecular marker for prion disease diagnosis. While the highest levels of PrP^Sc are present in the central nervous system, the development of a reasonable diagnostic assay requires the use of body fluids that characteristically contain exceedingly low levels of PrP^Sc. PrP^Sc has been detected in the blood of sick animals by means of PMCA technology. However, repeated cycling over several days, which is necessary for PMCA of blood material, has been reported to result in decreased specificity (false positives). To generate an assay for PrP^Sc in blood that is both highly sensitive and specific, we have utilized limited serial PMCA (sPMCA) with SOFIA. We did not find any enhancement of sPMCA with the addition of polyadenylic acid nor was it necessary to match the genotypes of the PrP^C and PrP^Sc sources for efficient amplification.