Axonal injury is detected by βAPP immunohistochemistry in rapid death from head injury following road traffic collision

Comparison of background characteristics and neuropathology findings between medico-legal autopsy cases with traumatic axonal injury, vascular axonal injury, or absence of axonal injury in β-amyloid precursor protein stain

In forensic neuropathology, the β-amyloid precursor protein (β-APP) immunostain is used to diagnose axonal injury (AI). The two most common aetiologies are traumatic (TAI) and ischaemic (vascular; VAI). We aimed to identify background characteristics and neuropathology findings that are suggestive of TAI, VAI, or no AI in neuropathologically examined medico-legal autopsy cases. The dataset comprised 166 cases from Finland over the period 2016-2023. The diagnosis of AI was based on β-APP stain (TAI, VAI, or no AI). Data on background characteristics and neuropathology findings were collected from cause-of-death investigation documents. Prevalence ratios were calculated for each variable to enable comparisons between the AI categories. The sample were 71.7% males; median age was 41 years (range 0-96). There were 26 cases with TAI, 44 with VAI, and 96 with no AI. The variables that showed statistical significance and had at least two-fold prevalence among TAI cases compared to VAI cases were: a documented recent injury; and presence of any extracranial/cranial/intracranial injury (including subdural haemorrhage [SDH], subarachnoid haemorrhage [SAH], intracerebral/ventricular haemorrhage [ICVH], or contusion) in autopsy or neuropathology. Correspondingly, variables indicating TAI over no AI were: a documented recent injury; postinjury survival ≥ 24 h; and presence of any extracranial/cranial/intracranial injury (including SDH, SAH, ICVH, contusion), herniation, or infarction in autopsy or neuropathology. Postinjury survival < 30 min was identified as an indicator of no AI over TAI. Finally, variables indicating VAI over no AI were: postinjury survival ≥ 24 h; lack of external injury to the head; and presence of SDH, brain oedema, herniation, or infarction in autopsy or neuropathology. In conclusion, we report several differences in characteristics and findings between cases diagnosed with TAI, VAI, and no AI. Our findings may help estimate the likelihood and potential aetiology of AI based on background characteristics and other neuropathology findings.

Expression of RIPK-1 and S-100B in traumatic brain injury- exploring a forensic cases series

Traumatic Brain Injury (TBI) represents one of the leading causes of disability and death globally, with a significant impact on public health. We present 12 cases (age 5-80 years old) of death due to TBI with different post-traumatic interval (PTI). The expression of S-100B and RIPK-1 in pericontusional zones of TBI were studied in forensic cases to understand the vitality and timing of injuries. The anti-RIPK-1 antibodies mainly stained the cytoplasm of the nerve cells. In 3 cases (48 to 56 years old with no other comorbidities; PTI: 2 days to 4 days) antibodies positive for RIPK-1 were found. In 5 cases (48 to 71 years old; PTI: 2 days to 12 days) astrocyte, oligodendrocyte and neurons positive for anti-S-100B were found. In 3 of these 5 cases both antibodies tested were positive. In 7 cases (5-80 years old; one with history of drug abuse, other with no comorbidities, PTI 0 h; ) the glial cells were swollen and the submeningeal glial limitans became immunopositive for S100B. Stain accumulations were also observed adjacent to the walls of cerebral vessels, sometimes within the intravascular compartment. The results of the study show that in subjects who suffered a TBI, the expression of RIPK-1 and S-100B at the level of neurons in the pericontusional area was significantly increased compared to the control group. Neurons were not stained for RIPK-1 in cases of sudden cardiac deaths and sudden deaths due to TBI but observed neurons became immunopositive for RIPK-1 some days after TBI. S100-immunopositive neurons were not seen in immediate deaths but were found in cases with survival up to 12 days. Results regarding S100B are in line with existing knowledge. The study of necroptosis with anti-RIPK-1 antibodies could be useful in understanding the extent of secondary injuries and survival time in forensic contexts. However, this is a pilot study and should be extended to a larger number of cases to achieve more reliable results.

Background characteristics and neuropathology findings of medico-legal autopsy cases with and without β-amyloid precursor protein positive diffuse traumatic axonal injury

The postmortem diagnosis of diffuse traumatic axonal injury (dTAI) relies on β-amyloid precursor protein (β-APP) immunohistochemistry. Most reports of factors associating with dTAI are decades old. We compared background characteristics and neuropathology findings of today's Finnish medico-legal autopsy cases with and without β-APP-positive dTAI (dTAI+ and dTAI-, respectively). The cases had suffered a head injury prior to death and underwent a full neuropathological examination including β-APP stain. Background and circumstantial data as well as neuropathology findings were collected from police documents, medical records, and autopsy and neuropathology reports. Prevalence ratios were calculated for each factor to facilitate comparisons between the dTAI+ and dTAI- groups. The dataset comprised 57 cases (66.7% males), with 17 classified as dTAI+ and 40 as dTAI-. Based on prevalence ratios, the factors that had at least two-fold prevalence among dTAI+ cases compared to dTAI- cases were: an unknown injury mechanism; concurrent epidural or subdural haemorrhage; and an accidental manner of death. In contrast, the factors that had at least two-fold prevalence among dTAI- cases compared to dTAI+ cases were: a short postinjury survival (<30 min); concurrent intracerebral/ventricular haemorrhage or contusion; vermal atrophy; and a natural or homicidal manner of death. This study revealed differences in circumstantial features and neuropathology findings between dTAI+ and dTAI- cases in today's medico-legal autopsy material. Data on typical case profiles may help estimate the prior probability of dTAI not only in medico-legal autopsies but also among living patients with head injuries.

A role for immunohistochemical stains in perinatal brain autopsies

Identification of central nervous system injury is a critical part of perinatal autopsies; however, injury is not always easily identifiable due to autolysis and immaturity of the developing brain. Here, the role of immunohistochemical stains in the identification of perinatal brain injury was investigated. Blinded semiquantitative scoring of injury was performed on sections of frontal lobe from 76 cases (51 liveborn and 25 stillborn) using H&E, GFAP, Iba-1, and β-APP stains. Digital image analysis was used to quantify GFAP and Iba-1 staining. Commonly observed pathologies included diffuse white matter gliosis (DWMG) and white matter necrosis (WMN). DWMG scores were very similar on H&E and GFAP stains for liveborn subjects. For stillborn subjects, DWMG scores were significantly higher on GFAP stain than H&E. β-APP was needed for identification of WMN in 71.4% of stillborn subjects compared to 15.4% of liveborn subjects. Diffuse staining for Iba-1 within cortex and white matter was positively correlated with subject age. Staining quantification on digital image analysis was highly correlated to semiquantitative scoring. Overall, GFAP and β-APP stains were most helpful in identifying white matter injury not seen on H&E in stillborn subjects. Immunostains may therefore be warranted as an integral part of stillborn brain autopsies.

The Labyrinthine Landscape of APP Processing: State of the Art and Possible Novel Soluble APP-Related Molecular Players in Traumatic Brain Injury and Neurodegeneration

Amyloid Precursor Protein (APP) and its cleavage processes have been widely investigated in the past, in particular in the context of Alzheimer’s Disease (AD). Evidence of an increased expression of APP and its amyloidogenic-related cleavage enzymes, β-secretase 1 (BACE1) and γ-secretase, at the hit axon terminals following Traumatic Brain Injury (TBI), firstly suggested a correlation between TBI and AD. Indeed, mild and severe TBI have been recognised as influential risk factors for different neurodegenerative diseases, including AD. In the present work, we describe the state of the art of APP proteolytic processing, underlining the different roles of its cleavage fragments in both physiological and pathological contexts. Considering the neuroprotective role of the soluble APP alpha (sAPPα) fragment, we hypothesised that sAPPα could modulate the expression of genes of interest for AD and TBI. Hence, we present preliminary experiments addressing sAPPα-mediated regulation of BACE1, Isthmin 2 (ISM2), Tetraspanin-3 (TSPAN3) and the Vascular Endothelial Growth Factor (VEGFA), each discussed from a biological and pharmacological point of view in AD and TBI. We finally propose a neuroprotective interaction network, in which the Receptor for Activated C Kinase 1 (RACK1) and the signalling cascade of PKCβII/nELAV/VEGF play hub roles, suggesting that vasculogenic-targeting therapies could be a feasible approach for vascular-related brain injuries typical of AD and TBI.

Role of integrin and its potential as a novel postmortem biomarker in traumatic axonal injury

Traumatic axonal injury (TAI) accounts for a large proportion of the mortality of traumatic brain injury (TBI). The diagnosis of TAI is currently of limited use for medicolegal purposes. It is known that axons in TAI are diffusely damaged by secondary processes other than direct head injury. However, the physiopathological mechanism of TAI is still elusive. The present study used RGD peptide, an antagonist of the mechanotransduction protein integrin, to explore the role of integrin-transmitted mechanical signalling in the pathogenesis of rat TAI. The rats were subjected to a linearly accelerating load, and changes in beta-amyloid precursor protein (β-APP) expression, skeleton ultrastructure, skeleton protein neurofilament light (NF-L), and α-tubulin in the brainstem were observed, indicating that RGD could relieve the severity of axonal injury in TAI rats. In addition, the expression of β-integrin was stronger and centralized in the brainstem of the deceased died from TAI compared to other nonviolent causes. This study examined the pathophysiology and biomechanics of TAI and assessed the role of integrin in the injury of microtubules and neurofilaments in TAI. Thus, we propose that integrin-mediated cytoskeletal injury plays an important role in TAI and that integrin has the potential as a biomarker for TAI.