Ronald L. Hamilton

Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer's disease

The positron emission tomography (PET) radiotracer Pittsburgh Compound-B (PiB) binds with high affinity to β-pleated sheet aggregates of the amyloid-β (Aβ) peptide in vitro. The in vivo retention of PiB in brains of people with Alzheimers disease shows a regional distribution that is very similar to distribution of Aβ deposits observed post-mortem. However, the basis for regional variations in PiB binding in vivo, and the extent to which it binds to different types of Aβ-containing plaques and tau-containing neurofibrillary tangles (NFT), has not been thoroughly investigated. The present study examined 28 clinically diagnosed and autopsy-confirmed Alzheimers disease subjects, including one Alzheimers disease subject who had undergone PiB-PET imaging 10 months prior to death, to evaluate region- and substrate-specific binding of the highly fluorescent PiB derivative 6-CN-PiB. These data were then correlated with region-matched Aβ plaque load and peptide levels, [3H]PiB binding in vitro, and in vivo PET retention levels. We found that in Alzheimers disease brain tissue sections, the preponderance of 6-CN-PiB binding is in plaques immunoreactive to either Aβ42 or Aβ40, and to vascular Aβ deposits. 6-CN-PiB labelling was most robust in compact/cored plaques in the prefrontal and temporal cortices. While diffuse plaques, including those in caudate nucleus and presubiculum, were less prominently labelled, amorphous Aβ plaques in the cerebellum were not detectable with 6-CN-PiB. Only a small subset of NFT were 6-CN-PiB positive; these resembled extracellular ‘ghost’ NFT. In Alzheimers disease brain tissue homogenates, there was a direct correlation between [3H]PiB binding and insoluble Aβ peptide levels. In the Alzheimers disease subject who underwent PiB-PET prior to death, in vivo PiB retention levels correlated directly with region-matched post-mortem measures of [3H]PiB binding, insoluble Aβ peptide levels, 6-CN-PiB- and Aβ plaque load, but not with measures of NFT. These results demonstrate, in a typical Alzheimers disease brain, that PiB binding is highly selective for insoluble (fibrillar) Aβ deposits, and not for neurofibrillary pathology. The strong direct correlation of in vivo PiB retention with region-matched quantitative analyses of Aβ plaques in the same subject supports the validity of PiB-PET imaging as a method for in vivo evaluation of Aβ plaque burden.

Chronic traumatic encephalopathy in a National Football League player.

OBJECTIVEWe present the second reported case of autopsy-confirmed chronic traumatic encephalopathy in a retired professional football player, with neuropathological features that differ from those of the first reported case. These differing pathological features underscore the need for further empirical elucidation of the pathoetiology and pathological cascades of long-term neurodegenerative sequelae of professional football. METHODSA psychological autopsy was performed with the next-of-kin and wife. Medical and hospital records were reviewed. A complete autopsy was accompanied by a comprehensive forensic neuropathological examination. Restriction fragment length polymorphism analysis was performed to determine apolipoprotein-E genotype. RESULTSPertinent premortem history included a 14-year span of play in organized football starting from the age of 18 years. The subject was diagnosed with severe major depressive disorder without psychotic features after retirement, attempted suicide multiple times and finally committed suicide 12 years after retirement by ingestion of ethylene glycol. Autopsy revealed cardiomegaly, mild to moderate coronary artery disease, and evidence of acute ethylene glycol overdose. The brain showed no atrophy, a cavum septi pellucidi was present, and the substantia nigra showed mild pallor. The hippocampus and cerebellum were not atrophic. Amyloid plaques, cerebral amyloid angiopathy, and Lewy bodies were completely absent. Sparse to frequent τ-positive neurofibrillary tangles and neuropil threads were present in all regions of the brain. Tufted and thorn astrocytes, as well as astrocytic plaques, were absent. The apolipoprotein-Egenotype was E3/E4. CONCLUSIONOur first and second cases both had long careers without multiple recorded concussions. Both manifested Major Depressive Disorder after retirement. Amyloid plaques were present in the first case and completely absent in the second case. Both cases exhibited neurofibrillary tangles, neuropil threads, and coronary atherosclerotic disease. Apolipoprotein-E4 genotypes were different. Reasons for the contrasting features in these two cases are not clear. Further studies are needed to identify and define the neuropathological cascades of chronic traumatic encephalopathy in football players, which may form the basis for prophylaxis and therapeutics.

Induction of CD8+ T-Cell Responses Against Novel Glioma–Associated Antigen Peptides and Clinical Activity by Vaccinations With α-Type 1 Polarized Dendritic Cells and Polyinosinic-Polycytidylic Acid Stabilized by Lysine and Carboxymethylcellulose in Patients With Recurrent Malignant Glioma

PURPOSE A phase I/II trial was performed to evaluate the safety and immunogenicity of a novel vaccination with α-type 1 polarized dendritic cells (αDC1) loaded with synthetic peptides for glioma-associated antigen (GAA) epitopes and administration of polyinosinic-polycytidylic acid [poly(I:C)] stabilized by lysine and carboxymethylcellulose (poly-ICLC) in HLA-A2(+) patients with recurrent malignant gliomas. GAAs for these peptides are EphA2, interleukin (IL)-13 receptor-α2, YKL-40, and gp100. PATIENTS AND METHODS Twenty-two patients (13 with glioblastoma multiforme [GBM], five with anaplastic astrocytoma [AA], three with anaplastic oligodendroglioma [AO], and one with anaplastic oligoastrocytoma [AOA]) received at least one vaccination, and 19 patients received at least four vaccinations at two αDC1 dose levels (1 × or 3 × 10(7)/dose) at 2-week intervals intranodally. Patients also received twice weekly intramuscular injections of 20 μg/kg poly-ICLC. Patients who demonstrated positive radiologic response or stable disease without major adverse events were allowed to receive booster vaccines. T-lymphocyte responses against GAA epitopes were assessed by enzyme-linked immunosorbent spot and HLA-tetramer assays. RESULTS The regimen was well-tolerated. The first four vaccines induced positive immune responses against at least one of the vaccination-targeted GAAs in peripheral blood mononuclear cells in 58% of patients. Peripheral blood samples demonstrated significant upregulation of type 1 cytokines and chemokines, including interferon-α and CXCL10. Nine (four GBM, two AA, two AO, and one AOA) achieved progression-free status lasting at least 12 months. One patient with recurrent GBM demonstrated sustained complete response. IL-12 production levels by αDC1 positively correlated with time to progression. CONCLUSION These data support safety, immunogenicity, and preliminary clinical activity of poly-ICLC-boosted αDC1-based vaccines.

Multiple recurrent genetic events converge on control of histone lysine methylation in medulloblastoma

We used high-resolution SNP genotyping to identify regions of genomic gain and loss in the genomes of 212 medulloblastomas, malignant pediatric brain tumors. We found focal amplifications of 15 known oncogenes and focal deletions of 20 known tumor suppressor genes (TSG), most not previously implicated in medulloblastoma. Notably, we identified previously unknown amplifications and homozygous deletions, including recurrent, mutually exclusive, highly focal genetic events in genes targeting histone lysine methylation, particularly that of histone 3, lysine 9 (H3K9). Post-translational modification of histone proteins is critical for regulation of gene expression, can participate in determination of stem cell fates and has been implicated in carcinogenesis. Consistent with our genetic data, restoration of expression of genes controlling H3K9 methylation greatly diminishes proliferation of medulloblastoma in vitro. Copy number aberrations of genes with critical roles in writing, reading, removing and blocking the state of histone lysine methylation, particularly at H3K9, suggest that defective control of the histone code contributes to the pathogenesis of medulloblastoma.

Common variants at 7p21 are associated with frontotemporal lobar degeneration with TDP-43 inclusions

Frontotemporal lobar degeneration (FTLD) is the second most common cause of presenile dementia. The predominant neuropathology is FTLD with TAR DNA-binding protein (TDP-43) inclusions (FTLD-TDP). FTLD-TDP is frequently familial, resulting from mutations in GRN (which encodes progranulin). We assembled an international collaboration to identify susceptibility loci for FTLD-TDP through a genome-wide association study of 515 individuals with FTLD-TDP. We found that FTLD-TDP associates with multiple SNPs mapping to a single linkage disequilibrium block on 7p21 that contains TMEM106B. Three SNPs retained genome-wide significance following Bonferroni correction (top SNP rs1990622, P = 1.08 × 10−11; odds ratio, minor allele (C) 0.61, 95% CI 0.53–0.71). The association replicated in 89 FTLD-TDP cases (rs1990622; P = 2 × 10−4). TMEM106B variants may confer risk of FTLD-TDP by increasing TMEM106B expression. TMEM106B variants also contribute to genetic risk for FTLD-TDP in individuals with mutations in GRN. Our data implicate variants in TMEM106B as a strong risk factor for FTLD-TDP, suggesting an underlying pathogenic mechanism.

Expression of Nrf2 in Neurodegenerative Diseases

In response to oxidative stress, the nuclear factor E2-related factor 2 (Nrf2) transcription factor translocates from the cytoplasm into the nucleus and transactivates expression of genes with antioxidant activity. Despite this cellular mechanism, oxidative damage is abundant in Alzheimer and Parkinson disease (AD and PD). To investigate mechanisms by which Nrf2 activity may be aberrant or insufficient in neurodegenerative conditions, we assessed Nrf2 localization in affected brain regions of AD, Lewy body variant of AD (LBVAD), and PD. By immunohistochemistry, Nrf2 is expressed in both the nucleus and the cytoplasm of neurons in normal hippocampi with predominant expression in the nucleus. In AD and LBVAD, Nrf2 was predominantly cytoplasmic in hippocampal neurons and was not a major component of beta amyloid plaques or neurofibrillary tangles. By immunoblotting, we observed a significant decrease in nuclear Nrf2 levels in AD cases. In contrast, Nrf2 was strongly nuclear in PD nigral neurons but cytoplasmic in substantia nigra of normal, AD, and LBVAD cases. These findings suggest that Nrf2-mediated transcription is not induced in neurons in AD despite the presence of oxidative stress. In PD, nuclear localization of Nrf2 is strongly induced, but this response may be insufficient to protect neurons from degeneration.

Increases in Bcl-2 and cleavage of caspase-1 and caspase-3 in human brain after head injury

The bcl‐2 and caspase families are important regulators of programmed cell death in experimental models of ischemic, excitotoxic, and traumatic brain injury. The Bcl‐2 family members Bcl‐2 and Bcl‐xL suppress programmed cell death, whereas Bax promotes programmed cell death. Activated caspase‐1 (interleukin‐1β converting enzyme) and caspase‐3 (Yama/Apopain/Cpp32) cleave proteins that are important in maintaining cytoskeletal integrity and DNA repair, and activate deoxyribonucleases, producing cell death with morphological features of apoptosis. To address the question of whether these Bcl‐2 and caspase family members participate in the process of delayed neuronal death in humans, we examined brain tissue samples removed from adult patients during surgical decompression for intracranial hypertension in the acute phase after traumatic brain injury (n=8) and compared these samples to brain tissue obtained at autopsy from non‐trauma patients (n=6). An increase in Bcl‐2 but not Bcl‐xL or Bax, cleavage of caspase‐1, up‐regulation and cleavage of caspase‐3, and evidence for DNA fragmentation with both apoptotic and necrotic morphologies were found in tissue from traumatic brain injury patients compared with controls. These findings are the first to demonstrate that programmed cell death occurs in human brain after acute injury, and identify potential pharmacological and molecular targets for the treatment of human head injury.—Clark, R. S. B., Kochanek, P. M., Chen, M., Watkins, S. C., Marion, D. W., Chen, J., Hamilton, R. L., Loeffert, J. E., Graham, S. H. Increases in Bcl‐2 and cleavage of caspase‐1 and caspase‐3 in human brain after head injury. FASEB J. 13, 813–821 (1999)

Emerging histomorphologic phenotypes of chronic traumatic encephalopathy in American athletes

BACKGROUND:We define chronic traumatic encephalopathy (CTE) as a progressive neurodegenerative syndrome caused by single, episodic, or repetitive blunt force impacts to the head and transfer of acceleration-deceleration forces to the brain. OBJECTIVE:We present emerging histomorphologic phenotypes of CTE that we identified in our cohort of CTE cases with apolipoprotein E genotyping and causes and manners of death. METHODS:Autopsy brain tissue of 14 professional athletes and 3 high school football players was examined after unexpected deaths. Histochemical and immunohistochemical tissue staining was performed with apolipoprotein E genotyping. RESULTS:Ten of 14 professional athletes (71%) were positive for CTE: 7 of 8 football players, 2 of 4 wrestlers, and 1 boxer. One of 3 high school players manifested incipient CTE. The age range of those with CTE was 18 to 52 years; they were all male athletes. In all cases of CTE, Alzheimer-type cerebral cortical atrophy was absent; negligible to mild neocortical neuronal dropout was present. The fundamental neuropathologic feature of CTE was the topographic distribution of sparse, moderate, and frequent band-shaped, flame-shaped, small and large globose neurofibrillary tangles and neuritic threads in the cerebral cortex, subcortical nuclei/basal ganglia, hippocampus, and brainstem nuclei. Sparse to frequent diffuse amyloid plaques may accompany tauopathy and was seen in only 2 CTE cases. No α-synucleinopathy was present. All 7 CTE-positive professional athletes with known apolipoprotein E genotypes had at least 1 E3 allele comprising 5 E3/E3 (71%) and 2 E3/E4 (29%). Alcohol- and drug-related deaths, suicides, and accidental deaths were overrepresented in our CTE cohort. CONCLUSION:The emerging histomorphologic features of our CTE cohort may specify histologic criteria for CTE diagnosis, may identify emerging histologic variants of CTE and may facilitate more objective surveillance and accurate identification of sentinel CTE cases.

COX-2 Blockade Suppresses Gliomagenesis by Inhibiting Myeloid-Derived Suppressor Cells

Epidemiologic studies have highlighted associations between the regular use of nonsteroidal anti-inflammatory drugs (NSAID) and reduced glioma risks in humans. Most NSAIDs function as COX-2 inhibitors that prevent production of prostaglandin E₂ (PGE₂). Because PGE₂ induces expansion of myeloid-derived suppressor cells (MDSC), we hypothesized that COX-2 blockade would suppress gliomagenesis by inhibiting MDSC development and accumulation in the tumor microenvironment (TME). In mouse models of glioma, treatment with the COX-2 inhibitors acetylsalicylic acid (ASA) or celecoxib inhibited systemic PGE₂ production and delayed glioma development. ASA treatment also reduced the MDSC-attracting chemokine CCL2 (C-C motif ligand 2) in the TME along with numbers of CD11b(+)Ly6G(hi)Ly6C(lo) granulocytic MDSCs in both the bone marrow and the TME. In support of this evidence that COX-2 blockade blocked systemic development of MDSCs and their CCL2-mediated accumulation in the TME, there were defects in these processes in glioma-bearing Cox2-deficient and Ccl2-deficient mice. Conversely, these mice or ASA-treated wild-type mice displayed enhanced expression of CXCL10 (C-X-C motif chemokine 10) and infiltration of cytotoxic T lymphocytes (CTL) in the TME, consistent with a relief of MDSC-mediated immunosuppression. Antibody-mediated depletion of MDSCs delayed glioma growth in association with an increase in CXCL10 and CTLs in the TME, underscoring a critical role for MDSCs in glioma development. Finally, Cxcl10-deficient mice exhibited reduced CTL infiltration of tumors, establishing that CXCL10 limited this pathway of immunosuppression. Taken together, our findings show that the COX-2 pathway promotes gliomagenesis by directly supporting systemic development of MDSCs and their accumulation in the TME, where they limit CTL infiltration.

Brain Membrane Phospholipid Alterations in Alzheimer's Disease

Studies have demonstrated alterations in brain membrane phospholipid metabolite levels in Alzheimers disease (AD). The changes in phospholipid metabolite levels correlate with neuropathological hallmarks of the disease and measures of cognitive decline. This 31P nuclear magnetic resonance (NMR) study of Folch extracts of autopsy material reveals significant reductions in AD brain levels of phosphatidylethanolamine (PtdEtn) and phosphatidylinositol (PtdIns), and elevations in sphingomyelin (SPH) and the plasmalogen derivative of PtdEtn. In the superior temporal gyrus, there were additional reductions in the levels of diphosphatidylglycerol (DPG) and phosphatidic acid (PtdA). The findings are present in 3/3 as well as 3/4 and 4/4 apolipoprotein E (apoE) genotypes. The AD findings do not appear to reflect non-specific neurodegeneration or the presence of gliosis. The present findings could possibly contribute to an abnormal membrane repair in AD brains which ultimately results in synaptic loss and the aggregation of Aβ peptide.