Mark L. Cohen

EphA2 Mediates Ligand-Dependent Inhibition and Ligand-Independent Promotion of Cell Migration and Invasion via a Reciprocal Regulatory Loop with Akt

Both pro- and antioncogenic properties have been attributed to EphA2 kinase. We report that a possible cause for this apparent paradox is diametrically opposite roles of EphA2 in regulating cell migration and invasion. While activation of EphA2 with its ligand ephrin-A1 inhibited chemotactic migration of glioma and prostate cancer cells, EphA2 overexpression promoted migration in a ligand-independent manner. Surprisingly, the latter effects required phosphorylation of EphA2 on serine 897 by Akt, and S897A mutation abolished ligand-independent promotion of cell motility. Ephrin-A1 stimulation of EphA2 negated Akt activation by growth factors and caused EphA2 dephosphorylation on S897. In human astrocytoma, S897 phosphorylation was correlated with tumor grades and Akt activation, suggesting that the Akt-EphA2 crosstalk may contribute to brain tumor progression.

Increased Iron and Free Radical Generation in Preclinical Alzheimer Disease and Mild Cognitive Impairment

It is now established that oxidative stress is one of the earliest, if not the earliest, change that occurs in the pathogenesis of Alzheimers disease (AD). Consistent with this, mild cognitive impairment (MCI), the clinical precursor of AD, is also characterized by elevations in oxidative stress. Since such stress does not operate in vacuo, in this study we sought to determine whether redox-active iron, a potent source of free radicals, was elevated in MCI and preclinical AD as compared to cognitively-intact age-matched control patients. Increased iron was found at the highest levels both in the cortex and cerebellum from the pre-clinical AD/MCI cases. Interestingly, glial accumulations of redox-active iron in the cerebellum were also evident in preclinical AD patients and tended to increase as patients became progressively cognitively impaired. Our findings suggests that an imbalance in iron homeostasis is a precursor to the neurodegenerative processes leading to AD and that iron imbalance is not necessarily unique to affected regions. In fact, an understanding of iron deposition in other regions of the brain may provide insights into neuroprotective strategies. Iron deposition at the preclinical stage of AD may be useful as a diagnostic tool, using iron imaging methods, as well as a potential therapeutic target, through metal ion chelators.

Astrocytes Regulate Microglial Phagocytosis of Senile Plaque Cores of Alzheimer's Disease ☆

We have developed an in vitro model in which isolated senile plaque (SP) cores are presented to rat microglial cells in culture. Microglia rapidly phagocytosed, broke apart, and cleared SP cores. However, when cocultured with astrocytes, microglial phagocytosis was markedly suppressed, allowing the SPs to persist. Suppression of phagocytosis by astrocytes appears to be a general phenomena since microglia in the presence of astrocytes showed reduced capacity to phagocytose latex beads as well. The astrocyte effect on microglia is related in part to a diffusible factor(s) since astrocyte- but not fibroblast-conditioned media also reduced phagocytosis. These results suggest that while microglia have the capacity to phagocytose and remove SPs, astrocytes which lie in close association to microglia may help prevent the efficient clearance of SP material allowing them to persist in Alzheimers disease.

Variably protease-sensitive prionopathy: a new sporadic disease of the prion protein

The objective of the study is to report 2 new genotypic forms of protease‐sensitive prionopathy (PSPr), a novel prion disease described in 2008, in 11 subjects all homozygous for valine at codon 129 of the prion protein (PrP) gene (129VV). The 2 new PSPr forms affect individuals who are either homozygous for methionine (129MM) or heterozygous for methionine/valine (129MV).

Treatable neurological disorders misdiagnosed as Creutzfeldt-Jakob disease.

Heightened awareness of Creutzfeldt‐Jakob disease (CJD) among physicians and the lay public has led to its frequent consideration in the differential diagnosis of patients with rapidly progressive dementia (RPD). Our goal was to determine which treatable disorders are most commonly mistaken for CJD.

Whole-genome and multisector exome sequencing of primary and post-treatment glioblastoma reveals patterns of tumor evolution

Glioblastoma (GBM) is a prototypical heterogeneous brain tumor refractory to conventional therapy. A small residual population of cells escapes surgery and chemoradiation, resulting in a typically fatal tumor recurrence ∼ 7 mo after diagnosis. Understanding the molecular architecture of this residual population is critical for the development of successful therapies. We used whole-genome sequencing and whole-exome sequencing of multiple sectors from primary and paired recurrent GBM tumors to reconstruct the genomic profile of residual, therapy resistant tumor initiating cells. We found that genetic alteration of the p53 pathway is a primary molecular event predictive of a high number of subclonal mutations in glioblastoma. The genomic road leading to recurrence is highly idiosyncratic but can be broadly classified into linear recurrences that share extensive genetic similarity with the primary tumor and can be directly traced to one of its specific sectors, and divergent recurrences that share few genetic alterations with the primary tumor and originate from cells that branched off early during tumorigenesis. Our study provides mechanistic insights into how genetic alterations in primary tumors impact the ensuing evolution of tumor cells and the emergence of subclonal heterogeneity.

Interobserver reproducibility among neuropathologists and surgical pathologists in fibrillary astrocytoma grading

UNLABELLED Many of the problems associated with the current grading approaches for fibrillary astrocytomas center around the lack of consistency in grading. This study compares the diagnoses of five neuropathologists with five experienced surgical pathologists with regard to assigning astrocytoma grade. Thirty neoplastic and non-neoplastic lesions were sent to each of five neuropathologists and five surgical pathologists for placement into one of three grades as outlined by modified Ringertz schema. Grading criteria (Burger et al., 1985. Cancer 56:1106-1111) were distributed to all participants, who have been practicing for at least 5 years. An additional category for non-neoplastic or normal tissue was also provided. The diagnoses, based on the majority opinion of the neuropathologist group, included six low grade astrocytomas, 11 anaplastic astrocytomas, seven glioblastoma multiforme, and six normal/reactive lesions. Agreement by all neuropathologists was reached in 12 cases (40%). A discrepant diagnosis was obtained in one of five neuropathologists in 14 additional cases (46.7%). In the remaining four cases, two neuropathologists deviated from the majority opinion; in each of these cases, the diagnostic problem involved differentiating tumor from reactive gliosis. All five surgical pathologists agreed in six cases (20%). One discrepant diagnosis among the surgical pathologist group was seen in seven cases (23.3%). In the remaining 17 cases, two or more discrepant diagnoses were obtained (56.7%); discrepancies in these cases included differences in assignment of tumor grade and in distinguishing low grade astrocytoma from gliosis. IN CONCLUSION (1) it is likely that experience with grading accounts for the better level of agreement among the neuropathologist group (kappa statistic 0.63) versus the surgical pathologist group (kappa statistic 0.36); (2) in most cases, the neuropathologists all agreed or had one discrepant diagnosis (86.7%) versus the surgical pathologist group (43.3%); (3) the discrepancies in diagnosis among both groups is likely related, in good part, to the limitations of the grading schema in fully enumerating the spectrum of such grading parameters as cytologic atypia and vascular proliferation.

Cytomegalovirus ventriculoencephalitis in AIDS: A syndrome with distinct clinical and pathologic features

Cytomegalovirus ventriculoencephalitis is a late and terminal complication of AIDS. Cytomegalovirus retinitis was diagnosed before the onset of encephalitis in all but 1 of the 7 patients in this series. A distinct clinical presentation was observed, with encephalitis often associated with cranial nerve deficits and gaze-directed nystagmus. Examination of CSF demonstrated pleocytosis with elevated protein and hypoglycorrhachia. Increased signal of periventricular white matter was visualized by MRI soon after the development of encephalitis, and progressive ventriculomegaly was detected by serial CT scanning. Cytomegalovirus ventriculoencephalitis developed in some patients while receiving ganciclovir or foscarnet maintenance therapy, and the response to higher doses of these agents was limited in the 2 patients so treated. Death ensued a median of 4 weeks after the onset of neurologic symptoms. Pathologic examination showed extensive necrotizing periventriculitis involving ependymal and subependymal regions with spread to the meninges and adjacent cranial nerve roots. The infection was associated with characteristic CMV inclusion-bearing cells. This entity should be considered in AIDS patients with encephalitis, particularly in the presence of cranial nerve impairment or ascending muscle weakness. With the improvement in survival of patients with AIDS it is expected that this manifestation of CMV infection will become increasingly common.

Abnormal Brain Iron Homeostasis in Human and Animal Prion Disorders

Neurotoxicity in all prion disorders is believed to result from the accumulation of PrP-scrapie (PrPSc), a β-sheet rich isoform of a normal cell-surface glycoprotein, the prion protein (PrPC). Limited reports suggest imbalance of brain iron homeostasis as a significant associated cause of neurotoxicity in prion-infected cell and mouse models. However, systematic studies on the generality of this phenomenon and the underlying mechanism(s) leading to iron dyshomeostasis in diseased brains are lacking. In this report, we demonstrate that prion disease–affected human, hamster, and mouse brains show increased total and redox-active Fe (II) iron, and a paradoxical increase in major iron uptake proteins transferrin (Tf) and transferrin receptor (TfR) at the end stage of disease. Furthermore, examination of scrapie-inoculated hamster brains at different timepoints following infection shows increased levels of Tf with time, suggesting increasing iron deficiency with disease progression. Sporadic Creutzfeldt-Jakob disease (sCJD)–affected human brains show a similar increase in total iron and a direct correlation between PrP and Tf levels, implicating PrPSc as the underlying cause of iron deficiency. Increased binding of Tf to the cerebellar Purkinje cell neurons of sCJD brains further indicates upregulation of TfR and a phenotype of neuronal iron deficiency in diseased brains despite increased iron levels. The likely cause of this phenotype is sequestration of iron in brain ferritin that becomes detergent-insoluble in PrPSc-infected cell lines and sCJD brain homogenates. These results suggest that sequestration of iron in PrPSc–ferritin complexes induces a state of iron bio-insufficiency in prion disease–affected brains, resulting in increased uptake and a state of iron dyshomeostasis. An additional unexpected observation is the resistance of Tf to digestion by proteinase-K, providing a reliable marker for iron levels in postmortem human brains. These data implicate redox-iron in prion disease–associated neurotoxicity, a novel observation with significant implications for prion disease pathogenesis.

Rapidly progressive Alzheimer's disease features distinct structures of amyloid-β.

Genetic and environmental factors that increase the risk of late-onset Alzheimer disease are now well recognized but the cause of variable progression rates and phenotypes of sporadic Alzheimers disease is largely unknown. We aimed to investigate the relationship between diverse structural assemblies of amyloid-β and rates of clinical decline in Alzheimers disease. Using novel biophysical methods, we analysed levels, particle size, and conformational characteristics of amyloid-β in the posterior cingulate cortex, hippocampus and cerebellum of 48 cases of Alzheimers disease with distinctly different disease durations, and correlated the data with APOE gene polymorphism. In both hippocampus and posterior cingulate cortex we identified an extensive array of distinct amyloid-β42 particles that differ in size, display of N-terminal and C-terminal domains, and conformational stability. In contrast, amyloid-β40 present at low levels did not form a major particle with discernible size, and both N-terminal and C- terminal domains were largely exposed. Rapidly progressive Alzheimers disease that is associated with a low frequency of APOE e4 allele demonstrates considerably expanded conformational heterogeneity of amyloid-β42, with higher levels of distinctly structured amyloid-β42 particles composed of 30-100 monomers, and fewer particles composed of < 30 monomers. The link between rapid clinical decline and levels of amyloid-β42 with distinct structural characteristics suggests that different conformers may play an important role in the pathogenesis of distinct Alzheimers disease phenotypes. These findings indicate that Alzheimers disease exhibits a wide spectrum of amyloid-β42 structural states and imply the existence of prion-like conformational strains.