Mark W. Becher

ALS-Linked SOD1 Mutant G85R Mediates Damage to Astrocytes and Promotes Rapidly Progressive Disease with SOD1-Containing Inclusions

High levels of familial Amyotrophic Lateral Sclerosis (ALS)-linked SOD1 mutants G93A and G37R were previously shown to mediate disease in mice through an acquired toxic property. We report here that even low levels of another mutant, G85R, cause motor neuron disease characterized by an extremely rapid clinical progression, without changes in SOD1 activity. Initial indicators of disease are astrocytic inclusions that stain intensely with SOD1 antibodies and ubiquitin and SOD1-containing aggregates in motor neurons, features common with some cases of SOD1 mutant-mediated ALS. Astrocytic inclusions escalate markedly as disease progresses, concomitant with a decrease in the glial glutamate transporter (GLT-1). Thus, the G85R SOD1 mutant mediates direct damage to astrocytes, which may promote the nearly synchronous degeneration of motor neurons.

Prolonged survival and decreased abnormal movements in transgenic model of Huntington disease, with administration of the transglutaminase inhibitor cystamine.

An expanded polyglutamine domain in huntingtin underlies the pathogenic events in Huntington disease (HD), characterized by chorea, dementia and severe weight loss, culminating in death. Transglutaminase (TGase) may be critical in the pathogenesis, via cross-linking huntingtin. Administration of the TGase competitive inhibitor, cystamine, to transgenic mice expressing exon 1 of huntingtin containing an expanded polyglutamine repeat, altered the course of their HD-like disease. Cystamine given intraperitoneally entered brain where it inhibited TGase activity. When treatment began after the appearance of abnormal movements, cystamine extended survival, reduced associated tremor and abnormal movements and ameliorated weight loss. Treatment did not influence the appearance or frequency of neuronal nuclear inclusions. Unexpectedly, cystamine treatment increased transcription of one of the two genes shown to be neuroprotective for polyglutamine toxicity in Drosophila, dnaj (also known as HDJ1 and Hsp40 in humans and mice, respectively). Inhibition of TGase provides a new treatment strategy for HD and other polyglutamine diseases.

The Neuropathology of CAG Repeat Diseases: Review and Update of Genetic and Molecular Features

Classification of inherited neurodegenerative diseases is increasingly based on their genetic features, which supplement, clarify, and sometimes replace the older clinical and pathologic schemata. This change has been particularly rapid and impressive for the CAG repeat disorders. In Huntingtons disease, X‐linked spinobulbar muscular atrophy, dentatorubropallidoluysian atrophy, and a series of autosomal dominant cerebellar atrophies, genetic advances have resolved many nosologic issues, and opened new avenues for exploration of pathogenesis. In this review, we summarize classic and current concepts in neuropathology of these CAG repeat diseases.

Huntington's disease and Dentatorubral-pallidoluysian atrophy: Proteins, pathogenesis and pathology

Each of the glutamine repeat neurodegenerative diseases has a particular pattern of pathology largely restricted to the CNS. However, there is considerable overlap among the regions affected, suggesting that the diseases share pathogenic mechanisms, presumably involving the glutamine repeats. We focus on Huntingtons disease (HD) and Dentatorubral‐pallidoluysian atrophy (DRPLA) as models for this family of diseases, since they have striking similarities and also notable differences in their clinical features and pathology. We review the pattern of pathology in adult and juvenile onset cases. Despite selective pathology, the disease genes and their protein products (huntingtin and atrophin‐1) are widely expressed. This presents a central problem for all the glutamine repeat diseases‐how do widely expressed gene products give rise to restricted pathology? The pathogenic effects are believed to occur via a “gain of function” mechanism at the protein level. Mechanisms of cell death may include excitotoxicity, metabolic toxicity, apop‐tosis, and free radical stress. Emerging data indicate that huntingtin and atrophin‐1 may have distinct protein interactions. The specific interaction partners may help explain the selective pathology of these diseases.

Evidence for a role for transglutaminase in Huntington's disease and the potential therapeutic implications

Transglutaminase (TGase) activity is increased in affected regions of brains from patients with Huntingtons disease (HD). TGase activity is particularly elevated in the nucleus compared with the cytoplasm from these brains. Gamma-glutaminyl-lysyl cross-links have been detected in nuclear inclusions in HD brain, indicating that TGase may play a prominent role in the aggregation of huntingtin (htt). Attempts to ameliorate experimental disease, via inhibition of TGase in transgenic models of HD in mice, are under investigation.

Intranuclear inclusions in oculopharyngeal muscular dystrophy contain poly(A) binding protein 2.

Intranuclear inclusions are one of the ultrastructural hallmarks of oculopharyngeal muscular dystrophy (OPMD), a disorder caused by small polyalanine (GCG) expansions in the gene that codes for a ubiquitous nuclear protein called poly(A) binding protein 2 (PABP2). We studied OPMD skeletal muscle and found that 1.0 to 10.0% of myocyte nuclei contained discreet PABP2 immunoreactive intranuclear inclusions, providing the first direct evidence of the relation between the proposed gene for OPMD and the pathology of OPMD. Ann Neurol 2000;48:812–815

Sudden Death Due to Primary Diffuse Leptomeningeal Gliomatosis

Tumors of the central nervous system are an unusual cause of sudden death. This report describes the sudden death of a presumed healthy 28-year-old woman from primary diffuse leptomeningeal gliomatosis. She presented to an emergency room with headache and vomiting, subsequently became unresponsive and was pronounced dead 14 h later. Autopsy revealed a diffuse extensive infiltrate of well-differentiated astrocytoma in the leptomeninges of the brain and spinal cord without an underlying parenchymal tumor. Primary diffuse leptomeningeal gliomatosis is a rare tumor that arises within the leptomeninges from small neuroglial heterotopic rests that undergo neoplastic transformation. Grossly. this tumor can mimic leptomeningeal carcinomatosis, pachymeningitis, tuberculosis, sarcoidosis, and fungal infections. However, the histologic features of primary diffuse leptomeningeal gliomatosis should allow it to be readily distinguished from grossly similar conditions. The mechanism of death in this case is most likely tumor obstruction of cerebrospinal fluid outflow resulting in the usual complications seen with increased intracranial pressure. Although this tumor is aggressive and is associated with a rapidly progressive fatal course, it has not been previously associated with sudden death.

Progressive myopathy in an inducible mouse model of oculopharyngeal muscular dystrophy.

The genetic basis of oculopharyngeal muscular dystrophy (OPMD) is a short expansion of a polyalanine tract (normal allele: 10 alanines, mutant allele: 11-17 alanines) in the nuclear polyadenylate binding protein PABPN1 which is essential for controlling poly(A) tail length in messenger RNA. Mutant PABPN1 forms nuclear inclusions in OPMD muscle. To investigate the pathogenic role of mutant PABPN1 in vivo, we generated a ligand-inducible transgenic mouse model by using the mifepristone-inducible gene expression system. Induction of ubiquitous expression of mutant PABPN1 resulted in skeletal and cardiac myopathy. Histological changes of degenerative myopathy were preceded by nuclear inclusions of insoluble PABPN1. Downregulation of mutant PABPN1 expression attenuated the myopathy and reduced the nuclear burden of insoluble PABPN1. These results support association between mutant PABPN1 accumulation and degenerative myopathy in mice. Resolution of myopathy in mice suggests that the disease process in OPMD patients may be treatable.

Kearns-Sayre syndrome with features of Pearson's marrow-pancreas syndrome and a novel 2905-base pair mitochondrial DNA deletion

Kearns-Sayre syndrome (KSS) and Pearsons marrow-pancreas syndrome (PMPS) are rare disorders caused by the same molecular defect, one of several deletion mutations in mitochondrial DNA (mtDNA). KSS is an encephalomyopathy with ophthalmoplegia, retinal degeneration, ataxia, and endocrine abnormalities. PMPS is a disorder of childhood characterized by refractory anemia, vacuolization of bone marrow cells, and exocrine pancreas dysfunction. Children with PMPS that have a mild phenotype, or are supported through bone marrow failure, often develop the encephalomyopathic features of KSS. The subject of numerous reports in the neuromuscular, genetic, and pediatric literature in recent years, very few cases of either disorder have ever been studied at autopsy. We report the results of our studies of a patient with clinically documented KSS who presented with renal dysfunction and was found to have a novel mtDNA deletion and degenerative changes in the central nervous system, retina, skeletal muscle, and pancreas.

Inherited Neurodegenerative Diseases and Transgenic Models

In recent years, the identification of mutations in specific genes in several inherited neurodegener‐ative disorders, combined with advances in the field of transgenic methods, has provided neurosci‐entists and neuropathologists with information and strategies to develop transgenic (Tg) models to study human diseases. These approaches have proved to be extraordinarily useful in modeling familial forms of amyotrophic lateral sclerosis (FALS) and Alzheimers disease (FAD) and the spectrum of triplet‐repeat disorders. Investigations of these models have begun to provide new insights into the roles of disease‐specific mutant proteins and the pathogenic mechanisms of disease as well as opportunities to test therapeutic interventions.