Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disorder characterized pathologically by ubiquitinated TAR DNA binding protein (TDP-43) inclusions. The function of TDP-43 in the nervous system is uncertain, and a mechanistic role in neurodegeneration remains speculative. We identified neighboring mutations in a highly conserved region of TARDBP in sporadic and familial ALS cases. TARDBPM337V segregated with disease within one kindred and a genome-wide scan confirmed that linkage was restricted to chromosome 1p36, which contains the TARDBP locus. Mutant forms of TDP-43 fragmented in vitro more readily than wild type and, in vivo, caused neural apoptosis and developmental delay in the chick embryo. Our evidence suggests a pathophysiological link between TDP-43 and ALS.

http://science.sciencemag.org/content/sci/319/5870/1668.full.pdf

TDP-43 Mutations in Familial and Sporadic Amyotrophic Lateral Sclerosis

TDP-43 is a component of ubiquitin-positive tau-negative inclusions in frontotemporal lobar degeneration and amyotrophic lateral sclerosis

Autosomal recessive juvenile parkinsonism (AR-JP), one of the most common familial forms of Parkinson disease, is characterized by selective dopaminergic neural cell death and the absence of the Lewy body, a cytoplasmic inclusion body consisting of aggregates of abnormally accumulated proteins. We previously cloned PARK2, mutations of which cause AR-JP (ref. 2), but the function of the gene product, parkin, remains unknown. We report here that parkin is involved in protein degradation as a ubiquitin-protein ligase collaborating with the ubiquitin-conjugating enzyme UbcH7, and that mutant parkins from AR-JP patients show loss of the ubiquitin-protein ligase activity. Our findings indicate that accumulation of proteins that have yet to be identified causes a selective neural cell death without formation of Lewy bodies. Our findings should enhance the exploration of the molecular mechanisms of neurodegeneration in Parkinson disease as well as in other neurodegenerative diseases that are characterized by involvement of abnormal protein ubiquitination, including Alzheimer disease, other tauopathies, CAG triplet repeat disorders and amyotrophic lateral sclerosis.

Familial Parkinson disease gene product, parkin, is a ubiquitin-protein ligase

Although Charcot described amyotrophic lateral sclerosis (ALS) more than 130 years ago, the mechanism underlying the characteristic selective degeneration and death of motor neurons in this common adult motor neuron disease has remained a mystery. There is no effective remedy for this progressive, fatal disorder. Modern genetics has now identified mutations in one gene [Cu/Zn superoxide dismutase (SOD1)] as a primary cause and implicated others [encoding neurofilaments, cytoplasmic dynein and its processivity factor dynactin, and vascular endothelial growth factor (VEGF)] as contributors to, or causes of, motor neuron diseases. These insights have enabled development of model systems to test hypotheses of disease mechanism and potential therapies. Along with errors in the handling of synaptic glutamate and the potential excitotoxic response this provokes, these model systems highlight the involvement of nonneuronal cells in disease progression and provide new therapeutic strategies.

/pdf/unraveling-the-mechanisms-involved-in-motor-neuron-3p76wp4vdw.pdf

Unraveling the mechanisms involved in motor neuron degeneration in ALS.

Since its description by Charcot more than 130 years ago, the mechanism underlying the characteristic selective degeneration and death of motor neurons in amyotrophic lateral sclerosis has remained a mystery. Modern genetics has now identified mutations in two genes — SOD1 and ALS2 — as primary causes of the disease, and has implicated others as potential contributors. Insights into these abnormalities, together with errors in the handling of synaptic glutamate and the potential excitotoxic response that this alteration provokes, have provided leads for the development of new strategies to identify an as yet elusive remedy for this progressive, fatal disorder.

/pdf/from-charcot-to-lou-gehrig-deciphering-selective-motor-1iw3b26yg0.pdf

From charcot to lou gehrig: deciphering selective motor neuron death in als

Antibodies to ubiquitin have been used to search for evidence of abnormal protein degradation in amyotrophic lateral sclerosis—motor neuron disease (ALS). Anterior horn cell ubiquitin-immunoreactive (IR) inclusions were present in all of 31 ALS cases but in none of 23 neurologically normal and in only 1 of 22 neurologically abnormal controls. These inclusions, which were present in familial and sporadic ALS cases, and in cases with dementia, took the form of dense rounded or irregular ubiquitin-IR cytoplasmic inclusions (dense bodies), or loosely arranged bundles (‘skeins’) of filamentous-appearing material. The presence of ubiquitin-IR inclusions corresponded to the pattern of selective neuronal vulnerability in ALS, although inclusions in pyramidal neurons of the motor cortex were infrequent and were noted in only a minority of cases. Ubiquitin-IR inclusions were more prevalent than Bunina Bodies. The latter were present in 67% of ALS cases but were seldom labelled by antibodies to ubiquitin. Intranuronal inclusions resembling Lewy bodies were present in 23% of ALS cases and were often identified by antibodies to ubiquitin. We conclude that the presence of ubiquitin-IR inclusions in lower motor neurons represents a characteristic pathological feature of ALS in its various clinical forms. Ubiquitin-IR inclusions in ALS differ from ubiquitinated inclusions in other neuronal degenerations in that they are not readily identified by antibodies to cytoskeletal proteins. They may represent accumulations of altered or abnormal neuronal proteins resistant to degradation via the ubiquitin proteolytic pathway.

H. Whitwell

Papers

Ubiquitin-immunoreactive intraneuronal inclusions in amyotrophic lateral sclerosis. Morphology, distribution, and specificity.