Peripherin is a type III intermediate filament protein that is predominately expressed in the peripheral nervous system and in subsets of efferent projections in the central nervous systems. While the exact role of peripherin remains unclear, it is found upregulated after traumatic neuronal injury and in the devastating neurodegenerative disease amyotrophic lateral sclerosis (ALS). Interestingly, peripherin overexpressing transgenic mice succumb to motor neuron disease with pathological hallmarks reminiscent of those found in ALS. Pathological peripherin abnormalities occur with high frequency in both familial and sporadic forms of ALS, with peripherin found associated with the majority intracellular inclusions present within degenerating motor neuron populations. The findings of peripherin mutations in sporadic ALS have reinforced the importance of peripherin as a prospective etiological or propagative factor of disease pathogenesis. Surprisingly, inherited peripherin gene mutations have not been identified; as such, understanding the post-transcriptional mechanism at which peripherin imparts its effect(s) is considered a key goal and represents a pathological point-of-convergence for an otherwise complex, multifaceted disease. Prior to the commencement of this work, our group identified the presence of an abnormal peripherin alternative splice variant upregulated in ALS. In doing so, we consistently observed the presence of a second peripherin species of ~45 kDa on immunoblots of cell lysates derived from full-length peripherin transfections. Here, we identified this protein as a constitutively expressed isoform, termed Per-45, that arises from alternative translation and that is required for normal filament assembly: changes to the normal isoform expression pattern are associated with malformed filaments and intracellular inclusions. In lieu of the possibility of distinct peripherin intra-isoform associations, we identified isoform-specific expression and ratio changes in traumatic neuronal injury, in mouse models of motor neuron disease, and in ALS. Finally, we explored the interrelationships between peripherin isoform expression, protein aggregation, and neuritic outgrowth by linking these phenotypes with major pathogenic features associated with ALS, including in vitro models of oxidation, glutamate excitotoxicity, and neuroinflammation. Overall, this thesis provides exciting new insight into our knowledge of basic IF biology and the role of peripherin isoforms in injury and in motor neuron disease.

No description available.

A mutation in ER membrane protein VAPB is responsible for causing a familial form of ALS (ALS8). The VAPB-P56S mutation causes protein aggregation and a nuclear envelope defect, where retrograde transport is disrupted. Over-expression of a FFAT peptide from OSBP1 reduces the size of VAPB-P56S aggregates and restores retrograde transport. A screen was performed on FFAT-motif containing ORPs to determine if any could rescue the mutant phenotype. ORP3 successfully reduced aggregate size and restored transport to the nuclear envelope. ER membrane protein Sac1, a PI4P phosphatase cycles between the ER and Golgi and becomes trapped in expanded ERGIC compartments with VAPB-P56S. Loss of Sac1 in the ER leads to an increase in intracellular PI4P. ORP3 may increase Sac1 phosphatase activity by acting as a lipid sensor. We propose that VAPB, Sac1 and ORP3 are interacting partners that together modulate levels of PI4P. Disruptions in the gradient of PI4P may result in the vesicle trafficking defects observed in VAPB-P56S cells.

Peripherin is a type III intermediate filament protein that is predominately expressed in the peripheral nervous system and in subsets of efferent projections in the central nervous systems. While the exact role of peripherin remains unclear, it is found upregulated after traumatic neuronal injury and in the devastating neurodegenerative disease amyotrophic lateral sclerosis (ALS). Interestingly, peripherin overexpressing transgenic mice succumb to motor neuron disease with pathological hallmarks reminiscent of those found in ALS. Pathological peripherin abnormalities occur with high frequency in both familial and sporadic forms of ALS, with peripherin found associated with the majority intracellular inclusions present within degenerating motor neuron populations. The findings of peripherin mutations in sporadic ALS have reinforced the importance of peripherin as a prospective etiological or propagative factor of disease pathogenesis. Surprisingly, inherited peripherin gene mutations have not been identified; as such, understanding the post-transcriptional mechanism at which peripherin imparts its effect(s) is considered a key goal and represents a pathological point-of-convergence for an otherwise complex, multifaceted disease. Prior to the commencement of this work, our group identified the presence of an abnormal peripherin alternative splice variant upregulated in ALS. In doing so, we consistently observed the presence of a second peripherin species of ~45 kDa on immunoblots of cell lysates derived from full-length peripherin transfections. Here, we identified this protein as a constitutively expressed isoform, termed Per-45, that arises from alternative translation and that is required for normal filament assembly: changes to the normal isoform expression pattern are associated with malformed filaments and intracellular inclusions. In lieu of the possibility of distinct peripherin intra-isoform associations, we identified isoform-specific expression and ratio changes in traumatic neuronal injury, in mouse models of motor neuron disease, and in ALS. Finally, we explored the interrelationships between peripherin isoform expression, protein aggregation, and neuritic outgrowth by linking these phenotypes with major pathogenic features associated with ALS, including in vitro models of oxidation, glutamate excitotoxicity, and neuroinflammation. Overall, this thesis provides exciting new insight into our knowledge of basic IF biology and the role of peripherin isoforms in injury and in motor neuron disease.

This thesis examines the pathophysiology of motor neurone dysfunction, along with site of disease onset, in amyotrophic lateral sclerosis (ALS). The rationale for this thesis is the "dying forward" hypothesis, which suggests that corticomotoneurons cause anterograde excitotoxic degeneration of motor neurons in ALS. Initially, axonal excitability studies were applied to ALS patients and revealed widespread axonal ion channel dysfunction, with increases in persistent Na+ conductances and reduction in K+ currents. Such changes result in axonal hyperexcitability, thereby resulting in generation of fasciculations and cramps. Subsequently, axonal excitability studies were applied to Kennedy's disease (KD) patients, a pathological control group, revealing similar changes to ALS and suggesting that upregulation of persistent Na+ conductances was responsible for generation of fasciculations. To better understand the mechanisms underlying fatigability and to assess whether Na+/K+ pump dysfunction contributes to neurodegeneration in ALS, activity-dependent changes in axonal excitability were measured after a maximal voluntary contraction. The increase in threshold was more pronounced in ALS patients with predominantly lower motor neuron involvement, suggesting that peripheral factors were responsible for fatigue in ALS and that Na+/K+ pump function was preserved. Having documented abnormalities of axonal excitability, a novel threshold tracking transcranial magnetic stimulation (TMS) technique was developed for assessment of cortical excitability. This technique overcomes the marked variability in the motor evoked potential with consecutive stimuli, a major limitation of the previous "constant stimulus" technique. After establishing normative data, threshold tracking TMS established that cortical hyperexcitability was an early and prominent feature in ALS. Similar changes were found in flail-arm variant ALS, a pure lower motor neuron form of ALS. In KD patients, cortical excitability was normal, thereby suggesting that cortical hyperexcitability is a primary event in ALS rather than a down-regulation of inhibitory control over the motor cortex in order to compensate for anterior horn cell loss. In order to determine whether cortical hyperexcitability underlies motor neurodegeneration, longitudinal studies were undertaken in familial ALS subjects with the copper/zinc superoxide-dismutase-1 gene mutation. These studies established that cortical hyperexcitability precedes the development of clinical ALS, thereby suggesting that cortical hyperexcitability underlies the basis of motor neurodegeneration in familial ALS.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 140-158).

Diss. (sammanfattning) Umeå : Univ., 2004. / Härtill 4 uppsatser.

Thesis (Ph. D.)--Cornell University, August, 2008. / Vita. Includes bibliographical references (leaves 131-153).

Thesis (Ph.D.). / Written for the Dept. of Neurological Sciences. Title from title page of PDF (viewed 2009/06/11). Includes bibliographical references.

Thesis (Ph. D.)--University of Virginia, 1997. / Spine title: Degenerative diseases of the CNS. Includes bibliographical references (250-259). Also available online through Digital Dissertations.