Inverse correlation between the formation of mitochondria-derived vacuoles and Lewy-body-like hyaline inclusions in G93A superoxide-dismutase-transgenic mice

Motor neuron degeneration, severe myopathy and TDP-43 increase in a transgenic pig model of SOD1-linked familiar ALS

Amyotrophic Lateral Sclerosis (ALS) is a neural disorder gradually leading to paralysis of the whole body. Alterations in superoxide dismutase SOD1 gene have been linked with several variants of familial ALS. Here, we investigated a transgenic (Tg) cloned swine model expressing the human pathological hSOD1^G93A allele. As in patients, these Tg pigs transmitted the disease to the progeny with an autosomal dominant trait and showed ALS onset from about 27 months of age. Post mortem analysis revealed motor neuron (MN) degeneration, gliosis and hSOD1 protein aggregates in brainstem and spinal cord. Severe skeletal muscle pathology including necrosis and inflammation was observed at the end stage, as well. Remarkably, as in human patients, these Tg pigs showed a quite long presymptomatic phase in which gradually increasing amounts of TDP-43 were detected in peripheral blood mononuclear cells. Thus, this transgenic swine model opens the unique opportunity to investigate ALS biomarkers even before disease onset other than testing novel drugs and possible medical devices.

Evidence that glial cells attenuate G47R transthyretin accumulation in the central nervous system

Amyloidogenic protein forms amyloid aggregations at membranes leading to dysfunction of amyloid clearance and amyloidosis. Glial cells function in the clearance and degradation of amyloid β (Aβ) in the brain. This study aimed to clarify the reason why amyloid transthyretin (ATTR) rarely accumulates in the CNS. We pathologically analyzed the relationship between amyloid deposition with basement membranes or glial cells in a rare case of ATTR leptomeningeal amyloidosis. In addition, we compared the cytotoxicity of ATTR G47R, the amyloidosis-causing mutation in the case studied (n = 1), and Aβ in brains from patients with cerebral amyloid angiopathy (n = 6). In the subarachnoid space of the ATTR G47R case, most amyloids accumulated at the components of basement membranes. On the CNS surface, ATTR accumulations were retained by astrocytic end feet. In areas where glial end feet enveloped ATTR, ubiquitination and micro-vacuolation of ATTR was evident. The colocalization of GFAP and ubiquitin was also evident. The accumulation of ATTR G47R in the CNS was negatively correlated with the prevalence of astrocytes. Quantitatively, amyloid deposits along the vessels were mostly partial in cerebral Aβ angiopathy cases and nearly complete along the basement membrane in the ATTR G47R case. The vascular expressions of type IV collagen and smooth muscle actin were severely reduced in areas with ATTR G47R deposition, but not in areas with Aβ deposition. The vascular protein level recovered in the ATTR G47R case when vessels entered into areas of parenchyma that were rich in astrocytes. In addition, the strong interactions between the transthyretin variant and basement membranes may have led to dysfunction of transthyretin clearance and leptomeningeal amyloidosis. The present study was the first to show that glial cells may attenuate G47R transthyretin accumulation in the CNS.

New Strategy That Delays Progression of Amyotrophic Lateral Sclerosis in G1H-G93A Transgenic Mice: Oral Administration of Xanthine Oxidoreductase Inhibitors That Are Not Substrates for the Purine Salvage Pathway

Amyotrophic lateral sclerosis (ALS), Lou Gehrig's disease, is a progressive fatal neurodegenerative disease that involves both upper and lower motor neurons. We orally administered 4 xanthine oxidoreductase (XOR) inhibitors to G1H-G93A mice carrying 25 transgene copy numbers of human mutant G93A superoxide dismutase 1, from 80 days of age. Three nonpurine-analogue inhibitors (TEI-6720: Febuxostat, Y-700 and FYX-051), but not allopurinol with a purine analogue ring (pyrazolo pyrimidine ring), significantly delayed disease onset, prolonged survival and the duration of disease stages, improved clinical signs, and alleviated weight loss. Exercise testing (extension reflex, inclined plane, footprint, rotarod, and beam balance tests) showed significantly improved motor function in the G1H-G93A mice treated with these 3 inhibitors. Significant amelioration of disease was seen even when TEI-6720 or Y-700 was administered after the appearance of early signs. Histopathological evaluation in the late stage revealed that G1H-G93A mice treated with TEI-6720 had well-preserved motor neurons and fewer inclusion bodies, compared with mice treated with placebo or with allopurinol. Our results indicate that these 3 nonpurine-analogue XOR inhibitors might increase the supply of high-energy compounds via the purine salvage pathway, thereby protecting motor neurons against death. This strategy may be applicable for oral therapy of ALS patients.

High expression of α-synuclein in damaged mitochondria with PLA2G6 dysfunction

To clarify the role of α-synuclein (αSyn) in neuronal membrane remodeling, we analyzed the expression of αSyn in neurons with a dysfunction of PLA2G6, which is indispensable for membrane remodeling. αSyn/phosphorylated-αSyn (PαSyn) distribution and neurodegeneration were quantitatively estimated in PLA2G6-knockout (KO) mice, which demonstrate marked mitochondrial membrane degeneration. We also assessed the relationship between αSyn deposits and mitochondria in brain tissue from patients with PLA2G6-associated neurodegeneration (PLAN) and Parkinson’s disease (PD), and quantitatively examined Lewy bodies (LBs) and neurons. The expression level of αSyn was elevated in PLA2G6-knockdown cells and KO mouse neurons. Strong PαSyn expression was observed in neuronal granules in KO mice before onset of motor symptoms. The granules were mitochondrial outer membrane protein (TOM20)-positive. Ultramicroscopy revealed that PαSyn-positive granules were localized to mitochondria with degenerated inner membranes. After symptom onset, TOM20-positive granules were frequently found in ubiquitinated spheroids, where PαSyn expression was low. Axons were atrophic, but the neuronal loss was not evident in KO mice. In PLAN neurons, small PαSyn-positive inclusions with a TOM20-positive edge were frequently observed and clustered into LBs. The surfaces of most LBs were TOM20-positive in PLAN and TOM20-negative in PD brains. The high proportion of LB-bearing neurons and the preserved neuronal number in PLAN suggested long-term survival of LB-bearing neurons. Elevated expression of αSyn/PαSyn in mitochondria appears to be the early response to PLA2G6-deficiency in neurons. The strong affinity of αSyn for damaged mitochondrial membranes may promote membrane stabilization of mitochondria and neuronal survival in neurons.

Neuroaxonal dystrophy in calcium-independent phospholipase A2β deficiency results from insufficient remodeling and degeneration of mitochondrial and presynaptic membranes

Infantile neuroaxonal dystrophy (INAD) is a fatal neurodegenerative disease characterized by the widespread presence of axonal swellings (spheroids) in the CNS and PNS and is caused by gene abnormality in PLA2G6 [calcium-independent phospholipase A(2)β (iPLA(2)β)], which is essential for remodeling of membrane phospholipids. To clarify the pathomechanism of INAD, we pathologically analyzed the spinal cords and sciatic nerves of iPLA(2)β knock-out (KO) mice, a model of INAD. At 15 weeks (preclinical stage), periodic acid-Schiff (PAS)-positive granules were frequently observed in proximal axons and the perinuclear space of large neurons, and these were strongly positive for a marker of the mitochondrial outer membrane and negative for a marker of the inner membrane. By 100 weeks (late clinical stage), PAS-positive granules and spheroids had increased significantly in the distal parts of axons, and ultrastructural examination revealed that these granules were, in fact, mitochondria with degenerative inner membranes. Collapse of mitochondria in axons was accompanied by focal disappearance of the cytoskeleton. Partial membrane loss at axon terminals was also evident, accompanied by degenerative membranes in the same areas. Imaging mass spectrometry showed a prominent increase of docosahexaenoic acid-containing phosphatidylcholine in the gray matter, suggesting insufficient membrane remodeling in the presence of iPLA(2)β deficiency. Prominent axonal degeneration in neuroaxonal dystrophy might be explained by the collapse of abnormal mitochondria after axonal transportation. Insufficient remodeling and degeneration of mitochondrial inner membranes and presynaptic membranes appear to be the cause of the neuroaxonal dystrophy in iPLA(2)β-KO mice.

A comprehensive assessment of the SOD1G93A low-copy transgenic mouse, which models human amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that results in the death of motor neurons in the brain and spinal cord. The disorder generally strikes in mid-life, relentlessly leading to paralysis and death, typically 3-5 years after diagnosis. No effective treatments are available. Up to 10% of ALS is familial, usually autosomal dominant. Several causative genes are known and, of these, mutant superoxide dismutase 1 (SOD1) is by far the most frequently found, accounting for up to 20% of familial ALS. A range of human mutant SOD1 transgenic mouse strains has been produced, and these largely successfully model the human disease. Of these, the most widely used is the SOD1 mouse, which expresses a human SOD1 transgene with a causative G93A mutation. This mouse model is excellent for many purposes but carries up to 25 copies of the transgene and produces a great excess of SOD1 protein, which might affect our interpretation of disease processes. A variant of this strain carries a deletion of the transgene array such that the copy number is dropped to eight to ten mutant SOD1 genes. This 'deleted' 'low-copy' mouse undergoes a slower course of disease, over many months. Here we have carried out a comprehensive analysis of phenotype, including nerve and muscle physiology and histology, to add to our knowledge of this 'deleted' strain and give baseline data for future studies. We find differences in phenotype that arise from genetic background and sex, and we quantify the loss of nerve and muscle function over time. The slowly progressive pathology observed in this mouse strain could provide us with a more appropriate model for studying early-stage pathological processes in ALS and aid the development of therapies for early-stage treatments.

Motor neuron diversity in development and disease

Although often considered as a group, spinal motor neurons are highly diverse in terms of their morphology, connectivity, and functional properties and differ significantly in their response to disease. Recent studies of motor neuron diversity have clarified developmental mechanisms and provided novel insights into neurodegeneration in amyotrophic lateral sclerosis (ALS). Motor neurons of different classes and subtypes--fast/slow, alpha/gamma--are grouped together into motor pools, each of which innervates a single skeletal muscle. Distinct mechanisms regulate their development. For example, glial cell line-derived neurotrophic factor (GDNF) has effects that are pool-specific on motor neuron connectivity, column-specific on axonal growth, and subtype-specific on survival. In multiple degenerative contexts including ALS, spinal muscular atrophy (SMA), and aging, fast-fatigable (FF) motor units degenerate early, whereas motor neurons innervating slow muscles and those involved in eye movement and pelvic sphincter control are strikingly preserved. Extrinsic and intrinsic mechanisms that confer resistance represent promising therapeutic targets in these currently incurable diseases.

Pre-symptomatic alterations in subcellular betaCGRP distribution in motor neurons precede astrogliosis in ALS mice

In our study we investigated the pathology-related expression patterns of the two calcitonin gene-related peptide (CGRP) isoforms in spinal cord motor neurons of SOD1(G93A) mice, an animal model of the human motor neuron disease, amyotrophic lateral sclerosis (ALS). We found that alphaCGRP and betaCGRP gene expression and alphaCGRP immunoreactivity remained unaltered throughout disease, and alphaCGRP gene deficiency had no effect on disease progression. In contrast, betaCGRP immunoreactivity appeared at atypical sites in degenerating motor neuron cell bodies, axons, and dendrites already in the early pre-symptomatic disease phase around postnatal day 40. A close association of betaCGRP-containing dysmorphic dendritic structures with processes of activated astrocytes, in combination with a selective expression of the CGRP receptor by astrocytes, suggests that betaCGRP may function as a motor neuron-derived signaling molecule for astrocyte activation in ALS.

Nuclear TAR DNA binding protein 43 expression in spinal cord neurons correlates with the clinical course in amyotrophic lateral sclerosis

TAR DNA binding protein 43 (TDP-43) has been considered a signature protein in frontotemporal dementia and amyotrophic lateral sclerosis (ALS), but not in ALS associated with the superoxide dismutase 1 (SOD1) gene mutations (ALS1). To clarify how TDP may be involved in ALS pathogenesis, clinical and pathological features in cases of sporadic ALS ([SALS] n = 18) and ALS1 (n = 6) were analyzed. In SALS patients with rapid clinical courses, TDP mislocalization (i.e. cytoplasmic staining and TDP-positive cytoplasmic inclusions) in anterior horn cells was frequent. In SALS patients with slow clinical courses, TDP-43 mislocalization was rare. In an ALS1 patient with the SOD1 gene mutation C111Y, there were numerous TDP-positive inclusions and colocalization of SOD1 and TDP. In mutant SOD1 transgenic (G93A) mice at the end stage (median, 256 days), TDP-positive inclusions and TDP colocalization with SOD1 were also observed; nuclear TDP-43 immunoreactivity was highly correlated with life span in these mice. In both humans and mice, nuclei that stained strongly for TDP were large and circular; weakly stained nuclei were atrophic or deformed. In conclusion, low levels of TDP expression in the nucleus cor relate with a rapid clinical course in SALS and in ALS1 model mice, suggesting that nuclear TDP may play a protective role against motor neuron death resulting from different underlying etiologies.

Neuroaxonal dystrophy caused by group VIA phospholipase A2 deficiency in mice: a model of human neurodegenerative disease

Calcium-independent group VIA phospholipase A2 (iPLA2beta) is considered to play a role in signal transduction and maintenance of homeostasis or remodeling of membrane phospholipids. A role of iPLA2beta has been suggested in various physiological and pathological processes, including immunity, chemotaxis, and cell death, but the details remain unclear. Accordingly, we investigated mice with targeted disruption of the iPLA2beta gene. iPLA2beta-/- mice developed normally and grew to maturity, but all showed evidence of severe motor dysfunction, including a hindlimb clasping reflex during tail suspension, abnormal gait, and poor performance in the hanging wire grip test. Neuropathological examination of the nervous system revealed widespread degeneration of axons and/or synapses, accompanied by the presence of numerous spheroids (swollen axons) and vacuoles. These findings provide evidence that impairment of iPLA2beta causes neuroaxonal degeneration, and indicate that the iPLA2beta-/- mouse is an appropriate animal model of human neurodegenerative diseases associated with mutations of the iPLA2beta gene, such as infantile neuroaxonal dystrophy and neurodegeneration with brain iron accumulation.

Mitochondrial changes in motor neurons of homozygotes of leucine 126 TT deletion SOD1 transgenic mice

We investigated the time course of ultrastructural changes of mitochondria in the spinal cord of homozygotes of Leu126TTdel SOD1 (superoxide dismutase 1) with FLAG (signal sequence at the C-terminal protein) transgenic mice (DF-homo). Non-Tg mice and wild-type human SOD1 with FLAG epitope transgenic mice (WF) were investigated as controls for non-onset Tg mice. Expansion and vacuolation of the mitochondrial matrix was exhibited in motor neurons in the anterior horns of DF-homo Tg mice at the presymptomatic stage. Such mitochondrial degeneration became severe at the postsymptomatic stage. In contrast, expansion of the mitochondrial inner-membrane space was not evident even at the terminal stage. Microvacuoles of cytoplasm and fibrillar inclusions were rarely shown from the early symptomatic stage. WF mice showed expansion and vacuolation of the mitochondrial inner membrane space at old age. Non-Tgs showed no obvious change in mitochondria. Gold-labeled human SOD1 immunoreactivity showed small amount of gold deposits in the vacuolated mitochondria. These results suggest that the expansion and vacuolation of mitochondrial matrix in the spinal cord of DF-homo transgenic mice is the first pathological change, but that it is not directly caused by the aggregation of an abnormal human SOD1 protein in intermembrane space of mitochondria.

Amyotrophic lateral sclerosis models and human neuropathology: similarities and differences

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that primarily involves the motor neuron system. The author initially summarizes the principal features of human ALS neuropathology, and subsequently describes in detail ALS animal models mainly from the viewpoint of pathological similarities and differences. ALS animal models in this review include strains of rodents that are transgenic for superoxide dismutase 1 (SOD1), ALS2 knockout mice, and mice that are transgenic for cytoskeletal abnormalities. Although the neuropathological results obtained from human ALS autopsy cases are valuable and important, almost all of such cases represent only the terminal stage. This makes it difficult to clarify how and why ALS motor neurons are impaired at each clinical stage from disease onset to death, and as a consequence, human autopsy cases alone yield little insight into potential therapies for ALS. Although ALS animal models cannot replicate human ALS, in order to compensate for the shortcomings of studies using human ALS autopsy samples, researchers must inevitably rely on ALS animal models that can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy. Of course, human ALS and all ALS animal models share one most important similarity in that both exhibit motor neuron degeneration/death. This important point of similarity has shed much light on the pathomechanisms of the motor neuron degeneration/death at the cellular and molecular levels that would not have been appreciated if only human ALS autopsy samples had been available. On the basis of the aspects covered in this review, it can be concluded that ALS animal models can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy only in combination with detailed neuropathological data obtained from human ALS autopsy cases.