Takanori Yokota

ALS-linked mutant SOD1 induces ER stress- and ASK1-dependent motor neuron death by targeting Derlin-1

Mutation in Cu/Zn-superoxide dismutase (SOD1) is a cause of familial amyotrophic lateral sclerosis (ALS). Mutant SOD1 protein (SOD1(mut)) induces motor neuron death, although the molecular mechanism of SOD1(mut)-induced cell death remains controversial. Here we show that SOD1(mut) specifically interacted with Derlin-1, a component of endoplasmic reticulum (ER)-associated degradation (ERAD) machinery and triggered ER stress through dysfunction of ERAD. SOD1(mut)-induced ER stress activated the apoptosis signal-regulating kinase 1 (ASK1)-dependent cell death pathway. Perturbation of binding between SOD1(mut) and Derlin-1 by Derlin-1-derived oligopeptide suppressed SOD1(mut)-induced ER stress, ASK1 activation, and motor neuron death. Moreover, deletion of ASK1 mitigated the motor neuron loss and extended the life span of SOD1(mut) transgenic mice. These findings demonstrate that ER stress-induced ASK1 activation, which is triggered by the specific interaction of Derlin-1 with SOD1(mut), is crucial for disease progression of familial ALS.

Delayed-onset ataxia in mice lacking α-tocopherol transfer protein: Model for neuronal degeneration caused by chronic oxidative stress

α-Tocopherol transfer protein (α-TTP) maintains the concentration of serum α-tocopherol (vitamin E), one of the most potent fat-soluble antioxidants, by facilitating α-tocopherol export from the liver. Mutations of the α-TTP gene are linked to ataxia with isolated vitamin E deficiency (AVED). We produced a model mouse of AVED by deleting the α-TTP gene, which showed ataxia and retinal degeneration after 1 year of age. Because the brain α-TTP functions in maintaining α-tocopherol levels in the brain, α-tocopherol was completely depleted in the α-TTP−/− mouse brain, and the neurological phenotype of α-TTP−/− mice is much more severe than that of wild-type mice when maintained on an α-tocopherol-deficient diet. Lipid peroxidation in α-TTP−/− mice brains showed a significant increase, especially in degenerating neurons. α-Tocopherol supplementation suppressed lipid peroxidation and almost completely prevented the development of neurological symptoms. This therapy almost completely corrects the abnormalities in a mouse model of human neurodegenerative disease. Moreover, α-TTP−/− mice may prove to be excellent animal models of delayed onset, slowly progressive neuronal degeneration caused by chronic oxidative stress.

Sleep-related periodic leg movements (nocturnal myoclonus) due to spinal cord lesion

Ten patients with involuntary leg movements due to myelopathy were studied clinically and polysomnographically. The clinical manifestation and polysomnographical findings of involuntary leg movements were identical to sleep-related periodic leg movement (PLM) (nocturnal myoclonus). Since 2 patients had complete transection of spinal cord due to injury or vascular accident, the spinal cord deprived of supraspinal influences was considered to generate the rhythm of PLM. Suppression of the leg movements during REM sleep was not obvious in the patients with complete transection of spinal cord. In addition, PLM alternated from one side to the other 1-4 times a night with intervals of 1-4 h in all patients. This alternation also seemed to be from the spinal cord. This PLM of spinal cord origin was different from spinal myoclonus in their clinical features although both were generated within the spinal cord. PLM of spinal cord origin showed a triple flexion of the ankle, knee and hip, and this was very similar to a flexor withdrawal reflex which all patients exhibited. Therefore, it was suggested that PLM of spinal cord origin has a common mechanisms with spinal automatism. Although all patients had extensor plantar responses, PLM preceded the paresis in three patients and the severity of paresis was variable. There was no laterality of left and right PLMs even in patients with weakness of the leg on one side. This suggested that PLM of spinal cord origin might be induced by the interruption of the tract which was separate from, but runs near the corticospinal tract.

Double cortical stimulation in amyotrophic lateral sclerosis.

OBJECTIVE: Transcranial double magnetic stimulation on the motor cortex was used to investigate central motor tract function in 16 patients with amyotrophic lateral sclerosis, five with spinal muscular atrophy, and 16 age matched normal controls. METHODS: Surface EMG responses were recorded from the relaxed abductor pollicis brevis (APB) muscle. RESULTS: Responses to test stimuli were markedly attenuated by a subthreshold conditioning stimulus given at a condition-test (C-T) interval of 1-4 ms in normal controls and patients with spinal muscular atrophy, but attenuation was mild in patients with amyotrophic lateral sclerosis. In the normal controls this suppression was caused by activation of the intracortical inhibitory mechanism because responses to electrical test stimuli and the H wave were not suppressed by the same magnetic subthreshold conditioning stimulus. In amyotrophic lateral sclerosis the effect of the conditioning cortical stimulus on the H wave was also in the normal range. CONCLUSION: The intracortical inhibitory mechanism may be impaired in patients with amyotrophic lateral sclerosis.

Localization of α-tocopherol transfer protein in rat brain

Vitamin E (α-tocopherol) is a fat-soluble antioxidant that is transported by plasma lipoproteins in the body. α-Tocopherol transfer protein (α-TTP), which was identified as a product of the causative gene for familial isolated vitamin E (FIVE) deficiency, is a cytosolic liver protein which plays an important role in the efficient circulation of plasma vitamin E in the body. In the present study, we detected the message for α-TTP at low levels in some rat tissues including brain, spleen, lung and kidney. In the brain, the α-TTP transcript was detected predominantly in the cerebellar cortex, as revealed by in situ hybridization histochemistry. In the cerebellar cortex, clusters of the hybridization signal were aligned with the Purkinje cell layer, although the signal was not detected in the Purkinje cells, but in the small cells around the Purkinje cells. This distribution pattern strongly suggests that the message for α-TTP is expressed in the Bergmann glial cells. Combined with the previous observation that there was severe Purkinje cell loss in patients with FIVE deficiency, the present data suggest that vitamin E is supplied to the Purkinje cells from the surrounding Bergmann glial cells with the help of α-TTP.

Can regional spreading of amyotrophic lateral sclerosis motor symptoms be explained by prion-like propagation?

Progressive accumulation of specific misfolded protein is a defining feature of amyotrophic lateral sclerosis (ALS), similarly seen in Alzheimer disease, Parkinson disease, Huntington disease and Creutzfeldt–Jakob disease. The intercellular transfer of inclusions made of tau, α-synuclein and huntingtin has been demonstrated, revealing the existence of mechanisms reminiscent of those by which prions spread through the nervous system. Evidence for such a prion-like propagation mechanism has now spread to the major misfolded proteins, superoxide dismutase 1 (SOD1) and the 43 kDa transactive response DNA binding protein (TDP-43), implicated in ALS. The focus in this review is on what is known about ALS progression in terms of clinical as well as molecular aspects. Furthermore, the concept of ‘propagation’ is dissected into contiguous and non-contiguous types, and this concept is expanded to the severity of the focal symptom as well as its regional spread which can be explained by cell to cell propagation in the local neuron pool.

Depletion of Vitamin E Increases Amyloid β Accumulation by Decreasing Its Clearances from Brain and Blood in a Mouse Model of Alzheimer Disease

Increased oxidative damage is a prominent and early feature in Alzheimer disease. We previously crossed Alzheimer disease transgenic (APPsw) model mice with α-tocopherol transfer protein knock-out (Ttpa−/−) mice in which lipid peroxidation in the brain was significantly increased. The resulting double-mutant (Ttpa−/−APPsw) mice showed increased amyloid β (Aβ) deposits in the brain, which was ameliorated with α-tocopherol supplementation. To investigate the mechanism of the increased Aβ accumulation, we here studied generation, degradation, aggregation, and efflux of Aβ in the mice. The clearance of intracerebral-microinjected 125I-Aβ1–40 from brain was decreased in Ttpa−/− mice to be compared with wild-type mice, whereas the generation of Aβ was not increased in Ttpa−/−APPsw mice. The activity of an Aβ-degrading enzyme, neprilysin, did not decrease, but the expression level of insulin-degrading enzyme was markedly decreased in Ttpa−/− mouse brain. In contrast, Aβ aggregation was accelerated in Ttpa−/− mouse brains compared with wild-type brains, and well known molecules involved in Aβ transport from brain to blood, low density lipoprotein receptor-related protein-1 (LRP-1) and p-glycoprotein, were up-regulated in the small vascular fraction of Ttpa−/− mouse brains. Moreover, the disappearance of intravenously administered 125I-Aβ1–40 was decreased in Ttpa−/− mice with reduced translocation of LRP-1 in the hepatocytes. These results suggest that lipid peroxidation due to depletion of α-tocopherol impairs Aβ clearances from the brain and from the blood, possibly causing increased Aβ accumulation in Ttpa−/−APPsw mouse brain and plasma.

Bax-inhibiting peptide protects cells from polyglutamine toxicity caused by Ku70 acetylation

Polyglutamine (polyQ) diseases, such as Huntingtons disease and Machado–Joseph disease (MJD), are caused by gain of toxic function of abnormally expanded polyQ tracts. Here, we show that expanded polyQ of ataxin-3 (Q79C), a gene that causes MJD, stimulates Ku70 acetylation, which in turn dissociates the proapoptotic protein Bax from Ku70, thereby promoting Bax activation and subsequent cell death. The Q79C-induced cell death was significantly blocked by Ku70 or Bax-inhibiting peptides (BIPs) designed from Ku70. Furthermore, expression of SIRT1 deacetylase and the addition of a SIRT1 agonist, resveratrol, reduced Q79C toxicity. In contrast, mimicking acetylation of Ku70 abolished the ability of Ku70 to suppress Q79C toxicity. These results indicate that Bax and Ku70 acetylation play important roles in Q79C-induced cell death, and that BIP may be useful in the development of therapeutics for polyQ diseases.

Proteolytic cleavage and cellular toxicity of the human α1A calcium channel in spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) is a neurodegenerative disease caused by small CAG repeat expansion in the alpha1A calcium channel gene. We found that the human alpha1A calcium channel protein expressed in human embryonic kidney 293T cells produces a 75 kDa C-terminal fragment. This fragment is more toxic to cells than the full-length alpha1A calcium channel, regardless of polyglutamine tract length. In cells stably transfected with plasmids of full-length alpha1A calcium channel cDNAs, the C-terminal fragment protein is present in the mutant transformant but not in the wild-type one, indicative that this C-terminal fragment with the expanded polyglutamine tract is more resistant to proteolysis than that with the normal sized polyglutamine tract. We speculate that the toxic C-terminal fragment, in which resistance to proteolysis is rendered by the expanded polyglutamine, has a key role in the pathological mechanism of SCA6.

Cerebral ischemic attack caused by postprandial hypotension.

BACKGROUND Food ingestion sometimes induces systemic hypotension (postprandial hypotension). Although the possibility of stroke occurring postprandially has been suggested, no cases have been reported until now. CASE DESCRIPTION A 78-year-old man experienced repeated transient ischemic attacks after almost every ingestion of food and showed orthostatic and postprandial hypotension. An angiogram revealed occlusion of his left carotid artery and stenosis of his right middle cerebral artery. CONCLUSIONS Postprandial as well as orthostatic hypotension can be a risk factor for stroke in patients with severe occlusive cerebrovascular disease.