Reduced voltage sensitivity of activation of P/Q-type Ca2+ channels is associated with the ataxic mouse mutation rolling Nagoya (tg(rol)).
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Recent genetic analyses have revealed an important association of the gene encoding the P/Q-type voltage-dependent Ca(2+) channel alpha(1A) subunit with hereditary neurological disorders. We have identified the ataxic mouse mutation, rolling Nagoya (tg(rol)), in the alpha(1A) gene that leads to a charge-neutralizing arginine-to-glycine substitution at position 1262 in the voltage sensor-forming segment S4 in repeat III. Ca(2+) channel currents in acutely dissociated Purkinje cells, where P-type is the dominant type, showed a marked decrease in slope and a depolarizing shift by 8 mV of the conductance-voltage curve and reduction in current density in tg(rol) mouse cerebella, compared with those in wild-type. Compatible functional change was induced by the tg(rol) mutation in the recombinant alpha(1A) channel, indicating that a defect in voltage sensor of P/Q-type Ca(2+) channels is the direct consequence of the tg(rol) mutation. Furthermore, somatic whole-cell recording of mutant Purkinje cells displayed only abortive Na(+) burst activity and hardly exhibited Ca(2+) spike activity in cerebellar slices. Thus, in tg(rol) mice, reduced voltage sensitivity, which may derive from a gating charge defect, and diminished activity of the P-type alpha(1A) Ca(2+) channel significantly impair integrative properties of Purkinje neurons, presumably resulting in locomotor deficits. (+info)
Urinary alpha-tocopherol metabolites in alpha-tocopherol transfer protein-deficient patients.
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Patients with alpha-tocopherol transfer protein (alpha-TTP) defects experience neurological symptoms characteristic of vitamin E deficiency and depend on continuous high alpha-tocopherol supplements. We investigated the excretion of 2,5,7, 8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), a urinary metabolite of alpha-tocopherol, as a putative marker for the alpha-tocopherol status of alpha-TTP-deficient patients and control subjects. In three patients vitamin E supplementation was stopped for short periods of time, during which plasma alpha-tocopherol concentrations and urinary alpha-CEHC excretion were measured. In the patients, plasma alpha-tocopherol decreased below normal (<5 micromol/l) but alpha-CEHC excretion remained above the range of unsupplemented control subjects (0.118-0.306 mg/day, n = 6). In healthy subjects, however, alpha-CEHC excretion was increased only after surpassing a plasma alpha-tocopherol threshold of 30-40 micromol/l. Such a threshold did not exist in patients. The general mechanism of alpha-tocopherol degradation did not appear to differ between patients and control subjects. The presumed mechanism of omega- and subsequent beta-oxidation was supported by the detection of alpha- CPHC, an alpha -CEHC homolog with a side chain longer by 3 carbon atoms, both in supplemented patients and in control subjects. (+info)
Sensory ataxic dominant neuropathy associated with polyarteritis nodosa.
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A 68-year-old man with sensory ataxic dominant neuropathy associated with polyarteritis nodosa (PAN) had deep sensory disturbance with unsteady gait and absence of the Achilles tendon reflex. Examination revealed weight loss, elevated CRP level, negative antineutrophil cytoplasm antibodies, decreased M-wave amplitude in the peroneal motor nerve and absence of action potentials in the sural sensory nerve. Sural nerve biopsy revealed a marked loss of myelinated fibers, myelin ovoid formation and necrotizing angiitis of large epineurial arterioles. Renal biopsy revealed global and/or segmental necrotizing angiitis in glomeruli, but not in the arcuate artery. These pathological findings were distinct from those of PAN, particularly microscopic polyangiitis (MPA). Treatment with a steroid improved the deep sensory disturbance, unsteady gait, and CRP level. This case is similar to ataxic neuropathy which can arise from various disorders. This is the first report of a case of sensory ataxic dominant neuropathy associated with MPA in PAN. (+info)
Molecular determinants of inactivation in voltage-gated Ca2+ channels.
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Evolution has created a large family of different classes of voltage-gated Ca2+ channels and a variety of additional splice variants with different inactivation properties. Inactivation controls the amount of Ca2+ entry during an action potential and is, therefore, believed to play an important role in tissue-specific Ca2+ signalling. Furthermore, mutations in a neuronal Ca2+ channel (Ca(v)2.1) that are associated with the aetiology of neurological disorders such as familial hemiplegic migraine and ataxia cause significant changes in the process of channel inactivation. Ca2+ channels of a given subtype may inactivate by three different conformational changes: a fast and a slow voltage-dependent inactivation process and in some channel types by an additional Ca2+-dependent inactivation mechanism. Inactivation kinetics of Ca2+ channels are determined by the intrinsic properties of their pore-forming alpha1-subunits and by interactions with other channel subunits. This review focuses on structural determinants of Ca2+ channel inactivation in different parts of Ca2+ channel alpha1-subunits, including pore-forming transmembrane segments and loops, intracellular domain linkers and the carboxyl terminus. Inactivation is also affected by the interaction of the alpha1-subunits with auxiliary beta-subunits and intracellular regulator proteins. The evidence shows that pore-forming S6 segments and conformational changes in extra- (pore loop) and intracellular linkers connected to pore-forming segments may play a principal role in the modulation of Ca2+ channel inactivation. Structural concepts of Ca2+ channel inactivation are discussed. (+info)
Physiological expression of the gene for PrP-like protein, PrPLP/Dpl, by brain endothelial cells and its ectopic expression in neurons of PrP-deficient mice ataxic due to Purkinje cell degeneration.
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Recently, a novel gene encoding a prion protein (PrP)-like glycoprotein, PrPLP/Dpl, was identified as being expressed ectopically by neurons of the ataxic PrP-deficient (PRNP(-/-)) mouse lines exhibiting Purkinje cell degeneration. In adult wild-type mice, PrPLP/Dpl mRNA was physiologically expressed at a high level by testis and heart, but was barely detectable in brain. However, transient expression of PrPLP/Dpl mRNA was detectable by Northern blotting in the brain of neonatal wild-type mice, showing maximal expression around 1 week after birth. In situ hybridization paired with immunohistochemistry using anti-factor VIII serum identified brain endothelial cells as expressing the transcripts. Moreover, in the neonatal wild-type mice, the PrPLP/Dpl mRNA colocalized with factor VIII immunoreactivities in spleen and was detectable on capillaries in lamina propria mucosa of gut. These findings suggested a role of PrPLP/Dpl in angiogenesis, in particular blood-brain barrier maturation in the central nervous system. Even in the ataxic Ngsk PRNP(-/-) mice, the physiological regulation of PrPLP/Dpl mRNA expression in brain endothelial cells was still preserved. This strongly supports the argument that the ectopic expression of PrPLP/Dpl in neurons, but not deregulation of its physiological expression in endothelial cells, is involved in the neuronal degeneration in ataxic PRNP(-/-) mice. (+info)
Impaired ATP synthase assembly associated with a mutation in the human ATP synthase subunit 6 gene.
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Mutations in human mitochondrial DNA are a well recognized cause of disease. A mutation at nucleotide position 8993 of human mitochondrial DNA, located within the gene for ATP synthase subunit 6, is associated with the neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP) syndrome. To enable analysis of this mutation in control nuclear backgrounds, two different cell lines were transformed with mitochondria carrying NARP mutant mitochondrial DNA. Transformant cell lines had decreased ATP synthesis capacity, and many also had abnormally high levels of two ATP synthase sub-complexes, one of which was F(1)-ATPase. A combination of metabolic labeling and immunoblotting experiments indicated that assembly of ATP synthase was slowed and that the assembled holoenzyme was unstable in cells carrying NARP mutant mitochondrial DNA compared with control cells. These findings indicate that altered assembly and stability of ATP synthase are underlying molecular defects associated with the NARP mutation in subunit 6 of ATP synthase, yet intrinsic enzyme activity is also compromised. (+info)
Defective neurogenesis in citron kinase knockout mice by altered cytokinesis and massive apoptosis.
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Citron-kinase (Citron-K) has been proposed by in vitro studies as a crucial effector of Rho in regulation of cytokinesis. To further investigate in vivo its biologic functions, we have inactivated Citron-K gene in mice by homologous recombination. Citron-K-/- mice grow at slower rates, are severely ataxic, and die before adulthood as a consequence of fatal seizures. Their brains display defective neurogenesis, with depletion of specific neuronal populations. These abnormalities arise during development of the central nervous system due to altered cytokinesis and massive apoptosis. Our results indicate that Citron-K is essential for cytokinesis in vivo but only in specific neuronal precursors. Moreover, they suggest a novel molecular mechanism for a subset of human malformative syndromes of the CNS. (+info)
Detection of Akabane viral antigens in spontaneous lymphohistiocytic encephalomyelitis in cattle.
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A 5-month-old Japanese black bull calf and twenty-seven 1-27-day-old calves exhibiting neurological signs between August and October 1998 were examined. The bull calf exhibited rapid breathing, fever, hypersensitivity, and ataxia and was euthanized 4 days after the onset of symptoms. The 27 calves primarily exhibited ataxia, and 15 had arthrogryposis. Histological examination of the bull calf revealed perivascular infiltraction by mononuclear cells, diffuse to multifocal gliosis, and neuronal necrosis in the brain and spinal cord. Multiple malacic foci were found in the midbrain in 5 cases. In contrast, in the 15 calves necropsied in October, there were fewer inflammatory changes, but there was neuronal cell loss in the ventral horn and a decrease in myelinated axons in the lateral and ventral funiculi. Immunohistochemical examination using a rabbit antiserum against Akabane virus strain OBE-1 revealed a large amount of viral antigen in the degenerating neurons and glial cells of the bull calf, mainly in the spinal gray matter. Small amounts of viral antigen in swollen axons and a few glial cells were found in 5 of 27 calves. Thirteen of the 27 calves had high neutralization antibody titers against the Akabane virus, whereas there was no significant antibody titer in most of the calves necropsied during August. The present study revealed that viral antigen detection was very useful for the diagnosis of Akabane diseases in the 5-month-old bull calf that was suspected to be infected postnatally, while it had limited usefulness in the other young calves. (+info)