A novel compound, denosomin, ameliorates spinal cord injury via axonal growth associated with astrocyte-secreted vimentin

BACKGROUND AND PURPOSE

In the spinal cord injury (SCI) axon regeneration is inhibited by the glial scar, which contains reactive astrocytes that secrete inhibitory chondroitin sulphate proteoglycan (CSPG). We previously reported that a novel compound, denosomin, promotes axonal growth under degenerative conditions in cultured cortical neurons. In this study, we investigated the effects of denosomin on functional recovery in SCI mice and elucidated the mechanism though which denosomin induces axonal growth in the injured spinal cord.

EXPERIMENTAL APPROACH

Denosomin was administered p.o. for 7 or 14 days to contusion mice. Behavioural evaluations and immunohistochemistry were done. Primary cultured cortical neurons and astrocytes were treated with denosomin to investigate the mechanism of axonal growth facilitation.

KEY RESULTS

Denosomin improved hind limb motor dysfunction and axonal growth, especially in the 5-HT-positive tracts across the scar and increased the density of astrocytes. Denosomin increased astrocyte proliferation, inhibited astrocytic death and increased the expression and secretion of vimentin in cultured astrocytes. Furthermore, vimentin increased axonal outgrowth in cultured neurons, even in the presence of inhibitory CSPG. Denosomin increased the number of vimentin-expressing astrocytes inside glial scars of SCI mice, and 5-HT-positive axonal growth occurred in a vimentin-associated manner.

CONCLUSION AND IMPLICATIONS

Denosomin increased the ratio of astrocytes that secrete vimentin as an axonal growth facilitator, which, we propose enhances axonal growth beyond the glial scar and promotes functional recovery in SCI mice. This study is the first to demonstrate this novel role of vimentin in SCI and drug-mediated modification of the inhibitory property of reactive astrocytes.

Structure-activity-relationship studies on dihydrofuran-fused perhydrophenanthrenes as an anti-Alzheimer's disease agent

As an extended study on development of anti-Alzheimer's disease agent, we newly synthesized various dihydrofuran-fused perhydrophenanthrenes via o-quinodimethane chemistry. This study revealed that the introduction of carbon side-chain on 8-position or removal of the acetal moiety on 3-position arose a cytotoxicity on rat cortical neurons. On the other hand, the ethereal or thio-ethereal substituent on 8-position enhanced the elongation effect on Aβ-damaged neurons. The necessity of the cyano group on 10b position was also proved in this structure-activity-relationship study.

Diosgenin is an exogenous activator of 1,25D₃-MARRS/Pdia3/ERp57 and improves Alzheimer's disease pathologies in 5XFAD mice

The aim of this study was to investigate the effects and the mechanism of diosgenin, a famous plant-derived steroidal sapogenin, on memory deficits in Alzheimer's disease (AD) model mice. Diosgenin-treated 5XFAD mice exhibited significantly improved performance of object recognition memory. Diosgenin treatment significantly reduced amyloid plaques and neurofibrillary tangles in the cerebral cortex and hippocampus. Degenerated axons and presynaptic terminals that were only observed in regions closely associated with amyloid plaques were significantly reduced by diosgenin treatment. The 1,25D₃-membrane-associated, rapid response steroid-binding protein (1,25D₃-MARRS) was shown to be a target of diosgenin. 1,25D₃-MARRS knockdown completely inhibited diosgenin-induced axonal growth in cortical neurons. Treatment with a neutralizing antibody against 1,25D₃-MARRS diminished the axonal regeneration effect of diosgenin in Aβ(1–42)-induced axonal atrophy. This is the first study to demonstrate that the exogenous stimulator diosgenin activates the 1,25D₃-MARRS pathway, which may be a very critical signaling target for anti-AD therapy.

Protective Effects of Rosa damascena and Its Active Constituent on Aβ(25-35)-Induced Neuritic Atrophy

Dementia is a clinical syndrome characterized by multiple cognitive deficits and causes progressive neurodegeneration leading eventually to death. The incidence of dementia is increasing worldwide with the increase in ageing population. However, no effective treatment is available yet. It has been hypothesized that drugs activating neurite outgrowth might induce neuronal reconstruction and help in the recovery of brain function. Working on this hypothesis, we recently observed that the chloroform extract of the Rosa damascena significantly induced the neurite outgrowth activity and inhibited the Aβ(25–35)-induced atrophy and cell death. Further workup led the isolation of a very long polyunsaturated fatty acid having molecular formula C₃₇H₆₄O₂ as an active constituent. The structure of this compound was established by extensive analysis of fragmentations observed in EI-MS mode. The isolated compound protected Aβ(25–35)-induced atrophy and displayed strong neurite outgrowth activity. The length of dendrite in the cells treated with this compound were comparable to those of nerve growth factor (NGF) treated cells.

Active components from Siberian ginseng (Eleutherococcus senticosus) for protection of amyloid β(25-35)-induced neuritic atrophy in cultured rat cortical neurons

Not only neuronal death but also neuritic atrophy and synaptic loss underlie the pathogenesis of Alzheimer's disease as direct causes of the memory deficit. Extracts of Siberian ginseng (the rhizome of Eleutherococcus senticosus) were shown to have protective effects on the regeneration of neurites and the reconstruction of synapses in rat cultured cortical neurons damaged by amyloid β (Aβ)(25-35), and eleutheroside B was one of the active constituents. In this study, a comprehensive evaluation of constituents was conducted to explore active components from Siberian ginseng which can protect against neuritic atrophy induced by Aβ(25-35) in cultured rat cortical neurons. The ethyl acetate, n-butanol and water fractions from the methanol extract of Siberian ginseng showed protective effects against Aβ-induced neuritic atrophy. Twelve compounds were isolated from the active fractions and identified. Among them, eleutheroside B, eleutheroside E and isofraxidin showed obvious protective effects against Aβ(25-35)-induced atrophies of axons and dendrites at 1 and 10 μM.

Icariin improves memory impairment in Alzheimer's disease model mice (5xFAD) and attenuates amyloid β-induced neurite atrophy

Essential therapeutic drugs for Alzheimer's disease (AD) have not been developed. Since the neuritic atrophy leading to synaptic losses is one of the critical causes of memory impairment in AD, the effects of several constituents in tonic herbal medicines on neuritic atrophy and memory deficits have been studied. The present study investigated the effects of icariin, a main constituent in Epimedii Herba, a well known tonic crude drug, in an in vitro AD model and transgenic mouse AD model (5xFAD). Amyloid β(1-42)-induced atrophies of axons and dendrites were restored by post-treatment with icariin in rat cortical neurons. Administration of icariin for 8 days (p.o.) improved spatial memory impairment in 5xFAD mice. These novel findings suggest that icariin may improve memory dysfunction in AD and have a potential to extend neurites even when amyloid β-induced neurite atrophy has already occurred.

Sominone enhances neurite outgrowth and spatial memory mediated by the neurotrophic factor receptor, RET

BACKGROUND AND PURPOSE

Orally administered withanoside IV (a compound isolated from the roots of Withania somnifera) improved memory deficits in mice with a model of Alzheimer's disease induced by the amyloid peptide Abeta(25-35). Sominone, an aglycone of withanoside IV, was identified as an active metabolite after oral administration of withanoside IV. We aimed to identify receptors or associated molecules of sominone, and to investigate the effects of sominone on memory in normal mice.

EXPERIMENTAL APPROACH

Phosphorylation levels of 71 molecules were compared between control and sominone-stimulated cortical cultured cells to search for target molecules of sominone. Object location memory and neurite density in the brain were evaluated in sominone-injected mice.

KEY RESULTS

Phosphorylation of RET (a receptor for the glial cell line-derived neurotrophic factor, GDNF) was increased in neurons by sominone, without affecting the synthesis and secretion of GDNF. Knockdown of RET prevented sominone-induced outgrowths of axons and dendrites. After a single i.p. injection of sominone into normal mice, they could better memorize scenery information than control mice. Sixty minutes after sominone injection, RET phosphorylation was increased, particularly in the hippocampus of mice. After the memory tests, the densities of axons and dendrites were increased in the hippocampus by sominone administration.

CONCLUSIONS AND IMPLICATIONS

Sominone could reinforce the morphological plasticity of neurons by activation of the RET pathway and thus enhance memory. Sominone, a compound with low molecular weight, may be a GDNF-independent stimulator of the RET pathway and/or a novel modulator of RET signalling.

Hyperactivity, memory deficit and anxiety-related behaviors in mice lacking the p85alpha subunit of phosphoinositide-3 kinase

We previously reported that knockout mice lacking the p85alpha regulatory subunit of phosphoinositide-3 kinase (PI3K) (p85alpha(-/-) mice) significantly showed spatial learning-deficits, restlessness and motivation-deficit in water maze tests. It was also shown in the report that decline of PI3K activity in several brain areas related to losses of synapses and myelinated axons. However, any other behavioral patterns have not been elucidated, the aim of the present study was to observe behavioral natures of in p85alpha(-/-) mice using several behavioral tests. In order to examine behaviors, a novel object recognition test, an open field test, an object exploring test, a hole-board test and an elevated plus maze test were carried out in p85alpha(-/-) mice. The p85alpha(-/-) mice significantly showed a deficit in object recognition memory, less exploring novel objects, and anxiety. Hyperactivity was observed in p85alpha(-/-) mice in male-specific manner. The present results suggest that deficiencies in PI3K activity result in hyperactivity, memory deficit and an increase in anxiety. Therefore, these behavioral phenotypes can be analyzed in a relationship with losses of synapses and myelinated axons in the brain, which resulted from deficiencies in PI3K activity.

[Overcoming several neurodegenerative diseases by traditional medicines: the development of therapeutic medicines and unraveling pathophysiological mechanisms]

Ashwagandha (root of Withania somnifera) has been used for many purposes, it is mainly considered a tonic in traditional Ayurvedic medicine. This review focuses on the effects of compounds isolated from Ashwagandha on dementia models and on the spinal cord injury model. Our study demonstrated that the active constituents, withanolide A, withanoside IV, and withanoside VI, restored presynapses and postsynapses, in addition to both axons and dendrites in cortical neurons after Abeta(25-35)-induced injury. In vivo, oral withanolide A, withanoside IV, and withanoside VI (10 micromol/kg/day for 12 days) improved Abeta(25-35)-induced memory impairment, neurite atrophy, and synaptic loss in the cerebral cortex and hippocampus in mice. Since spinal cord injury (SCI) is also difficult to treat, and therefore practical and curable strategies for SCI are desired. Oral treatment with withanoside IV improved locomotor functions in mice with SCI. In mice treated with withanoside IV (10 micromol/kg/day for 21 days), the axonal density and peripheral nervous system myelin level increased. The loss of CNS myelin and increase in reactive gliosis were not affected by withanoside IV. Additionally, sominone, an aglycone of withanoside IV, was identified as the main metabolite after oral administration of withanoside IV in mice. Withanolide A, withanoside IV, and withanoside VI are therefore important candidates for the therapeutic treatment of neurodegenerative diseases. In particular, withanoside IV was shown to control neurons as well as glial cells for reconstruction neuronal networks. To clarify key events in overcoming neurodegeneration, we are now studying the molecular targets and signal cascades of sominone.

Kihi-to, a herbal traditional medicine, improves Abeta(25-35)-induced memory impairment and losses of neurites and synapses

BACKGROUND

We previously hypothesized that achievement of recovery of brain function after the injury requires the reconstruction of neuronal networks, including neurite regeneration and synapse reformation. Kihi-to is composed of twelve crude drugs, some of which have already been shown to possess neurite extension properties in our previous studies. The effect of Kihi-to on memory deficit has not been examined. Thus, the goal of the present study is to determine the in vivo and in vitro effects of Kihi-to on memory, neurite growth and synapse reconstruction.

METHODS

Effects of Kihi-to, a traditional Japanese-Chinese traditional medicine, on memory deficits and losses of neurites and synapses were examined using Alzheimer's disease model mice. Improvements of Abeta(25-35)-induced neuritic atrophy by Kihi-to and the mechanism were investigated in cultured cortical neurons.

RESULTS

Administration of Kihi-to for consecutive 3 days resulted in marked improvements of Abeta(25-35)-induced impairments in memory acquisition, memory retention, and object recognition memory in mice. Immunohistochemical comparisons suggested that Kihi-to attenuated neuritic, synaptic and myelin losses in the cerebral cortex, hippocampus and striatum. Kihi-to also attenuated the calpain increase in the cerebral cortex and hippocampus. When Kihi-to was added to cells 4 days after Abeta(25-35) treatment, axonal and dendritic outgrowths in cultured cortical neurons were restored as demonstrated by extended lengths of phosphorylated neurofilament-H (P-NF-H) and microtubule-associated protein (MAP)2-positive neurites. Abeta(25-35)-induced cell death in cortical culture was also markedly inhibited by Kihi-to. Since NF-H, MAP2 and myelin basic protein (MBP) are substrates of calpain, and calpain is known to be involved in Abeta-induced axonal atrophy, expression levels of calpain and calpastatin were measured. Treatment with Kihi-to inhibited the Abeta(25-35)-evoked increase in the calpain level and decrease in the calpastatin level. In addition, Kihi-to inhibited Abeta(25-35)-induced calcium entry.

CONCLUSION

In conclusion Kihi-to clearly improved the memory impairment and losses of neurites and synapses.

Learning deficits and agenesis of synapses and myelinated axons in phosphoinositide-3 kinase-deficient mice

Although previous studies have reported a role for phosphoinositide-3 kinase (PI3K) in axonal definition and growth in vitro, it is not clear whether PI3K regulates axonal formation and synaptogenesis in vivo. The goal of the present study was to clarify the role of PI3K in behavioral functions and some underlying neuroanatomical structures. Immunohistochemistry, an electron-microscopic analysis and behavioral tests were carried out. Knockout mice lacking the p85alpha regulatory subunit of PI3K (p85alpha-/- mice) significantly showed learning deficits, restlessness and motivation deficit. Expression of phosphorylated Akt, which indirectly shows the activity of PI3K, was high in myelinated axons, especially in axonal bundles in the striatum of wild-type mice, but was significantly low in the striatum, cerebral cortex and the hippocampal CA3 of p85alpha-/- mice. The axonal marker protein level decreased mainly in the striatum and cerebral cortex of p85alpha-/- mice. In these two regions, myelinated axons are rich in the wild-type mice. However, the density of myelinated axons and myelin thickness were significantly low in the striatum and cerebral cortex of p85alpha-/- mice. Synaptic protein level was clearly decreased in the striatum, cerebral cortex, and hippocampus of p85alpha-/- mice when compared with wild mice. The present results suggest that PI3K plays a role in the generation and/or maintenance of synapses and myelinated axons in the brain and that deficiencies in PI3K activity result in abnormalities in several neuronal functions, including learning, restlessness and motivation.

Withanoside IV improves hindlimb function by facilitating axonal growth and increase in peripheral nervous system myelin level after spinal cord injury

Although methylprednisolone is the clinically standard medication and almost the only therapy for spinal cord injury (SCI), its effect on functional recovery remains questionable. Transplantation strategies using sources such as neural stem cells and embryonic spinal cord still have some hurdles to overcome before practical applications become available. We therefore aimed to develop a practical medication for SCI. Per oral treatment with withanoside IV, which was previously shown to regenerate neuronal networks in the brain, improved locomotor functions in mice with SCI. In the spinal cord after SCI, axons were crushed in the white matter and gray matter, and central nervous system (CNS) myelin level decreased. In mice treated with withanoside IV (10micromol/kg body weight/day, for 21 days), axonal density and peripheral nervous system (PNS) myelin level increased. The loss of CNS myelin and increase in reactive gliosis were not affected by withanoside IV. These results suggest that oral administration of withanoside IV may ameliorate locomotor functions by facilitating both axonal regrowth and increase in PNS myelin level.

GAMMA.-Aminobutyric Acid Specifically Inhibits Progression of Tubular Fibrosis and Atrophy in Nephrectomized Rats

Gamma-aminobutyric acid (GABA) was administered orally to rats for 60 d after excision of five-sixths of their kidney volume. A decrease in renal function parameters was observed in these nephrectomized rats. However, the administration of GABA ameliorated renal dysfunction, and a longer administration period of GABA increased its protective effect. In addition, tubular fibrosis was markedly increased at 10 and 60 d in nephrectomized control rats, while GABA administration for 10 d reduced tubular fibrosis to the normal level. Tubular atrophy was markedly induced by nephrectomy, and was significantly reduced by the administration of GABA at 60 d. Furthermore, the nephrectomized control rats exhibited an increased expression level of transforming growth factor-beta1, where GABA significantly decreased it after administration for 10 d. The expression of fibronectin in the tubuli of rats administrated GABA for 60 d was completely and dose-dependently reduced as compared with nephrectomized control rats. However, the improvement effects in glomeruli were less. We also found that GABAA and GABAB receptors were specifically localized in tubuli. Specific agonists for GABAA and GABAB receptors improved renal function. These results suggest that GABA may have a beneficial effect on renal function in nephrectomized rats by inhibiting fibrosis and atrophy primarily in tubuli, and that it ameliorates losses of renal function in renal failure.