Neuronal origin of cerebral amyloidogenic proteins: their role in Alzheimer's disease and unconventional virus diseases of the nervous system

Danggui-Shaoyao-San: New Hope for Alzheimer's Disease

Danggui-Shaoyao-San (DSS), also called Toki-shakuyaku-san (TJ-23) or Dangguijakyak-san (DJS), is a well-known herbal formula (Angelica sinensis (Oliv.) Diels., Ligusticum chuanxiong Hort., Paeonia lactiflora pall., Poria cocos (Schw.) Wolf, Alisma orientalis (Sam.) Juzep., Atractylodes macrocephala Koidz.), which has been widely used in oriental countries for the treatment of various gynecological diseases. Recent studies show that DSS has an effect on free radical-mediated neurological diseases and exhibits anti-inflammatory and antioxidant activities and reduces cell apoptosis in the hippocampus. In addition, DSS mediates the modulation of central monoamine neurotransmitter systems and ameliorates dysfunction of the central cholinergic nervous system and scopolamine-induced decrease in ACh levels. DSS improves the function of the dopaminergic, adrenergic, and serotonergic nervous systems. Interestingly, DSS can alleviate cognitive dysfunction of Alzheimer's disease (AD) patients, suggesting that it is a useful therapeutic agent for AD. This paper reviews the mechanism of DSS for the treatment of AD.

The role of the tripartite glutamatergic synapse in the pathophysiology of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in individuals over 65 years of age and is characterized by accumulation of beta-amyloid (Aβ) and tau. Both Aβ and tau alter synaptic plasticity, leading to synapse loss, neural network dysfunction, and eventually neuron loss. However, the exact mechanism by which these proteins cause neurodegeneration is still not clear. A growing body of evidence suggests perturbations in the glutamatergic tripartite synapse, comprised of a presynaptic terminal, a postsynaptic spine, and an astrocytic process, may underlie the pathogenic mechanisms of AD. Glutamate is the primary excitatory neurotransmitter in the brain and plays an important role in learning and memory, but alterations in glutamatergic signaling can lead to excitotoxicity. This review discusses the ways in which both beta-amyloid (Aβ) and tau act alone and in concert to perturb synaptic functioning of the tripartite synapse, including alterations in glutamate release, astrocytic uptake, and receptor signaling. Particular emphasis is given to the role of N-methyl-D-aspartate (NMDA) as a possible convergence point for Aβ and tau toxicity.

Chondroitin sulfate proteoglycans in the nervous system: inhibitors to repair

Chondroitin sulfate proteoglycans (CSPGs) are widely expressed in the normal central nervous system, serving as guidance cues during development and modulating synaptic connections in the adult. With injury or disease, an increase in CSPG expression is commonly observed close to lesioned areas. However, these CSPG deposits form a substantial barrier to regeneration and are largely responsible for the inability to repair damage in the brain and spinal cord. This review discusses the role of CSPGs as inhibitors, the role of inflammation in stimulating CSPG expression near site of injury, and therapeutic strategies for overcoming the inhibitory effects of CSPGs and creating an environment conducive to nerve regeneration.

Aβ oligomer-induced synapse degeneration in Alzheimer's disease

Aβ oligomers cause a collection of molecular events associated with memory loss in Alzheimer's disease, centering on disrupting the maintenance of synapse structure and function. In this brief review of the synaptotoxic effects of Aβ oligomers, we focus on the neuronal properties governing oligomer targeting and toxicity-especially with respect to binding sites and mechanisms of binding. We also discuss ways in which mechanistic insights from other diseases offer clues in the pursuit of the molecular basis of Alzheimer's disease.

Deposition of beta/A4 protein along neuronal plasma membranes in diffuse senile plaques

The origin of the extracellular beta-amyloid protein (beta/A4) found in senile plaques and the cellular mechanisms responsible for its deposition in cerebral tissues are still an unresolved issue in Alzheimer's disease. In this study we analyzed in detail the distribution of various epitopes of beta/A4 in relation to local cellular elements in diffuse plaques of the hippocampal region. We also correlated our findings with the presence and distribution of non-beta/A4 epitopes of the amyloid precursor protein (APP) and with synaptophysin immunoreactivity in the cortical neuropil. Discontinuous beta/A4-immunoreactive deposits were found along dendrites, and around the soma of neurons included in the plaques. Furthermore, increased synaptophysin reactivity with slightly dilated synaptophysin-immunolabeled presynaptic terminals were found in diffuse plaques. APP epitopes could not be found in diffuse plaques. However, some of the APP antibodies, mainly those to the C-terminal portion of APP, and antibodies to beta/A4 recognized clusters of flat vesicular profiles (0.6-1.4 micron in width and 2-3 microns in length) in the neuropil of cortical areas where plaques had developed. Our findings are compatible with a neuronal origin of beta/A4 in diffuse plaques and with a primary release of beta/A4 at synaptic sites along the immunostained neurites. They also suggest that diffuse plaques might be preceded by minute lesions of the neuropil where beta/A4 is not yet released from the precursor molecule.