Amyloid beta protein enhances the survival of hippocampal neurons in vitro

What is the significance of the binding of proteoglycans to amyloid?

While proteoglycans seem to bind to amyloids, the consequence of this binding on amyloid formation or deposition is unknown. The hypothesized roles of this binding that were suggested by Drs. Snow and Wight are discussed and other potential roles are addressed.

How well do we understand neurotrophic factors and the control of CNS neuronal growth?

The review of Hefti et al. (7) presents current theories and concepts about the functions and activities of neurotrophic factors (NTF). The validity of several components and assumptions may be questionable. Should NTFs be divided into small diffusible survival-promoting factors and large, insoluble neurite-promoting factors? How are NTFs and neurotransmitters related? Do neurons need one or several NTFs? Can NTFs be multifunctional trophic factors? Are there endogenous inhibitory modulators of neuronal growth? Answers to these questions may have significant impact on the design of therapies using NTFs.

Molecular pathology of amyloidogenic proteins and the role of vascular amyloidosis in Alzheimer's disease

Progress in the study of Alzheimer's disease (AD) has been spurred by the recent application of molecular approaches in many laboratories. Attention has centered on the nature of the proteinaceous deposits that accumulate progressively both within and outside of cerebral neurons. Evidence reviewed herein suggests that intraneuronal paired helical filaments are distinct from extracellular amyloid filaments and contain altered forms of the microtubule-associated phosphoprotein, tau. Antibodies to tau detect an extensive neuritic dystrophy in AD cerebral cortex that includes aberrant somatodendritic sprouting, suggesting a role for local growth-promoting molecules in the pathogenesis of AD. Perhaps preceding these neuronal changes, deposits of the beta-amyloid protein (beta AP) occur in a diffuse, nonfibrillar form in AD and Down's syndrome brains in the absence of surrounding neuritic or glial response. Such deposits may represent the earliest structural abnormality yet detected in AD brain. Since the gene encoding the beta AP precursor appears to be distinct from a putative familial AD gene defect also localized to chromosome 21 in some families, changes in transcriptional and posttranslational processing of the precursor in aging and AD are being sought. The central and unresolved question of the origin of the beta AP molecules deposited progressively in brain is reviewed in detail. In concert with other human amyloidoses, growing evidence points to a blood-borne or vascular source for beta AP, although rigorous proof is not at hand. Advances in the molecular analysis of AD brain lesions point to new experimental strategies that should bear directly on unsolved diagnostic and therapeutic issues in the disease.

Secreted form of amyloid beta protein precursor is involved in the growth regulation of fibroblasts

Fibroblasts that harbor an antisense construct of amyloid beta protein precursor (ABPP) cDNA, A-1, produced less ABPP mRNA and ABPP and grew poorly. Normal growth was restored when either parent cell conditioned medium (CM) or purified ABPP was provided. The capacity of the CM to restore cell growth was abolished by passage through an anti-ABPP immunoaffinity column; the activity was in the bound fraction. A Mr 90,000 protein recognized by the anti-ABPP antibody was diminished in the CM of A-1. CM from ABPP cDNA-transfected cells expressing high levels of ABPP was more potent than that from non-transfected parent cells in restoring A-1 growth. These results indicate that ABPP is released from cells into the medium and has an autocrine function in growth regulation.

Neurotoxicity of a fragment of the amyloid precursor associated with Alzheimer's disease

Amyloid deposition in senile plaques and the cerebral vasculature is a marker of Alzheimer's disease. Whether amyloid itself contributes to the neurodegenerative process or is simply a by-product of that process is unknown. Pheochromocytoma (PC12) and fibroblast (NIH 3T3) cell lines were transfected with portions of the gene for the human amyloid precursor protein. Stable PC12 cell transfectants expressing a specific amyloid-containing fragment of the precursor protein gradually degenerated when induced to differentiate into neuronal cells with nerve growth factor. Conditioned medium from these cells was toxic to neurons in primary hippocampal cultures, and the toxic agent could be removed by immunoabsorption with an antibody directed against the amyloid polypeptide. Thus, a peptide derived from the amyloid precursor may be neurotoxic.