A Novel Therapeutic Approach to Treat Alzheimer's Disease by Neurotrophic Support During the Period of Synaptic Compensation

Abstract

Alzheimer's disease (AD), at present, is considered an incurable disease and a major dilemma with no drug to stop or slow down its progression. Drugs that are currently available in the market are able to only transiently improve the clinical symptoms. The repeated failures in developing an effective drug has led to the suggestion that the medical intervention was probably too late to be effective since the pathology starts many years before the appearance of the clinical symptoms. Probably, at the time of the appearance of clinical symptoms the brain has undergone major neuronal and synaptic loss. Because of the uncertainty on when to use a prevention therapy, especially targeting amyloid-β (Aβ) and tau pathologies, interventions that rely on the regenerative capacity of the brain such as the modulation of the inherent neurogenesis and neuronal plasticity represent a promising therapeutic strategy. Such an approach can act both at early as well as late stages of the disease and remove the barrier of the time of intervention. In this article, we review studies mainly from our laboratory that show the merit of early intervention during the synaptic and neuronal compensation period where the brain still has the capacity to self-repair by offering neurotrophic support in reversing cognitive impairment, neuronal and synaptic deficits, Aβ, and tau pathologies and decreasing mortality in a transgenic mouse model of AD.

Keywords: 3xTg-AD mice; Alzheimer’s disease; amyloid-β; ciliary neurotrophic factor; neurodegeneration; neuronal connectivity; neurotrophic factors; prevention; synaptic plasticity; tau; therapeutics.

Fig.1

A diagrammatic representation of AD neurofibrillary degeneration and beneficial therapeutic effect of neurotrophic compound P021 and immunization with antibodies to amino-terminal projection domain of tau. Dendrite and synaptic degeneration associated with formation of intraneuronal tau (in red) and Aβ (intraneuronal as black dots and extracellular as plaques) pathologies is a hallmark of AD. Increase in dendritogenesis and synaptogenesis (shown in green) can prevent loss of neuronal connectivity and thereby inhibit tau and Aβ pathologies, especially if the neurotrophic support such as P021is provided before any pathology. Clearance of tau pathology by passive immunization probably rescues neuronal connectivity deficit and consequently prevents Aβ pathology by inhibiting the amyloidogenic processing of AβPP. a.tau, anti tau.