Up-regulation of soluble amyloid precursor protein fragment secretion in the rat retina in vivo by metabotropic glutamate receptor stimulation

Therapeutic promise and principles: metabotropic glutamate receptors

For a number of disease entities, oxidative stress becomes a significant factor in the etiology and progression of cell dysfunction and injury. Therapeutic strategies that can identify novel signal transduction pathways to ameliorate the toxic effects of oxidative stress may lead to new avenues of treatment for a spectrum of disorders that include diabetes, Alzheimer's disease, Parkinson's disease and immune system dysfunction. In this respect, metabotropic glutamate receptors (mGluRs) may offer exciting prospects for several disorders since these receptors can limit or prevent apoptotic cell injury as well as impact upon cellular development and function. Yet the role of mGluRs is complex in nature and may require specific mGluR modulation for a particular disease entity to maximize clinical efficacy and limit potential disability. Here we discuss the potential clinical translation of mGluRs and highlight the role of novel signal transduction pathways in the metabotropic glutamate system that may be vital for the clinical utility of mGluRs.

Differential effects of interleukin-1beta and S100B on amyloid precursor protein in rat retinal neurons

Purpose:

Interleukin-1β (IL-1β) and S100B calcium binding protein B (S100B) have been implicated in the pathogenesis of Alzheimer’s disease. Both are present in and around senile plaques and have been shown to increase levels of amyloid precursor protein (APP) mRNA in vitro. However, it is not known how either of these substances affects APP in vivo.

Methods:

We have studied the effects of IL-1β and S100B on the expression and processing of APP using a retinal-vitreal model. We have also investigated the effect of amyloid beta peptide (Aβ) on APP in the same system and the regulation of S100B production by Aβ and IL-1β from retinal glial cells.

Results:

Retinal ganglion cells constitutively express APP. However, after intravitreal injection of IL-1β or Aβ there was a marked reduction in APP levels as detected by Western blotting and IL-1β produced a decrease in APP immunoreactivity (IR). Nissl staining showed that the integrity of the injected retinas was unchanged after injection. Two days after S100B injection, there was a small reduction in APP-IR but this was accompanied by the appearance of some intensely stained large ganglion cells and there was some up-regulation in APP holoprotein levels on Western blot. Seven days post-S100B injection, these large, highly stained cells had increased in number throughout the retina. Injection of Aβ and IL-1β also caused an increase in S100B production within the retinal Müller glial cells.

Conclusion:

These results support the hypothesis that S100B (a glial-derived neurotrophic factor) and IL-1β (a pro-inflammatory cytokine) can modulate the expression and processing of APP in vivo and so may contribute to the progression of Alzheimer’s disease.

Time for a change in the research paradigm for Alzheimer's disease: the value of a chaotic matrix modeling approach

The amyloid cascade hypothesis, based on the genetic data from early onset, familial forms of the disease, has been the dominant model for many years and involves over production and deposition of the beta amyloid protein as causal in the disease process. However, it does not apply very well to the more common, later onset, sporadic form of the disease, where a wider range of factors appear to be involved in disease progression. Over recent years, data illustrating reciprocal interactions between the amyloid precursor protein (APP) and its various metabolites with many factors involved in normal synaptic plasticity have emerged. These feedback relationships have the potential to affect the complex kinase cascades involved in every aspect of neuronal function. Further, data regarding the multiple roles of the presenilins have the potential to allow the over expression and deposition of the amyloid beta protein to be both a cause and consequence of disease progression, with relevance in both sporadic and familial of Alzheimer's disease (AD). Disease progression might be better explained by a chaotic matrix of factors and raises the question again whether AD should be approached as a single entity or as a syndrome, with important consequences for disease identification and treatment.

Driving cellular plasticity and survival through the signal transduction pathways of metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) share a common molecular morphology with other G protein-linked receptors, but there expression throughout the mammalian nervous system places these receptors as essential mediators not only for the initial development of an organism, but also for the vital determination of a cell's fate during many disorders in the nervous system that include amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, Multiple Sclerosis, epilepsy, trauma, and stroke. Given the ubiquitous distribution of these receptors, the mGluR system impacts upon neuronal, vascular, and glial cell function and is activated by a wide variety of stimuli that includes neurotransmitters, peptides, hormones, growth factors, ions, lipids, and light. Employing signal transduction pathways that can modulate both excitatory and inhibitory responses, the mGluR system drives a spectrum of cellular pathways that involve protein kinases, endonucleases, cellular acidity, energy metabolism, mitochondrial membrane potential, caspases, and specific mitogen-activated protein kinases. Ultimately these pathways can converge to regulate genomic DNA degradation, membrane phosphatidylserine (PS) residue exposure, and inflammatory microglial activation. As we continue to push the envelope for our understanding of this complex and critical family of metabotropic receptors, we should be able to reap enormous benefits for both clinical disease as well as our understanding of basic biology in the nervous system.