PET imaging studies show enhanced expression of mGluR5 and inflammatory response during progressive degeneration in ALS mouse model expressing SOD1-G93A gene.

Anna-Liisa Brownell,Kimmo Jokivarsi,Kun-Eek Kil,Darshini Kuruppu,Pekka Poutiainen,Michelle Maxwell,Aijun Zhu

doi:10.1186/s12974-015-0439-9

Abstract

BackgroundAmyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative motor neuron disorder. Genetic studies have linked mutation of the gene SOD1 to ALS pathology as well as several other pathological processes including modulation of glutamatergic function and inflammatory processes. Since therapeutic approaches for ALS are focused on glutamatergic function, we investigated modulation of glutamate transport based on its receptor function as well as excitotoxicity-induced inflammatory response.MethodsIn vivo positron emission tomography (PET) imaging studies of metabotropic glutamate receptor subtype 5 (mGluR5) using [18F]FPEB ([18F]3-fluoro-5-(2-pyridylethynyl)benzonitrile) and inflammatory response using [11C]PBR28 (peripheral benzodiazepine receptor ligand 28) were done in an early and a late phase of neurodegeneration in four ALS mice expressing SOD1-G93A gene and four control base mice (C57/BL6). Accumulation of [18F]FPEB and [11C]PBR28 were quantitated in several brain areas and spinal cord to determine degeneration-induced modulation. The studies were completed with immunohistochemical analyses of mGluR5 and inflammatory response.ResultsThese studies showed enhanced binding potential of [18F]FPEB in several brain areas including striatum, hippocampus, and frontal cortex. In the whole brain, the binding potential increased 49 ± 9 % from base mice to ALS-type mice and further enhanced 23 ± 4 % during disease progression. Also, in the spinal cord 6–22 %, enhanced accumulation of [18F]FPEB was observed during progression of the disease. The accumulation of [11C]PBR28 increased by 110 ± 33 % in the whole brain during progression of the disease indicating significant inflammatory process. [11C]PBR28 accumulation enhanced 89–264 % in the spinal cord and 204 % in the lungs. The end point immunohistochemical analyses verified the enhanced mGluR5 expression and inflammation.ConclusionsThese results confirm the role of glutamate and inflammation in ALS-type pathology. These data also support the hypothesis that excessive glutamate may contribute to inflammation in the chronic neurodegenerative processes in ALS.

Highlights

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative motor neuron disorder
The pathological processes linked to ALS are formation of intraneuronal aggregates of neurofilament [1]; microglia mediated neurotoxicity as a result of enhanced inflammatory response [2,3,4,5]; glutamatergic neurotoxicity as a result of deficit in glutamate transporter or receptor function [6,7,8,9,10,11]; and mitochondrial dysfunction as a result of failure in oxidative metabolism [12, 13] and superoxide dismutase-1 (SOD1) mediated neurotoxicity, which is associated to gene mutation and found in familiar form of ALS [14, 15]
With in vivo positron emission tomography (PET) imaging studies, we have shown that SOD1-G93A gene will significantly enhance metabotropic glutamate receptor subtype 5 (mGluR5) expression in the brain and spinal cord in ALS mouse model

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative motor neuron disorder. Since therapeutic approaches for ALS are focused on glutamatergic function, we investigated modulation of glutamate transport based on its receptor function as well as excitotoxicity-induced inflammatory response. The pathological processes linked to ALS are formation of intraneuronal aggregates of neurofilament [1]; microglia mediated neurotoxicity as a result of enhanced inflammatory response [2,3,4,5]; glutamatergic neurotoxicity as a result of deficit in glutamate transporter or receptor function [6,7,8,9,10,11]; and mitochondrial dysfunction as a result of failure in oxidative metabolism [12, 13] and superoxide dismutase-1 (SOD1) mediated neurotoxicity, which is associated to gene mutation and found in familiar form of ALS [14, 15]. It is noticeable that neurotransmitter glutamate does not cross blood-brain barrier but its function can be investigated based on its receptors

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