6-methyl-2-(phenylethynyl)pyridine and Amyotrophic-Lateral-Sclerosis

Astrocytes emerge as key players in motor neuron degeneration in Amyotrophic Lateral Sclerosis (ALS). Whether astrocytes cause direct damage by releasing toxic factors or contribute indirectly through the loss of physiological functions is unclear. Here we identify in the hSOD1(G93A) transgenic mouse model of ALS a degenerative process of the astrocytes, restricted to those directly surrounding spinal motor neurons. This phenomenon manifests with an early onset and becomes significant concomitant with the loss of motor cells and the appearance of clinical symptoms. Contrary to wild-type astrocytes, mutant hSOD1-expressing astrocytes are highly vulnerable to glutamate and undergo cell death mediated by the metabotropic type-5 receptor (mGluR5). Blocking mGluR5 in vivo slows down astrocytic degeneration, delays the onset of the disease and slightly extends survival in hSOD1(G93A) transgenic mice. We propose that excitotoxicity in ALS affects both motor neurons and astrocytes, favouring their local interactive degeneration. This new mechanistic hypothesis has implications for therapeutic interventions.

Topics: Amyotrophic Lateral Sclerosis; Animals; Astrocytes; Caspase 3; Cell Survival; Cytoskeleton; Enzyme Activation; Glial Fibrillary Acidic Protein; Glutamates; Humans; Lumbar Vertebrae; Mice; Motor Neurons; Mutant Proteins; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Spheroids, Cellular; Superoxide Dismutase; Superoxide Dismutase-1

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by a selective loss of motor neurones accompanied by intense gliosis in lesioned areas of the brain and spinal cord. Glutamate-mediated excitotoxicity resulting from impaired astroglial uptake constitutes one of the current pathophysiological hypotheses explaining the progression of the disease. In this study, we examined the regulation of glutamate transporters by type 5 metabotropic glutamate receptor (mGluR5) in activated astrocytes derived from transgenic rats carrying an ALS-related mutated human superoxide dismutase 1 (hSOD1(G93A)) transgene. Cells from transgenic animals and wild-type littermates showed similar expression of glutamate-aspartate transporter and glutamate transporter 1 (GLT-1) after in vitro activation, whereas cells carrying the hSOD1 mutation showed a three-fold higher expression of functional mGluR5, as observed in the spinal cord of end-stage animals. In cells from wild-type animals, (S)-3,5-dihydroxyphenylglycine (DHPG) caused an immediate protein kinase C (PKC)-dependent up-regulation of aspartate uptake that reflected the activation of GLT-1. Although this effect was mimicked in both cultures by direct activation of PKC using phorbol myristate acetate, DHPG failed to up-regulate aspartate uptake in cells derived from the transgenic rats. The failure of activated mGluR5 to increase glutamate uptake in astrocytes derived from this animal model of ALS supports the theory of glutamate excitotoxicity in the pathogenesis of the disease.

Topics: Amyotrophic Lateral Sclerosis; Animals; Animals, Genetically Modified; Aspartic Acid; Astrocytes; Blotting, Northern; Calcium; Carbachol; Cholinergic Agonists; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Excitatory Amino Acid Transporter 2; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Glutamic Acid; Humans; Immunohistochemistry; Male; Methoxyhydroxyphenylglycol; Protein Kinase C; Pyridines; Rats; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sodium; Superoxide Dismutase; Tritium