Glutamate and Amyloid β-Protein Rapidly Inhibit Fast Axonal Transport in Cultured Rat Hippocampal Neurons by Different Mechanisms

Abstract

Impairment of axonal transport leads to neurodegeneration and synapse loss. Glutamate and amyloid beta-protein (Abeta) have critical roles in the pathogenesis of Alzheimer's disease (AD). Here we show that both agents rapidly inhibit fast axonal transport in cultured rat hippocampal neurons. The effect of glutamate (100 microm), but not of Abeta25-35 (20 microm), was reversible, was mimicked by NMDA or AMPA, and was blocked by NMDA and AMPA antagonists and by removal of extracellular Ca2+. The effect of Abeta25-35 was progressive and irreversible, was prevented by the actin-depolymerizing agent latrunculin B, and was mimicked by the actin-polymerizing agent jasplakinolide. Abeta25-35 induced intracellular actin aggregation, which was prevented by latrunculin B. Abeta31-35 but not Abeta15-20 exerted effects similar to those of Abeta25-35. Full-length Abeta1-42 incubated for 7 d, which specifically contained 30-100 kDa molecular weight assemblies, also caused an inhibition of axonal transport associated with intracellular actin aggregation, whereas freshly dissolved Abeta1-40, incubated Abeta1-40, and fresh Abeta1-42 had no effect. These results suggest that glutamate inhibits axonal transport via activation of NMDA and AMPA receptors and Ca2+ influx, whereas Abeta exerts its inhibitory effect via actin polymerization and aggregation. The ability of Abeta to inhibit axonal transport seems to require active amino acid residues, which is probably present in the 31-35 sequence. Full-length Abeta may be effective when it represents a structure in which these active residues can access the cell membrane. Our results may provide insight into the early pathogenetic mechanisms of AD.

β-Secretase-Cleaved Amyloid Precursor Protein Accumulates at Actin Inclusions Induced in Neurons by Stress or Amyloid β: A Feedforward Mechanism for Alzheimer's Disease

“…A␤ 1-42 concentrations as low as 10 nM induce ADF/cofilinactin rod formation in one-half of the hippocampal neurons that respond to higher concentrations (half-maximum percentage response), the lowest concentration that has been shown to have a physiological effect on neurons (Lambert et al, 1998;Dahlgren et al, 2002;Walsh et al, 2002a;Hiruma et al, 2003;Kim et al, 2003;Takahashi et al, 2004;Cleary et al, 2005). The amount of soluble A␤ extracted from the frontal cortex of control human brains is 0.09 Ϯ 0.05 g/g and from AD brain is 0.29 Ϯ 0.25 g/g (McLean et al, 1999).…”

“…Mutations leading to increased production of the more amyloidogenic A␤ species are linked to early-onset familial AD (FAD) (ChartierHarlin et al, 1991a,b;Goate et al, 1991;Murrell et al, 1991;Price et al, 1995). Treatment of cultured neurons with A␤ 1-42 inhibits fast axonal transport (Hiruma et al, 2003). Furthermore, blockage of axonal transport is the earliest measured disturbance in the brains of transgenic mice expressing mutant human APP (Stokin et al, 2005).…”

Neuritic Beading Induced by Activated Microglia Is an Early Feature of Neuronal Dysfunction Toward Neuronal Death by Inhibition of Mitochondrial Respiration and Axonal Transport

“…The number of particles (diameter Ն50 nm) moving antegrade and retrograde in axons were counted for each hour (0ϳ6 h) as described previously (46). Three independent fields were assessed blindly.…”

Molecular and Electrical Abnormalities in the Mouse Model of Amyotrophic Lateral Sclerosis

“…In ALS, both slow and fast axon transport appear to be altered (Zhang et al, 1997, Warita et al, 1999, Williamson and Cleveland, 1999, Kieran et al, 2005, De Vos et al, 2007, Bilsland et al, 2010. Excessive glutamate could cause these deficiencies: high levels of glutamate activate a family of mitogen-activated protein kinases that phosphorylate neurofilaments, thereby decreasing transport (Ackerley et al, 2000, Hiruma et al, 2003, Stevenson et al, 2009). This process can be induced by NMDA or AMPA, blocked by removal of extracellular Ca 2+ , or reduced by application of riluzole (Hiruma et al, 2003, Stevenson et al, 2009).…”

“…Excessive glutamate could cause these deficiencies: high levels of glutamate activate a family of mitogen-activated protein kinases that phosphorylate neurofilaments, thereby decreasing transport (Ackerley et al, 2000, Hiruma et al, 2003, Stevenson et al, 2009). This process can be induced by NMDA or AMPA, blocked by removal of extracellular Ca 2+ , or reduced by application of riluzole (Hiruma et al, 2003, Stevenson et al, 2009). The protein kinases JNKs, cdk/p35 and p38, which phosphorylate heavy and light chains of kinesin and medium and heavy neurofilament sidearms, may link glutamate neurotransmission and axon transport deficits (Kawasaki et al, 1997, Schwarzschild et al, 1997, Ackerley et al, 2000, Brownlees et al, 2000, Lee et al, 2000.…”