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Aging represents a major risk factor for numerous illnesses that are of increasing importance to society, including two of the most prevalent: diabetes and Alzheimer's disease. Studies have shown that diabetes is a risk factor for spontaneous Alzheimer's disease. While these studies suggest that diabetes can contribute to Alzheimer's disease, the implications of AD on diabetes are practically unexplored. The major mediator of the pathophysiological effects, the Aβ42 peptide, has been shown to enter neurons and lead to an alteration of the intracellular distribution of the molecular motor myosin Vb. Myosin Vb functions in memory and learning by participating in the strengthening of the long-term potentiation (LTP) of synaptic transmissions. It has also been implicated in the translocation of the glucose transporter, GLUT4, to the plasma membrane in response to insulin, a process that is defective in diabetes. Here, the effect on GLUT4 upon entry of the Aβ42 peptide into cultured chick retinal neurons was explored. The results suggest an alteration in distribution and a reduced level at the cell surface, as well as an increased colocalization with myosin Vb, which can partially explain the changes in glucose metabolism associated with AD. It is also shown that the presence of the Aβ40 peptide inhibits the internalization of the Aβ42 peptide in cultured cells. Together, the results provide additional targets for the development of therapeutics against the progression and effects of Alzheimer's disease., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The most common neurodegenerative disorder afflicting the aging human population is Alzheimer's disease (AD). A major hallmark of AD is dementia from a loss of neuronal function, attributed to the presence and accumulation of β-amyloid (Aβ) peptide into senile plaques. Preceding senile plaque formation, abnormalities in axons can be observed as changes in morphologies and intracellular trafficking. Recently, it has been recognized that Aβ also accumulates within neurons and this intraneuronal Aβ accumulation has been reported to be critical in the disruption of synapses and cognitive function. Here, we report on the internalization of a fluorescently labeled Aβ peptide into cultured chick retinal neurons. The pattern of Aβ distribution during the time course of incubation is reminiscent of the endocytic pathway. Furthermore, the distribution of the internalized Aβ peptide converges with that of myosin Vb and both relocalize from the axon to cell body. These observations are consistent with the hypothesis that AD proceeds as a result of an imbalance between Aβ production and Aβ clearance, suggesting a role for myosin Vb in this process., (Copyright © 2012 Wiley Periodicals, Inc.)

Myosin-Va (Myo5a) is a motor protein associated with synaptic vesicles (SVs) but the mechanism by which it interacts has not yet been identified. A potential class of binding partners are Rab GTPases and Rab3A is known to associate with SVs and is involved in SV trafficking. We performed experiments to determine whether Rab3A interacts with Myo5a and whether it is required for transport of neuronal vesicles. In vitro motility assays performed with axoplasm from the squid giant axon showed a requirement for a Rab GTPase in Myo5a-dependent vesicle transport. Furthermore, mouse recombinant Myo5a tail revealed that it associated with Rab3A in rat brain synaptosomal preparations in vitro and the association was confirmed by immunofluorescence imaging of primary neurons isolated from the frontal cortex of mouse brains. Synaptosomal Rab3A was retained on recombinant GST-tagged Myo5a tail affinity columns in a GTP-dependent manner. Finally, the direct interaction of Myo5a and Rab3A was determined by sedimentation velocity analytical ultracentrifugation using recombinant mouse Myo5a tail and human Rab3A. When both proteins were incubated in the presence of 1 mm GTPγS, Myo5a tail and Rab3A formed a complex and a direct interaction was observed. Further analysis revealed that GTP-bound Rab3A interacts with both the monomeric and dimeric species of the Myo5a tail. However, the interaction between Myo5a tail and nucleotide-free Rab3A did not occur. Thus, our results show that Myo5a and Rab3A are direct binding partners and interact on SVs and that the Myo5a/Rab3A complex is involved in transport of neuronal vesicles.