Leader: Marcello Melone (INRCA); Other collaborator(s):
To explore the multifaced mechanisms of age-related synaptic impairment induced by the interaction between the glutamate transporters and Abeta, we will apply high-resolution microscopy techniques to geriatric animal models exhibiting high levels of Abeta for deciphering: i) the mislocalization of glutamate transporters at the synaptic domains (astrocytic vs neuronal) as a consequence of the interaction between glutamate transporters and Abeta ; ii) the fractions of excitatory and inhibitory synapses expressing glutamate transporters; iii) the geometries of astrocytic processes associated with both excitatory and inhibitory synapses; iv) the presence of ultrastructural signs of neurodegeneration induced by the age-related synaptopathy.
Brief description of the activities and of the intermediate results: Related to experimental steps i, ii, and iii, we have obtained microscopical data on the expression of the main synaptic glutamate transporter (sGLT-1) at excitatory cortical synapses of animals at symptomatic stages (old, 12-15 months). Despite GLT-1 levels unchanged, we unveiled a loss of GLT-1+ perisynaptic astrocytic processes contacting excitatory synapses (sGLT-1+ AsP). More importantly, the distances of sGLT-1+ AsP increased, supporting a reduction in the perisynaptic coverage of glial cells. This evidence pointed to astrocytic defects, which can lead to abnormal glutamate spillover from active synapses. In the following months, we plan to gather data on sGLT-1+ AsP of inhibitory synapses, which could cause an altered glutamate spill-in at GABAergic synapses, envisaging a modification of E/I synaptic balance and, thus, diffuse synaptic impairment.
Main policy, industrial and scientific implications: The preliminary results indicated that the spatial relationship between astrocytes expressing glutamate transporters and neuronal synaptic domains is altered in age-synaptic impairment, thus highlighting astrocytes expressing glutamate transporters as potential novel targets of therapeutic interventions.
To verify whether sGLT-1+ AsP of inhibitory synapses might also contribute to modify E/I synaptic balance by altering glutamate spill-in at GABAergic synapses, we started a new analysis on sGLT-1+AsP contacting symmetric synapses. At the initial steps of analysis, we unveiled that GLT-1 is widely expressed at astrocytic AsP contacting symmetric synapses with a comparable rate of positivity among the different subsets of GABAergic synapses (i.e., proximal, axo-somatic, axo-dendritic proximal and axo-dendritic distal) and that GLT-1+ AsP of symmetric synapses targeting distal post-synaptic dendritic domains (Axo-den) exhibits shortened distances from the edges of symmetric synaptic specialization. These results prompted the verification of whether an alteration of E/I synaptic balance might be due to a diffuse alteration of the architecture of GLT-1-expressing processes.
The analysis of sGLT-1+ AsP is ongoing by studying, through high-resolution immunogold electron microscopy techniques, the membrane pool of the transporter in the different subsets of GABAergic synapses. Additionally, we are performing comparisons and analysis of synapses from adult healthy and aged-impaired synapses.
Coming soon