Affiliations: [a] CNC – Center for Neuroscience and Cell Biology, University of Coimbra, Portugal
| [b] Department of Life Sciences, Faculty of Sciences and Technology, University of Coimbra, Portugal
| [c] Faculty of Medicine, University of Coimbra, Portugal
Correspondence:
[*]
Correspondence to: Rodrigo A. Cunha, CNC - Center for Neuroscience and Cell Biology, University of Coimbra, Polo I, Rua Larga, Edifício da Faculdade de Medicina, Piso 1, 3004-504 Coimbra, Portugal. Tel.: +351 304502904; E-mail: cunharod@gmail.com.
Abstract: Mitochondrial dysfunction is proposed to trigger memory deficits and synaptic damage at the onset of Alzheimer’s disease (AD). However, it is unknown how mitochondria dysfunction might trigger synaptotoxicity and if a differential susceptibility of mitochondria located in synapses underlies the greater glutamatergic than GABAergic synaptotoxicity in early AD. Hippocampal synaptosomes (purified synapses) of a rat model of early AD, typified by selective memory deficits two weeks after intracerebroventricular injection of amyloid-β peptides (Aβ1–42, 2 nmol), simultaneously displayed three mitochondria-associated deleterious alterations: 1) hampered metabolism (decreased MTT reduction); 2) increased oxygen radical production (increased hydrogen peroxide production); 3) increased caspase-3 activity. The direct exposure of hippocampal synaptosomes to Aβ1–42 (500 nM) similarly decreased mitochondrial membrane potential (TMRM+ fluorescence) and increased mitochondria-derived oxygen radicals (MitoTraker®red-CM-H2Xros fluorescence) in individual glutamatergic (vesicular glutamate transporter-immunopositive) and GABAergic (vesicular GABA transporter-immunopositive) synaptosomes. However, significantly more glutamatergic than GABAergic synaptosomes were endowed with mitochondria (Tom20-immunopositive). These results indicate that dysfunctional mitochondria located in synapses can trigger synaptotoxicity through multifaceted mechanisms and that it is not the susceptibility of mitochondria to Aβ but more likely a different impact of dysfunctional mitochondria that underlies the greater sensitivity to synaptotoxicity of glutamatergic than GABA synapses in early AD.
