Mapping changes in synaptic vesicle protein 2A (SV2A) in neurodegenerative diseases

Abstract

AbstractBackgroundSynaptic loss is an early feature of neurodegenerative diseases and the best correlate of clinical decline. Synaptophysin is a pre‐synaptic protein used as a marker of synaptic integrity. Although no biomarker is available to measure synaptic integrity in the clinical setting, various potential PET‐scan tracers are under development. Tracers to detect synaptic vesicle protein 2A (SV2A), an integral glycoprotein in the membrane of synaptic vesicles, are among the most promising among those in development. However, the topographical distribution of SV2A in the human brain and the degree of regional changes in different neurodegenerative conditions are unclear, making it challenging to establish the utility of SV2A tracers in clinical practice. To close this gap, we mapped the density of SV2A in five areas vulnerable to age‐related neuropathology in postmortem brain tissue of subjects with four different types of neurodegenerative disease and healthy controls. Furthermore, we compared SV2A maps to synaptophysin maps obtained from adjacent slides.MethodTable 1 details the subjects' features. The regions of interest include middle and inferior frontal gyri, inferior temporal gyrus, angular gyrus, and CA1 sector/entorhinal cortex. 8 µm thick FFPE adjacent slides underwent immunohistochemistry for SV2A (1:150, Atlas Antibodies, rabbit polyclonal) or synaptophysin (1:75, Atlas Antibodies, rabbit polyclonal). All slides were scanned using a calibrated Zeiss Axioscan and quantified using the Zen software. Density was measured in 40 cortical ROIs (20 white & 20 gray matter) per area/case, randomly distributed. Values were normalized for white matter intensity.ResultSVA2 loss was present in all disease conditions. The pattern of change was region and disease‐specific (Fig 1). Interestingly, the correlation between SV2A and synaptophysin density was poor to moderate (Fig 2).ConclusionReduced SV2A expression/level in all diseases indicates that SV2A is a potential marker to detect neurodegeneration. However, the lack of correlation between synaptophysin and SV2A level changes suggests that these markers signal different pathways. Additional research is needed to investigate the relationship between regional loss of SV2A and its potential significance as a marker for neurodegenerative disorders. We are performing Western blotting and autoradiography in the same samples to confirm the immunohistochemistry findings.