SEQUIN Multiscale Imaging of Mammalian Central Synapses Reveals Loss of Synaptic Connectivity Resulting from Diffuse Traumatic Brain Injury

Abstract

The complex microconnectivity of the mammalian brain underlies its computational abilities, and its vulnerability to injury and disease. It has been challenging to illuminate the features of this synaptic network due in part to the small size and exceptionally dense packing of its elements. Here we describe a rapid and accessible super-resolution imaging and image analysis workflow-SEQUIN-that identifies, quantifies, and characterizes central synapses in animal models and in humans, enabling automated volumetric imaging of mesoscale synaptic networks without the laborious production of large histological arrays. Using SEQUIN, we identify delayed cortical synapse loss resulting from diffuse traumatic brain injury. Similar synapse loss is observed in an Alzheimer disease model, where SEQUIN mesoscale mapping of excitatory synapses across the hippocampus identifies region-specific synaptic vulnerability to neurodegeneration. These results establish a novel, easily implemented and robust nano-to-mesoscale synapse quantification and molecular characterization method. They furthermore identify a mechanistic link-synaptopathy-between Alzheimer neurodegeneration and its bestestablished epigenetic risk factor, brain trauma.

Establishment and Maintenance of Neural Circuit Architecture

“…The continuous function of the nervous system relies on the integrity of the circuits established during development. Indeed, the hallmark of many neurodegenerative diseases is a loss of synapses resulting in the destabilization of axons or dendrites (Terry et al, 1991;Scheff et al, 2006;Lin and Koleske, 2010;Hong et al, 2016;Mariano et al, 2018;Sauerbeck et al, 2020). Understanding how the architecture of the nervous system is maintained might therefore aid in the development of therapeutics that prevent or restore synapse loss in disease states.…”

Neuronal VCP loss of function recapitulates FTLD-TDP pathology

“…There was an increase in BIP, phosphorylated (phospho-)PERK, and phospho-IRE1 ( Figures S3C and S3D ). Immunofluorescence staining with the pre- and post-synaptic marker synapsin and PSD-95 was performed on coronal brain sections of control and 1- and 2-month-old VCP cKO mice, and Synaptic Evaluation and Quantification by Imaging of Nanostructure (SEQUIN) quantitated synaptic loci ( Figure S3E ) ( Sauerbeck et al, 2020 ). Quantitation from the CA1 region of the hippocampus demonstrated a 25% reduction in synaptic loci in 2-month-old VCP cKO mice, consistent with our proteomic and transcriptomic studies ( Figure S3F ).…”

Can Developments in Tissue Optical Clearing Aid Super-Resolution Microscopy Imaging?

“…TOC with Mowiol 4-88 was indispensable for Sauerbeck et al [62] to describe SEQUIN (synaptic evaluation and quantification by imaging nanostructure), a technique of imaging and data analysis that consists of immunolabeling, TOC and image scanning microscopy (ISM) of pre-and postsynaptic markers and data processing that allows for the localization of synaptic centroid and for the identification of synaptic loci. With SEQUIN, characteristic patterns of synapse loss were presented in murine models of tauopathy, amyloidosis and diffuse traumatic brain injury, proving the reliability of this new approach to advance studies of the synaptome.…”