A closer look into the diseased brain: discovering the ultrastructure of astrocytes in the Alzheimer's model
Astrocytes are highly complex cells that are crucial in the maintenance of brain function. Their morphology is closely tied with their major role in supporting neurons by providing nutrients, buffering of ions and neurotransmitters, and controlling synapse function. Recently, astrocytes have been implicated to play a major role in neurodegenerative disorders such as Alzheimer's disease (AD) Much research is focused on the functional aspect of astrocytes in the AD brain, but the morphological changes these cells undergo during AD is profound and not well understood. To better understand the morphology of astrocytes in both healthy and AD mice, we looked at both ultrastructure and topographical features in astrocytes (including subcellular organelles and metabolic substrates) of mice from the double transgenic APP/PS1 background. We used focused ion beam serial electron microscopy (FIB SEM) to image an 8 10mm block of tissue from layer 2/3 of the barrel cortex. These images were first analysed on ImageJ using the TrakEM2 plugin which allows for 2D manual tracing of astrocyte features. The traced images were then transformed into a 3D structure using Blender. Quantitative data was acquired through MATLAB 3D volumetric image processing and novel image analysis using python language. With these tools, we were able to measure curvature, thickness, and surface to volume ratio of the AD astrocyte and compared these measurements with a healthy control. In order to observe changes in intracellular features such as organelles and metabolic substrates, machine learning is being implemented using Ilastik. Ilastik's Pixel Classification can identify unique objects within 2D images and perform automated tracing. We propose using Ilastik to successfully identify mitochondria and glycogen granules. Using this data, we can identify morphological changes in mitochondria (energy producing organelle) and alterations in glycogen granule (energy substrate) distribution. The data provided by these imaging techniques provide an important structural framework for understanding how astrocyte morphology is changed during AD and how this may relate to both normal and abnormal brain function.