Measuring cell connectivity in ancient bones

Lay summary authored by Justyna Miszkiewicz. Read the full paper here: http://doi.org/10.5334/oq.117

Histology is the study of microscopic structure of biological tissues, and typically involves extracting a small piece of tissue, processing it into a thin slice (about 0.1 mm), and then shining a light through it using an optical microscope. While mostly needed in hospitals to examine biopsies, we can also apply histology to bone from archaeological and fossil animals, including humans.

Palaeontologists and archaeologists can find bone histology to be very informative. In adult cortical bone (the thick bone wall that surrounds yellow marrow in long bones such as the femur) they can observe longitudinal structures called (secondary) osteons which form as a result of bone metabolic processes. When alive, our bones actively remodel meaning that they replace old bone with new bone to ensure bone strength and health. Amongst other factors, these osteons accumulate with age and physical activity. Because bone microstructure is sometimes well preserved in specimens spanning the Quaternary period, characteristics of these osteons can be examined to reconstruct remodelling in animals from the past.

False coloured image of archaeological human bone histology showing a remnant of a blood vessel (the ‘hole’ in the centre of the image) surrounded by multiple osteocyte lacunae (the ‘shiny’ star-like features). The white arrow points to connections of the neighbouring lacunae. The protocol published by Miszkiewicz and colleagues measures this distance. Image credit: Justyna Miszkiewicz.

A common approach in this type of analysis is to measure the area and density of osteons and their micro-anatomical components such as blood vessels. The density of bone maintenance cells, known as osteocytes, which reside in cavities called lacunae (Figure 1), can also be considered. These osteocyte lacunae form a complex and inter-connected network where important signals and nutrients are exchanged. Thus, understanding this network can provide vital clues as to cell communication.

In order to measure these aspects, researchers need to use an image analysis software where histology images taken using a microscope camera can be imported. ImageJ, part of the FIJI package, is an open access software. It is user-friendly and allows researchers to save raw data in a spreadsheet. In their recent methods article, Justyna Miszkiewicz and colleagues provide a protocol for calculating distances between neighboring osteocyte lacunae that can be easily obtained from an ImageJ data window.

They based their protocol on Cartesian (XY) coordinates. They used a hypothetical example of an osteon to illustrate the nature of osteocyte lacunae dispersal, and then replicated their protocol on an authentic sample using an archaeological human bone thin section (dated to the Medieval period in England). Justyna Miszkiewicz said: “We found that our protocol successfully estimated the distances between neighbouring osteocyte lacunae. When applied in future bone histology research, more refined reconstructions of bone remodelling in the past can now be made”.

Full paper: Miszkiewicz, J.J., Louys, J. and Mahoney, P., 2022. Cartesian Coordinates in Two-Dimensional Bone Histology Images for Quaternary Bone Remodelling Research. Open Quaternary, 8(1), p.12. DOI: http://doi.org/10.5334/oq.117

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