Abstract
Microglia play an important role in the pathology of CNS disorders, however, there remains significant uncertainty about the neuroprotective/degenerative role of these cells due to a lack of techniques to adequately assess their complex behaviour in response to injury. Advancing microscopy techniques, transgenic lines and well-characterized molecular markers, have made histological assessment of microglia populations more accessible. However, there is a distinct lack of tools to adequately extract information from these images to fully characterise microglia behaviour. This, combined with growing economic pressures and the ethical need to minimise the use of laboratory animals, led us to develop tools to maximise the amount of information obtained. This study describes a novel approach, combining image analysis with spatial statistical techniques. In addition to monitoring morphological parameters and global changes in microglia density, nearest neighbour distance, and regularity index, we used cluster analyses based on changes in soma size and roundness to yield novel insights into the behaviour of different microglia phenotypes in a murine optic nerve injury model. These methods should be considered a generic tool to quantitatively assess microglia activation, to profile phenotypic changes into microglia subpopulations, and to map spatial distributions in virtually every CNS region and disease state.
Highlights
Microglia play an important role in the pathology of CNS disorders, there remains significant uncertainty about the neuroprotective/degenerative role of these cells due to a lack of techniques to adequately assess their complex behaviour in response to injury
The left-shift in the cumulative density graphs (Fig. 2c, arrow) and the larger nearest neighbour distance (NND) at increasing distance from the optic nerve head (ONH) (Fig. 2d, arrows), are suggestive of a microglia redistribution from the periphery to the centre in response to the optic nerve crush (ONC) injury. This microglial response appeared to be almost identical in ONC and contralateral eyes at 4 days post ONC, and – given that the overall microglia density did not change in the contralateral eyes – proposes that at least part of the increased central cell density in the ONC retinas is the result of relocating resident microglia
Given that changes in microglia activation can be elucidated from changes in population size and morphology, independent of any molecular markers of activation, quantitative analysis these parameters can be used to assess the pathologic state of a given tissue
Summary
Microglia play an important role in the pathology of CNS disorders, there remains significant uncertainty about the neuroprotective/degenerative role of these cells due to a lack of techniques to adequately assess their complex behaviour in response to injury. No signs of activation were found when analysing cell soma size and roundness in the retina of the contralateral eye of the ONC animals (Fig. 3a–d).
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