Hypoxia‐induced changes in microglia in the vhl‐/‐ zebrafish

AbstractBackgroundAge‐associated white matter lesions are associated with chronic cerebral hypoperfusion resulting in a hypoxic environment, and are characterised by high levels of microglia with an amoeboid phenotype. These observations suggest that sustained activation of the hypoxia‐inducible factor (HIF) signalling pathway modifies the microglial phenotype. This study aimed to perform a detailed characterisation of the microglial response associated with hypoxia by exploiting vhl‐/‐ zebrafish, a model which displays highly up‐regulated hypoxic signalling.MethodIn order to exploit the in vivo imaging capabilities of zebrafish and visualise microglia, a reporter for macrophage‐expressed gene‐1 (mpeg1) was crossed into the vhl‐/‐. The number and morphology of mpeg1::mCherry microglia were characterized by light‐sheet florescence microscopy for ten mutant vhl‐/‐ zebrafish and their wild‐type siblings, at a single time point between the ages 3.2 ‐ 3.6 dpf. Furthermore, time lapse video was employed to monitor the microglial response to hypoxia across 24 hours.ResultAt the single time‐point measurement, vhl‐/‐ zebrafish contained 59±0.1 microglia (14±1.3 with a resting morphology, 46±0.2 with an amoeboid morphology), while their wild‐type siblings contained 59±2 total microglia (12.5±1.5 resting morphology and 45±1.8 amoeboid morphology. There was no significant different in the total (p=0.69), resting (p=0.26) or amoeboid microglia (p=0.91). Time‐lapse recordings over 24 hours confirmed this result.ConclusionNo significant differences in microglia numbers or morphology was detected at 3 dpf. At 5 dpf, microglia number increased and adopted a round, amoeboid morphology. This represent is similar to the microglia phenotype associated with age‐associated WML.