The effect of genetic background and immunophenotype on microglial response to AD pathology

Abstract

AbstractBackgroundA major hurdle in developing effective treatments for Alzheimer’s Disease (AD) is the fact that pathological hallmarks, such as amyloid beta (Aβ) plaques, develop decades before the first clinical symptoms emerge. Moreover, the risk of developing AD is strongly influenced by genetic background. In addition, the role of microglia in the disease pathway is undeniable, albeit dual and complex. We therefore aim to determine the influence of patient genetic background and immunophenotype on the microglial response to AD pathology.MethodSubject material was sequenced and underwent deep immunophenotyping. Based on their scores patient iPSCs were divided in a high risk and low risk group of developing AD. This microglial response is determined by (i) their phagocytic capacity and (ii) their (change in) morphology. iPSC cells were differentiated into microglia (Mancuso et al., 2019), followed by RT‐qPCR to verify their identity. When microglia are incubated with pHrodo beads, these are phagocytosed and transported to the acidic lysosome, yielding a pH dependent increase in fluorescence, measured with an Operetta confocal microscope. Microglial morphology was recorded in an Incucyte and tracked and scored (e.g. amoeboid, rod‐like, size, motility …) automatically by AI based software. The change in morphology was assessed after addition of stressors such as LPS or Aβ1‐42.ResultPhagocytotic capacity of a reference microglia strain, measured by pHrodo intensity, reached a maximum level approximately 2 hours after addition of the pHrodo beads. When cytochalasin D, an Actin polymerization inhibitor, was added to the medium, the phagocytosis process is inhibited and baseline pHrodo intensity levels are observed. In addition, the addition of LPS seemed to change the morphology of microglia to a more elongated rod‐like shape with less motility.ConclusionThe phagocytic capacity of microglia could be dependent on the genetic background and immunophenotype of the iPSC strain. Similarly, the effect on morphology (e.g. more rod‐like shape) as an answer to stressors (e.g. LPS) could be dependent on the microglia strain. The differential microglial response based on genetic background and immunophenotype might yield insight into the further segmentation of different types of Alzheimer’s Disease and personalized therapeutic approaches.