Assessing inflammasome activity in mouse models of Down syndrome and organotypic brain slice cultures

Background Down syndrome (DS) is caused by trisomy of chromosome 21 (Hsa21) and is a leading genetic cause of Alzheimer’s disease. Neuroinflammation occurs in the DS brain, with altered microglial morphology and transcriptional profiles, and upregulated proinflammatory cytokines, including IL‐1β. IL‐1β is produced by inflammasome activity. We hypothesize that IL‐1β levels are raised in the DS brain via upregulation of inflammasome activity or heightened sensitivity to inflammasome stimuli, which persists when people with DS develop AD. Method Levels of 10 cytokines, including IL‐1β, TNFα and IL‐6 were measured (MSD) in the 3‐month hippocampus of a panel of segmental duplication mouse models of DS; Dp1Tyb, Dp2Tyb, Dp3Tyb, Dp9Tyb, Dp10Yey and Dp17Yey. These models have a duplication on one chromosome of a number of orthologues for Hsa21 genes. Organotypic brain slice cultures (OBSCs) were prepared from Dp1Tyb mice and stimulated with LPS ± nigericin, to determine if they have an altered response to inflammasome stimuli, as measured by ELISA for cytokines and IHC for IBA1 and ASC. Result Raised IL‐1β abundance was identified in the hippocampus of the Dp1Tyb mouse, which has an additional copy of 148 mouse orthologues for Hsa21 genes. No difference in IL‐1β or other cytokines measured were identified in the Dp3Tyb, Dp9Tyb, Dp2Tyb, Dp10Yey or Dp17Yey hippocampus, which have 37, 76, 33, 31 and 19 genes in three copies respectively. LPS + nigericin treatment does not affect the secretion of IL‐1β from Dp1Tyb OHSCs compared to WT controls, nor the number of ASC specks formed. Conclusion Raised IL‐1β in the Dp1Tyb brain is a multigenic phenotype, with three‐copies of more than one gene/region of Hsa21 required to drive the phenotype. This is not due to increased sensitivity to inflammasome stimuli in Dp1Tyb OBSCs. Next, we will determine what products are raised in the Dp1Tyb brain that have the potential to increase IL‐1β production, and Dp1Tyb OBSCs will be treated with these products, E.g. Aβ. Here, we are further understanding the mechanisms of neuroinflammation in DS, which is critical in determining how AD‐DS differs from AD, and if people with DS can be included in AD research and clinical trials.