Dissecting deregulated cell-to-cell communication in in vitro Alzheimer’s disease models

Abstract

The interplay between neurons and glia cells has recently gained new interest in Alzheimer’s disease (AD) pathogenesis. Neuroinflammation is a well-known hallmark, where microglia and astrocytes play a major role. Extracellular vesicles, such as exosomes, are crucial in the interplay between neurons and glial cells, and in AD spreading. However, exosomes may have both beneficial and harmful effects in AD process, thus requiring further clarification. Our first goal was to assess microglia response to exosomes derived from an AD in vitro neuronal cell model, using respectively human CHME3 microglia and SH-SY5Y neurons expressing APP Swedish mutation (SH-SY5Y APPSwe). Exosomes were collected by differential centrifugation and incubated with microglia for 24 h to assess microglia direct response. Microglia was then left for an additional 24 h period to evaluate microglia recovery ability. SH-SY5Y APPSwe cells displayed increased levels of miR-155 and miR-21, which were recapitulated in their exosomes. They also showed upregulated levels of alarmins and cytokines, from which two of them (HMGB1 and TNF-α) were not part of exosomal cargo. Exosome-treated microglia revealed an increase in miR-155 and miR-21, as well as in S100B and TNF-α gene expression, together with miR-124 decrease. In addition, uptake of exosomes by microglia led to lysosomal impairment and to a sustained elevation of miR-155 over the 24 h recovery period. Induced pluripotent stem cells (iPSCs) are indicated as a gold model to investigate AD pathology. Such feature, led us to the second goal of evaluating the phenotype of iPSCs-derived astrocytes from AD patients with the PSEN1ΔE9 mutation. AD-astrocytes evidenced a depressed RAGE/miR-155 axis, not recapitulated in their exosomal cargo with decreased levels of HMGB1, TNF-α and S100B genes. In sum, AD-neurons determine microglia activation and dysfunction through their exosomes, and AD-astrocytes display a less reactive phenotype, while releasing exosomes depleted in inflammatory machinery.