Role of oligodendrocyte-derived IL-33 in brain aging and Alzheimer's disease

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Abstract The aged brain is thought to be more vulnerable to stresses than its young counterpart, and different in its coping with neuroinflammation and ability to repair an injury. A better understanding of the brain aging process will provide valuable information. This knowledge enables one to mitigate age-related declines in cognitive, emotional, sensory, and motor functions. Such information may also promote effective strategies for treating age-related neurodegenerative diseases, such as Alzheimer’s disease (AD). The brain is composed of multiple types of non-neuronal cells besides neurons, and each type seems to undergo unique age-related changes following its genetic program. Oligodendrocytes (OLs), a major glial cell population, form myelin sheaths, essential for rapid axonal conduction in the central nervous system (CNS). OLs also provide metabolic and nutritional support to neurons and contribute to other homeostatic regulations for axonal communication. Recently, our OL-specific transcriptomic analyses revealed that IL-33, a member of the IL-1 family known to contribute to neural circuit refining and neural repair, is increasingly expressed in OLs with age. Consequently, at one year of age, OLs become the predominant source of IL-33 (> 90% of all IL33-expressing cells) in the mouse CNS. Interestingly, IL-33 genetic variations are correlated with the risk of AD in patients, and higher levels of IL-33 in the brain significantly benefited amyloid plaque clearance in mice. Given the critical functions of IL-33, it is crucial to identify detailed source cell-specific mechanisms of IL-33 in the aged brain. To understand how OL-derived IL-33 shapes brain aging and AD-like disease progression, we will employ mouse genetic tools that allow OL-specific IL-33 conditional knockout (cKO) or overexpression. We will examine the effects of those genetic manipulations on OL survival and myelin maintenance in the aged brain. Moreover, these IL33-related genetic manipulations will be applied to a mouse model of AD (APP/PS1), and we will determine whether OL-derived IL-33 regulates AD-like diseases and cognitive deficits, as well as microglia-mediated clearance of beta-amyloid (Aβ) deposits. The same genetic manipulations will also be used on astrocytes; thus, the relative importance of OL-derived IL33 will be compared with astroglial IL33. If successfully conducted, this study will advance our understanding of cell-cell interactions, especially those mediated by IL-33 in brain aging and during AD progression. Our results may promote the development of a therapeutic strategy with an oligodendroglia-targeted approach and identify related molecular mechanisms and targets for treating AD patients.