Reversal of β-amyloid induced microglial toxicityin vitroby activation of Fpr2/3

Abstract

19Background and Purpose 20 Microglial inflammatory activity is thought to be a major contributor to the pathology of 21 neurodegenerative conditions such as Alzheimer's disease (AD), and strategies to restrain 22 their behaviour are under active investigation. Classically, anti-inflammatory approaches aim 23 to suppress pro-inflammatory mediator production, but exploitation of inflammatory resolution, 24 the endogenous process whereby an inflammatory reaction is terminated, has not been fully 25 investigated as a therapeutic approach in AD. In this study, we sought to provide proof-of-26 principal that the major pro-resolving actor, formyl peptide receptor 2, Fpr2, could be targeted 27 to reverse microglial activation induced by the AD-associated pro-inflammatory stimulus, 28 oligomeric β-amyloid (oAβ). 30Experimental Approach 31The immortalised murine microglial cell line BV2 was employed as a model system to 32 investigate the pro-resolving effects of the Fpr2 ligand QC1 upon oAβ-induced inflammatory, 33 oxidative and metabolic behaviour. Cytotoxic behaviour of BV2 cells was assessed through 34 use of co-cultures with retinoic acid-differentiated human SH-SY5Y cells. 36 Key Results 37Stimulation of BV2 cells with oAβ at 100nM did not induce classical inflammatory marker 38 production but did stimulate production of reactive oxygen species (ROS), an effect that could 39 be reversed by subsequent treatment with the Fpr2 ligand QC1. Further investigation revealed 40 that oAβ-induced ROS production was associated with NADPH oxidase activation and a shift 41 in BV2 cell metabolic phenotype, activating the pentose phosphate pathway and NADPH 42 production, changes that were again reversed by QC1 treatment. Microglial oAβ-stimulated 43 ROS production was sufficient to induce apoptosis of bystander SH-SY5Y cells, an effect that 44 could be prevented by QC1 treatment. 46 Conclusion and Implications 47In this study, we provide proof-of-concept data that indicate exploitation of the pro-resolving 48 receptor Fpr2 can reverse damaging oAβ-induced microglial activation. Future strategies 49 aiming to restrain neuroinflammation in conditions such as AD should examine pro-resolving 50 actors as a mechanism to harness the brain's endogenous healing pathways and limit 51 neuroinflammatory damage. 52 53 Keywords: Fpr2/3, Microglia, Oxidative stress, Alzheimer's disease 54 Background 55 56 AD is the single greatest cause of dementia, affecting approximately 4% of individuals aged 57 over 65 years and with a global disease burden of around 37 million individuals [1]. This figure 58 is set to increase as the population ages, and is expected to reach around 78 million people 59 by 2050 [2]. There are currently no effective treatments for the condition.60 61 Whilst the two core pathological lesions of AD, extracellular β-amyloid (Aβ) plaques and 62 intraneuronal tau tangles, have long been studied, the contribution to pathology provided by 63 neuroinflammation, and the role of the microglia in AD pathogenesis, has only recently been...

The N-Formyl Peptide Receptor 2 (FPR2) Agonist MR-39 Improves Ex Vivo and In Vivo Amyloid Beta (1–42)-Induced Neuroinflammation in Mouse Models of Alzheimer’s Disease

“…Recently data suggest that FPR2 may play a complex role in the inflammatory process in AD. Indeed FPR2 is a highaffinity binding partner of Aβ 1-42 that induces cell activation and the release of proinflammatory mediators upon binding of FPR2 [37]. On the other hand, FPR2 mediates antiinflammatory and pro-resolving effects when activated by LXA4 and AnxA1 [13,38].…”

Exploiting formyl peptide receptor 2 to promote microglial resolution: a new approach to Alzheimer’s disease treatment

“…This generates soluble Ab monomers, which can spontaneously aggregate into oligomers (oAb) and subsequent insoluble fibrils (fAb), which are the basis for plaque formation [8]. While plaques were initially suggested as the toxic moiety [9], opinion has shifted in recent years to focus on the detrimental actions of soluble oAb and their potent pro-inflammatory and neurotoxic effects [10][11][12][13]. Under normal circumstances, tau protein is a regulator of microtubule formation [14], but for reasons that are still not fully understood, it undergoes hyperphosphorylation in AD, driving the formation of filamentous intraneuronal inclusions thought to impair trafficking and ultimately lead to neuronal death [15].…”

“…Murine age-related cognitive impairment is also directly associated with chronic neuroinflammation [136], wherein microglia may damage and remove healthy neurones, further contributing to pathology [137]. Direct interaction of microglia with oAb also appears to cause the release of a battery of pro-inflammatory cytokines, chemokines and ROS [10,138,139]. Moreover, microglial phagocytic ability appears to be hindered following Ab-elicited activation [140], suggesting that Ab may therefore promote its own accumulation, manifesting a self-propagating inflammatory cycle [141].…”

“…Moreover, the evidence describing the intricate allosteric interactions between FPR2 agonists and the complex signalling patterns that result raises the possibility of selective targeting of pro-resolving functions for therapeutic development. Such pro-resolving FPR2 agonists will be able to exert a number of beneficial effects in the brain, including suppression of pro-inflammatory cytokine and ROS production [10,190,235], improving clearance of fAb [180,190] and apoptotic cells and debris [224] and promoting an anti-inflammatory microglial phenotype [193,238]. More hypothetically, if microglia do behave in a similar manner to their peripheral macrophage cousins [214,227], induction of a pro-resolving phenotype by FPR2 activation may also downregulate expression of the receptor itself, helping to shield microglia from further pro-inflammatory activation by oAb.…”

“…The relationship between microglial behaviour and AD pathology is complex. Microglia actively phagocytose Ab plaques and dead/dying cells in what is thought to be an attempt to clear pathology [120], but Ab, particularly in its oligomeric form, potently activates microglia and can directly contribute to neuronal damage and loss [10,[121][122][123]. Moreover, several AD risk genes are associated with microglial phagocytosis, including APOE [124] and TREM2 [32], suggesting risk variants may compound the defective effects of ageing on microglial function.…”