TSPO Modulates Oligomeric Amyloid-β-Induced Monocyte Chemotaxis: Relevance for Neuroinflammation in Alzheimer’s Disease

Abstract

Background:

Neuroinflammation is one of the cardinal mechanisms of Alzheimer’s disease (AD). with amyloid-β (Aβ) playing a critical role by activating microglia to produce soluble inflammatory mediators, including several chemokines. Peripheral monocytes are, therefore, attracted into the central nervous system (CNS), where they change into blood-born microglia and participate in the attempt of removing toxic Aβ species. The translocator protein-18 kDa (TSPO) is a transmembrane protein overexpressed in response to neuroinflammation and known to regulate human monocyte chemotaxis.

Objective:

We aimed to evaluate the role of the oligomeric Aβ_1-42 isoform at inducing peripheral monocyte chemotaxis, and the possible involvement of TSPO in this process.

Methods:

In vitro cell lines, and ex vivo monocytes from consecutive AD patients (n = 60), and comparable cognitively intact controls (n = 30) were used. Chemotaxis analyses were carried out through both μ-slide chambers and Boyden assays, using 125 pM oligomeric Aβ_1-42 as chemoattractant. TSPO agonists and antagonists were tested (Ro5-4864, Emapunil, PK11195).

Results:

Oligomeric Aβ directly promoted chemotaxis in all our models. Interestingly, AD monocytes displayed a stronger response (about twofold) with respect to controls. Aβ-induced chemotaxis was prevented by the TSPO antagonist PK11195; the expression of the TSPO and of the C-C chemokine receptor type 2 (CCR2) was unchanged by drug exposure.

Conclusion:

Oligomeric Aβ_1-42 is able to recruit peripheral monocytes, and we provide initial evidence sustaining a role for TSPO in modulating this process. This data may be of value for future therapeutic interventions aimed at modulating monocytes motility toward the CNS.