Ent condition) were analyzed by cytokine array (Fig. 6d). Compared with A-CM, lower levels of proinflammatory mediators (CD40, TNF-, IL-1, IL-12) with higher the levels of the M2a inducer (IL-4) and the M2a marker (YM1) were observed in A/DcR3-CM (Fig. 6d and Additional file 11: Figure S9a). In contrast, the levels of M2b and M2c markers (CXCL2 and IL-10) were not altered by DcR3 (Fig. 6d). All these observations suggest that DcR3 has the potent effect to modulate cytokine secretion by modulating the activation and differentiation of microglia. It is interesting to note that DcR3 did not alter the expression of MMP9, which contributes to plaque clearance in the brain [33], suggesting MMP9-dependent proteolytic degradation of A was not influenced by DcR3 (Additional file 11: Figure S9b). The complete list of all the changes from this cytokines array is listed in Additional file 12: Table S3. Thus, we concluded that DcR3 is able to skew microglia differentiation into IL-4+YM1+ M2a-like microglia in vivo and in vitro. Because the interaction between DcR3 and HSPG is critical for modulating macrophage activation in vitro [24] we asked whether DcR3 also interacts with glypicans and syndecans, which are the most abundant HSPGs to modulate myeloid cell differentiation in the brain [22, 34, 35]. We found that DcR3 interacts with glypican-1 (Fig. 7a) and syndecan (Fig. 7b) by co-immunoprecipitation assay. In contrast, DcR3 did not interact with A or APP (Fig. 7c), thus excluding the possibility that the neuroprotective effect of DcR3 is via direct neutralization of A or APP. The interaction between DcR3 and HSPGs suggested that human DcR3 may modulate the activation and differentiation of microglia via interacting with HSPGs in vivo. To further confirm the role of HSPG in DcR3mediated protection against A-836339 supplier A-induced neurotoxicity, heparin sulfate (HS) was used to block DcR3-HSPG interaction by a competition assay as described in Fig. 4a [22].In the presence of HS, DcR3-mediated neuroprotective effect against A was attenuated (Fig 7d), suggesting DcR3-HSPG interaction contributes partially against A-induced toxicity [36].Discussion In this study a human secreted protein DcR3 prevented A-induced functional and pathological deficits in both in vivo and in vitro AD models. Three potential mechanisms involve in DcR3 neuroprotective effect against amyloid pathogenesis (Fig. 8). First, under A stress, DcR3 induces IL-4+YM1+ M2a-like microglia that reduce the proinflammation cytokines to prevent neurotoxicity. Second, DcR3 enhances microglia recruitment to plaques and phagocytic efficiency to clear A. Finally, DcR3 interacts with surface HSPGs. This interaction may eliminate AHSPGs downstream cytotoxicity or inhibit the HSPGsmediated inflammatory responses [37, 38].DcR3 promotes anti-inflammatory effectThe importance of microglia-neuron interaction has been implicated in many neuroinflammatory-related disorders [39]. In the pre-plaque AD mouse oA and complement C1q initiate complement cascade and recruit microglia PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/26266977 via CR3 to eliminate synapses [40]. Manipulation of the innate immune system into alternatively M2 activated microglia has been considered as a promising therapeutic strategy for AD [11, 41]. For example, intracerebral injections of IL4/IL-13 or IL-33 reverse memory deficits and reduce A plaque load in AD mouse models [41, 42]. In addition, YM1+ cells could protect neurons during acute brain injury [43, 44]. We found that DcR3-triggered IL-4+YM1+.
