Monocytic cells exhibit a high level of heterogeneity and have two distinct modes of their activation: 1) classical M1 path associated with inflammation and tissue damage, and 2) alternative M2 path. Although it has been demonstrated that M2 macrophages play an important role in the regulation of the allergic immune responses, tissue maintenance and repair, little is known about the mechanisms that determine the M2 phenotype. We have previously shown that miR-124 is expressed in microglia that exhibit the M2 phenotype and overexpression of miR-124 in macrophages resulted in downregulation of a number of M1 markers (MHC class II, CD86) and up-regulation of several M2 markers (Fizz1, Arg1). We further investigated whether the polarization of macrophages towards the M2 phenotype induced miR-124 expression. We found that exposure of cells to IL-4 and IL-13 resulted in the upregulation of miR-124 in macrophages. We also demonstrated that IL-4 induced expression of three miR-124 precursor transcripts with predominant expression of pri-miR-124.3, suggesting regulation of miR-124 expression by IL-4 on a transcriptional level. Expression of miR-124 in microglia did not depend on IL-4 and/or IL-13, whereas expression of miR-124 in lung resident macrophages was IL-4 and IL-13-dependent and was upregulated by systemic administration of IL-4 or during allergic inflammation. Upregulation of several M2 markers (CD206, Ym1) and downregulation of the M1 markers (CD86, iNOS, TNF) in M2-polarized macrophages was abrogated by a miR-124 inhibitor, suggesting that this microRNA contributed to the M2 phenotype development and maintenance. Finally we showed that human CD14+CD16+ intermediate monocytes, which are found in increased numbers in patients with allergies and bronchial asthma, expressed high levels of miR-124 and exhibited other properties of M2-like cells. Thus, our study suggests that miR-124 serves as a regulator of the M2 polarization in various subsets of monocytic cells both in vitro and in vivo.

Platelets respond to vascular damage and contribute to inflammation, but their role in the neurodegenerative diseases is unknown. We found that the systemic administration of brain lipid rafts induced a massive platelet activation and degranulation resulting in a life-threatening anaphylactic-like response in mice. Platelets were engaged by the sialated glycosphingolipids (gangliosides) integrated in the rigid structures of astroglial and neuronal lipid rafts. The brain-abundant gangliosides GT1b and GQ1b were specifically recognized by the platelets and this recognition involved multiple receptors with P-selectin (CD62P) playing the central role. During the neuroinflammation, platelets accumulated in the central nervous system parenchyma, acquired an activated phenotype and secreted proinflammatory factors, thereby triggering immune response cascades. This study determines a new role of platelets which directly recognize a neuronal damage and communicate with the cells of the immune system in the pathogenesis of neurodegenerative diseases.