Mesenchymal stem cells induce the ramification of microglia via the small RhoGTPases Cdc42 and Rac1

Abstract

Activated microglia play a central role in the course of neurodegenerative diseases as they secrete cytotoxic substances which lead to neuronal cell death. Understanding the mechanisms that drive activation of microglia is essential to reverse this phenotype and to protect from neurodegeneration. With some exceptions, evidence indicates that changes in cell morphology from a star shape to a round and flat shape accompany the process of activation in microglia. In this study, we investigated the effect of adipose-tissue-derived mesenchymal stem cells (ASCs), which exert important anti-inflammatory actions, in microglia morphology. Microglia exposed to ASCs or their secreted factors (conditioned medium) underwent a cell shape change into a ramifying morphology in basal and inflammatory conditions, similar to that observed in microglia found in healthy brain. Colony-stimulating factor-1 secreted by ASCs played a critical role in the induction of this phenotype. Importantly, ASCs reversed the activated round phenotype induced in microglia by bacterial endotoxins. The ramifying morphology of microglia induced by ASCs was associated with a decrease of the proinflammatory cytokines tumor necrosis factor-α and interleukin-6, an increase in phagocytic activity, and the upregulation of neurotrophic factors and of Arginase-1, a marker for M2-like regulatory microglia. In addition, activation of the phosphoinositide-3-kinase/Akt pathway and the RhoGTPases Rac1 and Cdc42 played a major role in the acquisition of this phenotype. Therefore, these RhoGTPases emerge as key players in the ramification of microglia by anti-inflammatory agents like ASCs, being fundamental to maintain the tissue-surveying, central nervous system supporting state of microglia in healthy conditions.

Deletion of Nuclear Factor kappa B p50 Subunit Decreases Inflammatory Response and Mildly Protects Neurons from Transient Forebrain Ischemia-induced Damage

“…6 J-L). Since in our previous study we detected an extremely low number of infiltrated leukocytes in BCCAo model [27], these cells are likely to be migrating microglia [30,31]. Counting of these CD45…”

Physical and mechanical regulation of macrophage phenotype and function

“…The activation of microglial cells, which are the resident macrophages of the central nervous system, occurs in concert with distinct morphological changes 55 . It was subsequently shown that soluble factors secreted by adipose-tissue-derived mesenchymal stem cells (ASCs) lead to elongated cell shape in microglia, which is also accompanied by a noninflammatory phenotype characterized by low TNF-α and IL-6, and high arginase-I production 56 (Fig. 3B).…”

“…53,56 B) Immunofluorescence images of CD11b expression in microglia cells exposed to medium conditioned (CM) by mesenchymal stem cells and/or LPS (top), and their secretion of IL-6 and TNF-α and expression of arginase-1 (bottom). Scale bar = 10 μm.…”

“…Scale bar = 10 μm. 56 C) Phase contrast images of BMDMs on unpatterned and patterned surfaces (left), and expression of iNOS and arginase-1 in these conditions (right). Scale bar = 50 μm 53 .…”

Mesenchymal stem cells for the treatment of neurological diseases: Immunoregulation beyond neuroprotection

“…Following these seminal studies, the immunomodulatory effects of MSCs on circulating adaptive, as well as innate, immune cells have been extensively studied [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. In vitro, MSCs affect also the behavior of CNS cells such as microglial cells, and particularly inhibit microglial proliferation and their release of proinflammatory molecules; more specifically, MSCs induce the release of neuroprotective molecules by microglia and increase their phagocytic capability through the release of soluble factors [30][31][32][33][34][35]. Similarly, MSCs are able to skew the phenotype of macrophages from M1 to M2 type [36] [37].…”