BackgroundMicroglia—the resident immune cells of the brain—are activated after brain lesions, e.g., cerebral ischemia, and polarize towards a classic “M1” pro-inflammatory or an alternative “M2” anti-inflammatory phenotype following characteristic temporo-spatial patterns, contributing either to secondary tissue damage or to regenerative responses. They closely interact with endogenous neural stem cells (NSCs) residing in distinct niches of the adult brain. The current study aimed at elucidating the dynamics of microglia polarization and their differential effects on NSC function.ResultsPrimary rat microglia in vitro were polarized towards a M1 phenotype by LPS, or to a M2 phenotype by IL4, while simultaneous exposure to LPS plus IL4 resulted in a hybrid phenotype expressing both M1- and M2-characteristic markers. M2 microglia migrated less but exhibit higher phagocytic activity than M1 microglia. Defined mediators switched microglia from one polarization state to the other, a process more effective when transforming M2 microglia towards M1 than vice versa. Polarized microglia had differential effects on the differentiation potential of NSCs in vitro and in vivo, with M1 microglia promoting astrocytogenesis, while M2 microglia supported neurogenesis. Regardless of their polarization, microglia inhibited NSC proliferation, increased NSC migration, and accelerated NSC differentiation.ConclusionOverall, this study shed light on the complex conditions governing microglia polarization and the effects of differentially polarized microglia on critical functions of NSCs in vitro and in vivo. Refining the understanding of microglia activation and their modulatory effects on NSCs is likely to facilitate the development of innovative therapeutic concepts supporting the innate regenerative capacity of the brain.Electronic supplementary materialThe online version of this article (10.1186/s12974-018-1261-y) contains supplementary material, which is available to authorized users.

IntroductionOsteopontin (OPN) is a phosphoglycoprotein with important roles in tissue homeostasis, wound healing, immune regulation, and stress responses. It is expressed constitutively in the brain and upregulated during neuroinflammatory responses; for example, after focal cerebral ischemia. To date, its effects on neural stem cells (NSC) remain to be elucidated and are, accordingly, the subject of this study.MethodPrimary fetal rat NSC were cultured as homogenous monolayers and treated with different concentrations of OPN. Fundamental properties of NSC were assessed following OPN exposure, including proliferative activity, survival under oxidative stress, migration, and differentiation potential. To elucidate a putative action of OPN via the CXC chemokine receptor type 4 (CXCR4), the latter was blocked with AMD3100. To investigate effects of OPN on endogenous NSC in vivo, recombinant OPN was injected into the brain of healthy adult rats as well as rats subjected to focal cerebral ischemia. Effects of OPN on NSC proliferation and neurogenesis in the subventricular zone were studied immunohistochemically.ResultsOPN dose-dependently increased the number of NSC in vitro. As hypothesized, this effect was mediated through CXCR4. The increase in NSC number was due to both enhanced cell proliferation and increased survival, and was confirmed in vivo. Additionally, OPN dose-dependently stimulated the migration of NSC via CXCR4. Moreover, in the presence of OPN, differentiation of NSC led to a significant increase in neurogenesis both in vitro as well as in vivo after cerebral ischemia.ConclusionData show positive effects of OPN on survival, proliferation, migration, and neuronal differentiation of NSC. At least in part these effects were mediated via CXCR4. Results suggest that OPN is a promising substance for the targeted activation of NSC in future experimental therapies for neurological disorders such as stroke.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-015-0098-x) contains supplementary material, which is available to authorized users.

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Background and Purpose: The translational roadblock has long impeded the implementation of experimental therapeutic approaches for stroke into clinical routine. Considerable interspecies differences, for example, in brain anatomy and function, render comparisons between rodents and humans tricky, especially concerning brain reorganization and recovery of function. We tested whether stroke-evoked changes in neural networks follow similar patterns in mice and patients using a systems-level perspective. Methods: We acquired resting-state functional magnetic resonance imaging data during the early poststroke phase in a sample of human patients and compared the observed network changes with data from 2 mouse stroke models, that is, photothrombosis and distal middle cerebral artery occlusion. Importantly, data were subjected to the same processing steps, allowing a direct comparison of global network changes using graph theory. Results: We found that network parameters computed for both mouse models of stroke and humans follow a similar pattern in the postacute stroke phase. Parameters indicating the global communication structure’s facilitation, such as small worldness and characteristic path length, were similarly changed in humans and mice in the first days after stroke. Additionally, small worldness correlated with concurrent motor impairment in humans. Longitudinal observation in the subacute phase revealed a negative correlation between initial small worldness and motor recovery in mice. Conclusions: We show that network measures based on resting-state functional magnetic resonance imaging data after stroke obtained in mice and humans share notable features. The observed network alterations could serve as therapeutic readout parameters for future translational studies in stroke research.