Cell lines which possess microglial or neuronal properties
Cell lines which possess microglial or neuronal properties are uncomplicated and convenient in vitro models for studying Natural Product Library injury at the cellular and molecular levels. Microglial BV-2 cells are derived from the immortalized mouse microglia and exhibit many of the morphological, phenotypical and functional characteristics described for freshly isolated microglial cells (Blasi et al., 1990). It is important that BV-2 cells, similar to primary microglia, display typical microglial phagocytic response and produce proinflammatory cytokines implicated in microglia-triggered neuronal damage (Chinta et al., 2012, Henn et al., 2009, Lee et al., 2008, Yu et al., 2014, Zhang et al., 2014a, Tran et al., 2008). These properties make BV-2 cells highly suitable for neuroinflammatory and neurodegenerative studies. Neuronal PC12 cells, established from a transplantable rat adrenal pheochromocytoma, synthesize and store the catecholamine neurotransmitters dopamine and norepinephrine (Greene and Tischler, 1976). It is reported that PC12 cells are sensitive to several neurotoxins, such as 1-methyl-4-phenylpyridinium, rotenone and 6-hydroxydopamine, that induce cellular degeneration and death in experimental PD (Grau and Greene, 2012, Liu et al., 2015, Sun et al., 2013, Zhang et al., 2011). Hence, PC12 cells have been extensively used to study neuronal cell death and to test potential neuroprotective drugs for PD. Microglial activation in experimental PD is usually induced by LPS, a common inflammogen. LPS stimulation triggers a variety of BV-2 microglial responses that consequently lead to neuroinflammation and neuronal death (Harun et al., 2015, Henn et al., 2009, Lee et al., 2008, Tran et al., 2008). Therefore, in this study, microglial BV-2 cells and neuronal PC12 cells were cultured to examine the impact of LPS-activated microglia on neurons. Our data suggest that LPS-activated BV-2 cells mediated PC12 cells death. Microglial activation is triggered by pathological signals and is characterized by proliferation, phagocytosis and production of bioactive substances, which can be both destructive and neuroprotective for the nervous tissue (Blandini, 2013, Ferreira and Bernardino, 2015, Sperlágh and Illes, 2007). Debris clearance by microglial phagocytosis without the production of proinflammatory mediators is beneficial for tissue repair following brain injury (Neumann et al., 2009, Ferreira and Bernardino, 2015, Sperlágh and Illes, 2007). However, overactivated microglia are responsible and/or strongly contribute to neuronal damage via pathological microglial phagocytosis and proinflammatory mediator release in neuroinflammatory and neurodegenerative diseases (Blandini, 2013, Brown and Neher, 2012, Emmrich et al., 2013, Ferreira and Bernardino, 2015, Marker et al., 2012, Neher et al., 2013, Neher et al., 2014). It is reported that leucine-rich repeat kinase 2 is a key player in microglial phagocytosis and inflammation. Inhibition of leucine-rich repeat kinase 2 kinase prevents pathological microglial responses and may provide an effective therapeutic strategy for neurocongnitive disorders as well as other neurodegeneration (Marker et al. 2012). Several recent publications from the Brown׳s group showed that preventing microglial phagocytosis is sufficient to attenuate neuronal death induced by various inflammatory stimuli such as LPS, rotenone or ischemic stroke (Brown and Neher, 2012, Emmrich et al., 2013, Neher et al., 2013, Neher et al., 2014). We recently demonstrated that OGD or rotenone induced significant primary microglia and BV-2 phagocytosis and release of proinflammatory cytokines, which plays an important role in neuronal death of ischemia and PD in vitro (Zhang et al., 2013, Zhang et al., 2014a). These data indicate a primary role of microglial phagocytosis under neuroinflammatory and neurodegenerative conditions. In this study, we focused on LPS-induced proinflammatory and deleterious response of microglia to neuronal injury. The microglial phagocytosis was determined as an indicator of microglial activation. The present results revealed that LPS induced a microglial phagocytic response, which is associated with release of proinflammatory cytokines. The inhibition of LPS-induced proinflammatory cytokine production by activated microglia attenuated microglia-mediated neuronal death.