Stress Induces the Danger-Associated Molecular Pattern HMGB-1 in the Hippocampus of Male Sprague Dawley Rats: A Priming Stimulus of Microglia and the NLRP3 Inflammasome

“A detailed description of the PCR amplification protocol has been published previously (Frank et al., 2006). cDNA sequences were obtained from GenBank at the National Center for Biotechnology Information (NCBI; www.ncbi.nlm. nih.gov).”

“Previous reports show that disulfide HMGB-1 is sufficient to stimulate proinflammatory cytokines (Scaffidi et al., 2002; Park et al., 2004; Agalave et al., 2014).”

“The concept has developed that innate immune receptors discriminate between danger and non-danger rather than self and non-self (Matzinger, 2002).”

“NLRP3 is induced by the transcription factor NF- B, and so we measured NF- B as an upstream NLRP3 marker (Bauernfeind et al., 2009).”

“Although TLRs on peripheral immune cells were first thought to recognize only pathogen-associated molecular patterns, more recent findings suggest that a variety of conditions can lead to the release of endogenous molecules called alarmins or dangerassociated molecular patterns (DAMPs; Bianchi, 2007) that can also sig…”

“However, HMGB-1 is located primarily in the nucleus and is not considered to be an alarmin unless released into the extracellular space (Lotze and Tracey, 2005).”

“However, the present IS paradigm does not alter IL-1 protein in the hippocampus 24 h after stressor termination (Frank et al., 2007), suggesting that the NLRP3 inflammasome is primed but not active.”

“However, BoxA occupancy of TLRs will keep HMGB-1 from binding and acts as a competitive antagonist to HMGB-1, displacing radiolabeled HMGB-1 from receptors on macrophages without any intrinsic inflammatory activity (Yang et al., 2004).”

“DOI:10.1523/JNEUROSCI.3561-14.2015 Copyright © 2015 the authors 0270-6474/15/350316-09$15.00/0 HMGB-1 plays a proinflammatory role in sterile injury and cellular stress in the periphery (Venereau et al., 2013) and is involved in a number of diseases (Kang et al., 2014).”

“Oxidation at all three cysteines abrogates both the chemotactic and proinflammatory properties of HMGB-1 (oxidized HMGB-1; Venereau et al., 2012).”

“It should be noted that stress exposure increases macrophage and monocyte trafficking into the brain (Wohleb et al., 2011, 2013) and microglia density in several stress-reactive brain areas, including the hippocampus (Nair and Bonneau, 2006; Tynan et al., 2010).”

“However, the present IS paradigm does not alter IL-1 protein in the hippocampus 24 h after stressor termination (Frank et al., 2007), suggesting that the NLRP3 inflammasome is primed but not active.”

“It should be noted that stress exposure increases macrophage and monocyte trafficking into the brain (Wohleb et al., 2011, 2013) and microglia density in several stress-reactive brain areas, including the hippocampus (Nair and Bonneau, 2006; Tynan et al., 2010).”

“It should be noted that stress exposure increases macrophage and monocyte trafficking into the brain (Wohleb et al., 2011, 2013) and microglia density in several stress-reactive brain areas, including the hippocampus (Nair and Bonneau, 2006; Tynan et al., 2010).”

“However, the present results do not exclude the possibility that other CNS cells produce HMGB-1 in response to stress (Qiu et al., 2008).”

“This result is consistent with other findings in which chronic stress increased NLRP3 in the prefrontal cortex (Pan et al., 2014).”

“However, other reports suggest that HMGB-1 does not always induce proinflammatory cytokines (Rouhiainen et al., 2007; Sha et al., 2008; Cassetta et al., 2009).”

“It should be noted that stress exposure increases macrophage and monocyte trafficking into the brain (Wohleb et al., 2011, 2013) and microglia density in several stress-reactive brain areas, including the hippocampus (Nair and Bonneau, 2006; Tynan et al., 2010).”

“IL-1 is often referred to as the “master regulator” of inflammation because it is a potent signal that stimulates the production of other inflammatory molecules (Basu et al., 2004).”

“The BoxB domain is critical for the proinflammatory actions of HMGB-1 (Li et al., 2003).”

“Importantly, HMGB-1 has been reported to be present in the CNS and to mediate neuroinflammatory responses to ischemia and other injuries (Yang and Tracey, 2009).”

“Previous studies show that glucocorticoids, and glucocorticoid receptor signaling in particular, are necessary and sufficient to prime microglia (Frank et al., 2010).”

“Indeed, it has been argued that DAMPs, such as HMGB-1, prime the NLRP3 inflammasome and potentiate inflammation (Leemans et al., 2011).”

“Chronic unpredictable stress (Munhoz et al., 2006) and repeated social defeat (Wohleb et al., 2012), for example, increase inflammatory processes to a later immune challenge.”

“Chronic unpredictable stress (Munhoz et al., 2006) and repeated social defeat (Wohleb et al., 2012), for example, increase inflammatory processes to a later immune challenge.”

“The hippocampus was targeted because it is an area that shows robust IS-induced priming of neuroinflammatory processes in vivo (Johnson et al., 2002) and ex vivo (Frank et al., 2007) and yields a sufficient number of microglia to perform ex vivo experiments.”

“When released in the periphery, HMGB-1 interacts with TLR2, TLR4, and the receptor for advanced glycation end products (RAGE) in which it acts as both a chemotactic and proinflammatory mediator (van Zoelen et al., 2009).”

“Exposure to stressors can lead to a proinflammatory environment within the brain, an outcome thought to be critical to the potential psychopathological effect of stressors (GadekMichalska et al., 2013, Fillman et al., 2014).”

“DOI:10.1523/JNEUROSCI.3561-14.2015 Copyright © 2015 the authors 0270-6474/15/350316-09$15.00/0 HMGB-1 plays a proinflammatory role in sterile injury and cellular stress in the periphery (Venereau et al., 2013) and is involved in a number of diseases (Kang et al., 2014).”

“Both acute and chronic stressors prime microglia (Frank et al., 2007) and amplify the neuroinflammatory response to a subsequent peripheral (Johnson et al., 2002, Wohleb et al., 2012) or central (de Pablos et al., 2006; Espinosa-Oliva et al., 2011) inflammatory challenge.”

“However, other reports suggest that HMGB-1 does not always induce proinflammatory cytokines (Rouhiainen et al., 2007; Sha et al., 2008; Cassetta et al., 2009).”

“Of particular relevance, TLR2 and TLR4 activation can lead to the formation of the NLRP3 inflammasome, a complex that is key to generating IL-1 protein (Hanamsagar et al., 2012).”

“HMGB-1 in the periphery has been demonstrated to induce the expression of the nucleotide-binding domain, leucine-rich repeat, pyrin domain containing protein 3 (NLRP3) inflammasome (Xiang et al., 2011).”

“, 2012) or central (de Pablos et al., 2006; Espinosa-Oliva et al., 2011) inflammatory challenge.”

“It should be noted that stress exposure increases macrophage and monocyte trafficking into the brain (Wohleb et al., 2011, 2013) and microglia density in several stress-reactive brain areas, including the hippocampus (Nair and Bonneau, 2006; Tynan et al., 2010).”

“The effects of HMGB-1 on microglial priming are consistent with previous work demonstrating that HMGB-1 is sufficient to prime the inflammatory response of isolated splenocytes (Valdes-Ferrer et al., 2013).”

“ICM administration was used to avoid implanting cannulae, which itself produces enduring neuroinflammation (Holguin et al., 2007).”

“However, other reports suggest that HMGB-1 does not always induce proinflammatory cytokines (Rouhiainen et al., 2007; Sha et al., 2008; Cassetta et al., 2009).”

“Stress can also alter the levels of heat-shock protein 70 (HSP70) [103,106], which also binds to TLR4 and which, together with its regulating chaperone BCL2-associated athanogene 1 (BAG1), has also been associated with depression [107,108].”

“Besides this, a recent research display that CNS innate immune system can respond to an acute stressor, thereby releasing the danger signal high mobility group box-1 (HMGB-1) in the brain to prime microglia by acting on the NLRP3 inflammasome, in preparation for IL-1β secretion (Weber et al., 2015).”

“Increased high mobility group box-1 (HMGB-1) protein was demonstrated to be increased in the hippocampus of male Sprague Dawley rats after tail shocks and to be responsible for microglia priming by acting on the NLRP3 inflammasome (Weber et al., 2015).”

“Of note, the effects of stress on hippocampal microglial activation have been shown in several studies (Diz-Chaves et al., 2012; Walker et al., 2013a,b; Weber et al., 2015), and it is likely that they might not only be relevant in the pathophysiology of MDD, but also in other psychiatric and stress-related disorders,…”