Inflammatory Response in the Hippocampus of PS1M146L/APP751SLMouse Model of Alzheimer's Disease: Age-Dependent Switch in the Microglial Phenotype from Alternative to Classic

“The soluble fractions (S1) were obtained by ultracentrifugation of the homogenates as described previously (Kayed et al., 2003).”

“The software calculated the estimated total number of cresyl-violet stained nuclei in the CA1 region using the optical fractionator formula (West et al., 1991; Schmitz and Hof, 2005), N 1/bsf.1/ssf.1/asf.1/hsf.”

“The recruitment of CD4 Th1-cells in experimental autoimmune encephalomyelitis (EAE; a disease similar to human multiple sclerosis) induced the production of, among other cytotoxic factors, TNF- (Dhib-Jalbut et al., 2006; Weaver et al., 2007).”

“…reported that aging and/or A could decrease the neuronal expression of microglial inhibitory factors, such as CD200, fractalkine or neurotransmitters (Acetylcholine or noradrenaline) (Cardona et al., 2006; Chitnis et al., 2007; Heneka and O’Banion, 2007; Lyons et al., 2007a; Duan et al., 2008).”

“The precision of the individual estimations is expressed by the coefficient of error (CE) (Gundersen et al., 1999) and here we have estimated the total CE (CE group value) that was calculated using the CEs in each individual animal.”

“As proposed by the inflammation hypothesis of Alzheimer’s disease (AD), the neurodegenerative process could be exacerbated by a chronic inflammatory response to -amyloid (A ) peptides (for review, see Griffin et al., 1998; Wyss-Coray, 2006; Heneka and O’Banion, 2007).”

“We observed a close spatial and temporal parallelism between A deposits and microglial activation (Simard et al., 2006).”

“These ADDLs were exclusively present in AD patients (Gong et al., 2003; Lacor et al., 2004) and their content increased with the disease severity (Lambert et al., 2007).”

“Thus, according with recent in vivo observations (Meyer-Luehmann et al., 2008), plaques attracted and stimulated microglial cells.”

“These ADDLs were exclusively present in AD patients (Gong et al., 2003; Lacor et al., 2004) and their content increased with the disease severity (Lambert et al., 2007).”

“…the decrease in the early recruitment of the microglial cells, by genetic ablation of either TLR2 receptor, in a PS1/APP model (Richard et al., 2008) or CCR2 in Tg2576 (El Khoury et al., 2007), increased A 42 levels, accelerated memory impairments and increased vascular amyloid pathology.”

“It is well known that diffusible aggregated A forms (ADDLs/oligomers) are highly toxic (De Felice et al., 2007).”

“We determined the expression of YM-1 and Arg-1 genes, considered markers of the alternative differentiation in peripheral macrophages (Edwards et al., 2006).”

“As proposed by the inflammation hypothesis of Alzheimer’s disease (AD), the neurodegenerative process could be exacerbated by a chronic inflammatory response to -amyloid (A ) peptides (for review, see Griffin et al., 1998; Wyss-Coray, 2006; Heneka and O’Banion, 2007).”

“As proposed by the inflammation hypothesis of Alzheimer’s disease (AD), the neurodegenerative process could be exacerbated by a chronic inflammatory response to -amyloid (A ) peptides (for review, see Griffin et al., 1998; Wyss-Coray, 2006; Heneka and O’Banion, 2007).”

“The software calculated the estimated total number of cresyl-violet stained nuclei in the CA1 region using the optical fractionator formula (West et al., 1991; Schmitz and Hof, 2005), N 1/bsf.1/ssf.1/asf.1/hsf.”

“Activated inflammatory cells could mediate neuronal damage by producing toxic products, such as inflammatory cytokines, excitatory amino acids, reactive oxygen intermediates and other factors (Mrak and Griffin, 2005; Craft et al., 2006; Ralay Ranaivo et al., 2006; Zipp and Aktas, 2006).”

“In this sense, Bolmont et al. (2008) have recently demonstrated the internalization of A peptides by plaque-associated microglia and proposed an active role in the maintenance of plaque size.”

“This potential cytotoxic effect was further emphasized by clinical studies demonstrating that the symptoms of AD could be attenuated by nonsteroidal antiinflammatory drugs (Aisen, 2000; McGeer and McGeer, 2007).”

“According with previous reports in AD and AD models (Itagaki et al., 1988; Togo et al., 2002; Stalder et al., 2005) we observed CD3-cells in 18-month-old PS1xAPP hippocampus.”

“, 2007a,b) and enhanced A phagocytosis (Koenigsknecht-Talboo and Landreth, 2005).”

“In presence of IL-4, microglia produces growth factors (i.e., IGF-1) (Butovsky et al., 2006; Zhao et al., 2006).”

“However, recent trials have not confirmed this positive effect (Aisen et al., 2003; Reines et al., 2004).”

“Multiple in vitro reports have probed the influence of IL-4 in the development of a non-proinflammatory alternative phenotype (Iribarren et al., 2005; Butovsky et al., 2005; Ponomarev et al., 2007; Lyons et al., 2007a,b).”

“Activated inflammatory cells could mediate neuronal damage by producing toxic products, such as inflammatory cytokines, excitatory amino acids, reactive oxygen intermediates and other factors (Mrak and Griffin, 2005; Craft et al., 2006; Ralay Ranaivo et al., 2006; Zipp and Aktas, 2006).”

“form the ADDLs (Lambert et al., 2001), we diluted the 5 mM DMSO”

“Multiple in vitro reports have probed the influence of IL-4 in the development of a non-proinflammatory alternative phenotype (Iribarren et al., 2005; Butovsky et al., 2005; Ponomarev et al., 2007; Lyons et al., 2007a,b).”

“The observed 6E10-positive bands corresponded with the reported Mr for the oligomeric A forms, detected by Western blots (see Lambert et al., 2007), and also similar to soluble oligomers identified in other aged tg models (Lesné et al., 2006).”

“In this sense, vaccination against the A peptides led to activation of microglia and successfully decreased amyloid load (Wilcock et al., 2003, 2004a,b).”

“The neuronal toxicity to TNF- , TNF- related factors and iNOS has been extensively probed (Cantarella et al., 2003; Lee et al., 2004; Li et al., 2004; Medeiros et al., 2007; Uberti et al., 2007).”

“The generation and initial characterization of the PS1M146L (PS1) and PS1xAPP751sl (PS1xAPP) tg mice have been reported previously (Blanchard et al., 2003).”

“However, despite the age-dependent accumulation of extracellular A (Blanchard et al., 2003; Ramos et al., 2006; Caballero et al., 2007), no significant pyramidal degeneration was detected until 17–18 months of age (Schmitz et al., 2004; Ramos et al., 2006; unpublished results).”

“According with previous reports in AD and AD models (Itagaki et al., 1988; Togo et al., 2002; Stalder et al., 2005) we observed CD3-cells in 18-month-old PS1xAPP hippocampus.”

“Furthermore, the decrease in the early recruitment of the microglial cells, by genetic ablation of either TLR2 receptor, in a PS1/APP model (Richard et al., 2008) or CCR2 in Tg2576 (El Khoury et al., 2007), increased A 42 levels, accelerated memory impairments and increased vascular amyloid…”

“…reported that aging and/or A could decrease the neuronal expression of microglial inhibitory factors, such as CD200, fractalkine or neurotransmitters (Acetylcholine or noradrenaline) (Cardona et al., 2006; Chitnis et al., 2007; Heneka and O’Banion, 2007; Lyons et al., 2007a; Duan et al., 2008).”

“, 2006), as well as neuroprotective factors that may protect against AD pathology (Streit, 2005).”

“In this sense, vaccination against the A peptides led to activation of microglia and successfully decreased amyloid load (Wilcock et al., 2003, 2004a,b).”

“Neuroinflammation is a key feature of AD pathology (Meda et al., 2001; Dudal et al., 2004; Craft et al., 2006).”

“However, despite the age-dependent accumulation of extracellular A (Blanchard et al., 2003; Ramos et al., 2006; Caballero et al., 2007), no significant pyramidal degeneration was detected until 17–18 months of age (Schmitz et al., 2004; Ramos et al., 2006; unpublished results).”

“According with previous reports in AD and AD models (Itagaki et al., 1988; Togo et al., 2002; Stalder et al., 2005) we observed CD3-cells in 18-month-old PS1xAPP hippocampus.”

“Although SDS-PAGE is a reductive technique and as such cannot provide an accurate reflection of the noncovalently associated A oligomers (Hepler et al., 2006), the presence of the soluble oligomeric A forms was also assayed in Western blots using 6E10.”

“The neuronal toxicity to TNF- , TNF- related factors and iNOS has been extensively probed (Cantarella et al., 2003; Lee et al., 2004; Li et al., 2004; Medeiros et al., 2007; Uberti et al., 2007).”

“In presence of IL-4, microglia produces growth factors (i.e., IGF-1) (Butovsky et al., 2006; Zhao et al., 2006).”

“Similarly, stimulating the immune system with lypopolisaccharide (LPS) led to a reduction in A plaques (DiCarlo et al., 2001; Herber et al., 2004).”

“…reported that aging and/or A could decrease the neuronal expression of microglial inhibitory factors, such as CD200, fractalkine or neurotransmitters (Acetylcholine or noradrenaline) (Cardona et al., 2006; Chitnis et al., 2007; Heneka and O’Banion, 2007; Lyons et al., 2007a; Duan et al., 2008).”

“The neuronal toxicity to TNF- , TNF- related factors and iNOS has been extensively probed (Cantarella et al., 2003; Lee et al., 2004; Li et al., 2004; Medeiros et al., 2007; Uberti et al., 2007).”

“Activated inflammatory cells could mediate neuronal damage by producing toxic products, such as inflammatory cytokines, excitatory amino acids, reactive oxygen intermediates and other factors (Mrak and Griffin, 2005; Craft et al., 2006; Ralay Ranaivo et al., 2006; Zipp and Aktas, 2006).”

“Furthermore, damaged neurons could release microglial stimulants, such as ATP, UDP or CCL21 (de Jong et al., 2005; Inoue et al., 2007).”

“Neuroinflammation is a key feature of AD pathology (Meda et al., 2001; Dudal et al., 2004; Craft et al., 2006).”

“…reported that aging and/or A could decrease the neuronal expression of microglial inhibitory factors, such as CD200, fractalkine or neurotransmitters (Acetylcholine or noradrenaline) (Cardona et al., 2006; Chitnis et al., 2007; Heneka and O’Banion, 2007; Lyons et al., 2007a; Duan et al., 2008).”

“Neuroinflammation is a key feature of AD pathology (Meda et al., 2001; Dudal et al., 2004; Craft et al., 2006).”

“Furthermore, damaged neurons could release microglial stimulants, such as ATP, UDP or CCL21 (de Jong et al., 2005; Inoue et al., 2007).”

“The neuronal toxicity to TNF- , TNF- related factors and iNOS has been extensively probed (Cantarella et al., 2003; Lee et al., 2004; Li et al., 2004; Medeiros et al., 2007; Uberti et al., 2007).”

“The recruitment of CD4 Th1-cells in experimental autoimmune encephalomyelitis (EAE; a disease similar to human multiple sclerosis) induced the production of, among other cytotoxic factors, TNF- (Dhib-Jalbut et al., 2006; Weaver et al., 2007).”

“…reported that aging and/or A could decrease the neuronal expression of microglial inhibitory factors, such as CD200, fractalkine or neurotransmitters (Acetylcholine or noradrenaline) (Cardona et al., 2006; Chitnis et al., 2007; Heneka and O’Banion, 2007; Lyons et al., 2007a; Duan et al., 2008).”

“Western blots were performed as described previously (Araujo et al., 1996).”

“The neuronal toxicity to TNF- , TNF- related factors and iNOS has been extensively probed (Cantarella et al., 2003; Lee et al., 2004; Li et al., 2004; Medeiros et al., 2007; Uberti et al., 2007).”

“Multiple in vitro reports have probed the influence of IL-4 in the development of a non-proinflammatory alternative phenotype (Iribarren et al., 2005; Butovsky et al., 2005; Ponomarev et al., 2007; Lyons et al., 2007a,b).”

“The induction of iNOS expression by astrocytes, because of TNF- and/or TRAIL, has been previously reported (Akama and Van Eldik, 2000; Cantarella et al., 2008).”

“This potential cytotoxic effect was further emphasized by clinical studies demonstrating that the symptoms of AD could be attenuated by nonsteroidal antiinflammatory drugs (Aisen, 2000; McGeer and McGeer, 2007).”

“However, despite the age-dependent accumulation of extracellular A (Blanchard et al., 2003; Ramos et al., 2006; Caballero et al., 2007), no significant pyramidal degeneration was detected until 17–18 months of age (Schmitz et al., 2004; Ramos et al., 2006; unpublished results).”

“However, recent trials have not confirmed this positive effect (Aisen et al., 2003; Reines et al., 2004).”

“With aging, A β - depositing mice increase in the expression of alternative activation state genes and deactivation state genes at the expense of classical activation state genes 220 , however see also 221 .”

“seems to maintain even at relative old ages, suggesting that activated microglia surrounding Aβ plaques adopted an alternative phenotype, regardless of the age [92].”

“[132] observed at 6 months, when Aβ begins to accumulate in the APP/ PS1 Alzheimer’s disease mouse model, that there were YM1 cells present in the CNS; however, by 18 months YM1 mRNA levels decreased and there was a massive upregulation in inflammatory factors, suggesting a switch from M2 to M1 as pathology worsened […”

“phenotypes can shift from M2-type to more M1-like with advancing age in AD transgenics (Jimenez et al., 2008) it is clear that microglia are not operating in a fully M1”

“And still others have seen no significant age-related differences in microglial activation phenotypes when studied in the absence of any pathological insults [105,111].”

“For example, aging itself triggers differential activation in microglia isolated from the APP/PS1 transgenic mouse model (54, 67).”

“During aging, M1 activation, but not M2 activation, can be further enhanced (48).”

“The ability of fibrillar Ab to trigger an inflammatory response is phenocopied in murine AD models that recapitulate Ab plaque formation (e.g. Matsuoka et al. 2001; Jimenez et al. 2008).”

“Recently, Jimenez (Jimenez et al., 2008) shows evidence of a switch in the activated microglia phenotype from alternative, at the beginning of Aβ pathology, to a classical at advanced stage of the disease in amicemodel of AD.”

“A oligomers have been demonstrated to cause these pathological changes in vitro when applied exogenously to cultured cells and brain slices (Hu et al., 1998; Lambert et al., 1998; Kayed et al., 2003; De Felice et al., 2008; Jimenez et al., 2008).”

“These include genes that repair damage to the extracellular matrix, such as arginase 1 (ARG1) (Gomi et al. 2011; Jimenez et al. 2008), mannose receptor (Akiyama et al. 2000), found in inflammatory zone 1, and chitinase 3-like 3 (YM1) (Colton et al. 2006a; Raes et al. 2002).”

“[128] described an age-dependent switch in microglial activation in the hippocampus of the APP/PS1 mouse model.”

“While M2 gene expression has been detected in the AD brain, little is known about the mechanisms modulating this phenotypic conversion (Colton et al., 2006; Jimenez et al., 2008; Maier et al., 2008).”

“In addition, an increased risk of AD has been associated with several polymorphisms of pro-inflammatory genes, including IL-1 (Nicoll et al., 2000), IL-6 (Capurso et al., 2004), TNF-α (McCusker et al., 2001; Perry et al., 2001), and α1-antichymotrypsin (Kamboh et al., 1995).”

“This is reminiscent of the establishment of an alternative macrophage M2 phenotype, albeit incomplete, described in PS1/APP mice where such plaque-associated microglia were shown to have beneficial phagocytic capabilities (22).”

“Jimenez et al. (2008) characterized age-dependent alteration of microglia phenotypes in the hippocampus of double PS1xAPP transgenic AD mice [260].”

“Recently, these finding have been supported by studies indicating that microglia change from alternative to classical phenotype over time (Colton et al., 2006; Hickman et al., 2008; Jimenez et al., 2008; Lucin and Wyss-Coray, 2009).”

“However, recent evidence has suggested that there is an age-related switch in microglial function in the hippocampus of APP × PS1 transgenic mice from a phagocytic function to a more cytotoxic function which coincided with increased expression of Aβ42 [131].”

“Interestingly, NLRP3 is a modulator of IL-1β, a proinflammatory cytokine which production is also stimulated by the presence of Aβ plaques, together with other inflammatory markers, including IL-6 and tumor necrosis factor alpha (TNF-α; Jekabsone et al., 2006; Jimenez et al., 2008).”

“Noteworthy, in Alzheimer's disease and in the elderly brain an imbalance of pro- and antiinflammatory microglia phenotypes have been reported (Hoozemans et al., 2006; Jimenez et al., 2008).”

“Although microglia express markers for both classical and alternative activation in AD [23], there seems to be a consensus that during the course of disease, similar to normal aging, microglia undergo a switch from a neuroprotective to a more classically activated phenotype at later stages of disease [69, 151].”

“This raises questions regarding how particular M2 activation state markers are regulated by proinflammatory stimuli and why RNA and protein levels of YM1 are increased in AD patients and animal models of amyloid deposition, which are typically considered to be associated with a proinflammatory (M1) cytokine environmen…”

“One study observed the exisence of an age-dependant phenotypic change of microglial ctivation in the hippocampus of an AD mouse model, from n alternative (expressing IL-4) activation state to a classic ytotoxic (expressing IL-1 and TNF- ) phenotype (Jimenez et al., 2008).”

“The increase of microglia number is typically observed in postmortem AD brains(90) and in AD preclinical models.(88,89,91) In our study, the presence of EVs”

“It was shown that microglia undergo a switch from a neuroprotective M2 to a more classically activated phenotype in the later stages of AD [131] [132].”

“Interestingly, a recent study demonstrated an agedependent phenotypic change of MG/MΦ activation in the hippocampus of AD transgenic (PS1M146L/APP751SL) mice from an M2 activation state with Aβ phagocytic capabilities to a M1 and neurotoxic phenotype, which promoted high levels of soluble Aβ oligomers and significant…”

“Similarly in a model of AD immune cell infiltration and localization of microglial populations in areas of amyloid β (Aβ) plaque deposits has been observed (69, 70).”

“We and others (Jimenez et al., 2008; Heneka et al., 2015) have previously described that this extensive Aβ accumulation was accompanied by intense local microglial activation (see Figures 1A,B).”

“The A11 or 6E10 immunoprecipitation experiments were also performed as described in detail previously [29, 30].”

“alternative activation state with Ab phagocytic capabilities to a classical cytotoxic phenotype, which promotes high levels of soluble Ab oligomers and significant pyramidal neurodegeneration (Jimenez et al. 2008).”

“activated microglia phenotypes occurs between the beginning of Aβ pathology (alternative phenotype) and advanced stages (classical phenotype), the latter of which may cause disease-associated neuron loss [57].”

“…of both the transgenic APP/PS1 model and Alzheimer’s patients (Braak V–VI) displays significant astrogliosis (measured by GFAP expression and by the area covered by the reactive astrocytes; see also Jimenez et al., 2008), which progresses in parallel to the extracellular amyloid pathology.”

“Activatedmicroglia can be neurotoxic or neuroprotective depending on the conditions, including the nature of any stimuli, degree of stimulation, spatiotemporal distribution, and age of the subject (Jimenez et al., 2008; Wu et al., 2008b; Nakanishi and Wu, 2009; Sawada, 2009).”

“The immune responses are altered and become dysfunctional during aging.(55) Therefore, infectious agents may not be as detrimental in young individuals when the immune responses can be properly regulated, but this becomes more deleterious in older individuals.”

“However, analysis of two alternative “M2” microglial phenotype markers, Ym-1 and Arg, that have been recently reported as potential markers for enhanced microglia-mediated Ab phagocytosis (40, 41) showed that these were unchanged in mIFN-g–expressing”

“PPARγ activation is positively related to ameliorating experimental autoimmune encephalomyelitis (EAE) in mice [28] and reducing amyloid deposition along with improving cognitive function in Alzheimer’s disease models [29].”

“This Aβ-induced inflammatory environment [126], combined with effect of immunosenescence on microglia [127,128], lead to a situation in which microglia that initially exhibited a neuroprotective M2 phenotype at the beginning of AD [129], become confined to a classical activated state (i.”

“However, in APP/PS1 transgenic mouse model, aging significantly influences the activation status of microglia, suggesting that it may exacerbate the progression of AD-related neuropathology [159].”

“Nevertheless, recent findings from in vitro cultures of the murine microglial cell line MMGT12 [23] and hippocampal microglia from the PS1xAPP Alzheimer’s mouse model [24] implicate that microglia have the ability to differentiate into M1 and M2 polarized phenotypes.”

“…the association of Ab oligomers with AVs in AD brains, we utilized the well-characterized A11 antibody that only recognizes soluble Ab oligomers, but not APP and its cleaved products C99, soluble monomer, or insoluble fibrils (Jimenez et al., 2008, 2011; Kayed et al., 2003; Zempel et al., 2010).”

“Microglia play a key role in the neuroinflammation associated with many neurodegenerative, ischemic, and traumatic disorders [4-12].”

“We found consistent results with those determined at the mRNA level for increased expression of IL-1b, TNF-a, CCL-3, and iNOS (Hickman et al., 2008; Jimenez et al., 2008; Minogue et al., 2014; Babcock et al., 2015), but we observed differences for IL-4, IL-10, and CD36 previously shown to be decreased (Hickman et al.”

“In agreement with this notion, a prior study has demonstrated that wild type microglia undergo an increase in mRNA levels of YM-1, an alternative activation marker, from 6 to 18 months of age while a transgenic AD line expressing human mutant APP and PS1 demonstrated significantly higher levels of YM-1 mRNA compared t…”

“Primary murine microglial or astroglial cultures were performed as previously described [22].”

“…illustrated that APP/PS1 mice, a transgenic mouse model of AD, shift from an M2 profile early on in the disease towards an M1 response after 18 months of pathogenesis, which is concomitant with a downregulation of the M2 marker Ym1 and upregulation of inflammatory factors (Jimenez et al., 2008).”

“However, evidence from transgenic Alzheimer’s disease mice suggests that a phenotypic shift from M2 to M1 microglia occurs in models of prolonged neuroinflammation potentially aggravating neuronal degeneration with increasing age [46].”

“This would be consistent with numerous in vitro studies such as those detailed earlier, as well as others showing that exogenously applied A oligomers activate astrocytes [106] and microglia [107], impair axonal transport [83], and cause selective neuronal death ([12]; see review by Ferreira and Klein [22]).”

“An age-dependent phenotypic shift from M2 to M1-like microglia might occur in mouse models of AD, such as APP/PS1, owing to accumulation of soluble Ab oligomers and neuronal loss (Jimenez et al., 2008).”

“inflammatory diseases, such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, traumatic brain injury and stroke (Hu et al., 2012; Jimenez et al., 2008; Perry et al., 2010), and the incidence and development of these diseases also accompanied”

“Interestingly CD3þ cells have been identified in brain tissue prepared from 18-month-old, but not 6-month-old, APP/PS1 mice (Jimenez et al., 2008).”

“It seems that, as AD progresses, microglia change toward a pro-inflammatory phenotype and lose their Ab-clearing activities, resulting in reduced Ab uptake and degradation (Jimenez et al. 2008).”

“Depending on the type of insult, the phenotype of microglial activation switches over time from M1 to M2 or vice versa (111).”

“In AD, microglia surrounding and infiltrating the Aβ plaques are generally activated as YM-1 positive M2 phenotype (Jimenez et al., 2008).”

“Therefore, whether activated microglia exert a neurotoxic or a neuroprotective effect may depend on their environment, the spatiotemporal distribution of the microglia themselves, and the type and magnitude of stimuli (Jimenez et al., 2008; Wu et al., 2008; Nakanishi and Wu, 2009; Sawada, 2009).”

“Recently, soluble oligomers of Aβ have been suggested as potent stimulators of microglial activation (Hashioka et al., 2005; Jimenez et al., 2008), although most studies have considered fAβ to be a more powerful stimulus (McDonald et al., 1997; Combs et al., 2001).”

“At an early age (4–6 months), activated microglia are restricted to amyloid deposits and characterized by the absence of cytotoxic factors (Jimenez et al. 2008).”

“In AD patients, the alternative activation of microglia appears to be inhibited favoring classical activation [85].”

“inflammatory molecules [33, 34] and increasing Aβ phagocytosis.”

“Although recent evidence has indicated that microglia surrounding Ab deposits in APP/PS1 mice may be alternatively activated and those distal to the deposits are classically activated in older animals (Jimenez et al., 2008), the effect of activation state on the capacity of microglia to phagocytose Ab remains to be cl…”