Efficacy of Chronic Paroxetine Treatment in Mitigating Amyloid Pathology and Microgliosis in APPSWE/PS1ΔE9 Transgenic Mice.

BACKGROUND: Modulation of serotonergic signaling by treatment with selective serotonin reuptake inhibitors (SSRIs) has been suggested to mitigate amyloid-ß (Aß) pathology in Alzheimer's disease, in addition to exerting an anti-depressant action. OBJECTIVE: To investigate the efficacy of chronic treatment with the SSRI paroxetine, in mitigating Aß pathology and Aß plaque-induced microgliosis in the hippocampus of 18-month-old APPswe/PS1ΔE9 mice. METHODS: Plaque-bearing APPswe/PS1ΔE9 and wildtype mice were treated with paroxetine per os at a dose of 5 mg/kg/day, from 9 to 18 months of age. The per os treatment was monitored by recording of the body weights and serum paroxetine concentrations, and by assessment of the serotonin transporter occupancy by [3H]DASB-binding in wildtype mice. Additionally, 5,7-dihydroxytryptamine was administered to 9-month-old APPswe/PS1ΔE9 mice, to examine the effect of serotonin depletion on Aß pathology. Aß pathology was evaluated by Aß plaque load estimation and the Aß42/Aß40 ratio by ELISA. RESULTS: Paroxetine treatment led to > 80% serotonin transporter occupancy. The treatment increased the body weight of wildtype mice, but not of APPswe/PS1ΔE9 mice. The treatment had no effect on the Aß plaque load (p = 0.39), the number and size of plaques, or the Aß plaque-induced increases in microglial numbers in the dentate gyrus. Three months of serotonin depletion did not significantly impact the Aß plaque load or Aß42/Aß40 ratio in APPswe/PS1ΔE9 mice at 12 months. CONCLUSION: Our results show that chronic treatment with the SSRI paroxetine does not mitigate Aß pathology and Aß plaque-induced microgliosis in the hippocampus of APPswe/PS1ΔE9 mice.

The Combined Effects of Amyloidosis and Serotonin Deficiency by Tryptophan Hydroxylase-2 Knockout Impacts Viability of the APP/PS1 Mouse Model of Alzheimer's Disease.

BACKGROUND: A decline of brain serotonin (5-HT) is held responsible for the changes in mood that can be observed in Alzheimer's disease (AD). However, 5-HT'ergic signaling is also suggested to reduce the production of pathogenic amyloid-ß (Aß). OBJECTIVE: To investigate the effect of targeted inactivation of tryptophan hydroxylase-2 (Tph2), which is essential for neuronal 5-HT synthesis, on amyloidosis in amyloid precursor protein (APP)swe/presenilin 1 (PS1) ΔE9 transgenic mice. METHODS: Triple-transgenic (3xTg) APP/PS1 mice with partial (+/-) or complete Tph2 knockout (-/-) were allowed to survive until 6 months old with APP/PS1, Tph2-/-, and wildtype mice. Survival and weight were recorded. Levels of Aß42/40/38, soluble APPα (sAßPPα) and sAßPPß, and cytokines were analyzed by mesoscale, neurotransmitters by mass spectrometry, and gene expression by quantitative PCR. Tph2, microglia, and Aß were visualized histologically. RESULTS: Tph2 inactivation in APP/PS1 mice significantly reduced viability, without impacting soluble and insoluble Aß42 and Aß40 in neocortex and hippocampus, and with only mild changes of soluble Aß42/Aß40. However, sAßPPα and sAßPPß in hippocampus and Aß38 and Aß40 in cerebrospinal fluid were reduced. 3xTg-/-mice were devoid of Tph2 immunopositive fibers and 5-HT. Cytokines were unaffected by genotype, as were neocortical TNF, HTR2a and HTR2b mRNA levels in Tph2-/- mice. Microglia clustered around Aß plaques regardless of genotype. CONCLUSION: The results suggest that Tph2 inactivation influences AßPP processing, at least in the hippocampus, although levels of Aß are unchanged. The reduced viability of 3xTg-/-mice could indicate that 5-HT protects against the seizures that can impact the viability of APP/PS1 mice.

Bone Marrow-Derived IL-1Ra Increases TNF Levels Poststroke.

Tumor necrosis factor (TNF) and interleukin-1 receptor antagonist (IL-1Ra) are key players in stroke, a disease in which cell-based therapies have shown great potential. Having shown an infarct-reducing effect of bone marrow (BM) cells, especially cells with high IL-1Ra expression, we here investigated the effect of BM cells on TNF and other stroke-related mediators in mice after transient middle cerebral artery occlusion (tMCAo) and in vitro using adult microglial cultures. We analyzed stroke-related genes and inflammatory mediators using qPCR stroke Tier panels, electrochemiluminescence, or enzyme-linked immunosorbent assays. We found a significant correlation and cellular colocalization between microglial-derived TNF and IL-1Ra, though IL-1Ra production was TNF independent. BM treatment significantly increased TNF, interleukin (IL)-10, and IL-4 levels, while C-X-C motif ligand 1 (CXCL1), IL-12p70, and Toll-like receptor 2 (TLR2) decreased, suggesting that BM treatment favors an anti-inflammatory environment. Hierarchical clustering identified Tnf and IL-1rn within the same gene cluster, and subsequent STRING analysis identified TLR2 as a shared receptor. Although IL-1Ra producing BM cells specifically modulated TNF levels, this was TLR2 independent. These results demonstrate BM cells as modulators of poststroke inflammation with beneficial effects on poststroke outcomes and place TNF and IL-1Ra as key players of the defense response after tMCAo.

Diverse Protein Profiles in CNS Myeloid Cells and CNS Tissue From Lipopolysaccharide- and Vehicle-Injected APPSWE/PS1ΔE9 Transgenic Mice Implicate Cathepsin Z in Alzheimer's Disease.

Neuroinflammation, characterized by chronic activation of the myeloid-derived microglia, is a hallmark of Alzheimer's disease (AD). Systemic inflammation, typically resulting from infection, has been linked to the progression of AD due to exacerbation of the chronic microglial reaction. However, the mechanism and the consequences of this exacerbation are largely unknown. Here, we mimicked systemic inflammation in AD with weekly intraperitoneal (i.p.) injections of APPSWE/PS1ΔE9 transgenic mice with E. coli lipopolysaccharide (LPS) from 9 to 12 months of age, corresponding to the period with the steepest increase in amyloid pathology. We found that the repeated LPS injections ameliorated amyloid pathology in the neocortex while increasing the neuroinflammatory reaction. To elucidate mechanisms, we analyzed the proteome of the hippocampus from the same mice as well as in unique samples of CNS myeloid cells. The repeated LPS injections stimulated protein pathways of the complement system, retinoid receptor activation and oxidative stress. CNS myeloid cells from transgenic mice showed enrichment in pathways of amyloid-beta clearance and elevated levels of the lysosomal protease cathepsin Z, as well as amyloid precursor protein, apolipoprotein E and clusterin. These proteins were found elevated in the proteome of both LPS and vehicle injected transgenics, and co-localized to CD11b+ microglia in transgenic mice and in primary murine microglia. Additionally, cathepsin Z, amyloid precursor protein, and apolipoprotein E appeared associated with amyloid plaques in neocortex of AD cases. Interestingly, cathepsin Z was expressed in microglial-like cells and co-localized to CD68+ microglial lysosomes in AD cases, and it was expressed in perivascular cells in AD and control cases. Taken together, our results implicate systemic LPS administration in ameliorating amyloid pathology in early-to-mid stage disease in the APPSWE/PS1ΔE9 mouse and attract attention to the potential disease involvement of cathepsin Z expressed in CNS myeloid cells in AD.

Serotonin augmentation therapy by escitalopram has minimal effects on amyloid-ß levels in early-stage Alzheimer's-like disease in mice.

BACKGROUND: Dysfunction of the serotonergic (5-HTergic) system has been implicated in the cognitive and behavioural symptoms of Alzheimer's disease (AD). Accumulation of toxic amyloid-ß (Aß) species is a hallmark of AD and an instigator of pathology. Serotonin (5-HT) augmentation therapy by treatment with selective serotonin reuptake inhibitors (SSRIs) in patients with AD has had mixed success in improving cognitive function, whereas SSRI administration to mice with AD-like disease has been shown to reduce Aß pathology. The objective of this study was to investigate whether an increase in extracellular levels of 5-HT induced by chronic SSRI treatment reduces Aß pathology and whether 5-HTergic deafferentation of the cerebral cortex could worsen Aß pathology in the APPswe/PS1ΔE9 (APP/PS1) mouse model of AD. METHODS: We administered a therapeutic dose of the SSRI escitalopram (5 mg/kg/day) in the drinking water of 3-month-old APP/PS1 mice to increase levels of 5-HT, and we performed intracerebroventricular injections of the neurotoxin 5,7-dihydroxytryptamine (DHT) to remove 5-HTergic afferents. We validated the effectiveness of these interventions by serotonin transporter autoradiography (neocortex 79.7 ± 7.6%) and by high-performance liquid chromatography for 5-HT (neocortex 64% reduction). After 6 months of escitalopram treatment or housing after DHT-induced lesion, we evaluated brain tissue by mesoscale multiplex analysis and sections by IHC analysis. RESULTS: Amyloid-ß-containing plaques had formed in the neocortex and hippocampus of 9-month-old APP/PS1 mice after 6 months of escitalopram treatment and 5-HTergic deafferentation. Unexpectedly, levels of insoluble Aß42 were unaffected in the neocortex and hippocampus after both types of interventions. Levels of insoluble Aß40 increased in the neocortex of SSRI-treated mice compared with those treated with vehicle control, but they were unaffected in the hippocampus. 5-HTergic deafferentation was without effect on the levels of insoluble/soluble Aß42 and Aß40 in both the neocortex and hippocampus. However, levels of soluble amyloid precursor protein α were reduced in the neocortex after 5-HTergic deafferentation. CONCLUSIONS: Because this study shows that modulation of the 5-HTergic system has either no effect or increases levels of insoluble/soluble Aß42 and Aß40 in the cerebral cortex of APP/PS1 mice, our observations do not support 5-HT augmentation therapy as a preventive strategy for reducing Aß pathology.

Cell therapy centered on IL-1Ra is neuroprotective in experimental stroke.

Cell-based therapies are emerging as new promising treatments in stroke. However, their functional mechanism and therapeutic potential during early infarct maturation has so far received little attention. Here, we asked if cell-based delivery of the interleukin-1 receptor antagonist (IL-1Ra), a known neuroprotectant in stroke, can promote neuroprotection, by modulating the detrimental inflammatory response in the tissue at risk. We show by the use of IL-1Ra-overexpressing and IL-1Ra-deficient mice that IL-1Ra is neuroprotective in stroke. Characterization of the cellular and spatiotemporal production of IL-1Ra and IL-1α/ß identifies microglia, not infiltrating leukocytes, as the major sources of IL-1Ra after experimental stroke, and shows IL-1Ra and IL-1ß to be produced by segregated subsets of microglia with a small proportion of these cells co-expressing IL-1α. Reconstitution of whole body irradiated mice with IL-1Ra-producing bone marrow cells is associated with neuroprotection and recruitment of IL-1Ra-producing leukocytes after stroke. Neuroprotection is also achieved by therapeutic injection of IL-1Ra-producing bone marrow cells 30 min after stroke onset, additionally improving the functional outcome in two different stroke models. The IL-1Ra-producing bone marrow cells increase the number of IL-1Ra-producing microglia, reduce the availability of IL-1ß, and modulate mitogen-activated protein kinase (MAPK) signaling in the ischemic cortex. The importance of these results is underlined by demonstration of IL-1Ra-producing cells in the human cortex early after ischemic stroke. Taken together, our results attribute distinct neuroprotective or neurotoxic functions to segregated subsets of microglia and suggest that treatment strategies increasing the production of IL-1Ra by infiltrating leukocytes or microglia may also be neuroprotective if applied early after stroke onset in patients.