Pharmacologic Manipulation of Complement Receptor 3 Prevents Dendritic Spine Loss and Cognitive Impairment After Acute Cranial Radiation

PURPOSE

Cranial irradiation induces healthy tissue damage that can lead to neurocognitive complications, negatively affecting patient quality of life. One damage indicator associated with cognitive impairment is loss of neuronal spine density. We previously demonstrated that irradiation-mediated spine loss is microglial complement receptor 3 (CR3) and sex dependent. We hypothesized that these changes are associated with late-delayed cognitive deficits and amenable to pharmacologic intervention.

METHODS AND MATERIALS

Our model of cranial irradiation (acute, 10 Gy gamma) used male and female CR3-wild type and CR3-deficient Thy-1 YFP mice of C57BL/6 background. Forty-five days after irradiation and behavioral testing, we quantified spine density and markers of microglial reactivity in the hippocampal dentate gyrus. In a separate experiment, male Thy-1 YFP C57BL/6 mice were treated with leukadherin-1, a modulator of CR3 function.

RESULTS

We found that male mice demonstrate irradiation-mediated spine loss and cognitive deficits but that female and CR3 knockout mice do not. These changes were associated with greater reactivity of microglia in male mice. Pharmacologic manipulation of CR3 with LA1 prevented spine loss and cognitive deficits in irradiated male mice.

CONCLUSIONS

This work improves our understanding of irradiation-mediated mechanisms and sex dependent responses and may help identify novel therapeutics to reduce irradiation-induced cognitive decline and improve patient quality of life.

Inconsistent Effects of Glatiramer Acetate Treatment in the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that involves strong inflammatory components. Aberrant and prolonged inflammation in the CNS is thought to contribute to the development of the pathology. The use of single cytokine approaches to curb or leverage inflammatory mechanisms for disease modifying benefit has often resulted in conflicting data. Furthermore, these treatments were usually delivered locally into the CNS parenchyma, complicating translational efforts. To overcome these hurdles, we tested the use of glatiramer acetate (GA) in reducing amyloid beta (Aβ) plaque pathology in the 5xFAD model of AD. GA immunizations were begun at the ages of 2.5 months, 5.5 months, and 8.5 months, and GA was delivered weekly for 8 weeks. While previous data describe potential benefits of GA immunization in decreasing Aβ levels in murine models of AD, we found modest decreases in Aβ levels if given during the development of pathology but, surprisingly, found increased Aβ levels if GA was administered at later stages. The impact of GA treatment was only significant for female mice. Furthermore, we observed no changes between microglial uptake of plaque, CD11c immunopositivity of microglia, or levels of TMEM119 and P2Ry12 on microglia. Overall, these data warrant exercising caution when aiming to repurpose GA for AD.

Gas6 induces inflammation and reduces plaque burden but worsens behavior in a sex-dependent manner in the APP/PS1 model of Alzheimer's disease

BACKGROUND

Alzheimer's disease is the leading cause of dementia worldwide. TAM receptor tyrosine kinases (Tyro3, Axl, MerTK) are known for their role in engagement of phagocytosis and modulation of inflammation, and recent evidence suggests a complex relationship between Axl, Mer, and microglial phagocytosis of amyloid plaques in AD. Gas6, the primary CNS TAM ligand, reduces neuroinflammation and improves outcomes in murine models of CNS disease. Therefore, we hypothesized that AAV-mediated overexpression of Gas6 would alleviate plaque pathology, reduce neuroinflammation, and improve behavior in the APP/PS1 model of Alzheimer's disease.

METHODS

Adeno-associated viral vectors were used to overexpress Gas6 in the APP/PS1 model of Alzheimer's disease. Nine-month-old male and female APP/PS1 and nontransgenic littermates received bilateral stereotactic hippocampal injections of AAV-Gas6 or AAV-control, which expresses a non-functional Gas6 protein. One month after injections, mice underwent a battery of behavioral tasks to assess cognitive function and brains were processed for immunohistochemical and transcriptional analyses.

RESULTS

Gas6 overexpression reduced plaque burden in male APP/PS1 mice. However, contrary to our hypothesis, Gas6 increased pro-inflammatory microglial gene expression and worsened contextual fear conditioning compared to control-treated mice. Gas6 overexpression appeared to have no effect on phagocytic mechanisms in vitro or in vivo as measured by CD68 immunohistochemistry, microglial methoxy-04 uptake, and primary microglial uptake of fluorescent fibrillar amyloid beta.

CONCLUSION

Our data describes a triad of worsened behavior, reduced plaque number, and an increase in proinflammatory signaling in a sex-specific manner. While Gas6 has historically induced anti-inflammatory signatures in the peripheral nervous system, our data suggest an alternative, proinflammatory role in the context of Alzheimer's disease pathology.

Evaluating Effects of Glatiramer Acetate Treatment on Amyloid Deposition and Tau Phosphorylation in the 3xTg Mouse Model of Alzheimer's Disease

Neuroinflammation driven by the accumulation of amyloid β (Aβ) can lead to neurofibrillary tangle formation in Alzheimer's Disease (AD). To test the hypothesis that an anti-inflammatory immunomodulatory agent might have beneficial effects on amyloid and tau pathology, as well as microglial phenotype, we evaluated glatiramer acetate (GA), a multiple sclerosis drug thought to bias type 2 helper T (T_h2) cell responses and alternatively activate myeloid cells. We administered weekly subcutaneous injections of GA or PBS to 15-month-old 3xTg AD mice, which develop both amyloid and tau pathology, for a period of 8 weeks. We found that subcutaneous administration of GA improved behavioral performance in novel object recognition and decreased Aβ plaque in the 3xTg AD mice. Changes in tau phosphorylation were mixed with specific changes in phosphoepitopes seen in immunohistochemistry but not observed in western blot. In addition, we found that there was a trend toward increased microglia complexity in 3xTg mice treated with GA, suggesting a shift toward homeostasis. These findings correlated with subtle changes in the microglial transcriptome, in which the most striking difference was the upregulation of Dcstamp. Lastly, we found no evidence of changes in proportions of major helper T cell (T_h) subtypes in the periphery. Overall, our study provides further evidence for the benefits of immunomodulatory therapies that alter the adaptive immune system with the goal of modifying microglia responses for the treatment of Alzheimer's Disease.

Space radiation does not alter amyloid or tau pathology in the 3xTg mouse model of Alzheimer's disease

Space radiation is comprised of highly charged ions (HZE particles) and protons that are able to pass through matter and cause radiation-induced injury, including neuronal damage and degeneration, glial activation, and oxidative stress. Previous work demonstrated a worsening of Alzheimer's disease pathology in the APP/PS1 transgenic mouse model, however effects of space radiation on tau pathology have not been studied. To determine whether tau pathology is altered by HZE particle or proton irradiation, we exposed 3xTg mice, which acquire both amyloid plaque and tau pathology with age, to iron, silicon, or solar particle event (SPE) irradiation at 9 months of age and evaluated behavior and brain pathology at 16 months of age. We found no differences in performance in fear conditioning and novel object recognition tasks between groups of mice exposed to sham, iron (10 and 100 cGy), silicon (10 and 100 cGy), or solar particle event radiation (200 cGy), though female mice had higher freezing responses than males. 200 cGy SPE irradiated female mice had fewer plaques than sham-irradiated females but had no differences in tau pathology. Overall, females had worse amyloid and tau pathology at 16 months of age and demonstrated a reduced neuroinflammatory gene expression response to radiation. These findings uncover differences between mouse models following radiation injury and corroborate prior reports of sex differences within the 3xTg mouse model.

Evaluating the Effect of Interleukin-4 in the 3xTg Mouse Model of Alzheimer's Disease

Chronic neuroinflammation has long been hypothesized to be involved in Alzheimer's Disease (AD) progression. Previous research suggests that both anti-inflammatory and inflammatory microglia ameliorate amyloid pathology, but the latter worsen tau pathology. In this study, we sought to determine whether induction of arginase-1 positive microglia with the anti-inflammatory cytokine IL-4 modulates pathology in the 3xTg mouse model of AD. Our findings indicate that a single intracranial IL-4 injection positively modulated performance of 3xTg AD mice in a Novel Object Recognition task, and locally increased the levels of arginase-1 positive myeloid cells when assessed one-week post injection. Furthermore, immunohistochemical analysis revealed decreased tau phosphorylation in IL-4 injected animals; however, we were not able to detect significant changes in tau phosphorylation utilizing Western blot. Lastly, IL-4 injection did not appear to cause significant changes in amyloid β load. In conclusion, acute intracranial IL-4 led to some positive benefits in the 3xTg mouse model of AD. Although more work remains, these results support therapeutic strategies aimed at modifying microglial activation states in neurodegenerative diseases.

Cranial irradiation mediated spine loss is sex-specific and complement receptor-3 dependent in male mice

Cranial irradiation is the main therapeutic treatment for primary and metastatic malignancies in the brain. However, cranial radiation therapy produces long-term impairment in memory, information processing, and attention that contribute to a decline in quality of life. The hippocampal neural network is fundamental for proper storage and retrieval of episodic and spatial memories, suggesting that hippocampal signaling dysfunction could be responsible for the progressive memory deficits observed following irradiation. Previous rodent studies demonstrated that irradiation induces significant loss in dendritic spine number, alters spine morphology, and is associated with behavioral task deficits. Additionally, the literature suggests a common mechanism in which synaptic elimination via microglial-mediated phagocytosis is complement dependent and associated with cognitive impairment in aging as well as disease. We demonstrate sexual dimorphisms in irradiation-mediated alterations of microglia activation markers and dendritic spine density. Further, we find that the significant dendritic spine loss observed in male mice following irradiation is microglia complement receptor 3 (CR3)-dependent. By identifying sex-dependent cellular and molecular factors underlying irradiation-mediated spine loss, therapies can be developed to counteract irradiation-induced cognitive decline and improve patient quality of life.

IL-1β-driven amyloid plaque clearance is associated with an expansion of transcriptionally reprogrammed microglia

BACKGROUND

Neuroinflammation is thought to contribute to the pathogenesis of Alzheimer's disease (AD), yet numerous studies have demonstrated a beneficial role for neuroinflammation in amyloid plaque clearance. We have previously shown that sustained expression of IL-1β in the hippocampus of APP/PS1 mice decreases amyloid plaque burden independent of recruited CCR2+ myeloid cells, suggesting resident microglia as the main phagocytic effectors of IL-1β-induced plaque clearance. To date, however, the mechanisms of IL-1β-induced plaque clearance remain poorly understood.

METHODS

To determine whether microglia are involved in IL-1β-induced plaque clearance, APP/PS1 mice induced to express mature human IL-1β in the hippocampus via adenoviral transduction were treated with the Aβ fluorescent probe methoxy-X04 (MX04) and microglial internalization of fibrillar Aβ (fAβ) was analyzed by flow cytometry and immunohistochemistry. To assess microglial proliferation, APP/PS1 mice transduced with IL-1β or control were injected intraperitoneally with BrdU and hippocampal tissue was analyzed by flow cytometry. RNAseq analysis was conducted on microglia FACS sorted from the hippocampus of control or IL-1β-treated APP/PS1 mice. These microglia were also sorted based on MX04 labeling (MX04+ and MX04- microglia).

RESULTS

Resident microglia (CD45loCD11b+) constituted > 70% of the MX04+ cells in both Phe- and IL-1β-treated conditions, and < 15% of MX04+ cells were recruited myeloid cells (CD45hiCD11b+). However, IL-1β treatment did not augment the percentage of MX04+ microglia nor the quantity of fAβ internalized by individual microglia. Instead, IL-1β increased the total number of MX04+ microglia in the hippocampus due to IL-1β-induced proliferation. In addition, transcriptomic analyses revealed that IL-1β treatment was associated with large-scale changes in the expression of genes related to immune responses, proliferation, and cytokine signaling.

CONCLUSIONS

These studies show that IL-1β overexpression early in amyloid pathogenesis induces a change in the microglial gene expression profile and an expansion of microglial cells that facilitates Aβ plaque clearance.

Exploiting microglial and peripheral immune cell crosstalk to treat Alzheimer's disease

Neuroinflammation is considered one of the cardinal features of Alzheimer’s disease (AD). Neuritic plaques composed of amyloid β and neurofibrillary tangle-laden neurons are surrounded by reactive astrocytes and microglia. Exposure of microglia, the resident myeloid cell of the CNS, to amyloid β causes these cells to acquire an inflammatory phenotype. While these reactive microglia are important to contain and phagocytose amyloid plaques, their activated phenotype impacts CNS homeostasis. In rodent models, increased neuroinflammation promoted by overexpression of proinflammatory cytokines can cause an increase in hyperphosphorylated tau and a decrease in hippocampal function. The peripheral immune system can also play a detrimental or beneficial role in CNS inflammation. Systemic inflammation can increase the risk of developing AD dementia, and chemokines released directly by microglia or indirectly by endothelial cells can attract monocytes and T lymphocytes to the CNS. These peripheral immune cells can aid in amyloid β clearance or modulate microglia responses, depending on the cell type. As such, several groups have targeted the peripheral immune system to modulate chronic neuroinflammation. In this review, we focus on the interplay of immunomodulating factors and cell types that are being investigated as possible therapeutic targets for the treatment or prevention of AD.

Fractionation enhances acute oligodendrocyte progenitor cell radiation sensitivity and leads to long term depletion

Ionizing radiation (IR) is commonly used to treat central nervous system (CNS) cancers and metastases. While IR promotes remission, frequent side effects including impaired cognition and white matter loss occur following treatment. Fractionation is used to minimize these CNS late side effects, as it reduces IR effects in differentiated normal tissue, but not rapidly proliferating normal or tumor tissue. However, side effects occur even with the use of fractionated paradigms. Oligodendrocyte progenitor cells (OPCs) are a proliferative population within the CNS affected by radiation. We hypothesized that fractionated radiation would lead to OPC loss, which could contribute to the delayed white matter loss seen after radiation exposure. We found that fractionated IR induced a greater early loss of OPCs than an equivalent single dose exposure. Furthermore, OPC recovery was impaired following fractionated IR. Finally, reduced OPC differentiation and mature oligodendrocyte numbers occurred in single dose and fractionated IR paradigms. This work demonstrates that fractionation does not spare normal brain tissue and, importantly, highlights the sensitivity of OPCs to fractionated IR, suggesting that fractionated schedules may promote white matter dysfunction, a point that should be considered in radiotherapy.

Neurogenic Effects of Low-Dose Whole-Body HZE (Fe) Ion and Gamma Irradiation

Understanding the dose-toxicity profile of radiation is critical when evaluating potential health risks associated with natural and man-made sources in our environment. The purpose of this study was to evaluate the effects of low-dose whole-body high-energy charged (HZE) iron (Fe) ions and low-energy gamma exposure on proliferation and differentiation of adult-born neurons within the dentate gyrus of the hippocampus, cells deemed to play a critical role in memory regulation. To determine the dose-response characteristics of the brain to whole-body Fe-ion vs. gamma-radiation exposure, C57BL/6J mice were irradiated with 1 GeV/n Fe ions or a static ¹³⁷Cs source (0.662 MeV) at doses ranging from 0 to 300 cGy. The neurogenesis was analyzed at 48 h and one month postirradiation. These experiments revealed that whole-body exposure to either Fe ions or gamma radiation leads to: 1. An acute decrease in cell division within the dentate gyrus of the hippocampus, detected at doses as low as 30 and 100 cGy for Fe ions and gamma radiation, respectively; and 2. A reduction in newly differentiated neurons (DCX immunoreactivity) at one month postirradiation, with significant decreases detected at doses as low as 100 cGy for both Fe ions and gamma rays. The data presented here contribute to our understanding of brain responses to whole-body Fe ions and gamma rays and may help inform health-risk evaluations related to systemic exposure during a medical or radiologic/nuclear event or as a result of prolonged space travel.

Fractionation Spares Mice From Radiation-Induced Reductions in Weight Gain But Does Not Prevent Late Oligodendrocyte Lineage Side Effects

PURPOSE

To determine the late effects of fractionated versus single-dose cranial radiation on murine white matter.

METHODS AND MATERIALS

Mice were exposed to 0 Gy, 6 × 6 Gy, or 1 × 20 Gy cranial irradiation at 10 to 12 weeks of age. Endpoints were assessed through 18 months from exposure using immunohistochemistry, electron microscopy, and electrophysiology.

RESULTS

Weight gain was temporarily reduced after irradiation; greater loss was seen after single versus fractionated doses. Oligodendrocyte progenitor cells were reduced early and late after both single and fractionated irradiation. Both protocols also increased myelin g-ratio, reduced the number of nodes of Ranvier, and promoted a shift in the proportion of small, unmyelinated versus large, myelinated axon fibers.

CONCLUSIONS

Fractionation does not adequately spare normal white matter from late radiation side effects.

Brain radiation injury leads to a dose- and time-dependent recruitment of peripheral myeloid cells that depends on CCR2 signaling

BACKGROUND

Cranial radiotherapy is used to treat tumors of the central nervous system (CNS), as well as non-neoplastic conditions such as arterio-venous malformations; however, its use is limited by the tolerance of adjacent normal CNS tissue, which can lead to devastating long-term sequelae for patients. Despite decades of research, the underlying mechanisms by which radiation induces CNS tissue injury remain unclear. Neuroinflammation and immune cell infiltration are a recognized component of the CNS radiation response; however, the extent and mechanisms by which bone marrow-derived (BMD) immune cells participate in late radiation injury is unknown. Thus, we set out to better characterize the response and tested the hypothesis that C-C chemokine receptor type 2 (CCR2) signaling was required for myeloid cell recruitment following brain irradiation.

METHODS

We used young adult C57BL/6 male bone marrow chimeric mice created with donor mice that constitutively express enhanced green fluorescent protein (eGFP). The head was shielded to avoid brain radiation exposure during chimera construction. Radiation dose and time response studies were conducted in wild-type chimeras, and additional experiments were performed with chimeras created using donor marrow from CCR2 deficient, eGFP-expressing mice. Infiltrating eGFP+ cells were identified and quantified using immunofluorescent microscopy.

RESULTS

Brain irradiation resulted in a dose- and time-dependent infiltration of BMD immune cells (predominately myeloid) that began at 1 month and persisted until 6 months following ≥15 Gy brain irradiation. Infiltration was limited to areas that were directly exposed to radiation. CCR2 signaling loss resulted in decreased numbers of infiltrating cells at 6 months that appeared to be restricted to cells also expressing major histocompatibility complex class II molecules.

CONCLUSIONS

The potential roles played by infiltrating immune cells are of current importance due to increasing interest in immunotherapeutic approaches for cancer treatment and a growing clinical interest in survivorship and quality of life issues. Our findings demonstrate that injury from brain radiation facilitates a dose- and time-dependent recruitment of BMD cells that persists for at least 6 months and, in the case of myeloid cells, is dependent on CCR2 signaling.

Aryl hydrocarbon receptor deletion in cerebellar granule neuron precursors impairs neurogenesis

The aryl hydrocarbon receptor (AhR) is a ligand-activated member of the basic-helix-loop-helix/PER-ARNT-SIM(PAS) transcription factor superfamily that also mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Increasing evidence suggests that AhR influences the development of many tissues, including the central nervous system. Our previous studies suggest that sustained AhR activation by TCDD and/or AhR deletion disrupts cerebellar granule neuron precursor (GNP) development. In the current study, to determine whether endogenous AhR controls GNP development in a cell-autonomous manner, we created a GNP-specific AhR deletion mouse, AhR(fx/fx) /Math1(CRE/+) (AhR CKO). Selective AhR deletion in GNPs produced abnormalities in proliferation and differentiation. Specifically, fewer GNPs were engaged in S-phase, as demonstrated by ∼25% reductions in thymidine (in vitro) and Bromodeoxyuridine (in vivo) incorporation. Furthermore, total granule neuron numbers in the internal granule layer at PND21 and PND60 were diminished in AhR conditional knockout (CKO) mice compared with controls. Conversely, differentiation was enhanced, including ∼40% increase in neurite outgrowth and 50% increase in GABARα6 receptor expression in deletion mutants. Our results suggest that AhR activity plays a role in regulating granule neuron number and differentiation, possibly by coordinating this GNP developmental transition. These studies provide novel insights for understanding the normal roles of AhR signaling during cerebellar granule cell neurogenesis and may have important implications for the effects of environmental factors in cerebellar dysgenesis.

Neuroinflammation and M2 microglia: the good, the bad, and the inflamed

The concept of multiple macrophage activation states is not new. However, extending this idea to resident tissue macrophages, like microglia, has gained increased interest in recent years. Unfortunately, the research on peripheral macrophage polarization does not necessarily translate accurately to their central nervous system (CNS) counterparts. Even though pro- and anti-inflammatory cytokines can polarize microglia to distinct activation states, the specific functions of these states is still an area of intense debate. This review examines the multiple possible activation states microglia can be polarized to. This is followed by a detailed description of microglial polarization and the functional relevance of this process in both acute and chronic CNS disease models described in the literature. Particular attention is given to utilizing M2 microglial polarization as a potential therapeutic option in treating diseases.

Interleukin-1β mediated amyloid plaque clearance is independent of CCR2 signaling in the APP/PS1 mouse model of Alzheimer's disease

Neuroinflammation is a key component of Alzheimer's disease (AD) pathogenesis. Particularly, the proinflammatory cytokine interleukin-1 beta (IL-1β) is upregulated in human AD and believed to promote amyloid plaque deposition. However, studies from our laboratory have shown that chronic IL-1β overexpression in the APPswe/PSEN1dE9 (APP/PS1) mouse model of AD ameliorates amyloid pathology, increases plaque-associated microglia, and induces recruitment of peripheral immune cells to the brain parenchyma. To investigate the contribution of CCR2 signaling in IL-1β-mediated amyloid plaque clearance, seven month-old APP/PS1/CCR2(-/-) mice were intrahippocampally transduced with a recombinant adeno-associated virus serotype 2 containing the cleaved form of human IL-1β (rAAV2-IL-1β). Four weeks after rAAV2-IL-1β transduction, we found significant reductions in 6E10 and Congo red staining of amyloid plaques that was confirmed by decreased levels of insoluble Aβ1-42 and Aβ1-40 in the inflamed hippocampus. Bone marrow chimeric studies confirmed the presence of infiltrating immune cells following IL-1β overexpression and revealed that dramatic reduction of CCR2(+) peripheral mononuclear cell recruitment to the inflamed hippocampus did not prevent the ability of IL-1β to induce amyloid plaque clearance. These results suggest that infiltrating CCR2(+) monocytes do not contribute to IL-1β-mediated amyloid plaque clearance.

Thermal injury lowers the threshold for radiation-induced neuroinflammation and cognitive dysfunction

The consequences of radiation exposure alone are relatively well understood, but in the wake of events such as the World War II nuclear detonations and accidents such as Chernobyl, other critical factors have emerged that can substantially affect patient outcome. For example, ~70% of radiation victims from Hiroshima and Nagasaki received some sort of additional traumatic injury, the most common being thermal burn. Animal data has shown that the addition of thermal insult to radiation results in increased morbidity and mortality. To explore possible synergism between thermal injury and radiation on brain, C57BL/6J female mice were exposed to either 0 or 5 Gy whole-body gamma irradiation. Irradiation was immediately followed by a 10% total-body surface area full thickness thermal burn. Mice were sacrificed 6 h, 1 week or 6 month post-injury and brains and plasma were harvested for histology, mRNA analysis and cytokine ELISA. Plasma analysis revealed that combined injury synergistically upregulates IL-6 at acute time points. Additionally, at 6 h, combined injury resulted in a greater upregulation of the vascular marker, ICAM-1 and TNF-α mRNA. Enhanced activation of glial cells was also observed by CD68 and Iba1 immunohistochemistry at all time points. Additionally, doublecortin staining at 6 months showed reduced neurogenesis in all injury conditions. Finally, using a novel object recognition test, we observed that only mice with combined injury had significant learning and memory deficits. These results demonstrate that thermal injury lowers the threshold for radiation-induced neuroinflammation and long-term cognitive dysfunction.

Sustained IL-1β expression impairs adult hippocampal neurogenesis independent of IL-1 signaling in nestin+ neural precursor cells

Alterations in adult hippocampal neurogenesis have been observed in numerous neurological diseases that contain a neuroinflammatory component. Interleukin-1β (IL-1β) is a pro-inflammatory cytokine that contributes to neuroinflammation in many CNS disorders. Our previous results reveal a severe reduction in adult hippocampal neurogenesis due to focal and chronic expression of IL-1β in a transgenic mouse model, IL-1β(XAT), that evokes a complex neuroinflammatory response. Other investigators have shown that IL-1β can bind directly to neural precursors to cause cell cycle arrest in vitro. In order to observe if IL-1 signaling is necessary in vivo, we conditionally knocked out MyD88, an adapter protein essential for IL-1 signaling, in nestin(+) neural precursor cells (NPCs) in the presence of IL-1β-dependent inflammation. Our results show that conditional knockout of MyD88 does not prevent IL-1β-induced reduction in neuroblasts using a genetic fate mapping model. Interestingly, MyD88 deficiency in nestin(+) NPCs causes an increase in the number of astrocytes in the presence of IL-1β, suggesting that MyD88-dependent signaling is important in limiting astroglial differentiation due to inflammation. MyD88 deficiency does not alter the fate of NPCs in the absence of inflammation. Furthermore, the inflammatory milieu due to IL-1β is not affected by the absence of MyD88 in nestin(+) NPCs. These results show that sustained IL-1β causes a reduction in adult hippocampal neurogenesis that is independent of MyD88-dependent signaling in nestin(+) NPCs, suggesting an indirect negative effect of IL-1β on neurogenesis.

Chronic neuron- and age-selective down-regulation of TNF receptor expression in triple-transgenic Alzheimer disease mice leads to significant modulation of amyloid- and Tau-related pathologies

Neuroinflammation, through production of proinflammatory molecules and activated glial cells, is implicated in Alzheimer's disease (AD) pathogenesis. One such proinflammatory mediator is tumor necrosis factor α (TNF-α), a multifunctional cytokine produced in excess and associated with amyloid β-driven inflammation and cognitive decline. Long-term global inhibition of TNF receptor type I (TNF-RI) and TNF-RII signaling without cell or stage specificity in triple-transgenic AD mice exacerbates hallmark amyloid and neurofibrillary tangle pathology. These observations revealed that long-term pan anti-TNF-α inhibition accelerates disease, cautions against long-term use of anti-TNF-α therapeutics for AD, and urges more selective regulation of TNF signaling. We used adeno-associated virus vector-delivered siRNAs to selectively knock down neuronal TNF-R signaling. We demonstrate divergent roles for neuronal TNF-RI and TNF-RII where loss of opposing TNF-RII leads to TNF-RI-mediated exacerbation of amyloid β and Tau pathology in aged triple-transgenic AD mice. Dampening of TNF-RII or TNF-RI+RII leads to a stage-independent increase in Iba-1-positive microglial staining, implying that neuronal TNF-RII may act nonautonomously on the microglial cell population. These results reveal that TNF-R signaling is complex, and it is unlikely that all cells and both receptors will respond positively to broad anti-TNF-α treatments at various stages of disease. In aggregate, these data further support the development of cell-, stage-, and/or receptor-specific anti-TNF-α therapeutics for AD.

Galactic cosmic radiation leads to cognitive impairment and increased aβ plaque accumulation in a mouse model of Alzheimer's disease

Galactic Cosmic Radiation consisting of high-energy, high-charged (HZE) particles poses a significant threat to future astronauts in deep space. Aside from cancer, concerns have been raised about late degenerative risks, including effects on the brain. In this study we examined the effects of (56)Fe particle irradiation in an APP/PS1 mouse model of Alzheimer's disease (AD). We demonstrated 6 months after exposure to 10 and 100 cGy (56)Fe radiation at 1 GeV/µ, that APP/PS1 mice show decreased cognitive abilities measured by contextual fear conditioning and novel object recognition tests. Furthermore, in male mice we saw acceleration of Aβ plaque pathology using Congo red and 6E10 staining, which was further confirmed by ELISA measures of Aβ isoforms. Increases were not due to higher levels of amyloid precursor protein (APP) or increased cleavage as measured by levels of the β C-terminal fragment of APP. Additionally, we saw no change in microglial activation levels judging by CD68 and Iba-1 immunoreactivities in and around Aβ plaques or insulin degrading enzyme, which has been shown to degrade Aβ. However, immunohistochemical analysis of ICAM-1 showed evidence of endothelial activation after 100 cGy irradiation in male mice, suggesting possible alterations in Aβ trafficking through the blood brain barrier as a possible cause of plaque increase. Overall, our results show for the first time that HZE particle radiation can increase Aβ plaque pathology in an APP/PS1 mouse model of AD.

X-ray microbeam irradiation of the contusion-injured rat spinal cord temporarily improves hind-limb function

Spinal cord injury is a devastating condition with no effective treatment. The physiological processes that impede recovery include potentially detrimental immune responses and the production of reactive astrocytes. Previous work suggested that radiation treatment might be beneficial in spinal cord injury, although the method carries risk of radiation-induced damage. To overcome this obstacle we used arrays of parallel, synchrotron-generated X-ray microbeams (230 μm with 150 μm gaps between them) to irradiate an established model of rat spinal cord contusion injury. This technique is known to have a remarkable sparing effect in tissue, including the central nervous system. Injury was induced in adult female Long-Evans rats at the level of the thoracic vertebrae T9-T10 using 25 mm rod drop on an NYU Impactor. Microbeam irradiation was given to groups of 6-8 rats each, at either Day 10 (50 or 60 Gy in-beam entrance doses) or Day 14 (50, 60 or 70 Gy). The control group was comprised of two subgroups: one studied three months before the irradiation experiment (n = 9) and one at the time of the irradiations (n = 7). Hind-limb function was blindly scored with the Basso, Beattie and Bresnahan (BBB) rating scale on a nearly weekly basis. The scores for the rats irradiated at Day 14 post-injury, when using t test with 7-day data-averaging time bins, showed statistically significant improvement at 28-42 days post-injury (P < 0.038). H&E staining, tissue volume measurements and immunohistochemistry at day ≈ 110 post-injury did not reveal obvious differences between the irradiated and nonirradiated injured rats. The same microbeam irradiation of normal rats at 70 Gy in-beam entrance dose caused no behavioral deficits and no histological effects other than minor microglia activation at 110 days. Functional improvement in the 14-day irradiated group might be due to a reduction in populations of immune cells and/or reactive astrocytes, while the Day 10/Day 14 differences may indicate time-sensitive changes in these cells and their populations. With optimizations, including those of the irradiation time(s), microbeam pattern, dose, and perhaps concomitant treatments such as immunological intervention this method may ultimately reach clinical use.

Conditional expression of human β-hexosaminidase in the neurons of Sandhoff disease rescues mice from neurodegeneration but not neuroinflammation

This study evaluated whether GM₂ ganglioside storage is necessary for neurodegeneration and neuroinflammation by performing β-hexosaminidase rescue experiments in neurons of HexB^−/− mice. We developed a novel mouse model, whereby the expression of the human HEXB gene was targeted to neurons of HexB^−/− mice by the Thy1 promoter. Despite β-hexosaminidase restoration in neurons was sufficient in rescuing HexB^−/− mice from GM₂ neuronal storage and neurodegeneration, brain inflammation persisted, including the presence of large numbers of reactive microglia/macrophages due to persisting GM₂ presence in this cell type. In conclusion, our results suggest that neuroinflammation is not sufficient to elicit neurodegeneration as long as neuronal function is restored.

Chronic IL-1β-mediated neuroinflammation mitigates amyloid pathology in a mouse model of Alzheimer's disease without inducing overt neurodegeneration

Neuroinflammation is a local tissue response to injurious stimuli in the central nervous system (CNS) and is characterized by glial reactivity, induction of cytokines and chemokines, and vascular permeability. The cytokine interleukin (IL)-1β is rapidly induced following CNS insult, and is chronically expressed in neurodegenerative disorders such as Alzheimer's disease (AD). We recently developed a novel method of sustained IL-1β production in the brain to study the link between IL-1β and AD pathogenesis. Utilizing this model, we have previously demonstrated reduction of plaque size and frequency accompanied by a robust neuroinflammatory response. These observations were limited to a single early time point in the course of AD plaque deposition and did not investigate other neurodegenerative endpoints. To extend these observations to other stages of disease progression and evaluate additional pathologic markers, we investigated the effects of age and duration of IL-1β overexpression in the APPswe/PS-1dE9 AD model on a congenic C57BL/6 background. We now report that IL1β overexpression leads to decreased 6E10 immunopositive plaque pathology regardless of age or duration. We also investigated whether IL-1β overexpression led to neuronal apoptosis or cholinergic axonal degeneration in the context of this AD model. Although we could demonstrate apoptosis of infiltrating inflammatory cells, we found no evidence for IL-1 associated apoptosis of neurons or cholinergic axon degeneration even after 5 months of chronic neuroinflammation. Together, these observations point to a neuroprotective role for IL-1β in AD neuropathogenesis.

Osteoarthritis accelerates and exacerbates Alzheimer's disease pathology in mice

Background

The purpose of this study was to investigate whether localized peripheral inflammation, such as osteoarthritis, contributes to neuroinflammation and neurodegenerative disease in vivo.

Methods

We employed the inducible Col1-IL1β^XAT mouse model of osteoarthritis, in which induction of osteoarthritis in the knees and temporomandibular joints resulted in astrocyte and microglial activation in the brain, accompanied by upregulation of inflammation-related gene expression. The biological significance of the link between peripheral and brain inflammation was explored in the APP/PS1 mouse model of Alzheimer's disease (AD) whereby osteoarthritis resulted in neuroinflammation as well as exacerbation and acceleration of AD pathology.

Results

Induction of osteoarthritis exacerbated and accelerated the development of neuroinflammation, as assessed by glial cell activation and quantification of inflammation-related mRNAs, as well as Aβ pathology, assessed by the number and size of amyloid plaques, in the APP/PS1; Col1-IL1β^XAT compound transgenic mouse.

Conclusion

This work supports a model by which peripheral inflammation triggers the development of neuroinflammation and subsequently the induction of AD pathology. Better understanding of the link between peripheral localized inflammation, whether in the form of osteoarthritis, atherosclerosis or other conditions, and brain inflammation, may prove critical to our understanding of the pathophysiology of disorders such as Alzheimer's, Parkinson's and other neurodegenerative diseases.

Cranial irradiation leads to acute and persistent neuroinflammation with delayed increases in T-cell infiltration and CD11c expression in C57BL/6 mouse brain

Radiotherapy is commonly employed to treat cancers of the head and neck and is increasingly used to treat other central nervous system (CNS) disorders. Exceeding the radiation tolerance of normal CNS tissues can result in sequelae contributing to patient morbidity and mortality. Animal studies and clinical experience suggest that neuroinflammation plays a role in the etiology of these effects; however, detailed characterization of this response has been lacking. Therefore, a dose-time investigation of the neuroinflammatory response after single-dose cranial irradiation was performed using C57BL/6 mice. Consistent with previous reports, cranial irradiation resulted in multiphasic inflammatory changes exemplified by increased transcript levels of inflammatory cytokines, along with glial and endothelial cell activation. Cranial irradiation also resulted in acute infiltration of neutrophils and a delayed increase in T cells, MHC II-positive cells, and CD11c-positive cells seen first at 1 month with doses ≥ 15 Gy. CD11c-positive cells were found almost exclusively in white matter and expressed MHC II, suggesting a "mature" dendritic cell phenotype that remained elevated out to 1 year postirradiation. Our results indicate that cranial irradiation leads to persistent neuroinflammatory changes in the C57BL/6 mouse brain that includes unique immunomodulatory cell populations.

Behavioral, structural and molecular changes following long-term hippocampal IL-1β overexpression in transgenic mice

Chronic neuroinflammation is associated with many neurodegenerative and neurocognitive disorders, yet few animal models exist to study the behavioral effects of prolonged neuroinflammation. Therefore, we recently developed a transgenic mouse model harboring an interleukin-1β excisional activation transgene (IL-1β(XAT)). These mice display localized IL-1β overexpression and resultant neuroinflammation for up to 1 year following transgene induction. Initial behavioral studies demonstrated long-term memory deficits after 2 weeks of hippocampal IL-1β overexpression. In the present studies, we extend these behavioral studies both in scope and timing. We find long-term contextual but not auditory fear memory impairments following 3 months of IL-1β overexpression. On a battery of other behavioral tests, IL-1β overexpression in IL-1β(XAT) mice increased locomotor activity, especially in female mice, and had slight anxiolytic effects. No differences were found in operant conditioning or in basal or stress-induced CORT levels, despite profound hippocampal glial activation. Interestingly, the volume of discrete hippocampal cell layers was reduced after 6 but not 3 months of IL-1β overexpression. Therefore, this animal model provides a novel tool for examining the effects of chronic inflammation on discrete brain regions.

Cyclooxygenase-1 mediates prostaglandin E(2) elevation and contextual memory impairment in a model of sustained hippocampal interleukin-1beta expression

Interleukin (IL)-1beta is a proinflammatory cytokine implicated in several neurodegenerative disorders. Downstream actions of IL-1beta include production of prostaglandin (PG) E(2) by increasing expression of cyclooxygenase (COX) enzymes and prostaglandin E synthase (PGES) isoforms. We recently developed a transgenic mouse carrying a dormant human IL-1beta eXcisional Activation Transgene (XAT) for conditional and chronic up-regulation of IL-1beta in selected brain regions. This model is characterized by regionally specific glial activation, immune cell recruitment, and induction of cytokines and chemokines. Here, we aimed to elucidate the effects of long-term IL-1beta expression on the PGE(2) synthetic pathway and to determine the effects of PGs on inflammation and memory in our model. As expected, PGE(2) levels were significantly elevated after IL-1beta up-regulation. Quantitative real-time PCR analysis indicated significant induction of mRNAs for COX-1 and membranous PGES-1, but not COX-2 or other PGES isoforms. Immunohistochemistry revealed elevation of COX-1 but no change in COX-2 following sustained IL-1beta production. Furthermore, pharmacological inhibition of COX-1 and use of COX-1 knockout mice abrogated IL-1beta-mediated PGE(2) increases. Although COX-1 deficient mice did not present a dramatically altered neuroinflammatory phenotype, they did exhibit improved contextual fear memory. This data suggests a unique role for COX-1 in mediating chronic neuroinflammatory effects through PGE(2) production.

Sustained hippocampal IL-1beta overexpression impairs contextual and spatial memory in transgenic mice

Neuroinflammatory conditions such as traumatic brain injury, aging, Alzheimer's disease, and Down syndrome are often associated with cognitive dysfunction. Much research has targeted inflammation as a causative mediator of these deficits, although the diverse cellular and molecular changes that accompany these disorders obscure the link between inflammation and impaired memory. Therefore, we used a transgenic mouse model with a dormant human IL-1beta excisional activation transgene to direct overexpression of IL-1beta with temporal and regional control. Two weeks of hippocampal IL-1beta overexpression impaired long-term contextual and spatial memory in both male and female mice, while hippocampal-independent and short-term memory remained intact. Human IL-1beta overexpression activated glia, elevated murine IL-1beta protein and PGE(2) levels, and increased pro-inflammatory cytokine and chemokine mRNAs specifically within the hippocampus, while having no detectable effect on inflammatory mRNAs in the liver. Sustained neuroinflammation also reduced basal and conditioning-induced levels of the plasticity-related gene Arc.

Peripheral blood mononuclear cell infiltration and neuroinflammation in the HexB-/- mouse model of neurodegeneration

Myeloid-derived immune cells, including microglia, macrophages and monocytes, have been previously implicated in neurodegeneration. We investigated the role of infiltrating peripheral blood mononuclear cells (PBMC) in neuroinflammation and neurodegeneration in the HexB-/- mouse model of Sandhoff disease. Ablation of the chemokine receptor CCR2 in the HexB-/- mouse resulted in significant inhibition of PBMC infiltration into the brain, decrease in TNFalpha and MHC-II mRNA abundance and retardation in clinical disease development. There was no change in the level of GM2 storage and pro-apoptotic activity or astrocyte activation in HexB-/-; Ccr2-/- double knockout mice, which eventually succumbed secondary to GM2 gangliosidosis.

Chronic interleukin-1beta expression in mouse brain leads to leukocyte infiltration and neutrophil-independent blood brain barrier permeability without overt neurodegeneration

The proinflammatory cytokine interleukin-1beta (IL-1beta) plays a significant role in leukocyte recruitment to the CNS. Although acute effects of IL-1beta signaling in the mouse brain have been well described, studies elucidating the downstream effects of sustained upregulation have been lacking. Using the recently described IL-1beta(XAT) transgenic mouse model, we triggered sustained unilateral hippocampal overexpression of IL-1beta. Transgene induction led to blood-brain barrier leakage, induction of MCP-1 (monocyte chemoattractant protein 1) (CCL2), ICAM-1 (intercellular adhesion molecule 1), and dramatic infiltration of CD45-positive leukocytes comprised of neutrophils, T-cells, macrophages, and dendritic cells. Despite prolonged cellular infiltration of the hippocampus, there was no evidence of neuronal degeneration. Surprisingly, neutrophils were observed in the hippocampal parenchyma as late as 1 year after transgene induction. Their presence was coincident with upregulation of the potent neutrophil chemotactic chemokines KC (keratinocyte-derived chemokine) (CXCL1) and MIP-2 (macrophage inflammatory protein 2) (CXCL2). Knock-out of their sole receptor CXCR2 abrogated neutrophil infiltration but failed to reduce leakage of the blood-brain barrier.

Sustained hippocampal IL-1 beta overexpression mediates chronic neuroinflammation and ameliorates Alzheimer plaque pathology

Neuroinflammation is a conspicuous feature of Alzheimer disease (AD) pathology and is thought to contribute to the ultimate neurodegeneration that ensues. IL-1 beta has emerged as a prime candidate underlying this response. Here we describe a transgenic mouse model of sustained IL-1 beta overexpression that was capable of driving robust neuroinflammation lasting months after transgene activation. This response was characterized by astrocytic and microglial activation in addition to induction of proinflammatory cytokines. Surprisingly, when triggered in the hippocampus of the APPswe/PS1dE9 mouse model of AD, 4 weeks of IL-1 beta overexpression led to a reduction in amyloid pathology. Congophilic plaque area fraction and frequency as well as insoluble amyloid beta 40 (A beta 40) and A beta 42 decreased significantly. These results demonstrate a possible adaptive role for IL-1 beta-driven neuroinflammation in AD and may help explain recent failures of antiinflammatory therapeutics for this disease.

Intraarticular induction of interleukin-1beta expression in the adult mouse, with resultant temporomandibular joint pathologic changes, dysfunction, and pain

OBJECTIVE

To examine the effects of intraarticular induction of interleukin-1beta (IL-1beta) expression in adult mice.

METHODS

We used somatic mosaic analysis in a novel transgenic mouse with an inducible IL-1beta transcription unit. Transgene activation was induced by Cre recombinase in the temporomandibular joints (TMJs) of adult transgenic mice (conditional knockin model). The effects of intraarticular IL-1beta induction were subsequently evaluated at the cellular, histopathologic, and behavioral levels.

RESULTS

We developed transgenic mice capable of germline transmission of a dormant transcription unit consisting of the mature form of human IL-1beta as well as the reporter gene beta-galactosidase driven by the rat procollagen 1A1 promoter. Transgene activation by a feline immunodeficiency virus Cre vector resulted in histopathologic changes, including articular surface fibrillations, cartilage remodeling, and chondrocyte cloning. We also demonstrated up-regulation of genes implicated in arthritis (cyclooxygenase 2, IL-6, matrix metalloproteinase 9). There was a lack of inflammatory cells in these joints. Behavioral changes, including increased orofacial grooming and decreased resistance to mouth opening, were used as measures of nociception and joint dysfunction, respectively. The significant increase in expression of the pain-related neurotransmitter calcitonin gene-related peptide (CGRP) in the sensory ganglia as well as the auxiliary protein CGRP receptor component protein of the calcitonin-like receptor in the brainstem further substantiated the induction of pain.

CONCLUSION

Induction of IL-1beta expression in the TMJs of adult mice led to pathologic development, dysfunction, and related pain in the joints. The somatic mosaic model presented herein may prove useful in the preclinical evaluation of existing and new treatments for the management of joint pathologic changes and pain, such as in osteoarthritis.

Acute morphine exposure potentiates the development of HSV-1-induced encephalitis

A devastating consequence of HSV-1 infection is development of HSV-1-induced encephalitis (HSVE). While only a minority of individuals infected with HSV-1 experiences HSVE, clearly defined variables that consistently predict development of the disease remain to be elucidated. The current study examined the effects of a single dose of morphine prior to infection with HSV-1 on the development of HSVE in BALB/cByJ mice. Acute morphine exposure was observed to potentiate the development of HSVE in HSV-1 infected mice. The present data implicate a potential role for the blood-brain barrier in the development of HSVE in morphine-treated mice.

Regulation of prostaglandin E2 synthesis after brain irradiation

PURPOSE

A local tissue reaction, termed neuroinflammation, occurs after irradiation of brain tissue. Previous work suggested that cyclooxygenase (COX)-2 activity was important for changes in gene expression associated with neuroinflammation as well as increased prostaglandin E2 (PGE2) levels seen after radiation treatment.

METHODS AND MATERIALS

To begin to determine the contributions of other enzymes involved in PGE2 production, we examined protein levels of COX-1 and COX-2 as well as 2 PGE synthases (membrane and cytosolic PGES) 4 h after 35 Gy single dose irradiation to the brains of C3HeN mice. We also evaluated the effects of specific COX inhibitors on PGE2 production and PGES expression.

RESULTS

As expected, COX-2 expression increased after radiation exposure. Brain irradiation also increased tissue protein levels for both PGES isoforms. Specific COX-2 inhibition with NS398 lowered brain PGE2 levels by about 60%. Surprisingly, COX-1 inhibition with SC560 completely prevented the elevation of PGE2 seen after irradiation. Interestingly, NS398 reduced the membrane-associated PGES isoform, whereas SC560 treatment lowered cytosolic isoform levels below those seen in unirradiated controls.

CONCLUSIONS

Taken together, these data indicate that both cyclooxygenases contribute to PGE2 production in irradiated brain and reveal dependence of PGES isoforms expression on specific cyclooxygenase activities.

β-hexosaminidase lentiviral vectors: transfer into the CNS via systemic administration

Brain inflammation in GM2 gangliosidosis has been recently realized as a key factor in disease development. The aim of this study was to investigate the effects of a FIV beta-hexosaminidase vector in the brain of HexB-deficient (Sandhoff disease) mice following intraperitoneal administration to pups of neonatal age. Since brain inflammation, lysosomal storage and neuromuscular dysfunction are characteristics of HexB deficiency, these parameters were employed as experimental outcomes in our study. The ability of the lentiviral vector FIV(HEX) to infect murine cells was initially demonstrated with success in normal mouse fibroblasts and human Tay-Sachs cells in vitro. Furthermore, systemic transfer of FIV(HEX) to P2 HexB-/- knockout pups lead to transduction of peripheral and central nervous system tissues. Specifically, beta-hexosaminidase expressing cells were immunolocalized in periventricular areas of the cerebrum as well as in the cerebellar cortex. FIV(HEX) neonatal treatment resulted in reduction of GM2 storage along with attenuation of the brain inflammation and amelioration of the attendant neuromuscular deterioration. In conclusion, these results demonstrate the effective transfer of a beta-hexosaminidase lentiviral vector to the brain of Sandhoff mice and resolution of the GM2 gangliosidosis after neonatal intraperitoneal administration.

Radiation-induced edema is dependent on cyclooxygenase 2 activity in mouse brain

Cerebrovascular dysfunction, characterized by compromise of the blood-brain barrier and formation of cerebral edema, is common during the acute period after brain irradiation and may contribute to delayed pathology (e.g. vascular collapse, white matter necrosis) that leads to functional deficits. Another response of normal brain tissue to radiation is the induction of inflammatory markers, such as cytokine expression and glial activation. In particular, radiation-induced neuroinflammation is associated with an elevation in cyclooxygenase 2 (COX2), one of two isoforms of the obligate enzyme in prostanoid synthesis and the principal target of non-steroid anti-inflammatory drugs. Since prostanoids serve as autocrine and paracrine mediators in numerous physiological and pathological processes, including vasoregulation, we investigated COX2 protein expression and COX2-mediated prostanoid production in radiation-induced cerebral edema in male C57/BL6 mice. We found that radiation induces COX2 protein that is accompanied by specific increases in prostaglandin E(2) and thromboxane A(2) within 4 and 24 h after brain irradiation. Furthermore, we showed that treatment with NS-398, a selective COX2 inhibitor, attenuated prostanoid induction and edema formation. These results suggest that radiation-induced changes in vascular permeability are dependent on COX2 activity, implicating this enzyme and its products as targets for potential therapeutic treatment/protection from the effects of radiation on normal brain tissue.

Microglial response is poorly correlated with neurodegeneration following chronic, low-dose MPTP administration in monkeys

Many investigators have reported extensive microglial activation in the mouse substantia nigra and striatum following acute, high-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. Our previous work demonstrated tyrosine hydroxylase (TH)-positive fiber sprouting in the striatum in monkeys that had received a partial dopaminergic lesion using a low-dose, chronic MPTP administration paradigm. To characterize the microglial response, we utilized HLA-DR (LN3) to immunolabel the class II major histocompatibility complex (MHC II). In MPTP-treated monkeys, there was an intense microglial response in the substantia nigra, nigrostriatal tract, and in both segments of the globus pallidus. This response was morphologically heterogeneous, with commingled ramified, activated, and multicellular morphologies throughout the extent of these basal ganglia structures. Surprisingly, there was little evidence of microglial reactivity in the striatum despite evidence of neurodegeneration-by silver labeling and by loss of TH immunolabeling. Moreover, this pattern of microglial reactivity was the same in all animals that had received MPTP and seemed to be independent of the degree of neurotoxin-induced neurodegeneration. Thus, we conclude that microglial reactivity, per se, is not consistently associated with neurodegeneration, but depends on regional differences.

Intraparenchymal administration of interleukin-1β induces cyclooxygenase-2-mediated expression of membrane- and cytosolic-associated prostaglandin E synthases in mouse brain

Interleukin (IL)-1beta is a proinflammatory cytokine expressed in neural tissue following injury and in neurodegenerative states. To understand the consequences of its presence in brain, we carried out intraparenchymal IL-1beta injections and found significant increases in prostaglandin (PG)E2, a critical factor in inflammatory and physiological processes. Elevated mRNA and protein expression of the PGE2-synthetic-related enzymes cyclooxygenase (COX)-2 and membrane-associated PGE synthase (PGES) accompanied local PGE2 production. In addition, IL-1beta stimulated protein expression of cytosolic PGES. Finally, we showed attenuation of these IL-1beta-inductions by COX-2 inhibition, suggesting in vivo regulation of both PGE synthase isoforms in the brain.

COX-3: a splice variant of cyclooxygenase-1 in mouse neural tissue and cells

We have detected an expressed mRNA encoding a splice variant of COX-1 in the mouse central nervous system. This isoform, referred to as COX-3, is identical in sequence to COX-1 except for the in-frame retention of intron 1. Like its counterpart COX-1, COX-3 does not generally appear to be induced by acute inflammatory stimulation.

Immune responses to replication-defective HSV-1 type vectors within the CNS: implications for gene therapy

Herpes simplex virus (HSV) is a naturally occurring double-stranded DNA virus that has been adapted into an efficient vector for in vivo gene transfer. HSV-based vectors exhibit wide tropism, large transgene size capacity, and moderately prolonged transgene expression profiles. Clinical implementation of HSV vector-based gene therapy for prevention and/or amelioration of human diseases eventually will be realized, but inherently this goal presents a series of significant challenges, one of which relates to issues of immune system involvement. Few experimental reports have detailed HSV vector-engendered immune responses and subsequent resolution events primarily within the confines of the central nervous system. Herein, we describe the immunobiology of HSV and its derived vector platforms, thus providing an initiation point from where to propose requisite experimental investigation and potential approaches to prevent and/or counter adverse antivector immune responses.

Helper-free HSV-1 amplicons elicit a markedly less robust innate immune response in the CNS

The development and implementation of direct gene transfer technologies for the study and treatment of chronic CNS disorders inherently requires consideration of vector safety. Virus-based vectors represent the most efficient modalities but harbor the potential to induce vigorous innate and adaptive immune responses when administered in vivo. These responses can arise because of virus particle components, resultant viral gene expression, and/or transgene expression. In the current study, we describe the innate responses elicited upon stereotactic delivery of herpes simplex virus type 1-based amplicon vectors. C57BL/6 mice were injected with sterile saline, beta-galactosidase-expressing amplicon (HSVlac) packaged by a conventional helper virus-based technique, or helper virus-free HSVlac. After killing the mice at either 1 or 5 days after transduction, we analyzed them by immunocytochemistry and quantitative RT-PCR for various chemokine, cytokine, and adhesion molecule gene transcripts. All injections induced inflammation, with blood/brain barrier opening on day 1 that was enhanced with both amplicon preparations as compared with saline controls. By day 5, mRNA levels for the pro-inflammatory cytokines (IL-1beta, TNF-alpha, IFN-gamma), chemokines (MCP-1, IP-10), and an adhesion molecule (ICAM-1) had returned to baseline in saline-injected mice and to near-baseline levels in helper virus-free amplicon groups. In contrast, mice injected with helper virus-packaged amplicon stocks elicited elevated inflammatory molecule expression and immune cell infiltration even at day 5. In aggregate, we demonstrate that helper virus-free amplicon preparations exhibit a safer innate immune response profile, presumably as a result of the absence of helper virus gene expression, and provide support for future amplicon-based CNS gene transfer strategies.

Temporomandibular joint nociception: effects of capsaicin on substance P-like immunoreactivity in the rabbit brain stem

AIMS

To specify the regions of the brain stem that are characterized by changes in substance P (SP)-like immunoreactivity following activation of capsaicin-sensitive afferents innervating temporomandibular joint (TMJ) tissues in New Zealand rabbits.

METHODS

Capsaicin, an activator of small-diameter unmyelinated and thinly myelinated nociceptive afferent fibers, was administered unilaterally to the right TMJ of experimental animals. Another group received vehicle solution and served as controls. The animals were sacrificed 6 hours post-treatment through transcardial perfusion. Their brain stems were removed and sectioned, and SP-like immunoreactivity was assessed in serial horizontal sections.

RESULTS

A decrease in brain stem SP-like immunoreactivity occurred ipsilateral to capsaicin application. This reduction was primarily localized in brain stem regions that correspond to the trigeminal main sensory nucleus, as well as subnucleus oralis, interpolaris, and caudalis of the trigeminal spinal tract nucleus.

CONCLUSION

The present study revealed central nervous system changes following TMJ capsaicin treatment in rabbits.