Astrocytes Infected with Chlamydia pneumonia Alter Amyloid Processing Implicated in Alzheimer’s Disease

Alzheimer’s Disease (AD) is a chronic, progressive neurodegenerative disease whose pathogenesis centers around the abnormal processing of amyloid precursor protein (APP) by proteases, resulting in the formation of neuritic plaques composed of toxic, insoluble fragments of amyloid protein (Aβ), including Aβ1-40 and Aβ1-42. Previously, our laboratory identified Chlamydia pneumoniae (Cpn) in autopsied sporadic AD brains. Additionally, an infection based animal model was developed using BALB/c mice that were intranasally inoculated with Cpn, in which the deposition of amyloid was consistent with that observed in the human AD brain. These studies have led to the pathogen hypothesis of AD that implicates Cpn as a trigger for the cleavage of APP into Aβ1-40 and Aβ1-42. Objective: Several studies have demonstrated the presence of astrocytes surrounding neuritic plaques within the AD brain; therefore, we speculate that astrocytes may be specifically involved in the pathological processes leading to Aβ deposition. This investigation addresses if an in vitro Cpn infection of human astrocytes affects processing of the ß amyloid precursor protein (ßAPP) and the enzyme ß APP cleaving enzyme-1 (BACE1), a type 1 transmembrane aspartyl protease directly involved in the processing of APP to Aβ and implicated in numerous neurodegenerative diseases, such as traumatic brain injury. Methods: Human astrocytes (CCF-STTG1) were infected in vitro with the respiratory strain AR39 Cpn (MOI=1). Analysis of protein levels for Aβ and the enzyme BACE1 post-infection was detected by immunocytochemistry and captured with the Olympus Confocal FV1000 microscope. Results: Amyloid processing in infected astrocytes was altered relative to that of uninfected astrocytes. BACE1 immunolabeling appeared more diffuse in the infected astrocytes as compared to membrane-localized BACE1 in the uninfected astrocytes. Conclusions: Neurons have been presumed to be the primary source of beta-amyloid peptides in AD brains; however, when astrocytes are activated, as occurs during infection with Cpn, astrocytic beta-amyloid generation may contribute to amyloid plaque formation. These data imply that infection of human astrocytes with Cpn affects the processing of ßAPP through altering the localization of BACE1 protein from the membrane to the cytoplasm. These data suggest an activation of BACE1 in the processing of amyloid by astrocytes as a major contributor to the neurotoxic amyloid deposition linked to pathology observed in AD

Chlamydia pneumoniae Infection of Monocytes in vitro Stimulates Innate and Adaptive Immune Responses Relevant to those in Alzheimer\u27s Disease.

Background: Alzheimer\u27s disease (AD) is a progressive neurodegenerative disorder in which infection with Chlamydia pneumoniae (Cpn) has been associated. Cpn is an obligate intracellular respiratory pathogen that may enter the central nervous system (CNS) following infection and trafficking of monocytes through the blood-brain barrier. Following this entry, these cells may secrete pro-inflammatory cytokines and chemokines that have been identified in the AD brain, which have been thought to contribute to AD neurodegeneration. The objectives of this work were: (i) to determine if Cpn infection influences monocyte gene transcript expression at 48 hours post-infection and (ii) to analyze whether pro-inflammatory cytokines are produced and secreted from these cells over 24 to 120 hours post-infection. Methods: Gene transcription was analyzed by RT-PCR using an innate and adaptive immunity microarray with 84 genes organized into 5 functional categories: inflammatory response, host defense against bacteria, antibacterial humoral response, septic shock, and cytokines, chemokines and their receptors. Statistical analysis of the results was performed using the Student\u27s t-test. P-values ≤ 0.05 were considered to be significant. ELISA was performed on supernatants from uninfected and Cpn-infected THP1 monocytes followed by statistical analysis with ANOVA. Results: When Cpn-infected THP1 human monocytes were compared to control uninfected monocytes at 48 hours post-infection, 17 genes were found to have a significant 4-fold or greater expression, and no gene expression was found to be down-regulated. Furthermore, cytokine secretion (IL-1ß, IL-6, IL-8) appears to be maintained for an extended period of infection. Conclusions: Utilizing RT-PCR and ELISA techniques, our data demonstrate that Cpn infection of THP1 human monocytes promotes an innate immune response and suggests a potential role in the initiation of inflammation in sporadic/late-onset Alzheimer\u27s disease

Herpes simplex virus type 1 and Chlamydia pneumoniae infection of astrocytes: the effects of co-infection on pathogen replication

Background: Chlamydia pneumoniae (Cpn) and Herpes simplex virus type 1 (HSV-1) have been studied as pathogens contributing to neurodegenerative diseases. Cpn and HSV-1 are both ubiquitous, thus many individuals presumably are exposed to both pathogens during their life time. Since Cpn can establish persistence under adverse environmental conditions, we speculate that productive HSV infection might induce Cpn persistence in cells infected with both pathogens. Intermittent reactivation of either or both pathogens might contribute to progressive pathology associated with neurodegenerative diseases. Objectives: Determine whether Cpn and HSV-1 can co-infect cells and whether the presence of one pathogen alters replication of the other. Methods: The ability of Cpn and HSV-1 to co-infect an astrocyte cell line (STTG-1) was analyzed by immunofluorescence (IF) labeling using antibodies specific for HSV and Cpn, and RT-PCR using primers specific for each pathogen. Cells were infected with HSV or Cpn alone, or co infected with both pathogens for 24 or 48 hours. Results: IF revealed that cells could be simultaneously infected with both pathogens. Gene expression data support the observation that HSV replication is somewhat diminished in the presence of Cpn; similarly, the developmental cycle of Cpn appears to be disrupted by HSV. Conclusions: IF and gene expression data suggest both HSV-1 and Cpn inhibit, but do not prevent, infection by the second pathogen, possibly by competing for the same cellular receptors. Moreover, disruption of host cell transcription by HSV-1 may modify normal Cpn developmen

Astrocytes Infected with Chlamydia Pneumoniae Demonstrate Altered Expression and Activity of Secretases Involved in the Generation of Β-amyloid Found in Alzheimer Disease

BACKGROUND: Epidemiologic studies strongly suggest that the pathophysiology of late-onset Alzheimer disease (AD) versus early-onset AD has environmental rather than genetic causes, thus revealing potentially novel therapeutic targets to limit disease progression. Several studies supporting the pathogen hypothesis of AD demonstrate a strong association between pathogens and the production of β-amyloid, the pathologic hallmark of AD. Although the mechanism of pathogen-induced neurodegeneration of AD remains unclear, astrocytes, a key player of the CNS innate immune response and producer/metabolizer of β-amyloid, have been implicated. We hypothesized that Chlamydia pneumoniae infection of human astrocytes alters the expression of the amyloid precursor protein (APP)-processing secretases, ADAM10, BACE1, and PSEN1, to promote β-amyloid formation. Utilizing immunofluorescent microscopy, molecular, and biochemical approaches, these studies explore the role of an intracellular respiratory pathogen, Chlamydia pneumoniae, as an environmental trigger for AD pathology. Human astrocytoma cells in vitro were infected with Chlamydia pneumoniae over the course of 6-72 h. The gene and protein expression, as well as the enzymatic activity of non-amyloidogenic (ADAM10), and pro-amyloidogenic (BACE1 and PSEN1) secretases were qualitatively and quantitatively assessed. In addition, the formation of toxic amyloid products as an outcome of pro-amyloidogenic APP processing was evaluated through various modalities. RESULTS: Chlamydia pneumoniae infection of human astrocytoma cells promoted the transcriptional upregulation of numerous genes implicated in host neuroinflammation, lipid homeostasis, microtubule function, and APP processing. Relative to that of uninfected astrocytes, BACE1 and PSEN1 protein levels were enhanced by nearly twofold at 48-72 h post-Chlamydia pneumoniae infection. The processing of APP in Chlamydia pneumoniae-infected astrocytes favors the pro-amyloidogenic pathway, as demonstrated by an increase in enzymatic activity of BACE1, while that of ADAM10 was decreased. Fluorescence intensity of β-amyloid and ELISA-quantified levels of soluble-APP by products revealed temporally similar increases, confirming a BACE1/PSEN1-mediated processing of APP. CONCLUSIONS: Our findings suggest that Chlamydia pneumoniae infection of human astrocytes promotes the pro-amyloidogenic pathway of APP processing through the upregulation of expression and activity of β-secretase, upregulated expression of γ-secretase, and decreased activity of α-secretase. These effects of astrocyte infection provide evidence for a direct link between Chlamydia pneumoniae and AD pathology

Mechanisms of Mouse Hepatitis Virus Entry into Cells

Background: Viruses can enter cells through several mechanisms, two common ones being clathrin-mediated and caveolin-mediated endocytosis. The clathrin pathway delivers viral particles to endosomes, with subsequent acidification of the endosome and endosome/lysosome fusion often a prerequisite for release of the viral genome into the cytoplasm. The caveolin-mediated pathway delivers virus initially into vesicles called caveosomes, which have a neutral pH, before viral uncoating occurs. Viral entry pathways can be examined by using various drugs to inhibit the different endocytosis pathways, as well as by siRNA technology to down-regulate expression of clathrin or caveolin proteins on the surface of host cells

Infection of neuronal cells by Chlamydia pneumoniae and Herpes simplex virus type 1 alters expression of genes associated with Alzheimer’s disease

Several studies have suggested an infectious etiology for Alzheimer’s disease (AD). We have been investigating a potential role for both Chlamydia pneumoniae and Herpes simplex virus type 1 (HSV1) in the initiation of sporadic late-onset AD. Our current study focuses on investigation of gene expression using Alzheimer-specific Real-Time PCR microarrays on RNA derived from SKNMC human neuronal cells infected with C. pneumoniae and/or HSV1. There are distinct differences in the patterns of gene regulation by the two pathogens. For example, C. pneumoniae induces expression of genes involved in amyloid production and processing, such as β-amyloid precursor protein (APP), β-site APP-cleaving enzyme 1 (BACE1), a γ-secretase complex protein (nicastrin [NCSTN]), NEDD8 activating enzyme E1 (NAE1), as well as a mitochondria-associated protein (hydroxysteroid (17-β) dehydrogenase 10 [HSD17B10]), α-2-macroglobulin (A2M) and the metallopeptidase ADAM9. Conversely, HSV1 tends to down-regulate expression of many genes, including those encoding a component of the γ-secretase complex (anterior pharynx defective 1 homolog A [APH1A]), low density lipoprotein related proteins (LRP1, LRP6, and LRP8), β-synuclein (SNCB) and ubiquinols (UQCRC1, UQCRC2). Co-infection with C. pneumoniae and HSV-1 produced a greater down-regulation of gene expression than that seen with HSV1 alone for several genes, including APP-like proteins (APLP1, APLP2) and kinases (cell division cycle 2 protein [CDC2], cyclin-dependent kinase [CDK5] and CDC2-related kinase [CDKL1]). Our data indicate that both C. pneumoniae and HSV1 can modulate expression of genes associated with AD, and thus could contribute to AD pathology, however these two pathogens likely act via different pathways. Furthermore, for several genes, co-infection with both C. pneumoniae and HSV1 appears to exacerbate the changes in gene expression seen with HSV1 alone.https://digitalcommons.pcom.edu/posters/1007/thumbnail.jp

Infection with Chlamydia Pneumoniae Alters Calcium-associated Gene Regulation and Processes in Neuronal Cells and Monocytes: Implications for Alzheimer’s Disease

Background: First proposed by Khachaturian in 1994, the calcium hypothesis postulates that sustained disturbance of intracellular calcium is the leading cause of neurodegenerative disorders. Studies showing alteration in calcium signaling in both sporadic and familial Alzheimer’s disease (AD) support this hypothesis. Intracellular calcium signaling is tightly regulated in time, intensity, and space, and is responsible for a variety of neuronal functions. Calcium influx from the extracellular environment modulates calcium levels, as do intracellular stores in the endoplasmic reticulum. The focus of this study was to test various calcium related genes in both monocytes and neuronal cells. Previous studies have shown that cells infected with Chlamydia pneumoniae (Cpn) exhibit altered protein processing, such as amyloid and tau modification, consistent with those found in AD. We expect to see significant alterations in calcium genes, as well as their protein products in Cpn infected cells. Every calcium gene has a unique function in the cell. Determining which genes are up or down regulated following infection may provide insight into how the neurodegeneration process observed in AD is initiated by Cpn infections

Herpes Simplex Virus 1 and Chlamydophila (Chlamydia) pneumoniae promote Ab 1-42 amyloid processing in murine astrocytes linking an infectious process to Alzheimer\u27s disease

Background: Several studies have suggested an infectious etiology for Alzheimer\u27s disease (AD). Previously, our laboratory identified Chlamydia pneumoniae (Cpn) from autopsied sporadic AD brains, as well as developed a BALB/c mouse model that demonstrated infection-induced amyloid plaques similar to those found in AD. Hypothesis: We propose that an additional pathogen such as herpes simplex virus type 1 (HSV1), also may be a contributing factor in toin the pathology seen in AD. HSV1, in addition to Cpn, may be triggering the abnormal cleavage of the beta amyloid precursor protein (bAPP) into Ab1-42 , thereby contributing to amyloid plaque formation. Our current study examines amyloid processing following infection of primary and C8-DIA murine astrocytes with Cpn and HSV1. Materials and Methods: Immunocytochemistry and western analysis was used to analyze the outcome of infection by these two pathogens. Results: Cpn infection resulted in an increase in cytoplasmic labeling of Ab 1-42 relative to uninfected cells, while increased nuclear labeling of Ab 1-42 was observed following HSV1 infection. Co-infections with Cpn and HSV1 resulted in amyloid labeling resembling that of HSV1 infection alone, though Ab 1-42 labeling appeared decreased specifically in Cpn-infected cells of the co-infected monolayers. Conclusions: These data suggest that infection of astrocytic cells by HSV1 and (Cpn) alter the processing of bAPP, thereby producing Ab1-42. Therefore, these studies, inaddition to the previous research reported by our laboratory, support an emerging linkage of the infectious processs to the neuropathology characteristic of Alzheimer\u27s disease.https://digitalcommons.pcom.edu/posters/1008/thumbnail.jp