Geeta Ramesh

Interaction of the Lyme Disease Spirochete Borrelia burgdorferi with Brain Parenchyma Elicits Inflammatory Mediators from Glial Cells as Well as Glial and Neuronal Apoptosis

Lyme neuroborreliosis, caused by the spirochete Borrelia burgdorferi, often manifests by causing neurocognitive deficits. As a possible mechanism for Lyme neuroborreliosis, we hypothesized that B. burgdorferi induces the production of inflammatory mediators in the central nervous system with concomitant neuronal and/or glial apoptosis. To test our hypothesis, we constructed an ex vivo model that consisted of freshly collected slices from brain cortex of a rhesus macaque and allowed live B. burgdorferi to penetrate the tissue. Numerous transcripts of genes that regulate inflammation as well as oligodendrocyte and neuronal apoptosis were significantly altered as assessed by DNA microarray analysis. Transcription level increases of 7.43-fold (P = 0.005) for the cytokine tumor necrosis factor-alpha and 2.31-fold (P = 0.016) for the chemokine interleukin (IL)-8 were also detected by real-time-polymerase chain reaction array analysis. The immune mediators IL-6, IL-8, IL-1beta, COX-2, and CXCL13 were visualized in glial cells in situ by immunofluorescence staining and confocal microscopy. Concomitantly, significant proportions of both oligodendrocytes and neurons undergoing apoptosis were present in spirochete-stimulated tissues. IL-6 production by astrocytes in addition to oligodendrocyte apoptosis were also detected, albeit at lower levels, in rhesus macaques that had received in vivo intraparenchymal stereotaxic inoculations of live B. burgdorferi. These results provide proof of concept for our hypothesis that B. burgdorferi produces inflammatory mediators in the central nervous system, accompanied by glial and neuronal apoptosis.

Pathogenesis of Lyme neuroborreliosis: Borrelia burgdorferi lipoproteins induce both proliferation and apoptosis in rhesus monkey astrocytes

Brain invasion by Borrelia burgdorferi, the agent of Lyme disease, results in an inflammatory and neurodegenerative disorder called neuroborreliosis. In humans, neuroborreliosis has been correlated with enhanced concentration of glial fibrillary acidic protein in the cerebrospinal fluid, a sign of astrogliosis. Rhesus monkeys infected by us with B. burgdorferi showed evidence of astrogliosis, namely astrocyte proliferation and apoptosis. We formulated the hypothesis that astrogliosis could be caused by spirochetal lipoproteins. We established primary cultures of rhesus monkey astrocytes and stimulated the cells with recombinant lipidated outer surface protein A (L‐OspA), a model B. burgdorferi lipoprotein, and tripalmitoyl‐S‐glyceryl‐Cys‐Ser‐Lys4‐OH (Pam3Cys), a synthetic lipopeptide that mimics the structure of the lipoprotein lipid moiety. L‐OspA elicited not only astrocyte proliferation but also apoptosis, two features observed during astrogliosis. Astrocytes produced both IL‐6 and TNF‐α in response to L‐OspA and Pam3Cys. Proliferation induced by L‐OspA was diminished in the presence of an excess of anti‐IL‐6 antibody, and apoptosis induced by this lipoprotein was completely suppressed with anti‐TNF‐α antibody. Hence, IL‐6 contributes to, and TNF‐α determines, astrocyte proliferation and apoptosis, respectively, as elicited by lipoproteins. Our results provide proof of the principle that spirochetal lipoproteins could be key virulence factors in Lyme neuroborreliosis, and that astrogliosis might contribute to neuroborreliosis pathogenesis.

Possible role of glial cells in the onset and progression of Lyme neuroborreliosis

BackgroundLyme neuroborreliosis (LNB) may present as meningitis, cranial neuropathy, acute radiculoneuropathy or, rarely, as encephalomyelitis. We hypothesized that glia, upon exposure to Borrelia burgdorferi, the Lyme disease agent, produce inflammatory mediators that promote the acute cellular infiltration of early LNB. This inflammatory context could potentiate glial and neuronal apoptosis.MethodsWe inoculated live B. burgdorferi into the cisterna magna of rhesus macaques and examined the inflammatory changes induced in the central nervous system (CNS), and dorsal root nerves and ganglia (DRG).ResultsELISA of the cerebrospinal fluid (CSF) showed elevated IL-6, IL-8, CCL2, and CXCL13 as early as one week post-inoculation, accompanied by primarily lymphocytic and monocytic pleocytosis. In contrast, onset of the acquired immune response, evidenced by anti-B. burgdorferi C6 serum antibodies, was first detectable after 3 weeks post-inoculation. CSF cell pellets and CNS tissues were culture-positive for B. burgdorferi. Histopathology revealed signs of acute LNB: severe multifocal leptomeningitis, radiculitis, and DRG inflammatory lesions. Immunofluorescence staining and confocal microscopy detected B. burgdorferi antigen in the CNS and DRG. IL-6 was observed in astrocytes and neurons in the spinal cord, and in neurons in the DRG of infected animals. CCL2 and CXCL13 were found in microglia as well as in endothelial cells, macrophages and T cells. Importantly, the DRG of infected animals showed significant satellite cell and neuronal apoptosis.ConclusionOur results support the notion that innate responses of glia to B. burgdorferi initiate/mediate the inflammation seen in acute LNB, and show that neuronal apoptosis occurs in this context.

A possible role for inflammation in mediating apoptosis of oligodendrocytes as induced by the Lyme disease spirochete Borrelia burgdorferi.

BackgroundInflammation caused by the Lyme disease spirochete B. burgdorferi is an important factor in the pathogenesis of Lyme neuroborreliosis. Our central hypothesis is that B. burgdorferi can cause disease via the induction of inflammatory mediators such as cytokines and chemokines in glial and neuronal cells. Earlier we demonstrated that interaction of B. burgdorferi with brain parenchyma induces inflammatory mediators in glial cells as well as glial (oligodendrocyte) and neuronal apoptosis using ex vivo and in vivo models of experimentation.MethodsIn this study we evaluated the ability of live B. burgdorferi to elicit inflammation in vitro in differentiated human MO3.13 oligodendrocytes and in differentiated primary human oligodendrocytes, by measuring the concentration of immune mediators in culture supernatants using Multiplex ELISA assays. Concomitant apoptosis was quantified in these cultures by the in situ terminal deoxynucleotidyl transferase mediated UTP nick end labeling (TUNEL) assay and by quantifying active caspase-3 by flow cytometry. The above phenomena were also evaluated after 48 h of stimulation with B. burgdorferi in the presence and absence of various concentrations of the anti-inflammatory drug dexamethasone.ResultsB. burgdorferi induced enhanced levels of the cytokine IL-6 and the chemokines IL-8 and CCL2 in MO3.13 cells as compared to basal levels, and IL-8 and CCL2 in primary human oligodendrocytes, in a dose-dependent manner. These cultures also showed significantly elevated levels of apoptosis when compared with medium controls. Dexamethasone reduced both the levels of immune mediators and apoptosis, also in a manner that was dose dependent.ConclusionsThis finding supports our hypothesis that the inflammatory response elicited by the Lyme disease spirochete in glial cells contributes to neural cell damage. As oligodendrocytes are vital for the functioning and survival of neurons, the inflammation and subsequent apoptosis of oligodendrocytes induced by B. burgdorferi could contribute to the pathogenesis of Lyme neuroborreliosis.

Inflammation in the Pathogenesis of Lyme Neuroborreliosis

Lyme neuroborreliosis, caused by the spirochete Borrelia burgdorferi, affects both peripheral and central nervous systems. We assessed a causal role for inflammation in Lyme neuroborreliosis pathogenesis by evaluating the induced inflammatory changes in the central nervous system, spinal nerves, and dorsal root ganglia (DRG) of rhesus macaques that were inoculated intrathecally with live B. burgdorferi and either treated with dexamethasone or meloxicam (anti-inflammatory drugs) or left untreated. ELISA of cerebrospinal fluid showed significantly elevated levels of IL-6, IL-8, chemokine ligand 2, and CXCL13 and pleocytosis in all infected animals, except dexamethasone-treated animals. Cerebrospinal fluid and central nervous system tissues of infected animals were culture positive for B. burgdorferi regardless of treatment. B. burgdorferi antigen was detected in the DRG and dorsal roots by immunofluorescence staining and confocal microscopy. Histopathology revealed leptomeningitis, vasculitis, and focal inflammation in the central nervous system; necrotizing focal myelitis in the cervical spinal cord; radiculitis; neuritis and demyelination in the spinal roots; and inflammation with neurodegeneration in the DRG that was concomitant with significant neuronal and satellite glial cell apoptosis. These changes were absent in the dexamethasone-treated animals. Electromyography revealed persistent abnormalities in F-wave chronodispersion in nerve roots of a few infected animals; which were absent in dexamethasone-treated animals. These results suggest that inflammation has a causal role in the pathogenesis of acute Lyme neuroborreliosis.

The Lyme disease spirochete Borrelia burgdorferi induces inflammation and apoptosis in cells from dorsal root ganglia

BackgroundLyme neuroborreliosis (LNB), caused by the spirochete Borrelia burgdorferi, affects both the peripheral and the central nervous systems. Radiculitis or nerve root inflammation, which can cause pain, sensory loss, and weakness, is the most common manifestation of peripheral LNB in humans. We previously reported that rhesus monkeys infected with B. burgdorferi develop radiculitis as well as inflammation in the dorsal root ganglia (DRG), with elevated levels of neuronal and satellite glial cell apoptosis in the DRG. We hypothesized that B. burgdorferi induces inflammatory mediators in glial and neuronal cells and that this inflammatory milieu precipitates glial and neuronal apoptosis.MethodsTo model peripheral neuropathy in LNB we incubated normal rhesus DRG tissue explants with live B. burgdorferi ex vivo and identified immune mediators, producer cells, and verified the presence of B. burgdorferi in tissue sections by immunofluorescence staining and confocal microscopy. We also set up primary cultures of DRG cells from normal adult rhesus macaques and incubated the cultures with live B. burgdorferi. Culture supernatants were subjected to multiplex ELISA to detect immune mediators, while the cells were evaluated for apoptosis by the in situ TUNEL assay. A role for inflammation in mediating apoptosis was assessed by evaluating the above phenomena in the presence and absence of various concentrations of the anti-inflammatory drug dexamethasone. As Schwann cells ensheath the dorsal roots of the DRG, we evaluated the potential of live B. burgdorferi to induce inflammatory mediators in human Schwann cell (HSC) cultures.ResultsRhesus DRG tissue explants exposed to live B. burgdorferi showed localization of CCL2 and IL-6 in sensory neurons, satellite glial cells and Schwann cells while IL-8 was seen in satellite glial cells and Schwann cells. Live B. burgdorferi induced elevated levels of IL-6, IL-8 and CCL2 in HSC and DRG cultures and apoptosis of sensory neurons. Dexamethasone reduced the levels of immune mediators and neuronal apoptosis in a dose dependent manner.ConclusionIn this model, B. burgdorferi induced an inflammatory response and neuronal apoptosis of DRG. These pathophysiological processes could contribute to peripheral neuropathy in LNB.

Visualizing Cytokine-Secreting Cells In Situ in the Rhesus Macaque Model of Chronic Gut Inflammation

ABSTRACT Cytokine-producing cells in gut-associated lymphoid tissues of rhesus macaques with chronic enterocolitis were studied. The confocal microscopy technique that we developed enables simultaneous in situ visualization of multiple extra- and/or intracellular antigens at a resolution higher than that allowed by light or epifluorescence microscopy. The presence of interleukin-6 (IL-6)-, tumor necrosis factor alpha (TNF-α)-, and IL-1-α-producing cells was focally intense in the colon lamina propria of the affected animals. The IL-1-α-producing cells were T lymphocytes (CD3+), while the TNF-α-producing cells were both macrophages (CD68+/HAM56+/LN5+) and T lymphocytes (CD3+). The IL-6-producing cells within the colon consisted of T lymphocytes and macrophages. The amount of IL-6-producing cells seen in macaques with enterocolitis was significantly higher (P < 0.001) than that seen in the healthy control animal, while TNF-α- and IL-1-α-producing cells were seen only in macaques with enterocolitis. Most of the T lymphocytes that produced cytokines were detected in the lamina propria, while the macrophages were most prominent in highly inflamed regions of the lamina propria. Taken together, our findings indicate that there might be immunological similarity between chronic enterocolitis of rhesus macaques and humans, suggesting the potential use of the nonhuman primate model for the validation of novel therapies.

Pathogenesis of Lyme neuroborreliosis: mitogen-activated protein kinases Erk1, Erk2, and p38 in the response of astrocytes to Borrelia burgdorferi lipoproteins.

Lyme borreliosis, which is prevalent both in the US and in Europe, is an infectious disease that may cause local inflammation in numerous organs. We have hypothesized that, as with some neurodegenerative diseases, the pathogenesis of the neurocognitive deficiencies associated with Lyme neuroborreliosis of the central nervous system also has an inflammatory component. Dysregulated production of pro-inflammatory cytokines such as IL-6 and TNF-alpha can lead to neuronal damage. Mitogen-activated protein kinases (MAPK) play a key role in the regulation of neuronal development, growth, and survival, as well as that of pro-inflammatory cytokine production. As a model, we explored the possibility that MAPK-mediated lipoprotein-induced apoptosis and gliosis of rhesus monkey astrocytes stimulated in vitro. Lipoproteins are the key inflammatory molecule type of Borrelia burgdorferi, the spirochete that causes Lyme disease, and we had previously shown that lipoprotein-induced TNF-alpha production in astrocytes caused astrocyte apoptosis, and IL-6 enhanced proliferation of these cells. Lipoproteins readily activated p38 and Erk1/2 MAPK, thus enlisting these pathways among the kinase pathways that spirochetes may address as they invade the central nervous system. We also investigated whether specific inhibition of p38 and Erk1/2 MAPK would inhibit TNF-alpha and IL-6 production and thus astrocyte apoptosis, and proliferation, respectively. Lipoprotein-stimulated IL-6 production was unaffected by the MAPK inhibitors. In contrast, inhibition of both p38 and Erk1/2 significantly diminished TNF-alpha production, and totally abrogated production of this cytokine when both MAPK pathways were inhibited simultaneously. MAPK inhibition thus may be considered as a strategy to control inflammation and apoptosis in Lyme neuroborreliosis.

Effects of dexamethasone and meloxicam on Borrelia burgdorferi -induced inflammation in glial and neuronal cells of the central nervous system

BackgroundLyme neuroborreliosis (LNB), caused by the spirochete Borrelia burgdorferi (Bb), affects both the central and peripheral nervous systems. Previously, we reported that in a model of acute LNB in rhesus monkeys, treatment with the anti-inflammatory drug dexamethasone significantly reduced both pleocytosis and levels of cerebrospinal fluid (CSF) immune mediators that were induced by Bb. Dexamethasone also inhibited the formation of inflammatory, neurodegenerative, and demyelinating lesions in the brain and spinal cord of these animals. In contrast, these signs were evident in the infected animals that were left untreated or in those that were treated with meloxicam, a non-steroidal anti-inflammatory drug.MethodsTo address the differential anti-inflammatory effects of dexamethasone and meloxicam in the central nervous system (CNS), we evaluated the potential of these drugs to alter the levels of Bb-induced inflammatory mediators in culture supernatants of rhesus frontal cortex (FC) explants, primary rhesus astrocytes and microglia, and human oligodendrocytes. We also ascertained the potential of dexamethasone to modulate Bb-induced apoptosis in rhesus FC explants. As meloxicam is a known COX-2 inhibitor, we evaluated whether meloxicam altered the levels of COX-2 as induced by live Bb in cell lysates of primary rhesus astrocytes and microglia.ResultsDexamethasone but not meloxicam significantly reduced the levels of several Bb-induced immune mediators in culture supernatants of FC explants, astrocytes, microglia, and oligodendrocytes. Dexamethasone also had a protective effect on Bb-induced neuronal and oligodendrocyte apoptosis in rhesus FC explants. Further, meloxicam significantly reduced the levels of Bb-induced COX-2 in microglia, while both Bb and meloxicam were unable to alter the constitutive levels of COX-2 in astrocytes.ConclusionsThese data indicate that dexamethasone and meloxicam have differential anti-inflammatory effects on Bb-induced inflammation in glial and neuronal cells of the CNS and help explain the in vivo findings of significantly reduced inflammatory mediators in the CSF and lack of inflammatory neurodegenerative lesions in the brain and spinal cord of Bb-infected animals that were treated with dexamethasone but not meloxicam. Signaling cascades altered by dexamethasone could serve as possible therapeutic targets for limiting CNS inflammation and tissue damage in LNB.

Anti-inflammatory effects of dexamethasone and meloxicam on Borrelia burgdorferi -induced inflammation in neuronal cultures of dorsal root ganglia and myelinating cells of the peripheral nervous system

BackgroundLyme neuroborreliosis (LNB), caused by the spirochete Borrelia burgdorferi (Bb), could result in cognitive impairment, motor dysfunction, and radiculoneuritis. We hypothesized that inflammation is a key factor in LNB pathogenesis and recently evaluated the effects of dexamethasone, a steroidal anti-inflammatory drug, and meloxicam a non-steroidal anti-inflammatory drug (NSAID), in a rhesus monkey model of acute LNB. Dexamethasone treatment significantly reduced the levels of immune mediators, and prevented inflammatory and/or neurodegenerative lesions in the central and peripheral nervous systems, and apoptosis in the dorsal root ganglia (DRG). However, infected animals treated with meloxicam showed levels of inflammatory mediators, inflammatory lesions, and DRG cell apoptosis that were similar to that of the infected animals that were left untreated.MethodsTo address the differential anti-inflammatory effects of dexamethasone and meloxicam on neuronal and myelinating cells of the peripheral nervous system (PNS), we evaluated the potential of these drugs to alter the levels of Bb-induced inflammatory mediators in rhesus DRG cell cultures and primary human Schwann cells (HSC), using multiplex enzyme-linked immunosorbent assays (ELISA). We also ascertained the ability of these drugs to modulate cell death as induced by live Bb in HSC using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) viability assay and the potential of dexamethasone to modulate Bb-induced apoptosis in HSC by the TUNEL assay.ResultsEarlier, we reported that dexamethasone significantly reduced Bb-induced immune mediators and apoptosis in rhesus DRG cell cultures. Here, we report that dexamethasone but not meloxicam significantly reduces the levels of several cytokines and chemokines as induced by live Bb, in HSC and DRG cell cultures. Further, meloxicam does not significantly alter Bb-induced cell death in HSC, while dexamethasone protects HSC against Bb-induced cell death.ConclusionsThese data help further explain our in vivo findings of significantly reduced levels of inflammatory mediators, DRG-apoptosis, and lack of inflammatory neurodegenerative lesions in the nerve roots and DRG of Bb-infected animals that were treated with dexamethasone, but not meloxicam. Evaluating the role of the signaling mechanisms that contribute to the anti-inflammatory potential of dexamethasone in the context of LNB could serve to identify therapeutic targets for limiting radiculitis and axonal degeneration in peripheral LNB.