Toll-like receptor 3 differently modulates inflammation in progressive or benign multiple sclerosis

Dysregulation of humoral immunity, iron homeostasis, and lipid metabolism is associated with multiple sclerosis progression

BACKGROUND

Though most patients with multiple sclerosis (MS) presented earlier on as a relapsing-remitting (RR) disease, disability progression eventually occurred. Uncovering the mechanisms underlying progression may facilitate the unmet need for developing therapies to prevent progression. Benign MS (BMS), a rare form of MS, is the opposite from secondary progressive MS (SPMS) in that it lacks disease progression defined as Expanded Disability Status Scale (EDSS) ≤3 after at least 15 years of disease onset. BMS is characterized by rare and mild relapses with complete remission of clinical symptoms (lower activity of the disease) and lack of progression. Our study aims to identify transcriptomic and immunological differences between BMS and SPMS to unravel the pathogenesis of disease progression.

METHODS

We took multi-modal approaches with microarrays, flow cytometry, and lipidomics by three-way comparisons of patients with BMS vs. RRMS (low disease activity vs. moderate or severe activity), RRMS vs. SPMS (continued activity vs. complete transformation into progressive phase) as well as BMS vs. SPMS, matched for age and disease-duration (low disease activity and no progression vs. progression with or without activity).

RESULTS

We found that patients with RRMS and SPMS have a significantly higher percentage of B cells than those with BMS. BMS shows a different transcriptomic profile than SPMS. Many of the differentially expressed genes (DEGs) are involved in B cell-mediated immune responses. Additionally, long-chain fatty acids (LCFA), which can act as inflammatory mediators, are also altered in SPMS. Overall, our data suggest a role for the dysregulation of B cell differentiation and function, humoral immunity, and iron and lipid homeostasis in the pathogenesis of MS disease progression.

CONCLUSION

BMS has a unique transcriptomic and immunological profile compared to RRMS and SPMS. These differences will allow for personalized precision medicine and may ultimately lead to the discovery of new therapeutic targets for disease progression.

Brain alarm by self-extracellular nucleic acids: from neuroinflammation to neurodegeneration

Neurological disorders such as stroke, multiple sclerosis, as well as the neurodegenerative diseases Parkinson's or Alzheimer's disease are accompanied or even powered by danger associated molecular patterns (DAMPs), defined as endogenous molecules released from stressed or damaged tissue. Besides protein-related DAMPs or "alarmins", numerous nucleic acid DAMPs exist in body fluids, such as cell-free nuclear and mitochondrial DNA as well as different species of extracellular RNA, collectively termed as self-extracellular nucleic acids (SENAs). Among these, microRNA, long non-coding RNAs, circular RNAs and extracellular ribosomal RNA constitute the majority of RNA-based DAMPs. Upon tissue injury, necrosis or apoptosis, such SENAs are released from neuronal, immune and other cells predominantly in association with extracellular vesicles and may be translocated to target cells where they can induce intracellular regulatory pathways in gene transcription and translation. The majority of SENA-induced signaling reactions in the brain appear to be related to neuroinflammatory processes, often causally associated with the onset or progression of the respective disease. In this review, the impact of the diverse types of SENAs on neuroinflammatory and neurodegenerative diseases will be discussed. Based on the accumulating knowledge in this field, several specific antagonistic approaches are presented that could serve as therapeutic interventions to lower the pathological outcome of the indicated brain disorders.

Analysis of Differential TLR Activation in a Mouse Model of Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative and autoimmune disease affecting the central nervous system (CNS). The precise etiology of MS is still undeciphered, and signs and symptoms of the disease are varied and complex, ranging from axonal degeneration, synaptic, and neuronal loss to demyelination. Inflammation plays a critical role in determining the onset and the progression of MS, but there is still a lot of information missing before scientists come to understand what are the factors that contribute to the establishment of the neuroinflammation. Thus, various murine models, each representative of a specific hallmark of MS, are used to study the processes underlying the pathogenetic mechanisms of the disease in an attempt to find effective drugs for its treatment. Among the many causes of MS, viral infections appear to be one of the most prominent ones. In this scenario, the comprehension of the role of receptors activated upon the recognition of viral, and in general microbial, components in determining onset and progression of the neuroinflammation is of paramount importance. Toll-like receptors (TLRs) are evolutionarily conserved receptors that recognize several pathogen-associated molecular patterns (PAMPs), common structures of the pathogens, or the damage caused by the pathogens within the host. TLRs are thus directly involved in the regulation of inflammatory reactions and in the activation of the innate and, subsequently, the adaptive immune responses crucial for the elimination of infectious pathogens. The role of TLR activation in the development of MS is widely studied in various murine models of MS, as well as in MS patients. In this chapter, we will summarize the current knowledge about the contribution of TLRs to the development or progression of MS, and we will illustrate different methods commonly used for the investigation of the role of different TLRs in various murine models of the disease.

Paeonol increases the antioxidant and anti-inflammatory capacity of gibel carp (Carassius auratus gibelio) challenged with Aeromonas hydrophila

Paeonol, a naturally occurring polyphenol isolated from medical plant, has been known to exhibit anti-oxidative and anti-inflammatory effects. In order to evaluate the effect of paeonol on Carassius auratus gibelio infected by pathogenic bacteria Aeromonas hydriphila. 750 fish were randomly divided into 5 groups, which separately treated with 0.85% sterile saline (blank), A. hydriphila (negative control), A. hydriphila with paeonol (4 mg/kg, 64 mg/kg), and A. hydriphila with enrofloxacin (12 mg/kg, positive control). Fish were anaesthetized with MS-222 (100 mg/L), and samples were collected at 6 and 72 h after A. hydriphila challenge. The results showed that compared with the negative group, the survival in paeonol groups marked increased by 14.75% and 18.94%. The plasma immunoglobulin M (IgM) was notably increased, and low density lipoprotein (LDL) was significantly decreased in paeonol groups at 6 h (P < 0.05). The antioxidative enzymes catalase (CAT), total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) were significantly increased in paeonol groups at 6 h, while malondialdehyde (MDA) and myeloperoxidase (MPO) contents were lower (P < 0.05). The inflammatory related genes MyD88 and TLR-5 were significantly downregulated, and the TLR-3 was significantly increased in paeonol groups at 72 h (P < 0.05). In addition, histopathological analyses showed that the lesion in liver, spleen and caudal kidney were considerably attenuated in paeonol groups. In conclusion, paeonol could increase the survival rate, mitigate oxidative damage, inflammation, tissue lesions, and improve the immunity of gibel carp challenged with A. hydrophila.

Role of Toll-Like Receptors in Neuroimmune Diseases: Therapeutic Targets and Problems

Toll-like receptors (TLRs) are a class of proteins playing a key role in innate and adaptive immune responses. TLRs are involved in the development and progression of neuroimmune diseases via initiating inflammatory responses. Thus, targeting TLRs signaling pathway may be considered as a potential therapy for neuroimmune diseases. However, the role of TLRs is elusive and complex in neuroimmune diseases. In addition to the inadequate immune response of TLRs inhibitors in the experiments, the recent studies also demonstrated that partial activation of TLRs is conducive to the production of anti-inflammatory factors and nervous system repair. Exploring the mechanism of TLRs in neuroimmune diseases and combining with developing the emerging drug may conquer neuroimmune diseases in the future. Herein, we provide an overview of the role of TLRs in several neuroimmune diseases, including multiple sclerosis, neuromyelitis optica spectrum disorder, Guillain-Barré syndrome and myasthenia gravis. Emerging difficulties and potential solutions in clinical application of TLRs inhibitors will also be discussed.

Triangle of cytokine storm, central nervous system involvement, and viral infection in COVID-19: the role of sFasL and neuropilin-1

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) is identified as the cause of coronavirus disease 2019 (COVID-19), and is often linked to extreme inflammatory responses by over activation of neutrophil extracellular traps (NETs), cytokine storm, and sepsis. These are robust causes for multi-organ damage. In particular, potential routes of SARS-CoV2 entry, such as angiotensin-converting enzyme 2 (ACE2), have been linked to central nervous system (CNS) involvement. CNS has been recognized as one of the most susceptible compartments to cytokine storm, which can be affected by neuropilin-1 (NRP-1). ACE2 is widely-recognized as a SARS-CoV2 entry pathway; However, NRP-1 has been recently introduced as a novel path of viral entry. Apoptosis of cells invaded by this virus involves Fas receptor-Fas ligand (FasL) signaling; moreover, Fas receptor may function as a controller of inflammation. Furthermore, NRP-1 may influence FasL and modulate cytokine profile. The neuroimmunological insult by SARS-CoV2 infection may be inhibited by therapeutic approaches targeting soluble Fas ligand (sFasL), cytokine storm elements, or related viral entry pathways. In the current review, we explain pivotal players behind the activation of cytokine storm that are associated with vast CNS injury. We also hypothesize that sFasL may affect neuroinflammatory processes and trigger the cytokine storm in COVID-19.

Altered Levels of Toll-Like Receptors in Circulating Extracellular Vesicles in Multiple Sclerosis

Extracellular vesicles (EVs) are involved in inter-cellular communication and their cargo may provide prognostic/diagnostic biomarkers. To discover EV-associated biomarkers for Multiple Sclerosis (MS), we used an immune marker array to identify surface proteins on circulating EVs that differ between MS patients and controls (n = 3 each). We identified toll-like receptor-3 (TLR3) as a potential target for further validation. We utilized prospectively collected serum from relapsing-remitting MS patients (n = 18) and controls (n = 16) and confirmed lower concentration of TLR3 and higher concentration of mechanistically related TLR4 in MS EVs compared to controls. Future studies may further evaluate the utility of EV-associated TLRs as MS biomarkers and uncover their mechanistic significance.

Enhanced TLR2 responses in multiple sclerosis

The roles of the microbiome and innate immunity in the pathogenesis of multiple sclerosis (MS) remain unclear. We have previously documented abnormally low levels of a microbiome‐derived Toll‐like receptor (TLR)2‐stimulating bacterial lipid in the blood of MS patients and postulated that this is indicative of a deficiency in the innate immune regulating function of the microbiome in MS. We postulated further that the resulting enhanced TLR2 responsiveness plays a critical role in the pathogenesis of MS. As proof‐of‐concept, we reported that decreasing systemic TLR2 responsiveness by administering very low‐dose TLR2 ligands attenuated significantly the mouse model of MS, experimental autoimmune encephalomyelitis. Studies of Toll‐like receptor responses in patients with MS have been conflicting. Importantly, most of these investigations have focused on the response to TLR4 ligation and few have characterized TLR2 responses in MS. In the present study, our goal was to characterize TLR2 responses of MS patients using multiple approaches. Studying a total of 26 MS patients and 32 healthy controls, we now document for the first time that a large fraction of MS patients (50%) demonstrate enhanced responsiveness to TLR2 stimulation. Interestingly, the enhanced TLR2 responders include a significant fraction of those with progressive forms of MS, a subset of patients considered unresponsive to adaptive immune system‐targeting therapies. Our results suggest the presence of a pathologically relevant TLR2 related innate immune abnormality in patients with both relapsing–remitting and progressive MS. These findings may have significant implications for understanding the role of innate immunity in the pathogenesis of MS.

B Lymphocytes in Multiple Sclerosis: Bregs and BTLA/CD272 Expressing-CD19+ Lymphocytes Modulate Disease Severity

B lymphocytes contribute to the pathogenesis of Multiple Sclerosis (MS) by secreting antibodies and producing cytokines. This latter function was analyzed in myelin olygodendrocyte protein (MOG)-stimulated CD19+ B lymphocytes of 71 MS patients with different disease phenotypes and 40 age-and sex-matched healthy controls (HC). Results showed that: 1) CD19+/TNFα+, CD19+/IL-12+ and CD19+/IFNγ+ lymphocytes are significantly increased in primary progressive (PP) compared to secondary progressive (SP), relapsing-remitting (RR), benign (BE) MS and HC; 2) CD19+/IL-6+ lymphocytes are significantly increased in PP, SP and RR compared to BEMS and HC; and 3) CD19+/IL-13+, CD19+/IL-10+, and CD19+/IL-10+/TGFβ+ (Bregs) B lymphocytes are reduced overall in MS patients compared to HC. B cells expressing BTLA, a receptor whose binding to HVEM inhibits TcR-initiated cytokine production, as well as CD19+/BTLA+/IL-10+ cells were also significantly overall reduced in MS patients compared to HC. Analyses performed in RRMS showed that fingolimod-induced disease remission is associated with a significant increase in Bregs, CD19+/BTLA+, and CD19+/BTLA+/IL-10+ B lymphocytes. B lymphocytes participate to the pathogenesis of MS via the secretion of functionally-diverse cytokines that might play a role in determining disease phenotypes. The impairment of Bregs and CD19+/BTLA+ cells, in particular, could play an important pathogenic role in MS.

p53 amplifies Toll-like receptor 5 response in human primary and cancer cells through interaction with multiple signal transduction pathways

The p53 tumor suppressor regulates transcription of genes associated with diverse cellular functions including apoptosis, growth arrest, DNA repair and differentiation. Recently, we established that p53 can modulate expression of Toll-like receptor (TLR) innate immunity genes but the degree of cross-talk between p53 and TLR pathways remained unclear. Here, using gene expression profiling we characterize the global effect of p53 on the TLR5-mediated transcription in MCF7 cells. We found that combined activation of p53 and TLR5 pathways synergistically increases expression of over 200 genes, mostly associated with immunity and inflammation. The synergy was observed in several human cancer cells and primary lymphocytes. The p53-dependent amplification of transcriptional response to TLR5 activation required expression of NFκB subunit p65 and was mediated by several molecular mechanisms including increased phosphorylation of p38 MAP kinase, PI3K and STAT3 signaling. Additionally, p53 induction increased cytokine expression in response to TNFα, another activator of NFκB and MAP kinase pathways, suggesting a broad interaction between p53 and these signaling pathways. The expression of many synergistically induced genes is elevated in breast cancer patients responsive to chemotherapy. We suggest that p53's capacity to enhance immune response could be exploited to increase antitumor immunity and to improve cancer treatment.

Early IFN-γ production together with decreased expression of TLR3 and TLR9 characterizes EAE development conditional on the presence of myelin

Experimental autoimmune encephalomyelitis (EAE) is a model for the study of multiple sclerosis, which is an inflammatory and demyelinating disease of the central nervous system (CNS). Despite increased efforts to elucidate the function of toll-like receptors (TLRs) in autoimmune diseases of the CNS, the relative contribution of other factors, including the immunomodulatory properties of TLR signaling, role of the innate response and the presence or absence of myelin peptides remain unclear. The aim was to evaluate TLR expression in the CNS during EAE development by investigating the expression of TLRs in the initial phase of EAE and establishing correlations with the modulation of inflammatory factors. Mice were subcutaneously immunized at the tail base with 100 μg of myelin oligodendrocyte glycoprotein peptide (MOG35-55), emulsified in complete Freund's adjuvant (CFA) supplemented with 400 μg of attenuated Mycobacterium tuberculosis H37RA. Pertussis toxin (300 ng per animal) was intraperitoneally injected on the day of immunization and 48 h later. Another group (MOG(-)) received an equal emulsion of CFA and M. tuberculosis, without MOG35-55, and the same protocol of Pertussis toxin. The immunized mice presented signs of disease with increased IFN-γ production and presence of NK cells on Day 2 postimmunization and reduced the expression of TLR-3 and TLR-9. In the spinal cord, CCL5 and CCL20 were higher in EAE. This study establishes a correlation between TLR-3 and TLR-9 expression with the development of EAE. In addition, evidence of a role for the myelin peptide in targeting the innate inflammatory response to the CNS is presented.

Close Encounters of the First Kind: Innate Sensors and Multiple Sclerosis

Although autoimmune diseases by definition imply adaptive immune system pathologies, growing evidence points to the relevance of innate receptors in modulating the initiation and progression of the autoreactive response. Multiple sclerosis (MS) is a chronic autoimmune disease characterised by central nervous system (CNS) demyelination, inflammation and axonal damage, in which the role of several pathogens such as herpes viruses have long been described as potential triggers. Encounters of these pathogens with altered innate receptors in susceptible individuals might drive pathological autoreactivity and inflammation, overcoming tolerance and causing subsequent CNS damage. In particular, functional and genetic studies reveal that Toll-like receptor (TLR) 2 and the Nod-like receptor (NLR) P3 could be involved in MS pathogenesis, whereas TLR3, the triggering receptor expressed on myeloid cells (TREM)-2 and the C-type lectin receptors (CLRs) MBL and MASP-3 would have a putative protective role. A better understanding of these interactions will provide important insights into the aetiopathogenesis of MS and could help design potential targets for novel therapies.

Role of inflammation and apoptosis in multiple sclerosis: Comparative analysis between the periphery and the central nervous system

Multiple sclerosis (MS) is a complex, multifactorial disease associated with damage to the axonal myelin sheaths and neuronal degeneration. The pathognomonic event in MS is oligodendrocyte loss accompanied by axonal damage, blood-brain barrier leakage, inflammation and infiltration of immune cells. The etiopathogenesis of MS is far from being elucidated. However, increasing evidence suggests that the inflammatory and apoptotic responses, occurring in patients either at the peripheral level or the central nervous system (CNS), can play a role. In this review, we give a comprehensive picture of general aspects of inflammation and apoptosis in MS, with special emphasis on the until now not well highlighted possible links between phenomena relevant to these aspects occurring in either the periphery or in the CNS during MS.

Increased CXCL10 expression in MS MSCs and monocytes is unaffected by AHSCT

Objective

To confirm CXCL10 over production in bone marrow mesenchymal stem cells (MSCs) and circulating monocytes isolated from multiple sclerosis patients (MS) and identify predate cell molecular signature; to extend this analysis after autologous hematopoietic stem cell transplantation (AHSCT) to test if therapy has modifying effects on MSCs and circulating monocytes.

Methods

MSCs and monocytes were isolated from 19 MS patients who undergone AHSCT before and seven of them at least 3 years after transplant. CXCL10 production was detected after LPS/IFN-γ stimulation. TLR4 signaling pathways were investigated by means of transcription factors phosphorylation/activation level. RT-PCR of activated transcription factors was performed to quantify their expression. All experiments were conducted in parallel with 24 matched healthy donors (HD).

Results

CXCL10 expression was significantly increased in both peripheral circulating monocytes and BM MSCs compared to HD. We showed that CXCL10 production is determined by an altered signaling pathway downstream TLR4, with the involvement of STAT-1, NF-κB, p38, JNK, and CREB. All upregulated transcription factors are more phosphorylated in MS patient sample. These features are not modified after AHSCT.

Interpretation

We demonstrated that in MS two different cell lineages are characterized by significantly increased production of CXCL10, due to altered signaling pathways of innate immune reaction mediated by TLR4, probably associated with disease phenotype. This characteristic is not modified by AHSCT, suggesting that when T and B lymphocytes are reset, other possible components of MS pathology, such as CXCL10 over production, do not determine therapy outcome.