Tumor necrosis factor alpha response elements in the HLA-DRA promoter: identification of a tumor necrosis factor alpha-induced DNA-protein complex in astrocytes

Spatial Transcriptomics Reveals Signatures of Histopathological Changes in Muscular Sarcoidosis

Sarcoidosis is a multisystemic disease characterized by non-caseating granuloma infiltrating various organs. The form with symptomatic muscular involvement is called muscular sarcoidosis. The impact of immune cells composing the granuloma on the skeletal muscle is misunderstood. Here, we investigated the granuloma-skeletal muscle interactions through spatial transcriptomics on two patients affected by muscular sarcoidosis. Five major transcriptomic clusters corresponding to perigranuloma, granuloma, and three successive muscle tissue areas (proximal, intermediate, and distal) around the granuloma were identified. Analyses revealed upregulated pathways in the granuloma corresponding to the activation of T-lymphocytes and monocytes/macrophages cytokines, the upregulation of extracellular matrix signatures, and the induction of the TGF-β signaling in the perigranuloma. A comparison between the proximal and distal muscles to the granuloma revealed an inverse correlation between the distance to the granuloma and the upregulation of cellular response to interferon-γ/α, TNF-α, IL-1,4,6, fibroblast proliferation, epithelial to mesenchymal cell transition, and the downregulation of muscle gene expression. These data shed light on the intercommunications between granulomas and the muscle tissue and provide pathophysiological mechanisms by showing that granuloma immune cells have a direct impact on proximal muscle tissue by promoting its progressive replacement by fibrosis via the expression of pro-inflammatory and profibrosing signatures. These data could possibly explain the evolution towards a state of disability for some patients.

Implications of fractalkine on glial function, ablation and glial proteins/receptors/markers—understanding its therapeutic usefulness in neurological settings: a narrative review

Background

Fractalkine (CX3CL1) is a chemokine predominantly released by neurons. As a signaling molecule, CX3CL1 facilitates talk between neurons and glia. CX3CL1 is considered as a potential target which could alleviate neuroinflammation. However, certain controversial results and ambiguous role of CX3CL1 make it inexorable to decipher the overall effects of CX3CL1 on the physiopathology of glial cells.

Main body of the abstract

Implications of cross-talk between CX3CL1 and different glial proteins/receptors/markers will give a bird eye view of the therapeutic significance of CX3CL1. Keeping with the need, this review identifies the effects of CX3CL1 on glial physiopathology, glial ablation, and gives a wide coverage on the effects of CX3CL1 on certain glial proteins/receptors/markers.

Short conclusion

Pinpoint prediction of the therapeutic effect of CX3CL1 on neuroinflammation needs further research. This is owing to certain obscure roles and implications of CX3CL1 on different glial proteins/receptors/markers, which are crucial under neurological settings. Further challenges are imposed due to the dichotomous roles played by CX3CL1. The age-old chemokine shows many newer scopes of research in near future. Thus, overall assessment of the effect of CX3CL1 becomes crucial prior to its administration in neuroinflammation.

Analysis of lncRNA, miRNA, and mRNA Expression Profiling in Type I IFN and Type II IFN Overexpressed in Porcine Alveolar Macrophages

Current data is scarce regarding the function of noncoding RNAs (ncRNAs) such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) in the interferon- (IFN-) mediated immune response. This is a comprehensive study that analyzes the lncRNA and miRNA expression profiles of the type I IFN and type II IFN in porcine alveolar macrophages using RNA sequencing. There was a total of 152 overexpressed differentially expressed (DE) lncRNAs and 21 DE miRNAs across type I IFN and type II IFN in porcine alveolar macrophages. Subsequent lncRNA-miRNA-mRNA network construction revealed the involvement of 36 DE lncRNAs and 12 DE miRNAs. LncRNAs such as the XLOC_211306, XLOC_100516, XLOC_00695, XLOC_149196, and XLOC_014459 were expressed at a higher degree in the type I IFN group, while XLOC_222640, XLOC_047290, XLOC_147777, XLOC_162298, XLOC_220210, and XLOC_165237 were expressed at a higher degree in the type II IFN group. These lncRNAs were found to act as "sponges" for miRNAs such as miR-34a, miR-328, miR-885-3p, miR-149, miR-30c-3p, miR-30b-5p, miR-708-5p, miR-193a-5p, miR-365-5p, and miR-7. Their target genes FADS2, RPS6KA1, PIM1, and NOD1 were found to be associated with several immune-related signaling pathways including the NOD-like receptor, Jak-STAT, mTOR, and PPAR signaling pathways. These experiments provide a comprehensive profile of overexpressed noncoding RNAs in porcine alveolar macrophages, providing new insights regarding the IFN-mediated immune response.

Efficient presentation of myelin oligodendrocyte glycoprotein peptides but not protein by astrocytes from HLA-DR2 and HLA-DR4 transgenic mice

The role of astrocytes in the pathogenesis of multiple sclerosis (MS) is not well understood. Astrocytes may modulate the activity of pathogenic T cells by presenting myelin antigens in combination with pro- or anti-inflammatory signals. Astrocytes have been shown to present myelin basic protein (MBP) and proteolipid protein (PLP) to T cells, but it has remained unresolved whether astrocytes present myelin oligodendrocyte glycoprotein (MOG), which has been implicated as an important autoantigen in MS. Here, we asked whether astrocytes presented MOG to T cells. To closer model presentation of human MOG by astrocytes in MS patients, we generated astrocytes from transgenic mice expressing the MS-associated MHC class II alleles HLA-DR2 (DRB1*1501) and HLA-DR4 (DRB1*0401). The results show that IFN-gamma-activated HLA-DR2 and HLA-DR4 expressing astrocytes efficiently presented immunodominant and subdominant MOG peptides to T cells. The hierarchy of the presented MOG epitopes was comparable to that of professional APCs, including dendritic cells and microglia. Importantly, astrocytes were poor at processing and presenting native MOG protein. Furthermore, astrocytes induced a mixed Th1/Th2 cytokine response in MOG-specific T cells, whereas dendritic cells induced a predominantly Th1 cell response. Collectively, the results suggest that astrocytes may modulate anti-MOG T cell responses in the CNS.

Toxoplasma gondii inhibits MHC class II expression in neural antigen-presenting cells by down-regulating the class II transactivator CIITA

Major histocompatibility complex (MHC) class II expression by microglia and astrocytes is critical for CD4+-mediated immune responses within the central nervous system. Here, we demonstrate that the obligate intracellular parasite, Toxoplasma gondii, down-regulates activation-induced MHC class II expression in human-derived glioblastoma cells as well as in primary astrocytes and microglia from cortices of rat fetuses. Down-regulation of MHC class II proteins was predominantly observed in parasite-positive, but not parasite-negative, host cells of T. gondii-infected cell cultures. MHC class II transcript levels induced by IFN-gamma alone or in combination with TNF-alpha were also clearly diminished after parasitic infection. Furthermore, T. gondii dose-dependently down-regulated the transcript levels of the class II transactivator CIITA. These results suggest that T. gondii partially evade CD4+-mediated intracerebral immune responses, a mechanism which may contribute to long-term persistence of the parasite within the CNS.

Immune function of astrocytes

Astrocytes are the major glial cell within the central nervous system (CNS) and have a number of important physiological properties related to CNS homeostasis. The aspect of astrocyte biology addressed in this review article is the astrocyte as an immunocompetent cell within the brain. The capacity of astrocytes to express class II major histocompatibility complex (MHC) antigens and costimulatory molecules (B7 and CD40) that are critical for antigen presentation and T-cell activation are discussed. The functional role of astrocytes as immune effector cells and how this may influence aspects of inflammation and immune reactivity within the brain follows, emphasizing the involvement of astrocytes in promoting Th2 responses. The ability of astrocytes to produce a wide array of chemokines and cytokines is discussed, with an emphasis on the immunological properties of these mediators. The significance of astrocytic antigen presentation and chemokine/cytokine production to neurological diseases with an immunological component is described.

Analysis of neural stem cells by flow cytometry: cellular differentiation modifies patterns of MHC expression

Neural stem cells are currently considered very hopeful candidates for cell replacement therapy in neurodegenerative pathologies such as Parkinson's disease. Here we show that different cell types derived from neurospheres amplified in vitro can be identified by FACS analysis relying solely on physical parameters (FSC/SSC) or autofluorescence. Additionally, after treatment with a panel of inflammatory cytokines, neurospheres and their differentiated progeny were shown to express MHC antigens which could potentially cause transplant rejection. Astrocytes expressed the highest levels of MHC. Hence removing such cells prior to transplantation could potentially optimise transplant survival.

Differential regulation of major histocompatibility complex class II expression and nitric oxide release by beta-amyloid in rat astrocyte and microglia

Astrocytes and microglial cells were examined for expression of two immunologically important molecules, major histocompatibility complex class II (MHC-II) and nitric oxide (NO) following treatment with IFN-gamma and beta-amyloid (betaA) peptides, betaA(1-42) and betaA(25-35). IFN-gamma is a potent inducer of both MHC-II gene expression and NO production. The induction of MHC-II was inhibited by both betaA peptides in astrocytes but they had little or no effect in microglia. betaA peptides had no effect on NO release in astrocytes but on microglia betaA(1-42) synergistically induced NO release with IFN-gamma. Transient transfection of astrocytes with 5' deletional mutants of MHC-II IAalpha promoter linked to the chloramphenicol acetyl transferase reporter gene (IAalpha-CAT), demonstrated that betaA acts at the transcriptional level to downregulate IFN-gamma induced MHC-II gene expression in astrocytes. In previous studies, the induction of MHC-II on glial cells were suggested to be involved in the pathogenesis of neurodegenerative diseases and MHC-II(+) microglial cells were observed at much higher frequency than astrocytes. This study provides information on the regulation of the MHC-II gene expression in astrocytes and in microglial cells by betaA and this pathway may be critically involved in the immune/inflammatory regulation within the central nervous system.

IFN-γ Regulation of the Type IV Class II Transactivator Promoter in Astrocytes

The transcriptional activation of class II MHC genes requires the class II transactivator (CIITA) protein, a regulator that is essential for both constitutive and IFN-γ-inducible class II MHC expression. The CIITA gene is controlled by multiple independent promoters; two promoters direct constitutive expression, while another, the type IV CIITA promoter, mediates IFN-γ-induced expression. We investigated the molecular regulation of IFN-γ-induced type IV CIITA promoter activity in astrocytes. IFN-γ inducibility of the type IV CIITA promoter is dependent on three cis-acting elements contained within a 154-bp fragment of the promoter; the proximal IFN-γ activation sequence (GAS) element, the E box, and the proximal IFN regulatory factor (IRF) element. Two IFN-γ-activated transcription factors, STAT-1α and IRF-1, bind the proximal GAS and IRF elements, respectively. The E box binds upstream stimulating factor-1 (USF-1), a constitutively expressed transcription factor. Furthermore, STAT-1α binding to the proximal GAS element is dependent on the binding of USF-1 to the adjacent E box. Functionally, the proximal IRF element is essential for IFN-γ induction of type IV CIITA promoter activity, while the proximal GAS and E box elements contribute to the IFN-γ inducibility of this promoter. In astrocytes, TNF-α enhances IFN-γ-induced class II MHC transcription. Our results demonstrate that TNF-α does not enhance IFN-γ-induced transcriptional activation of the type IV CIITA promoter, indicating that the enhancing effect of TNF-α is mediated downstream of CIITA transcription. These results define the molecular basis of IFN-γ activation of the type IV CIITA promoter in astrocytes.

A 3' cis-acting element is involved in tumor necrosis factor-alpha gene expression in astrocytes

Tumor necrosis factor-alpha (TNF-alpha) contributes to demyelinating diseases in the central nervous system. Astrocytes, the major glial cells in the CNS, do not constitutively express TNF-alpha, but the TNF-alpha gene is transcriptionally activated in response to a variety of stimuli, including TNF-alpha itself. Because of the importance of TNF-alpha in the CNS, we examined the mechanisms underlying transcriptional regulation of the TNF-alpha gene in astrocytes. In transient transfection assays, a plasmid construct containing 1.3 kilobase pairs (kb) of 5' flanking sequence of the rat TNF-alpha gene showed high basal activity that could not be further enhanced by TNF-alpha stimulation. A "marked" 10-kb TNF-alpha gene construct, which contains the whole TNF-beta gene with 1.2 kb of 5' flanking sequence, 1.1 kb of intergenic sequence, and the whole TNF-alpha gene with 3 kb of 3' flanking sequence, was able to respond to TNF-alpha stimulation. Analysis of a series of 5' and 3' deletion constructs of the marked TNF-alpha genes demonstrated that upstream sequence elements such as NF-kappaB are not required for TNF-alpha induction and that TNF-alpha responsive elements are located in the 3' flanking region of the TNF-alpha gene. We also found that a TNF-alpha-inducible DNase I-hypersensitive (DH) site is present in this 3' region whose deletion abolishes TNF-alpha inducibility of the marked TNF-alpha gene. Electrophoresis mobility shift assays showed that TNF-alpha-inducible nuclear proteins, consisting of p50 and p65 NF-kappaB proteins, specifically bind to two consecutive NF-kappaB binding sites within the 3' DH site. These results indicate that TNF-alpha-induced TNF-alpha gene expression in astrocytes involves p50 and p65 NF-kappaB proteins binding to downstream NF-kappaB sites and concomitant modulation of the chromatin structure.

EFIA/YB-1 is a component of cardiac HF-1A binding activity and positively regulates transcription of the myosin light-chain 2v gene

Transient assays in cultured ventricular muscle cells and studies in transgenic mice have identified two adjacent regulatory elements (HF-1a and HF-1b/MEF-2) as required to maintain ventricular chamber-specific expression of the myosin light-chain 2v (MLC-2v) gene. A rat neonatal heart cDNA library was screened with an HF-1a binding site, resulting in the isolation of EFIA, the rat homolog of human YB-1. Purified recombinant EFIA/YB-1 protein binds to the HF-1a site in a sequence-specific manner and contacts a subset of the HF-1a contact points made by the cardiac nuclear factor(s). The HF-1a sequence contains AGTGG, which is highly homologous to the inverted CCAAT core of the EFIA/YB-1 binding sites and is found to be essential for binding of the recombinant EFIA/YB-1. Antiserum against Xenopus YB-3 (100% identical in the DNA binding domain and 89% identical in overall amino acid sequence to rat EFIA) can specifically abolish a component of the endogenous HF-1a complex in the rat cardiac myocyte nuclear extracts. In cotransfection assays, EFIA/YB-1 increased 250-bp MLC-2v promoter activity by 3.4-fold specifically in the cardiac cell context and in an HF-1a site-dependent manner. EFIA/YB-1 complexes with an unknown protein in cardiac myocyte nuclear extracts to form the endogenous HF-1a binding activity. Immunocoprecipitation revealed that EFIA/YB-1 has a major associated protein of approximately 30 kDa (p30) in cardiac muscle cells. This study suggests that EFIA/YB-1, together with the partner p30, binds to the HF-1a site and, in conjunction with HF-1b/MEF-2, mediates ventricular chamber-specific expression of the MLC-2v gene.

Temporal pattern of host responses against intrastriatal grafts of syngeneic, allogeneic or xenogeneic embryonic neuronal tissue in rats

The host response to immunologically incompatible intrastriatal neural grafts was studied using immunohistochemical techniques. Dissociated ventral mesencephalic tissue from embryonic donors of either syngeneic, allogeneic or xenogeneic (mouse) origin was stereotaxically implanted into adult rats. The brains were analysed 4 days, 2 weeks or 6 weeks after grafting with antibodies against the following antigenic structures: major histocompatibility complex (MHC) class I antigens; MHC class II antigens; complement receptor (CR) 3 (marker for microglia and macrophages); helper T-lymphocyte antigen-cluster of differentiation (CD) 4; cytotoxic T-lymphocyte antigen-CD8; tyrosine hydroxylase (TH) (marker for transplanted dopaminergic neurons). The number of surviving TH-positive cells was not different at the various time points in either the syngeneic or allogeneic groups, whereas the xenogeneic cells were all rejected by 6 weeks. The host reactions were similar in character in the syngeneic and allogeneic groups. At 4 days after implantation, there were increased levels of expression of MHC class I and II antigens. In and around the grafts, there were cellular infiltrates consisting of activated microglia, macrophages, CD4- and CD8-positive lymphocytes. At 6 weeks, MHC expression was reduced and the cellular infiltrates had subsided with only low numbers of activated microglia cells and CD8-positive lymphocytes remaining. In the xenogeneic group, at 4 days, some grafts contained cavities, possibly reflecting acute rejection. At later stages, the xenografts were heavily infiltrated by macrophages, activated microglial cells and T-lymphocytes, and at 6 weeks all the xenografts were rejected. Taken together, the results suggest that there is an inflammation caused by the implantation process which leads to an accumulation of host defence cells. This, in turn, leads to increased MHC expression in and around the grafts. In syngeneic grafts, these reactions are short lasting and weak; for allografts slightly more pronounced and longer lasting than syngeneic grafts, but not sufficient to cause rejection. For xenografts, the reactions are more intense and lead to transplant rejection. Thus, a strong sustained inflammatory response may be an important determinator for the failure of histoincompatible neural grafts. It can be speculated that a short-term anti-inflammatory treatment of graft recipients may be a sufficient immunosuppressive regimen to allow long-term graft survival.