Genetic and Epigenetic Factors of Takotsubo Syndrome: A Systematic Review

Takotsubo syndrome (TTS), recognized as stress's cardiomyopathy, or as left ventricular apical balloon syndrome in recent years, is a rare pathology, described for the first time by Japanese researchers in 1990. TTS is characterized by an interindividual heterogeneity in onset and progression, and by strong predominance in postmenopausal women. The clear causes of these TTS features are uncertain, given the limited understanding of this intriguing syndrome until now. However, the increasing frequency of TTS cases in recent years, and particularly correlated to the SARS-CoV-2 pandemic, leads us to the imperative necessity both of a complete knowledge of TTS pathophysiology for identifying biomarkers facilitating its management, and of targets for specific and effective treatments. The suspect of a genetic basis in TTS pathogenesis has been evidenced. Accordingly, familial forms of TTS have been described. However, a systematic and comprehensive characterization of the genetic or epigenetic factors significantly associated with TTS is lacking. Thus, we here conducted a systematic review of the literature before June 2021, to contribute to the identification of potential genetic and epigenetic factors associated with TTS. Interesting data were evidenced, but few in number and with diverse limitations. Consequently, we concluded that further work is needed to address the gaps discussed, and clear evidence may arrive by using multi-omics investigations.

Common genetic susceptibility loci link PFAPA syndrome, Behçet's disease, and recurrent aphthous stomatitis

Periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) syndrome is the most common periodic fever syndrome in children. The disease appears to cluster in families, but the pathogenesis is unknown. We queried two European-American cohorts and one Turkish cohort (total n = 231) of individuals with PFAPA for common variants previously associated with two other oropharyngeal ulcerative disorders, Behçet's disease and recurrent aphthous stomatitis. In a metaanalysis, we found that a variant upstream of IL12A (rs17753641) is strongly associated with PFAPA (OR 2.13, P = 6 × 10-9). We demonstrated that monocytes from individuals who are heterozygous or homozygous for this risk allele produce significantly higher levels of IL-12p70 upon IFN-γ and LPS stimulation than those from individuals without the risk allele. We also found that variants near STAT4, IL10, and CCR1-CCR3 were significant susceptibility loci for PFAPA, suggesting that the pathogenesis of PFAPA involves abnormal antigen-presenting cell function and T cell activity and polarization, thereby implicating both innate and adaptive immune responses at the oropharyngeal mucosa. Our results illustrate genetic similarities among recurrent aphthous stomatitis, PFAPA, and Behçet's disease, placing these disorders on a common spectrum, with recurrent aphthous stomatitis on the mild end, Behçet's disease on the severe end, and PFAPA intermediate. We propose naming these disorders Behçet's spectrum disorders to highlight their relationship. HLA alleles may be factors that influence phenotypes along this spectrum as we found new class I and II HLA associations for PFAPA distinct from Behçet's disease and recurrent aphthous stomatitis.

[Genetic mechanisms of adaptive immunity emergence in vertebrates]

The adaptive immune system in vertebrates emerged in a multistep process that can be reconstructed on the basis of the data concerning the structure of immune systems of modern cartilaginous and bony fishes, as well as of cyclostomes. The most probable evolutionary scenario is likely to be as follows: the T cell receptor loci emerged on the basis of NK cell-like receptor genes; the antibody loci evolved on the basis of T cell receptor loci; the MHC locus arose on the basis of the locus responsible for innate immunity of early chordates. The ancestral MHC molecules likely participated in the transplantation immunity before they acquired the ability of antigen peptide presentation.

Coherent somatic mutation in autoimmune disease

BACKGROUND

Many aspects of autoimmune disease are not well understood, including the specificities of autoimmune targets, and patterns of co-morbidity and cross-heritability across diseases. Prior work has provided evidence that somatic mutation caused by gene conversion and deletion at segmentally duplicated loci is relevant to several diseases. Simple tandem repeat (STR) sequence is highly mutable, both somatically and in the germ-line, and somatic STR mutations are observed under inflammation.

RESULTS

Protein-coding genes spanning STRs having markers of mutability, including germ-line variability, high total length, repeat count and/or repeat similarity, are evaluated in the context of autoimmunity. For the initiation of autoimmune disease, antigens whose autoantibodies are the first observed in a disease, termed primary autoantigens, are informative. Three primary autoantigens, thyroid peroxidase (TPO), phogrin (PTPRN2) and filaggrin (FLG), include STRs that are among the eleven longest STRs spanned by protein-coding genes. This association of primary autoantigens with long STR sequence is highly significant (p<3.0x10(-7)). Long STRs occur within twenty genes that are associated with sixteen common autoimmune diseases and atherosclerosis. The repeat within the TTC34 gene is an outlier in terms of length and a link with systemic lupus erythematosus is proposed.

CONCLUSIONS

The results support the hypothesis that many autoimmune diseases are triggered by immune responses to proteins whose DNA sequence mutates somatically in a coherent, consistent fashion. Other autoimmune diseases may be caused by coherent somatic mutations in immune cells. The coherent somatic mutation hypothesis has the potential to be a comprehensive explanation for the initiation of many autoimmune diseases.

Epigenetic silencing of the human NOS2 gene: rethinking the role of nitric oxide in human macrophage inflammatory responses

Macrophages, including alveolar macrophages, are primary phagocytic cells of the innate immune system. Many studies of macrophages and inflammation have been done in mouse models, in which inducible NO synthase (NOS2) and NO are important components of the inflammatory response. Human macrophages, in contrast to mouse macrophages, express little detectable NOS2 and generate little NO in response to potent inflammatory stimuli. The human NOS2 gene is highly methylated around the NOS2 transcription start site. In contrast, mouse macrophages contain unmethylated cytosine-phosphate-guanine (CpG) dinucleotides proximal to the NOS2 transcription start site. Further analysis of chromatin accessibility and histone modifications demonstrated a closed conformation at the human NOS2 locus and an open conformation at the murine NOS2 locus. In examining the potential for CpG demethylation at the NOS2 locus, we found that the human NOS2 gene was resistant to the effects of demethylation agents both in vitro and in vivo. Our data demonstrate that epigenetic modifications in human macrophages are associated with CpG methylation, chromatin compaction, and histone modifications that effectively silence the NOS2 gene. Taken together, our findings suggest there are significant and underappreciated differences in how murine and human macrophages respond to inflammatory stimuli.

The sst1 resistance locus regulates evasion of type I interferon signaling by Chlamydia pneumoniae as a disease tolerance mechanism

The sst1, “supersusceptibility to tuberculosis,” locus has previously been shown to be a genetic determinant of host resistance to infection with the intracellular pathogen, Mycobacterium tuberculosis. Chlamydia pneumoniae is an obligate intracellular bacterium associated with community acquired pneumonia, and chronic infection with C. pneumoniae has been linked to asthma and atherosclerosis. C. pneumoniae is a highly adapted pathogen that can productively infect macrophages and inhibit host cell apoptosis. Here we examined the role of sst1 in regulating the host response to infection with C. pneumoniae. Although mice carrying the sst1 susceptible (sst1^S) locus were not impaired in their ability to clear the acute infection, they were dramatically less tolerant of the induced immune response, displaying higher clinical scores, more severe lung inflammation, exaggerated macrophage and neutrophil influx, and the development of fibrosis compared to wild type mice. This correlated with increased activated caspase-3 in the lungs of infected sst1^S mice. Infection of sst1^S macrophages with C. pneumoniae resulted in a shift in the secreted cytokine profile towards enhanced production of interferon-β and interleukin-10, and induced apoptotic cell death, which was dependent on secretion of interferon-β. Intriguingly macrophages from the sst1^S mice failed to support normal chlamydial growth, resulting in arrested development and failure of the organism to complete its infectious cycle. We conclude that the sst1 locus regulates a shared macrophage-mediated innate defense mechanism against diverse intracellular bacterial pathogens. Its susceptibility allele leads to upregulation of type I interferon pathway, which, in the context of C. pneumoniae, results in decreased tolerance, but not resistance, to the infection. Further dissection of the relationship between type I interferons and host tolerance during infection with intracellular pathogens may provide identification of biomarkers and novel therapeutic targets.

Chlamydia pneumoniae is a highly adapted intracellular pathogen and a common cause of atypical, community acquired pneumonia. It has also been suggested as a trigger or promoter of asthma and atherosclerosis. In this study, we examined the role of a genetic locus on mouse chromosome 1 that has been associated with susceptibility to another intracellular pathogen, Mycobacterium tuberculosis, in the pathogenesis of respiratory infections secondary to Chlamydia pneumoniae. We have determined that a variant at this locus, known as sst1 and associated with destructive pulmonary tuberculosis, makes mice dramatically more sensitive in vivo to the inflammatory changes following respiratory infection with C. pneumoniae. This appears to arise from activation of type I interferons and apoptotic cell death, two signaling pathways that are normally silent during productive C. pneumoniae infection. Despite a noted inability of sst1 susceptible macrophages to support chlamydial development, exuberant lung tissue damage resulted in overall more severe disease in vivo. We conclude the sst1-mediated control of lung tissue damage is an important determinant of the genetic susceptibility of a given host to a number of diverse intracellular bacterial pathogens, which may provide predictors of outcomes to infectious diseases as well as possible target for novel therapeutics.

Dense genotyping of immune-related disease regions identifies nine new risk loci for primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a severe liver disease of unknown etiology leading to fibrotic destruction of the bile ducts and ultimately to the need for liver transplantation. We compared 3,789 PSC cases of European ancestry to 25,079 population controls across 130,422 SNPs genotyped using the Immunochip. We identified 12 genome-wide significant associations outside the human leukocyte antigen (HLA) complex, 9 of which were new, increasing the number of known PSC risk loci to 16. Despite comorbidity with inflammatory bowel disease (IBD) in 72% of the cases, 6 of the 12 loci showed significantly stronger association with PSC than with IBD, suggesting overlapping yet distinct genetic architectures for these two diseases. We incorporated association statistics from 7 diseases clinically occurring with PSC in the analysis and found suggestive evidence for 33 additional pleiotropic PSC risk loci. Together with network analyses, these findings add to the genetic risk map of PSC and expand on the relationship between PSC and other immune-mediated diseases.

Chromatin conformation governs T-cell receptor Jβ gene segment usage

T cells play fundamental roles in adaptive immunity, relying on a diverse repertoire of T-cell receptor (TCR) α and β chains. Diversity of the TCR β chain is generated in part by a random yet intrinsically biased combinatorial rearrangement of variable (Vβ), diversity (Dβ), and joining (Jβ) gene segments. The mechanisms that determine biases in gene segment use remain unclear. Here we show, using a high-throughput TCR sequencing approach, that a physical model of chromatin conformation at the DJβ genomic locus explains more than 80% of the biases in Jβ use that we measured in murine T cells. This model also predicts correctly how differences in intersegment genomic distances between humans and mice translate into differences in Jβ bias between TCR repertoires of these two species. As a consequence of these structural and other biases, TCR sequences are produced with different a priori frequencies, thus affecting their probability of becoming public TCRs that are shared among individuals. Surprisingly, we find that many more TCR sequences are shared among all five mice we studied than among only subgroups of three or four mice. We derive a necessary mathematical condition explaining this finding, which indicates that the TCR repertoire contains a core set of receptor sequences that are highly abundant among individuals, if their a priori probability of being produced by the recombination process is higher than a defined threshold. Our results provide evidence for an expanded role of chromatin conformation in VDJ rearrangement, from control of gene accessibility to precise determination of gene segment use.

[Model of chronic salmonellosis: parameters of infection and immune response in inbred mice genetically variable in susceptibility to salmonellosis]

AIM

Study parameters of chronic infection and immune response in I/St and A/Sn line mice in the model of per oral infection of mice with Salmonella enterica serovar Typhimurium.

MATERIALS AND METHODS

Studies were carried out in I/StSnEgYCit (I/St), A/JsnYCit (A/Sn) inbred line mice as well as their back crossing hybrids [I/StrxF1(I/StxA/Sn)]BC. Mice were infected per os by S. enterica serovar Typhimurium strain IE147 at a dose of 2 x 10(5) PFU per mice. The number of salmonellae was determined at days 3, 5 and 7, weeks 3 and 4 after the infection in various organs, the number of antibody producers--by cell EIA. Pathomorphologic changes in mice spleens were studied histologically by using hematoxylin and eosin staining. In offspring of back crossing [I/St x F1(I/St x A/Sn)]BCl segregation genetic analysis of sensitivity to salmonella infection trait and mapping of loci taking part in salmonella infection were carried out.

RESULTS

The course of chronic salmonellosis in susceptible I/St line was characterized by the presence of more pronounced pathomorphologic changes in spleen and significantly higher microbial load in organs (approximately by 1000 times) when compared with A/Sn mice. Interlinear differences in susceptibility to infection correlated with differences in the type of early local and systemic immune response. In I/St mice a higher level of salmonella specific IgG2a-, IgG1- and IgA forming cells in spleen compared with A/Sn mice was detected which correlates with a pronounced splenomegaly and high concentration of salmonellae. On the contrary A/Sn mice demonstrated a higher level of salmonella specific IgA forming cells in Peyer patches that probably leads to protection of A/Sn line during per oral infection. Genetic analysis of susceptibility to salmonellosis trait inheritance showed the presence of its coupling with D9Mit89 locus of chromosome 9 on which previously Tbs2 locus was mapped that plays a role in the control of tuberculosis infection.

CONCLUSION

There is a probability of the presence of general mechanisms of genetic control of tuberculosis and salmonella infections in A/Sn and I/St mice.

Differential association of gene content polymorphisms of killer cell immunoglobulin-like receptors with placental malaria in HIV- and HIV+ mothers

Pregnant women have abundant natural killer (NK) cells in their placenta, and NK cell function is regulated by polymorphisms of killer cell immunoglobulin-like receptors (KIRs). Previous studies report different roles of NK cells in the immune responses to placental malaria (PM) and human immunodeficiency virus (HIV-1) infections. Given these references, the aim of this study was to determine the association between KIR gene content polymorphism and PM infection in pregnant women of known HIV-1 status. Sixteen genes in the KIR family were analyzed in 688 pregnant Kenyan women. Gene content polymorphisms were assessed in relation to PM in HIV-1 negative and HIV-1 positive women, respectively. Results showed that in HIV-1 negative women, the presence of the individual genes KIR2DL1 and KIR2DL3 increased the odds of having PM, and the KIR2DL2/KIR2DL2 homozygotes were associated with protection from PM. However, the reverse relationship was observed in HIV-1 positive women, where the presence of individual KIR2DL3 was associated with protection from PM, and KIR2DL2/KIR2DL2 homozygotes increased the odds for susceptibility to PM. Further analysis of the HIV-1 positive women stratified by CD4 counts showed that this reverse association between KIR genes and PM remained only in the individuals with high CD4 cell counts but not in those with low CD4 cell counts. Collectively, these results suggest that inhibitory KIR2DL2 and KIR2DL3, which are alleles of the same locus, play a role in the inverse effects on PM and PM/HIV co-infection and the effect of KIR genes on PM in HIV positive women is dependent on high CD4 cell counts. In addition, analysis of linkage disequilibrium (LD) of the PM relevant KIR genes showed strong LD in women without PM regardless of their HIV status while LD was broken in those with PM, indicating possible selection pressure by malaria infection on the KIR genes.

The role of Pbx1 in T cells

Tissue and organ differentiation is tightly controlled to ensure proper development and function of the growing embryo as well as cells such as lymphocytes that differentiate throughout the adult stage. Therefore it is vital that the genes and the protein they encode that are involved in these processes function accurately. Hence, any mutation or error that occurs along the way can result in extensive damage, which is expressed in various ways in the embryo and can result in immune pathogenesis, including immunodeficiency and autoimmune diseases, when lymphocyte development is altered. A number of studies have been carried out to look at the genes regulating transcription in tissue differentiation, including the transcription factors Pbx1. This gene is of particular interest to us as we have identified that it is associated with systemic lupus erythematosus susceptibility (Cuda et al., in press). This perspective summarizes the known roles of Pbx1 in tissue differentiation as well as our recent findings associating genetic variations in Pbx1 to lupus susceptibility, and we will speculate on how this gene controls the maintenance of immune tolerance in T cells.

A Salmonella Typhimurium-Typhi genomic chimera: a model to study Vi polysaccharide capsule function in vivo

The Vi capsular polysaccharide is a virulence-associated factor expressed by Salmonella enterica serotype Typhi but absent from virtually all other Salmonella serotypes. In order to study this determinant in vivo, we characterised a Vi-positive S. Typhimurium (C5.507 Vi⁺), harbouring the Salmonella pathogenicity island (SPI)-7, which encodes the Vi locus. S. Typhimurium C5.507 Vi⁺ colonised and persisted in mice at similar levels compared to the parent strain, S. Typhimurium C5. However, the innate immune response to infection with C5.507 Vi⁺ and SGB1, an isogenic derivative not expressing Vi, differed markedly. Infection with C5.507 Vi⁺ resulted in a significant reduction in cellular trafficking of innate immune cells, including PMN and NK cells, compared to SGB1 Vi⁻ infected animals. C5.507 Vi⁺ infection stimulated reduced numbers of TNF-α, MIP-2 and perforin producing cells compared to SGB1 Vi⁻. The modulating effect associated with Vi was not observed in MyD88^−/− and was reduced in TLR4^−/− mice. The presence of the Vi capsule also correlated with induction of the anti-inflammatory cytokine IL-10 in vivo, a factor that impacted on chemotaxis and the activation of immune cells in vitro.

Pathogens of the genus Salmonella are closely related yet cause distinct diseases and have different host-range. Salmonella Typhi causes a systemic disease called typhoid fever specifically in humans, and is commonly modelled using a surrogate host-pathogen combination, namely Salmonella Typhimurium infection in mice. However, key virulence mechanisms of S. Typhi depend on the Vi polysaccharide capsule that is not expressed by S. Typhimurium. In order to study the function of the Vi capsule we characterised a S. Typhimurium/S. Typhi chimera that expresses the Vi polysaccharide in a regulated manner similar to that previously described in S. Typhi. The impact of Vi expression on immune cell populations in the spleen and mesenteric lymph nodes, and the pattern of intracellular cytokine response was determined 24 hours after i.v or i.g inoculation. Infection of mice with S. Typhimurium expressing Vi polysaccharide resulted in a blunted response in recruitment of NK and PMN cells. This was reflected in a blunted proinflammatory cytokine response, but a striking increase in the anti-inflammatory cytokine IL-10. IL-10 was expressed in macrophage, dendritic cells and NK cells in the mouse spleen, specifically in response to infection with S. Typhimurium expressing Vi polysaccharide. Indeed, neutralisation of this IL-10 production lead to increased migration and activation of splenocytes in vitro. This model can be used to develop Vi based vaccines as well as to study the impact of Vi expression on pathogenesis.

A novel HURRAH protocol reveals high numbers of monomorphic MHC class II loci and two asymmetric multi-locus haplotypes in the Père David's deer

The Père David's deer is a highly inbred, but recovered, species, making it interesting to consider their adaptive molecular evolution from an immunological perspective. Prior to this study, genomic sequencing was the only method for isolating all functional MHC genes within a certain species. Here, we report a novel protocol for isolating MHC class II loci from a species, and its use to investigate the adaptive evolution of this endangered deer at the level of multi-locus haplotypes. This protocol was designated “HURRAH” based on its various steps and used to estimate the total number of MHC class II loci. We confirmed the validity of this novel protocol in the giant panda and then used it to examine the Père David's deer. Our results revealed that the Père David's deer possesses nine MHC class II loci and therefore has more functional MHC class II loci than the eight genome-sequenced mammals for which full MHC data are currently available. This could potentially account at least in part for the strong survival ability of this species in the face of severe bottlenecking. The results from the HURRAH protocol also revealed that: (1) All of the identified MHC class II loci were monomorphic at their antigen-binding regions, although DRA was dimorphic at its cytoplasmic tail; and (2) these genes constituted two asymmetric functional MHC class II multi-locus haplotypes: DRA1*01 ∼ DRB1 ∼ DRB3 ∼ DQA1 ∼ DQB2 (H1) and DRA1*02 ∼ DRB2 ∼ DRB4 ∼ DQA2 ∼ DQB1 (H2). The latter finding indicates that the current members of the deer species have lost the powerful ancestral MHC class II haplotypes of nine or more loci, and have instead fixed two relatively weak haplotypes containing five genes. As a result, the Père David's deer are currently at risk for increased susceptibility to infectious pathogens.