Association of a genetic variant of BTN2A1 with metabolic syndrome in East Asian populations

BTN2A1, an immune checkpoint targeting Vγ9Vδ2 T cell cytotoxicity against malignant cells

The anti-tumor response of Vγ9Vδ2 T cells requires the sensing of accumulated phosphoantigens (pAgs) bound intracellularly to butyrophilin 3A1 (BTN3A1). In this study, we show that butyrophilin 2A1 (BTN2A1) is required for BTN3A-mediated Vγ9Vδ2 T cell cytotoxicity against cancer cells, and that expression of the BTN2A1/BTN3A1 complex is sufficient to trigger Vγ9Vδ2 TCR activation. Also, BTN2A1 interacts with all isoforms of BTN3A (BTN3A1, BTN3A2, BTN3A3), which appears to be a rate-limiting factor to BTN2A1 export to the plasma membrane. BTN2A1/BTN3A1 interaction is enhanced by pAgs and, strikingly, B30.2 domains of both proteins are required for pAg responsiveness. BTN2A1 expression in cancer cells correlates with bisphosphonate-induced Vγ9Vδ2 T cell cytotoxicity. Vγ9Vδ2 T cell killing of cancer cells is modulated by anti-BTN2A1 monoclonal antibodies (mAbs), whose action relies on the inhibition of BTN2A1 binding to the Vγ9Vδ2TCR. This demonstrates the potential of BTN2A1 as a therapeutic target and adds to the emerging butyrophilin-family cooperation pathway in γδ T cell activation.

Distinct Gene Expression Profiles in Colonic Organoids from Normotensive and the Spontaneously Hypertensive Rats

Hypertension is associated with gut bacterial dysbiosis and gut pathology in animal models and people. Butyrate-producing gut bacteria are decreased in hypertension. RNA-seq analysis of gut colonic organoids prepared from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats was used to test the hypothesis that impaired interactions between the gut microbiome and gut epithelium are involved and that these would be remediated with butyrate supplementation. Gene expressions in immune responses including antigen presentation and antiviral pathways were decreased in the gut epithelium of the SHR in organoids and confirmed in vivo; these deficits were corrected by butyrate supplementation. Deficits in gene expression driving epithelial proliferation and differentiation were also observed in SHR. These findings highlight the importance of aligned interactions of the gut microbiome and gut immune responses to blood pressure homeostasis.

Prediction of Disordered Regions and Their Roles in the Anti-Pathogenic and Immunomodulatory Functions of Butyrophilins

Butyrophilins (BTNs) are a group of the moonlighting proteins, some members of which are secreted in milk. They constitute a large family of structurally similar type 1 transmembrane proteins from the immunoglobulin superfamily. Although the founding member of this family is related to lactation, participating in the secretion, formation and stabilization of milk fat globules, it may also have a cell surface receptor function. Generally, the BTN family members are known to modulate co-stimulatory responses, T cell selection, differentiation, and cell fate determination. Polymorphism of these genes was shown to be associated with the pathology of several human diseases. Despite their biological significance, structural information on human butyrophilins is rather limited. Based on their remarkable multifunctionality, butyrophilins seem to belong to the category of moonlighting proteins, which are known to contain intrinsically disordered protein regions (IDPRs). However, the disorder status of human BTNs was not systematically investigated as of yet. The goal of this study is to fill this gap and to evaluate peculiarities of intrinsic disorder predisposition of the members of human BTN family, and to find if they have IDPRs that can be attributed to the multifunctionality of these important proteins.

Evolutionary and polymorphism analyses reveal the central role of BTN3A2 in the concerted evolution of the BTN3 gene family

The butyrophilin 3 (BTN3) receptors are implicated in the T lymphocytes regulation and present a wide plasticity in mammals. In order to understand how these genes have been diversified, we studied their evolution and show that the three human BTN3 are the result of two successive duplications in Primates and that the three genes are present in Hominoids and the Old World Monkey groups. A thorough phylogenetic analysis reveals a concerted evolution of BTN3 characterized by a strong and recurrent homogenization of the region encoding the signal peptide and the immunoglobulin variable (IgV) domain in Hominoids, where the sequences of BTN3A1 or BTN3A3 are replaced by BTN3A2 sequence. In human, the analysis of the diversity of these genes in 1683 individuals representing 26 worldwide populations shows that the three genes are polymorphic, with more than 46 alleles for each gene, and marked by extreme homogenization of the IgV sequences. The same analysis performed for the BTN2 genes shows also a concerted evolution; however, it is not as strong and recurrent as for BTN3. This study shows that BTN3 receptors are marked by extreme concerted evolution at the IgV domain and that BTN3A2 plays a central role in this evolution.

Location of cerebral atherosclerosis: Why is there a difference between East and West?

Intracranial atherosclerosis is more prevalent in Asian patients, whereas extracranial atherosclerosis is more common in individuals from western countries. The reasons for this discrepancy remain unknown. We reviewed the relevant literature and discussed the currently available information. Although the study population, diagnostic modality, and risk factor definitions differ between studies, hypercholesterolemia is more correlated with extracranial atherosclerosis than intracranial atherosclerosis. The difference in hypercholesterolemia prevalence is one of the main reasons for racial differences. Intracranial arteries contain higher antioxidant level than extracranial arteries and may be more vulnerable to risk factors for antioxidant depletion (e.g., metabolic syndrome and diabetes mellitus). Intracranial arteries may be vulnerable to factors associated with hemodynamic stress (e.g., advanced, salt-retaining hypertension and arterial tortuosity) because of a smaller diameter, thinner media and adventitia, and fewer elastic medial fibers than extracranial arteries. Additionally, non-atherosclerotic arterial diseases (e.g., moyamoya disease) that commonly occur in the intracranial arteries of East Asians may contaminate the reports of intracranial atherosclerosis cases. Genes, including RNF 213 or those associated with high salt sensitivity, may also explain racial differences in atherosclerotic location. To understand racial differences, further well-designed studies on various risk and genetic factors should be performed in patients with cerebral atherosclerosis. Additionally, improvements in diagnostic accuracy via advancements in imaging technologies and increased genetic data will aid in the differentiation of atherosclerosis from non-atherosclerotic intracranial diseases.

Association of genetic variants with hypertension in a longitudinal population-based genetic epidemiological study

We previously identified 9 genes and chromosomal region 3q28 as susceptibility loci for Japanese patients with myocardial infarction, ischemic stroke, or chronic kidney disease by genome-wide or candidate gene association studies. In the present study, we investigated the possible association of 13 single nucleotide polymorphisms (SNPs) at these 10 loci with the prevalence of hypertension or their association with blood pressure (BP) in community-dwelling individuals in Japan. The study subjects comprised 6,027 individuals (2,250 subjects with essential hypertension, 3,777 controls) who were recruited into the Inabe Health and Longevity Study, a longitudinal genetic epidemiological study on atherosclerotic, cardiovascular and metabolic diseases. The subjects were recruited from individuals who visited the Health Care Center of Inabe General Hospital for an annual health checkup, and they are followed up each year (mean follow-up period, 5 years). Longitudinal analysis with a generalized estimating equation and with adjustment for age, gender, body mass index and smoking status revealed that rs2116519 of family with sequence similarity 78, member B (FAM78B; P=0.0266), rs6929846 of butyrophilin, subfamily 2, member A1 (BTN2A1; P= 0.0013), rs146021107 of pancreatic and duodenal homeobox 1 (PDX1; P=0.0031) and rs1671021 of lethal giant larvae homolog 2 (Drosophila) (LLGL2; P=0.0372) were significantly (P<0.05) associated with the prevalence of hypertension. Longitudinal analysis with a generalized linear mixed-effect model and with adjustment for age, gender, body mass index and smoking status among individuals not taking anti-hypertensive medication revealed that rs6929846 of BTN2A1 was significantly associated with systolic (P=0.0017), diastolic (P=0.0008) and mean (P=0.0005) BP, and that rs2116519 of FAM78B, rs146021107 of PDX1 and rs1671021 of LLGL2 were significantly associated with diastolic (P=0.0495), systolic (P=0.0132), and both diastolic (P=0.0468) and mean (0.0471) BP, respectively. BTN2A1 may thus be a susceptibility gene for hypertension.

Association of genetic variants with dyslipidemia and chronic kidney disease in a longitudinal population-based genetic epidemiological study

We previously identified 9 genes and chromosomal region 3q28 as susceptibility loci for myocardial infarction, ischemic stroke, or chronic kidney disease (CKD) in Japanese individuals by genome-wide or candidate gene association studies. In the present study, we examined the association of 13 polymorphisms at these 10 loci with the prevalence of hypertriglyceridemia, hyper-low-density lipoprotein (LDL) cholesterolemia, hypo-high-density lipoprotein (HDL) cholesterolemia, or CKD in community-dwelling Japanese individuals. The study subjects comprised 6,027 individuals who were recruited to the Inabe Health and Longevity Study, a longitudinal genetic epidemiological study of atherosclerotic, cardiovascular and metabolic diseases. The subjects were recruited from individuals who visited the Health Care Center at Inabe General Hospital for an annual health checkup, and they were followed up each year (mean follow‑up period, 5 years). Longitudinal analysis with a generalized estimating equation and with adjustment for covariates revealed that rs6929846 of butyrophilin, subfamily 2, member A1 gene (BTN2A1) was significantly associated with the prevalence of hypertriglyceridemia (P=0.0001), hyper-LDL cholesterolemia (P=0.0004), and CKD (P=0.0007); rs2569512 of interleukin enhancer binding factor 3 (ILF3) was associated with hyper-LDL cholesterolemia (P=0.0029); and rs2074379 (P=0.0019) and rs2074388 (P=0.0029) of alpha-kinase 1 (ALPK1) were associated with CKD. Longitudinal analysis with a generalized linear mixed-effect model and with adjustment for covariates among all individuals revealed that rs6929846 of BTN2A1 was significantly associated with the serum concentrations of triglycerides (P=0.0011), LDL cholesterol (P=3.3 x 10(-5)), and creatinine (P=0.0006), as well as with the estimated glomerular filtration rate (eGFR) (P=0.0004); rs2569512 of ILF3 was shown to be associated with the serum concentration of LDL cholesterol (P=0.0221); and rs2074379 (P=0.0302) and rs2074388 (P=0.0336) of ALPK1 were shown to be associated with the serum concentration of creatinine. Similar analysis among individuals not taking any anti‑dyslipidemic medication revealed that rs6929846 of BTN2A1 was significantly associated with the serum concentrations of triglycerides (P=8.3 x 10‑5) and LDL cholesterol (P=0.0004), and that rs2569512 of ILF3 was associated with the serum concentration of LDL cholesterol (P=0.0010). BTN2A1 may thus be a susceptibility gene for hypertriglyceridemia, hyper‑LDL cholesterolemia and CKD in Japanese individuals.

Association of a butyrophilin, subfamily 2, member A1 gene polymorphism with hypertension

The C→T polymorphism (rs6929846) of the butyrophilin, subfamily 2, member A1 (BTN2A1) gene has been previously identified as a susceptibility locus for myocardial infarction by a genome-wide association study. As hypertension is a major risk factor for myocardial infarction, the association between the BTN2A1 polymorphism, rs6929846, and myocardial infarction may be partly due to its effect on hypertension susceptibility. The aim of the present study was to examine the possible association of rs6929846 with hypertension. The study subjects comprised 5,959 community-dwelling individuals (2,183 subjects with hypertension and 3,776 controls) who were recruited to a population-based cohort study. The rs6929846 genotype was determined by a method that combined polymerase chain reaction and sequence-specific oligonucleotide probes with suspension array technology. Comparisons between the genotype distributions (P=0.0090) and allele frequencies (P=0.0051) by the χ² test revealed that rs6929846 was significantly associated with hypertension. Multivariable logistic regression analysis with adjustment for age, gender, body mass index and smoking status revealed that rs6929846 was significantly associated with hypertension (P=0.0008; odds ratio, 1.29; dominant model), with the minor T allele representing a risk factor for this condition. Among all the individuals, systolic, diastolic and mean blood pressure was significantly higher in the combined group of individuals with the CT or TT genotypes compared to the CC genotype group. BTN2A1 may thus be a susceptibility gene for hypertension. Therefore, determining the genotype for this polymorphism may provide genetic risk assessment information for hypertension.

Sequence of a complete chicken BG haplotype shows dynamic expansion and contraction of two gene lineages with particular expression patterns

Many genes important in immunity are found as multigene families. The butyrophilin genes are members of the B7 family, playing diverse roles in co-regulation and perhaps in antigen presentation. In humans, a fixed number of butyrophilin genes are found in and around the major histocompatibility complex (MHC), and show striking association with particular autoimmune diseases. In chickens, BG genes encode homologues with somewhat different domain organisation. Only a few BG genes have been characterised, one involved in actin-myosin interaction in the intestinal brush border, and another implicated in resistance to viral diseases. We characterise all BG genes in B12 chickens, finding a multigene family organised as tandem repeats in the BG region outside the MHC, a single gene in the MHC (the BF-BL region), and another single gene on a different chromosome. There is a precise cell and tissue expression for each gene, but overall there are two kinds, those expressed by haemopoietic cells and those expressed in tissues (presumably non-haemopoietic cells), correlating with two different kinds of promoters and 5′ untranslated regions (5′UTR). However, the multigene family in the BG region contains many hybrid genes, suggesting recombination and/or deletion as major evolutionary forces. We identify BG genes in the chicken whole genome shotgun sequence, as well as by comparison to other haplotypes by fibre fluorescence in situ hybridisation, confirming dynamic expansion and contraction within the BG region. Thus, the BG genes in chickens are undergoing much more rapid evolution compared to their homologues in mammals, for reasons yet to be understood.

Many immune genes are multigene families, presumably in response to pathogen variation. Some multigene families undergo expansion and contraction, leading to copy number variation (CNV), presumably due to more intense selection. Recently, the butyrophilin family in humans and other mammals has come under scrutiny, due to genetic associations with autoimmune diseases as well as roles in immune co-regulation and antigen presentation. Butyrophilin genes exhibit allelic polymorphism, but gene number appears stable within a species. We found that the BG homologues in chickens are very different, with great changes between haplotypes. We characterised one haplotype in detail, showing that there are two single BG genes, one on chromosome 2 and the other in the major histocompatibility complex (BF-BL region) on chromosome 16, and a family of BG genes in a tandem array in the BG region nearby. These genes have specific expression in cells and tissues, but overall are expressed in either haemopoietic cells or tissues. The two singletons have relatively stable evolutionary histories, but the BG region undergoes dynamic expansion and contraction, with the production of hybrid genes. Thus, chicken BG genes appear to evolve much more quickly than their closest homologs in mammals, presumably due to increased pressure from pathogens.

Association of a polymorphism of BTN2A1 with chronic kidney disease in community-dwelling individuals

Results of recent studies have shown that the C→T polymorphism (rs6929846) of the butyrophilin, subfamily 2, member A1 gene (BTN2A1) was significantly associated with myocardial infarction. The aim of the current study was to examine the association of rs6929846 of BTN2A1 with chronic kidney disease (CKD) in community-dwelling individuals. Study subjects comprised 1,709 community-dwelling individuals, including 435 subjects with CKD [estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m²] and 1,274 controls (eGFR≥90 ml/min per 1.73 m²) who were recruited to a population-based cohort study. Genotype distributions (P=0.0010) and allele frequencies (P=0.0002) of rs6929846 were significantly associated with CKD. Multivariate logistic regression analysis with adjustment for covariates revealed that the rs6929846 of BTN2A1 was significantly (P=0.0002; odds ratio, 2.02; dominant model) associated with CKD, with the minor T allele representing a risk for this condition. The serum concentrations of creatinine were significantly (P=0.0107) higher for all the individuals, whereas eGFR was significantly (P=0.0468) lower for individuals in the combined group of CT and TT genotypes compared to those with the CC genotype. BTN2A1 may therefore be a susceptibility gene for CKD.