beta 2-Microglobulin

The HLA-B27 gene is a major risk factor for clinical diseases including ankylosing spondylitis, acute anterior uveitis, reactive arthritis, and psoriatic arthritis, but its mechanism of risk enhancement is not completely understood. The gut microbiome has recently been shown to influence several HLA-linked diseases. However, the role of HLA-B27 in shaping the gut microbiome has not been previously investigated. In this study, we characterize the differences in the gut microbiota mediated by the presence of the HLA-B27 gene. We identified differences in the cecal microbiota of Lewis rats transgenic for HLA-B27 and human β2-microglobulin (hβ2m), compared with wild-type Lewis rats, using biome representational in situ karyotyping (BRISK) and 16S rRNA gene sequencing. 16S sequencing revealed significant differences between transgenic animals and wild type animals by principal coordinates analysis. Further analysis of the data set revealed an increase in Prevotella spp. and a decrease in Rikenellaceae relative abundance in the transgenic animals compared to the wild type animals. By BRISK analysis, species-specific differences included an increase in Bacteroides vulgatus abundance in HLA-B27/hβ2m and hβ2m compared to wild type rats. The finding that HLA-B27 is associated with altered cecal microbiota has not been shown before and can potentially provide a better understanding of the clinical diseases associated with this gene.

ESAT-6, an abundantly secreted protein of Mycobacterium tuberculosis (M. tuberculosis) is an important virulence factor, inactivation of which leads to reduced virulence of M. tuberculosis. ESAT-6 alone, or in complex with its chaperone CFP-10 (ESAT-6:CFP-10), is known to modulate host immune responses; however, the detailed mechanisms are not well understood. The structure of ESAT-6 or ESAT-6:CFP-10 complex does not suggest presence of enzymatic or DNA-binding activities. Therefore, we hypothesized that the crucial role played by ESAT-6 in the virulence of mycobacteria could be due to its interaction with some host cellular factors. Using a yeast two-hybrid screening, we identified that ESAT-6 interacts with the host protein beta-2-microglobulin (β2M), which was further confirmed by other assays, like GST pull down, co-immunoprecipitation and surface plasmon resonance. The C-terminal six amino acid residues (90-95) of ESAT-6 were found to be essential for this interaction. ESAT-6, in complex with CFP-10, also interacts with β2M. We found that ESAT-6/ESAT-6:CFP-10 can enter into the endoplasmic reticulum where it sequesters β2M to inhibit cell surface expression of MHC-I-β2M complexes, resulting in downregulation of class I-mediated antigen presentation. Interestingly, the ESAT-6:β2M complex could be detected in pleural biopsies of individuals suffering from pleural tuberculosis. Our data highlight a novel mechanism by which M. tuberculosis may undermine the host adaptive immune responses to establish a successful infection. Identification of such novel interactions may help us in designing small molecule inhibitors as well as effective vaccine design against tuberculosis.

All amyloid fibrils contain a cross-β fold. How this structure differs in fibrils formed from proteins associated with different diseases remains unclear. Here, we combine cryo-EM and MAS-NMR to determine the structure of an amyloid fibril formed in vitro from β2-microglobulin (β2m), the culprit protein of dialysis-related amyloidosis. The fibril is composed of two identical protofilaments assembled from subunits that do not share β2m's native tertiary fold, but are formed from similar β-strands. The fibrils share motifs with other amyloid fibrils, but also contain unique features including π-stacking interactions perpendicular to the fibril axis and an intramolecular disulfide that stabilises the subunit fold. We also describe a structural model for a second fibril morphology and show that it is built from the same subunit fold. The results provide insights into the mechanisms of fibril formation and the commonalities and differences within the amyloid fold in different protein sequences.

Chronic inflammation in adipose tissue is widely recognized as a pivotal link connecting obesity to a spectrum of related chronic diseases, including type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular disorders. In this pathogenic process, the dysregulated interaction between adipocytes and adipose-resident immune cells plays a critical regulatory role; however, the underlying mechanisms governing this abnormal interaction remain largely unknown. In this study, we showed that upregulated β2-microglobulin expression in hypertrophic adipocytes during obesity not only mediated the activation of adipose-resident CD8+ T cells in a cell contact-dependent manner but also facilitated iron overload and the ferroptosis of adipocytes, thereby promoting the M1 polarization of adipose tissue macrophages. Conversely, specific ablation of β2-microglobulin in adipocytes effectively suppressed the activation and accumulation of adipose-resident CD8+ T cells, as well as adipocyte ferroptosis and M1 polarization, ultimately preventing high-fat diet-induced obesity and its related inflammation and metabolic disorders. Additionally, adeno-associated virus-mediated adipose-targeted knockdown of β2-microglobulin has been demonstrated to therapeutically alleviate high-fat diet-induced obesity, as well as its related chronic inflammation and metabolic disorders. Furthermore, our bioinformatic analysis of human adipose transcriptome data revealed a strong correlation between adipose β2-microglobulin and obesity. More importantly, β2-microglobulin is significantly upregulated in adipocytes isolated from patients with obesity. Thus, our findings highlight the pivotal role of adipocytes in obesity-associated chronic inflammation and metabolic disorders via β2-microglobulin-dependent mechanisms.