Lipid-binding properties of α-synuclein play a central role in protein aggregation and progression of Parkinson’s disease (PD). α-Synuclein, an intrinsically disordered protein, binds to lipid ...membranes through the formation of two amphipathic helices that insert into the lipid bilayer. All disease-associated single point mutations have been identified to be within these helical regions of α-synuclein: V15A, A30P, E46K, H50Q, G51D, A53T, and A53V. However, the effects of these mutations on the bound states of the two α helices of the protein have yet to be fully characterized. In this report, we use a tryptophan fluorescence assay to measure the binding of the α helices of these PD-associated mutants to lipid membranes within the lipid-depletion regime. We characterize the binding behavior of each helix, revealing that, generally, the PD-associated mutants shift the equilibrium bound state away from the N-terminal helix of the protein toward helix 2 at lower lipid concentrations. Altogether, our results indicate that disruption to the equilibrium binding of the two α helices of α-synuclein could play a role in PD progression.
Mucosal associated invariant T (MAIT) cells are an innate-like T cell subset prevalent in humans and distributed throughout the blood and mucosal sites. Human MAIT cells are defined by the expression ...of the semi-invariant TCRα chain TRAV1-2/TRAJ12/20/33 and are restricted by the non-polymorphic major histocompatibility complex (MHC) class I-like molecule, MHC-related protein 1, MR1. MAIT cells are activated by small organic molecules, derived from the riboflavin biosynthesis pathway of bacteria and fungi, presented by MR1. Traditionally, MAIT cells were thought to recognize a limited number of antigens due to usage of an invariant TCRα chain and restriction by a non-polymorphic MHC molecule. However, recent studies demonstrate that the TCR repertoire of MAIT cells is more heterogeneous, suggesting there is a more diverse array of MR1 antigens that MAIT cells can recognize. In response to infected cells, MAIT cells produce the pro-inflammatory cytokines, IFN-γ and TNF, and are cytolytic. Studies performed in MR1-deficient mice suggest that MAIT cells can provide anti-bacterial control within the first few days post-infection, as well as contribute to enhanced adaptive immunity in murine models of respiratory infections. In humans, the role of MAIT cells is unclear; however, evidence points to interplay between MAIT cells and microbial infections, including Mycobacterium tuberculosis. Given that MAIT cells are pro-inflammatory, serve in early control of bacterial infections, and appear enriched at tissue sites where microbes interface and gain access to the body, we postulate that they play an important role in antimicrobial immune responses. In this review, we discuss the most recent studies on the function and phenotype of MAIT cells, including their TCR diversity and antigenic repertoire, with a focus on the contribution of human MAIT cells in the immune response to microbial infection.
Despite playing critical roles in the immune response and having significant potential in immunotherapy, γδ T cells have garnered little of the limelight. One major reason for this paradox is that ...their antigen recognition mechanisms are largely unknown, limiting our understanding of their biology and our potential to modulate their activity. One of the best-studied γδ subsets is the human Vγ9Vδ2T cell population, which predominates in peripheral blood and can combat both microbial infections and cancers. Although it has been known for decades that Vγ9Vδ2T cells respond to the presence of small pyrophosphate-based metabolites, collectively named phosphoantigens (pAgs), derived from microbial sources or malignant cells, the molecular basis for this response has been unclear. A major breakthrough in this area came with the identification of the Butyrophilin 3A (BTN3A) proteins, members of the Butyrophilin/Butyrophilin-like protein family, as mediators between pAgs and Vγ9Vδ2T cells. In this article, we review the most recent studies regarding pAg activation of human Vγ9Vδ2T cells, mainly focusing on the role of BTN3A as the pAg sensing molecule, as well as its potential impact on downstream events of the activation process.
Poor fitness in middle age is a risk factor for heart failure, particularly heart failure with a preserved ejection fraction. The development of heart failure with a preserved ejection fraction is ...likely mediated through increased left ventricular (LV) stiffness, a consequence of sedentary aging. In a prospective, parallel group, randomized controlled trial, we examined the effect of 2 years of supervised high-intensity exercise training on LV stiffness.
Sixty-one (48% male) healthy, sedentary, middle-aged participants (53±5 years) were randomly assigned to either 2 years of exercise training (n=34) or attention control (control; n=27). Right heart catheterization and 3-dimensional echocardiography were performed with preload manipulations to define LV end-diastolic pressure-volume relationships and Frank-Starling curves. LV stiffness was calculated by curve fit of the diastolic pressure-volume curve. Maximal oxygen uptake (Vo
max) was measured to quantify changes in fitness.
Fifty-three participants completed the study. Adherence to prescribed exercise sessions was 88±11%. Vo
max increased by 18% (exercise training: pre 29.0±4.8 to post 34.4±6.4; control: pre 29.5±5.3 to post 28.7±5.4, group×time
<0.001) and LV stiffness was reduced (right/downward shift in the end-diastolic pressure-volume relationships; preexercise training stiffness constant 0.072±0.037 to postexercise training 0.051±0.0268,
=0.0018), whereas there was no change in controls (group×time
<0.001; pre stiffness constant 0.0635±0.026 to post 0.062±0.031,
=0.83). Exercise increased LV end-diastolic volume (group×time
<0.001), whereas pulmonary capillary wedge pressure was unchanged, providing greater stroke volume for any given filling pressure (loading×group×time
=0.007).
In previously sedentary healthy middle-aged adults, 2 years of exercise training improved maximal oxygen uptake and decreased cardiac stiffness. Regular exercise training may provide protection against the future risk of heart failure with a preserved ejection fraction by preventing the increase in cardiac stiffness attributable to sedentary aging.
URL: https://www.clinicaltrials.gov. Unique identifier: NCT02039154.
Cross-sectional studies in athletes suggest that endurance training augments cardiovascular structure and function with apparently different phenotypes in athletic males and females. It is unclear ...whether the longitudinal response to endurance training leads to similar cardiovascular adaptations between sexes. We sought to determine whether males and females demonstrate similar cardiovascular adaptations to 1 yr of endurance training, matched for training volume and intensity. Twelve previously sedentary males (26 ± 7, n = 7) and females (31 ± 6, n = 5) completed 1 yr of progressive endurance training. All participants underwent a battery of tests every 3 mo to determine maximal oxygen uptake (V̇o2max) and left ventricle (LV) function and morphology (cardiac magnetic resonance imaging). Pulmonary artery catheterization was performed before and after 1 yr of training, and pressure-volume and Starling curves were constructed during decreases (lower-body negative pressure) and increases (saline infusion) in cardiac volume. Males progressively increased V̇o2max, LV mass, and mean wall thickness, before reaching a plateau from month 9 to 12 of training. In contrast, despite exactly the same training, the response in females was markedly blunted, with V̇o2max, LV mass, and mean wall thickness plateauing after only 3 mo of training. The response of LV end-diastolic volume was not influenced by sex (males +20% and females +18%). After training Starling curves were shifted upward and left, but the effect was greatest in males (interaction P = 0.06). We demonstrate for the first time clear sex differences in response to 1 yr of matched endurance training, such that the development of ventricular hypertrophy and increase in V̇o2max in females is markedly blunted compared with males.
MR1-restricted mucosal-associated invariant T (MAIT) cells represent a subpopulation of αβ T cells with innate-like properties and limited TCR diversity. MAIT cells are of interest because of their ...reactivity against bacterial and yeast species, suggesting that they play a role in defense against pathogenic microbes. Despite the advances in understanding MAIT cell biology, the molecular and structural basis behind their ability to detect MR1-Ag complexes is unclear. In this study, we present our structural and biochemical characterization of MAIT TCR engagement of MR1 presenting an Escherichia coli-derived stimulatory ligand, rRL-6-CH2OH, previously found in Salmonella typhimurium. We show a clear enhancement of MAIT TCR binding to MR1 due to the presentation of this ligand. Our structure of a MAIT TCR/MR1/rRL-6-CH2OH complex shows an evolutionarily conserved binding orientation, with a clear role for both the CDR3α and CDR3β loops in recognizing the rRL-6-CH2OH stimulatory ligand. We also present two additional xenoreactive MAIT TCR/MR1 complexes that recapitulate the docking orientation documented previously, despite having variation in the CDR2β and CDR3β loop sequences. Our data support a model by which MAIT TCRs engage MR1 in a conserved fashion, with their binding affinities modulated by the nature of the MR1-presented Ag or diversity introduced by alternate Vβ usage or CDR3β sequences.
αβ T‐cell lines specific for sulfatide, an abundant myelin glycosphingolipid presented by various CD1 molecules, have been previously derived from PBMCs of patients with demyelinating diseases such ...as multiple sclerosis (MS) but also from healthy subjects. Using an unbiased tetramer‐based MACS enrichment method to enrich for rare antigen‐specific cells, we confirmed the presence of CD1d‐sulfatide‐specific T cells in all healthy individuals examined. Surprisingly, the great majority of fresh sulfatide‐specific T cells belonged to the γδ lineage. Furthermore, these cells used the Vδ1 TCR variable segment, which is uncommon in the blood but predominates in tissues such as the gut and specifically accumulates in MS lesions. Recombinant Vδ1 TCRs from different individuals were shown to bind recombinant CD1d‐sulfatide complexes in a sulfatide‐specific manner. These results provide the first direct demonstration of MHC‐like‐restricted, antigen‐specific recognition by γδ TCRs. Together with previous reports, they support the notion that human Vδ1 T cells are enriched in CD1‐specific T cells and suggest that the Vδ1 T‐cell population that accumulates in MS lesions might be enriched in CD1‐sulfatide‐specific cells.
The predominant population of γδ T cells in human blood express a T cell receptor (TCR) composed of a Vγ9 (Vγ2 in an alternate nomenclature) and Vδ2 domains. These cells came into the limelight when ...it was discovered they can respond to certain microbial infections and tumorigenic cells through the detection of small, pyrophosphate containing organic molecules collectively called "phosphoantigens" or "pAgs." These molecules are intermediates in both eukaryotic and prokaryotic metabolic pathways. Chemical variants of these intermediates have been used in the clinic to treat a range of different cancers, however, directed optimization of these molecules requires a full understanding of their mechanism of action on target cells. We and others have identified a subclass of butyrophilin-related molecules (BTN3A1-3) that are directly involved in pAg sensing in the target cell, leading to engagement and activation of the T cell through the TCR. Our data and that of others support the pAg binding site to be the intracellular B30.2 domain of BTN3A1, which is the only isoform capable of mediating pAg-dependent stimulation of Vγ9Vδ2 T cells. Here, we review the data demonstrating pAg binding to the B30.2 domain and our studies of the structural conformations of the BTN3A extracellular domains. Finally, we synthesize a model linking binding of pAg to the intracellular domain with T cell detection via the extracellular domains in an "inside-out" signaling mechanism of the type characterized first for integrin molecule signaling. We also explore the role of Vγ9Vδ2 TCR variability in the CDR3 γ and δ loops and how this may modulate Vγ9Vδ2 cells as a population in surveillance of human health and disease.
Diversity in recognition and function of human γδ T cells Castro, Caitlin D.; Boughter, Christopher T.; Broughton, Augusta E. ...
Immunological reviews,
November 2020, 2020-11-00, 20201101, Letnik:
298, Številka:
1
Journal Article
Recenzirano
As interest increases in harnessing the potential power of tissue‐resident cells for human health and disease, γδ T cells have been thrust into the limelight due to their prevalence in peripheral ...tissues, their sentinel‐like phenotypes, and their unique antigen recognition capabilities. This review focuses primarily on human γδ T cells, highlighting their distinctive characteristics including antigen recognition, function, and development, with an emphasis on where they differ from their αβ T cell comparators, as well as from γδ T cell populations in the mouse. We review the antigens that have been identified thus far to regulate members of the human Vδ1 population and discuss what players are involved in transducing phosphoantigen‐mediated signals to human Vγ9Vδ2 T cells. We also briefly review distinguishing features of these cells in terms of TCR signaling, use of coreceptor and costimulatory molecules and their development. These cells have great potential to be harnessed in a clinical setting, but caution must be taken to understand their unique capabilities and how they differ from the populations to which they are commonly compared.
Human Vγ9Vδ2 T cells are well known for their rapid and potent response to infection and tumorigenesis when in the presence of endogenous or exogenous phosphoisoprenoids. However, the molecular ...mechanisms behind the activation of this γδ T cell population remains unclear. Evidence pointing to a role for the CD277/butyrophilin-3 (BTN3A) molecules in this response led us to investigate the structures of these molecules and their modifications upon binding to an agonist antibody (20.1) that mimics phosphoisoprenoid-mediated Vγ9Vδ2 activation and an antagonist antibody (103.2) that inhibits this reactivity. We find that the three BTN3A isoforms: BTN3A1, BTN3A2, and BTN3A3, have high structural homology to the B7 superfamily of proteins and exist as V-shaped homodimers in solution, associating through the membrane proximal C-type Ig domain. The 20.1 and 103.2 antibodies bind to separate epitopes on the BTN3A Ig-V domain with high affinity but likely with different valencies based on their binding orientation. These structures directly complement functional studies of this system that demonstrate that BTN3A1 is necessary for Vγ9Vδ2 activation and begin to unravel the extracellular events that occur during stimulation through the Vγ9Vδ2 T cell receptor.
Background: Phosphoisoprenoid stimulation of Vγ9Vδ2 T cells can be modulated by anti-BTNA3 antibodies.
Results: Agonist and antagonist antibodies associate differently with BTN3A structurally and biophysically.
Conclusion: Differential binding of antibodies to BTN3A modulates its oligomerization on the cell surface.
Significance: Defining how γδ T cells recognize antigen is critical for understanding their functions in the immune response.
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