Invariant chain processing is independent of cathepsin variation between primary human B cells/dendritic cells and B-lymphoblastoid cells

As part of the endocytic antigen processing pathway, proteolytic cleavage of the invariant chain (Ii) is important for the generation of class II-associated invariant chain peptide (CLIP). CLIP remains associated with the major histocompatibility complex (MHC) class II molecule to prevent premature loading of antigenic peptides. Cysteine proteases, such as Cathepsin S (CatS), CatL, or CatV, play a pivotal role in the final stage of Ii degradation depending on the cell type studied. Less is known regarding the early stages of Ii processing. We therefore explored whether the serine protease CatG is involved in the initial step of Ii degradation in primary antigen presenting cells (APC), since the cathepsin distribution differs between primary APC and cell lines. While primary human B cells and dendritic cells (DC) do harbor CatG, this protease is absent in B-lymphoblastoid cells (BLC) or monocyte-derived DC generated in vitro. In addition, other proteases, such as CatC, CatL, and the asparagine endoprotease (AEP), are active in BLC and monocyte-derived DC. Here we demonstrate that CatG progressively degraded Ii in vitro resulting in several intermediates. However, pharmacological inhibition of CatG in primary B cells and DC did not alter Ii processing, indicating that CatG is dispensable in Ii degradation. Interestingly, stalling of cysteine proteases by inhibition in BLC vs. primary B cells and DC did not result in any differences in the generation of distinct Ii intermediates between the cells tested, suggesting that Ii processing is independent of the cathepsin variation within professional human APC.

Was the serine protease cathepsin G discovered by S. G. Hedin in 1903 in bovine spleen?

In the beginning of the 20th century, enzymes with proteolytic activity were classified as peptidases, Erepsin, and proteases. Among these, pepsin, trypsin, and autolytic enzymes were of the protease class. Spleen-derived proteases were poorly characterized until Sven Gustaf Hedin performed several digestion experiments with bovine spleen. He incubated minced bovine spleen under acidic or neutral conditions and characterized two active proteases; the results were published in 1903. The first protease was named α-protease and was active under neutral conditions. The second was named β-protease and was active under acidic conditions. We replicated Hedin's experiments according to his methods and found, by using activity-based probes to visualize proteases, that the historical α-protease is the present-day serine protease cathepsin G (CatG), which is known to be important in several immune processes, including antigen processing, chemotaxis, and activation of surface receptors. The β-protease, however, comprised different proteases including CatX, B, S, and D. We suggest that Hedin described CatG activity in bovine spleen over 100 years ago.

Was the serine protease cathepsin G discovered by S. G. Hedin in 1903 in bovine spleen?

In the beginning of the 20th century, enzymes with proteolytic activity were classified as peptidases, Erepsin, and proteases. Among these, pepsin, trypsin, and autolytic enzymes were of the protease class. Spleen-derived proteases were poorly characterized until Sven Gustaf Hedin performed several digestion experiments with bovine spleen. He incubated minced bovine spleen under acidic or neutral conditions and characterized two active proteases; the results were published in 1903. The first protease was named α-protease and was active under neutral conditions. The second was named β-protease and was active under acidic conditions. We replicated Hedin's experiments according to his methods and found, by using activity-based probes to visualize proteases, that the historical α-protease is the present-day serine protease cathepsin G (CatG), which is known to be important in several immune processes, including antigen processing, chemotaxis, and activation of surface receptors. The β-protease, however, comprised different proteases including CatX, B, S, and D. We suggest that Hedin described CatG activity in bovine spleen over 100 years ago.

Vitamin D status and mortality in chronic kidney disease

BACKGROUND

Vitamin D deficiency is found in the majority of patients with chronic kidney disease (CKD) and may contribute to various chronic diseases. Current guidelines suggest correcting reduced 25-hydroxyvitamin D [25(OH)D] concentrations in CKD patients with an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2). Whether low 25(OH)D levels in these patients are associated with higher mortality is unclear. This issue was addressed in the present work.

METHODS

We examined 444 patients with eGFR <60 mL/min/1.73 m(2) from the Ludwigshafen Risk and Cardiovascular Health Study. This prospective cohort study includes Caucasian patients without primary kidney disease who were routinely referred to coronary angiography at baseline (1997-2000).

RESULTS

During a median follow-up time of 9.4 years, 227 patients died including 159 deaths from cardiovascular causes. Multivariate adjusted hazard ratios (HRs) (with 95% confidence intervals) in severely vitamin D-deficient [25(OH)D <10 ng/mL] compared to vitamin D-sufficient patients [25(OH)D ≥ 30 ng/mL] were 3.79 (1.71-8.43) for all-cause and 5.61 (1.89-16.6) for cardiovascular mortality. Adjusted HRs per 10 ng/mL increase in 25(OH)D levels were 0.63 (0.50-0.79) for all-cause and 0.59 (0.45-0.79) for cardiovascular mortality. There was no significant interaction with parathyroid hormone concentrations.

CONCLUSIONS

Low 25(OH)D levels are associated with increased all-cause and cardiovascular mortality in CKD patients. These findings support suggestions to correct vitamin D deficiency, but whether vitamin D supplementation improves survival remains to be proven in randomized controlled trials.

Low free testosterone is associated with heart failure mortality in older men referred for coronary angiography

AIMS

Accumulating evidence suggests that androgen deficiency is associated with cardiovascular disease. We aimed at evaluating whether total testosterone (TT) and free testosterone (FT) are associated with specific cardiovascular events.

METHODS AND RESULTS

We measured TT and sex-hormone-binding globulin levels in 2078 men who were routinely referred for coronary angiography between 1997 and 2000. Free testosterone was calculated according to Vermeulen. Main outcome measures were Cox proportional hazard ratios (HRs) for sudden cardiac death, fatal myocardial infarction, death from congestive heart failure (CHF), as well as other cardiac deaths according to quartiles of TT and FT. The median follow-up time was 7.7 years. Multivariable adjusted HRs (with 95% confidence intervals) in the fourth compared with the first FT quartile and per 1 SD increase in FT for CHF mortality were 0.38 (0.17-0.87) and 0.37 (0.15-0.89), respectively. We observed no independent significant association of FT with sudden cardiac death, fatal myocardial infarction, or other cardiac death. There was no independent association of TT levels with cardiovascular events or cardiac disease.

CONCLUSION

Low levels of FT are independently associated with increased CHF mortality.

Lipoprotein associated phospholipase A2 concentration predicts total and cardiovascular mortality independently of established risk factors (The Ludwigshafen Risk and Cardiovascular Health Study)

BACKGROUND

Lipoprotein-associated phospholipase A2 (LpPLA2) is a lipoprotein-bound enzyme involved in inflammation and atherosclerosis. This cohort study investigates LpPLA2 concentration to predict cardiovascular and total mortality in patients scheduled for coronary angiography.

METHODS

LpPLA2 concentration was determined in 2298 patients with and in 661 patients without angiographically confirmed coronary artery disease (CAD). During the median observation period of 8.0 years 686 patients died.

RESULTS

In patients with tertiles of LpPLA2 of 307 - 475 ng/mL, or > or = 475 ng/mL unadjusted hazard ratios (HR) for total mortality were 1.47 (95% CI 1.21 - 1.80; p < 0.001), and 1.63 (95% CI 135 - 1.97; p < 0.001), respectively, compared to patients with LpPLA2 < or = 307 ng/mL. HRs for cardiovascular death were 1.33 (95% CI 1.04 - 1.71; p = 0.026), and 1.59 (95% CI 1.26 - 2.02; p < 0.001), respectively. After accounting for established risk factors and including angiographic CAD status and high sensitivity C-reactive protein (hsCRP), the 3rd tertile of LpPLA2 concentration predicted death from all causes with a HR of 1.40 (95% CI 1.15 - 1.71; p = 0.001) and cardiovascular death with a HR of 1.35 (95% CI 1.05 - 1.73; p = 0.018). LpPLA2 increased the risk of cardiovascular death significantly even in individuals with high hsCRP. In patients with hsCRP > 33 mg/L and LpPLA2 > 392 ng/mL the risk of cardiovascular death was almost two-fold higher compared to patients with low hsCRP and low LpPLA2 with a HR of 1.98 (95% CI 1.50 - 2.62; p < 0.001).

CONCLUSIONS

LpPLA2 concentration predicts risk for total and cardiovascular mortality independently from established risk factors and indicates risk for cardiovascular death even in patients with high hsCRP levels.

Loci from a genome-wide analysis of bilirubin levels are associated with gallstone risk and composition

BACKGROUND & AIMS

Genome-wide association studies have mapped loci that are associated with serum levels of bilirubin. Bilirubin is a major component of gallstones so we investigated whether these variants predict gallstone bilirubin content and overall risk for gallstones.

METHODS

Loci that were identified in a meta-analysis to attain a genome-wide significance level of a P value less than 1.0×10(-7) (UGT1A1, SLCO1B1, LST-3TM12, SLCO1A2) were analyzed in 1018 individuals with known gallstone composition. Gallstone risk was analyzed in 2606 German choleystecomized individuals and 1121 controls and was replicated in 210 cases and 496 controls from South America.

RESULTS

By using the presence of bilirubin as a phenotype, variants rs6742078 (UGT1A1; P = .003), rs4149056 (SLCO1B1; P = .003), and rs4149000 (SLCO1A2; P = .015) were associated with gallstone composition. In regression analyses, only UGT1A1 and SLCO1B1 were independently retained in the model. UGT1A1 (rs6742078; P = .018) was associated with overall gallstone risk. In a sex-stratified analysis, only male carriers of rs6742078 had an increased risk for gallstone disease (P = 2.1×10(-7); odds ratio(recessive), 2.34; P(women) = .47). The sex-specific association of rs6742078 was confirmed in samples from South America (P(men) = .046; odds ratio(recessive), 2.19; P(women) = .96).

CONCLUSIONS

The UGT1A1 Gilbert syndrome variant rs6742078 is associated with gallstone disease in men; further studies are required regarding the sex-specific physiology of bilirubin and bile acid metabolism. Variants of ABCG8 and UGT1A1 are the 2 major risk factors for overall gallstone disease, they contribute a population attributable risk of 21.2% among men.

Genome-wide association study identifies two novel regions at 11p15.5-p13 and 1p31 with major impact on acute-phase serum amyloid A

Elevated levels of acute-phase serum amyloid A (A-SAA) cause amyloidosis and are a risk factor for atherosclerosis and its clinical complications, type 2 diabetes, as well as various malignancies. To investigate the genetic basis of A-SAA levels, we conducted the first genome-wide association study on baseline A-SAA concentrations in three population-based studies (KORA, TwinsUK, Sorbs) and one prospective case cohort study (LURIC), including a total of 4,212 participants of European descent, and identified two novel genetic susceptibility regions at 11p15.5-p13 and 1p31. The region at 11p15.5-p13 (rs4150642; p = 3.20×10⁻¹¹¹) contains serum amyloid A1 (SAA1) and the adjacent general transcription factor 2 H1 (GTF2H1), Hermansky-Pudlak Syndrome 5 (HPS5), lactate dehydrogenase A (LDHA), and lactate dehydrogenase C (LDHC). This region explains 10.84% of the total variation of A-SAA levels in our data, which makes up 18.37% of the total estimated heritability. The second region encloses the leptin receptor (LEPR) gene at 1p31 (rs12753193; p = 1.22×10⁻¹¹) and has been found to be associated with CRP and fibrinogen in previous studies. Our findings demonstrate a key role of the 11p15.5-p13 region in the regulation of baseline A-SAA levels and provide confirmative evidence of the importance of the 1p31 region for inflammatory processes and the close interplay between A-SAA, leptin, and other acute-phase proteins.

An elevated level of acute-phase serum amyloid A (A-SAA), a sensitive marker of the acute inflammatory state with high heritability estimates, causes amyloidosis and is a risk factor for atherosclerosis and its clinical complications, type 2 diabetes, as well as various malignancies. This study describes the first genome-wide association study on baseline A-SAA concentrations. In a meta-analysis of four genome-wide scans totalling 4,212 participants of European descent, we identified two novel genetic susceptibility regions on chromosomes 11 and 1 to be associated with baseline A-SAA concentrations. The chromosome 11 region contains the serum amyloid A1 gene and the adjacent genes and explains a high percentage of the total estimated heritability. The chromosome 1 region is a known genetic susceptibility region for inflammation. Taken together, we identified one region, which seems to be of key importance in the regulation of A-SAA levels and represents a novel potential target for the investigation of related clinical entities. In addition, our findings indicate a close interplay between A-SAA and other inflammatory proteins, as well as a larger role of a known genetic susceptibility region for inflammatory processes as it has been assumed in the past.

Sex steroids and mortality in men referred for coronary angiography

OBJECTIVE

Accumulating evidence suggests that sex steroids are associated with various chronic diseases. We aimed at evaluating whether total testosterone (TT), free testosterone (FT) and sex hormone-binding globulin (SHBG) are associated with all-cause mortality and specific fatal events.

DESIGN, SETTING AND PARTICIPANTS

We measured TT and SHBG levels in 2078 men who were routinely referred for coronary angiography (1997-2000). FT was calculated according to Vermeulen.

MEASUREMENTS

The main outcome measures were Cox proportional hazard ratios (HRs) for mortality from all causes, from cardiovascular and non-cardiovascular causes and from cancer according to SHBG, FT and TT.

RESULTS

Multivariable-adjusted HRs (with 95% confidence intervals) in the fourth compared to the first SHBG quartile for all-cause, non-cardiovascular and cancer mortality were 1·61 (1·16-2·23), 2·44 (1·39-4·28), and 2·86 (1·03-7·32), respectively. There was no significant association of SHBG levels with cardiovascular mortality. All-cause mortality was significantly reduced per 1 SD increase in FT in the multivariate-adjusted analyses [0·49 (0·30-0·81)]. We observed no significant associations of FT with cardiovascular and cancer mortality, and TT levels were not independently related to any fatal events.

CONCLUSION

High levels of SHBG are associated with adverse health outcomes in a large cohort of older men referred for coronary angiography. Further studies are warranted to confirm our results and to elucidate the underlying mechanisms for our findings.

Symmetrical and asymmetrical dimethylarginine as predictors for mortality in patients referred for coronary angiography: the Ludwigshafen Risk and Cardiovascular Health study

BACKGROUND

Asymmetrical dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, has been linked to cardiovascular risk. The clinical role of its structural isomer symmetrical dimethylarginine (SDMA) remains largely unclear.

METHODS

We measured SDMA and ADMA in 3229 patients undergoing coronary angiography at baseline (1997-2000) and recorded total and cardiovascular mortality during a median follow-up time of 7.7 years. We investigated associations of SDMA with cardiovascular risk factors and mortality and compared its role as a cardiovascular risk factor with ADMA, which predicted mortality in previous analyses of our study.

RESULTS

In linear regression analyses including common cardiovascular risk factors as covariates, SDMA and ADMA were significantly associated with cystatin C, N-terminal pro-B-type natriuretic peptide, New York Heart Association classification, and homocysteine. The regression coefficients were higher for SDMA than for ADMA. In Cox proportional-hazards models adjusted for cardiovascular risk factors, the hazard ratios (HRs) (with 95% CI) in the second, third, and fourth SDMA quartile compared to the lowest quartile were 0.77 (0.60-0.99), 0.99 (0.78-1.25), and 1.51 (1.20-1.91) for total mortality and 0.92 (0.68-1.25), 0.93 (0.68-1.26), and 1.54 (1.14-2.01) for cardiovascular mortality. The same calculations for ADMA quartiles revealed HRs of 1.05 (0.83-1.32), 1.19 (0.95-1.50), and 1.61 (1.30-1.99) for total mortality and HR of 1.00 (0.74-1.34), 1.26 (0.95-1.68), and 1.54 (1.18-2.02) for cardiovascular mortality.

CONCLUSIONS

Serum concentrations of SDMA are independently associated with increased cardiovascular and all-cause mortality in patients undergoing coronary angiography. The pattern of risk linked to SDMA is different from that linked to ADMA, suggesting different pathophysiological roles of these 2 methylarginine metabolites.

Impact of CYP2C8 and 2C9 polymorphisms on coronary artery disease and myocardial infarction in the LURIC cohort

Aims: As data on the cardiovascular risk associated with CYP2C8 and CYP2C9 polymorphisms is controversial, we performed a cross-sectional analysis of subjects enrolled in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study. Materials & methods: CYP2C8 and CYP2C9 genetic polymorphisms were determined with real-time PCR in 2827 patients. Based on angiography, 1052 of these patients had coronary artery disease (CAD) and 615 did not; 1160 patients had signs or a history of myocardial infarction (MI) in addition to CAD. The association of genotypes with CAD and MI was determined by logistic regression analysis, adjusted for age, sex, dyslipidemia, hypertension, diabetes mellitus and smoking status. Results: Frequencies of CYP2C8 and 2C9 variants were neither significantly different between CAD and control patients, nor between MI and control patients. Men carrying the CYP2C9*3 allele had an increased risk of MI (odds ratio [OR]: 1.67; 95% CI: 1.06–2.63; p = 0.03) and women carrying the CYP2C9*3 allele had a decreased risk of CAD (OR: 0.65; 95%CI: 0.42–0.9; p = 0.05). Conclusion: Overall, LURIC data confirmed that there is no major cardiovascular risk associated with CYP2C8 and CYP2C9 variants in a cardiovascular risk population of patients having undergone coronary angiography.

Twelve type 2 diabetes susceptibility loci identified through large-scale association analysis

By combining genome-wide association data from 8,130 individuals with type 2 diabetes (T2D) and 38,987 controls of European descent and following up previously unidentified meta-analysis signals in a further 34,412 cases and 59,925 controls, we identified 12 new T2D association signals with combined P<5x10(-8). These include a second independent signal at the KCNQ1 locus; the first report, to our knowledge, of an X-chromosomal association (near DUSP9); and a further instance of overlap between loci implicated in monogenic and multifactorial forms of diabetes (at HNF1A). The identified loci affect both beta-cell function and insulin action, and, overall, T2D association signals show evidence of enrichment for genes involved in cell cycle regulation. We also show that a high proportion of T2D susceptibility loci harbor independent association signals influencing apparently unrelated complex traits.

Association of vitamin D status with serum androgen levels in men

OBJECTIVE

Studies in rodents indicate a role of vitamin D in male reproduction, but the relationship between vitamin D and androgen levels in men is largely unexplored. We aimed to investigate the association of 25-hydroxyvitamin D [25(OH)D] levels with testosterone, free androgen index (FAI) and SHBG. Moreover, we examined whether androgen levels show a similar seasonal variation to 25(OH)D.

DESIGN

In this cross-sectional study, 25(OH)D, testosterone and SHBG levels were assessed by immunoassay in 2299 men who were routinely referred for coronary angiography (1997-2000).

MEASUREMENTS

Main outcome measures were associations of 25(OH)D levels with testosterone, SHBG and FAI. FAI was calculated as testosterone (nmol/l)/SHBG (nmol/l) x 100.

RESULTS

Men with sufficient 25(OH)D levels (> or =30 microg/l) had significantly higher levels of testosterone and FAI and significantly lower levels of SHBG when compared to 25(OH)D insufficient (20-29.9 microg/l) and 25(OH)D-deficient (<20 microg/l) men (P < 0.05 for all). In linear regression analyses adjusted for possible confounders, we found significant associations of 25(OH)D levels with testosterone, FAI and SHBG levels (P < 0.05 for all). 25(OH)D, testosterone and FAI levels followed a similar seasonal pattern with a nadir in March (12.2 microg/l, 15.9 nmol/l and 40.8, respectively) and peak levels in August (23.4 microg/l, 18.7 nmol/l and 49.7, respectively) (P < 0.05 for all).

CONCLUSION

Androgen levels and 25(OH)D levels are associated in men and reveal a concordant seasonal variation. Randomized controlled trials are warranted to evaluate the effect of vitamin D supplementation on androgen levels.

Enhanced weight loss with protein-enriched meal replacements in subjects with the metabolic syndrome

BACKGROUND

The objective of this study was to investigate the effects of a protein-rich diet in comparison with a conventional protein diet on weight loss, weight maintenance, and body composition in subjects with the metabolic syndrome.

METHODS

Obese subjects received instructions for an energy-restricted diet with a calorie deficit of 500 kcal/day and were randomly assigned to either high-protein (1.34 g/kg body weight) or conventional protein (0.8 g/kg body weight) diets for 12 months. Protein-enriched meal replacements were used to enrich one arm of the diet with protein throughout the study. In all, 67% of the participants completed the 1-year study.

RESULTS

Subjects following the high-protein diet lost more body weight and more fat mass compared with those on the conventional protein diet, whereas the loss of fat-free mass was similar in both diet groups. Biochemical parameters associated with the metabolic syndrome improved in both diet groups. Improvements were modestly greater in subjects with the high-protein diet. After 12 months of treatment, 64.5% of the subjects in the high-protein diet group and 34.8% of the subjects in the conventional diet group no longer met three or more of the criteria for having the metabolic syndrome.

CONCLUSIONS

Individuals with the metabolic syndrome achieved significant weight loss while preserving fat-free mass when treated with an energy-restricted, high-protein diet that included nutrient-dense meal replacements, as compared with the results for conventional protein intake. An intervention with a protein-enriched diet may have advantages for the management of the metabolic syndrome.

HLA-DR genotypes influence age at disease onset in children and juveniles with type 1 diabetes mellitus

OBJECTIVE

To investigate HLA-DR genotype in association with chronological age or calendar year of disease onset and the time trend of genotype frequencies from 1969 to 2009. Additionally, to examine genotype frequency in relation to B-cell-, islet cell antibodies (ICA)-, autoantibodies to insulin-, insulinoma antigen 2 (IA2)-, glutamic acid decarboxylase-antibody positivity, thyroid antibody positivity, thyroid diseases or coeliac antibody positivity. Genotype associations with gender and ethnicity are also analyzed.

SUBJECTS AND METHODS

HLA-typed children and juveniles (n=1445) aged <or=20 years at disease onset from the German/Austrian DPV-database were examined. chi(2) statistics and mixed hierarchical logistic regression models were used to compare genotype frequencies and establish associations with age at disease manifestation, autoimmune antibodies/diseases, ethnicity and time trend.

RESULTS

Subjects aged <6 years predominantly carried the genotype HLA-DR3/4 (25.2%), whereas in subjects aged >12 years the most prevalent HLA-DR genotype was X/X (18.1%). IA2 positivity was associated with HLA-DR4/X and HLA-DR3/4 positivity (P=0.011), and hypothyroidism was linked to HLA-DR4/4 (P=0.0103). More females carried the HLA-DR4/4 genotype (18.2 vs 12.7% P=0.0048) or were thyroid antibody positive (24.5 vs 14.7% P=0.0001). Larger numbers of <6 year olds were coeliac antibody positive than >12 year olds (14.8 vs 9.1% P=0.0037). No associations between migration background and B-cell-, thyroid- or coeliac-antibody positivity, and no time trend were found.

CONCLUSION

HLA-DR genotype associated with age at disease onset, ICA positivity and hypothyroidism; female gender with thyroid antibody positivity and low age of diabetes onset with coeliac antibody positivity.

Parathyroid hormone level is associated with mortality and cardiovascular events in patients undergoing coronary angiography

AIMS

Elevated parathyroid hormone (PTH) levels have been associated with increased cardiovascular risk in the general population. We aimed to elucidate whether PTH levels are associated with mortality and fatal cardiovascular events in patients referred for coronary angiography.

METHODS AND RESULTS

Intact PTH was measured in 3232 Caucasian patients from the LUdwigshafen RIsk and Cardiovascular Health (LURIC) study, who underwent coronary angiography at baseline (1997-2000). During a median follow-up time of 7.7 years, 742 patients died including 467 deaths due to cardiovascular causes. Unadjusted Cox proportional hazard ratios (HRs) (with 95% confidence intervals) in the fourth when compared to the first PTH quartile were 2.13 (1.75-2.60) for all-cause and 2.47 (1.92-3.17) for cardiovascular mortality. After adjustments for common cardiovascular risk factors, these HRs remained significant with 1.71 (1.39-2.10) for all-cause and 2.02 (1.55-2.63) for cardiovascular mortality. Among specific cardiovascular events we observed a particularly strong association of PTH with sudden cardiac death (SCD). The adjusted HR for SCD in the first vs. the fourth PTH quartile was 2.68 (1.71-4.22).

CONCLUSION

Our results among patients undergoing coronary angiography show that PTH levels are an independent risk factor for mortality and cardiovascular events warranting further studies to evaluate whether PTH modifying treatments reduce cardiovascular risk.

Processing and presentation of (pro)-insulin in the MHC class II pathway: the generation of antigen-based immunomodulators in the context of type 1 diabetes mellitus

Both CD4(+) and CD8(+) T lymphocytes play a crucial role in the autoimmune process leading to T1D. Dendritic cells take up foreign antigens and autoantigens; within their endocytic compartments, proteases degrade exogenous antigens for subsequent presentation to CD4(+) T cells via MHC class II molecules. A detailed understanding of autoantigen processing and the identification of autoantigenic T cell epitopes are crucial for the development of antigen-based specific immunomodulators. APL are peptide analogues of auto-immunodominant T cell epitopes that bind to MHC class II molecules and can mediate T cell activation. However, APL can be rapidly degraded by proteases occurring in the extracellular space and inside cells, substantially weakening their efficiency. By contrast, protease-resistant APL function as specific immunomodulators and can be used at low doses to examine the functional plasticity of T cells and to potentially interfere with autoimmune responses. Here, we review the latest achievements in (pro)-insulin processing in the MHC class II pathway and the generation of APL to mitigate autoreactive T cells and to activate Treg cells.

Masking of a cathepsin G cleavage site in vivo contributes to the proteolytic resistance of major histocompatibility complex class II molecules

SUMMARY

The expression of major histocompatibility complex class II (MHC II) molecules is post-translationally regulated by endocytic protein turnover. Here, we identified the serine protease cathepsin G (CatG) as an MHC II-degrading protease by in vitro screening and examined its role in MHC II turnover in vivo. CatG, uniquely among endocytic proteases tested, initiated cleavage of detergent-solubilized native and recombinant soluble MHC II molecules. CatG cleaved human leukocyte antigen (HLA)-DR isolated from both HLA-DM-expressing and DM-null cells. Even following CatG cleavage, peptide binding was retained by pre-loaded, soluble recombinant HLA-DR. MHC II cleavage occurred on the loop between fx1 and fx2 of the membrane-proximal beta2 domain. All allelic variants of HLA-DR tested and murine I-A(g7) class II molecules were susceptible, whereas murine I-E(k) and HLA-DM were not, consistent with their altered sequence at the P1' position of the CatG cleavage site. CatG effects were reduced on HLA-DR molecules with DRB mutations in the region implicated in interaction with HLA-DM. In contrast, addition of CatG to intact B-lymphoblastoid cell lines (B-LCLs) did not cause degradation of membrane-bound MHC II. Moreover, inhibition or genetic ablation of CatG in primary antigen-presenting cells did not cause accumulation of MHC II molecules. Thus, in vivo, the CatG cleavage site is sterically inaccessible or masked by associated molecules. A combination of intrinsic and context-dependent proteolytic resistance may allow peptide capture by MHC II molecules in harshly proteolytic endocytic compartments, as well as persistent antigen presentation in acute inflammatory settings with extracellular proteolysis.

The associations of cholesterol metabolism and plasma plant sterols with all-cause and cardiovascular mortality

Moderately elevated levels of plasma plant sterols have been suspected to be causally involved in atherosclerosis. The aim of this study was to investigate whether plant sterols and other markers of sterol metabolism predicted all-cause and cardiovascular mortality in participants of the Ludwigshafen Risk and Cardiovascular health (LURIC) study. A total of 1,257 individuals who did not use statins and at baseline had a mean (+/- SD) age of 62.8 (+/- 11.0) years were included in the present analysis. Lathosterol, cholestanol, campesterol, and sitosterol were measured to estimate cholesterol synthesis and absorption. The mean (+/- SD) time of the follow-up for all-cause and cardiovascular mortality was 7.32 (+/- 2.3) years. All-cause (P = 0.001) and cardiovascular (P = 0.006) mortality were decreased in the highest versus the lowest lathosterol to cholesterol tertile. In contrast, subjects in the third cholestanol to cholesterol tertile had increased all-cause (P < 0.001) and cardiovascular mortality (P = 0.010) compared with individuals in the first tertile. The third campesterol to cholesterol tertile was associated with increased all-cause mortality (P = 0.025). Sitosterol to cholesterol tertiles were not significantly related to all-cause or cardiovascular mortality. The data suggest that high absorption and low synthesis of cholesterol predict increased all-cause and cardiovascular mortality in LURIC participants.