Deamidation enables pathogenic SMAD6 variants to activate the BMP signaling pathway

The BMP signaling pathway plays a crucial role in regulating early embryonic development and tissue homeostasis.SMAD6 encodes a negative regulator of BMP,and rare variants of SMAD6 are recurrently found in individuals with birth defects.However,we observed that a subset of rare pathogenic variants of SMAD6 consistently exhibited positive regulatory effects instead of the initial negative effects on the BMP signaling pathway.We sought to determine whether these SMAD6 variants have common pathogenic mechanisms.Here,we showed that pathogenic SMAD6 variants accompanying this functional reversal exhibit similar increases in deamidation.Mechanistically,increased deamidation of SMAD6 variants promotes the accumulation of the BMP receptor BMPR1A and the formation of new complexes,both of which lead to BMP signaling pathway activation.Specifically,two residues,N262 and N404,in SMAD6 were identified as the crucial sites of deamidation,which was catalyzed primarily by glutamine-fructose-6-phosphate transaminase 2(GFPT2).Additionally,treatment of cells harboring SMAD6 variants with a deamidase inhibitor restored the inhibitory effect of SMAD6 on the BMP signaling pathway.Conversely,when wild-type SMAD6 was manually simulated to mimic the deamidated state,the reversed function of activating BMP signaling was reproduced.Taken together,these findings show that deamidation of SMAD6 plays a crucial role in the functional reversal of BMP signaling activity,which can be induced by a subset of various SMAD6 variants.Our study reveals a common pathogenic mechanism shared by these variants and provides a potential strategy for preventing birth defects through deamidation regulation,which might prevent the off-target effects of gene editing.

Effect of succinic acid deamidation-induced modification on wheat gluten

The effect of succinic acid deamidationinduced modification on wheat gluten was investigated in the present study.The changes of surface hydrophobicity,functional properties,secondary structure,and sensibility of proteolysis of modified samples were determined.The solubility of deamidated proteins increased in the isoelectric region of untreated wheat gluten.The isoelectric point of succinic acid deamidated wheat gluten was shifted to a basic pH and existed in the broad pH regions.Foaming property and molecular flexibility of wheat gluten were improved after the modification.The hydrolysis degree of the hydrolysates in proteolysis with flavorzyme and pancreatin increased after succinic acid deamidation.Moreover,succinic acid deamidation-induced modification resulted in little change in molecular weight and secondary structure of the protein.Thus,succinic acid could facilitate unfolding protein conformation.In addition,it could improve protein-water interactions,surface properties,and sensibility of the proteolysis of the deamidated wheat gluten.

Diagnostic accuracy of a new point-of-care screening assay for celiac disease

AIM: To determine the diagnostic accuracy of a new point-of-care assay detecting anti-deamidated gliadin peptides in celiac disease(CD) patients.METHODS: One-hundred-and-twelve patients(age range: 1.8-79.2 years old) with clinical symptoms suggestive of CD and/or first-degree relatives(FDR) of CD patients(n = 66),and confirmed CD on a gluten-free diet(GFD)(n = 46),were prospectively enrolled in the study at Gastroenterology outpatient clinics for adult patients and from the Gastroenterology Consultation Ward at the Pediatric Department of the University Hospital of Geneva.Written informed consent was obtained from all subjects enrolled.The study received approval from the local ethics committee.The original CD diagnosis had been based on serum-positive IgA anti-tissue transglutaminase enzyme-linked immunosorbent assay(ELISA)(QuantaLite,Inova Diagnostics,San Diego,CA,United States) and on biopsy results.Serum samples from all study participants were tested by the new CD lateral flow immunochromatographic assay(CD-LFIA) device,Simtomax Blood Drop(Augurix SA,BioArk,Monthey,Switzerland) to detect immunoglobulin(Ig)A and IgG antibodies against deamidated gliadin peptides.The diagnostic performance was evaluated using receiver operating characteristic curves with 95%CIs.A cut-off of 2 on the Rann colorimetric scale was used to calculate the device's sensitivity and specificity.RESULTS: CD-LFIA was highly accurate in detecting untreated celiac patients.In the group of patients with CD symptoms and/or FDR,eight new cases of CD were detected by ELISA and biopsy.All of these new cases were also correctly identified by CD-LFIA.The test yielded four false positive and four false negative results.The false positive results were all within the groups with clinical symptoms suggestive of CD and/or FDR,whereas the false negative results were all within the GFD group.The test yeld a sensitivity of 78.9%(95%CI: 54.4-93.9) and specificity of 95.7%(95%CI: 89.4-98.8),and the area under the curve reached 0.893(95%CI: 0.798-0.988).The Kappa coefficient,calculated according to the values obtained by two readers from the same device,was of 0.96(SE: 0.06).When the GFD patients were excluded from the analysis,the area under the curve reached 0.989(95%CI: 0.971-1.000) and the Kappa coefficient,calculated according to the values obtained by two readers from the same device,became 0.96(SE: 0.07).Furthermore,using the Rann scale cut-off of 2 without the GFD patients,sensitivity was 100% and specificity was 93.1%(95%CI: 83.3-98.1).CONCLUSION: The new CD-LFIA rapid screening test shows good diagnostic accuracy,sensitivity and specificity,and may rule out CD in patients with CD-related symptoms.

Correlation analysis of celiac sprue tissue transglutaminase and deamidated gliadin IgG/IgA

AIM:To indirectly determine if tissue transglutaminase(tTG)-specific T cells play a crucial role in the propagation of celiac disease.METHODS:Anti-deamidated gliadin peptide(DGP) and anti-tTG IgA and IgG were measured in the sera of celiac patients(both untreated and treated).The correlations were determined by Spearman's rank correlation test.RESULTS:In celiac patients,we found a very significant correlation between the production of DGP IgA and IgG(r = 0.75),indicating a simultaneous and ongoing production of these two isotypes reminiscent of oral vaccination studies.However,there was far less association between the production of tTG IgA and tTG IgG in celiac patients(r = 0.52).While tTG IgA was significantly correlated with DGP IgA(r = 0.80) and DGP IgG(r = 0.67),there was a weak correlation between production of anti-tTG IgG and the production of anti-DGP IgA(r = 0.38) and anti-DGP IgG(r = 0.43).CONCLUSION:These data demonstrate that the production of anti-tTG IgA is directly correlated to the production of anti-DGP IgG and IgA,whereas anti-tTG IgG is only weakly correlated.This result therefore supports the hapten-carrier theory that in well-established celiac patients anti-tTG IgA is produced by a set of B cells that are reacting against the complex of tTG-DGP in the absence of a tTG-specific T cell.

Clinical utility of quantitative multi-antibody Polycheck immunoassays in the diagnosis of coeliac disease

AIM:To evaluate the clinical utility of multi-antibody strategies in the diagnosis of coeliac disease(CD),the new quantitative Polycheck immunoassays were analysed.METHODS:Polycheck Celiac Panels(PCPs)are immunoenzyme screening assays for the quantitative measurement of coeliac-specific immunoglobulin class G(Ig G)or class A(Ig A)in serum.Lines of relevant antigens are coated together with five Ig G or Ig A standard lines used for the standard curve as positive control.PCP IgA consists of human recombinant human tissue transglutaminase(t TG)and deamidated gliadin peptides(DGP)as targets to detect Ig A antibodies.PCP IgG consists of t TG,DGP and IF(intrinsic factor)antigens to detect antibodies in Ig G class.PCPs were performed on 50 CD patients,including 6 cases with selective Ig A deficiency,and 50 non-coeliac controls.CD diagnosis was performed according to the ESPGHAN recommendations:The presence of specific anti-t TG-Ig A or anti-DGP-Ig G(in the case of Ig A deficiency)antibodies,typical histopathological changes in duodenal mucosa described in Marsh-Oberhüber classification as at least grade 2.The diagnosis of the majority of the control subjects was functional gastrointestinal disorders.The PCP results were compared with reference EliA Celikey.RESULTS:The usage of PCPs led to the correct identification of all CD patients.In our study,PCPs showed 100%agreement with the histopathological results.PCP IgA test showed a 98%concordance and correlated positively(R=0.651,P=0.0014)with Eli A Celikey test.The highest specificity and positive predictive value(both 100%)were observed for the detection of Polycheck anti-t TG-Ig A antibodies.The highest sensitivity and negative predictive value(both 100%)were achieved by Polycheck anti-DGPIg G antibody detection.The best performance(98%sensitivity and negative predictive value,100%specificity and positive predictive value,diagnostic accuracy-AU ROC 99%)was observed for the strategy of using both PCP IgA and IgG and determining positive outcomes of the test with two or more coeliac-specific antibodies detected.The majority of coeliac patients had multiple antibodies.All four antibodies were detected in 7(14%)cases,19 children(38%)were positive for three antibodies and 23(46%)were positive for two antibodies.CONCLUSION:The present study showed that detection of coeliac-specific antibodies with multi-antibody PCPs is effective and efficacious in the diagnosis of CD.

Elucidating the Degradation Pathways of Human Insulin in the Solid State

While there have been significant advances in the development of peptide oral dosage forms in recent years,highlighted by the clinical and commercial success of approved peptides such as Rybelsus®,there remain several barriers in the way of broad range applicability of this approach to peptide delivery.One such barrier includes the poor physical and chemical stability inherent to their structures,which persists in the solid state although degradation typically occurs at different rates and via different pathways in comparison to the solution state.Using insulin as a model peptide,this work sought to contribute to the development of analytical techniques for investigating common insulin degradation pathways.Chemically denatured,deamidated and aggregated samples were prepared and used to benchmark circular dichroism spectroscopy,reverse phase HPLC and size exclusion chromatography methods for the investigation of unfolding,chemical modifications and covalent aggregation of the insulin molecule respectively.Solid state degraded samples were prepared by heating insulin powder at 60°C and 75%relative humidity for 1,3,5 and 7 d,and the degradation profiles of the samples were evaluated and compared with those observed in solution.While no unfolding was observed to occur,significant deamidation and covalent aggregation were detected.Reductive disulfide bond cleavage using dithiothreitol allowed for separation of the insulin A-and B-chains,offering a facile yet novel means of assessing the mechanisms of deamidation and covalent aggregation occurring in the solid state.