Mapping Salivary Proteases in Sjögren's Syndrome Patients Reveals Overexpression of Dipeptidyl Peptidase-4/CD26

Soluble CD26: From Suggested Biomarker for Cancer Diagnosis to Plausible Marker for Dynamic Monitoring of Immunotherapy

Soluble CD26 (sCD26), a glycoprotein with dipeptidyl peptidase (DPP4) enzymatic activity, can contribute to early diagnosis of colorectal cancer and advanced adenomas and has been studied, including for prognostic purposes, across various other types of cancer and disease. The latest research in this field has confirmed that most, though not all, serum/plasma sCD26 is related to inflammation. The shedding and/or secretion of sCD26 from different immune cells are being investigated, and blood DPP4 activity levels do not correlate very strongly with protein titers. Some of the main substrates of this enzyme are key chemokines involved in immune cell migration, and both soluble and cell-surface CD26 can bind adenosine deaminase (ADA), an enzyme involved in the metabolism of immunosuppressor extracellular adenosine. Of note, there are T cells enriched in CD26 expression and, in mice tumor models, tumor infiltrating lymphocytes exhibited heightened percentages of CD26+ correlating with tumor regression. We employed sCD26 as a biomarker in the follow-up after curative resection of colorectal cancer for the early detection of tumor recurrence. Changes after treatment with different biological disease-modifying antirheumatic drugs, including Ig-CTLA4, were also observed in rheumatoid arthritis. Serum soluble CD26/DPP4 titer variation has recently been proposed as a potential prognostic biomarker after a phase I trial in cancer immunotherapy with a humanized anti-CD26 antibody. We propose that dynamic monitoring of sCD26/DPP4 changes, in addition to well-known inflammatory biomarkers such as CRP already in use as informative for immune checkpoint immunotherapy, may indicate resistance or response during the successive steps of the treatment. As tumor cells expressing CD26 can also produce sCD26, the possibility of sorting immune- from non-immune-system-originated sCD26 is discussed.

Exploring Salivary Epithelial Dysfunction in Sjögren's Disease

Sjögren's Disease (SjD) is an autoimmune disease of the exocrine tissues. Etiological events result in the loss of epithelial homeostasis alongside extracellular matrix (ECM) destruction within the salivary and lacrimal glands, followed by immune cell infiltration. In this review, we have assessed the current understanding of epithelial-mesenchymal transition (EMT)-associated changes within the salivary epithelium potentially involved in salivary dysfunction and SjD pathogenesis. We performed a PubMed literature review pertaining to the determination of pathogenic events that lead to EMT-related epithelial dysfunction and signaling in SjD. Molecular patterns of epithelial dysfunction in SjD salivary glands share commonalities with EMT mediating wound healing. Pathological changes altering salivary gland integrity and function may precede direct immune involvement while perpetuating MMP9-mediated ECM destruction, inflammatory mediator expression, and eventual immune cell infiltration. Dysregulation of EMT-associated factors is present in the salivary epithelium of SjD and may be significant in initiating and perpetuating the disease. In this review, we further highlight the gap regarding mechanisms that drive epithelial dysfunction in salivary glands in the early or subclinical pre-lymphocytic infiltration stages of SjD.

Comparative Proteomics Inspired Self-Stimulated Release Hydrogel Reinforces the Therapeutic Effects of MSC-EVs on Alzheimer's Disease

The clinical application of extracellular vesicles (EVs)-based therapeutics continues to be challenging due to their rapid clearance, restricted retention, and low yields. Although hydrogel possesses the ability to impede physiological clearance and increase regional retention, it typically fails to effectively release the incorporated EVs, resulting in reduced accessibility and bioavailability. Here an intelligent hydrogel in which the release of EVs is regulated by the proteins on the EVs membrane is proposed. By utilizing the EVs membrane enzyme to facilitate hydrogel degradation, sustained retention and self-stimulated EVs release can be achieved at the administration site. To achieve this goal, the membrane proteins with matrix degrading activity in the mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) are identified using comparative proteomics. After that, a hydrogel comprised of self-assembled peptides that are susceptible to degradation by the membrane enzymes present in MSC-EVs is designed and synthesized. After intranasal administration, this peptide hydrogel facilitates sustained and thermo-sensitive release of MSC-EVs, thereby extending the retention of the MSC-EVs and substantially enhancing their potential for treating Alzheimer's disease. This research presents a comparative proteomics-driven approach to intelligent hydrogel design, which holds the capacity to significantly enhance the applicability of EVs in clinical settings.

Application of omics in Sjögren's syndrome

OBJECTIVE

The pathogenesis, diagnosis, and treatment of Sjögren's syndrome (SS) face many challenges, and there is an urgent need to develop new technologies to improve our understanding of SS.

METHODS

By searching the literature published domestically and internationally in the past 20 years, this artical reviewed the research of various omics techniques in SS.

RESULTS

Omics technology provided valuable insights into the pathogenesis, early diagnosis, condition and efficacy evaluation of SS. It is helpful to reveal the pathogenesis of the disease and explore new treatment schemes, which will open a new era for the study of SS.

CONCLUSION

At present, omics research has made some gratifying achievements, but there are still many uncertainties. Therefore, in the future, we should improve research techniques, standardize the collection of samples, and adopt a combination of multi-omics techniques to jointly study the pathogenesis of SS and provide new schemes for its treatment.

Potential relevance of salivary legumain for the clinical diagnostic of hand, foot, and mouth disease

The fight against hand, foot, and mouth disease (HFMD) remains an arduous challenge without existing point-of-care (POC) diagnostic platforms for accurate diagnosis and prompt case quarantine. Hence, the purpose of this salivary biomarker discovery study is to set the fundamentals for the realization of POC diagnostics for HFMD. Whole salivary proteome profiling was performed on the saliva obtained from children with HFMD and healthy children, using a reductive dimethylation chemical labeling method coupled with high-resolution mass spectrometry-based quantitative proteomics technology. We identified 19 upregulated (fold change = 1.5-5.8) and 51 downregulated proteins (fold change = 0.1-0.6) in the saliva samples of HFMD patients in comparison to that of healthy volunteers. Four upregulated protein candidates were selected for dot blot-based validation assay, based on novelty as biomarkers and exclusions in oral diseases and cancers. Salivary legumain was validated in the Singapore (n = 43 healthy, 28 HFMD cases) and Taiwan (n = 60 healthy, 47 HFMD cases) cohorts with an area under the receiver operating characteristic curve of 0.7583 and 0.8028, respectively. This study demonstrates the feasibility of a broad-spectrum HFMD POC diagnostic test based on legumain, a virus-specific host systemic signature, in saliva.

Identification of potential salivary biomarkers for Sjögren's syndrome with an untargeted metabolomic approach

INTRODUCTION

Despite the rise of metabolomics over the past years, and particularly salivary metabolomics, little research on Sjögren's syndrome (SS) biomarkers has focused on the salivary metabolome.

OBJECTIVES

This study aims to identify metabolites that could be used as biomarkers for SS.

METHODS

Using the software called XCMS online, the salivary metabolic profiles obtained with liquid chromatography coupled to high-resolution mass spectrometry for 18 female SS patients were compared to those obtained for 22 age-matched female healthy controls.

RESULTS AND CONCLUSION

A total of 91 metabolites showed differential expression in SS patients. A putative identification was proposed with the use of a database for 37 of these metabolites and, of these, 16 identifications were confirmed. Given the identified metabolites, some important metabolic pathways, such as amino acid metabolism, purine metabolism, or even the citric acid cycle seem to be affected. Through the analyses of the ROC (receiver operating characteristic) curves, three metabolites, namely alanine, isovaleric acid, and succinic acid, showed both good sensitivity (respectively 1.000, 1.000, and 0.750) and specificity (respectively 0.692, 0.615, and 0.692) for identifying SS and could then be interesting biomarkers for a potential salivary diagnosis test.

A haplotype in the dipeptidyl peptidase 4 gene impacts glycemic-related traits of Brazilian older adults

Dipeptidyl peptidase 4 (DPP4) regulates various physiological pathways and has a pivotal role in glucose homeostasis. The objective of this study was to verify the association of a haplotype constituted by two single nucleotide polymorphisms (rs2268894 and rs6741949) in the DPP4 gene with type 2 diabetes mellitus (T2DM) and fasting glycemia-related variables in a sample of Brazilian older adults, taking serum levels and enzymatic activity of DPP4 into account. Clinical, biochemical, and anthropometric characteristics as well as DPP4 serum levels and enzymatic activity were determined in 800 elderly (≥60 years old) individuals. Assessment of polymorphic sites was performed by real-time PCR whereas haplotypes were inferred from genotypic frequencies. Statistical analyses compared measures and proportions according to T2DM diagnosis and DPP4 haplotypic groups. The most common haplotype consisted of the T-rs2268894/G-rs6741949 string, which was 20% more frequent among non-diabetics. Considering non-diabetic patients alone, carriers of the T/G haplotype had significantly lower levels of blood glucose, insulin, HOMA-IR index, and DPP4 activity. Among diabetic patients, the T/G haplotype was associated with lower DPP4 levels whereas glycemic scores were not affected by allelic variants. Our results suggested that the genetic architecture of DPP4 affects the glycemic profile and DPP4 serum levels and activity among elderly individuals according to the presence or absence of T2DM, with a possible implication of the T/G haplotype to the risk of T2DM onset.

Emerging Role of Dipeptidyl Peptidase-4 in Autoimmune Disease

Dipeptidyl-peptidase IV (DPP4), originally identified as an aminopeptidase in 1960s, is an ubiquitously expressed protease presented as either a membrane-bound or soluble form. DPP4 cleaves dipeptide off from the N-terminal of its substrates, altering the bioactivity of its substrates. Subsequent studies reveal that DPP4 is also involved in various cellular processes by directly binding to a number of ligands, including adenosine deaminase, CD45, fibronectin, plasminogen, and caveolin-1. In recent years, many novel functions of DPP4, such as promoting fibrosis and mediating virus entry, have been discovered. Due to its implication in fibrotic response and immunoregulation, increasing studies are focusing on the potential role of DPP4 in inflammatory disorders. As a moonlighting protein, DPP4 possesses multiple functions in different types of cells, including both enzymatic and non-enzymatic functions. However, most of the review articles on the role of DPP4 in autoimmune disease were focused on the association between DPP4 enzymatic inhibitors and the risk of autoimmune disease. An updated comprehensive summary of DPP4’s immunoregulatory actions including both enzymatic dependent and independent functions is needed. In this article, we will review the recent advances of DPP4 in immune regulation and autoimmune rheumatic disease.

Cellular expression of CD26/dipeptidyl peptidase IV

Dipeptidyl peptidase 4 (DPP4), a serine protease expressed on luminal and apical cell membrane, is identical to the lymphocyte cell surface protein CD26. DPP4 rapidly deactivates hormones and cytokines by cleaving their NH₂-terminal dipeptides. Its functions are based on membrane digestion and/or binding of bioactive peptides, signal molecules, and extracellular matrix components. The soluble form is also present in body fluids such as serum, urine, semen, and synovial fluid. The extremely broad distribution of CD26/DPP4 indicates its divergent roles depending on cell type and activated conditions. The cellular localization was earlier examined by enzyme histochemistry and subsequently by immunohistochemistry. Although immunohistochemical analyses are higher in specificity and easier to use at electron microscopic levels than enzyme histochemistry, the immunoreaction is considerably affected by the animal species, types of tissue sections, and specificity of antibodies. Understanding of the functional significance and advancement of its clinical use (diagnosis and treatment of diseases) require precise information on the cellular distribution including subcellular localization and pathological changes. This short review summarizes in particular immunohistochemical findings on CD26/DPP4.

Proteomics Analysis of Tears and Saliva From Sjogren's Syndrome Patients

Sjogren's syndrome (SS) is characterized by dysfunctional mucous membranes and dysregulated moisture-secreting glands resulting in various symptoms, including dry mouth and dry eyes. Here, we wanted to profile and compare the tear and saliva proteomes of SS patients to healthy controls. Tear and saliva samples were collected and subjected to an isotopic dimethylation labeling shotgun proteomics workflow to identify alterations in protein levels. In tear samples, we identified 83 upregulated and 112 downregulated proteins. Pathway enrichment analysis of the changing proteins by Metascape identified leukocyte transendothelial migration, neutrophil degranulation, and post-translation protein phosphorylation in tears of SS patients. In healthy controls' tears, an enrichment for proteins related to glycolysis, amino acid metabolism and apoptotic signaling pathway were identified. In saliva, we identified 108 upregulated and 45 downregulated proteins. Altered pathways in SS patients' saliva included cornification, sensory perception to taste and neutrophil degranulation. In healthy controls' saliva, an enrichment for proteins related to JAK-STAT signaling after interleukin-12 stimulation, phagocytosis and glycolysis in senescence were identified. Dysregulated protease activity is implicated in the initiation of inflammation and immune cell recruitment in SS. We identified 20 proteases and protease inhibitors in tears and 18 in saliva which are differentially expressed between SS patients and healthy controls. Next, we quantified endogenous proteoglycan 4 (PRG4), a mucin-like glycoprotein, in tear wash and saliva samples via a bead-based immune assay. We identified decreased levels of PRG4 in SS patients' tear wash compared to normal samples. Conversely, in saliva, we found elevated levels of PRG4 concentration and visualized PRG4 expression in human parotid gland via immunohistological staining. These findings will improve our mechanistic understanding of the disease and changes in SS patients' protein expression will help identify new potential drug targets. PRG4 is among the promising targets, which we identified here, in saliva, for the first time.