Immune-Intrinsic Myd88 Directs the Production of Antibodies With Specificity for Extracellular Matrix Components in Primary Sjögren's Syndrome

Primary Sjögren's syndrome: new perspectives on salivary gland epithelial cells

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease primarily affecting exocrine glands such as the salivary glands, leading to impaired secretion and sicca symptoms. As the mainstay of salivation, salivary gland epithelial cells (SGECs) have an important role in the pathology of pSS. Emerging evidence suggests that the interplay between immunological factors and SGECs may not be the initial trigger or the sole mechanism responsible for xerostomia in pSS, challenging conventional perceptions. To deepen our understanding, current research regarding SGECs in pSS was reviewed. Among the extensive aberrations in cellular architecture and function, this review highlighted certain alterations of SGECs that were identified to occur independently of or in absence of lymphocytic infiltration. In particular, some of these alterations may serve as upstream factors of immuno-inflammatory responses. These findings underscore the significance of introspecting the pathogenesis of pSS and developing interventions targeting SGECs in the early stages of the disease.

TLR7 activation of age-associated B cells mediates disease in a mouse model of primary Sjögren's disease

Primary Sjögren's disease (pSD) (also referred to as Sjögren's syndrome) is an autoimmune disease that primarily occurs in women. In addition to exocrine gland dysfunction, pSD patients exhibit B cell hyperactivity. B cell-intrinsic TLR7 activation is integral to the pathogenesis of systemic lupus erythematosus, a disease that shares similarities with pSD. The role of TLR7-mediated B cell activation in pSD, however, remains poorly understood. We hypothesized that age-associated B cells (ABCs) were expanded in pSD and that TLR7-stimulated ABCs exhibited pathogenic features characteristic of disease. Our data revealed that ABC expansion and TLR7 expression were enhanced in a pSD mouse model in a Myd88-dependent manner. Splenocytes from pSD mice showed enhanced sensitivity to TLR7 agonism as compared with those derived from control animals. Sort-purified marginal zone B cells and ABCs from pSD mice showed enhanced inflammatory cytokine secretion and were enriched for antinuclear autoantibodies following TLR7 agonism. Finally, IgG from pSD patient sera showed elevated antinuclear autoantibodies, many of which were secreted preferentially by TLR7-stimulated murine marginal zone B cells and ABCs. These data indicate that pSD B cells are hyperresponsive to TLR7 agonism and that TLR7-activated B cells contribute to pSD through cytokine and autoantibody production. Thus, therapeutics that target TLR7 signaling cascades in B cells may have utility in pSD patients.

Bioinformatics Analysis and Experimental Validation of Differential Genes and Pathways in Bone Nonunions

Non-union fractures pose a significant clinical challenge, often leading to prolonged pain and disability. Understanding the molecular mechanisms underlying non-union fractures is crucial for developing effective therapeutic interventions. This study integrates bioinformatics analysis and experimental validation to unravel key genes and pathways associated with non-union fractures. We identified differentially expressed genes (DEGs) between non-union and fracture healing tissues using bioinformatics techniques. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were employed to elucidate the biological processes and pathways involved. Common DEGs were identified, and a protein-protein interaction (PPI) network was constructed. Fibronectin-1 (FN1), Thrombospondin-1 (THBS1), and Biglycan (BGN) were pinpointed as critical target genes for non-union fracture treatment. Experimental validation involved alkaline phosphatase (ALP) and Alizarin Red staining to confirm osteogenic differentiation. Our analysis revealed significant alterations in pathways related to cell behavior, tissue regeneration, wound healing, infection, and immune responses in non-union fracture tissues. FN1, THBS1, and BGN were identified as key genes, with their upregulation indicating potential disruptions in the bone remodeling process. Experimental validation confirmed the induction of osteogenic differentiation. The study provides comprehensive insights into the molecular mechanisms of non-union fractures, emphasizing the pivotal roles of FN1, THBS1, and BGN in extracellular matrix dynamics and bone regeneration. The findings highlight potential therapeutic targets and pathways for further investigation. Future research should explore interactions between these genes, validate results using in vivo fracture models, and develop tailored treatment strategies for non-union fractures, promising significant advances in clinical management.

Integrative analysis of transcriptome and proteome in primary Sjögren syndrome

OBJECTIVE

Primary Sjögren's syndrome (pSS) is a intricate autoimmune disease mainly characterized of immune-mediated destruction of exocrine tissues, such as salivary and lacrimal glands, occurring dry mouth and eyes. Although some breakthroughs in understanding pSS have been uncovered, many questions remain about its pathogenesis, especially the internal relations between exocrine glands and secretions.

METHOD

Transcriptomic and proteomic analyses were conducted on salivary tissues and saliva in experimental Sjögren syndrome (ESS). The ESS model was established by immunization with salivary gland protein. The expression of mRNAs and proteins in salivary tissues and saliva were determined by high-throughput sequencing transcriptomic analysis and LC-MS/MS-based proteome, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were used to recognize dysregulated genes and proteins. The association between RNA and protein abundance was investigated to provides a comprehensive understanding of RNA-protein correlations in the pathogenesis of pSS.

RESULTS

As a result, we successfully established the ESS model. We recognized 3221 differentially expressed genes (DEGs) and 253 differentially expressed proteins (DEPs). The sample analysis showed that 61 proteins overlapped through the integrative analysis of transcriptomics and proteomics data. The enrichment pathway analysis of DEGs and DEPs in samples showed alterations in renin-angiotensin-system (RAS), lysosome, and apoptosis. Notably, we found that some genes, such as AGT, FN1, Klk1b26, Klk1, Klk1b5, Klk1b3 had a consistent trend in the regulation at the RNA and protein levels and might be potential diagnostic biomarkers of pSS.

CONCLUSION

Herein, we found critical processes and potential biomakers that may contribute to pSS pathogenesis by analyzing dysregulated genes and pathways. Additionally, the integrative multi-omics datasets provided additional insight into understanding complicated disease mechanisms.

Extracellular matrix turnover in salivary gland disorders and regenerative therapies: Obstacles and opportunities

Salivary gland (SG) extracellular matrix (ECM) has a major influence on tissue development, homeostasis, and tissue regeneration after injury. During aging, disease, and physical insult, normal remodeling of the SG microenvironment (i.e. ECM) becomes dysregulated, leading to alterations in matrix composition which disrupt tissue architecture/structure, alter cell activity, and negatively impact gland function. Matrix metalloproteinases (MMPs) are a large and diverse family of metalloendopeptidases which play a major role in matrix degradation and are intimately involved in regulating development and cell function; dysregulation of these enzymes leads to the production of a fibrotic matrix. In the SG this altered fibrotic ECM (or cell microenvironment) negatively impacts normal cell function and the effectiveness of gene and stem cell therapies which serve as a foundation for many SG regenerative therapies. For this reason, prospective regenerative strategies should prioritize the maintenance and/or restoration of a healthy SG ECM. Mesenchymal stem cells (MSCs) have great potential for mitigating damage to the SG microenvironment by ameliorating inflammation, reducing fibrosis, and repairing the damaged milieu of extracellular regulatory cues, including the matrix. This review addresses our current understanding of the impact of aging and disease on the SG microenvironment and suggests critical deficiencies and opportunities in ECM-targeted therapeutic interventions.

The role of neutrophil extracellular traps and proinflammatory damage-associated molecular patterns in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a group of systemic autoimmune diseases characterized by immune-mediated muscle injury. Abnormal neutrophil extracellular traps (NETs) can be used as a biomarker of IIM disease activity, but the mechanism of NET involvement in IIMs needs to be elucidated. Important components of NETs, including high-mobility group box 1, DNA, histones, extracellular matrix, serum amyloid A, and S100A8/A9, act as damage-associated molecular patterns (DAMPs) to promote inflammation in IIMs. NETs can act on different cells to release large amounts of cytokines and activate the inflammasome, which can subsequently aggravate the inflammatory response. Based on the idea that NETs may be proinflammatory DAMPs of IIMs, we describe the role of NETs, DAMPs, and their interaction in the pathogenesis of IIMs and discuss the possible targeted treatment strategies in IIMs.

Autologous mesenchymal stem cells offer a new paradigm for salivary gland regeneration

Salivary gland (SG) dysfunction, due to radiotherapy, disease, or aging, is a clinical manifestation that has the potential to cause severe oral and/or systemic diseases and compromise quality of life. Currently, the standard-of-care for this condition remains palliative. A variety of approaches have been employed to restore saliva production, but they have largely failed due to damage to both secretory cells and the extracellular matrix (niche). Transplantation of allogeneic cells from healthy donors has been suggested as a potential solution, but no definitive population of SG stem cells, capable of regenerating the gland, has been identified. Alternatively, mesenchymal stem cells (MSCs) are abundant, well characterized, and during SG development/homeostasis engage in signaling crosstalk with the SG epithelium. Further, the trans-differentiation potential of these cells and their ability to regenerate SG tissues have been demonstrated. However, recent findings suggest that the "immuno-privileged" status of allogeneic adult MSCs may not reflect their status post-transplantation. In contrast, autologous MSCs can be recovered from healthy tissues and do not present a challenge to the recipient's immune system. With recent advances in our ability to expand MSCs in vitro on tissue-specific matrices, autologous MSCs may offer a new therapeutic paradigm for restoration of SG function.

Nucleic acid-sensing toll-like receptors: Important players in Sjögren’s syndrome

Sjögren’s syndrome (SS) is a chronic systemic autoimmune disease that affects the salivary and lacrimal glands, as well as other organ systems like the lungs, kidneys and nervous system. SS can occur alone or in combination with another autoimmune disease, such as systemic lupus erythematosus (SLE) or rheumatoid arthritis. The etiology of SS is unknown but recent studies have revealed the implication of the activation of innate immune receptors, including Toll-like receptors (TLRs), mainly through the detection of endogenous nucleic acids, in the pathogenesis of systemic autoimmune diseases. Studies on SS mouse models suggest that TLRs and especially TLR7 that detects single-stranded RNA of microbial or endogenous origin can drive the development of SS and findings in SS patients corroborate those in mouse models. In this review, we will give an overview of the function and signaling of nucleic acid-sensing TLRs, the interplay of TLR7 with TLR8 and TLR9 in the context of autoimmunity, summarize the evidence for the critical role of TLR7 in the pathogenesis of SS and present a possible connection between SARS-CoV-2 and SS.

The Role of Decorin in Autoimmune and Inflammatory Diseases

Decorin is an extracellular matrix protein that belongs to the family of small leucine-rich proteoglycans. As a matrix protein, the first discovered role of decorin is participating in collagen fibril formation. Many other functions of decorin in various biological processes have been subsequently identified. Decorin is involved in an extensive signaling network and can interact with other extracellular matrix components, growth factors, receptor tyrosine kinases, and various proteases. Decorin has been shown to be involved in wound repair, cell cycle, angiogenesis, tumor metastasis, and autophagy. Recent evidence indicates that it also plays a role in immune regulation and inflammatory diseases. This review summarizes the characteristics of decorin in immune and inflammatory diseases, including inflammatory bowel disease (IBD), Sjögren's syndrome (SS), chronic obstructive pulmonary disease (COPD), IgA nephropathy, rheumatoid arthritis (RA), spondyloarthritis (SpA), osteoarthritis, multiple sclerosis (MS), idiopathic inflammatory myopathies (IIM), and systemic sclerosis (SSc) and discusses the potential role in these disorders.

The Aberrant Levels of Decorin Induce Damages of Human Salivary Gland Epithelial Cells and Polarization of Macrophages

OBJECTIVE

This study aimed to preliminarily address the levels of decorin (DCN, a critical component of extracellular matrix), and its potential roles in primary sjögren's syndrome (pSS).

METHODS

DCN levels were determined in the salivary glands of experimental SS (ESS) mice and pSS patients by RNA sequencing, bioinformatics analysis, or immunohistochemical (IHC) staining. Its correlation with interested genes and co-localization with a putative receptor was studied in pSS patients. In addition, its potential roles on salivary gland epithelium and macrophages were tested by exogenous administration to corresponding cell lines, followed by the evaluation of apoptosis using flow cytometry or cytokines expression using quantitative real time PCR.

RESULTS

Our data revealed a significant elevation of DCN in the salivary glands of experimental SS (ESS) mice model and pSS patients. In addition, the bioinformatics analysis of DCN in GSE40611 (RNA-seq, parotid glands) dataset displayed an elevation of DCN level in the parotid glands of pSS patients that positively correlated with several chemokines (CXCL13, CXCL9, CCL20), IL-1ß, and caspase3 but negatively correlated with the proliferation relative gene MKI67. The stimulatory effects of DCN on the salivary gland epithelial cells (A253 cell line) and macrophages have been determined as they are considered active participants in the progression of SS. The data showed that DCN induced apoptosis of A253 cells and polarization of macrophages toward the M1 phenotype, characterized by the expression of pro-inflammatory cytokines.

CONCLUSION

Our study provided preliminary evidence to understand the clinical significance of DCN in pSS and broadened our horizons in understanding the mechanism of pSS.