Maladaptive autophagy in the pathogenesis of autoimmune epithelitis in Sjӧgren'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.

Downregulated GPX4 in salivary gland epithelial cells contributes to salivary secretion dysfunction in Sjogren's syndrome via lipid ROS/pSTAT4/AQP5 axis

Sjogren's syndrome (SS) is an autoimmune disease characterized by dysfunction of exocrine glands, such as salivary glands. However, the molecular mechanism of salivary secretion dysfunction in SS is still unclear. Given the significance of glutathione peroxidase 4 (GPX4) in cellular redox homeostasis, we hypothesized that dysregulation of GPX4 may play a pivotal role in the pathogenesis of salivary secretion dysfunction observed in SS. The salivary gland of SS patients and the SS mouse model exhibited reduced expression of the ferroptosis inhibitor GPX4 and the important protein aquaporin 5 (AQP5), which is involved in salivary secretion. GPX4 overexpression upregulated and GPX4 knockdown downregulated AQP5 expression in salivary gland epithelial cells (SGECs) and salivary secretion. Bioinformatics analysis of GSE databases from SS patients' salivary glands revealed STAT4 as a key intermediary regulator between GPX4 and AQP5. A higher level of nuclear pSTAT4 was observed in the salivary gland of the SS mouse model. GPX4 overexpression inhibited and GPX4 knockdown promoted STAT4 phosphorylation and nuclear translocation in SGECs. CHIP assay confirmed the binding of pSTAT4 within the promoter of AQP5 inhibiting AQP5 transcription. GPX4 downregulation accumulates intracellular lipid ROS in SGECs. Lipid ROS inhibitor ferrostatin-1 treatment during in vitro and in vivo studies confirmed that lipid ROS activates STAT4 phosphorylation and nuclear translocation in SGECs. In summary, the downregulated GPX4 in SGECs contributes to salivary secretion dysfunction in SS via the lipid ROS/pSTAT4/AQP5 axis. This study unraveled novel targets to revitalize the salivary secretion function in SS patients.

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

Rapamycin can alleviate the submandibular gland pathology of Sjögren's syndrome by limiting the activation of cGAS-STING signaling pathway

BACKGROUND

Sjögren's Syndrome (SS) is also known as autoimmune exocrine gland disease. Previous studies have confirmed that adaptive immunity plays an important role in the development of this disease. But less is known about the role of the innate immune system.

METHODS

To identify the core pathways, and local infiltrated immune cells in the local immune microenvironment of SS. We verified the activation of these core genes and core signaling pathways in SS model mice by in vivo experiment and transcriptome sequencing.

RESULTS

Finally, we identified 6 core genes EPSTI1, IFI44L, MX1, CXCL10, IFIT3, and IFI44. All the 6 genes had good diagnostic value. Based on multi-omics sequencing results and experimental studies, we found that cGAS-STING signaling pathway is most relevant to the pathogenesis of SS. By in vivo experiments, we verified that autophagy is the key brake to limit the activation of cGAS-STING signaling pathway.

CONCLUSIONS

Maladaptive activation of autophagy and cGAS-STING signaling pathway are central contributors to the SG pathogenesis of pSS patient. Regulating autophagy by rapamycin may be a possible treatment for Sjögren's syndrome in the future.

Modes and Mechanisms of Salivary Gland Epithelial Cell Death in Sjogren's Syndrome

Sjogren's syndrome is an autoimmune disease in middle and old-aged women with a dry mucosal surface, which is caused by the dysfunction of secretory glands, such as the oral cavity, eyeballs, and pharynx. Pathologically, Sjogren's syndrome are characterized by lymphocyte infiltration into the exocrine glands and epithelial cell destruction caused by autoantibodies Ro/SSA and La/SSB. At present, the exact pathogenesis of Sjogren's syndrome is unclear. Evidence suggests epithelial cell death and the subsequent dysfunction of salivary glands as the main causes of xerostomia. This review summarizes the modes of salivary gland epithelial cell death and their role in Sjogren's syndrome progression. The molecular mechanisms involved in salivary gland epithelial cell death during Sjogren's syndrome as potential leads to treating the disease are also discussed.

LncRNA-mediated cell autophagy: An emerging field in bone destruction in rheumatoid arthritis

In recent years, research on the mechanism of bone destruction in rheumatoid arthritis (RA) has remained in the initial stages, and the mechanism has not been fully elucidated to date. Recent studies have shown that long noncoding RNAs (lncRNAs) participate in RA bone destruction via autophagy, but the specific regulatory mechanism of lncRNA-mediated autophagy is unclear. Therefore, in this article, we review the mechanisms of lncRNA-mediated autophagy in fibroblast-like synoviocytes and chondrocytes in RA bone destruction. We explain that lncRNAs mediate autophagy and participate in many specific pathological processes of RA bone destruction by regulating signalling pathways and the expression of target genes. Specific lncRNAs can be used as markers for molecular diagnosis, mechanistic regulation, treatment and prognosis of RA.

The role of inflammation in autoimmune disease: a therapeutic target

Autoimmune diseases (AIDs) are immune disorders whose incidence and prevalence are increasing year by year. AIDs are produced by the immune system's misidentification of self-antigens, seemingly caused by excessive immune function, but in fact they are the result of reduced accuracy due to the decline in immune system function, which cannot clearly identify foreign invaders and self-antigens, thus issuing false attacks, and eventually leading to disease. The occurrence of AIDs is often accompanied by the emergence of inflammation, and inflammatory mediators (inflammatory factors, inflammasomes) play an important role in the pathogenesis of AIDs, which mediate the immune process by affecting innate cells (such as macrophages) and adaptive cells (such as T and B cells), and ultimately promote the occurrence of autoimmune responses, so targeting inflammatory mediators/pathways is one of emerging the treatment strategies of AIDs. This review will briefly describe the role of inflammation in the pathogenesis of different AIDs, and give a rough introduction to inhibitors targeting inflammatory factors, hoping to have reference significance for subsequent treatment options for AIDs.

Lysosome-Associated Membrane Protein 3 Induces Lysosome-Dependent Cell Death by Impairing Autophagic Caspase 8 Degradation in the Salivary Glands of Individuals With Sjögren's Disease

OBJECTIVE

Lysosome-associated membrane protein 3 (LAMP3) overexpression is implicated in the development and progression of Sjögren's disease (SjD) by inducing lysosomal membrane permeabilization (LMP) and apoptotic cell death in salivary gland epithelium. The aim of this study was to clarify the molecular details of LAMP3-induced lysosome-dependent cell death and to test lysosomal biogenesis as a therapeutic intervention.

METHODS

Human labial minor salivary gland biopsies were analyzed using immunofluorescence staining for LAMP3 expression levels and galectin-3 puncta formation, a marker of LMP. Expression level of caspase 8, an initiator of LMP, was determined by Western blotting in cell culture. Galectin-3 puncta formation and apoptosis were evaluated in cell cultures and a mouse model treated with glucagon-like peptide 1 receptor (GLP-1R) agonists, a known promoter of lysosomal biogenesis.

RESULTS

Galectin-3 puncta formation was more frequent in the salivary glands of SjD patients compared to control glands. The proportion of galectin-3 puncta-positive cells was positively correlated with LAMP3 expression levels in the glands. LAMP3 overexpression increased caspase 8 expression, and knockdown of caspase 8 decreased galectin-3 puncta formation and apoptosis in LAMP3-overexpressing cells. Inhibition of autophagy increased caspase 8 expression, while restoration of lysosomal function using GLP-1R agonists decreased caspase 8 expression, which reduced galectin-3 puncta formation and apoptosis in both LAMP3-overexpressing cells and mice.

CONCLUSION

LAMP3 overexpression induced lysosomal dysfunction, resulting in lysosome-dependent cell death via impaired autophagic caspase 8 degradation, and restoring lysosomal function using GLP-1R agonists could prevent this. These findings suggested that LAMP3-induced lysosomal dysfunction is central to disease development and is a target for therapeutic intervention in SjD.

Interferon-γ induces salivary gland epithelial cell ferroptosis in Sjogren's syndrome via JAK/STAT1-mediated inhibition of system Xc. Free Radic Biol Med 2023;205:116-128. [PMID: 37286044 DOI: 10.1016/j.freeradbiomed.2023.05.027]

The elevated level of interferon-γ (IFN-γ) in Sjogren's syndrome (SS) triggers salivary gland epithelial cells (SGEC) death. However, the underlying mechanisms of IFN-γ-induced SGEC death modes are still not fully elucidated. We found that IFN-γ triggers SGEC ferroptosis via Janus kinase/signal transducer and activator of transcription 1 (JAK/STAT1)-mediated inhibition of cystine-glutamate exchanger (System Xc-). Transcriptome analysis revealed that ferroptosis-related markers are differentially expressed in SS human and mouse salivary glands with distinct upregulation of IFN-γ and downregulation of glutathione peroxidase 4 (GPX4) and aquaporin 5 (AQP5). Inducing ferroptosis or IFN-γ treatment in the Institute of cancer research (ICR) mice aggravated and inhibition of ferroptosis or IFN-γ signaling in SS model non-obese diabetic (NOD) mice alleviated ferroptosis in the salivary gland and SS symptoms. IFN-γ activated STAT1 phosphorylation and downregulated system Xc- components solute carrier family 3 member 2 (SLC3A2), glutathione, and GPX4 thereby triggering ferroptosis in SGEC. JAK or STAT1 inhibition in SGEC rescued IFN-γ-downregulated SLC3A2 and GPX4 as well as IFN-γ-induced cell death. Our results indicate the role of ferroptosis in SS-related death of SGEC and SS pathogenicity.

JAK/STAT Pathway Targeting in Primary Sjögren Syndrome

Primary Sjögren's syndrome (pSS) is an autoimmune systemic disease mainly affecting exocrine glands and resulting in disabling symptoms, as dry eye and dry mouth. Mechanisms underlying pSS pathogenesis are intricate, involving multiplanar and, at the same time, interlinked levels, e.g., genetic predisposition, epigenetic modifications and the dysregulation of both immune system and glandular-resident cellular pathways, mainly salivary gland epithelial cells. Unravelling the biological and molecular complexity of pSS is still a great challenge but much progress has been made in recent years in basic and translational research field, allowing the identification of potential novel targets for therapy development. Despite such promising novelties, however, none therapy has been specifically approved for pSS treatment until now. In recent years, growing evidence has supported the modulation of Janus kinases (JAK) - signal transducers and activators of transcription (STAT) pathways as treatment strategy immune mediated diseases. JAK-STAT pathway plays a crucial role in autoimmunity and systemic inflammation, being involved in signal pathways of many cytokines. This review aims to report the state-of-the-art about the role of JAK-STAT pathway in pSS, with particular focus on available research and clinical data regarding the use of JAK inhibitors in pSS.

Alterations of m6A RNA methylation regulators contribute to autophagy and immune infiltration in primary Sjögren's syndrome

N6-methyladenosine (m6A) RNA modification is a new epigenetic regulation mechanism on eukaryotic mRNA. Few autoimmune diseases focused on the role of m6A in their pathogenies, and m6A modulation in the pathological process of primary Sjögren's syndrome (pSS) is still unknown. In this work, three microarray datasets of pSS patients were downloaded from the GEO database: datasets #1 and #2 from the whole peripheral blood (PB) samples, dataset #3 from the labial salivary gland tissue samples, as well as a PB cohort collected from our hospital. Six differentially expressed m6A regulators were identified by comparing the PB dataset #1 of pSS and healthy controls using the Wilcox test and logistic regression analysis. Among them, four (ALKBH5, RBMX, RBM15B, and YTHDF1) were confirmed as down-regulated in PB dataset #2 and in our PB cohort by RT-PCR, and four (ALKBH5, METTL3, RBM15B, and YTHDF1) were confirmed as down-regulated in the dataset #3 of the labial gland tissue. In addition, discrepantly expressed m6A regulators accompanied by diverse immunocytes, including dendritic cells (DCs), T cells, and CD56dim natural killer cells, and among the regulators, ALKBH5 and METTL3 were comprehensively linked with the infiltrated immune cells. Notably, the most enriched autophagy mechanism mediated by m6A was observed in pSS using functional annotation analysis. Ten hub genes were identified using a protein-protein interaction network, and their expression in PB dataset #2 and the expression of three genes (PIK3CA, STAT1, and MAPK3) in the labial gland tissue dataset #3 were confirmed. Our study provides evidence that m6A methylation is widely involved in the immune infiltration and autophagy of pSS, thus contributing to the pathogenesis of this disease and potentially representing a novel therapeutic target.

The mosaic of autoimmunity - Finally discussing in person. The 13th international congress on autoimmunity 2022 (AUTO13) Athens

While autoimmunity is a branch of medicine linked to every single organ system via direct and indirect pathways, meeting in person to discuss autoimmunity during the 13^th international congress on autoimmunity (AUTO13) with participants from all over the world had a very good reason. The mechanisms involved in autoimmune diseases are of extreme importance and in fact critical in understanding the course of diseases as well as selecting proper therapies. COVID-19 has served as a great example of how autoimmunity is deeply involved in the disease and directly correlated to severity, morbidity, and mortality. For instance, initially the term cytokine storm dominated, then COVID-19 was addressed as the new member of the hyperferritinemic syndrome, and also the use of immunosuppressants in patients with COVID-19 throughout the pandemic, all shed light on the fundamental role of autoimmunity. Unsurprisingly, SARS-CoV-2 was called the “autoimmune virus” during AUTO13. Subsequently, the correlation between autoimmunity and COVID-19 vaccines and post-COVID, all were discussed from different autoimmune aspects during the congress. In addition, updates on the mechanisms of diseases, autoantibodies, novel diagnostics and therapies in regard to autoimmune diseases such as antiphospholipid syndrome, systemic lupus erythematosus, systemic sclerosis and others, were discussed in dedicated sessions. Due to the magnificence of the topics discussed, we aimed to bring in our article hereby, the pearls of AUTO13 in terms of updates, new aspects of autoimmunity, and interesting findings. While more than 500 abstract were presented, concluding all the topics was not in reach, hence major findings were summarized.

Impaired GATE16-mediated exocytosis in exocrine tissues causes Sjögren's syndrome-like exocrinopathy

Sjögren's syndrome (SjS) is a chronic autoimmune disease characterized by immune cell infiltration of the exocrine glands, mainly the salivary and lacrimal glands. Despite recent advances in the clinical and mechanistic characterization of the disease, its etiology remains largely unknown. Here, we report that mice with a deficiency for either Atg7 or Atg3, which are enzymes involved in the ubiquitin modification pathway, in the salivary glands exhibit a SjS-like phenotype, characterized by immune cell infiltration with autoantibody detection, acinar cell death, and dry mouth. Prior to the onset of the SjS-like phenotype in these null mice, we detected an accumulation of secretory vesicles in the acinar cells of the salivary glands and found that GATE16, an uncharacterized autophagy-related molecule activated by ATG7 (E1-like enzyme) and ATG3 (E2-like enzyme), was highly expressed in these cells. Notably, GATE16 was activated by isoproterenol, an exocytosis inducer, and localized on the secretory vesicles in the acinar cells of the salivary glands. Failure to activate GATE16 was correlated with exocytosis defects in the acinar cells of the salivary glands in Atg7 and Atg3 cKO mice. Taken together, our results show that GATE16 activation regulated by the autophagic machinery is crucial for exocytosis and that defects in this pathway cause SjS.

Autophagy in Rheumatic Diseases: Role in the Pathogenesis and Therapeutic Approaches

Autophagy is a lysosomal pathway for the degradation of damaged proteins and intracellular components that promotes cell survival under specific conditions. Apoptosis is, in contrast, a critical programmed cell death mechanism, and the relationship between these two processes influences cell fate. Recent evidence suggests that autophagy and apoptosis are involved in the self-tolerance promotion and in the regulatory mechanisms contributing to disease susceptibility and immune regulation in rheumatic diseases. The aim of this review is to discuss how the balance between autophagy and apoptosis may be dysregulated in multiple rheumatic diseases and to dissect the role of autophagy in the pathogenesis of rheumatoid arthritis, systemic lupus erythematosus, and Sjögren’s syndrome. Furthermore, to discuss the potential capacity of currently used disease-modifying antirheumatic drugs (DMARDs) to target and modulate autophagic processes.