Activation of Myd88-Dependent TLRs Mediates Local and Systemic Inflammation in a Mouse Model of Primary Sjögren's Syndrome

Abstract

Toll-like receptors (TLRs) are important mediators of chronic inflammation in numerous autoimmune diseases, although the role of these receptors in primary Sjögren's syndrome (pSS) remains incompletely understood. Previous studies in our laboratory established Myd88 as a crucial mediator of pSS, although the disease-relevant ligands and the upstream signaling events that culminate in Myd88 activation have yet to be established. The objective of this study was to identify specific Myd88-dependent TLR-related pathways that are dysregulated both locally and systemically in a mouse model of pSS [NOD.B10Sn-H2 b /J (NOD.B10)]. We performed RNA-sequencing on spleens derived from NOD.B10 mice. We then harvested salivary tissue and spleens from Myd88-sufficient and deficient C57BL/10 (BL/10) and NOD.B10 mice and performed flow cytometry to determine expression of Myd88-dependent TLRs. We cultured splenocytes with TLR2 and TLR4 agonists and measured production of inflammatory mediators by ELISA. Next, we evaluated spontaneous and TLR4-mediated inflammatory cytokine secretion in NOD.B10 salivary tissue. Finally, we assessed spontaneous Myd88-dependent cytokine secretion by NOD.B10 salivary cells. We identified dysregulation of numerous TLR-related networks in pSS splenocytes, particularly those employed by TLR2 and TLR4. We found upregulation of TLRs in both the splenic and salivary tissue from pSS mice. In NOD.B10 splenic tissue, robust expression of B cell TLR1 and TLR2 required Myd88. Splenocytes from NOD.B10 mice were hyper-responsive to TLR2 ligation and the endogenous molecule decorin modulated inflammation via TLR4. Finally, we observed spontaneous secretion of numerous inflammatory cytokines and this was enhanced following TLR4 ligation in female NOD.B10 salivary tissue as compared to males. The spontaneous production of salivary IL-6, MCP-1 and TNFα required Myd88 in pSS salivary tissue. Thus, our data demonstrate that Myd88-dependent TLR pathways contribute to the inflammatory landscape in pSS, and inhibition of such will likely have therapeutic utility.

Frutescone O from Baeckea frutescens Blocked TLR4-Mediated Myd88/NF-κB and MAPK Signaling Pathways in LPS Induced RAW264.7 Macrophages

“…After LPS stimulation, the expression of TLR4-related signaling proteins was upregulated in macrophages ( Xia et al, 2012 ; Li et al, 2017 ; Muralidharan et al, 2018 ). Myd88-dependent TLRs are important mediators of chronic inflammation in local and systemic inflammation diseases ( Kiripolsky et al, 2019 ). The adaptor protein Myd88 played a significant role in activating the NF-κB signaling pathway and MAPKs signaling pathway ( Aderem and Ulevitch, 2000 ; Kagan and Medzhitov, 2006 ).…”

Long Term Delta-9-tetrahydrocannabinol Administration Inhibits Proinflammatory Responses in Minor Salivary Glands of Chronically Simian Immunodeficieny Virus Infected Rhesus Macaques

“…Table S1 lists the Top 50 differentially upregulated genes in OPM of VEH-untreated SIV rhesus macaques. Notable genes that were significantly upregulated exclusively in OPM of VEH-untreated/SIV rhesus macaques ( Figure 1 A) included IL1RN (inhibits activity of interleukin-1) [ 40 ], PELI3 (interacts with complex containing IRAK kinases and TRAF6 of IL1 and TLR signaling pathways) [ 41 ], BST2 (Interferon induced anti-viral protein) [ 42 ], alarmins ( IL1A , IL36A and S100A9 ) [ 43 , 44 ], IRF1 (innate and adaptive immune response) [ 45 ], DEFB103A (antimicrobial peptide), CD207 (major receptor on langerhans cells for Candida species) [ 46 ], STAT2 (type 1 interferon signaling) [ 45 ] and MYD88 (adapter protein in Toll-like receptor signaling) [ 47 ].…”

Communications via the Small Leucine-rich Proteoglycans: Molecular Specificity in Inflammation and Autoimmune Diseases

“…In contrast to pSS where decorin acts as an inducer of the disease phenotype, 97 , 98 in experimental IBD, decorin has protective effects on intestinal cells. 101 IBD is an autoimmune disease characterized by chronic inflammatory gastrointestinal disorders.…”

“…100 Moreover, multiple interactions of decorin with receptor tyrosine kinases may provide another level of complexity into the inflammatory signaling of decorin. 86 In contrast to pSS where decorin acts as an inducer of the disease phenotype, 97,98 in experimental IBD, decorin has protective effects on intestinal cells. 101 IBD is an autoimmune disease characterized by chronic inflammatory gastrointestinal disorders.…”

“…There are several reports suggesting the involvement of decorin in the progression of autoimmune diseases. 97 , 98 A recent study identified decorin as a crucial trigger of sterile inflammation in an NOD.B10 mouse model of primary Sjögren’s syndrome (pSS), 97 a chronic autoimmune disease characterized by exocrine gland dysfunction and immune hyperactivity. 99 Mechanistically, decorin via TLR4 signaling stimulates the production of TNF-α and several other inflammatory cytokines in splenocytes.…”