Sam68 is a regulator of Toll-like receptor signaling

Role of Sam68 as an adaptor protein in inflammatory signaling

Sam68 is a ubiquitously expressed KH-domain containing RNA-binding protein highly studied for its involvement in regulating multiple steps of RNA metabolism. Sam68 also contains multiple protein-protein interaction regions such as proline-rich regions, tyrosine phosphorylation sites, and arginine methylation sites, all of which facilitate its participation as an adaptor protein in multiple signaling pathways, likely independent of its RNA-binding role. This review focuses on providing a comprehensive report on the adaptor roles of Sam68 in inflammatory signaling and inflammatory diseases. The insights presented here have the potential to open new avenues in inflammation research and justify targeting Sam68 to control aberrant inflammatory responses.

Sam68 promotes osteogenic differentiation of aortic valvular interstitial cells by TNF-α/STAT3/autophagy axis

Calcified aortic valve disease (CAVD) is a major non-rheumatic heart valve disease in the world, with a high mortality rate and without suitable pharmaceutical therapy due to its complex mechanisms. Src-associated in mitosis 68-KD (Sam68), an RNA binding protein, has been reported as a signaling adaptor in numerous signaling pathways (Huot in Mol Cell Biol, 29(7), 1933-1943, 2009), particularly in inflammatory signaling pathways. The effects of Sam68 on the osteogenic differentiation process of hVICs and its regulation on signal transducer and activator of transcription 3 (STAT3) signaling pathway have been investigated in this study. Human aortic valve samples detection found that Sam68 expression was up-regulated in human calcific aortic valves. We used tumor necrosis factor α (TNF-α) as an activator for osteogenic differentiation in vitro and the result indicated that Sam68 was highly expressed after TNF-α stimulation. Overexpression of Sam68 promoted osteogenic differentiation of hVICs while Sam68 knockdown reversed this effect. Sam68 interaction with STAT3 was predicted by using String database and was verified in this study. Sam68 knockdown reduced phosphorylation of STAT3 activated by TNF-α and the downstream gene expression, which further influenced autophagy flux in hVICs. STAT3 knockdown alleviated the osteogenic differentiation and calcium deposition promoted by Sam68 overexpression. In conclusion, Sam68 interacts with STAT3 and participates in its phosphorylation to promote osteogenic differentiation of hVICs to induce valve calcification. Thus, Sam68 may be a new therapeutic target for CAVD. Regulatory of Sam68 in TNF-α/STAT3/Autophagy Axis in promoting osteogenesis of hVICs.

Splicing machinery is profoundly altered in systemic lupus erythematosus and antiphospholipid syndrome and directly linked to key clinical features

OBJECTIVES

To characterize the splicing machinery (SM) of leukocytes from primary antiphospholipid syndrome (APS), systemic lupus erythematosus (SLE) and antiphospholipid syndrome with lupus (APS + SLE) patients, and to assess its clinical involvement.

METHODS

Monocytes, lymphocytes and neutrophils from 80 patients (22 APS, 35 SLE and 23 APS + SLE) and 50 HD were purified, and 45 selected SM components were evaluated by qPCR-microfluidic array. Relationship with clinical features and underlying regulatory mechanisms were assessed.

RESULTS

APS, SLE and APS + SLE leukocytes displayed significant and specific alterations in SM-components (SMC), associated with clinical features [autoimmune profiles, disease activity, lupus nephritis (LN), and CV-risk markers]. A remarkable relationship among dysregulated SMC in monocytes and the presence of LN in SLE was highlighted, revealing a novel pathological mechanism, which was further explored. Immunohistology analysis of renal biopsies highlighted the pathological role of the myeloid compartment in LN. Transcriptomic analysis of monocytes from SLE-LN(+) vs SLE-LN(-) identified 271 genes differentially expressed, mainly involved in inflammation and IFN-signaling. Levels of IFN-related genes correlated with those of SMC in SLE-LN(+). These results were validated in two external SLE-LN(+) datasets of whole-blood and kidney biopsies. In vitro, SLE-LN(+)-serum promoted a concomitant dysregulation of both, the IFN signature and several SMC, further reversed by JAKinibs treatment. Interestingly, IFNs, key inflammatory cytokines in SLE pathology, also altered SMC. Lastly, the over/down-expression of selected SMC in SLE-monocytes reduced the release of inflammatory cytokines and their adhesion capacity.

CONCLUSION

Overall, we have identified, for the first time, a specific alteration of SMC in leukocytes from APS, SLE and APS + SLE patients that would be responsible for the development of distinctive clinical profiles.

Ferrostatin-1 Inhibits Toll-Like Receptor 4/NF-κB Signaling to Alleviate Intervertebral Disc Degeneration in Rats

Ferrostatin-1 (Fer-1) is an inhibitor of ferroptosis and has been documented to be implicated in the development of intervertebral disc degeneration (IDD). This study intends to explore the role of Fer-1 in IDD via the toll-like receptor 4 (TLR4)/NF-κB signaling pathway. Through the Gene Expression Omnibus database, IDD-related gene expression microarray GSE124272 and high-throughput sequencing data set GSE175710 were obtained. Then, differentially expressed genes in IDD were identified, followed by implementation of protein-protein interaction network analysis and receiver operating characteristic curve analysis. Main pathways in IDD were obtained through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional analyses, and target genes of Fer-1 were obtained through PubChem and PharmMapper websites. Finally, GPX4, FTH, and TLR4 expression was determined in a constructed IDD rat model. Three key co-expression modules involved in IDD were obtained through Weighted Gene Co-Expression Network Analysis. Thirteen differentially expressed genes were found to be associated with IDD, and eight key genes (TLR4, BCL2A1, CXCL1, IL1R1, NAMPT, SOCS3, XCL1, and IRAK3) were found to affect IDD. These eight key genes had the diagnostic potential for IDD. The NF-κB signaling pathway played a predominant role in IDD development. From network pharmacologic analysis, Fer-1 might suppress ferroptosis and ameliorate IDD via the TLR4/NF-κB signaling pathway, and the in vivo animal experiment further verified it. Fer-1 down-regulates TLR4 to inactivate NF-κB signaling pathway, suppressing ferroptosis and finally alleviating IDD in rats.

Toll-Like Receptors/TNF-α Pathway Crosstalk and Impact on Different Sites of Recurrent Myocardial Infarction in Elderly Patients

Background

Recurrent myocardial infarction is associated with increased mortality. Risk and predictive factors of recurrent myocardial infarction in elderly patients after coronary stenting are not well known. This research sought to investigate the effects of proinflammatory cytokines and toll-like receptor on recurrent myocardial infarction after coronary stenting in elderly patients.

Methods

We measured the levels of toll-like receptor 2 (TLR2), toll-like receptor 3 (TLR3), toll-like receptor 4 (TLR4), tumor necrosis factor-α (TNF-α), soluble tumor necrosis factor-α receptor-1 (sTNFR-1), soluble tumor necrosis factor-α receptor-2 (sTNFR-2), endothelial progenitor cells (EPCs), and vascular endothelial growth factor (VEGF) in elderly patients with recurrent myocardial infarction and assessed the changes of proinflammatory cytokines and toll-like receptors in elderly patients with recurrent myocardial infarction after coronary stenting.

Results

Levels of TLR2, TLR3, TLR4, TNF-α, sTNFR-1, and sTNFR-2 were remarkably increased (P < 0.001), and EPCs and VEGF were remarkably lowered (P < 0.001) in the elderly patients with recurrent myocardial infarction after coronary stent implantation. Increased expressions of proinflammatory cytokines and toll-like receptors induced recurrent myocardial infarction after coronary stenting. Elevated expressions of proinflammatory cytokines and toll-like receptors may be used to identify elderly patients who have an increased risk of developing recurrent myocardial infarction after coronary stenting.

Conclusion

The increase levels of proinflammatory cytokines and toll-like receptors were associated with recurrent myocardial infarction after coronary stenting. Increased expressions of proinflammatory cytokines and toll-like receptors may be clinically useful biomarkers for predicting recurrent myocardial infarction in the elderly patients after coronary stent implantation.

Sam68 contributes to intestinal inflammation in experimental and human colitis

Sam68 is an RNA-binding protein with an adaptor role in signal transduction. Our previous work identified critical proinflammatory and apoptotic functions for Sam68, downstream of the TNF/TNFR1 and TLR2/3/4 pathways. Recent studies have shown elevated Sam68 in inflamed tissues from rheumatoid arthritis and ulcerative colitis (UC) patients, suggesting that Sam68 contributes to chronic inflammatory diseases. Here, we hypothesized that deletion of Sam68 is protective against experimental colitis in vivo, via reductions in TNF-associated inflammatory signaling. We used Sam68 knockout (KO) mice to study the role of Sam68 in experimental colitis, including its contributions to TNF-induced inflammatory gene expression in three-dimensional intestinal organoid cultures. We also studied the expression of Sam68 and inflammatory genes in colon tissues of UC patients. Sam68 KO mice treated with an acute course of DSS exhibited significantly less weight loss and histopathological inflammation compared to wild-type controls, suggesting that Sam68 contributes to experimental colitis. Bone marrow transplants showed no pathologic role for hematopoietic cell-specific Sam68, suggesting that non-hematopoietic Sam68 drives intestinal inflammation. Gene expression analyses showed that Sam68 deficiency reduced the expression of proinflammatory genes in colon tissues from DSS-treated mice, as well as TNF-treated three-dimensional colonic organoids. We also found that inflammatory genes, such as TNF, CCR2, CSF2, IL33 and CXCL10, as well as Sam68 protein, were upregulated in inflamed colon tissues of UC patients. This report identifies Sam68 as an important inflammatory driver in response to intestinal epithelial damage, suggesting that targeting Sam68 may hold promise to treat UC patients.

Virus-Host Interactions in Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals, which has been regarded as a persistent challenge for the livestock industry in many countries. Foot-and-mouth disease virus (FMDV) is the etiological agent of FMD that can spread rapidly by direct and indirect transmission. FMDV is internalized into host cell by the interaction between FMDV capsid proteins and cellular receptors. When the virus invades into the cells, the host antiviral system is quickly activated to suppress the replication of the virus and remove the virus. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate host machine and circumvent the host antiviral responses. Therefore, identification of virus-host interactions is critical for understanding the host defense against virus infections and the pathogenesis of the viral infectious diseases. This review elaborates on the virus-host interactions during FMDV infection to summarize the pathogenic mechanisms of FMD, and we hope it can provide insights for designing effective vaccines or drugs to prevent and control the spread of FMD and other diseases caused by picornaviruses.

Activation of TLR Signaling in Sensitization-Recruited Inflammatory Monocytes Attenuates OVA-Induced Allergic Asthma

The activation of Toll-like receptor (TLR) signaling is widely reported to be involved in preventing the development of allergic asthma. However, the mechanism of the protective function of TLR signaling remains limited. Here, we studied the mouse model of ovalbumin (OVA)-induced allergic asthma and found that deficiency of TLR signaling or activating TLR signaling with agonist would aggravate or attenuate OVA-induced allergic asthma, respectively, and TLR signaling-mediated protective effect mainly affected the sensitization phase. After OVA/alum sensitization, neutrophils and inflammatory monocytes were recruited into peritoneal cavity and up-regulated TLRs expression. However, adoptive transfer of inflammatory monocytes but not peritoneal macrophages or neutrophils induced allergic symptoms in recipient mice after OVA challenge even without OVA/alum sensitization, and treating the inflammatory monocytes with TLR agonist in vitro before transfer could abolish this effect, indicating that recruited inflammatory monocytes played a determinant role in OVA-induced allergic asthma, and activation of TLR signaling in them could attenuate allergic symptoms. Finally, we found that activation of TLR signaling could increase the expression of T-helper (Th) 1-associated cytokines in inflammatory monocytes. Our results suggest that activation of TLR signaling in sensitization-recruited inflammatory monocytes attenuates OVA-induced allergic asthma by promoting the expression of Th1-associated cytokines.

Viruses Seen by Our Cells: The Role of Viral RNA Sensors

The role of the innate immune response in detecting RNA viruses is crucial for the establishment of proper inflammatory and antiviral responses. Different receptors, known as pattern recognition receptors (PRRs), are present in the cytoplasm, endosomes, and on the cellular surface. These receptors have the capacity to sense the presence of viral nucleic acids as pathogen-associated molecular patterns (PAMPs). This recognition leads to the induction of type 1 interferons (IFNs) as well as inflammatory cytokines and chemokines. In this review, we provide an overview of the significant involvement of cellular RNA helicases and Toll-like receptors (TLRs) 3, 7, and 8 in antiviral immune defenses.

Picornaviruses and Apoptosis: Subversion of Cell Death

Infected cells can undergo apoptosis as a protective response to viral infection, thereby limiting viral infection. As viruses require a viable cell for replication, the death of the cell limits cellular functions that are required for virus replication and propagation. Picornaviruses are single-stranded RNA viruses that modify the host cell apoptotic response, probably in order to promote viral replication, largely as a function of the viral proteases 2A, 3C, and 3CD. These proteases are essential for viral polyprotein processing and also cleave cellular proteins. Picornavirus proteases cleave proapoptotic adaptor proteins, resulting in downregulation of apoptosis. Picornavirus proteases also cleave nucleoporins, disrupting the orchestrated manner in which signaling pathways use active nucleocytoplasmic trafficking, including those involved in apoptosis. In addition to viral proteases, the transmembrane 2B protein alters intracellular ion signaling, which may also modulate apoptosis. Overall, picornaviruses, via the action of virally encoded proteins, exercise intricate control over and subvert cell death pathways, specifically apoptosis, thereby allowing viral replication to continue.

Wnt2b attenuates HSCs activation and liver fibrosis through negative regulating TLR4 signaling

The Wingless-type MMTV integration site family member 2b (Wnt2b) has been found to be a principal mediator of liver development and regeneration. However, the significance of Wnt2b in the pathogenesis of fibrosis-related liver diseases remains undefined. Here, we report that Wnt2b was highly expressed in the fibrotic liver tissues, exhibiting protective effects against activation of hepatic stellate cells (HSCs) and fibrosis progression. We identified a negative regulation of Wnt2b on the toll-like receptor 4 (TLR4) activation-mediated pro-fibrogenic effects. Wnt2b was shown not only to directly suppress LPS-induced HSCs activation, but also to inhibit TLR4-enhanced the sensitivity of HSCs to transforming growth factor beta (TGF-β). Mechanistic study showed that Wnt2b suppresses TLR4 signaling through inhibiting the expression of TLR4 as well as the activation of NF-κB and MAPKs. These findings provided new insights into the pathophysiology of liver fibrosis by characterizing Wnt2b as a novel endogenous suppressor of TLR4 signaling, maintaining tissue homeostasis during the early stage of hepatic fibrosis-associated liver diseases.