Stimulatory effect of interleukin-6 on plasminogen activator activity from human dental pulp cells

Nell-1 attenuates lipopolysaccharide-induced inflammation in human dental pulp cells

Nel-like molecule type 1 (Nell-1) is a secreted protein that plays an important role in osteoinduction in multiple animal models. A previous study has suggested the anti-inflammatory effect of Nell-1 on bone inflammation inhibition. However, its role in pulpitis has not been investigated. The present study aims to explore the effect of human recombinant Nell-1 (Nell-1) on rat pulp inflammation response, and its effect on lipopolysaccharide-induced inflammation in human dental pulp cells and its related intracellular signaling pathways. 30 Wistar rats with healthy non-carious maxillary first molars were chosen, Nell-1 was absorbed onto a sterile collagen sponge and capped onto exposed pulps. The expression of IL-6 and IL-8 were detected by immunohistochemical staining. Human dental pulp cells (hDPCs) were isolated from healthy extracted premolars and third molars. hDPCs were co-cultured with Escherichia coli lipopolysaccharide (LPS), Nell-1 protein, and mitogen-activated protein kinase (MAPK) inhibitors. The expression of pro-inflammatory cytokines and chemokines, such as IL-6 and IL-8, was examined via quantitative real-time PCR and enzyme-linked immunosorbent assay. The results showed that Nell-1 inhibited the inflammatory response of rat pulp. LPS treatment contributed to the expression of inflammatory factors in hDPCs, whereas Nell-1 obviously suppressed the LPS-induced inflammation. p38 MAPK and extracellular signal-regulated kinase (ERK) MAPK inhibitors attenuated the anti-inflammatory effect of hrNell-1, whereas the c-Jun N-terminal kinases (JNK) MAPK inhibitor exerted minimal effect. Therefore Nell-1 could inhibit LPS-induced inflammation in human dental pulp cells, and this effect may be mediated by p38 and ERK MAPK signaling pathways, but not JNK MAPK signaling pathway.

The multifaceted role of plasminogen in inflammation

A fine-tuned activation and deactivation of proteases and their inhibitors are involved in the execution of the inflammatory response. The zymogen/proenzyme plasminogen is converted to the serine protease plasmin, a key fibrinolytic factor by plasminogen activators including tissue-type plasminogen activator (tPA). Plasmin is part of an intricate protease network controlling proteins of initial hemostasis/coagulation, fibrinolytic and complement system. Activation of these protease cascades is required to mount a proper inflammatory response. Although best known for its ability to dissolve clots and cleave fibrin, recent studies point to the importance of fibrin-independent functions of plasmin during acute inflammation and inflammation resolution. In this review, we provide an up-to-date overview of the current knowledge of the enzymatic and cytokine-like effects of tPA and describe the role of tPA and plasminogen receptors in the regulation of the inflammatory response with emphasis on the cytokine storm syndrome such as observed during coronavirus disease 2019 or macrophage activation syndrome. We discuss tPA as a modulator of Toll like receptor signaling, plasmin as an activator of NFkB signaling, and summarize recent studies on the role of plasminogen receptors as controllers of the macrophage conversion into the M2 type and as mediators of efferocytosis during inflammation resolution.

Therapeutics targeting the fibrinolytic system

The function of the fibrinolytic system was first identified to dissolve fibrin to maintain vascular patency. Connections between the fibrinolytic system and many other physiological and pathological processes have been well established. Dysregulation of the fibrinolytic system is closely associated with multiple pathological conditions, including thrombosis, inflammation, cancer progression, and neuropathies. Thus, molecules in the fibrinolytic system are potent therapeutic and diagnostic targets. This review summarizes the currently used agents targeting this system and the development of novel therapeutic strategies in experimental studies. Future directions for the development of modulators of the fibrinolytic system are also discussed.

The fibrinolytic system was originally identified to dissolve blood clots, and is shown to have important roles in other pathological processes, including cancer progression, inflammation, and thrombosis. Molecules or therapeutics targeting fibrinolytic system have been successfully used in the clinical treatments of cancer and thrombotic diseases. The clinical studies and experimental models targeting fibrinolytic system are reviewed by Haili Lin at Sanming First Hosipital, Mingdong Huang at Fuzhou University in China, and Peng Xu at A*STAR in Singapore to demonstrate fibrinolytic system as novel therapeutic targets. As an example, the inhibition of fibrinolytic system protein can be used to suppress cancer prolifieration and metastasis. This review also discusses the potential therapeutic effects of inhibitiors of fibrinolytic system on inflammatory disorders.

Inflammatory cytokines in normal and irreversibly inflamed pulps: A systematic review

OBJECTIVE

To review the available literature in regard to the inflammatory process and pulpitis. Setting forth to evaluate if differences in the levels of various cytokines (TNF-α, IL-1β, IL-2, IL-6 and IL-8) can be observed in clinically diagnosed normal and irreversibly inflamed pulps that could serve as possible markers and/or diagnostic tools to predict and differentiate between certain states of inflammation. Methods used to measure and assess levels of cytokines have been limited to two protein quantification methods ELISA and/or Multiplex Array.

DESIGN

The databases PubMed, EMBASE/Ovid, The Cochrane Central Register of Controlled Trials, Cochrane Reviews and Scopus were consulted for the electronic literature search. Screening of titles and abstracts followed the PRISMA guidelines while data extraction and the assessment of the full texts were carried out in accordance to the GRADES assessment.

RESULTS

The review showed that significant increases in levels of IL-1β, IL-2, IL-6, IL-8 and TNF-α in irreversible pulpitis samples exist, in comparison to normal pulp samples which serve as a good basis for potential markers. Due to larger discrepancies in available literature, IL-2 seems rather unsuitable at the moment, while IL-6 and TNF alpha seem to be more promising.

CONCLUSION

It may be concluded that even by combining two protein quantification methods inconsistencies between studies exist. At the moment it is difficult to select just one specific cytokine suitable for testing, rather it supports the rationale that further high-quality clinical studies are needed.

Relevance of the plasminogen system in physiology, pathology, and regeneration of oral tissues - From the perspective of dental specialties

Plasmin is a proteolytic enzyme that is crucial in fibrinolysis. In oral tissues, the plasminogen system plays an essential role in physiological and pathological processes, which in addition to fibrinolysis include degradation of extracellular matrix, inflammation, immune response, angiogenesis, tissue remodeling, cell migration, and wound healing. Oral tissues reveal a change in the plasminogen system during pathological processes such as periodontitis, peri-implantitis, or pulpitis, as well as in response to mechanical load. The plasminogen system is also a key element in tissue regeneration. The number of studies investigating the plasminogen system in dentistry have grown continuously in recent years, highlighting its increasing relevance in dental medicine. In this review, we present the diverse functions of the plasminogen system in physiology and its importance for dental specialists in pathology and regeneration. We thus provide an overview of the current knowledge on the role of the plasminogen system in the different fields of dentistry, including endodontics, orthodontics, periodontics, and oral surgery.

Human tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA ) plays an important role in the removal of intravascular fibrin deposits and has several physiological roles and pathological activities in the brain. Its production by many other cell types suggests that t-PA has additional functions outside the vascular and central nervous system. Activity of t-PA is regulated at the level of its gene transcription, its mRNA stability and translation, its storage and regulated release, its interaction with cofactors that enhance its activity, its inhibition by inhibitors such as plasminogen activator inhibitor type 1 or neuroserpin, and its removal by clearance receptors. Gene transcription of t-PA is modulated by a large number of hormones, growth factors, cytokines or drugs and t-PA gene responses may be tissue-specific. The aim of this review is to summarise current knowledge on t-PA function and regulation of its pericellular activity, with an emphasis on regulation of its gene expression.

An insight into neurophysiology of pulpal pain: facts and hypotheses

Pain and pain control are important to the dental profession because the general perception of the public is that dental treatment and pain go hand in hand. Successful dental treatment requires that the source of pain be detected. If the origin of pain is not found, inappropriate dental care and, ultimately, extraction may result. Pain experienced before, during, or after endodontic therapy is a serious concern to both patients and endodontists, and the variability of discomfort presents a challenge in terms of diagnostic methods, endodontic therapy, and endodontic knowledge. This review will help clinicians understand the basic neurophysiology of pulpal pain and other painful conditions of the dental pulp that are not well understood.

The effects of tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and transforming growth factor-beta1 on pulp fibroblast mediated collagen degradation

Dental pulp destruction is believed to be regulated, in part, by the matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Cytokines are believed to be important in the pathogenesis of pulpitis. This study examined the effects that TNF-alpha, IL-1beta, IL-6, and TGF-beta1 have on the collagen degradation mediated by pulp fibroblasts utilizing a cell-mediated collagen degradation assay. Reverse transcriptase-polymerase chain reaction, Western blot analyses, and zymography were utilized to examine multiple MMPs and TIMPs. The collagen degradation mediated by these cells was stimulated by these cytokines. TNF-alpha, IL-1beta, and IL-6 increased the mRNA and/or protein expression of MMP-1, MMP-2, and MMP-3. TGF-beta1 decreased MMP-1 mRNA expression, while only slightly affecting the MMP-2 and MMP-3 mRNA and/or protein. These cytokines did not affect the expression of TIMP-1 or TIMP-2. These results suggest that these cytokines affect pulp destruction, in part, by differentially regulating the MMPs and TIMPs.

Evaluation of low PAI-1 activity as a risk factor for hemorrhagic diathesis

BACKGROUND

Prospective studies of the epidemiology and clinical significance of low plasminogen activator inhibitor type 1 (PAI-1) activity are lacking.

OBJECTIVE

To evaluate the prevalence of low PAI-1 activity in patients with a bleeding tendency in comparison with a normal population.

METHODS

In 586 consecutive patients, referred because of bleeding symptoms, we added analyses of PAI-1 activity and tissue plasminogen activator complex with PAI-1 (t-PA-PAI-1) to the routine investigation, consisting of platelet count, bleeding time, prothrombin time, activated partial thromboplastin time, fibrinogen, factor VIII, von Willebrand factor activity, and antigen. Controls were 100 blood donors and 100 age- and sex-matched healthy individuals. The latter were also evaluated regarding the previous bleeding episodes. The bleeding history was classified as clinically significant or not, and the criteria were fulfilled in 75% of the patients and 18% of the healthy controls.

RESULTS

The routine laboratory investigation of the patients was negative in 57%. Low PAI-1 activity, defined as <1.0 U mL(-1), was found in 23% of the patients and in 13% and 10% of the blood donors and healthy controls, respectively (odds ratio and 95% CI, 2.04; 1.11-3.77 and 2.75; 1.39-5.42, respectively). The difference remained statistically significant after the adjustment for body mass index, use of estrogens, sex and age (odds ratio for patients vs. healthy controls 3.23; 95% CI, 1.22-8.56, P = 0.019). The distribution of the 4G/5G genotypes in the patients was not different from that of two control populations. No specific symptom predicted for low PAI-1, which did not aggravate the clinical picture in association with the other hemostatic defects. Low tPA-PAI-1 was not associated with the increased bleeding tendency.

CONCLUSION

Low PAI-1 activity is common in patients with a bleeding diathesis, but it is a risk factor of minor clinical importance and not associated with specific bleeding manifestations.

Upregulation of tissue-type plasminogen activator in inflamed human dental pulps

AIM

To compare tissue-type plasminogen activator (t-PA) expression in normal human pulp and inflamed human pulp tissue specimens.

METHODOLOGY

Thirty pulpal tissue specimens (13 normal and 17 inflamed pulps) were obtained from extracted third molars. The levels of t-PA between normal pulp and inflamed pulp tissues were compared using the quantitative reverse-transcriptase polymerase chain reaction analysis. In addition, immunohistochemistry was used to identify the in situ localization of t-PA expression in pulp specimens. Wilcoxon-Mann-Whitney rank sum test was applied for the statistical analysis of the results.

RESULTS

t-PA mRNA gene was found more in inflamed pulps when compared with normal pulp tissue (P<0.05). The results from immunohistochemistry demonstrated that t-PA expression was significantly higher in the inflamed pulp (P=0.025). t-PA stain was detected in the fibroblasts, inflammatory infiltrates and endothelial cells.

CONCLUSIONS

t-PA expression was significantly higher in inflamed pulp tissue. t-PA may play an important role in the pathogenesis of pulpal inflammation.

Proinflammatory cytokine profiles in pulp fibroblasts stimulated with lipopolysaccharide and methyl mercaptan

Pulpal disease is intimately associated with the immune system's response to bacteria products. Clinical pathology is mediated in part by the production of pyrogenic cytokines, especially interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, and IL-6. Methyl mercaptan (CH3SH), a volatile sulfur compound produced by anaerobic Gram-negative bacteria, has been shown to contribute to the production of IL-1 by human mononuclear cells. In this report, we investigated the production of IL-1, TNF-alpha, and IL-6 by human pulp fibroblasts when stimulated for various periods of time with lipopolysaccharide (LPS) with or without the presence of CH3SH. We found that LPS and CH3SH had no effect on the production of IL-1 or TNF-alpha. However, LPS stimulated IL-6 production, and this production was augmented when CH3SH was present. We conclude that the volatile sulfur compound CH3SH plays a role in activation and modulation of the immune response through its role in production of IL-6.

Tissue plasminogen activator induced by dengue virus infection of human endothelial cells

Dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) are severe complications of dengue virus (DV) infection. However, the pathogenesis of hemorrhage induced by dengue virus infection is poorly understood. Since endothelial cells play a pivotal role in the regulation of hemostasis, we studied the effect of DV infection on the production of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1) in vitro using both primary isolated endothelial cells, human umbilical cord veins cells, and a human microvascular endothelial cell line. DV infection significantly induced the secretion of tPA but not PAI-1 of human endothelial cells. In addition, tPA mRNA of endothelial cells was induced by DV as demonstrated by RT-PCR. Antibody against IL-6 but not control antibody inhibited DV-induced tPA production of endothelial cells. Furthermore, a good correlation between sera levels of IL-6 and tPA was found in DHF but not DF patients. These results suggest that IL-6 can regulate DV-induced tPA production of endothelial cells, which may play important roles in the pathogenic development of DHF/DSS.

Smooth muscle cell migration stimulated by interleukin 6 is associated with cytoskeletal reorganization

BACKGROUND

Interleukin 6 (IL-6) is elevated in the arterial wall in atherosclerosis and restenosis after angioplasty. An important contributor to these pathologies is migration of vascular smooth muscle cells (VSMC), which is often associated with cytoskeletal reorganization initiated by growth factors and chemokines. We recently reported that IL-6 stimulated migration of VSMC. Here, we examined the cytoskeleton of VSMC and cytoskeletal associated proteins to determine potential mechanisms associated with IL-6 induced migration.

MATERIALS AND METHODS

Studies were performed in VSMC cultured from rat aortas.

RESULTS

IL-6 significantly stimulated VSMC migration. IL-6 induced actin polymerization, and tyrosine phosphorylation of focal adhesion-associated cytoskeletal proteins including focal adhesion kinase (FAK) and paxillin. Cytochalasin D, an inhibitor of actin polymerization, blocked phosphorylation of FAK and paxillin as well as cell motility induced by the cytokine.

CONCLUSIONS

Collectively, these data demonstrate for the first time that IL-6 stimulates VSMC motility which correlated with induction of actin cytoskeletal reorganization and tyrosine phosphorylation of FAK and paxillin.

Differential regulation of interleukin-6 and inducible cyclooxygenase gene expression by cytokines through prostaglandin-dependent and -independent mechanisms in human dental pulp fibroblasts

Increased levels of interleukin-1 (IL)-1, tumor necrosis factor-alpha (TNF-alpha), IL-6, and prostaglandin E2 (PGE2) have been detected in inflamed pulp tissue. To gain further insight into the molecular pathogenesis of pulpitis, we investigated the effects of IL-1alpha or TNF-alpha and PGE2, either alone or in combination on IL-6 and cyclooxygenase (COX)-2 messenger RNA (mRNA) production in cultured human dental pulp (HDP) fibroblasts. Exposure of HDP fibroblasts to IL-1alpha or TNF-alpha resulted in elevated levels of IL-6 (approximately 3.4 to approximately 10.4-fold) and COX-2 (approximately 5 to approximately 6.2-fold) mRNA. Simultaneous addition of IL-1alpha and PGE2 or TNF-alpha and PGE2 to the cultures significantly reduced the cytokine-induced IL-6 mRNA synthesis ranging from 45% to 65%. However, indomethacin enhanced the cytokine-stimulated IL-6 mRNA synthesis by approximately 1.7 to approximately 3.4-fold. This action could be reversed by exogenous PGE2. In contrast, PGE2 or indomethacin failed to modify the stimulatory effect of IL-1alpha or TNF-alpha on COX-2 gene expression. Because excessive levels of IL-6 and prostaglandins have been connected with the pathogenesis of several inflammatory diseases, our results suggest the involvement of HDP fibroblasts in the development of pulpitis via producing IL-6 and COX-2. Furthermore, expression of IL-6 and COX-2 genes in this cell seems to be differentially regulated by cytokines through prostaglandin-dependent and -independent pathways.