Expression of small leucine-rich proteoglycans during experimental fungal keratitis

Osteomodulin modulates the inflammatory responses via the interleukin-1 receptor 1/nuclear factor-κB signaling pathway in dental pulpitis

Pulpitis is a common infective oral disease in clinical situations. The regulatory mechanisms of immune defense in pulpitis are still being investigated. Osteomodulin (OMD) is a small leucine-rich proteoglycan family member distributed in bones and teeth. It is a bioactive protein that promotes osteogenesis and suppresses the apoptosis of human dental pulp stem cells (hDPSCs). In this study, the role of OMD in pulpitis and the OMD-induced regulatory mechanism were investigated. The OMD expression in normal and inflamed human pulp tissues was detected via immunofluorescence staining. Intriguingly, the OMD expression decreased in the inflammatory infiltration area of pulpitis specimens. The cellular experiments demonstrated that recombined human OMD could resist the detrimental effects of lipopolysaccharide (LPS)-induced inflammation. A conditional Omd knockout mouse model with pulpal inflammation was established. LPS-induced inflammatory impairment significantly increased in conditional Omd knockout mice, whereas OMD administration exhibited a protective effect against pulpitis. Mechanistically, the transcriptome alterations of OMD overexpression showed significant enrichment in the nuclear factor-κB (NF-κB) signaling pathway. Interleukin-1 receptor 1 (IL1R1), a vital membrane receptor activating the NF-κB pathway, was significantly downregulated in OMD-overexpressing hDPSCs. Additionally, the interaction between OMD and IL1R1 was verified using co-immunoprecipitation and molecular docking. In vivo, excessive pulpal inflammation in Omd-deficient mice was rescued using an IL1R antagonist. Overall, OMD played a protective role in the inflammatory response via the IL1R1/NF-κB signaling pathway. OMD may optimize the immunomodulatory functions of hDPSCs and can be used for regenerative endodontics.

A Degradation Motif in STAU1 Defines a Novel Family of Proteins Involved in Inflammation

Cancer development is regulated by inflammation. Staufen1 (STAU1) is an RNA-binding protein whose expression level is critical in cancer cells as it is related to cell proliferation or cell death. STAU1 protein levels are downregulated during mitosis due to its degradation by the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C). In this paper, we map the molecular determinant involved in STAU1 degradation to amino acids 38-50, and by alanine scanning, we shorten the motif to F³⁹PxPxxLxxxxL⁵⁰ (FPL-motif). Mutation of the FPL-motif prevents STAU1 degradation by APC/C. Interestingly, a search in databases reveals that the FPL-motif is shared by 15 additional proteins, most of them being involved in inflammation. We show that one of these proteins, MAP4K1, is indeed degraded via the FPL-motif; however, it is not a target of APC/C. Using proximity labeling with STAU1, we identify TRIM25, an E3 ubiquitin ligase involved in the innate immune response and interferon production, as responsible for STAU1 and MAP4K1 degradation, dependent on the FPL-motif. These results are consistent with previous studies that linked STAU1 to cancer-induced inflammation and identified a novel degradation motif that likely coordinates a novel family of proteins involved in inflammation. Data are available via ProteomeXchange with the identifier PXD036675.

ROS-induced Oxidative Injury involved in Pathogenesis of Fungal Keratitis via p38 MAPK Activation

This study was to explore the mechanism by which reactive oxygen species (ROS)-induced oxidative stress involved in the pathogenesis of fungal keratitis using an in vivo experimental keratitis mouse model and an in vitro culture model of human corneal epithelial cells (HCECs). Compared to normal control mice and HCECs, ROS production was markedly increased in fungal corneas and HCECs exposed to Candida albicans, accompanied by p38 mitogen-activated protein kinases (MAPK) activation. Increased products of oxidative markers, malondialdehyde (MDA), 4–hydroxynonenal (HNE), mitochondria DNA 8-OHdG and aconitase-2 were observed in fungal infected corneas and HCECs. Fungal infection also increased the mRNA expression and protein production of heme oxygenase-1 (HMOX1) and cyclooxygenase-2 (COX2), with suppressed levels of antioxidant enzymes, superoxide dismutase-1 (SOD1), glutathione peroxidase-1 (GPx1) and peroxiredoxin-4 (PRDX4). Interestingly, the levels of ROS, oxidative markers and oxygenases were significantly reduced by co-cultured p38 inhibitor SB203580. Furthermore, SB203580 restored the levels of antioxidant enzymes suppressed by fungus. Our findings demonstrated for the first time that ROS-induced oxidative injury is involved in pathogenesis of fungal keratitis via p38 MAPK pathway, suggesting the novel therapeutic targets for the potential treatment of fungal keratitis.

Small leucine-rich repeat proteoglycans in corneal inflammation and wound healing

The small leucine rich repeat proteoglycans are major components of the cornea. Lumican, keratocan, decorin, biglycan and osteoglycin are present throughout the adult corneal stroma, and fibromodulin in the peripheral limbal area. In the cornea literature these proteoglycan have been reviewed as structural, collagen fibril-regulating proteins of the cornea. However, these proteoglycans are members of the leucine-rich-repeat superfamily, and share structural similarities with pathogen recognition toll-like receptors. Emerging studies are showing that these have a range of interactions with cell surface receptors, chemokines, growth factors and pathogen associated molecular patterns and are able to regulate host immune response, inflammation and wound healing. This review discusses what is known about their innate immune-related role directly in the cornea, and studies outside the field that find interesting links with innate immune and wound healing responses that are likely to be relevant to the ocular surface. In addition, the review discusses phenotypes of mice with targeted deletion of proteoglycan genes and genetic variants associated with human pathologies.

The diverse functions of osteoglycin: a deceitful dwarf, or a master regulator of disease?

Small leucine-rich proteoglycans are emerging as important regulatory proteins within the extracellular matrix, where they exert both structural and nonstructural functions and hence are modulators of numerous biological processes, such as inflammation, fibrosis, and cell proliferation. One proteoglycan in particular, osteoglycin (OGN), also known as mimecan, shows great structural and functional diversity in normal physiology and in disease states, therefore making it a very interesting candidate for the development of novel therapeutic strategies. Unfortunately, the literature on OGN is confusing, as it has different names, and different transcript and protein variants have been identified. This review will give a clear overview of the different structures and functions of OGN that have been identified to date, portray its central role in pathophysiology, and highlight the importance of posttranslational processing, such as glycosylation, for the diversity of its functions.-Deckx, S., Heymans, S., Papageorgiou, A.-P. The diverse functions of osteoglycin: a deceitful dwarf, or a master regulator of disease?

A Novel Innate Response of Human Corneal Epithelium to Heat-killed Candida albicans by Producing Peptidoglycan Recognition Proteins

Fungal infections of the cornea can be sight-threatening and have a worse prognosis than other types of microbial corneal infections. Peptidoglycan recognition proteins (PGLYRP), which are expressed on the ocular surface, play an important role in the immune response against bacterial corneal infections by activating toll-like receptors (TLRs) or increasing phagocytosis. However, the role of PGLYRPs in innate immune response to fungal pathogens has not been investigated. In this study, we observed a significant induction of three PGLYRPs 2–4 in primary human corneal epithelial cells (HCECs) exposed to live or heat-killed Candida albicans (HKCA). The C-type lectin receptor dectin-1 plays a critical role in controlling Candida albicans infections by promoting phagocytic activity and cytokine production in macrophages and dendritic cells. Here, we demonstrate that dectin-1 is expressed by normal human corneal tissue and primary HCECs. HKCA exposure increased expression of dectin-1 on HCECs at mRNA and protein levels. Interestingly, dectin-1 neutralizing antibody, IκB-α inhibitor BAY11-7082, and NF-κB activation inhibitor quinazoline blocked NF-κB p65 nuclear translocation, as well as the induction of the PGLYRPs by HKCA in HCECs. Furthermore, rhPGLYRP-2 was found to suppress colony-forming units of Candida albicans in vitro. In conclusion, these findings demonstrate that dectin-1 is expressed by human corneal epithelial cells, and dectin-1/NF-κB signaling pathway plays an important role in regulating Candida albicans/HKCA-induced PGLYRP secretion by HCECs.