A T cell-specific knockout reveals an important role for protease-activated receptor 2 in lymphocyte development

Protease-Activated Receptor 2 in inflammatory skin disease: current evidence and future perspectives

Protease-activated receptor-2 (PAR2) is a class-A G protein-coupled receptor (GPCR) activated by serine proteases and is expressed by multiple tissues, including the skin. PAR2 is involved in the skin inflammatory response, promoting Th2 inflammation, delaying skin barrier repair, and affecting the differentiation of keratinocytes. It also participates in the transmission of itch and pain sensations in the skin. Increasing evidence indicates that PAR2 plays an important role in the pathogenesis of inflammatory skin diseases such as acne vulgaris, rosacea, psoriasis, and atopic dermatitis. Additional focus will be placed on potential targeted therapies based on PAR2. The Goal of this review is to outline the emerging effects of PAR2 activation in inflammatory skin disease and highlight the promise of PAR2 modulators.

Effect of a protease‐activated receptor‐2 antagonist ( GB88 ) on inflammation‐related loss of alveolar bone in periodontal disease

BACKGROUND AND OBJECTIVE

Protease-activated receptor-2 (PAR₂ ), a pro-inflammatory G-protein coupled receptor, has been associated with pathogenesis of periodontitis and the resulting bone loss caused by oral pathogens, including the keystone pathogen Porphyromonas gingivalis (P. gingivalis). We hypothesised that administration of a PAR₂ antagonist, GB88, might prevent inflammation and subsequent alveolar bone resorption in a mouse model of periodontal disease.

METHODS

Periodontitis was induced in mice by oral inoculations with P. gingivalis for a total of eight times over 24 days. The infected mice were treated with either GB88 or vehicle for the duration of the trial. Following euthanasia on day 56, serum was collected and used for the detection of mast cell tryptase. The right maxillae were defleshed and stained with methylene blue to measure the exposed cementum in molar teeth. The left maxillae were prepared for cryosections followed by staining for tartrate-resistant acid phosphatase to identify osteoclasts or with toluidine blue to identify mast cells. Reverse transcription quantitative PCR (RT-qPCR) was used to quantify the expression of inflammatory cytokines in the gingival tissue. Supernatants of T-lymphocyte cultures isolated from the regional lymph nodes were assayed using a cytometric bead array to measure the Th1/Th2/Th17 cytokine levels.

RESULTS

Measurement of the exposed cementum showed that GB88 reduced P. gingivalis-induced alveolar bone loss by up to 69%. GB88 also prevented the increase in osteoclast numbers observed in the infected mice. Serum tryptase levels were significantly elevated in both the infected groups, and not altered by treatment. RT-qPCR showed that GB88 prevented the upregulation of Il1b, Il6, Ifng and Cd11b. In T-lymphocyte supernatants, only IFNγ and IL-17A levels were increased in response to infection, but this was prevented by GB88 treatment.

CONCLUSIONS

GB88 significantly reduced osteoclastic alveolar bone loss in mice infected with P. gingivalis, seemingly by preventing the upregulation of several inflammatory cytokines. PAR₂ antagonism may be an effective treatment strategy for periodontal disease.

Protease-activated receptor-2 dependent and independent responses of bone cells to prostate cancer cell secretory products

BACKGROUND

Metastatic prostate cancer lesions in the skeleton are frequently characterized by excessive formation of bone. Prostate cancer cells secrete factors, including serine proteases, that are capable of influencing the behavior of surrounding cells. Some of these proteases activate protease-activated receptor-2 (PAR₂ ), which is expressed by osteoblasts (bone-forming cells) and precursors of osteoclasts (bone-resorbing cells). The aim of the current study was to investigate a possible role for PAR₂ in regulating the behavior of bone cells exposed to metastatic prostate cancer cells.

METHODS

The effect of medium conditioned by the PC3, DU145, and MDA-PCa-2b prostate cancer cell lines was investigated in assays of bone cell function using cells isolated from wildtype and PAR₂ -null mice. Osteoclast differentiation was assessed by counting tartrate-resistant acid phosphatase-positive multinucleate cells in bone marrow cultured in osteoclastogenic medium. Osteoblasts were isolated from calvariae of neonatal mice, and BrdU incorporation was used to assess their proliferation. Assays of alkaline phosphatase activity and quantitative PCR analysis of osteoblastic gene expression were used to assess osteoblast differentiation. Responses of osteoblasts to medium conditioned by MDA-PCa-2b cells were analyzed by RNAseq.

RESULTS

Conditioned medium (CM) from all three cell lines inhibited osteoclast differentiation independently of PAR₂ . Media from PC3 and DU145 cells had no effect on assays of osteoblast function. Medium conditioned by MDA-PCa-2b cells stimulated BrdU incorporation in both wildtype and PAR₂ -null osteoblasts but increased alkaline phosphatase activity and Runx2 and Col1a1 expression in wildtype but not PAR₂ -null cells. Functional enrichment analysis of RNAseq data identified enrichment of multiple gene ontology terms associated with lysosomal function in both wildtype and PAR₂ -null cells in response to MDA-PCa-2b-CM. Analysis of individual genes identified osteogenesis-associated genes that were either upregulated by MDA-PCa-2b-CM selectively in wildtype cells or downregulated selectively in PAR₂ -null cells.

CONCLUSIONS

Factors secreted by prostate cancer cells influence bone cell behavior through both PAR₂ -dependent and -independent mechanisms. Both PAR₂ -independent suppression of osteoclast differentiation and PAR₂ -dependent stimulation of osteogenesis are likely to determine the nature of prostate cancer metastases in bone.

Keratinocyte-specific ablation of protease-activated receptor 2 prevents gingival inflammation and bone loss in a mouse model of periodontal disease

Chronic periodontitis is characterised by gingival inflammation and alveolar bone loss. A major aetiological agent is Porphyromonas gingivalis, which secretes proteases that activate protease-activated receptor 2 (PAR₂ ). PAR₂ expressed on oral keratinocytes is activated by proteases released by P. gingivalis, inducing secretion of interleukin 6 (IL-6), and global knockout of PAR₂ prevents bone loss and inflammation in a periodontal disease model in mice. To test the hypothesis that PAR₂ expressed on gingival keratinocytes is required for periodontal disease pathology, keratinocyte-specific PAR₂ -null mice were generated using K14-Cre targeted deletion of the PAR₂ gene (F2rl1). These mice were subjected to a model of periodontitis involving placement of a ligature around a tooth, combined with P. gingivalis infection ("Lig + Inf"). The intervention caused a significant 44% decrease in alveolar bone volume (assessed by microcomputed tomography) in wildtype (K14-Cre:F2rl1^wt/wt ), but not littermate keratinocyte-specific PAR₂ -null (K14-Cre:F2rl1^fl/fl ) mice. Keratinocyte-specific ablation of PAR₂ prevented the significant Lig + Inf-induced increase (2.8-fold) in the number of osteoclasts in alveolar bone and the significant up-regulation (2.4-4-fold) of the inflammatory markers IL-6, IL-1β, interferon-γ, myeloperoxidase, and CD11b in gingival tissue. These data suggest that PAR₂ expressed on oral epithelial cells is a critical regulator of periodontitis-induced bone loss and will help in designing novel therapies with which to treat the disease.