Identification and Characterization of the Lactating Mouse Mammary Gland Citrullinome

Distinct mucosal endotypes as initiators and drivers of rheumatoid arthritis

Rheumatoid arthritis (RA) is a potentially devastating autoimmune disease. The great majority of patients with RA are seropositive for anti-citrullinated protein antibodies (ACPAs), rheumatoid factors, or other autoantibodies. The onset of clinically apparent inflammatory arthritis meeting classification criteria (clinical RA) is preceded by ACPA seropositivity for an average of 3-5 years, a period that is designated as 'at-risk' of RA for ACPA-positive individuals who do not display signs of arthritis, or 'pre-RA' for individuals who are known to have progressed to developing clinical RA. Prior studies of individuals at-risk of RA have associated pulmonary mucosal inflammation with local production of ACPAs and rheumatoid factors, leading to development of the 'mucosal origins hypothesis'. Recent work now suggests the presence of multiple distinct mucosal site-specific mechanisms that drive RA evolution. Indicatively, subsets of individuals at-risk of RA and patients with RA harbour a faecal bacterial strain that has exhibited arthritogenic activity in animal models and that favours T helper 17 (TH17) cell responses in patients. Periodontal inflammation and oral microbiota have also been suggested to promote the development of arthritis through breaches in the mucosal barrier. Herein, we argue that mucosal sites and their associated microbial strains can contribute to RA evolution via distinct pathogenic mechanisms, which can be considered causal mucosal endotypes. Future therapies instituted for prevention in the at-risk period, or, perhaps, during clinical RA as therapeutics for active arthritis, will possibly have to address these individual mechanisms as part of precision medicine approaches.

GnRH Induces Citrullination of the Cytoskeleton in Murine Gonadotrope Cells

Peptidylarginine deiminases (PADs or PADIs) catalyze the conversion of positively charged arginine to neutral citrulline, which alters target protein structure and function. Our previous work established that gonadotropin-releasing hormone agonist (GnRHa) stimulates PAD2-catalyzed histone citrullination to epigenetically regulate gonadotropin gene expression in the gonadotrope-derived LβT2 cell line. However, PADs are also found in the cytoplasm. Given this, we used mass spectrometry (MS) to identify additional non-histone proteins that are citrullinated following GnRHa stimulation and characterized the temporal dynamics of this modification. Our results show that actin and tubulin are citrullinated, which led us to hypothesize that GnRHa might induce their citrullination to modulate cytoskeletal dynamics and architecture. The data show that 10 nM GnRHa induces the citrullination of β-actin, with elevated levels occurring at 10 min. The level of β-actin citrullination is reduced in the presence of the pan-PAD inhibitor biphenyl-benzimidazole-Cl-amidine (BB-ClA), which also prevents GnRHa-induced actin reorganization in dispersed murine gonadotrope cells. GnRHa induces the citrullination of β-tubulin, with elevated levels occurring at 30 min, and this response is attenuated in the presence of PAD inhibition. To examine the functional consequence of β-tubulin citrullination, we utilized fluorescently tagged end binding protein 1 (EB1-GFP) to track the growing plus end of microtubules (MT) in real time in transfected LβT2 cells. Time-lapse confocal microscopy of EB1-GFP reveals that the MT average lifetime increases following 30 min of GnRHa treatment, but this increase is attenuated by PAD inhibition. Taken together, our data suggest that GnRHa-induced citrullination alters actin reorganization and MT lifetime in gonadotrope cells.

A Pilot Study on Peptidylarginine Deiminases and Protein Deimination in Animal Cancers across Vertebrate Species

PADs are a group of calcium-dependent enzymes that play key roles in inflammatory pathologies and have diverse roles in cancers. PADs cause irreversible post-translational modification of arginine to citrulline, leading to changes in protein function in different cellular compartments. PAD isozyme diversity differs throughout phylogeny in chordates, with five PAD isozymes in mammals, three in birds, and one in fish. While the roles for PADs in various human cancers are mounting (both in regards to cancer progression and epigenetic regulation), investigations into animal cancers are scarce. The current pilot-study therefore aimed at assessing PAD isozymes in a range of animal cancers across the phylogeny tree. In addition, the tissue samples were assessed for total protein deimination and histone H3 deimination (CitH3), which is strongly associated with human cancers and also indicative of gene regulatory changes and neutrophil extracellular trap formation (NETosis). Cancers were selected from a range of vertebrate species: horse, cow, reindeer, sheep, pig, dog, cat, rabbit, mink, hamster, parrot, and duck. The cancers chosen included lymphoma, kidney, lung, testicular, neuroendocrine, anaplastic, papilloma, and granulosa cell tumour. Immunohistochemical analysis revealed that CitH3 was strongly detected in all of the cancers assessed, while pan-deimination detection was overall low. Both PAD2 and PAD3 were the most predominantly expressed PADs across all of the cancers assessed, while PAD1, PAD4, and PAD6 were overall expressed at lower, albeit varying, levels. The findings from this pilot study provide novel insights into PAD-mediated roles in different cancers across a range of vertebrate species and may aid in the understanding of cancer heterogeneity and cancer evolution.

Hypothesis: Rheumatoid arthritis and periodontitis: A new possible link via prolactin hormone

Rheumatoid arthritis and periodontitis are two common chronic inflammatory diseases affecting human population worldwide. The association between the two conditions have been the focus of many researches, trying to explore the possible mechanisms underlying this association. Prolactin hormone, besides its known lactogenic effects acts as a cytokine secreted from various tissues other than the pituitary gland with multiple pleotropic actions in immunity and inflammation. Several data showed that prolactin levels are increased significantly in the synovial and periodontal tissues, and this increase is correlated with disease activity and tissue destruction. Our hypothesis suggests that local prolactin can represent a link between the two conditions. In this work, we suggest a possible mechanistic interactions, hypothesized to form a common path linking between rheumatoid arthritis, periodontitis and prolactin. This is because of the need to develop new treatment strategies for the most effective long term control of inflammation in both conditions.