Peptidylarginine Deiminase and Citrullination: Potential Therapeutic Targets for Inflammatory Diseases

The multiple post-translational modifications of proteins display specific gain- or loss-of-function under normal and abnormal conditions. These modifications are precisely regulated by post-translational modification enzymes. The altered molecular status perturbs the pattern of gene expression and decides on a direction to signal transduction cascades as well as intrinsic properties of the proteins. Ultimately, it strictly maintains intracellular environment or results in disease manifestations. Recently, it has become that enzyme-dependent modification of arginine residue to citrulline exerts an important role in the induction of autoimmunity including rheumatoid arthritis, multiple sclerosis, and cancer. The modification of arginine residue to citrulline on proteins is called 'citrullination' or 'deimination' and is regulated by the calcium-dependent enzyme peptidylarginine deiminase (PAD). Now many effective PAD inhibitors (for example, Cl-amidine) have developed that ameliorates disease phenotypes. In this review, we discuss crucial roles of PAD enzyme and citrullination, the effectiveness of PAD inhibitors, and the implication in pathology.ope

Peptidylarginine deiminase inhibition impairs Toll-like receptor agonist-induced functional maturation of dendritic cells, resulting in the loss of T cell?proliferative capacity: a partial mechanism with therapeutic potential in inflammatory settings

Cl-amidine, which is a small-molecule inhibitor of PAD, has therapeutic potential for inflammation-mediated diseases. However, little is known regarding the manner by which PAD inhibition by Cl-amidine regulates inflammatory conditions. Here, we investigated the effects of PAD inhibition by Cl-amidine on the functioning of DCs, which are pivotal immune cells that mediate inflammatory diseases. When DC maturation was induced by TLR agonists, reduced cytokine levels (IL-6, IL-1β, and IL-12p70) were observed in Cl-amidine-treated DCs. Cl-amidine-treated, LPS-activated DCs exhibited alterations in their mature and functional statuses with up-regulated antigen uptake, down-regulated CD80, and MHC molecules. In addition, Cl-amidine-treated DCs dysregulated peptide-MHC class formations. Interestingly, the decreased cytokines were independent of MAPK/NF-κB signaling pathways and transcription levels, indicating that PAD inhibition by Cl-amidine may be involved in post-transcriptional steps of cytokine production. Transmission electron microscopy revealed morphotypical changes with reduced dendrites in the Cl-amidine-treated DCs, along with altered cellular compartments, including fragmented ERs and the formation of foamy vesicles. Furthermore, in vitro and in vivo Cl-amidine treatments impaired the proliferation of naïve CD4(+) and CD8(+) T cells. Overall, our findings suggest that Cl-amidine has therapeutic potential for treating inflammation-mediated diseases.ope

Mycobacterium tuberculosis RpfB drives Th1-type T cell immunity via a TLR4-dependent activation of dendritic cells

The failure of Mycobacterium bovis BCG as a TB vaccine against TB reactivation suggests that latency-associated proteins should be included in alternative TB vaccine development. Further, antigens known to generate protective immunity against the strong Th1 stimulatory response to reactivated TB should be included in novel vaccine design. Recent studies have emphasized the importance of Rpfs from Mycobacterium tuberculosis in the reactivation process and cellular immunity. However, little is known about how RpfB mediates protective immunity against M. tuberculosis. Here, we investigated the functional roles and signaling mechanisms of RpfB in DCs and its implications in the development of T cell immunity. DCs treated with RpfB displayed features of mature and functional status, with elevated expression of cell surface molecules (CD80, CD86, and MHC class I and II) and proinflammatory cytokine production (TNF-α, IL-1β, IL-6, and IL-12p70). Activation of DCs was mediated by direct binding of RpfB to TLR4, followed by MyD88/TRIF-dependent signaling to MAPKs and NF-κB signaling pathways. Specifically, we found that the RpfB G5 domain is the most important part in RpfB binding to TLR4. RpfB-treated DCs effectively polarized naïve CD4(+) and CD8(+) T cells to secrete IFN-γ and IL-2. Importantly, RpfB induced the expansion of memory CD4(+)/CD8(+)CD44(high)CD62L(low) T cells in the spleen of M. tuberculosis-infected mice. Our data suggest that RpfB regulates innate immunity and activates adaptive immunity through TLR4, a finding that may help in the design of more effective vaccines.ope