No prolongation of skin allograft survival by immunoproteasome inhibition in mice

The Significant Role of PA28αβ in CD8+ T Cell-Mediated Graft Rejection Contrasts with Its Negligible Impact on the Generation of MHC-I Ligands

The proteasome generates the majority of peptides presented on MHC class I molecules. The cleavage pattern of the proteasome has been shown to be changed via the proteasome activator (PA)28 alpha beta (PA28αβ). In particular, several immunogenic peptides have been reported to be PA28αβ-dependent. In contrast, we did not observe a major impact of PA28αβ on the generation of different major histocompatibility complex (MHC) classI ligands. PA28αβ-knockout mice infected with the lymphocytic choriomeningitis virus (LCMV) or vaccinia virus showed a normal cluster of differentiation (CD) 8 response and viral clearance. However, we observed that the adoptive transfer of wild-type cells into PA28αβ-knockout mice led to graft rejection, but not vice versa. Depletion experiments showed that the observed rejection was mediated by CD8+ cytotoxic T cells. These data indicate that PA28αβ might be involved in the development of the CD8+ T cell repertoire in the thymus. Taken together, our data suggest that PA28αβ is a crucial factor determining T cell selection and, therefore, impacts graft acceptance.

PR-957 retards rheumatoid arthritis progression and inflammation by inhibiting LMP7-mediated CD4+ T cell imbalance

OBJECTIVE

Low molecular mass polypeptide 7 (LMP7) is an immunoproteasome subunit that regulates T cell amplification, differentiation, and inflammation and is involved in rheumatoid arthritis (RA) progression. This study intended to apply PR-957 (an anti-LMP7 agent) for RA treatment in vitro and in vivo and evaluate its interaction with LMP7-mediated CD4+ T cell imbalance.

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from 30 RA patients and 30 healthy controls. RA fibroblast-like synoviocytes (RA-FLSs) and CD4+ T cells were isolated from RA patients and then cocultured with PR-957 and/or LMP7 overexpression adenovirus (Ad-LMP7). Collagen-induced arthritis (CIA) mice were constructed and then treated with PR-957 and/or Ad-LMP7.

RESULTS

LMP7 was higher in RA patients (versus healthy controls) and positively correlated with T helper (Th)1 cells, the Th1/Th2 ratio, Th17 cells, and the Th17/Treg ratio but not with Th2 or T regulatory (Treg) cells. PR-957 reduced Th1 and Th17 cells but increased Th2 and Treg cells in RA-CD4+ T cells, and this effect was partially reversed by Ad-LMP7 transfection. Interestingly, when cocultured with RA-CD4+ T cells, PR-957 increased RA-FLS apoptosis and decreased its invasive ability, viability, and inflammation, as suggested by IL-6, CCL2, MMP1, and MMP3; however, these phenomena were weakened in RA-FLSs without RA-CD4+ T cell coculture. In addition, Ad-LMP7 transfection attenuated the above effects of PR-957. In CIA mice, PR-957 decreased the arthritis score, synovial hyperproliferation and articular injury, inflammation in the synovium and serum, and the imbalance of Th1/Th2 and Th17/Treg in the spleen, and these effects were attenuated by Ad-LMP7.

CONCLUSION

PR-957 ameliorates RA progression and inflammation by repressing LMP7-mediated CD4+ T cell imbalance.

LMP7 polymorphism may modify the presentation and clinical impact of minor histocompatibility antigens in matched related hematopoietic stem cell transplantation

Differential expression of minor histocompatibility antigens between the recipient and donor determines their disparity and can be modified by immunoproteasomes that regulate their processing and presentation. We examined the impact of HA-1 and HA-8 disparity, and immunoproteasome LMP7 polymorphism in 130 pairs. In multivariate analysis, HA-1 disparity showed a statistically significant association with an increased incidence of acute graft-versus-host disease (aGVHD) II-IV (p = 0.043, HR: 3.71, 95%CI = 1.04-13.26), while LMP7-Q/Q showed a trend toward increased incidence of aGVHD compared to LMP7-Q/K and K/K genotypes (p = 0.087, HR: 2.36, 95%CI = 0.88-6.31). All HA-1 and HA-8 disparate patients who developed aGVHD had the LMP7-Q/Q genotype. No significant association could be detected between HA-1, HA-8, or LMP7 and chronic GVHD, relapse-free survival (RFS), overall survival (OS), or transplant-related mortality (TRM). In conclusion, we suggested an association between the HA-1 disparity and the risk of developing aGVHD with a possible modifying effect of LMP7.

On the role of the immunoproteasome in transplant rejection

The immunoproteasome is expressed in cells of hematopoietic origin and is induced during inflammation by IFN-γ. Targeting the immunoproteasome with selective inhibitors has been shown to be therapeutically effective in pre-clinical models for autoimmune diseases, colitis-associated cancer formation, and transplantation. Immunoproteasome inhibition prevents activation and proliferation of lymphocytes, lowers MHC class I cell surface expression, reduces the expression of cytokines of activated immune cells, and curtails  T helper 1 and 17 cell differentiation. This might explain the in vivo efficacy of immunoproteasome inhibition in different pre-clinical disease models for autoimmunity, cancer, and transplantation. In this review, we summarize the effect of immunoproteasome inhibition in different animal models for transplantation.

The ubiquitin proteasome system as a potential therapeutic target for systemic sclerosis

The present review aims to summarize available knowledge on the role of the ubiquitin-proteasome system (UPS) in the pathogenesis of scleroderma and scleroderma-related disease mechanisms. This will provide the reader with a more mechanistic understanding of disease pathogenesis and help to identify putative novel targets within the UPS for potential therapeutic intervention. Because of the heterogenous manifestations of scleroderma, we will primarily focus on conserved mechanisms that are involved in the development of lung scleroderma phenotypes.