Expression, subcellular localisation, and possible roles of dipeptidyl peptidase 9 (DPP9) in murine macrophages

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

The effect of CD26-deficiency on dipeptidyl peptidase 8 and 9 expression profiles in a mouse model of Crohn's disease

The involvement of dipeptidyl peptidase (DP) IV/CD26 (DPP IV/CD26) family members in the pathogenesis of Crohn's disease (CD), an autoimmune inflammatory condition of the gut, is effected mainly through proteolytic cleavage of immunomodulatory substrates and DPP IV/CD26's costimulatory function. DP8 and DP9 are proteases with diverse functions including cell interactions, apoptosis, and immune response but their localization remains to be clarified. We assessed the impact of DPP IV/CD26 deficiency (CD26^-/- ) on the expression profiles of DP8 and DP9 by qPCR and immunodetection as well as quantified DP8/9 enzyme activity in distinctive phases of a chemically-induced CD model in mice. CD26^-/- did not affect colon DP8 mRNA expression, while the physiological concentration of DP8 protein is decreased in CD26^-/- mice but rises in inflammation (P < 0.05). On the other hand, DP9 mRNA level is significantly increased in CD26^-/- mice in inflammation as well as healing with the DP9 concentration being almost twofold increased (P < 0.05) in all experimental points in CD26^-/- mice compared to wild-type indicating the expected up-regulation in CD26^-/- conditions. Surprisingly, dominantly intracellular DP8 and DP9 were found in abundance in serum. DP8/9 activity is decreased in the inflamed colon, whereas its contribution to the overall serum DPP IV/CD26-like activity is negligible, suggesting the importance of their extra-enzymatic functions. To summarize, CD induction generated gene, protein and enzymatic changes of DP8 and DP9 so their involvement in inflammation development and/or healing process is implicated, especially in CD26^-/- , and the question of their subcellular localization should be revised.