Differential effect of DJ-1/PARK7 on development of natural and induced regulatory T cells

Regulatory T cells (Tregs) are pivotal for maintenance of thymic and peripheral self-tolerance and protection against unwanted collateral damage induced during inflammation1,2. In addition, these cells are similarly induced in bacterial infections such as Mycobacterium tuberculosis and debilitate the host to combat the infection3. Tregs further promote the growth of cancer4,5. Tregs not only modulate adaptive immunity but are also involved in the modulation of innate immunity6. Adequate development and function of Tregs is thus vital to maintain the homeostatic balance and overcome pathological conditions. Accordingly, Tregs are an attractive immunotherapeutic target7. Tregs are generated in the thymus designated as natural Tregs (nTregs) and in the peripheral organs by antigen driven conversion of naive CD4+ T cells in the presence of TGF-β and IL-2 considered as induced Tregs (iTregs)8. The Fork-head box p3 (Foxp3) transcription factor governs most of the functions and developmental pathways of both thymic and peripheral Tregs. Induction of Foxp3 in peripheral naive T cells is controlled by various pathways such as Phosphatidylinositide 3-kinase (PI3K)/AKT/mTOR and TGF-β/SMAD2/39,10. The proteins involved in these pathways are instrumental in modulating the functions and development of Tregs. Potential regulators of PI3K-dependent signalling include Parkinsons Disease Protein 7 (PARK7) or Oncogene DJ-1 (PARK7 or DJ-1), which negatively regulate the Phosphatase and tensin homolog (PTEN) acivity11,12 thus leading to activation of the PI3K pathway. Increased activity of PI3K-dependent AKT/mTOR signalling fosters cell growth and proliferation and downregulates Foxp3 protein, a transcription factor decisive in the development of Tregs (Tregs)13,14. DJ-1 or PARK7 is ubiquitously expressed in human tissues and might play an important role in post-transcriptional gene expression15,16. Furthermore, DJ-1 acts as a positive transcriptional co-regulator of the androgen receptor (AR) by preventing protein inhibitor of activated STAT (PIASxα)/androgen receptor interacting protein 3 (ARIP3) and DJ-1 binding protein (DJBP)17. This protein is a redox-sensitive chaperone and protects neurons and the heart against oxidative stress and cell death15,18. Deletion of the DJ-1 gene exacerbates the progression of Parkinson´s disease19. As DJ-1 protein is also involved in the regulation of cell survival through AKT/mTOR, it protects cancer cells against hypoxia-induced cell death and is required for adaptation to hypoxic stress12. In cardiomyocytes, the DJ-1/PTEN/AKT pathway similarly protects against oxidative stress18,20,21. Oxidative stress engaged defences induce transient, mild mitochondrial depolarization22. Recent observations suggest that DJ-1 protein regulates CD3+ T cell migration through controlling the expression of the CXCR4 receptor23. However, to the best of our knowledge, an impact of the DJ-1 protein in the CD4+CD25+Foxp3+ regulatory T cell development has not been reported. Here, we show (based on Foxp3 flow staining) that DJ-1 deficiency leads to enhanced percentage of thymic as well as peripheral nTregs in the CD4+ T cells compartment. DJ-1 deficiency further modifies the CD4+/CD8+ T cell ratio. DJ-1 deficient mice have lower total number of CD4+ T cells compared to control littermates in both thymus and spleen. However, when naive T cells are differentiated into induced Tregs (iTregs) using TGF-β and IL-2, Foxp3 induction was significantly attenuated in DJ-1 deficient mice, which was contrary to naturally occurring peripheral Tregs development. Functions of nTregs from both mice strains were not impaired. Furthermore, DJ-1 deficient iTregs also had defective cell cycle progression and were more prone to cell death compared to the respective WT cells. Additionally, iTregs from DJ-1 mice were less sensitive towards phosphorylation of Smad2 and Stat5 proteins and had higher AKT phosphorylation and Rictor/mTOR activity, which could lead to impaired development. Thus, our data reveals a unique role of DJ-1 in iTregs development.