New opportunities for organ transplantation research: epigenetics is likely to be an important determinant of the host immune response

Unveiling the Role of DNA Methylation in Kidney Transplantation: Novel Perspectives toward Biomarker Identification

The burden of chronic kidney disease is dramatically rising, making it a major public health concern worldwide. Kidney transplantation is now the best treatment for patients with end-stage renal disease. Although kidney transplantation may improve survival and quality of life, its long-term results are hampered by immune- and/or non-immune-mediated complications. Thus, the identification of transplanted patients with a higher risk of posttransplant complications has become a big challenge for public health. However, current biomarkers of posttransplant complications have a poor predictive value, rising the need to explore novel approaches for the management of transplant patient. In this review we summarize the emerging literature about DNA methylation in kidney transplant complications, in order to highlight its perspectives toward biomarker identification. In the forthcoming future the monitoring of DNA methylation in kidney transplant patients could become a plausible strategy toward the prevention and/or treatment of kidney transplant complications.

Variations in DNA methylation of interferon gamma and programmed death 1 in allograft rejection after kidney transplantation

Background

The role of DNA methylation in the regulation of the anti-donor-directed immune response after organ transplantation is unknown. Here, we studied the methylation of two mediators of the immune response: the pro-inflammatory cytokine interferon γ (IFNγ) and the inhibitory receptor programmed death 1 (PD1) in naïve and memory CD8+ T cell subsets in kidney transplant recipients receiving immunosuppressive medication. Both recipients experiencing an episode of acute allograft rejection (rejectors) as well as recipients without rejection (non-rejectors) were included.

Results

CpGs in the promoter regions of both IFNγ and PD1 were significantly (p < 0.001) higher methylated in the naïve CD8+ T cells compared to the memory T cell subsets. The methylation status of both IFNγ and PD1 inversely correlated with the percentage of IFNγ or PD1-producing cells. Before transplantation, the methylation status of both IFNγ and PD1 was not significantly different from healthy donors. At 3 months after transplantation, irrespective of rejection and subsequent anti-rejection therapy, the IFNy methylation was significantly higher in the differentiated effector memory CD45RA+ (EMRA) CD8+ T cells (p = 0.01) whereas the PD1 methylation was significantly higher in all memory CD8+ T cell subsets (CD27+ memory; p = 0.02: CD27− memory; p = 0.02: EMRA; p = 0.002). Comparing the increase in methylation in the first 3 months after transplantation between rejectors and non-rejectors demonstrated a significantly more prominent increase in the PD1 methylation in the CD27− memory CD8+ T cells in rejectors (increase in rejectors 14%, increase in non-rejectors 1.9%, p = 0.04). The increase in DNA methylation in the other memory CD8+ T cells was not significantly different between rejectors and non-rejectors. At 12 months after transplantation, the methylation of both IFNγ and PD1 returned to baseline levels.

Conclusions

The DNA methylation of both IFNγ and PD1 increases the first 3 months after transplantation in memory CD8+ T cells in kidney transplant recipients. This increase was irrespective of a rejection episode indicating that general factors of the kidney transplantation procedure, including the use of immunosuppressive medication, contribute to these variations in DNA methylation.

Epigenetics in Kidney Transplantation: Current Evidence, Predictions, and Future Research Directions

Epigenetic modifications are changes to the genome that occur without any alteration in DNA sequence. These changes include cytosine methylation of DNA at cytosine-phosphate diester-guanine dinucleotides, histone modifications, microRNA interactions, and chromatin remodeling complexes. Epigenetic modifications may exert their effect independently or complementary to genetic variants and have the potential to modify gene expression. These modifications are dynamic, potentially heritable, and can be induced by environmental stimuli or drugs. There is emerging evidence that epigenetics play an important role in health and disease. However, the impact of epigenetic modifications on the outcomes of kidney transplantation is currently poorly understood and deserves further exploration. Kidney transplantation is the best treatment option for end-stage renal disease, but allograft loss remains a significant challenge that leads to increased morbidity and return to dialysis. Epigenetic modifications may influence the activation, proliferation, and differentiation of the immune cells, and therefore may have a critical role in the host immune response to the allograft and its outcome. The epigenome of the donor may also impact kidney graft survival, especially those epigenetic modifications associated with early transplant stressors (e.g., cold ischemia time) and donor aging. In the present review, we discuss evidence supporting the role of epigenetic modifications in ischemia-reperfusion injury, host immune response to the graft, and graft response to injury as potential new tools for the diagnosis and prediction of graft function, and new therapeutic targets for improving outcomes of kidney transplantation.