Lung Allograft Epithelium DNA Methylation Age Is Associated With Graft Chronologic Age and Primary Graft Dysfunction

Abstract

Advanced donor age is a risk factor for poor survival following lung transplantation. However, recent work identifying epigenetic determinants of aging has shown that biologic age may not always reflect chronologic age and that stressors can accelerate biologic aging. We hypothesized that lung allografts that experienced primary graft dysfunction (PGD), characterized by poor oxygenation in the first three post-transplant days, would have increased biologic age. We cultured airway epithelial cells isolated by transbronchial brush at 1-year bronchoscopies from 13 subjects with severe PGD and 15 controls matched on age and transplant indication. We measured epigenetic age using the Horvath epigenetic clock. Linear models were used to determine the association of airway epigenetic age with chronologic ages and PGD status, adjusted for recipient PGD risk factors. Survival models assessed the association with chronic lung allograft dysfunction (CLAD) or death. Distributions of promoter methylation within pathways were compared between groups. DNA methyltransferase (DNMT) activity was quantified in airway epithelial cells under hypoxic or normoxic conditions. Airway epigenetic age appeared younger but was strongly associated with the age of the allograft (slope 0.38 per year, 95% CI 0.27–0.48). There was no correlation between epigenetic age and recipient age (P = 0.96). Epigenetic age was 6.5 years greater (95% CI 1.7–11.2) in subjects who had experienced PGD, and this effect remained significant after adjusting for donor and recipient characteristics (P = 0.03). Epigenetic age was not associated with CLAD-free survival risk (P = 0.11). Analysis of differential methylation of promoters of key biologic pathways revealed hypomethylation in regions related to hypoxia, inflammation, and metabolism-associated pathways. Accordingly, airway epithelial cells cultured in hypoxic conditions showed suppressed DNMT activity. While airway methylation age was primarily determined by donor chronologic age, early injury in the form of PGD was associated with increased allograft epigenetic age. These data show how PGD might suppress key promoter methylation resulting in long-term impacts on the allograft.

The Association Between Frailty and Chronic Lung Allograft Dysfunction After Lung Transplantation

“…Emerging research shows that lung transplant-related injury may lead to accelerated aging in the graft and that senescence can be transmitted from transplanted cells. 13,14 Finally, it is possible that some latent driver of both frailty and CLAD could explain our findings. If it turns out that 1 of the latter 2 broad potential relationships is true, it would suggest that frailty may be an early "biomarker" of CLAD risk rather than lying on the causal pathway.…”

NKG2D receptor activation drives primary graft dysfunction severity and poor lung transplantation outcomes

“…For coculture experiments, primary human airway epithelial cells were seeded at 10,00 cells/well in sterile round-bottom 96-well plates and allowed to grow to 80%–90% confluence ( 61 ). Cells were exposed to hypoxia or normoxia for 24 hours.…”

The epigenetic legacy of ICU feeding and its consequences

“…Strategies to reduce such bias include adjusting for cell heterogeneity [68 ▪ ,77], purifying leukocyte subpopulations [58], or discarding any DNA-methylation differences potentially explained by changes in leukocyte composition [85,86]. Scarce studies used other samples and also found epigenetic abnormalities in muscle of adult critically ill patients [84 ▪ ], muscle stem cells of children after TBI [73 ▪ ], cerebrospinal fluid or surgically-resected brain biopsies of adult TBI patients [71 ▪ ,72], or airway epithelial cells from lung-transplant patients [70 ▪ ]. Second, due to the frequent urgency of ICU-admission, it is difficult to establish to what extent epigenetic abnormalities were already preexisting before ICU-admission or occurred de novo .…”

“…Epigenetic research found its way to the field of critical illness only recently. Whereas initial studies focused on animal models, the last few years epigenetic abnormalities have also been documented in adult and pediatric patients with different types of critical illness, including sepsis [58–66], transplant and other major surgery [67,68 ▪ ,69,70 ▪ ], traumatic brain injury (TBI) or other major trauma [71 ▪ ,72,73 ▪ ,74], acute pancreatitis [75], and COVID-19 [76–79,80 ▪ ,81,82,83 ▪ ], as well as in heterogeneous cohorts [84 ▪ ,85–86]. Most studies focused on DNA-methylation [58–60,63–65,67,68 ▪ ,69,70 ▪ ,71 ▪ ,72,73 ▪ ,80 ▪ ,83 ▪ ,84 ▪ ,85–86], but also histone-modification/chromatin-accessibility [58,69,82] and noncoding RNAs [61,62,66,69,74,81] have been investigated.…”