Organ donor circadian clocks in transplantation acceptance

SUMMARY Circadian rhythms are daily variations in biological function that adapt physiology to the earth’s day-night cycle18, 19. They arise from a hierarchal system consisting of a master pacemaker in the CNS that synchronizes autonomous circadian “clocks” found within all nucleated cells20, 104. Mounting evidence indicates the circadian system is important to medical interventions18, 19, 29. One reason for this is that circadian clocks temporally organize basic immune processes 2, 31, 32. Another reason is that circadian clocks regulate cellular defenses to metabolic and oxidative stress as occurs during ischemia-reperfusion injury46-49. Together, clock control of immunity and ischemic responses have implications for solid organ transplantation4-7, 105, 106. There is clinical evidence that the risk of solid organ graft dysfunction varies with the time of surgery4-7. However, prior studies of biological rhythms in transplantation do not examine biological mechanisms and focus almost exclusively on the transplant recipient. In this application, we show that brain-dead organ donors frequently exhibit rhythms in core body temperature and cortisol. They also exhibit functioning circadian clocks in transplantable organs like the lungs. Moreover, data in mice suggest that donor clocks and recipient clocks both are important for organ acceptance. Deleting the master clock gene Bmal1 in transplanted lungs or lung graft recipients exacerbates primary graft dysfunction (PGD), a form of ischemic lung injury. Finally, data suggest a pathway for these effects involving clock control of neutrophil glycolysis, which in turn regulates neutrophil extracellular trap (NET) formation. The goal of this proposal is to characterize circadian rhythms in organ donors and to identify mechanisms by which clocks in organ donors and recipients affect transplant acceptance. We focus here on the lung since long-term survival after lung transplantation remains poor (median of about 5 years9), and needs new approaches. Aim 1 will generate an atlas of brain-dead organ donors' biological rhythms and circadian clock function. It will also develop a spot assay to infer circadian clock time and robustness in donors. These experiments leverage a unique collaboration with Mid-America Transplant Services (MTS), a high-volume regional organ procurement organization in our area. Aim 2 will examine how the regulation of donor neutrophil glycolysis by master clock gene Bmal1 contributes to lung PGD. This Aim will employ an established mouse orthotopic lung transplant model to induce PGD in the presence or absence of Bmal1 or circadian clock disruption via chronic jet lag. Together, these two independent but complementary Aims will pioneer the study of biological rhythms in organ donors. It will characterize a novel immune-metabolic mechanism with the potential to improve transplanted organ acceptance. It directly answers NIH research priorities described in NOT-HL-22-043: Basic and Translational Research on Circadian Regulation of Heart, Lung, Blood, and Sleep Disorders.