Organoid technology holds great promise for regenerative medicine but has not yet been applied to humans. We address this challenge using cholangiocyte organoids in the context of cholangiopathies, which represent a key reason for liver transplantation. Using single-cell RNA sequencing, we show that primary human cholangiocytes display transcriptional diversity that is lost in organoid culture. However, cholangiocyte organoids remain plastic and resume their in vivo signatures when transplanted back in the biliary tree. We then utilize a model of cell engraftment in human livers undergoing ex vivo normothermic perfusion to demonstrate that this property allows extrahepatic organoids to repair human intrahepatic ducts after transplantation. Our results provide proof of principle that cholangiocyte organoids can be used to repair human biliary epithelium.

During heart transplantation, storage in cold preservation solution is thought to protect the organ by slowing metabolism; by providing osmotic support; and by minimising ischaemia-reperfusion (IR) injury upon transplantation into the recipient 1,2 . Despite its widespread use our understanding of the metabolic changes prevented by cold storage and how warm ischaemia leads to damage is surprisingly poor. Here, we compare the metabolic changes during warm ischaemia (WI) and cold Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Aims Succinate accumulates several-fold in the ischemic heart and is then rapidly oxidised upon reperfusion, contributing to reactive oxygen species (ROS) production by mitochondria. In addition, a significant amount of the accumulated succinate is released from the heart into the circulation at reperfusion, potentially activating the G-protein coupled succinate receptor (SUCNR1). However, the factors that determine the proportion of succinate oxidation or release, and the mechanism of this release, are not known. Methods and results To address these questions, we assessed the fate of accumulated succinate upon reperfusion of anoxic cardiomyocytes, and of the ischemic heart both ex vivo and in vivo. The release of accumulated succinate was selective and was enhanced by acidification of the intracellular milieu. Furthermore, pharmacological inhibition, or haploinsufficiency of the monocarboxylate transporter 1 (MCT1) significantly decreased succinate efflux from the reperfused heart. Conclusion Succinate release upon reperfusion of the ischemic heart is mediated by MCT1 and is facilitated by the acidification of the myocardium during ischemia. These findings will allow the signalling interaction between succinate released from reperfused ischemic myocardium and SUCNR1 to be explored. Translational Perspectives In this study we demonstrate that succinate efflux upon reperfusion of the ischemic myocardium is mediated by the monocarboxylate transporter 1 (MCT1) and is enhanced by the ischemic acidification of the heart. These findings are an important advance in understanding how succinate is released upon reperfusion of ischemic organs. While this pathway is therapeutically tractable, greater understanding of the effects of succinate release is required before exploring this possibility.

Acute kidney injury (AKI) remains a major problem in critically unwell children and young adults. Ischaemia reperfusion (IR) injury is a major contributor to the development of AKI in a significant proportion of these cases and mitochondria are increasingly recognised as being central to this process through generation of a burst of reactive oxygen species early in reperfusion. Mitochondria have additionally been shown to have key roles in downstream processes including activation of the immune response, immunomodulation, and apoptosis and necrosis. The recognition of the central role of mitochondria in IR injury and an increased understanding of the pathophysiology that undermines these processes has resulted in identification of novel therapeutic targets and potential biomarkers. This review summarises a variety of therapeutic approaches that are currently under exploration and may have potential in ameliorating AKI in children in the future.

Purpose Mitochondrial reactive oxygen species (ROS) production upon reperfusion of ischemic tissue initiates the ischemia/ reperfusion (I/R) injury associated with heart attack. During ischemia, succinate accumulates and its oxidation upon reperfusion by succinate dehydrogenase (SDH) drives ROS production. Inhibition of succinate accumulation and/or oxidation by dimethyl malonate (DMM), a cell permeable prodrug of the SDH inhibitor malonate, can decrease I/R injury. However, DMM is hydrolysed slowly, requiring administration to the heart prior to ischemia, precluding its administration to patients at the point of reperfusion, for example at the same time as unblocking a coronary artery following a heart attack. To accelerate malonate delivery, here we developed more rapidly hydrolysable malonate esters. Methods We synthesised a series of malonate esters and assessed their uptake and hydrolysis by isolated mitochondria, C2C12 cells and in mice in vivo. In addition, we assessed protection against cardiac I/R injury by the esters using an in vivo mouse model of acute myocardial infarction. Results We found that the diacetoxymethyl malonate diester (MAM) most rapidly delivered large amounts of malonate to cells in vivo. Furthermore, MAM could inhibit mitochondrial ROS production from succinate oxidation and was protective against I/R injury in vivo when added at reperfusion. Conclusions The rapidly hydrolysed malonate prodrug MAM can protect against cardiac I/R injury in a clinically relevant mouse model.