Dianne B. McKay

Reproduction and Transplantation: Report on the AST Consensus Conference on Reproductive Issues and Transplantation

Vincent T. Armenti, MD, PhD, Professor of Surgery, Temple University School of Medicine, Abdominal Transplant Program, Philadelphia, Pennsylvania

TLR2 is constitutively expressed within the kidney and participates in ischemic renal injury through both MyD88-dependent and -independent pathways.

TLRs are an evolutionarily conserved family of cell membrane proteins believed to play a significant role in innate immunity and the response to tissue injury, including that induced by ischemia. TLR signaling pathways activate transcription factors that regulate expression of prosurvival proteins, as well as proinflammatory cytokines and chemokines through one of two proximal adapter proteins, MyD88 or Toll/IL-1R domain-containing adaptor-inducing IFN-β (Trif). Our study defines the constitutive protein expression of TLR2 in kidneys of humans and mice, and provides insight into the signaling mechanisms by which a deficiency of TLR2 protects from ischemic organ injury. Our study compared and contrasted the effects of renal ischemia in wild-type mice and mice deficient in TLR2, MyD88, Trif, and MyD88 × Trif. TLR2 protein was evident in many cell types in the kidney, including renal tubules of the outer stripe of the medulla, glomeruli, and in the renal vasculature. The pattern of protein expression was similar in humans and mice. The absence of TLR2, MyD88, and MyD88 × Trif conferred both physiologic and histologic protection against sublethal ischemia at 24 h. Interestingly, TLR2-deficient mice were better protected from ischemic renal injury than those deficient for the adapter protein MyD88, raising the intriguing possibility that TLR-2-dependent/MyD88-independent pathways also contribute to kidney injury. We conclude that TLR2 protein is constitutively expressed in the kidney and plays an important role in the pathogenesis of acute ischemic injury by signaling both MyD88-dependent and MyD88-independent pathways.

Nonadherence Consensus Conference Summary Report

This report is a summary of a ‘Consensus Conference’ on nonadherence (NA) to immunosuppressants. Its aims were: (1) to discuss the state‐of‐the‐art on the definition, prevalence and measurement of NA, its risk factors and impact on clinical and economical outcomes and interventions and (2) to provide recommendations for future studies. A two‐day meeting was held in Florida in January 2008, inviting 66 medical and allied health adherence transplant and nontransplant experts. A scientific committee prepared the meeting. Consensus was reached using plenary and interactive presentations and discussions in small break‐out groups. Plenary presenters prepared a summary beforehand. Break‐out group leaders initiated discussion between the group members prior to the meeting using conference calls and e‐mail and provided a summary afterward. Conclusions were that NA: (a) is more prevalent than we assume; (b) is hard to measure accurately; (c) tends to confer worse outcomes; (d) happens for a number of reasons, and system‐related factors including the patients culture, the healthcare provider and the setting and (e) it is not currently known how to improve adherence. This consensus report provided some roadmaps for future studies on this complicated, multifaceted problem.

An Inflammasome-Independent Role for Epithelial-Expressed Nlrp3 in Renal Ischemia-Reperfusion Injury

Cytoplasmic innate immune receptors are important therapeutic targets for diseases associated with overproduction of proinflammatory cytokines. One cytoplasmic receptor complex, the Nlrp3 inflammasome, responds to an extensive array of molecules associated with cellular stress. Under normal conditions, Nlrp3 is autorepressed, but in the presence of its ligands, it oligomerizes, recruits apoptosis-associated speck-like protein containing a caspase recruitment domain (Asc), and triggers caspase 1 activation and the maturation of proinflammatory cytokines such as IL-1β and IL-18. Because ischemic tissue injury provides a potential source for Nlrp3 ligands, our study compared and contrasted the effects of renal ischemia in wild-type mice and mice deficient in components of the Nlrp3 inflammasome (Nlrp3−/− and Asc−/− mice). To examine the role of the inflammasome in renal ischemia-reperfusion injury (IRI) we also tested its downstream targets caspase 1, IL-1β, and IL-18. Both Nlrp3 and Asc were highly expressed in renal tubular epithelium of humans and mice, and the absence of Nlrp3, but not Asc or the downstream inflammasome targets, dramatically protected from kidney IRI. We conclude that Nlrp3 contributes to renal IRI by a direct effect on renal tubular epithelium and that this effect is independent of inflammasome-induced proinflammatory cytokine production.

Pregnancy after Kidney Transplantation

Reproductive success is a common, expected outcome for male and female recipients of solid-organ transplants. Men can father children, and women can become pregnant and carry the fetus to delivery. There are, however, important maternal and fetal complications that need to be considered to provide optimal care to the mother and her infant. Although pregnancy is common after the transplantation of all solid organs, guidelines for optimal counseling and clinical management are limited. This review discusses information to help the physician counsel the kidney transplant recipient about risks of pregnancy for the mother and the fetus and provides information to help guide treatment of the pregnant transplant recipient.

Nod1 and Nod2 Are Expressed in Human and Murine Renal Tubular Epithelial Cells and Participate in Renal Ischemia Reperfusion Injury

Nucleotide-binding oligomerization domain (Nod) 1 and Nod2 are members of a family of intracellular innate sensors that participate in innate immune responses to pathogens and molecules released during the course of tissue injury, including injury induced by ischemia. Ischemic injury to the kidney is characterized by renal tubular epithelial apoptosis and inflammation. Among the best studied intracellular innate immune receptors known to contribute to apoptosis and inflammation are Nod1 and Nod2. Our study compared and contrasted the effects of renal ischemia in wild-type mice and mice deficient in Nod1, Nod2, Nod(1 × 2), and in their downstream signaling molecule receptor-interacting protein 2. We found that Nod1 and Nod2 were present in renal tubular epithelial cells in both mouse and human kidneys and that the absence of these receptors in mice resulted in protection from kidney ischemia reperfusion injury. Significant protection from kidney injury was seen with a deficiency of Nod2 and receptor-interacting protein 2, and the simultaneous deficiency of Nod1 and Nod2 provided even greater protection. We conclude that the intracellular sensors Nod1 and Nod2 play an important role in the pathogenesis of acute ischemic injury of the kidney, although possibly through different mechanisms.

Inflammation in AKI: Current Understanding, Key Questions, and Knowledge Gaps

Inflammation is a complex biologic response that is essential for eliminating microbial pathogens and repairing tissue after injury. AKI associates with intrarenal and systemic inflammation; thus, improved understanding of the cellular and molecular mechanisms underlying the inflammatory response has high potential for identifying effective therapies to prevent or ameliorate AKI. In the past decade, much knowledge has been generated about the fundamental mechanisms of inflammation. Experimental work in small animal models has revealed many details of the inflammatory response that occurs within the kidney after typical causes of AKI, including insights into the molecular signals released by dying cells, the role of pattern recognition receptors, the diverse subtypes of resident and recruited immune cells, and the phased transition from destructive to reparative inflammation. Although this expansion of the basic knowledge base has increased the number of mechanistically relevant targets of intervention, progress in developing therapies that improve AKI outcomes by modulation of inflammation remains slow. In this article, we summarize the most important recent developments in understanding the inflammatory mechanisms of AKI, highlight key limitations of the commonly used animal models and clinical trial designs that may prevent successful clinical application, and suggest priority approaches for research toward clinical translation in this area.

Renal insufficiency and end-stage renal disease in the heart transplant population☆

BACKGROUND Renal insufficiency and end-stage renal disease (ESRD) are important problems in the cardiac transplant population, and are associated with significant morbidity, mortality and financial cost. We undertook this study to define pre-operative or early post-operative predictors of subsequent renal insufficiency and ESRD. METHODS We studied 370 patients at Brigham and Womens Hospital who received heart transplants between 1984 and 1999, with up to 10-year follow-up. We evaluated 2 time-dependent primary outcomes: early reduction in GFR, and development of ESRD at any timepoint. Cox proportional hazards modeling was used in both univariate and multivariate analyses. RESULTS The mean estimated glomerular filtration rate (GFR) fell 24% within the first post-transplant year, and remained stable thereafter. By actuarial analysis, 23% of patients developed a 50% reduction in GFR by the third year, and 20% developed ESRD by the tenth year of follow-up. In Cox multivariate analysis, significant predictors of post-transplant ESRD included: GFR <50 ml/min (hazards ratio [HR] 3.69, p = 0.024); high mean cyclosporine trough in the first 6 months (HR 5.10, p = 0.0059); and presence of diabetes (HR 3.53, p = 0.021). Conclusions about renal insufficiency outcome were limited by difficulties with accurate estimation of GFR and with definition of renal insufficiency. CONCLUSIONS The results of this study underscore the magnitude of the problem of renal insufficiency and ESRD in the heart transplant population. In addition, these data suggest that patients at high risk for these outcomes can be identified early, even pre-operatively, to guide post-operative management.

Signaling T‐Cell Survival and Death by IL‐2 and IL‐15

Interleukin 2 (IL‐2) and interleukin 15 (IL‐15) bind to common T‐cell surface receptors comprised of unique alpha (IL‐2Rα or IL‐15Rα) and shared β/γ chain subunits. Ligation of this receptor by IL‐2 can lead to apoptosis whereas IL‐15 ligation favors cell survival. Our study examined intra‐cellular signaling events associated with IL‐2‐ and IL‐15‐induced apoptosis and survival in human T cells. We found IL‐2 and IL‐15 could both induce apoptosis and survival; the outcome depended on cytokine concentration. No qualitative differences in Jak/Stat, Ras/MAPK or PI3K/AKT signaling were seen over a wide range of IL‐2 and IL‐15 concentrations. These findings suggest that, like T‐cell receptor signaling, IL‐2R β/γ chain signaling is regulated, or “tuned,” by the concentration of cytokine.

Defects in Skin γδ T Cell Function Contribute to Delayed Wound Repair in Rapamycin-Treated Mice

Disruptions in the normal program of tissue repair can result in poor wound healing, which perturbs the integrity of barrier tissues such as the skin. Such defects in wound repair occur in transplant recipients treated with the immunosuppressant drug rapamycin (sirolimus). Intraepithelial lymphocytes, such as γδ T cells in the skin, mediate tissue repair through the production of cytokines and growth factors. The capacity of skin-resident T cells to function during rapamycin treatment was analyzed in a mouse model of wound repair. Rapamycin treatment renders skin γδ T cells unable to proliferate, migrate, and produce normal levels of growth factors. The observed impairment of skin γδ T cell function is directly related to the inhibitory action of rapamycin on mammalian target of rapamycin. Skin γδ T cells treated with rapamycin are refractory to IL-2 stimulation and attempt to survive in the absence of cytokine and growth factor signaling by undergoing autophagy. Normal wound closure can be restored in rapamycin-treated mice by addition of the skin γδ T cell-produced factor, insulin-like growth factor-1. These studies not only reveal that mammalian target of rapamycin is a master regulator of γδ T cell function but also provide a novel mechanism for the increased susceptibility to nonhealing wounds that occurs during rapamycin administration.