The overall long-term goal of our research is to improve heart transplant outcomes and well being of heart transplant patients. The data obtained from these studies will be utilized for developing novel selective immune therapies.
Main Research Areas
- Cardiac Transplantation
- Prevention and Treatment of Acute Cardiac Transplant Rejection
- Prevention and Treatment of Chronic Transplant Rejection (Heart and Lung)
- Role of Ubiquitination in Bcl-2 Regulation During Ischemia-Reperfusion Injury
- Apoptosis in Immune Activation and GCAD
- JAK-3 Inhibition in the Prevention of Chronic Airway Allograft Rejection (Transplant Immunology and Stem Cell Immunobiology Group)
- Role of Mast Cells in the Development of Acute and Chronic Rejection in Transplanted Hearts
- Effects of Prenylation Inhibitors on GCAD
- Prevention of Ischemic Cardiomyopathy
Cardiac Transplantation
Ischemia-Reperfusion injury and graft coronary
artery disease:
Anti-apoptotoc gene bcl-2 as a regulator of GCAD
Chronic rejection of allografts is mediated by a
tandem of alloantigen-dependent and -independent factors.
The oxidative stress inherent to the transplantation
procedure operates within a milieu of immunologic factors
that contribute to the later development of chronic
rejection. The aim of this study is investigate the
role that early myocardial oxidative stress signaling
pathways may have in the development of GCAD using
rodent heart transplant models. Our working hypothesis
is that myocardial oxidative stress following cardiac
transplantation contributes to the development of GCAD
via a bcl-2-associated mechanism.To dissect
the mechanisms by which anti-apoptotic bcl-2 protein
may regulate GCAD pathogenesis, we transplant cardiac
grafts expressing either genetically introduced anti-apoptotic
protein bcl-2 (bcl-2 Tg mice), or adenovirus-transferred
bcl-2 (rat model).
Among the results obtained so far are the following observations:
- Donor graft overexpression of bcl-2 attenuates GCAD, and is associated with reduction of intra-graft inflammatory cytokines
- Overexpression of bcl-2 in donor coronary artery smooth muscle cells leads to an early Th2 cytokine profile in rodent cardiac allografts
- Caspase-3 and -8 blockade reduces I/R directed apoptosis and inflammatory chemokine and cytokine production in donor rat allografts
We have accumulated evidence that suggest involvement of this oncogene in graft apoptosis, and in production of later cytokines (IL-4). Therefore, bcl-2 may interfere with GCAD development also at the alloantigen-dependent phase of host response, when adaptive immunity significantly contributes to graft outcome (for example, during CTL-mediated apoptosis). It has been suggested that oxidative stress might affect the selection of self-determinants presented for recognition by autoreactive CD4+ T cells. The contribution of bcl-2 to host anti-graft immunity has not been yet investigated. Among novel projects, there is one to answer the question whether bcl-2 mediates its protection at the stage of adaptive immune response, and how it can be connected to the events of early oxidation cascade.
Immune-mediated pathways of graft coronary
artery disease:
Cross-talk between alloresponse and tissue-specific
autoimmunity
Among immune pathways, host immunity to processed
fragments of donor MHC molecules (indirect alloresponse)
is known to play a major role in the pathogenesis of
chronic graft rejection. In addition, we have previously
found that the heart-specific antigen, cardiac myosin
(CM), serves as a target for the transplant-associated
immune response. CM is also a target autoantigen during
experimental autoimmune myocarditis, an experimental
mouse model for human myocarditis. In our experiments,
induction of post-transplant autoimmunity depended
on initial host alloresponsiveness. However, this process
could occur without activation of CD4 + T cell-mediated
direct alloimmunity, suggesting that the indirect alloresponse
is sufficient for the activation of the tissue-specific
response. This observation is supported by our studies
in another model in which allografts heart transplant
recipients develop chronic rejection in the absence
of direct alloimmunity. In this model, we have observed
high frequencies of inflammatory CM-specific T cells.
In addition, we have detected a T cell response to
dominant myocardiogenic CM peptide in the late post-transplantation
periods. This indicates that spreading of indirect
alloreactivity to tissue-specific autoimmunity could
contribute to perpetuation of GCAD.
Dr. M. Tanaka together with Dr. Monika Zwhether recently completed the study addressing the question: whether anti-CM response occurs in the course of natural GCAD in the absence of alloresponse? Using novel immunosuppression-free model of GCAD in mice (FVB (H-2 q) à DBA/1 (H-2 q)), they found that the CM-specific T cell response is induced during GCAD in the absence of direct alloreactivity, and that it is preceded by a low frequency indirect alloresponse and early production of IgG1 anti-myosin autoab. At late post-transplant periods, tissue-specific autoimmunity becomes the dominant form of host immune response (Figure 2). Recently, using another experimental mouse model, we found that CM-specific myocardial injury may influence the pathogenesis of chronic cardiac transplant rejection. The aim of this study is to analyze the capacity of CM-specific T cells and autoantibodies to mediate chronic cardiac allograft rejection in mice (supported by American Heart Association grant to EVF).
Prevention and Treatment of Acute Cardiac Transplant Rejection
JAK-3 Inhibition in Acute Rejection (Transplant Immunology and Stem Cell Immunobiology Group)
We have continued our research into the molecular biology of acute rejection of transplanted hearts. We have completed initial studies evaluating a panel of selective JAK-3 inhibitors in rodents, with very encouraging results. Animals treated with these drugs did not develop acute rejection during the study period. They experienced fewer and less severe side effects than the control group treated with standard immunosuppression. These molecules therefore appear capable of preventing acute rejection, with fewer side effects compared to the current regimens of anti-rejection drugs.
For more information, please refer to the Transplant Immunology and Stem Cell Immunobiology Group webpage.
Role of IL-17 in Acute Rejection
Numerous investigators have described the important role CD4 and CD8 T cell subsets play in the development of transplant rejection. Recently, a new CD4 effector cell subset that produces IL-17 (Th17) has emerged. Th17 cells promote autoimmunity in mice and have been implicated in the pathogenesis of human inflammatory diseases. IL-17 is a pro-inflammatory cytokine that activates T cells and ultimately results in the production of a variety of other cytokines, chemokines, and cell adhesion molecules. An interesting finding is the reciprocal developmental relationship between Th17 and regulatory T cells (Treg). In contrast to Th17 cells, Tregs control immune responses and are anti-inflammatory in nature. Our laboratory has found that donor hearts transplanted into IL-17 deficient mice develop tolerance. Interestingly, the tolerant recipients have increased numbers of Tregs within the donor hearts. The current goal of the laboratory is to understand the mechanism of Treg development in IL-17 deficient mice. Additionally we will study the role of IL-17 blockade in the prevention of chronic rejection.
Prevention and Treatment of Chronic Transplant Rejection (Heart and Lung)
Role of Ubiquitination in Bcl-2 Regulation During Ischemia-Reperfusion Injury
Over the past decade, our laboratory has demonstrated that increased cardiac allograft oxidative stress is associated with the development of chronic rejection, also known as Graft Coronary Artery Disease (GCAD). We found that increasing cold donor ischemia during heart transplantation increases both myocardial apoptosis and GCAD severity, and that this apoptosis was coupled with the reduction of one particular anti-apoptotic protein, Bcl-2. Moreover, donor organ Bcl-2 over-expression attenuates myocardial apoptosis, pro-inflammatory cytokine expression, and GCAD development. Recently, we have found that ubiquitination of Bcl-2 may regulate its function during ischemia. We postulate that myocardial ischemia/reperfusion injury leads to the ubiquitin-proteasome mediated Bcl-2 degradation, thereby promoting the following: (1) apoptosis of donor organ cells; (2) uptake of shed apoptotic antigen by antigen presenting cells; and (3) activation of the immune system. Therefore, the critical goal of our laboratory is to demonstrate how oxidative stress decreases donor organ Bcl-2 protein levels. An understanding of Bcl-2 regulation would result in potential new therapeutic targets. We are currently examining strategies to decrease Bcl-2 ubiquitination in order to prevent GCAD.
Apoptosis in Immune Activation and GCAD
We have reported that Bcl-2 over-expression can prevent the development of chronic rejection, however, the mechanism is unknown. Therefore, the aim of our laboratory is to identify mechanisms of Bcl-2 mediated GCAD reduction. We believe that Bcl-2 over-expression reduces the burden of shed donor organ apoptotic cells that could potentially activate the immune system. However, there exists conflicting findings regarding the ability of apoptotic cells to stimulate immune activation. This project attempts to illustrate that apoptotic endothelial cells, not only necrotic cells, activate the immune system and play a major role in the development of chronic rejection and eventual graft failure.
JAK-3 Inhibition in the Prevention of Chronic Airway Allograft Rejection (Transplant Immunology and Stem Cell Immunobiology Group)
Chronic rejection in lung transplant recipients, also known as Obliterative Bronchiolitis (OB), continues to be the major cause of death one year after lung transplantation.
JAK3, a tyrosine kinase vital for signal transduction cascades, especially the cytokine IL-2, prevents CD4 lymphocyte clonal expansion. Using a rat heterotopic trachea transplantation model, we have shown that JAK3 inhibition attenuates luminal obliteration, reduces mononuclear cell infiltration, and decreases donor reactive antibody compared to untreated recipients. Thus, JAK3 inhibition is an effective immunosuppressant in the prevention of OB and will provide a favorable alternative to other mainstream immunosuppressive medications.
After finding that JAK3 inhibition prevents OB in a rat heterotopic trachea transplantation model, our goal is to further elucidate mechanisms of JAK3 inhibition on respiratory epithelial preservation. Interestingly, preliminary studies illustrate MUC4 stabilization in the tracheal respiratory epithelium compared to untreated animals. We also plan to look at the role of effect of JAK3 inhibition on smooth muscle cells in both murine and human coronary artery smooth muscle cells proliferation assays.
For more information, please refer to the Transplant Immunology and Stem Cell Immunobiology Group webpage.
Role of Mast Cells in the Development of Acute and Chronic Rejection in Transplanted Hearts
Mast cells are known as primary responders in allergic reactions and innate immunity. Mast cells can produce an array of both pro- and anti-inflammatory mediators and can act as antigen-presenting cells. Investigators have detected mast cells at sites of chronic inflammation and in human transplanted organ specimens (heart, liver, kidney) presenting with severe rejection. However, recent studies in experimental rodent models have shown that mast cells may play a protective role and are anti-inflammatory condition in the heart, as well as in other organs. The critical goal of our laboratory is to investigate the role mast cells play in the development of both acute and chronic allograft rejection using mast cell-deficient mice. Specifically, we are continuing studies to determine if mast cells are pro- or anti-inflammatory in the setting of heart transplantation.
Effects of Prenylation Inhibitors on GCAD
HMG-CoA Reductase Inhibitors (statins) increase patient survival and decrease GCAD in human heart transplant patients, although the exact mechanism is unknown. HMG-CoA reductase is the rate-limiting step responsible for the conversion of mevalonate to cholesterol. In addition to decreasing cholesterol, HMG-CoA reductase inhibition also results in the reduction of two other end products: the isoprenoids, farnesyl and geranylgeranyl. Farnesyl and geranylgeranyl, 15 and 20 carbon hydrocarbon chains, respectively, are transferred to various proteins by Farnesyl Protein Transferase (FPT) and Geranylgeranyl Protein Transferase (GGPT), and are ultimately involved in cell signaling. Importantly, selective blockade of the isoprenoids have not been studied in transplant rejection models. The goal of the current study is to first compare the efficacy of HMG-CoA reductase pathway inhibition (statins) to the selective inhibition of isoprenoid metabolism in GCAD prevention. Secondly, we will determine if selective isoprenoid inhibition results in alterations in G-protein signaling in both the host immune system and in graft endothelial and smooth muscle cells. This will be the first study to evaluate the effects of prenylation inhibition on both recipient and graft responses to heart transplantation.
Prevention of Ischemic Cardiomyopathy
Role of Tempol in the Prevention of Ischemic Cardiomyopathy
Heart failure affects over 5 million patients in the United States, with 550,000 new patients diagnosed each year. Despite improvements in both medical and surgical therapies, almost 300,000 patients die with heart failure in the United States annually. Our laboratory has focused on the development of new treatment strategies for the prevention of ischemic cardiomyopathy after myocardial infarctions. We have found that Tempol (TPL), a nitroxyl radical, decreases infarct size and improves myocardial function after myocardial ischemia-reperfusion ex vivo, although the exact mechanism remains controversial. Currently, we are studying the protective mechanism of TPL. Our preliminary results suggest that the beneficial effects of TPL may be related to increased Hypoxia-inducible factor (HIF-1α) signaling in the early post-infarct period. HIF-1α is an oxygen-dependent transcriptional activator, which plays crucial roles in angiogenesis and cell proliferation/survival.
Back to top »
Lab Members Login