Congenital and acquired defects of cardiac pacemakers are leading causes of morbidity and mortality in our society. Dysfunctions of the SA node and the lower conduction cells lead to a variety of complex arrhythmias that typically necessitate anti-arrhythmic therapy and implantation of devices. These treatments have significant limitations in their efficacy and risk-benefit ratio. Thus, it would be ideal to generate cell-based therapeutic approaches towards treating arrhythmias. Experimental data has provided compelling evidence that pacemaker and conduction cells of the heart separate early in development from the working myocardium and retain a relatively undifferentiated state. Prior cell-based approaches in regenerating myocardial damage in the heart have met limited success in part due to implantation of a diverse population of cells. This generally results in poor engraftment and undesirable outcomes. There is now evidence for resident conduction progenitor cells in myocardium that orchestrate the process of cell recruitment into the conduction tissue. In the current proposal we aim to identify the molecular events that lead to differentiation and formation of cardiac pacemaker cells. We will utilize the information obtained from the above experiments to generate cell based methods to treat cardiac arrhythmias. We aim to genetically manipulate the human embryonic stem cells so we can identify a selected population that is destined to become pacemaker cells. By replacing the cells responsible for normal beating of the heart, we hope to provide natural therapies for human conduction system disease
Statement of Benefit to California:
The ultimate of goal of our proposal is identify a reliable mechanism for implementing a cell-based approach for treating human arrhythmias. Sudden cardiac death related to cardiac arrhythmia is a leading cause of morbidity and mortality in our society. The people of California have voted to implement new innovative ways of treating human disease by using human stem cells, the current project is in line with such wishes to create new therapeutic modalities towards treating heart disease.
Year 1Cardiovascular disease is a major source of morbidity and mortality in our society. In this case, cardiac arrhythmias are leading cause of sudden cardiac death. Therefore, it is empirical to identify the source and mechanisms of cardiac arrhythmias. The long-term objectives of our laboratory is identify the key molecules that are involved in differentiation and formation of cardiac conduction system. We utilize mouse as a model system to identify the molecular pathways leading the formation of cardiac conduction cells.
In the past year we have identified some of regulatory pathways that allows for the proper formation of cardiac conduction tissue. We are using mice that have specific mutations in the cells of cardiac conduction system to identify these special pathways. One such molecule that orchestrates the differentiation of cardiac conduction cells is Nkx2-5. We have determined that loss of this transcription factor is of significant detriment to the health of cardiac conduction and is the underlying factor in common arrhythmias. Our ultimate goal is to utilize the information obtained by our studies in mice, and apply them towards therapeutic functions in humans. To this end, we are trying to develop a mechanism to reprogram cardiac stem cells to behave like conduction system cells. Ultimately, this approach would be used towards stem cell therapy for cardiac arrhythmias.
Year 2 A leading cause of heart related morbidity and mortality is cardiac rhythm disturbances. In fact sudden cardiac death is primarily due to abnormalities of cardiac electrical conduction abnormalities. At present, the therapeutic approaches to treatment of cardiac arrhythmias are limited to cardiac device including pacemakers and defibrillators. These devices are expensive and carry additional risks to the patients during after surgical implantation. Our overall goal is to identify the key regulatory pathways that lead to differentiation and formation of various cells type of cardiac conduction cells.
Our laboratories focuses on the molecular pathways that guide the formation of distinct cell types in the human heart. The proper formation of these cell types from a unique cardiac progenitor is an important, yet complex biological question that our laboratory is aiming to answer. In this regard, in the past year we have identified a unique molecular pathway by which a unique population of cardiac progenitor cells are added to heart and also participate in the formation and patterning of the cardiac pacemaker cells. We are using mouse models to study the formation of cardiac stem cells and also the mechanisms by which they acquire distinct identities. To this end, our mutant mouse models display abnormal formation of the SA node which is the primary site of cardiac beating. By studying the mutant mice generated by genetic manipulation of stem cells, we aim to further advance our knowledge of different forms of cardiac stem cell formation. During the past year we have made significant progress in elucidating the ways by which cardiac progenitor cells contribute the pacemaker cell formation and putting forth new paradigms for cardiac pacemaker stem cell formation.
Year 3Heart disease is a major cause of morbidity and mortality in our society. Congestive heart failure and cardiac arrhythmias are the most common mechanism by which heart disease leads to sudden cardiac death. Genetic studies in the general population have determined that susceptibility to cardiac arrhythmia and congestive heart failure is due to mutations in certain genes that guide cardiac development. Specifically, mutations in certain molecules called transcription factors are the leading mechanisms by which genetic defects lead to congenital heart defects and cardiac arrhythmias. Our laboratory studies the mechanism by which transcription factors and signaling molecules guide cardiac development and lead to selective formation of different cardiac cells. Our laboratory has pioneered work that has lead to the discovery of mutations that lead to cardiac arrhythmia and heart failure. In the past year, we have made steady progress in characterization of some of the key factors that guide cardiac cell development. To this end, we have identified a molecule called R-spondin-3 (Rspo3) that is critical for cardiac cell growth and probably survival. We have determined that Rspo3 functions to keep cardiac cell proliferating and loss of Rspo3 leads to thin cardiac muscle and heart failure. The mutation of Rspo3 in mouse leads to not only heart failure, but also leads to arrhythmias and valvlular heart disease. Therefore, Rspo3 functions in multiple aspect cardiac development and plays an essential role in proliferation of resident cardiac stem cells. Since, Rspo3 is known to function in a specific cardiac pathway called Wnt pathway, our hypothesis is that Rspo3 is a needed growth factor that is guiding cardiac stem cells towards growth and proliferation. We have submitted a manuscript about our work with Rspo3.
Our laboratory has also identified a molecule called OSR1 which plays a critical role in cardiac septation and development of conduction system. Mice that lack Osr1 have defects in atrial septation and show evidence of cardiac arrhythmias. We are in the process of submitting a manuscript that describes our results with OSR1. In summary, the generous funding by CIRM has helped us identify important new molecules with novel mechanisms critical in cardiac development.