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RS1-00198-1: Specification of Ventricular Myocyte and Pacemaker Lineages Utilizing Human Embryonic Stem Cells

Recommendation: Recommended if funds available
Scientific Score: 90

First Year Funds Requested: $321,249.00
Total Funds Requested: $609,999.00

Public Abstract (provided by applicant)

Heart failure is a leading cause of mortality in California and the United States. Currently, there are no “cures” for heart failure.Other life threatening forms of heart disease include dysfunction of cardiac pacemaker cells, necessitating implantation of mechanical pacemakers. Although mechanical pacemakers can be efficacious, there are potential associated problems, including infection, limited battery half-life, and lack of responsiveness to normal biological cues.

Our research with human embryonic stem cells will be aimed at developing therapies for heart failure, and cardiac pacemaker dysfunction. In each of these disease settings, one might effect a “cure” by replacing worn out or dysfunctional cardiac cells with new ones. In the case of heart failure, the cells that need to be replaced are heart muscle cells, which do the majority of the work in the heart. In the case of pacemaker dysfunction, the cells that need to be replaced are pacemaker cells, a highly specialized type of heart muscle cell. To replace these cells, we need to find cells that can become heart muscle or cardiac pacemaker cells, understand how to generate fairly large numbers of them, and how to persuade them to become either heart muscle or cardiac pacemaker cells. Potential cardiac progenitor cells may come from a number of different sources, either from patients themselves, or from extrinsic sources. Regardless of the source,we need to define factors which will make the cells multiply and will make them become the cell type that we need for repair.

The biology of human heart cells is likely to be distinctive from that of heart cells from other animals. For example, a human heart has to function for multiple decades, unlike hearts of other animals who live in general for shorter periods of time. The size, required function, and rhythm of the human heart are also distinct from that of other animals. For these reasons, for repair of human heart, it is important to study human cardiac progenitors and to define pathways required to grow them and to differentiate them utilizing human cells as a model experimental system.

Our proposed research will utilize human embryonic stem cells as a source of cardiac progenitors. As human embryonic stem cells can turn into many different kinds of cells, we will create special lines of human embryonic stem cells that will become fluorescent when they adopt the cardiac progenitor, heart muscle, or pacemaker state. These lines will then be treated with a large number of small molecules to find small molecules which amplify cells the number of fluorescent cells in each of these states. The small molecules activate known biochemical pathways, so we can then use the small molecules themselves, or activate identified pathways to achieve the goal of obtaining sufficient numbers of specific cardiac cell types for cardiac therapy.

Statement of Benefit to California (provided by applicant)

More Californians die each year of cardiovascular disease than from the next four leading causes of death combined. Californians continue to die or be disabled as a direct result of cardiovascular disease. Although advances in medical treatment have improved post-infarct survival, heart failure is an increasingly abundant manifestation of cardiovascular disease. A secondary complication of heart failure, and other cardiac diseases, is cardiac pacemaker dysfunction, a potentially fatal condition which is currently ameliorated by mechanical pacemakers. However, mechanical pacemakers have many associated complications,particularly for pediatric patients. For both heart failure and pacemaker dysfunction, replacement of heart muscle cells or biological pacemaker cells offers the hope of improving upon current medical practice. Our research is aimed toward developing new therapies which will allow for the replacement of these critical cell types in diseased heart.

Review

SYNOPSIS PROPOSAL: In this proposal, the investigators wish to generate cardiomyocytes from hESCs. This will be accomplished using genetically-engineered cells using a relevant reporter. Libraries of small molecules will be screened to identify those that support conversion to cardiomyocytes and subsequently to other cell types of the heart.

INNOVATION AND SIGNIFICANCE: This proposal targets the differentiation of cardiac cell types from hESC. These cells can then be used as both a platform to understand the basics of cell lineage specification and alternatively as a source of cell-based cardiovascular therapy. The Principal Investigator (PI) is a leader in the field.

Understanding the pathways required for specification, proliferation, and differentiation of hESC into cardiac cell lineages is a necessary and essential component for both the basic understanding of this important differentiation event as well as the potential for clinical settings. It is thus extremely significant and of the highest priority. This grant is also innovative, as it courageously tackles genetic engineering of hESCs, which unlike the mouse system, is in its infancy.

STRENGTHS OF THE PROPOSAL: The PI has a track record of high productivity in solving the molecular basis of lineage restrictions toward cardiac cell fates. Previous work from the applicant’s laboratory in model systems has established the basis of our current understanding in this lineage acquisition. Although technical problems are predicted, desired results would be of value. The small molecule screen has a reasonable chance of identifying compounds with desired activities.

WEAKNESSES OF THE PROPOSAL: Previous attempts in characterizing small molecules with specific activities toward the induction of a particular cell type using stably marked ES cells have been efficient in characterizing compounds. However, limiting factors downstream of this characterization have been to address the specificity of these compounds toward other biological activities. So while many good candidates can be identified by this type of approach, and most are very useful in the context of basic science approaches, it is not very clear how these compounds will be useful in clinical settings.

DISCUSSION: The proposal was regarded as very well written and very well reasoned. The use of non-federally-approved lines for screening is deemed a smart choice. It was felt that the use of these cells over federally-approved lines might also allow knock-in strategies to work, although there was concern that a two-step knock-in approach presents a significant challenge; the proposed back-up strategy was praised.

The following Working Group members had a conflict of interest with this application and were therefore recused from participating in review of, discussion of, and voting on the application:

• Lansing, Sherry