Mobility is critical for human social interactions and quality of life. In the aged mobility is progressively impaired due to painful joints. The articular cartilage in the joints is damaged. The long-term goal of our research is the utilization of human embryonic stem cells (hESCs) for cartilage formation and therefore, regeneration of articular cartilage. Stem cells have enormous potential. Their potential can be directed by morphogens governing chondrogenesis. Bone and cartilage morphogenetic proteins induce stem cells to form cartilage cells. This research will contribute directly to the development of therapy for osteoarthritis for the aging Californians.
The State of California is a magnet for people from all over the world who seek opportunities for employment and improving the quality of life. However, it is inevitable that as Californians become older and old, their mobility is decreased due to painful joints due to osteoarthritis. Osteoarthritis is a common painful malady of the aging Californians. The proposed research on harnessing the potential of human embryonic stem cells to differentiate into articular cartilage can contribute novel strategies to regenerate damage articular cartilage.
SYNOPSIS: In this proposal the investigators wish to determine if hESCs can be induced to differentiate to articular cartilage. This will be achieved by a combination of specific morphogens, as well as by subjecting the precursors generated from ESCs to mechanical shear forces known to play a role in articular cartilage phenotype. the phenotype of such "articular cartilage" will then be extensively studied with other gene array analyses.
SIGNIFICANCE AND INNOVATION: As the population ages, problems like osteoarthritis become more prevalent. Developing stem cell-based or -derived therapies to repair cartilage are therefore significant. Studying mesenchyme formation and subsequent articular cartilage formation from hESCs might yield cells to gain novel insights in the earliest developemntal steps and processes in humans. Little work on differentiation of hESCs to chondrocytes has been done to date, so the work is innovative, and potentially could lead to translational therapies in a relatively short time frame.
STRENGTHS: A major strength of the proposal is the deep experience of the PI in chondrocyte and bone biology. The PI of the proposal has a longstanding and outstanding track-record in studies directed towards articular cartilage differentiation and repair. He and his team are very knowledgeable regarding the methods to be used that may induce ESCs to this cell type. The proposal is very well written, and possible pitfalls addressed.
WEAKNESSES: Although studies aimed at differentiation of hESCs are relatively novel (even though a number of recent papers have demonstrated that this is possible), the primary reviewer would have liked to see a comparative study, which will be needed to determine whether ESCs are a superior source of cells to be used in cartilage repair. If that were not to be the case, MSCs would be a much safer source of cells. The possibility of teratoma formation from ESC-derived cartilage progenitors and cartilaginous tissue is addressed by the PI although no methods are designed to circumvent such a problem. Microarray studies are proposed to characterize the articular cartilage generated from ESCs. It is acknowledged that this may be hard to interpret due to impurity of the to-be-tested cell population. What is also not addressed is what will be done using the information gained, and how this will be applied to improve or alter differentiation methods.
The secondary reviewer noted that the PI is an expert in the area chosen, so despite the lack of hESC experience, the work is not high risk and likely to be informative. However, the time frame for the initial and most important aim may be a little underestimated because of the pace of differentiation of hESCs, the numbers of lines the PI proposes to examine, and because the initial plan may not work. It may be necessary, for example, to induce the cells to a mesenchymal precursor, and then add the BMP/TGFbeta. Although the PI states that no work has been done in this area (perhaps the papers came out as the grant was being written) there are now several publications about chondrocyte generation from hESCs, and there may be some time-saving steps in this literature that could benefit the PI. Getting started may also be a little problematic since it seems most of the hands-on work is going to be done by a post-doctoral fellow to be named. So there is some concern that the optimization of differentiation will take longer than expected, leaving little time for the aims. Finally, the aims might be achieved earlier if not so many cell lines were examined.
DISCUSSION: The PI is considered the "father of this field", as the first person to describe ectopic bone formation and bone morphogenetic proteins. Although it would be a strong investment for CIRM to develop methods for cartilage formation, there is a "me too" element in the proposal now that there are several publications that describe the differentiation of hESCs into chondrocytes. The PI will look at the effects of pressure on cartilage made in the laboratory from hESCs, and compare gene expression on hESC-made cartilage compared to real cartilage. Reviewers recommend that the investigator study expression patterns during differentiation. The third aim of articular cartilege characterization by DNA microarray was considered the weakest aim. It is not clear what the PI will do with the results of this work, especially the microarray data. Note that 3 reviewers commented on this proposal and conveyed their enthusiam.