A new paradigm of lineage-specific reprogramming
Recently, we devised and reported a new regenerative medicine paradigm that entails temporal/transient overexpression of induced pluripotent stem cell based reprogramming factors in skin cells, leading to the rapid generation of “activated” cells, which can then be directed by specific growth factors and small molecules to “relax” back into various defined and homogenous tissue-specific precursor cell types (including nervous cells, heart cells, blood vessel cells, and pancreas and liver progenitor cells), which can be expanded and further differentiated into mature cells entirely distinct from fibroblasts.
In this proposal, combined with small molecules that can functionally replace reprogramming transcription factors as well as substantially improve reprogramming efficiency and kinetics, we aim to further develop and mechanistically characterize chemically defined, non-integrating approaches (e.g., mRNA, miRNA, episomal plasmids and/or small molecule-based) to robustly and efficiently reprogram skin fibroblast cells into expandable heart precursor cells. Specifically, we will: determine if we can use non-integrating methods to destabilize human fibroblasts and facilitate their direct reprogramming into the heart precursor cells; characterize of heart cells generated by the direct programming methods, both in the tissue culture dish and in a mouse model of heart attack; and characterize newly identified reprogramming enhancing small molecules mechanistically.
This study will develop and mechanistically characterize a new method of generating safe patient specific heart cells that could be useful in treating heart failure which afflicts millions of Californians and accounts for billions of dollars in healthcare spending annually. Additionally, the small molecules discovered in this study could be good candidates for future drug development as well as being broadly useful for other regenerative medicine applications. These advances could also be a platform for new personalized medicine/ cell banking businesses which could bring economic growth in addition to improving the health of Californians.
During the reporting period, we have made very significant progress toward the following research aims: (1) Using the Oct4-based reprogramming assay system established, we were able to screen for and identify small molecules that can replace the other three genes in the Cell-Activation and Signaling-Directed (CASD) lineage conversion paradigm for reprogramming fibroblasts into cardiac lineage. (2) Using in-depth assays, we have examined the process using lineage-tracing methods and characterized those Oct4/small molecules-reprogrammed cardiac cells in vitro. (3) Most importantly, we were able to identify a baseline condition that appears to reprogram human fibroblasts into cardiac cells using defined conditions.
Cardiomyocyte-like cells can be reprogrammed from somatic fibroblasts by combinations of genes in vitro1 and in vivo, providing a new avenue for cardiac regenerative therapy. However, transdifferentiating human cells to generate fully functional cardiomyocytes remains a challenge. Moreover, genetic manipulations with multiple factors used in such conventional strategies pose safety, efficacy, and technical concerns that may limit their clinical potential. In the work funded by CIRM we identified and demonstrated that functional cardiomyocytes can be rapidly and efficiently generated from fibroblasts by a combination of small molecules. These cardiomyocytes express characteristic cardiac markers, have a well-organized sarcomeric structure, contract spontaneously, and respond to pharmacological modulations. They closely resemble cardiomyocytes in their global gene expression profiles, and electrophysiological properties. This novel pharmacological reprogramming approach may have important implications in cardiac regenerative medicine.