Stem cells (both normal and cancerous) are defined by their ability to self-renew, in order to maintain their numbers, and their ability to differentiate into distinct cell types.  Our lab is interested in uncovering new pathways regulating these stem cell properties. We are particularly interested in characterizing the functions of apoptotic proteins in maintaining self-renewal and pluripotency and in the regulation of differentiation and reprogramming. Using genetics, biochemistry, proteomics and live cell imaging we are uncovering the role of apoptotic proteins for the maintenance of the stem cell phenotype. We use embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and cancer stem cells (Glioblastoma and Medulloblastoma) as model systems.

Regulation of apoptotic proteins during differentiation. The initial step of differentiation of hES cells into any lineage can be achieved by growing the cells in suspension on a non-adherent surface where they form aggregates known as embryoid bodies (EBs). EBs provide an environment that mimics early embryonic development and can hence be used for the differentiation of hES cells towards specific lineages. Interestingly, Bax was no longer present in its active state after just two days of differentiation into EBs.Consistent with the idea that the presence of active Bax in undifferentiated hES cells primes them for rapid apoptosis, the two-day differentiated cells that did not have active Bax were also no longer acutely sensitive to DNA damage. There is limited information about the mechanisms used by early-differentiated cells to limit the risks for apoptosis. We are interested in examining global changes changes in expression, posttranslational modifications and subcellular localization to the apoptotic machinery at these early stages of differentiation. 

Role of apoptotic proteins as modulators of stem cell self-renewal, pluripotency and differentiation.   Using loss/gain function studies we will examine if modulation of Bcl-2 family of proteins affects the maintenance of stem cell self-renewal or the induction of differentiation and de-differentiation.  Our findings that the modulation of the apoptotic components affect not only the thresholds of apoptosis but also the ability of stem cells to self-renew is significant for cancer, since several apoptotic proteins are either inactivated or overexpressed in tumors, and cancer stem cells (CSCs) in particular, are known to maintain the ability of self-renewal.  We are interested in examining the role of apoptotic proteins in the acquisition of cancer stem cell phenotype using glyoblastoma and medulloblastoma cancer stem cells.   

Mechanisms by which mitochondrial network dynamics regulate normal and cancer stem cell fate.   Mitochondria are dynamic organelles that constantly fuse and divide. Interestingly, mitochondrial dynamics has been shown to be also linked to metabolism. For instance, studies in cancer cells have shown that fusion of mitochondria increase when cells are forced to rely on oxidative phosphorylation by withdrawing glucose as a carbon source. hES cells rely heavily on glycolysis, while differentiated cells, rely preferentially on oxidative phosphorylation.  However, it is not known whether this metabolic switch also induces a mitochondrial re-organization in hES cells or whether the re-organization of the mitochondria precedes the metabolic changes associated with differentiation. We are interested in examining this phenomenon in human embryonic stem cells.