Genetically Variant Human Pluripotent Stem Cells Selectively Eliminate Wild-Type Counterparts Through YAP-Mediated Cell Competition

Abstract

The appearance of genetic changes in human pluripotent stem cells (hPSCs) presents a concern for their use in research and regenerative medicine. Variant hPSCs that harbor recurrent culture-acquired aneuploidies display growth advantages over wild-type diploid cells, but the mechanisms that yield a drift from predominantly wild-type to variant cell populations remain poorly understood. Here, we show that the dominance of variant clones in mosaic cultures is enhanced through competitive interactions that result in the elimination of wild-type cells. This elimination occurs through corralling and mechanical compression by faster-growing variants, causing a redistribution of F-actin and sequestration of yes-associated protein (YAP) in the cytoplasm that induces apoptosis in wild-type cells. YAP overexpression or promotion of YAP nuclear localization in wild-type cells alleviates their ''loser'' phenotype. Our results demonstrate that hPSC fate is coupled to mechanical cues imposed by neighboring cells and reveal that hijacking this mechanism allows variants to achieve clonal dominance in cultures.

Acquired genetic changes in human pluripotent stem cells: origins and consequences

“…The nature of these interactions can determine the fate of wild-type cells in a non-cell autonomous manner, thereby impacting on the dynamics of the variant's overtake of cultures (Figure 3). Some of the commonly occurring PSC variants were shown to suppress the growth of wild-type populations by inducing apoptosis in their neighbouring wild-type cells (Price et al, 2019), in a manner similar to the phenomenon of cell competition described in other model systems (Bowling et al, 2019). In PSC cultures, a differential sensitivity of wild-type and variant PSC to mechanical pressures imposed by cell crowding allowed variants to effectively eliminate wild-type cells from mixed cultures, therefore enhancing the ability of variants to rapidly achieve the clonal dominance (Price et al, 2019).…”

“…Some of the commonly occurring PSC variants were shown to suppress the growth of wild-type populations by inducing apoptosis in their neighbouring wild-type cells (Price et al, 2019), in a manner similar to the phenomenon of cell competition described in other model systems (Bowling et al, 2019). In PSC cultures, a differential sensitivity of wild-type and variant PSC to mechanical pressures imposed by cell crowding allowed variants to effectively eliminate wild-type cells from mixed cultures, therefore enhancing the ability of variants to rapidly achieve the clonal dominance (Price et al, 2019). Therefore, consideration of cell interactions, in addition to cell autonomous mechanisms, is needed in developing effective strategies for prevention of growth supremacy of variant cells.…”

“…Although little more than 20 years has passed since the first human embryonic stem cells (ESC) were reported (Thomson et al, 1998, Reubinoff et al, 2000, and less than 14 years since human induced pluripotent cells (iPSC) were described (Takahashi et al, 2007, Yu et al, 2007, clinical trials for regenerative medicine using derivatives of these cells are already underway or on the horizon (da Cruz et al, 2018, Schwartz et al, 2012, Song et al, 2015, Mandai et al, 2017, Barker et al, 2017). Yet over this period it has become evident that both human ESC and iPSC (collectively here denoted as PSC), although mostly diploid when first derived, may acquire genetic alterations, ranging from large scale structural modifications readily recognized as karyotypic variants through to single base pair changes on subsequent passage (Figure 1).…”

“…Cell autonomous mechanisms: mutation (a) drives faster cell cycle, or (b) blocks differentiation, or (c) blocks apoptosis. Cell interactive mechanisms: mutation (d) causes variant cell to inhibit the growth of its wild-type counterpart(Price et al, 2019) or (e) alters the patterns of differentiation. The latter could generate a selective advantage either if certain differentiated derivatives produced factors that promote differentiation (advantage would derive from blocking such lineages) or produced factors that blocked general differentiation (advantage would derive from enhancing differentiation to such lineages).…”

Fitness selection in human pluripotent stem cells and interspecies chimeras: Implications for human development and regenerative medicine

“…Nonetheless, genetic, epigenetic and phenotypic heterogeneity in human PSC cultures is an inevitability of an expanding embryonic-like cellular population. Consequently, relative cellular fitness in PSC cultures plays a major role in determining the composition of human PSC population ( Price et al., 2019 ). With several PSC-based regenerative medicine applications currently in clinical or preclinical phases of development, a thorough understanding of the dynamics of PSC cellular interactions is essential to enabling efficient and safe clinical translation of PSC-derived cell therapies.…”