Superior Induced Pluripotent Stem Cell Generation through Phactr3-Driven Mechanomodulation of Both Early and Late Phases of Cell Reprogramming.

Human cell reprogramming traditionally involves time-intensive, multistage, costly tissue culture polystyrene-based cell culture practices that ultimately produce low numbers of reprogrammed cells of variable quality. Previous studies have shown that very soft 2- and 3-dimensional hydrogel substrates/matrices (of stiffnesses ≤ 1 kPa) can drive ~2× improvements in human cell reprogramming outcomes. Unfortunately, these similarly complex multistage protocols lack intrinsic scalability, and, furthermore, the associated underlying molecular mechanisms remain to be fully elucidated, limiting the potential to further maximize reprogramming outcomes. In screening the largest range of polyacrylamide (pAAm) hydrogels of varying stiffness to date (1 kPa to 1.3 MPa), we have found that a medium stiffness gel (~100 kPa) increased the overall number of reprogrammed cells by up to 10-fold (10×), accelerated reprogramming kinetics, improved both early and late phases of reprogramming, and produced induced pluripotent stem cells (iPSCs) having more naïve characteristics and lower remnant transgene expression, compared to the gold standard tissue culture polystyrene practice. Functionalization of these pAAm hydrogels with poly-l-dopamine enabled, for the first-time, continuous, single-step reprogramming of fibroblasts to iPSCs on hydrogel substrates (noting that even the tissue culture polystyrene practice is a 2-stage process). Comparative RNA sequencing analyses coupled with experimental validation revealed that a novel reprogramming regulator, protein phosphatase and actin regulator 3, up-regulated under the gel condition at a very early time point, was responsible for the observed enhanced reprogramming outcomes. This study provides a novel culture protocol and substrate for continuous hydrogel-based cell reprogramming and previously unattained clarity of the underlying mechanisms via which substrate stiffness modulates reprogramming kinetics and iPSC quality outcomes.

Enhanced effects of secreted soluble factor preserve better pluripotent state of embryonic stem cell culture in a membrane-based compartmentalized micro-bioreactor.

Pluripotent stem cells are under the influence of soluble factors in a diffusion dominant in vivo microenvironment. In order to investigate the effects of secreted soluble factors on embryonic stem cell (ESC) behavior in a diffusion dominant microenvironment, we cultured mouse ESCs (mESCs) in a membrane-based two-chambered micro-bioreactor (MB). To avoid disturbing the cellular environment in the top chamber of the MB, only the culture medium of the bottom chamber was exchanged. Cell growth in the MB after 5 days of culture was similar to that in conventional 6-well plate (6-WP) and membrane-based Transwell insert (TW) cultures, indicating adequate nutrient supply in the MB. However, the cells retained higher expression of pluripotency markers (Oct4, Sox2 and Rex1) and secreted soluble factors (FGF4 and BMP4) in the MB. Inhibition of FGF4 activity in the MB and TW resulted in a similar cellular response. However, in contrast to the TW, inhibition of BMP4 activity revealed that autocrine action of the upregulated BMP4, which acted cooperatively with leukemia inhibitory factor (LIF), upregulated the pluripotency markers expression in the MB culture. We propose that BMP4 accumulated in the diffusion dominant microenvironment of the MB upregulated its own expression by a positive feedback mechanism-in contrast to the macro-scale culture systems-thereby enhancing the pluripotency of mESCs. The micro-scale culture platform developed in this study enables the investigation of the effects of soluble factors on ESCs in a diffusion dominant microenvironment, and is expected to be used to modulate the ESC fate choices.

Adhesion of pancreatic cancer cells in a liver-microvasculature mimicking coculture correlates with their propensity to form liver-specific metastasis in vivo.

Organ-specific characteristic of endothelial cells (ECs) is crucial for specific adhesion of cancer cells to ECs, which is a key factor in the formation of organ-specific metastasis. In this study, we developed a coculture of TMNK-1 (immortalized liver sinusoidal ECs) with 10T1/2 (resembling hepatic stellate cells) to augment organ-specific characteristic of TMNK-1 and investigated adhesion of two pancreatic cancer cells (MIA-PaCa-2 and BxPC-3) in the culture. MIA-PaCa-2 and BxPC-3 adhesion in TMNK-1+10T1/ 2|coating culture (TMNK-1 monolayer over 10T1/2 layer on collagen coated surface) were similar. However, in TMNK-1+10T1/ 2|gel (coculture on collagen gel surface), MIA-PaCa-2 adhesion was significantly higher than BxPC-3, which was congruent with the reported higher propensity of MIA-PaCa-2 than BxPC-3 to form liver metastasis in vivo. Notably, as compared to BxPC-3, MIA-PaCa-2 adhesion was lower and similar in TMNK-1 only culture on the collagen coated and gel surfaces, respectively. Investigation of the adhesion in the representative human umbilical vein ECs (HUVECs) cultures and upon blocking of surface molecules of ECs revealed that MIA-PaCa-2 adhesion was strongly dependent on the organ-specific upregulated characteristics of TMNK-1 in TMNK-1+10T1/ 2|gel culture. Therefore, the developed coculture would be a potential assay for screening novel drugs to inhibit the liver-microvasculature specific adhesion of cancer cells.

Importance of a diffusion-dominant small volume to activate cell-secreted soluble factor signaling in embryonic stem cell culture in microbioreactors: a mathematical model based study.

In our previous studies, we observed that cell-secreted BMP4 had a prominent influence on mouse embryonic stem cell (mESC) behaviors in a membrane-based two-chambered microbioreactor (MB), but not in a macro-scale culture (6-well plate/6WP). In this study, we investigated how the physical aspects of these cultures regulated BMP4 signaling by developing mathematical models of the cultures. The models estimated signaling activity in the cultures by considering size of the undifferentiated mESC colonies and their growth, diffusion of BMP4, and BMP4 trafficking process in the colonies. The models successfully depicted measured profile of BMP4 concentration in the culture medium which was two times higher in the MB than that in the 6WP during 5-day culture. The models estimated that, owing to the small volume and the membrane, cells were exposed to a higher BMP4 concentration in the top chamber of the MB than that in the 6WP culture. The higher concentration of BMP4 induced a higher concentration of BMP4-bound receptor in the colony in the MB than in the 6WP, thereby leading to the higher activation of BMP4 signaling in the MB. The models also predicted that the size of the MB, but not that of the 6WP, was suitable for maximizing BMP4 accumulation and upregulating its signaling. This study will be helpful in analyzing culture systems, designing microfluidic devices for controlling ESC or other cell behavior.