Wnt signaling regulates hepatocyte cell division by a transcriptional repressor cascade

Binucleated human hepatocytes arise through late cytokinetic regression during endomitosis M phase

Binucleated polyploid cells are common in many animal tissues, where they arise by endomitosis, a non-canonical cell cycle in which cells enter M phase but do not undergo cytokinesis. Different steps of cytokinesis have been shown to be inhibited during endomitosis M phase in rodents, but it is currently unknown how human cells undergo endomitosis. In this study, we use fetal-derived human hepatocyte organoids (Hep-Orgs) to investigate how human hepatocytes initiate and execute endomitosis. We find that cells in endomitosis M phase have normal mitotic timings, but lose membrane anchorage to the midbody during cytokinesis, which is associated with the loss of four cortical anchoring proteins, RacGAP1, Anillin, SEPT9, and citron kinase (CIT-K). Moreover, reduction of WNT activity increases the percentage of binucleated cells in Hep-Orgs, an effect that is dependent on the atypical E2F proteins, E2F7 and E2F8. Together, we have elucidated how hepatocytes undergo endomitosis in human Hep-Orgs, providing new insights into the mechanisms of endomitosis in mammals.

Design principles and therapeutic applications of novel synthetic WNT signaling agonists

Wingless-related integration site or Wingless and Int-1 or Wingless-Int (WNT) signaling is crucial for embryonic development, and adult tissue homeostasis and regeneration, through its essential roles in cell fate, patterning, and stem cell regulation. The biophysical characteristics of WNT ligands have hindered efforts to interrogate ligand activity in vivo and prevented their development as therapeutics. Recent breakthroughs have enabled the generation of synthetic WNT signaling molecules that possess characteristics of natural ligands and potently activate the pathway, while also providing distinct advantages for therapeutic development and manufacturing. This review provides a detailed discussion of the protein engineering of these molecular platforms for WNT signaling agonism. We discuss the importance of WNT signaling in several organs and share insights from the initial application of these new classes of molecules in vitro and in vivo. These molecules offer a unique opportunity to enhance our understanding of how WNT signaling agonism promotes tissue repair, enabling targeted development of tailored therapeutics.

PRDM14 extinction enables the initiation of trophoblast stem cell formation

Trophoblast stem cells (TSCs) can be chemically converted from embryonic stem cells (ESCs) in vitro. Although several transcription factors (TFs) have been recognized as essential for TSC formation, it remains unclear how differentiation cues link elimination of stemness with the establishment of TSC identity. Here, we show that PRDM14, a critical pluripotent circuitry component, is reduced during the formation of TSCs. The reduction is further shown to be due to the activation of Wnt/β-catenin signaling. The extinction of PRDM14 results in the erasure of H3K27me3 marks and chromatin opening in the gene loci of TSC TFs, including GATA3 and TFAP2C, which enables their expression and thus the initiation of the TSC formation process. Accordingly, PRDM14 reduction is proposed here as a critical event that couples elimination of stemness with the initiation of TSC formation. The present study provides novel insights into how induction signals initiate TSC formation.

The G1/S transition is promoted by Rb degradation via the E3 ligase UBR5

Mammalian cells make the decision to divide at the G1/S transition in response to diverse signals impinging on the retinoblastoma protein Rb, a cell cycle inhibitor and tumor suppressor. Rb is inhibited by two parallel pathways. In the canonical pathway, Cyclin D-Cdk4/6 kinase complexes phosphorylate and inactivate Rb. In the second, recently discovered pathway, Rb's concentration decreases during G1 to promote cells progressing through the G1/S transition. However, the mechanisms underlying this second pathway are unknown. Here, we found that Rb's concentration drop in G1 and recovery in S/G2 is controlled by phosphorylation-dependent protein degradation. In early G1 phase, un- and hypo-phosphorylated Rb is targeted by the E3 ligase UBR5. UBR5 knockout cells have higher Rb concentrations in early G1, exhibit a lower G1/S transition rate, and are more sensitive to Cdk4/6 inhibition. This last observation suggests that UBR5 inhibition can strengthen the efficacy of Cdk4/6 inhibitor-based cancer therapies.

GSK3β/NF-κB -dependent transcriptional regulation of homeostatic hepatocyte Tnf production

Maintenance of hepatocyte homeostasis plays an important role in mediating the pathogenesis of many diseases. A growing body of literature has established a critical role played by tumor necrosis factor-α (TNFα) in maintaining hepatocyte homeostasis; however, the transcriptional mechanisms underlying constitutive Tnf expression are unknown. Whole liver fractions and primary hepatocytes from adult control C57BL/6 mice and the murine hepatocyte cell line AML12 were assessed for constitutive Tnf expression. Impacts of glycogen synthase kinase-3 β (GSK3β) and nuclear factor κB (NF-κB) inhibition on constitutive Tnf expression were assessed in AML12 cells. Finally, AML12 cell proliferation following GSK3β and NF-κB inhibition was evaluated. Constitutive Tnf gene expression is present in whole liver, primary hepatocytes, and cultured AML12 hepatocytes. Cytokine-induced Tnf gene expression is regulated by NF-κB activation. Pharmacological inhibition of GSK3β resulted in a time- and dose-dependent inhibition of Tnf gene expression. GSK3β inhibition decreased nuclear levels of the NF-κB subunits p65 and p50. We determined that NF-κB transcription factor subunit p65 binds to consensus sequence elements present in the murine TNFα promoter and inhibition of GSK3β decreases binding and subsequent Tnf expression. Finally, AML12 cell growth was significantly reduced following GSK3β and NF-κB inhibition. These results demonstrate that GSK3β and NF-κB are essential for mediating Tnf expression and constitutive hepatocyte cell growth. These findings add to a growing body of literature on TNFα mediated hepatocyte homeostasis and identify novel molecular mechanisms involved in mediating response to various disease states in the liver.NEW & NOTEWORTHY Maintenance of hepatocyte homeostasis plays an important role in controlling the pathogenesis of many diseases. Our findings add to a growing body of literature on tumor necrosis factor-α (TNFα)-mediated hepatocyte homeostasis and identify novel molecular mechanisms involved in regulating this response.

Light-manipulated binary droplet transport on a high-energy surface

Flexible and precise manipulation of droplet transport is of significance for scientific and engineering applications, but real-time and on-demand droplet manipulation remains a challenge. Herein, we report a strategy using light for the outstanding manipulation of binary droplet motion on a high-energy surface and reveal the underlying mechanism. Upon irradiation to a substrate by a focused light beam, the substrate can provide a localized heating source via photothermal conversion, and a binary droplet can be flexibly transported on a high-energy surface with free contact-line pinning, exhibiting light-propelled droplet transport. We theoretically showed that the surface tension gradient across the droplet interface resulting from the localized photothermal effect is responsible for actuating droplet transport. Remarkably, the high reconfigurability and flexibility of light allowed for binary droplet transport with dynamically tunable velocity and direction as well as arbitrary trajectory assisted by 2D channels on a high-energy surface. Complex droplet transportation, controllable droplet coalescence, and anti-gravity motion were realized. The promising applicability of this light-fueled droplet platform was also demonstrated by directional transport of biosample droplets containing DNA molecules and cells, as well as successional microreactions.

Drug metabolic activity as a selection factor for pluripotent stem cell-derived hepatic progenitor cells

As a metabolic organ, the liver plays a variety of roles, including detoxification. It has been difficult to obtain stable supplies of hepatocytes for transplantation and for accurate hepatotoxicity determination in drug discovery research. Human pluripotent stem cells, capable of unlimited self-renewal, may be a promising source of hepatocytes. In order to develop a stable supply of embryonic stem cell (ESC)-derived hepatocytes, we have purified human ESC-derived hepatic progenitor cells with exposure to cytocidal puromycin by using their ability to metabolize drugs. Hepatic progenitor cells stably proliferated at least 220-fold over 120 days, maintaining hepatic progenitor cell-like properties. High drug-metabolizing hepatic progenitor cells can be matured into liver cells by suppressing hepatic proliferative signals. The method we developed enables the isolation and proliferation of functional hepatic progenitors from human ESCs, thereby providing a stable supply of high-quality cell resources at high efficiency. Cells produced by this method may facilitate cell therapy for hepatic diseases and reliable drug discovery research.

The time-resolved genomic impact of Wnt/β-catenin signaling

Wnt signaling orchestrates gene expression via its effector, β-catenin. However, it is unknown whether β-catenin binds its target genomic regions simultaneously and how this impacts chromatin dynamics to modulate cell behavior. Using a combination of time-resolved CUT&RUN against β-catenin, ATAC-seq, and perturbation assays in different cell types, we show that Wnt/β-catenin physical targets are tissue-specific, β-catenin "moves" on different loci over time, and its association to DNA accompanies changing chromatin accessibility landscapes that determine cell behavior. In particular, Wnt/β-catenin progressively shapes the chromatin of human embryonic stem cells (hESCs) as they undergo mesodermal differentiation, a behavior that we define as "plastic." In HEK293T cells, on the other hand, Wnt/β-catenin drives a transient chromatin opening, followed by re-establishment of the pre-stimulation state, a response that we define as "elastic." Future experiments shall assess whether other cell communication mechanisms, in addition to Wnt signaling, are ruled by time, cellular idiosyncrasies, and chromatin constraints. A record of this paper's transparent peer review process is included in the supplemental information.

Notch4 participates in mesenchymal stem cell-induced differentiation in 3D-printed matrix and is implicated in eccrine sweat gland morphogenesis

Background

Eccrine sweat gland (SG) plays a crucial role in thermoregulation but exhibits very limited regenerative potential. Although SG lineage-restricted niches dominate SG morphogenesis and benefit SG regeneration, rebuilding niches in vivo is challenging for stem cell therapeutic applications. Hence, we attempted to screen and tune the critical niche-responding genes that dually respond to both biochemical and structural cues, which might be a promising strategy for SG regeneration.

Methods

An artificial SG lineage-restricted niche consisting of mouse plantar dermis homogenates (i.e. biochemical cues) and 3D architecture (i.e. structural cues) was built in vitro by using an extrusion-based 3D bioprinting approach. Mouse bone marrow-derived mesenchymal stem cells (MSCs) were then differentiated into the induced SG cells in the artificial SG lineage-restricted niche. To decouple biochemical cues from structural cues, the transcriptional changes aroused by pure biochemical cues, pure structural cues and synergistic effects of both cues were analyzed pairwise, respectively. Notably, only niche-dual-responding genes that are differentially expressed in response to both biochemical and structural cues and participate in switching MSC fates towards SG lineage were screened out. Validations in vitro and in vivo were respectively conducted by inhibiting or activating the candidate niche-dual-responding gene(s) to explore the consequent effects on SG differentiation.

Results

Notch4 is one of the niche-dual-responding genes that enhanced MSC stemness and promoted SG differentiation in 3D-printed matrix in vitro. Furthermore, inhibiting Notch4 specifically reduced keratin 19-positive epidermal stem cells and keratin 14-positive SG progenitor cells, thus further delaying embryonic SG morphogenesis in vivo.

Conclusions

Notch4 not only participates in mouse MSC-induced SG differentiation in vitro but is also implicated in mouse eccrine SG morphogenesis in vivo.

Role of T-box transcription factor 3 in gastric cancers

The expression of T-box transcription factor 3 (TBX3) has been identified in various cancers, including gastric cancers. Its role in breast cancers and melanomas has been intensively studied, and its contribution to the progression of cancers through suppressing senescence and promoting epithelial-mesenchymal transition has been reported. Recent reports on the role of TBX3 in gastric cancers have implied its involvement in gastric carcinogenesis. Considering its pivotal role in the initiation and progression of cancers, TBX3 could be a promising therapeutic target for gastric cancers.

Intermittent fasting induces rapid hepatocyte proliferation to restore the hepatostat in the mouse liver

Nutrient availability fluctuates in most natural populations, forcing organisms to undergo periods of fasting and re-feeding. It is unknown how dietary changes influence liver homeostasis. Here, we show that a switch from ad libitum feeding to intermittent fasting (IF) promotes rapid hepatocyte proliferation. Mechanistically, IF-induced hepatocyte proliferation is driven by the combined action of systemic FGF15 and localized WNT signaling. Hepatocyte proliferation during periods of fasting and re-feeding re-establishes a constant liver-to-body mass ratio, thus maintaining the hepatostat. This study provides the first example of dietary influence on adult hepatocyte proliferation and challenges the widely held view that liver tissue is mostly quiescent unless chemically or mechanically injured.

The cell cycle inhibitor RB is diluted in G1 and contributes to controlling cell size in the mouse liver

Every type of cell in an animal maintains a specific size, which likely contributes to its ability to perform its physiological functions. While some cell size control mechanisms are beginning to be elucidated through studies of cultured cells, it is unclear if and how such mechanisms control cell size in an animal. For example, it was recently shown that RB, the retinoblastoma protein, was diluted by cell growth in G1 to promote size-dependence of the G1/S transition. However, it remains unclear to what extent the RB-dilution mechanism controls cell size in an animal. We therefore examined the contribution of RB-dilution to cell size control in the mouse liver. Consistent with the RB-dilution model, genetic perturbations decreasing RB protein concentrations through inducible shRNA expression or through liver-specific Rb1 knockout reduced hepatocyte size, while perturbations increasing RB protein concentrations in an Fah ^-/- mouse model increased hepatocyte size. Moreover, RB concentration reflects cell size in G1 as it is lower in larger G1 hepatocytes. In contrast, concentrations of the cell cycle activators Cyclin D1 and E2f1 were relatively constant. Lastly, loss of Rb1 weakened cell size control, i.e., reduced the inverse correlation between how much cells grew in G1 and how large they were at birth. Taken together, our results show that an RB-dilution mechanism contributes to cell size control in the mouse liver by linking cell growth to the G1/S transition.