Polyploidization in liver tissue

Ascending E2F7a/b ratio facilitates KLF13 transcription in hepatocellular carcinoma and correlates with the abundance of binuclear hepatocytes (ABH) modulation for short-term recurrence

Short-term recurrence after surgery severely threatens patients' lives and leads to dismal outcomes in hepatocellular carcinoma (HCC). Our previous research proposed the abundance of binuclear hepatocytes (ABH) as an independent indicator related to the cytokinesis regulator Anillin and significantly associated with HCC recurrence. The exact mechanism of ABH modulation has not been clearly illustrated. In this study, we intensively investigated the probable regulation mechanism and noticed a contradiction between E2F7 upregulation and ABH attenuation. As we discovered, E2F7 has two isoforms, E2F7a and E2F7b, and we innovatively define a value of the E2F7a/b ratio using a cutoff value of 6.5. E2F7 upregulation in the paracancerous tissues was predominantly presented by the E2F7a isoform, leading to an increase in the E2F7a/b ratio, instead of E2F7b as a main component in non-cancerous tissues, and is associated with short-term recurrence. We further found that KLF13 transcriptionally promotes Anillin expression in HCC and was suppressively impacted by E2F7b, but not by the highly expressed E2F7a. Hence, the ascending E2F7a/b ratio induced significant upregulation of KLF13 and participated in the attenuation of ABH in the paracancerous liver tissues. In conclusion, E2F7 presents a particular expression status in HCC by predominantly upregulating E2F7a rather than E2F7b. The ascending E2F7a/b ratio weakens the suppressive effect on KLF13 transcription and sequentially participates in ABH attenuation, associated with short-term HCC recurrence post-operation.

ESRP2-microRNA-122 axis promotes the postnatal onset of liver polyploidization and maturation

Hepatocyte polyploidy and maturity are critical to acquiring specialized liver functions. Multiple intracellular and extracellular factors influence ploidy, but how they cooperate temporally to steer liver polyploidization and maturation or how post-transcriptional mechanisms integrate into these paradigms is unknown. Here, we identified an important regulatory hierarchy in which postnatal activation of epithelial splicing regulatory protein 2 (ESRP2) stimulates processing of liver-specific microRNA (miR-122) to facilitate polyploidization, maturation, and functional competence of hepatocytes. By determining transcriptome-wide protein-RNA interactions in vivo and integrating them with single-cell and bulk hepatocyte RNA-seq data sets, we delineated an ESRP2-driven RNA processing program that drives sequential replacement of fetal-to-adult transcript isoforms. Specifically, ESRP2 binds the primary miR-122 host gene transcript to promote its processing/biogenesis. Combining constitutive and inducible ESRP2 gain- and loss-of-function mouse models with miR-122 rescue experiments, we demonstrated that timed activation of ESRP2 augments the miR-122-driven program of cytokinesis failure, ensuring the proper onset and extent of hepatocyte polyploidization.

Somatic polyploidy supports biosynthesis and tissue function by increasing transcriptional output

Cell size and biosynthetic capacity generally increase with increased DNA content. Somatic polyploidy has therefore been proposed to be an adaptive strategy to increase cell size in specialized tissues with high biosynthetic demands. However, if and how DNA concentration limits cellular biosynthesis in vivo is not well understood. Here, we show that polyploidy in the Caenorhabditis elegans intestine is critical for cell growth and yolk biosynthesis, a central role of this organ. Artificially lowering the DNA/cytoplasm ratio by reducing polyploidization in the intestine gave rise to smaller cells with dilute mRNA. Highly expressed transcripts were more sensitive to this mRNA dilution, whereas lowly expressed genes were partially compensated-in part by loading more RNA Polymerase II on the remaining genomes. Polyploidy-deficient animals produced fewer and slower-growing offspring, consistent with reduced synthesis of highly expressed yolk proteins. DNA-dilute cells had normal total protein concentration, which we propose is achieved by increasing the expression of translational machinery at the expense of specialized, cell-type-specific proteins.

Diacylglycerol kinase alpha regulates post-hepatectomy liver regeneration

Diacylglycerol kinases (DGKs) phosphorylate diacylglycerol to generate phosphatidic acid, which plays important roles in intracellular signal transduction. DGKα is reportedly associated with progression of tumors, including hepatocellular carcinomas, but its relationship with liver regeneration has not been examined. The purpose of this research is to elucidate the role of DGKα in liver regeneration. Here, we provide a detailed examination of C57BL/6 wild-type and DGKα knockout (KO) mice subjected to 70% partial hepatectomy (70% PH) modeling, including survival rates, hematological marker and gene expression levels, and histological analyses of factors related to liver regeneration. Following 70% PH, DGKα KO mice produce higher levels of hepatobiliary enzymes and have a higher incidence of jaundice compared with wild-type mice, with a death rate of ~ 40%. Furthermore, they exhibit impaired glycogen and lipid consumption, low liver energy charge, and hepatocyte hypertrophy disorder, accompanied by significantly reduced liver expression of proliferating cell nuclear antigen and cyclin D. We conclude that DGKα is a key molecule in the post-PH liver regeneration process and may have potential as a therapeutic target for the acceleration of liver regeneration.

Uncovering gene expression signatures and diagnostic - Biomarkers in hepatocellular carcinoma through multinomial logistic regression analysis

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death worldwide, and classifying the developmental stages of HCC can help with early prognosis and treatment. This study aimed to investigate diagnostic and prognostic molecular signatures underlying the progression of HCC, including tumor initiation and growth, and to classify its developmental stages based on gene expression levels. We integrated data from two cancer systems, including 78 patients with Edmondson-Steiner (ES) grade and 417 patients with TNM stage cancer. Functional profiling was performed using identified signatures. Using a multinomial logistic regression model (MLR), we classified controls, early-stage HCC, and advanced-stage HCC. The model was validated in three independent cohorts comprising 45 patients (neoplastic stage), 394 patients (ES grade), and 466 patients (TNM stage). Multivariate Cox regression was employed for HCC prognosis prediction. We identified 35 genes with gradual upregulation or downregulation in both ES grade and TNM stage patients during HCC progression. These genes are involved in cell division, chromosome segregation, and mitotic cytokinesis, promoting tumor cell proliferation through the mitotic cell cycle. The MLR model accurately differentiated controls, early-stage HCC, and advanced-stage HCC across multiple cancer systems, which was further validated in various independent cohorts. Survival analysis revealed a subset of five genes from TNM stage (HR: 3.27, p < 0.0001) and three genes from ES grade (HR: 7.56, p < 0.0001) that showed significant association with HCC prognosis. The identified molecular signature not only initiates tumorigenesis but also promotes HCC development. It has the potential to improve clinical diagnosis, prognosis, and therapeutic interventions for HCC. This study enhances our understanding of HCC progression and provides valuable insights for precision medicine approaches.

Polyploid giant cancer cells: origin, possible pathways of formation, characteristics, and mechanisms of regulation

Polyploid giant cancer cells (PGCCs) are characterized by the presence of either a single enlarged nucleus or multiple nuclei and are closely associated with tumor progression and treatment resistance. These cells contribute significantly to cellular heterogeneity and can arise from various stressors, including radiation, chemotherapy, hypoxia, and environmental factors. The formation of PGCCs can occur through mechanisms such as endoreplication, cell fusion, cytokinesis failure, mitotic slippage, or cell cannibalism. Notably, PGCCs exhibit traits similar to cancer stem cells (CSCs) and generate highly invasive progeny through asymmetric division. The presence of PGCCs and their progeny is pivotal in conferring resistance to chemotherapy and radiation, as well as facilitating tumor recurrence and metastasis. This review provides a comprehensive analysis of the origins, potential formation mechanisms, stressors, unique characteristics, and regulatory pathways of PGCCs, alongside therapeutic strategies targeting these cells. The objective is to enhance the understanding of PGCC initiation and progression, offering novel insights into tumor biology.

ESRP2-microRNA-122 axis directs the postnatal onset of liver polyploidization and maturation

Hepatocyte polyploidy and maturity are critical to acquiring specialized liver functions. Multiple intra- and extracellular factors influence ploidy, but how they cooperate temporally to steer liver polyploidization and maturation or how post-transcriptional mechanisms integrate into these paradigms is unknown. Here, we identified an important regulatory hierarchy in which postnatal activation of Epithelial-Splicing-Regulatory-Protein-2 (ESRP2) stimulates biogenesis of liver-specific microRNA (miR-122), thereby facilitating polyploidization, maturation, and functional competence of hepatocytes. By determining transcriptome-wide protein-RNA interactions in vivo and integrating them with single-cell and bulk hepatocyte RNA-seq datasets, we delineate an ESRP2-driven RNA processing program that drives sequential replacement of fetal-to-adult transcript isoforms. Specifically, ESRP2 binds the primary miR-122 host gene transcript to promote its processing/biogenesis. Combining constitutive and inducible ESRP2 gain- and loss-of-function mice models with miR-122 rescue experiments, we demonstrate that timed activation of ESRP2 augments miR-122-driven program of cytokinesis failure, ensuring proper onset and extent of hepatocyte polyploidization.

Reprogramming canine cryopreserved hepatocytes to hepatic progenitor cells using small molecule compounds

Introduction

Exploring techniques for differentiating and culturing canine hepatocytes serves as a means to establish systems for liver transplantation and drug metabolism testing. However, establishing consistent methods for culturing stable hepatocytes remains a challenge. Recently, several investigations have shown the reprogramming of mature hepatocytes into hepatic progenitor cells by applying specific small molecule compounds, including Y-27632, (a ROCK inhibitor), A-83-01 (a TGFβ inhibitor), and CHIR99021 (a GSK3 inhibitor) (termed YAC) in rat, mouse, and humans, respectively. However, reports or evidence of successful reprogramming using these small-molecule compounds in dogs are absent. This study aimed to induce the differentiation of mature canine hepatocytes into progenitor cells.

Methods

Cryopreserved canine hepatocytes (cHep) were cultured for 14 d in a YAC-supplemented hepatocyte growth medium. Subsequently, an assessment was conducted involving morphological observations, quantitative real-time polymerase chain reaction (qRT-PCR), and immunocytochemistry.

Results

Notably, cryopreserved cHep cells emerged and exhibited ongoing proliferation and concurrently developed colonies within the YAC-enriched culture. These observations indicated that the mature hepatocytes reprogrammed into hepatic progenitor cells. Moreover, qRT-PCR analysis revealed a notable enhancement in gene expression levels. Specifically, the genes encoding α-fetoprotein (AFP), epithelial cell adhesion molecule (EpCAM), Cytokeratin 19 (CK19) and SRY-box9 (Sox9) displayed approximately 12-, 2.2-, 517- and 2.9- increases in hepatic progenitor cells, respectively, on day 14 as compared to their state before induction of differentiation. Hepatocyte-related protein expression of AFP, EPCAM, SOX9 and CK19 was confirmed via immunocytochemistry on day 21. In contrast, ALB and MRP2, which are highly expressed in mature hepatocytes, were decreased compared to those before YAC addition, which is consistent with the characteristics of undifferentiated hepatocytes.

Conclusions

Herein, we effectively promoted the reprogramming of cryopreserved cHep cells into hepatic progenitor cells using three small-molecule compounds. The mRNA and protein expression analyses demonstrated increased levels of hepatic progenitor cells-specific markers, whereas markers related to mature hepatocytes decreased, suggesting that reprogramming cryopreserved cHep cells to hepatic progenitor cells was achieved using YAC. Therefore, cultivating liver progenitor cells holds the potential to offer valuable insights into the development of artificial livers for drug discovery research and transplantation therapy aimed at addressing liver diseases in dogs.

Polyploidy in Cancer: Causal Mechanisms, Cancer-Specific Consequences, and Emerging Treatments

Drug resistance is the major determinant for metastatic disease and fatalities, across all cancers. Depending on the tissue of origin and the therapeutic course, a variety of biological mechanisms can support and sustain drug resistance. Although genetic mutations and gene silencing through epigenetic mechanisms are major culprits in targeted therapy, drug efflux and polyploidization are more global mechanisms that prevail in a broad range of pathologies, in response to a variety of treatments. There is an unmet need to identify patients at risk for polyploidy, understand the mechanisms underlying polyploidization, and to develop strategies to predict, limit, and reverse polyploidy thus enhancing efficacy of standard-of-care therapy that improve better outcomes. This literature review provides an overview of polyploidy in cancer and offers perspective on patient monitoring and actionable therapy.

Characterization of polyploidy in cancer: Current status and future perspectives

Various cancers frequently exhibit polyploidy, observed in a condition where a cell possesses more than two sets of chromosomes, which is considered a hallmark of the disease. The state of polyploidy often leads to aneuploidy, where cells possess an abnormal number or structure of chromosomes. Recent studies suggest that oncogenes contribute to aneuploidy. This finding significantly underscores its impact on cancer. Cancer cells exposed to certain chemotherapeutic drugs tend to exhibit an increased incidence of polyploidy. This occurrence is strongly associated with several challenges in cancer treatment, including metastasis, resistance to chemotherapy and the recurrence of malignant tumors. Indeed, it poses a significant hurdle to achieve complete tumor eradication and effective cancer therapy. Recently, there has been a growing interest in the field of polyploidy related to cancer for developing effective anti-cancer therapies. Polyploid cancer cells confer both advantages and disadvantages to tumor pathogenicity. This review delineates the diverse characteristics of polyploid cells, elucidates the pivotal role of polyploidy in cancer, and explores the advantages and disadvantages it imparts to cancer cells, along with the current approaches tried in lab settings to target polyploid cells. Additionally, it considers experimental strategies aimed at addressing the outstanding questions within the realm of polyploidy in relation to cancer.

Review of the evidence of radioprotective potential of creatine and arginine as dietary supplements

PURPOSE

Creatine (Cr) and l-arginine are naturally occurring guanidino compounds, commonly used as ergogenic dietary supplements. Creatine and l-arginine exhibit also a number of non-energy-related features, such as antioxidant, anti-apoptotic, and anti-inflammatory properties, which contribute to their protective action against oxidative stress (OS). In this regard, there are a number of studies emphasizing the protective effect of Cr against OS, which develops in the process of aging, increased physical loads as part of athletes' workouts, as well as a number of neurological diseases and toxic effects associated with xenobiotics and UV irradiation. Against this backdrop, and since ionizing radiation causes OS in cells, leading to radiotoxicity, there is an increasing interest to understand whether Cr has the full potential to serve as an effective radioprotective agent. The extensive literature search did not provide any data on this issue. In this narrative review, we have summarized some of our own experimental data published over the last years addressing the respective radioprotective effects of Cr. Next, we have additionally reviewed the existing data on the radiomodifying effects of l-arginine presented earlier by other research groups.

CONCLUSIONS

Creatine possesses significant radioprotective potential including: (1) radioprotective effect on the survival rate of rats subjected to acute whole-body X-ray irradiation in a LD70/30 dose of 6.5 Gy, (2) radioprotective effect on the population composition of peripheral blood cells, (3) radioprotective effect on the DNA damage of peripheral blood mononuclear cells, (4) radioprotective effect on the hepatocyte nucleus-nucleolar apparatus, and (5) radioprotective effect on the brain and liver Cr-Cr kinase systems of the respective animals. Taking into account these cytoprotective, gene-protective, hepatoprotective and energy-stimulating features of Cr, as well as its significant radioprotective effect on the survival rate of rats, it can be considered as a potentially promising radioprotector for further preclinical and clinical studies. The review of the currently available data on radiomodifying effects of l-arginine has indicated its significant potential as a radioprotector, radiomitigator, and radiosensitizer. However, to prove the effectiveness of arginine (Arg) as a radioprotective agent, it appears necessary to expand and deepen the relevant preclinical studies, and, most importantly, increase the number of proof-of-concept clinical trials, which are evidently lacking as of now.

Somatic polyploidy supports biosynthesis and tissue function by increasing transcriptional output

Cell size and biosynthetic capacity generally increase with increased DNA content. Polyploidy has therefore been proposed to be an adaptive strategy to increase cell size in specialized tissues with high biosynthetic demands. However, if and how DNA concentration limits cellular biosynthesis in vivo is not well understood, and the impacts of polyploidy in non-disease states is not well studied. Here, we show that polyploidy in the C. elegans intestine is critical for cell growth and yolk biosynthesis, a central role of this organ. Artificially lowering the DNA/cytoplasm ratio by reducing polyploidization in the intestine gave rise to smaller cells with more dilute mRNA. Highly-expressed transcripts were more sensitive to this mRNA dilution, whereas lowly-expressed genes were partially compensated - in part by loading more RNA Polymerase II on the remaining genomes. DNA-dilute cells had normal total protein concentration, which we propose is achieved by increasing production of translational machinery at the expense of specialized, cell-type specific proteins.

Polyploid Cancer Cell Models in Drosophila

Cells with an abnormal number of chromosomes have been found in more than 90% of solid tumors, and among these, polyploidy accounts for about 40%. Polyploidized cells most often have duplicate centrosomes as well as genomes, and thus their mitosis tends to promote merotelic spindle attachments and chromosomal instability, which produces a variety of aneuploid daughter cells. Polyploid cells have been found highly resistant to various stress and anticancer therapies, such as radiation and mitogenic inhibitors. In other words, common cancer therapies kill proliferative diploid cells, which make up the majority of cancer tissues, while polyploid cells, which lurk in smaller numbers, may survive. The surviving polyploid cells, prompted by acute environmental changes, begin to mitose with chromosomal instability, leading to an explosion of genetic heterogeneity and a concomitant cell competition and adaptive evolution. The result is a recurrence of the cancer during which the tenacious cells that survived treatment express malignant traits. Although the presence of polyploid cells in cancer tissues has been observed for more than 150 years, the function and exact role of these cells in cancer progression has remained elusive. For this reason, there is currently no effective therapeutic treatment directed against polyploid cells. This is due in part to the lack of suitable experimental models, but recently several models have become available to study polyploid cells in vivo. We propose that the experimental models in Drosophila, for which genetic techniques are highly developed, could be very useful in deciphering mechanisms of polyploidy and its role in cancer progression.

The Ploidy State as a Determinant of Hepatocyte Proliferation

The liver's unique chromosomal variations, including polyploidy and aneuploidy, influence hepatocyte identity and function. Among the most well-studied mammalian polyploid cells, hepatocytes exhibit a dynamic interplay between diploid and polyploid states. The ploidy state is dynamic as hepatocytes move through the "ploidy conveyor," undergoing ploidy reversal and re-polyploidization during proliferation. Both diploid and polyploid hepatocytes actively contribute to proliferation, with diploids demonstrating an enhanced proliferative capacity. This enhanced potential positions diploid hepatocytes as primary drivers of liver proliferation in multiple contexts, including homeostasis, regeneration and repopulation, compensatory proliferation following injury, and oncogenic proliferation. This review discusses the influence of ploidy variations on cellular activity. It presents a model for ploidy-associated hepatocyte proliferation, offering a deeper understanding of liver health and disease with the potential to uncover novel treatment approaches.

Attenuation of binuclear hepatocytes in the paracancerous liver tissue is associated with short-term recurrence of hepatocellular carcinoma post-radical surgery

Short-term recurrence of hepatocellular carcinoma (HCC) after radical resection leads to dismal outcomes. To screen high-recurrence risk patients to provide adjuvant treatment is necessary. Herein, based on our previous research, we further focused on the changes in the abundance of binuclear hepatocytes (ABH) in the paracancerous liver tissue to discuss the relationship between the attenuation of binuclear hepatocytes and postoperative short-term recurrence, by combining with the assessment of the value of a reported independent early recurrence risk factor in HCC, protein induced by vitamin K absence or antagonist-II (PIVKA-II). A cohort of 142 paracancerous liver tissues from HCC patients who received radical resection was collected. Binuclear hepatocytes were reduced in the paracancerous liver tissues, compared with the liver tissues from normal donors. ABH was negatively correlated with clinical features such as tumor size, TNM stages, tumor microsatellite formation, venous invasion, and Alpha-fetoprotein (AFP) level, as well as the expression of E2F7 and Anillin, which are two critical regulators concerning the hepatocyte polyploidization. According to the short-term recurrence information, ABH value was laminated, and univariate and multivariate logistic regression was performed to analyze the relationship between paracancerous ABH and short-term tumor relapse. Simultaneously, the predictive effectiveness of the ABH value was compared with the preoperative PIVKA-II value. As observed, the paracancerous ABH value below 1.5% was found to be an independent risk factor for recurrence. In conclusion, the paracancerous ABH is a credible indicator of short-term recurrence of HCC patients after radical resection, and regular assessment of ABH might help to prevent short-term HCC recurrence.

Cytoplasmic SIRT1 promotes paclitaxel resistance in ovarian carcinoma through increased formation and survival of polyploid giant cancer cells

Therapeutic resistance is a notable cause of death in patients with ovarian carcinoma. Polyploid giant cancer cells (PGCCs), commonly arising in tumor tissues following chemotherapy, have recently been considered to contribute to drug resistance. As a type III deacetylase, Sirtuin1 (SIRT1) plays essential roles in the cell cycle, cellular senescence, and drug resistance. Accumulating evidence has suggested that alteration in its subcellular localization via nucleocytoplasmic shuttling is a critical process influencing the functions of SIRT1. However, the roles of SIRT1 subcellular localization in PGCC formation and subsequent senescence escape remain unclear. In this study, we compared the differences in the polyploid cell population and senescence state of PGCCs following paclitaxel treatment between tumor cells overexpressing wild-type SIRT1 (WT SIRT1) and those expressing nuclear localization sequence (NLS)-mutated SIRT1 (SIRT1NLSmt ). We investigated the involvement of cytoplasmic SIRT1 in biological processes and signaling pathways, including the cell cycle and cellular senescence, in ovarian carcinoma cells' response to paclitaxel treatment. We found that the SIRT1NLSmt tumor cell population contained more polyploid cells and fewer senescent PGCCs than the SIRT1-overexpressing tumor cell population. Comparative proteomic analyses using co-immunoprecipitation (Co-IP) combined with liquid chromatography-mass spectrometry (LC-MS)/MS showed the differences in the differentially expressed proteins related to PGCC formation, cell growth, and death, including CDK1 and CDK2, between SIRT1NLSmt and SIRT1 cells or PGCCs. Our results suggested that ovarian carcinoma cells utilize polyploidy formation as a survival mechanism during exposure to paclitaxel-based treatment via the effect of cytoplasmic SIRT1 on PGCC formation and survival, thereby boosting paclitaxel resistance. © 2023 The Pathological Society of Great Britain and Ireland.

Mcl-1 deficiency in murine livers leads to nuclear polyploidisation and mitotic errors: Implications for hepatocellular carcinoma

Background & Aims

Mcl-1, an antiapoptotic protein overexpressed in many tumours, including hepatocellular carcinoma (HCC), represents a promising target for cancer treatment. Although Mcl-1 non-apoptotic roles might critically influence the therapeutic potential of Mcl-1 inhibitors, these functions remain poorly understood. We aimed to investigate the effects of hepatic Mcl-1 deficiency (Mcl-1Δhep) on hepatocyte ploidy and cell cycle in murine liver in vivo and the possible implications on HCC.

Methods

Livers of young Mcl-1Δhep and wild-type (WT) mice were analysed for ploidy profile, mitotic figures, in situ chromosome segregation, gene set enrichment analysis and were subjected to two-thirds partial hepatectomy to assess Mcl-1 deficiency effect on cell cycle progression in vivo. Mcl-1Δhep tumours in older mice were analysed for ploidy profile, chromosomal instability, and mutational signatures via whole exome sequencing.

Results

In young mice, Mcl-1 deficiency leads to nuclear polyploidy and to high rates of mitotic errors with abnormal spindle figures and chromosome mis-segregation along with a prolonged spindle assembly checkpoint activation signature. Chromosomal instability and altered ploidy profile are observed in Mcl-1Δhep tumours of old mice as well as a characteristic mutational signature of currently unknown aetiology.

Conclusions

Our study suggests novel non-apoptotic effects of Mcl-1 deficiency on nuclear ploidy, mitotic regulation, and chromosomal segregation in hepatocytes in vivo. In addition, the Mcl-1 deficiency characteristic mutational signature might reflect mitotic issues. These results are of importance to consider when developing anti-Mcl-1 therapies to treat cancer.

Impact and implications

Although Mcl-1 inhibitors represent promising hepatocellular carcinoma treatment, the still poorly understood non-apoptotic roles of Mcl-1 might compromise their successful clinical application. Our study shows that Mcl-1 deficiency leads to nuclear polyploidy, mitotic errors, and aberrant chromosomal segregation in hepatocytes in vivo, whereas hepatocellular tumours spontaneously induced by Mcl-1 deficiency exhibit chromosomal instability and a mutational signature potentially reflecting mitotic issues. These results have potential implications for the development of anti-Mcl-1 therapies to treat hepatocellular carcinoma, especially as hyperproliferative liver is a clinically relevant situation.

Rapid in vivo multiplexed editing (RIME) of the adult mouse liver

BACKGROUND AND AIMS

Assessing mammalian gene function in vivo has traditionally relied on manipulation of the mouse genome in embryonic stem cells or perizygotic embryos. These approaches are time-consuming and require extensive breeding when simultaneous mutations in multiple genes is desired. The aim of this study is to introduce a rapid in vivo multiplexed editing (RIME) method and provide proof of concept of this system.

APPROACH AND RESULTS

RIME, a system wherein CRISPR/caspase 9 technology, paired with adeno-associated viruses (AAVs), permits the inactivation of one or more genes in the adult mouse liver. The method is quick, requiring as little as 1 month from conceptualization to knockout, and highly efficient, enabling editing in >95% of target cells. To highlight its use, we used this system to inactivate, alone or in combination, genes with functions spanning metabolism, mitosis, mitochondrial maintenance, and cell proliferation.

CONCLUSIONS

RIME enables the rapid, efficient, and inexpensive analysis of multiple genes in the mouse liver in vivo .

Distinct hepatocyte identities in liver homeostasis and regeneration

The process of metabolic liver zonation is spontaneously established by assigning distributed tasks to hepatocytes along the porto-central blood flow. Hepatocytes fulfil critical metabolic functions, while also maintaining hepatocyte mass by replication when needed. Recent technological advances have enabled us to fine-tune our understanding of hepatocyte identity during homeostasis and regeneration. Subsets of hepatocytes have been identified to be more regenerative and some have even been proposed to function like stem cells, challenging the long-standing view that all hepatocytes are similarly capable of regeneration. The latest data show that hepatocyte renewal during homeostasis and regeneration after liver injury is not limited to rare hepatocytes; however, hepatocytes are not exactly the same. Herein, we review the known differences that give individual hepatocytes distinct identities, recent findings demonstrating how these distinct identities correspond to differences in hepatocyte regenerative capacity, and how the plasticity of hepatocyte identity allows for division of labour among hepatocytes. We further discuss how these distinct hepatocyte identities may play a role during liver disease.

Cardiomyocyte Ploidy, Metabolic Reprogramming and Heart Repair

The adult heart is made up of cardiomyocytes (CMs) that maintain pump function but are unable to divide and form new myocytes in response to myocardial injury. In contrast, the developmental cardiac tissue is made up of proliferative CMs that regenerate injured myocardium. In mammals, CMs during development are diploid and mononucleated. In response to cardiac maturation, CMs undergo polyploidization and binucleation associated with CM functional changes. The transition from mononucleation to binucleation coincides with unique metabolic changes and shift in energy generation. Recent studies provide evidence that metabolic reprogramming promotes CM cell cycle reentry and changes in ploidy and nucleation state in the heart that together enhances cardiac structure and function after injury. This review summarizes current literature regarding changes in CM ploidy and nucleation during development, maturation and in response to cardiac injury. Importantly, how metabolism affects CM fate transition between mononucleation and binucleation and its impact on cell cycle progression, proliferation and ability to regenerate the heart will be discussed.

Whole-Genome Doubling as a source of cancer: how, when, where, and why?

Chromosome instability is a well-known hallmark of cancer, leading to increased genetic plasticity of tumoral cells, which favors cancer aggressiveness, and poor prognosis. One of the main sources of chromosomal instability are events that lead to a Whole-Genome Duplication (WGD) and the subsequently generated cell polyploidy. In recent years, several studies showed that WGD occurs at the early stages of cell transformation, which allows cells to later become aneuploid, thus leading to cancer progression. On the other hand, other studies convey that polyploidy plays a tumor suppressor role, by inducing cell cycle arrest, cell senescence, apoptosis, and even prompting cell differentiation, depending on the tissue cell type. There is still a gap in understanding how cells that underwent WGD can overcome the deleterious effect on cell fitness and evolve to become tumoral. Some laboratories in the chromosomal instability field recently explored this paradox, finding biomarkers that modulate polyploid cells to become oncogenic. This review brings a historical view of how WGD and polyploidy impact cell fitness and cancer progression, and bring together the last studies that describe the genes helping cells to adapt to polyploidy.

Effect of Hepatic Pathology on Liver Regeneration: The Main Metabolic Mechanisms Causing Impaired Hepatic Regeneration

Liver regeneration has been studied for many decades, and the mechanisms underlying regeneration of normal liver following resection are well described. However, no less relevant is the study of mechanisms that disrupt the process of liver regeneration. First of all, a violation of liver regeneration can occur in the presence of concomitant hepatic pathology, which is a key factor reducing the liver's regenerative potential. Understanding these mechanisms could enable the rational targeting of specific therapies to either reduce the factors inhibiting regeneration or to directly stimulate liver regeneration. This review describes the known mechanisms of normal liver regeneration and factors that reduce its regenerative potential, primarily at the level of hepatocyte metabolism, in the presence of concomitant hepatic pathology. We also briefly discuss promising strategies for stimulating liver regeneration and those concerning methods for assessing the regenerative potential of the liver, especially intraoperatively.

Deep-Learning-Based Hepatic Ploidy Quantification Using H&E Histopathology Images

Polyploidy, the duplication of the entire genome within a single cell, is a significant characteristic of cells in many tissues, including the liver. The quantification of hepatic ploidy typically relies on flow cytometry and immunofluorescence (IF) imaging, which are not widely available in clinical settings due to high financial and time costs. To improve accessibility for clinical samples, we developed a computational algorithm to quantify hepatic ploidy using hematoxylin-eosin (H&E) histopathology images, which are commonly obtained during routine clinical practice. Our algorithm uses a deep learning model to first segment and classify different types of cell nuclei in H&E images. It then determines cellular ploidy based on the relative distance between identified hepatocyte nuclei and determines nuclear ploidy using a fitted Gaussian mixture model. The algorithm can establish the total number of hepatocytes and their detailed ploidy information in a region of interest (ROI) on H&E images. This is the first successful attempt to automate ploidy analysis on H&E images. Our algorithm is expected to serve as an important tool for studying the role of polyploidy in human liver disease.

PRMT5 determines the pattern of polyploidization and prevents liver from cirrhosis and carcinogenesis

Human hepatocellular carcinoma (HCC) occurs almost exclusively in cirrhotic livers. Here, we report that hepatic loss of protein arginine methyltransferase 5 (PRMT5) in mice is sufficient to cause cirrhosis and HCC in a clinically relevant way. Furthermore, pathological polyploidization induced by hepatic loss of PRMT5 promotes liver cirrhosis and hepatic tumorigenesis in aged liver. The loss of PRMT5 leads to hyper-accumulation of P21 and endoreplication-dependent formation of pathological mono-nuclear polyploid hepatocytes. PRMT5 and symmetric dimethylation at histone H4 arginine 3 (H4R3me2s) directly associate with chromatin of P21 to suppress its transcription. More importantly, loss of P21 rescues the pathological mono-nuclear polyploidy and prevents PRMT5-deficiency-induced liver cirrhosis and HCC. Thus, our results indicate that PRMT5-mediated symmetric dimethylation at histone H4 arginine 3 (H4R3me2s) is crucial for preventing pathological polyploidization, liver cirrhosis and tumorigenesis in mouse liver.

Single-cell resolved ploidy and chromosomal aberrations in nonalcoholic steatohepatitis-(NASH) induced hepatocellular carcinoma and its precursor lesions

Nonalcoholic steatohepatitis (NASH)-induced hepatocellular carcinoma (HCC) and its precursor, nonalcoholic fatty liver disease (NAFLD) are an unmet health issue due to widespread obesity. We assessed copy number changes of genes associated with hepatocarcinogenesis and oxidative pathways at a single-cell level. Eleven patients with NASH-HCC and 11 patients with NAFLD were included. Eight probes were analyzed using multiplex interphase fluorescence in situ hybridization (miFISH), single-cell imaging and phylogenetic tree modelling: Telomerase reverse transcriptase (TERT), C-Myc (MYC), hepatocyte growth factor receptor tyrosine kinase (MET), tumor protein 53 (TP53), cyclin D1 (CCND1), human epidermal growth factor receptor 2 (HER2), the fragile histidine triad gene (FHIT) and FRA16D oxidoreductase (WWOX). Each NASH-HCC tumor had up to 14 distinct clonal signal patterns indicating multiclonality, which correlated with high tumor grade. Changes frequently observed were TP53 losses, 45%; MYC gains, 36%; WWOX losses, 36%; and HER2 gains, 18%. Whole-genome duplications were frequent (82%) with aberrant tetraploid cells evolving from diploid ancestors. Non-tumorous NAFLD/NASH biopsies did not harbor clonal copy number changes. Fine mapping of NASH-HCC using single-cell multiplex FISH shows that branched tumor evolution involves genome duplication and that multiclonality increases with tumor grade. The loss of oxidoreductase WWOX and HER2 gains could be potentially associated with NASH-induced hepatocellular carcinoma.

The regulation of adipocyte growth in white adipose tissue

Adipocytes can increase in volume up to a thousand-fold, storing excess calories as triacylglycerol in large lipid droplets. The dramatic morphological changes required of adipocytes demands extensive cytoskeletal remodeling, including lipid droplet and plasma membrane expansion. Cell growth-related signalling pathways are activated, stimulating the production of sufficient amino acids, functional lipids and nucleotides to meet the increasing cellular needs of lipid storage, metabolic activity and adipokine secretion. Continued expansion gives rise to enlarged (hypertrophic) adipocytes. This can result in a failure to maintain growth-related homeostasis and an inability to cope with excess nutrition or respond to stimuli efficiently, ultimately leading to metabolic dysfunction. We summarize recent studies which investigate the functional and cellular structure remodeling of hypertrophic adipocytes. How adipocytes adapt to an enlarged cell size and how this relates to cellular dysfunction are discussed. Understanding the healthy and pathological processes involved in adipocyte hypertrophy may shed light on new strategies for promoting healthy adipose tissue expansion.

Liver regeneration after partial hepatectomy is improved in the absence of aryl hydrocarbon receptor

The liver is among the few organs having the ability to self-regenerate in response to a severe damage compromising its functionality. The Aryl hydrocarbon receptor (Ahr) is a transcription factor relevant for the detoxification of xenobiotics but also largely important for liver development and homeostasis. Hence, liver cell differentiation is developmentally modulated by Ahr through the controlled expression of pluripotency and stemness-inducing genes. Here, 2/3 partial hepatectomy (PH) was used as a clinically relevant approach to induce liver regeneration in Ahr-expressing (Ahr^+/+) and Ahr-null (Ahr^−/−) mice. Ahr expression and activity were early induced after 2/3 PH to be gradually downmodulated latter during regeneration. Ahr^−/− mice triggered liver regeneration much faster than AhR^+/+ animals, although both reached full regeneration at the latest times. At initial stages after PHx, earlier regenerating Ahr^−/− livers had upregulation of cell proliferation markers and increased activation of signalling pathways related to stemness such as Hippo-YAP and Wnt/β-catenin, concomitantly with the induction of pro-inflammatory cytokines TNFa, IL6 and p65. These phenotypes, together with the improved metabolic adaptation of Ahr^−/− mice after PHx and their induced sustained cell proliferation, could likely result from the expansion of undifferentiated stem cells residing in the liver expressing OCT4, SOX2, KLF4 and NANOG. We propose that Ahr needs to be induced early during regeneration to fine-tune liver regrowth to physiological values. Since Ahr deficiency did not result in liver overgrowth, its transient pharmacological inhibition could serve to improve liver regeneration in hepatectomized and transplanted patients and in those exposed to damaging liver toxins and carcinogens.

Polyploidization of Hepatocytes: Insights into the Pathogenesis of Liver Diseases

Polyploidization is a process by which cells are induced to possess more than two sets of chromosomes. Although polyploidization is not frequent in mammals, it is closely associated with development and differentiation of specific tissues and organs. The liver is one of the mammalian organs that displays ploidy dynamics in physiological homeostasis during its development. The ratio of polyploid hepatocytes increases significantly in response to hepatic injury from aging, viral infection, iron overload, surgical resection, or metabolic overload, such as that from non-alcoholic fatty liver diseases (NAFLDs). One of the unique features of NAFLD is the marked heterogeneity of hepatocyte nuclear size, which is strongly associated with an adverse liver-related outcome, such as hepatocellular carcinoma, liver transplantation, and liver-related death. Thus, hepatic polyploidization has been suggested as a potential driver in the progression of NAFLDs that are involved in the control of the multiple pathogenicity of the diseases. However, the importance of polyploidy in diverse pathophysiological contexts remains elusive. Recently, several studies reported successful improvement of symptoms of NAFLDs by reducing pathological polyploidy or by controlling cell cycle progression in animal models, suggesting that better understanding the mechanisms of pathological hepatic polyploidy may provide insights into the treatment of hepatic disorders.

Methodological Progress of Stereology in Cardiac Research and Its Application to Normal and Pathological Heart Development

Design-based stereology is the gold standard for obtaining unbiased quantitative morphological data on volume, surface area, and length, as well as the number of tissues, cells or organelles. In cardiac research, the introduction of a stereological method to unbiasedly estimate the number of cardiomyocytes has considerably increased the use of stereology. Since its original description, various modifications to this method have been described. A particular field in which this method has been employed is the normal developmental life cycle of cardiomyocytes after birth, and particularly the question of when, during postnatal development, cardiomyocytes lose their capacity to divide and proliferate, and thus their inherent regenerative ability. This field is directly related to a second major application of stereology in recent years, addressing the question of what consequences intrauterine growth restriction has on the development of the heart, particularly of cardiomyocytes. Advances have also been made regarding the quantification of nerve fibers and collagen deposition as measures of heart innervation and fibrosis. In the present review article, we highlight the methodological progress made in the last 20 years and demonstrate how stereology has helped to gain insight into the process of normal cardiac development, and how it is affected by intrauterine growth restriction.

Diploid hepatocytes drive physiological liver renewal in adult humans

Physiological liver cell replacement is central to maintaining the organ's high metabolic activity, although its characteristics are difficult to study in humans. Using retrospective radiocarbon (¹⁴C) birth dating of cells, we report that human hepatocytes show continuous and lifelong turnover, allowing the liver to remain a young organ (average age <3 years). Hepatocyte renewal is highly dependent on the ploidy level. Diploid hepatocytes show more than 7-fold higher annual birth rates than polyploid hepatocytes. These observations support the view that physiological liver cell renewal in humans is mainly dependent on diploid hepatocytes, whereas polyploid cells are compromised in their ability to divide. Moreover, cellular transitions between diploid and polyploid hepatocytes are limited under homeostatic conditions. With these findings, we present an integrated model of homeostatic liver cell generation in humans that provides fundamental insights into liver cell turnover dynamics.

Targeting anillin inhibits tumorigenesis and tumor growth in hepatocellular carcinoma via impairing cytokinesis fidelity

Targeting cytokinesis can suppress tumor growth by blocking cell division and promoting apoptosis. We aimed to characterize key cytokinesis regulator in hepatocellular carcinoma (HCC) progression, providing insights into identifying promising HCC therapeutic targets. The unbiased bioinformatic screening identified Anillin actin binding protein (ANLN) as a critical cytokinesis regulator involved in HCC development. Functional assay demonstrated that knockdown of ANLN inhibited HCC growth by inducing cytokinesis failure and DNA damage, leading to multinucleation and mitotic catastrophe. Mechanistically, ANLN acts as a scaffold to strengthen interaction between RACGAP1 and PLK1. ANLN promotes PLK1-mediated RACGAP1 phosphorylation and RhoA activation to ensure cytokinesis fidelity. To explore the function of ANLN in HCC tumorigenesis, we hydrodynamically transfected c-Myc and NRAS plasmids into Anln^+/+, Anln^+/-, and Anln^-/- mice through tail vein injection. Hepatic Anln ablation significantly impaired c-Myc/NRAS-driven hepatocarcinogenesis. Moreover, enhanced hepatic polyploidization was observed in Anln ablation mice, manifesting as increasing proportion of cellular and nuclear polyploidy. Clinically, ANLN is upregulated in human HCC tissues and high level of ANLN is correlated with poor patients' prognosis. Additionally, the proportion of cellular polyploidy decreases during HCC progression and ANLN level is significantly correlated with cellular polyploidy proportion in human HCC samples. In conclusion, ANLN is identified as a key cytokinesis regulator contributing to HCC initiation and progression. Our findings revealed a novel mechanism of ANLN in the regulation of cytokinesis to promote HCC tumorigenesis and growth, suggesting targeting ANLN to inhibit cytokinesis may be a promising therapeutic strategy for HCC.

Influence of Liver Extracellular Matrix in Predicting Drug-Induced Liver Injury: An Alternate Paradigm

In vitro drug-induced liver injury (DILI) models are promising tools for drug development to predict adverse events during clinical usage. However, the currently available DILI models are not specific or not able to predict the injury accurately. This is believed to be mainly because of failure to conserve the hepatocyte phenotype, lack of longevity, and difficulty in maintaining the tissue-specific microenvironment. In this study, we have assessed the potential of decellularized liver extracellular matrix (DLM) in retaining the hepatic cellular phenotype and functionality in the presence of a tissue-specific microenvironment along with its role in influencing the effect of the drug on hepatic cells. We show that DLM helps maintain the phenotype of the hepatic cell line HepG2, a well-known cell line for secretion of human proteins that is easily available. Also, the DLM enhanced the expression of a metabolic marker carbamoyl phosphate synthetase I (CPS1), a regulator of urea cycle, and bile salt export pump (BSEP), a marker of hepatocyte polarity. We further validated the DLM for its influence on the sensitivity of cells toward different classes of drugs. Interestingly, the coculture model, in the presence of endothelial cells and stellate cells, exhibited a higher sensitivity for both acetaminophen and trovafloxacin, a toxic compound that does not show any toxicity on preclinical screening. Thus, our results demonstrate for the first time that a multicellular combination along with DLM can be a potential and reliable DILI model to screen multiple drugs.

The Controversial Role of Polyploidy in Hepatocellular Carcinoma

Polyploidy, a physiological phenomenon in which cells contain more than two sets of homologous chromosomes, commonly exists in plants, fish, and amphibians but is rare in mammals. In humans, polyploid cells are detected commonly in specific organs or tissues including the heart, marrow, and liver. As the largest solid organ in the body, the liver is responsible for a myriad of functions, most of which are closely related to polyploid hepatocytes. It has been confirmed that polyploid hepatocytes are related to liver regeneration, homeostasis, terminal differentiation, and aging. Polyploid hepatocytes accumulate during the aging process as well as in chronically injured livers. The relationship between polyploid hepatocytes and hepatocellular carcinoma, the endpoint of most chronic liver diseases, is not yet fully understood. Recently, accumulated evidence has revealed that polyploid involves in the process of tumorigenesis and development. The study of the correlation and relationship between polyploidy hepatocytes and the development of hepatocellular carcinoma can potentially promote the prevention, early diagnosis, and treatment of hepatocellular carcinoma. In this review, we conclude the potential mechanisms of polyploid hepatocytes formation, focusing on the specific biological significance of polyploid hepatocytes. In addition, we examine recent discoveries that have begun to clarify the relevance between polyploid hepatocytes and hepatocellular carcinoma and discuss recent excellent findings that reveal the role of polyploid hepatocytes as resisters of hepatocellular carcinoma or as promoters of hepatocarcinogenesis.

Hepatocyte Polyploidy: Driver or Gatekeeper of Chronic Liver Diseases

Polyploidy, also known as whole-genome amplification, is a condition in which the organism has more than two basic sets of chromosomes. Polyploidy frequently arises during tissue development and repair, and in age-associated diseases, such as cancer. Its consequences are diverse and clearly different between systems. The liver is a particularly fascinating organ in that it can adapt its ploidy to the physiological and pathological context. Polyploid hepatocytes are characterized in terms of the number of nuclei per cell (cellular ploidy; mononucleate/binucleate hepatocytes) and the number of chromosome sets in each nucleus (nuclear ploidy; diploid, tetraploid, octoploid). The advantages and disadvantages of polyploidy in mammals are not fully understood. About 30% of the hepatocytes in the human liver are polyploid. In this review, we explore the mechanisms underlying the development of polyploid cells, our current understanding of the regulation of polyploidization during development and pathophysiology and its consequences for liver function. We will also provide data shedding light on the ways in which polyploid hepatocytes cope with centrosome amplification. Finally, we discuss recent discoveries highlighting the possible roles of liver polyploidy in protecting against tumor formation, or, conversely, contributing to liver tumorigenesis.

Obesity and hyperinsulinemia drive adipocytes to activate a cell cycle program and senesce

Obesity is considered an important factor for many chronic diseases, including diabetes, cardiovascular disease and cancer. The expansion of adipose tissue in obesity is due to an increase in both adipocyte progenitor differentiation and mature adipocyte cell size. Adipocytes, however, are thought to be unable to divide or enter the cell cycle. We demonstrate that mature human adipocytes unexpectedly display a gene and protein signature indicative of an active cell cycle program. Adipocyte cell cycle progression associates with obesity and hyperinsulinemia, with a concomitant increase in cell size, nuclear size and nuclear DNA content. Chronic hyperinsulinemia in vitro or in humans, however, is associated with subsequent cell cycle exit, leading to a premature senescent transcriptomic and secretory profile in adipocytes. Premature senescence is rapidly becoming recognized as an important mediator of stress-induced tissue dysfunction. By demonstrating that adipocytes can activate a cell cycle program, we define a mechanism whereby mature human adipocytes senesce. We further show that by targeting the adipocyte cell cycle program using metformin, it is possible to influence adipocyte senescence and obesity-associated adipose tissue inflammation.

Polyploidy in development and tumor models in Drosophila

Polyploidy, a cell status defined as more than two sets of genomic DNA, is a conserved strategy across species that can increase cell size and biosynthetic production, but the functional aspects of polyploidy are nuanced and vary across cell types. Throughout Drosophila developmental stages (embryo, larva, pupa and adult), polyploid cells are present in numerous organs and help orchestrate development while contributing to normal growth, well-being and homeostasis of the organism. Conversely, increasing evidence has shown that polyploid cells are prevalent in Drosophila tumors and play important roles in tumor growth and invasiveness. Here, we summarize the genes and pathways involved in polyploidy during normal and tumorigenic development, the mechanisms underlying polyploidization, and the functional aspects of polyploidy in development, homeostasis and tumorigenesis in the Drosophila model.

Cancer recurrence and lethality are enabled by enhanced survival and reversible cell cycle arrest of polyaneuploid cells

We present a unifying theory to explain cancer recurrence, therapeutic resistance, and lethality. The basis of this theory is the formation of simultaneously polyploid and aneuploid cancer cells, polyaneuploid cancer cells (PACCs), that avoid the toxic effects of systemic therapy by entering a state of cell cycle arrest. The theory is independent of which of the classically associated oncogenic mutations have already occurred. PACCs have been generally disregarded as senescent or dying cells. Our theory states that therapeutic resistance is driven by PACC formation that is enabled by accessing a polyploid program that allows an aneuploid cancer cell to double its genomic content, followed by entry into a nondividing cell state to protect DNA integrity and ensure cell survival. Upon removal of stress, e.g., chemotherapy, PACCs undergo depolyploidization and generate resistant progeny that make up the bulk of cancer cells within a tumor.

Polyploid cardiomyocytes: implications for heart regeneration

Terminally differentiated cells are generally thought to have arrived at their final form and function. Many terminally differentiated cell types are polyploid, i.e. they have multiple copies of the normally diploid genome. Mammalian heart muscle cells, termed cardiomyocytes, are one such example of polyploid cells. Terminally differentiated cardiomyocytes are bi- or multi-nucleated, or have polyploid nuclei. Recent mechanistic studies of polyploid cardiomyocytes indicate that they can limit cellular proliferation and, hence, heart regeneration. In this short Spotlight, we present the mechanisms generating bi- and multi-nucleated cardiomyocytes, and the mechanisms generating polyploid nuclei. Our aim is to develop hypotheses about how these mechanisms might relate to cardiomyocyte proliferation and cardiac regeneration. We also discuss how these new findings could be applied to advance cardiac regeneration research, and how they relate to studies of other polyploid cells, such as cancer cells.

Comparative analysis of liver involvement caused by two DENV-2 lineages using an immunocompetent murine model

Dengue (DEN) is the most prevalent arbovirus among humans, and four billion people live at risk of infection. The clinical manifestations of DEN are variable, and the disease may present subclinically or asymptomatically. A quarter of patients develop classical dengue (CD) or severe dengue (SD), which is potentially lethal and involves vascular permeability changes, severe hemorrhage and organ damage. The involvement of the liver is a fairly common feature in DEN, and alterations range from asymptomatic elevation of transaminases to acute liver failure. Since its introduction in Brazil in 1990, two strains of Dengue virus (DENV) serotype 2 (DENV-2) have been detected: Lineage I, which is responsible for an outbreak in 1991, and Lineage II, which caused an epidemic greater than the previous one and had a different epidemiological profile. To date, studies on different strains of the same serotype/genotype and their association with disease severity are scarce. In addition, one of the greatest challenges regarding the study of DEN pathogenesis and the development of drug and vaccine therapies is the absence of an animal model that reproduces the disease as it occurs in humans. The main goals of this study were to assess BALB/c mouse susceptibility experimentally infected by two distinct DENV-2 strains and characterize possible differences in the clinical signs and alterations induced in the liver resulting from those infections. Mice infected by the two DENV-2 lineages gained less weight than uninfected mice; however, their livers were slightly heavier. Increased AST and AST levels were observed in infected mice, and the number of platelets increased in the first 72 h of infection and subsequently decreased. Mice infected with both lineages presented leukocytosis but at different times of infection. The histopathological changes induced by both lineages were similar and comparable to the changes observed in DEN fatal cases. The viral genome was detected in two liver samples. The results demonstrate the susceptibility of BALB/c mice to both DENV-2 lineages and suggest that the changes induced by those strains are similar, although for some parameters, they are manifested at different times of infection.

Human cell polyploidization: The good and the evil

Therapeutic resistance represents a major cause of death for most lethal cancers. However, the underlying mechanisms of such resistance have remained unclear. The polyploid cells are due to an increase in DNA content, commonly associated with cell enlargement. In human, they play a variety of roles in physiology and pathologic conditions and perform the specialized functions during development, inflammation, and cancer. Recent work shows that cancer cells can be induced into polyploid giant cancer cells (PGCCs) that leads to reprogramming of surviving cancer cells to acquire resistance. In this article, we will review the polyploidy involved in development and inflammation, and the process of PGCCs formation and propagation that benefits to cell survival. We will discuss the potential opportunities in fighting resistant cancers. The increased knowledge of PGCCs will offer a completely new paradigm to explore the therapeutic intervention for lethal cancers.

Ssu72 Dual-Specific Protein Phosphatase: From Gene to Diseases

More than 70% of eukaryotic proteins are regulated by phosphorylation. However, the mechanism of dephosphorylation that counteracts phosphorylation is less studied. Phosphatases are classified into 104 distinct groups based on substrate-specific features and the sequence homologies in their catalytic domains. Among them, dual-specificity phosphatases (DUSPs) that dephosphorylate both phosphoserine/threonine and phosphotyrosine are important for cellular homeostasis. Ssu72 is a newly studied phosphatase with dual specificity that can dephosphorylate both phosphoserine/threonine and phosphotyrosine. It is important for cell-growth signaling, metabolism, and immune activation. Ssu72 was initially identified as a phosphatase for the Ser5 and Ser7 residues of the C-terminal domain of RNA polymerase II. It prefers the cis configuration of the serine-proline motif within its substrate and regulates Pin1, different from other phosphatases. It has recently been reported that Ssu72 can regulate sister chromatid cohesion and the separation of duplicated chromosomes during the cell cycle. Furthermore, Ssu72 appears to be involved in the regulation of T cell receptor signaling, telomere regulation, and even hepatocyte homeostasis in response to a variety of stress and damage signals. In this review, we aim to summarize various functions of the Ssu72 phosphatase, their implications in diseases, and potential therapeutic indications.

Type I Interferon Signaling Accelerates Liver Regeneration by Metabolic Modulation in Noninfectious Conditions

Type I interferon (IFN-I) has a well-known function in controlling viral infections, but its contribution in hepatocyte proliferation and hepatocellular carcinoma (HCC) formation remains unclear. Mice deficient in IFN-α receptor expression in whole mice or only in hepatocytes (Ifnar^-/- and Ifnar^Δliver) were used to investigate the role of IFN-I signaling in cell proliferation and cancer formation in the liver. Ifnar^-/- mice were resistant to chemical-induced HCC formation in the absence of infection. The results show that low grade of IFN-I and interferon-stimulated gene were expressed substantially in naïve mouse liver. The low level of IFN-I activation is constantly present in mouse liver after weaning and negatively modulates forkhead box O hepatic expression. The IFN-I signaling can be partially blocked by the clearance of lipopolysaccharide. Mice lacking IFN-I signaling have lower basal proliferation activity and delayed liver regeneration processes after two-thirds partial hepatectomy. The activation of IFN-I signaling on hepatocyte controls glucose homeostasis and lipid metabolism to support proliferation potency and long-term tumorigenesis. Our results reveal a positive role of low-grade IFN-I singling to hepatocyte proliferation and HCC formation by modulating glucose homeostasis and lipid metabolism.

Hepatocyte ploidy in cats with and without hepatocellular carcinoma

BACKGROUND

Domestic cats rarely develop hepatocellular carcinoma. The reason for the low prevalence is unknown. Reductions in hepatocellular ploidy have been associated with hepatic carcinogenesis. Recent work in mice has shown that livers with more polyploid hepatocytes are protected against the development of hepatocellular carcinoma. Hepatocyte ploidy in the domestic cat has not been evaluated. We hypothesized that ploidy would be reduced in peri-tumoral and neoplastic hepatocytes compared to normal feline hepatocytes. Using integrated fluorescence microscopy, we quantified the spectra of ploidy in hepatocellular carcinoma and healthy control tissue from paraffin embedded tissue sections.

RESULTS

Feline hepatocytes are predominantly mononuclear and the number of nuclei per hepatocyte did not differ significantly between groups. Normal cats have a greater number of tetraploid hepatocytes than cats with hepatocellular carcinoma.

CONCLUSIONS

Total hepatocellular polyploidy in normal cat liver is consistent with values reported in humans, yet cellular ploidy (nuclei per cell) is greater in humans than in cats. Tetraploid cat hepatocytes are predominantly mononuclear.

Proliferative polyploid cells give rise to tumors via ploidy reduction

Polyploidy is a hallmark of cancer, and closely related to chromosomal instability involved in cancer progression. Importantly, polyploid cells also exist in some normal tissues. Polyploid hepatocytes proliferate and dynamically reduce their ploidy during liver regeneration. This raises the question whether proliferating polyploids are prone to cancer via chromosome missegregation during mitosis and/or ploidy reduction. Conversely polyploids could be resistant to tumor development due to their redundant genomes. Therefore, the tumor-initiation risk of physiologic polyploidy and ploidy reduction is still unclear. Using in vivo lineage tracing we here show that polyploid hepatocytes readily form liver tumors via frequent ploidy reduction. Polyploid hepatocytes give rise to regenerative nodules with chromosome aberrations, which are enhanced by ploidy reduction. Although polyploidy should theoretically prevent tumor suppressor loss, the high frequency of ploidy reduction negates this protection. Importantly, polyploid hepatocytes that undergo multiple rounds of cell division become predominantly mononucleated and are resistant to ploidy reduction. Our results suggest that ploidy reduction is an early step in the initiation of carcinogenesis from polyploid hepatocytes.

Microdissected "cuboids" for microfluidic drug testing of intact tissues

As preclinical animal tests often do not accurately predict drug effects later observed in humans, most drugs under development fail to reach the market. Thus there is a critical need for functional drug testing platforms that use human, intact tissues to complement animal studies. To enable future multiplexed delivery of many drugs to one small biopsy, we have developed a multi-well microfluidic platform that selectively treats cuboidal-shaped microdissected tissues or "cuboids" with well-preserved tissue microenvironments. We create large numbers of uniformly-sized cuboids by semi-automated sectioning of tissue with a commercially available tissue chopper. Here we demonstrate the microdissection method on normal mouse liver, which we characterize with quantitative 3D imaging, and on human glioma xenograft tumors, which we evaluate after time in culture for viability and preservation of the microenvironment. The benefits of size uniformity include lower heterogeneity in future biological assays as well as facilitation of their physical manipulation by automation. Our prototype platform consists of a microfluidic circuit whose hydrodynamic traps immobilize the live cuboids in arrays at the bottom of a multi-well plate. Fluid dynamics simulations enabled the rapid evaluation of design alternatives and operational parameters. We demonstrate the proof-of-concept application of model soluble compounds such as dyes (CellTracker, Hoechst) and the cancer drug cisplatin. Upscaling of the microfluidic platform and microdissection method to larger arrays and numbers of cuboids could lead to direct testing of human tissues at high throughput, and thus could have a significant impact on drug discovery and personalized medicine.

Differential Roles for Diploid and Polyploid Hepatocytes in Acute and Chronic Liver Injury

Hepatocytes are the primary functional cells of the liver that perform essential roles in homeostasis, regeneration, and injury. Most mammalian somatic cells are diploid and contain pairs of each chromosome, but there are also polyploid cells containing additional sets of chromosomes. Hepatocytes are among the best described polyploid cells, with polyploids comprising more than 25 and 90% of the hepatocyte population in humans and mice, respectively. Cellular and molecular mechanisms that regulate hepatic polyploidy have been uncovered, and in recent years, diploid and polyploid hepatocytes have been shown to perform specialized functions. Diploid hepatocytes accelerate liver regeneration induced by resection and may accelerate compensatory regeneration after acute injury. Polyploid hepatocytes protect the liver from tumor initiation in hepatocellular carcinoma and promote adaptation to tyrosinemia-induced chronic injury. This review describes how ploidy variations influence cellular activity and presents a model for context-specific functions for diploid and polyploid hepatocytes.

Communal living: the role of polyploidy and syncytia in tissue biology

Multicellular organisms are composed of tissues with diverse cell sizes. Whether a tissue primarily consists of numerous, small cells as opposed to fewer, large cells can impact tissue development and function. The addition of nuclear genome copies within a common cytoplasm is a recurring strategy to manipulate cellular size within a tissue. Cells with more than two genomes can exist transiently, such as in developing germlines or embryos, or can be part of mature somatic tissues. Such nuclear collectives span multiple levels of organization, from mononuclear or binuclear polyploid cells to highly multinucleate structures known as syncytia. Here, we review the diversity of polyploid and syncytial tissues found throughout nature. We summarize current literature concerning tissue construction through syncytia and/or polyploidy and speculate why one or both strategies are advantageous.

Cancer cells employ an evolutionarily conserved polyploidization program to resist therapy

Unusually large cancer cells with abnormal nuclei have been documented in the cancer literature since 1858. For more than 100 years, they have been generally disregarded as irreversibly senescent or dying cells, too morphologically misshapen and chromatin too disorganized to be functional. Cell enlargement, accompanied by whole genome doubling or more, is observed across organisms, often associated with mitigation strategies against environmental change, severe stress, or the lack of nutrients. Our comparison of the mechanisms for polyploidization in other organisms and non-transformed tissues suggest that cancer cells draw from a conserved program for their survival, utilizing whole genome doubling and pausing proliferation to survive stress. These polyaneuploid cancer cells (PACCs) are the source of therapeutic resistance, responsible for cancer recurrence and, ultimately, cancer lethality.