Side Population: Its Use in the Study of Cellular Heterogeneity and as a Potential Enrichment Tool for Rare Cell Populations

Trophoblast Side-Population Markers are Dysregulated in Preeclampsia and Fetal Growth Restriction

Dysregulated progenitor cell populations may contribute to poor placental development and placental insufficiency pathogenesis. Side-population cells possess progenitor properties. Recent human trophoblast side-population isolation identified enrichment of 8 specific genes (CXCL8, ELL2, GATA6, HK2, HLA-DPB1, INTS6, SERPINE3 and UPP1) (Gamage et al. 2020, Stem Cell Rev Rep). We characterised these trophoblast side-population markers in human placenta and in placental insufficiency disorders: preeclampsia and fetal growth restriction (FGR). Trophoblast side-population markers localised to mononuclear trophoblasts lining the placental villous basement membrane in preterm control, preeclamptic and FGR placental sections (n = 3, panel of 3 markers/serial section). Analysis of single-cell transcriptomics of an organoid human trophoblast stem cell (hTSC) to extravillous trophoblast (EVT) differentiation model (Shannon et al. 2022, Development) identified that all side-population genes were enriched in mononuclear trophoblast and trophoblasts committed to differentiation under hTSC culture conditions. In vitro validation via 96 h time course hTSC differentiation to EVTs or syncytiotrophoblasts (n = 5) demonstrated ELL2 and HK2 increased with differentiation (p < 0.0024, p < 0.0039 respectively). CXCL8 and HLA-DPB1 were downregulated (p < 0.030, p < 0.011 respectively). GATA6 and INTS6 increased with EVT differentiation only, and UPP1 reduced with syncytialisation. SERPINE3 was undetectable. Trophoblast side-population marker mRNA was measured in human placentas (< 34-weeks' gestation; n = 78 preeclampsia, n = 30 FGR, and n = 18 gestation-matched controls). ELL2, HK2 and CXCL8 were elevated in preeclamptic (p = 0.0006, p < 0.0001, p = 0.0335 respectively) and FGR placentas (p = 0.0065, p < 0.0001, p = 0.0001 respectively) versus controls. Placental GATA6 was reduced in pregnancies with preeclampsia and FGR (p = 0.0014, p = 0.0146 respectively). Placental INTS6 was reduced with FGR only (p < 0.0001). This study identified the localisation of a unique trophoblast subset enriched for side-population markers. Aberrant expression of some side-population markers may indicate disruptions to unique trophoblast subtypes in placental insufficiency.

Transcriptional profiling reveals ataxia telangiectasia mutated pathways regulate joint copper and arsenic toxicity for hepatic metalloplasia and anti-cancer therapies

AIMS

Exposures to toxic metals, including arsenic (As), pose health risks but joint effects of physiologically needed metals, e.g., copper (Cu), are ill-defined for regulated metal-dependent cell proliferation (or metalloplasia). This study elucidated hepatic toxicities of As and Cu.

MAIN METHODS

Human HuH-7 cells were exposed to As and Cu and mRNA profiling obtained for molecular networks, regulators and signaling pathways. This followed biological testing of ATM signaling-related DNA damage response, mitochondrial dysfunction and lysosome activity using HuH-7 cells and primary hepatocytes. Free Cu ions were bound to 3-indole propionic acid for finding their contribution in toxicity.

KEY FINDINGS

The As or As plus Cu toxicities in HuH-7 cells produced dimorphic down- or up-regulation patterns in mRNA profiles. Significant differences extended for ontologies in protein synthesis, intermediary metabolism, mitochondrial function, autophagy, or cell survival and growth. Bioassays revealed ATM signaling regulated As and Cu toxicity for oxidative phosphorylation, mitochondrial membrane potential, lysosomal activity, DNA damage response, and cell growth-arrest. Removal of reactive Cu ions decreased As and Cu toxicity. Primary hepatocytes withstood Cu and As toxicity better.

SIGNIFICANCE

This joint As and Cu toxicity offers further mechanisms for metalloplasia, carcinogenesis and tissue damage in other settings, e.g., during excess Cu accumulation in Wilson disease. Moreover, joint As and Cu toxicities are relevant for anti-cancer therapies, potentially including manipulations to increase intracellular Cu through altered uptake or efflux processes and incorporating ATM-related checkpoint inhibitors. Superior tolerance of healthy hepatocytes to Cu and As toxicity should improve safety margins for anti-cancer therapies.

Cancer stem-like cells contribute to paclitaxel resistance in esophageal squamous cell carcinoma

OBJECTIVE

To examine the role of esophageal squamous cell carcinoma (ESCC) stem cells in paclitaxel resistance through the molecular characterization of ESCC stem cells.

METHODS

A resistant cell line (RR-ECl09) of cells were established using intermittent induction and time increments of high-dose paclitaxel in a human esophageal squamous cell carcinoma line (EC109). The multidrug resistance of RR-ECl09 cells to anticancer agents was evaluated by MTT assay. The RR-EC109 and EC109 cells were used for sphere formation assays, clonogenicity assays, stem cell gene expression, and the expression of epithelial-mesenchymal transition markers.

RESULTS

The RR-EC109 cells were established over 7 months. RR-ECl09 cells had 67.258 fold resistance to paclitaxel. The percentage of sphere formation and clone proliferation ability of RR-EC109 cells was higher than that of EC109 cells (P < 0.05). The amount of side population cells in RR-EC109 cells was higher than that of EC109 cells (P < 0.05). RR-EC109 cells produced more mRNA for Bmi1, Nanog, Oct4, Sox2, ABCG2, Nestin, and Ki-67 than EC109 cells (P < 0.05). E-cadherin expression was lower in RR-EC109 cells than in EC109 cells, while N-cadherin, Snail, and Twist expressions were higher in RR-EC109 cells than in EC109 cells (P < 0.05).

CONCLUSIONS

Cancer stem cell (CSC)-like cells exist among paclitaxel-resistant cells in ESCC and may play a role in ESCC drug resistance.

Cancer Stem Cells and the Tumor Microenvironment in Gastric Cancer

Gastric cancer (GC) remains one of the leading causes of cancer-related death worldwide. Cancer stem cells (CSCs) might be responsible for tumor initiation, relapse, metastasis and treatment resistance of GC. The tumor microenvironment (TME) comprises tumor cells, immune cells, stromal cells and other extracellular components, which plays a pivotal role in tumor progression and therapy resistance. The properties of CSCs are regulated by cells and extracellular matrix components of the TME in some unique manners. This review will summarize current literature regarding the effects of CSCs and TME on the progression and therapy resistance of GC, while emphasizing the potential for developing successful anti-tumor therapy based on targeting the TME and CSCs.

EpCAM-Mediated Cellular Plasticity Promotes Radiation Resistance and Metastasis in Breast Cancer

Substantial number of breast cancer (BC) patients undergoing radiation therapy (RT) develop local recurrence over time. During RT therapy, cells can gradually acquire resistance implying adaptive radioresistance. Here we probe the mechanisms underlying this acquired resistance by first establishing radioresistant lines using ZR-75-1 and MCF-7 BC cells through repeated exposure to sub-lethal fractionated dose of 2Gy up to 15 fractions. Radioresistance was found to be associated with increased cancer stem cells (CSCs), and elevated EpCAM expression in the cell population. A retrospective analysis of TCGA dataset indicated positive correlation of high EpCAM expression with poor response to RT. Intriguingly, elevated EpCAM expression in the radioresistant CSCs raise the bigger question of how this biomarker expression contributes during radiation treatment in BC. Thereafter, we establish EpCAM overexpressing ZR-75-1 cells (ZR-75-1^EpCAM), which conferred radioresistance, increased stemness through enhanced AKT activation and induced a hybrid epithelial/mesenchymal phenotype with enhanced contractility and invasiveness. In line with these observations, orthotopic implantation of ZR-75-1^EpCAM cells exhibited faster growth, lesser sensitivity to radiation therapy and increased lung metastasis than baseline ZR-75-1 cells in mice. In summary, this study shows that similar to radioresistant BC cells, EpCAM overexpressing cells show high degree of plasticity and heterogeneity which ultimately induces radioresistant and metastatic behavior of cancer cells, thus aggravating the disease condition.

Therapeutic Potential of Endothelial Colony-Forming Cells in Ischemic Disease: Strategies to Improve their Regenerative Efficacy

Cardiovascular disease (CVD) comprises a range of major clinical cardiac and circulatory diseases, which produce immense health and economic burdens worldwide. Currently, vascular regenerative surgery represents the most employed therapeutic option to treat ischemic disorders, even though not all the patients are amenable to surgical revascularization. Therefore, more efficient therapeutic approaches are urgently required to promote neovascularization. Therapeutic angiogenesis represents an emerging strategy that aims at reconstructing the damaged vascular network by stimulating local angiogenesis and/or promoting de novo blood vessel formation according to a process known as vasculogenesis. In turn, circulating endothelial colony-forming cells (ECFCs) represent truly endothelial precursors, which display high clonogenic potential and have the documented ability to originate de novo blood vessels in vivo. Therefore, ECFCs are regarded as the most promising cellular candidate to promote therapeutic angiogenesis in patients suffering from CVD. The current briefly summarizes the available information about the origin and characterization of ECFCs and then widely illustrates the preclinical studies that assessed their regenerative efficacy in a variety of ischemic disorders, including acute myocardial infarction, peripheral artery disease, ischemic brain disease, and retinopathy. Then, we describe the most common pharmacological, genetic, and epigenetic strategies employed to enhance the vasoreparative potential of autologous ECFCs by manipulating crucial pro-angiogenic signaling pathways, e.g., extracellular-signal regulated kinase/Akt, phosphoinositide 3-kinase, and Ca²⁺ signaling. We conclude by discussing the possibility of targeting circulating ECFCs to rescue their dysfunctional phenotype and promote neovascularization in the presence of CVD.

4,4'‑Bond secalonic acid D targets SP cells and inhibits metastasis in hepatocellular carcinoma

The existence of cancer stem cells (CSCs) is considered to be the main reason for chemoresistance, metastasis and the ultimate failure of treatment in hepatocellular carcinoma (HCC). However, there are a few chemical agents that may inhibit CSCs. The present study identified that 4,4'‑bond secalonic acid D (4,4'‑SAD), a compound isolated from the marine‑derived fungus Penicillium oxalicum, inhibited the growth of side population (SP) cells isolated from human liver cancer cell lines PLC/PRF/5 and HuH‑7 by attenuating the expression of ATP‑binding cassette superfamily G member 2. Furthermore, the results of wound healing, Transwell, western blotting and reverse transcription‑quantitative PCR assays demonstrated that 4,4'‑SAD suppressed the invasion and migration of SP cells by downregulating matrix metallopeptidase 9 (MMP‑9) and upregulating the antagonist tissue inhibitor of metalloproteinases 1 in vitro. Moreover, in vivo study results found that 4,4'‑SAD had anti‑lung metastasis efficacy via the decrease of MMP‑9 expression in the H22 HCC model of Kunming mice. Therefore, the present study identified the potential of 4,4'‑SAD as a promising candidate for the treatment of advanced liver cancer.