iPSC microtissue gives clues to heart disease

Researchers at Leiden University Medical Center have developed a three cell type microtissue from human induced pluripotent stem cells (iPSCs) that increased the maturation of iPSC-derived heart muscle cells, and afforded the researchers new insights into how different heart cell types communicate in healthy and diseased heart tissue. Heart muscle cells, or cardiomyocytes, can be developed from iPSCs to a point, but such cells do not mature fully. The authors sought to help their development by co-culturing them with other cell types, which has improved the realism of cell cultures in organoid models. The team separately derived heart muscle cells, fibroblasts and endothelial cells, which allowed them to investigate the consequences of genetic mutations specifically in one cell type. They found that microtissues made from healthy heart muscle cells but fibroblasts derived from iPSCs of patients with arrhythmogenic cardiomyopathy “strikingly recapitulated features of the disease,” the authors wrote. “Our [microtissue] model is thus a simple and versatile platform for modeling multicellular cardiac diseases that will facilitate industry and academic engagement in high-throughput molecular screening.” Their work appeared in the May 26, 2020, issue of Cell Stem Cell.

Tumor types have distinct microbiomes

Investigators at the Weizmann Institute of Science have profiled the tumor microbiomes of seven solid tumor types, and found that each tumor type had a distinct microbiome profile, and that microbiome profiles also correlated with tumor subtypes, as well as smoking status and the response to immunotherapy. It has long been known that tumors have bacteria associated with them, but gaining a detailed understanding of that tumor microbiome has been challenging because such bacteria are present in low levels, making them difficult to sequence without contamination. The Weizmann team developed multiple protocols for identifying contamination, and were able to establish microbiome profiles for breast, lung, ovarian, pancreatic, melanoma, bone and brain tumors. The experiments did not give insight into whether bacteria were causal in tumor development, but the authors argued that “whether or not bacteria play a causal role in tumorigenesis, it is of interest to further explore the effects that intratumor bacteria may have on different phenotypes of cancer cells and on the immune system and its interactions with tumor cells. Just as manipulation of the gut microbiome has been shown to affect the response of tumors to immune-checkpoint blockade therapy, we speculate that manipulation of the tumor microbiome may also affect tumor immunity and the response to immune therapy.” Their study appeared in the May 9, 2020, issue of Science.

Kinase helps prepare pre-metastatic niche

Before the formation of overt metastases, circulating cells from the primary tumor prepare future landing spots through the induction of a pre-metastatic niche. Researchers at the University of Pennsylvania have identified the induction of p38a kinase signaling as an important step in the formation of the pre-metastatic niche. Many signaling molecules from primary tumor cells have been implicated in niche formation, prompting the researchers to look for common signaling pathways that were induced by such cells. They showed that tumor-derived factors from cultured tumor cells activated p38a kinase, suppressing antitumor type I interferon signaling and inducing remodeling of the extracellular matrix in the lungs of mice, which led to greater tumor formation. Treatment with the p38a kinase inhibitor ralimetinib (LY2228820) could prevent the formation of the premetastatic niche when it was administered together with tumor-derived factors. Previous work has shown that p38 kinase inhibitors could increase metastasis formation in immunocompromised mice, but decrease them in immune competent animals. The authors wrote that “given the efficacy of p38 inhibitors… shown in this work, these agents might be of translational importance in the context of adjuvant or/and neoadjuvant therapy.” Their work appeared in the May 25, 2020, online issue of Nature Cancer.

Estrogen and dopamine

Researchers at the University of Illinois at Chicago have found that both estrogen receptors and metabotropic glutamate receptors on dopaminergic neurons in the ventral tegmental area played a role in binge drinking in female rats. Estrogen potentiates the effects of the dopamine system, and females are more vulnerable to addiction to a variety of substances, including alcohol. Estrogen also appears to play a role in binge drinking, which accounts for much of alcohol’s negative effects. The authors used RNA knockdown of estrogen receptors alpha and beta specifically in the midbrain ventral tegmental area to tease out how both receptors affected binge drinking. They demonstrated that the alpha receptor had a greater effect on binge drinking, and cooperated with the metabotropic glutamate receptor to increase neuronal excitability. The authors wrote that “these studies provide important mechanistic and behavioral insights into estrogen receptor signaling in the brain that are relevant to [alcohol use disorder] in females.” They reported their results in the May 26, 2020, issue of the Journal of Neuroscience.

EZH2 has dual role

EZH2 can act as a transcription factor, and in doing so, facilitates the development of brain metastases, scientists at MD Anderson Cancer Center have found. Neurons and glia contribute to the tumor microenvironment that allows brain metastases to establish themselves, but whether the same is true for immune cells has remained controversial. The authors showed that neutrophils, which are peripheral innate immune cells, could breach the blood-brain barrier in cancer. Neutrophils were attracted by cancer cells in the brain where EZH2, normally a protein that contributes to epigenetic silencing of genes, was phosphorylated by Src kinase and acted as a transcription factor to drive the expression of the proinflammatory cytokine granulocyte-colony stimulating factor (G-CSF) instead. “G-CSF-blocking antibodies or immune checkpoint blockade therapies combined with Src inhibitors impeded brain metastasis in multiple mouse models,” the authors wrote. These findings indicate that [phosphorylated] EZH2 can function as a methyltransferase-independent transcription factor to facilitate the brain infiltration of immunosuppressive neutrophils, which could be clinically targeted for brain metastasis treatment.” They reported their findings in the May 27, 2020, issue of Science Translational Medicine.

New alcohol risk genes in Caucasians

Researchers at Yale University have used meta-analysis of studies of more than 450,000 European-ancestry individuals to identify new risk loci for problematic alcohol use. The heritability of alcohol use disorders looks to be around 6% to 10%, with previously identified risk genes clustering in alcohol-metabolizing enzymes. By conducting a meta-analysis on four large datasets, the authors were able to identify almost 20 new risk loci, and show that alcohol use disorder co-occurred with other substance abuse and psychiatric disorders. However, “we limited the focus here to European samples because we could not achieve a substantial increment in African-ancestry subjects over previous studies.” They published their results in the May 25, 2020, online issue of Nature Neuroscience.

Assay system identifies mitochondria-targeting drugs for PD

Researchers at the Juntendo University School of Medicine have developed a high-throughput screening method to measure disease phenotypes in iPSC-derived dopaminergic neurons, and the effects of drugs on those phenotypes. Mitochondrial dysfunction is a key problem in Parkinson’s disease (PD), and risk variants in several genes, including Parkin, PINK1 and LRRK2, result in mitochondrial dysfunction. The authors developed an imaging-based assay system that could identify mitochondrial dysfunction, and used it to screen more than 300 compounds for their ability to reverse deficits in mitochondrial clearance, ROS accumulation and increased apoptosis in patient-derived iPSCs. They identified four candidate drugs. “Some of these drugs improved the locomotion defects and reduced ATP production caused by PINK1 inactivation in Drosophila and were effective for idiopathic PD-derived neurons with impaired mitochondrial clearance. Our findings suggest that the proposed high-throughput system has potential for identifying effective drugs for familial and idiopathic PD,” they wrote. They published their paper in the May 28, 2020, online issue of Stem Cell Reports.

Evasin proteins produced by ticks attach to chemokines, preventing inflammation. Credit: University of Sydney

Imitating ticks to evade immunity

Ticks are able to attach and feed for prolonged periods – and spread diseases while they do so – in part because they inject evasins into their hosts, proteins which disrupts the recruitment of immune cells by chemokines. Researchers at the University of Sydney have synthesized and characterized the evasin ACA-01, and shown that sulfates attached to the protein strengthened its ability to disrupt signaling between chemokines and immune cells. Chemokine signaling underlies a number of autoimmune inflammatory diseases, and the authors concluded that “our work lays the foundation for the development of engineered sulfopeptides and sulfoproteins to target a range of inflammatory diseases associated with dysregulated chemokine-receptor signaling.” They published their findings in the May 27, 2020, online issue of the Proceedings of the National Academy of Sciences.

Ovarian organoids implicate oviducts

Scientists at the Hubrecht Institute have investigated the origins of ovarian cancer using organoids. Ovarian cancer is often diagnosed in advanced stages, and as a result, less is known about its early stages than for other tumor types. One question is which tissues ovarian tumors originate from, with the two main suspects being the fallopian tube, or oviduct, and the epithelial tissue. Using CRISPR editing, the investigators generated organoids with mutations in the genes that are most frequently mutated in ovarian tumors, which are Trp53, Brca1, Nf1 and Pten. They showed that tumors could arise from either oviducts or epithelial cells. However, they wrote, “the mutated oviductal organoids expand much faster in vitro and more readily form malignant tumors upon transplantation. Furthermore, in vitro drug testing reveals distinct lineage-dependent sensitivities to the common drugs used to treat [high-grade serous ovarian cancer] in patients.” They reported their results in the May 27, 2020, online issue of Nature Communications.

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