Topics overview: Highlight ITGA7 can act as a glioblastoma biomarker and candidate therapeutic target, Transient Activation of BMP Signaling, The function of Intestinal Enteroendocrine Lineage Cells, How stem cells are triggered to enter this proliferative TA state, The role of immune cells in lung regeneration.
1. Integrin α7 Is a Functional Marker and Potential Therapeutic Target in Glioblastoma
Functionally relevant markers of glioblastoma stem-like cells (GSCs) have potential for therapeutic targeting to treat this aggressive disease. Here Tobias L. Haas at Institute of General Pathology, Università Cattolica del Sacro Cuore in Rome, Italy and his colleagues used generation and screening of thousands of monoclonal antibodies to search for receptors and signaling pathways preferentially enriched in GSCs. They identified integrin α7 (ITGA7) as a major laminin receptor in GSCs and in primary high-grade glioma specimens. Analyses of mRNA profiles in comprehensive datasets revealed that high ITGA7 expression negatively correlated with survival of patients with both low- and high-grade glioma. In vitro and in vivo analyses showed that ITGA7 plays a key functional role in growth and invasiveness of GSCs. They also found that targeting of ITGA7 by RNAi or blocking mAbs impaired laminin-induced signaling, and it led to a significant delay in tumor engraftment plus a strong reduction in tumor size and invasion. Their data, therefore, highlight ITGA7 as a glioblastoma biomarker and candidate therapeutic target.
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2. Differentiation of Human Pluripotent Stem Cells into Colonic Organoids via Transient Activation of BMP Signaling
Gastric and small intestinal organoids differentiated from human pluripotent stem cells (hPSCs) have revolutionized the study of gastrointestinal development and disease. Distal gut tissues such as cecum and colon, however, have proved considerably more challenging to derive in vitro. Here Jorge O. Múnera at Division of Developmental Biology, Cincinnati Children’s Hospital Research Foundation in Cincinnati, USA and his colleagues report the differentiation of human colonic organoids (HCOs) from hPSCs. They found that BMP signaling is required to establish a posterior SATB2+ domain in developing and postnatal intestinal epithelium. Brief activation of BMP signaling is sufficient to activate a posterior HOX code and direct hPSC-derived gut tube cultures into HCOs. In vitro, HCOs express colonic markers and contained colon-specific cell populations. Following transplantation into mice, HCOs undergo morphogenesis and maturation to form tissue that exhibits molecular, cellular, and morphologic properties of human colon. Together these data show BMP-dependent patterning of human hindgut into HCOs, which will be valuable for studying diseases including colitis and colon cancer.
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3. Intestinal Enteroendocrine Lineage Cells Possess Homeostatic and Injury-Inducible Stem Cell Activity
Several cell populations have been reported to possess intestinal stem cell (ISC) activity during homeostasis and injury-induced regeneration. Here, Kelley S. Yan at Stanford University School of Medicine in Stanford, USA and his colleagues explored inter-relationships between putative mouse ISC populations by comparative RNA-sequencing (RNA-seq). The transcriptomes of multiple cycling ISC populations closely resembled Lgr5+ ISCs, the most well-defined ISC pool, but Bmi1-GFP+ cells were distinct and enriched for enteroendocrine (EE) markers, including Prox1. Prox1-GFP+ cells exhibited sustained clonogenic growth in vitro, and lineage-tracing of Prox1+ cells revealed long-lived clones during homeostasis and after radiation-induced injury in vivo. Single-cell mRNA-seq revealed two subsets of Prox1-GFP+ cells, one of which resembled mature EE cells while the other displayed low-level EE gene expression but co-expressed tuft cell markers, Lgr5 and Ascl2, reminiscent of label-retaining secretory progenitors. Their data suggest that the EE lineage, including mature EE cells, comprises a reservoir of homeostatic and injury-inducible ISCs, extending our understanding of cellular plasticity and stemness.
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4. An FAK-YAP-mTOR Signaling Axis Regulates Stem Cell-Based Tissue Renewal in Mice
Tissue homeostasis requires the production of newly differentiated cells from resident adult stem cells. Central to this process is the expansion of undifferentiated intermediates known as transit-amplifying (TA) cells, but how stem cells are triggered to enter this proliferative TA state remains an important open question. Using the continuously growing mouse incisor as a model of stem cell-based tissue renewal, Jimmy Kuang-Hsien Hu at University of California in San Francisco, USA and his colleagues found that the transcriptional cofactors YAP and TAZ are required both to maintain TA cell proliferation and to inhibit differentiation. Specifically, they identified a pathway involving activation of integrin α3 in TA cells that signals through an LATS-independent FAK/CDC42/PP1A cascade to control YAP-S397 phosphorylation and nuclear localization. This leads to Rheb expression and potentiates mTOR signaling to drive the proliferation of TA cells. These findings thus reveal a YAP/TAZ signaling mechanism that coordinates stem cell expansion and differentiation during organ renewal, the authors suggest.
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5. Recruited Monocytes and Type 2 Immunity Promote Lung Regeneration following Pneumonectomy
To investigate the role of immune cells in lung regeneration, Andrew J. Lechner at University of California in San Francisco, USA and his colleagues used a unilateral pneumonectomy model that promotes the formation of new alveoli in the remaining lobes. Immunofluorescence and single-cell RNA sequencing found CD115+ and CCR2+ monocytes and M2-like macrophages accumulating in the lung during the peak of type 2 alveolar epithelial stem cell (AEC2) proliferation. Genetic loss of function in mice and adoptive transfer studies revealed that bone marrow-derived macrophages (BMDMs) traffic to the lung through a CCL2-CCR2 chemokine axis and are required for optimal lung regeneration, along with Il4ra-expressing leukocytes. Their data suggest that these cells modulate AEC2 proliferation and differentiation. Finally, they provide evidence that group 2 innate lymphoid cells are a source of IL-13, which promotes lung regeneration. Together, their data highlight the potential for immunomodulatory therapies to stimulate alveologenesis in adults.
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