Probes for INS

Fibroblasts are highly dynamic cells that play a central role in tissue repair and fibrosis. However, the mechanisms by which they contribute to both physiologic and pathologic states of extracellular matrix deposition and remodeling are just starting to be understood. In this review article, we discuss the current state of knowledge in fibroblast biology and heterogeneity, with a primary focus on the role of fibroblasts in skin wound repair. We also consider emerging techniques in the field, which enable an increasingly nuanced and contextualized understanding of these complex systems, and evaluate limitations of existing methodologies and knowledge. Collectively, this review spotlights a diverse body of research examining an often-overlooked cell type-the fibroblast-and its critical functions in wound repair and beyond.

A central factor in the maintenance of tissue integrity is the response of stem cells to variations in the levels of niche signals. In the gut, intestinal stem cells (ISCs) depend on Wnt ligands for self-renewal and proliferation. Transient increases in Wnt signaling promote regeneration after injury or in inflammatory bowel diseases, whereas constitutive activation of this pathway leads to colorectal cancer. Here, we report that Discs large 1 (Dlg1), although dispensable for polarity and cellular turnover during intestinal homeostasis, is required for ISC survival in the context of increased Wnt signaling. RNA sequencing (RNA-seq) and genetic mouse models demonstrated that DLG1 regulates the cellular response to increased canonical Wnt ligands. This occurs via the transcriptional regulation of Arhgap31, a GTPase-activating protein that deactivates CDC42, an effector of the non-canonical Wnt pathway. These findings reveal a DLG1-ARHGAP31-CDC42 axis that is essential for the ISC response to increased niche Wnt signaling.

In adults, hepatocytes are mainly replenished from the existing progenitor pools of hepatocytes and cholangiocytes during chronic liver injury. However, it is unclear whether other cell types in addition to classical hepatocytes and cholangiocytes contribute to hepatocyte regeneration after chronic liver injuries. Here, we identified a new biphenotypic cell population that contributes to hepatocyte regeneration during chronic liver injuries. We found that a cell population expressed Gli1 and EpCAM (EpCAM+Gli1+), which was further characterized with both epithelial and mesenchymal identities by single-cell RNA sequencing. Genetic lineage tracing using dual recombinases revealed that Gli1+ nonhepatocyte cell population could generate hepatocytes after chronic liver injury. EpCAM+Gli1+ cells exhibited a greater capacity for organoid formation with functional hepatocytes in vitro and liver regeneration upon transplantation in vivo. Collectively, these findings demonstrate that EpCAM+Gli1+ cells can serve as a new source of liver progenitor cells and contribute to liver repair and regeneration.

RNA expression data from all timepoints of perforation were merged and analyzed, revealing 8 distinct major populations of cells and revealing time-dependent transcriptional shifts in each layer of the TM. From both cross-sectional and whole-mount views, the TM shows a rapid, proliferative response to injury by 18 hours post-injury, predominantly in the KCs. 3 days after perforation, there are large transcriptional shifts in the immune, mesenchymal, and mucosal populations. The multi-layered tissue shows a large volumetric increase by day 7 but quickly remodels and restores the original volume of the TM by day 14. At slightly longer timepoints, the radial and circular collagen patterning of the TM is also restored, creating a scar-free structure. We identified a regeneration-induced “wounded epithelial” population, characterized by a combination of distinct marker genes. A _K5Cre-ERT2;Confetti_ mouse model shows that the population migrates from known stem cell regions of the organ to the site of injury. Based on expression values and immunostaining, EGFR signaling is upregulated during regeneration, corresponding with increased expression of EGFR ligands and processing co-factors. When EGFR is deleted _in vivo_, using a _K5-CreERT2_;_Egfrfl/fl; R26mTmG/mTmG_ mouse model, TMs no longer display proliferation post-injury and cannot repair perforations.