Meflin/ISLR is a marker of adipose stem and progenitor cells in mice and humans that suppresses white adipose tissue remodeling and fibrosis.

Identifying specific markers of adipose stem and progenitor cells (ASPCs) in vivo is crucial for understanding the biology of white adipose tissues (WAT). PDGFRα-positive perivascular stromal cells represent the best candidates for ASPCs. This cell lineage differentiates into myofibroblasts that contribute to the impairment of WAT function. However, ASPC marker protein(s) that are functionally crucial for maintaining WAT homeostasis are unknown. We previously identified Meflin as a marker of mesenchymal stem cells (MSCs) in bone marrow and tissue-resident perivascular fibroblasts in various tissues. We also demonstrated that Meflin maintains the undifferentiated status of MSCs/fibroblasts. Here, we show that Meflin is expressed in WAT ASPCs. A lineage-tracing experiment showed that Meflin+ ASPCs proliferate in the WAT of obese mice induced by a high-fat diet (HFD), while some of them differentiate into myofibroblasts or mature adipocytes. Meflin knockout mice fed an HFD exhibited a significant fibrotic response as well as increases in adipocyte cell size and the number of crown-like structures in WAT, accompanied by impaired glucose tolerance. These data suggested that Meflin expressed by ASPCs may have a role in reducing disease progression associated with WAT dysfunction.

Synthetic retinoid-mediated preconditioning of cancer-associated fibroblasts and macrophages improves cancer response to immune checkpoint blockade.

BACKGROUND: The proliferation of cancer-associated fibroblasts (CAFs) hampers drug delivery and anti-tumor immunity, inducing tumor resistance to immune checkpoint blockade (ICB) therapy. However, it has remained a challenge to develop therapeutics that specifically target or modulate CAFs. METHODS: We investigated the involvement of Meflin+ cancer-restraining CAFs (rCAFs) in ICB efficacy in patients with clear cell renal cell carcinoma (ccRCC) and urothelial carcinoma (UC). We examined the effects of Am80 (a synthetic retinoid) administration on CAF phenotype, the tumor immune microenvironment, and ICB efficacy in cancer mouse models. RESULTS: High infiltration of Meflin+ CAFs correlated with ICB efficacy in patients with ccRCC and UC. Meflin+ CAF induction by Am80 administration improved ICB efficacy in the mouse models of cancer. Am80 exerted this effect when administered prior to, but not concomitant with, ICB therapy in wild-type but not Meflin-deficient mice. Am80-mediated induction of Meflin+ CAFs was associated with increases in antibody delivery and M1-like tumor-associated macrophage (TAM) infiltration. Finally, we showed the role of Chemerin produced from CAFs after Am80 administration in the induction of M1-like TAMs. CONCLUSION: Our data suggested that Am80 administration prior to ICB therapy increases the number of Meflin+ rCAFs and ICB efficacy by inducing changes in TAM phenotype.

Endothelial cells regulate alveolar morphogenesis by constructing basement membranes acting as a scaffold for myofibroblasts.

Alveologenesis is a spatially coordinated morphogenetic event, during which alveolar myofibroblasts surround the terminal sacs constructed by epithelial cells and endothelial cells (ECs), then contract to form secondary septa to generate alveoli in the lungs. Recent studies have demonstrated the important role of alveolar ECs in this morphogenetic event. However, the mechanisms underlying EC-mediated alveologenesis remain unknown. Herein, we show that ECs regulate alveologenesis by constructing basement membranes (BMs) acting as a scaffold for myofibroblasts to induce septa formation through activating mechanical signaling. Rap1, a small GTPase of the Ras superfamily, is known to stimulate integrin-mediated cell adhesions. EC-specific Rap1-deficient (Rap1iECKO) mice exhibit impaired septa formation and hypo-alveolarization due to the decreased mechanical signaling in myofibroblasts. In Rap1iECKO mice, ECs fail to stimulate integrin ß1 to recruit Collagen type IV (Col-4) into BMs required for myofibroblast-mediated septa formation. Consistently, EC-specific integrin ß1-deficient mice show hypo-alveolarization, defective mechanical signaling in myofibroblasts, and disorganized BMs. These data demonstrate that alveolar ECs promote integrin ß1-mediated Col-4 recruitment in a Rap1-dependent manner, thereby constructing BMs acting as a scaffold for myofibroblasts to induce mechanical signal-mediated alveologenesis. Thus, this study unveils a mechanism of organ morphogenesis mediated by ECs through intrinsic functions.

Protocol for the isolation of GFP-expressing ferroptosis-dependent extracellular vesicles in in vitro cell culture models.

Extracellular vesicles (EVs) are complex structures that transport various DNA, RNA, and protein. Recently, new EV secretion mechanisms have been identified through the iron regulatory system in mammalian cells. We revealed that ferroptosis increases EV secretion, which is named ferroptosis-dependent EVs (FedEVs). Here, we describe a step-by-step procedure to isolate GFP-expressing FedEVs for in vitro analysis. The FedEVs are further analyzed by imaging and flow cytometry analysis. For complete details on the use and execution of this protocol, please refer to Ito et al.1.

Meflin is a marker of pancreatic stellate cells involved in fibrosis and epithelial regeneration in the pancreas.

Pancreatic stellate cells (PSCs) are stromal cells in the pancreas that play an important role in pancreatic pathology. In chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC), PSCs are known to get activated to form myofibroblasts or cancer-associated fibroblasts (CAFs) that promote stromal fibroinflammatory reactions. However, previous studies on PSCs were mainly based on the findings obtained using ex vivo expanded PSCs, with few studies that addressed the significance of in situ tissue-resident PSCs using animal models. Their contributions to fibrotic reactions in CP and PDAC are also lesser-known. These limitations in our understanding of PSC biology have been attributed to the lack of specific molecular markers of PSCs. Herein, we established Meflin (Islr), a glycosylphosphatidylinositol-anchored membrane protein, as a PSC-specific marker in both mouse and human by using human pancreatic tissue samples and Meflin reporter mice. Meflin-positive (Meflin+ ) cells contain lipid droplets and express the conventional PSC marker Desmin in normal mouse pancreas, with some cells also positive for Gli1, the marker of pancreatic tissue-resident fibroblasts. Three-dimensional analysis of the cleared pancreas of Meflin reporter mice showed that Meflin+ PSCs have long and thin cytoplasmic protrusions, and are localised on the abluminal side of vessels in the normal pancreas. Lineage tracing experiments revealed that Meflin+ PSCs constitute one of the origins of fibroblasts and CAFs in CP and PDAC, respectively. In these diseases, Meflin+ PSC-derived fibroblasts showed a distinctive morphology and distribution from Meflin+ PSCs in the normal pancreas. Furthermore, we showed that the genetic depletion of Meflin+ PSCs accelerated fibrosis and attenuated epithelial regeneration and stromal R-spondin 3 expression, thereby implying that Meflin+ PSCs and their lineage cells may support tissue recovery and Wnt/R-spondin signalling after pancreatic injury and PDAC development. Together, these data indicate that Meflin may be a marker specific to tissue-resident PSCs and useful for studying their biology in both health and disease. © 2023 The Pathological Society of Great Britain and Ireland.