Meflin defines mesenchymal stem cells and/or their early progenitors with multilineage differentiation capacity

Abstract

Mesenchymal stem cells (MSCs) are the likely precursors of multiple lines of mesenchymal cells. The existence of bona fide MSCs with self‐renewal capacity and differentiation potential into all mesenchymal lineages, however, has been unclear because of the lack of MSC‐specific marker(s) that are not expressed by the terminally differentiated progeny. Meflin, a glycosylphosphatidylinositol‐anchored protein, is an MSC marker candidate that is specifically expressed in rare stromal cells in all tissues. Our previous report showed that Meflin expression becomes down‐regulated in bone marrow‐derived MSCs cultured on plastic, making it difficult to examine the self‐renewal and differentiation of Meflin‐positive cells at the single‐cell level. Here, we traced the lineage of Meflin‐positive cells in postnatal and adult mice, showing that those cells differentiated into white and brown adipocytes, osteocytes, chondrocytes and skeletal myocytes. Interestingly, cells derived from Meflin‐positive cells formed clusters of differentiated cells, implying the in situ proliferation of Meflin‐positive cells or their lineage‐committed progenitors. These results, taken together with previous findings that Meflin expression in cultured MSCs was lost upon their multilineage differentiation, suggest that Meflin is a useful potential marker to localize MSCs and/or their immature progenitors in multiple tissues.

Roles of the Mesenchymal Stromal/Stem Cell Marker Meflin/Islr in Cancer Fibrosis

“…A mouse line was crossed with a Rosa26-LoxP-stop-LoxP (LSL)-tdTomato gene to detect Meflin-lineage cells by tdTomato expression. Our data clearly demonstrated that Meflin-positive cells in various mesenchymal tissues can give rise to mature osteocytes, chondrocytes, adipocytes, and skeletal myocytes in the postnatal and adult stages ( Hara et al, 2021 ). Another previous study showed the differentiation of Meflin-positive cells into mature white adipocytes and beige-like adipocytes under physiological and cold-stress conditions, respectively, using mice carrying a transgene in which the Meflin promoter drives the expression of the TAM-inducible Cre recombinase ( Kuwano et al, 2021 ).…”

“…When TAM was administered at postnatal day 1 (P1), P2, and P3, we found that some differentiated Meflin lineage cells (e.g., adipocytes or chondrocytes) were detected in groups or clusters at P21 and P49, suggesting that they may have originated from the same MSCs or progenitors ( Hara et al, 2021 ). In addition, most tdTomato + Meflin-lineage cells in the BM were also positive for PDGFRα(a marker of the most primitive MSCs in the BM) at P21 and P49.…”

Conversion of cancer-associated fibroblasts from pro- to antitumor improves the sensitivity of pancreatic cancer to chemotherapeutics

“…In conclusion, our current findings showed that Meflin expression in CAFs improved tumor sensitivity to chemotherapeutics, consistent with our previous studies identifying Meflin as a marker of rCAFs, which are functionally different from protumorigenic pCAFs (7, 22, 43). Consistent with this, the induction of Meflin expression by either genetic or pharmacological approaches improved tumor sensitivity to chemotherapeutics in a PDAC xenograft model.…”

“…Moreover, induction of Meflin expression in Meflin -CAFs blocks PDAC progression in a tumor transplantation model, indicating that CAF function is determined by the net balance of the expression of cancerpromoting and -restraining proteins (20). In normal tissues, Meflin is expressed by pancreatic stellate cells (PSCs) in the pancreas and mesenchymal stem cells (MSCs) in the bone marrow (BM) and most other tissues, both of which are known to be major CAF origins (20)(21)(22)(23)(24)(25). Therefore, rCAFs may be proliferating naïve (undifferentiated) PSCs or MSCs, which, as the tumor progresses, differentiate into Meflin-negative or weaklypositive cancer-promoting CAFs (pCAFs) (7,20).…”

Meflin-positive cancer-associated fibroblasts enhance tumor response to immune checkpoint blockade

“…To prove this, we generated a transgenic mouse line expressing mouse Meflin under the tetracycline response element (TRE) promoter (TRE-Meflin) ( Fig 8A ). This line was then crossed with Meflin-Cre ( Hara et al, 2019 , 2021 ; Mizutani et al, 2019 ) and Rosa26-LSL (LoxP-stop-LoxP)-rtTA3 (third-generation reverse tetracycline-regulated transactivator) mice (JAX stock #029617, Dow et al, 2014 ) to generate mice with doxycycline-induced expression of Meflin in Meflin-lineage cells. To confirm induced Meflin expression in mice carrying all three alleles (hereafter referred to as Meflin-TO), we administered doxycycline in drinking water (2 mg/ml) to Meflin-TO mice and transplanted MC-38 and EO771 cells subcutaneously and orthotopically, respectively, followed by the analysis of Meflin expression ( Fig S7A ).…”