Roles of the Mesenchymal Stromal/Stem Cell Marker Meflin in Cardiac Tissue Repair and the Development of Diastolic Dysfunction

Abstract

Rationale: Myofibroblasts have roles in tissue repair following damage associated with ischemia, aging, and inflammation and also promote fibrosis and tissue stiffening, causing organ dysfunction. One source of myofibroblasts is mesenchymal stromal/stem cells that exist as resident fibroblasts in multiple tissues. We previously identified meflin (mesenchymal stromal cell- and fibroblast-expressing Linx paralogue), a glycosylphosphatidylinositol-anchored membrane protein, as a specific marker of mesenchymal stromal/stem cells and a regulator of their undifferentiated state. The roles of meflin in the development of heart disease, however, have not been investigated. Objective: We examined the expression of meflin in the heart and its involvement in cardiac repair after ischemia, fibrosis, and the development of heart failure. Methods and Results: We found that meflin has an inhibitory role in myofibroblast differentiation of cultured mesenchymal stromal/stem cells. Meflin expression was downregulated by stimulation with TGF (transforming growth factor)-β, substrate stiffness, hypoxia, and aging. Histological analysis revealed that meflin-positive fibroblastic cells and their lineage cells proliferated in the hearts after acute myocardial infarction and pressure-overload heart failure mouse models. Analysis of meflin knockout mice revealed that meflin is essential for the increase in the number of cells that highly express type I collagen in the heart walls after myocardial infarction induction. When subjected to pressure overload by transverse aortic constriction, meflin knockout mice developed marked cardiac interstitial fibrosis with defective compensation mechanisms. Analysis with atomic force microscopy and hemodynamic catheterization revealed that meflin knockout mice developed stiff failing hearts with diastolic dysfunction. Mechanistically, we found that meflin interacts with bone morphogenetic protein 7, an antifibrotic cytokine that counteracts the action of TGF-β and augments its intracellular signaling. Conclusions: These data suggested that meflin is involved in cardiac tissue repair after injury and has an inhibitory role in myofibroblast differentiation of cardiac fibroblastic cells and the development of cardiac fibrosis.

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“…For example, the Islr promoter was methylated in MSC isolated from the umbilical cord and expanded in vitro, which was consistent with our finding that ex vivo culture on plastic induces a significant downregulation of Meflin expression in bone marrow‐derived MSC . Further analysis revealed that culture substrate stiffness is key for downregulating Meflin expression . The elastic modulus of normal body fluids and tissues is 10 2 ‐2 × 10 4 Pa, whereas that of culture plastic is 2‐3 GPa, indicating that MSC cultured on Petri dishes experience significant changes in mechanical stress, gene expression and the epigenome over time .…”

“… Mechanistically, Meflin binds to BMP‐7, a member of the BMP family, which counteracts the action of TGF‐β to prevent fibrosis . Studies on cultured cells have revealed that Meflin augments BMP‐7 signaling and inhibits TGF‐β signaling, suggesting that the primary function of Meflin is to inhibit profibrotic signaling in cardiac fibroblasts . Consistent herewith, failing hearts of Meflin‐deficient mice were stiffer than those of control mice and recapitulated the characteristics of an entity of diastolic heart failure in humans called “heart failure with preserved ejection fraction (HFpEF).” It is intriguing to note that Meflin + fibroblasts and undifferentiated MSC exert a protective effect against the development of heart failure, and an antitumor function in PDAC development (Figure 4).…”

“…This phenotypic conversion was recapitulated in cultured MSC, where α‐SMA expression was upregulated while Meflin expression was significantly downregulated in response to transforming growth factor‐β (TGF‐β) signaling, substrate stiffness and hypoxia (Figure 2A). Given that TGF‐β is abundant in the TME and that tumors are stiffer and more hypoxic than normal tissues, it has been hypothesized that Meflin + CAF first appear in close proximity to transformed cells as sentinel cells, and later differentiate into α‐SMA + CAF in which Meflin expression is downregulated (Figure 2A). This phenotypic conversion of CAF may represent one aspect of the stromagenic switch that accompanies, and promotes, tumor progression.…”

“…Our recent study revealed that Meflin + MSC or fibroblasts rarely reside within the epicardium, endocardium and perivascular area of capillaries in the interstitium of the heart. Alternatively, they proliferate extensively and are recruited from other tissues immediately after acute myocardial infarction . Interestingly, a large proportion of the Meflin‐deficient mice died immediately after infarction due to cardiac rupture, suggesting that Meflin expression in fibroblasts or MSC is essential for acute repair of the injured cardiac tissue (Figure 4).…”

“…Meflin deficiency also resulted in increased fibrosis and tissue stiffening in hearts with increased α‐SMA expression and fibrosis in a chronic heart failure condition, suggesting that Meflin may inhibit fibroblast differentiation into myofibroblasts (Figure 4). Mechanistically, Meflin binds to BMP‐7, a member of the BMP family, which counteracts the action of TGF‐β to prevent fibrosis . Studies on cultured cells have revealed that Meflin augments BMP‐7 signaling and inhibits TGF‐β signaling, suggesting that the primary function of Meflin is to inhibit profibrotic signaling in cardiac fibroblasts .…”