Human mesenchymal stem cells express a myofibroblastic phenotype in vitro: comparison to human cardiac myofibroblasts.

Cardiac fibrosis accompanies a variety of myocardial disorders, and is induced by myofibroblasts. These cells may be composed of a heterogeneous population of parent cells, including interstitial fibroblasts and circulating progenitor cells. Direct comparison of human bone marrow-derived mesenchymal stem cells (BM-MSCs) and cardiac myofibroblasts (CMyfbs) has not been previously reported. We hypothesized that BM-MSCs readily adopt a myofibroblastic phenotype in culture. Human primary BM-MSCs and human CMyfbs were isolated from patients undergoing open heart surgery and expanded under standard culture conditions. We assessed and compared their phenotypic and functional characteristics by examining their gene expression profile, their ability to contract collagen gels and synthesize collagen type I. In addition, we examined the role of non-muscle myosin II (NMMII) in modulating MSC myogenic function using NMMII siRNA knockdown and blebbistatin, a specific small molecule inhibitor of NMMII. We report that, while human BM-MSCs retain pluripotency, they adopt a myofibroblastic phenotype in culture and stain positive for the myofibroblast markers α-SMA, vimentin, NMMIIB, ED-A fibronectin, and collagen type 1 at each passage. In addition, they contract collagen gels in response to TGF-ß1 and synthesize collagen similar to human CMyfbs. Moreover, inhibition of NMMII activity with blebbistatin completely attenuates gel contractility without affecting cell viability. Thus, human BM-MSCs share and exhibit similar physiological and functional characteristics as human CMyfbs in vitro, and their propensity to adopt a myofibroblast phenotype in culture may contribute to cardiac fibrosis.

Statins impair survival of primary human mesenchymal progenitor cells via mevalonate depletion, NF-κB signaling, and Bnip3.

Circulating progenitor cells of bone marrow origin have been implicated in transplant cardiac allograft vasculopathy (CAV) and cardiac fibrosis. HMG-CoA reductase inhibitors, called "statins," have been shown to impair the progression of CAV and improve patient survival. We examined the in vitro effects of three HMG-CoA reductase inhibitors atorvastatin, simvastatin, and pravastatin on the viability of MSCs and expression of nuclear factor kappa B (NF-κB). Mesenchymal stem cells (MSCs) isolated from human patients were treated with atorvastatin, simvastatin, and pravastatin at 0.1, 1.0, or 10 µM ± mevalonate. Human MSC treatment with 1 and 10 µM simvastatin or atorvastatin resulted in progressively reduced cell viability, which was associated with a decline in NF-κB p65. Viability was rescued by co-incubation with mevalonate or by pretreatment with Inhibitor of nuclear factor kappa-B kinase subunit beta (Iκκ-ß). Pravastatin did not affect MSC viability or NF-κB expression. Mevalonate depletion through HMG-CoA reductase inhibition impairs the viability of primary human MSC through down-regulating NF-κB.