Study On Oxidized LDL-induced Transdifferentiation Of Bone Marrow-derived Smooth Muscle-like Cells Into Foam-like Cells In Vitro

Vascular smooth muscle cells (SMCs) are the predominant cell type in atherosclerotic plaques and play a crucial role in the development of vascular diseases. Unlike either terminally differentiated skeletal or cardiac muscle cells, SMCs in adult animals retain remarkable plasticity and can undergo profound and reversible phenotype changes in response to various factors in their local environment. During early atherogenesis, SMCs change to a phenotype characterized by decreased expression of SMC differentiation marker proteins, a high rate of cellular proliferation, and increased synthesis of extracellular matrix proteins. The increased phagocytosis of oxidized low density lipoprotein (ox-LDL) via scavenger LDL receptor pathways in SMCs contributes to the development of foam-like cells within atherosclerotic lesions.Although much effort has been devoted to understanding the molecular pathways regulating migration and proliferation of medial SMCs, no effective therapy to prevent occlusive vascular remodeling has been established.It has been suggested that bone marrow cells may have the potential to give rise to smooth muscle progenitor cells (SMPCs) that home to the damaged vessels and differentiate into smooth muscle-like cells (SMLCs), thereby contributing to the pathogenesis of vascular diseases. It is well known that myocardin is a CArG-dependent critical serum response factor/cofactor in the transcriptional program regulating smooth muscle cell differentiation from bone-marrow derived stem cells (BMSCs) and is required for vascular smooth muscle development. However, there have been few studies closely following the development of SMCs from BMSCs. This is due to the difficulty of isolating smooth muscle progenitor cells (SMPCs) from bulk BMSCs because SMPCs coexist with several other progenitor cells.Oxidized low density lipoprotein (ox-LDL) is believed to contribute to atherogenesis in part by being taken up into smooth muscle cells (SMC) via specific scavenger receptors; however, it is not clear whether ox-LDL receptor(s) are expressed in bone marrow-derived smooth muscle-like cells (SMLCs) and whether they play a role in the process of SMLC development. Therefore, we examined the ox-LDL induced transdifferentiation of SMLCs that is mediated by lectin-like ox-LDL receptor-1 (LOX-1).Smooth muscle progenitor cells (SMPCs) from bone marrow mesenchymal stem cells (BMSCs) were isolated using a tissue-specific promoter sorting method with a mouse recombinant plasmid SM22-promoter(-480bp)/green fluorescent protein. The SMPCs were myocardin+CD105+KDR+CD45-CD34-, but did not express SMC-specific markers a smooth muscle actin (α-SMA), SM22, smooth muscle myosin heavy chain (SM-MHC) and smoothelin. After long-term culture with platelet-derived growth factor-BB (PDGF-BB), SMPCs expressed a-SMA, SM22 and SM-MHC, and differentiated into SMLCs. When SMLCs were incubated with different concentrations of ox-LDL, LOX-1 expression on the surface of SMLCs gradually increased with the increase of the ox-LDL concentration, but myocardin and SMC-specific marker genes decreased, accordingly. Furthermore, receptor-mediated endocytosis was enhanced and lipid droplets accumulated in the cytoplasm of SMLCs. A subpopulation of myocardin+ CD105+KDR+ CD31+CD45-CD34- SMPCs exist in BMSCs that can differentiate into SMLCs under induction with PDGF-BB. Moreover, LOX-1 contributes to the ox-LDL-induced transdifferentiation of bone marrow-derived SMLCs into foam-like cells.