Organizing motility: LIM domains, LPP, and smooth muscle migration.
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Biomedical subjects
Publications and source records attributed to Mark W Majesky.
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Vascular smooth muscle cells (SMCs) originate from multiple types of progenitor cells. In the embryo, the most well studied SMC progenitor is the cardiac neural crest stem cell. Smooth muscle differentiation in the neural crest lineage is controlled by a combination of cell intrinsic factors, including Pax3, Tbx1, FoxC1, and serum response factor, interacting with various extrinsic factors in the local environment such as bone morphogenetic proteins (BMPs), Wnts, endothelin (ET)-1, and FGF8. Additional sources of multipotential cells that give rise to vascular SMCs in the embryo include proepicardial cells and possibly endothelial progenitor cells. In the adult, vascular SMCs must continually repair arterial injuries and maintain functional mass in response to changing demands upon the vessel wall. Recent evidence suggests that this is accomplished, in part, by recruiting multipotential vascular progenitors from bone marrow-derived stem cells as well as from less well defined sources within adult tissues themselves. This article will review our current understanding of the origins of vascular SMCs from multipotential stem and progenitor cells in developing as well as adult vasculature.
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Vascular smooth muscle exhibits remarkable structural and functional diversity. For many years, this diversity was thought to be due to plasticity of a single type of smooth muscle cell responding to biologic and mechanical variations in the local environment. However, recent studies of vascular development employing novel lineage mapping and mouse mutagenesis approaches suggest that much of the smooth muscle diversity found in adult blood vessels may have a developmental basis.
Cysteine-rich LIM-only proteins, CRP1 and CRP2, expressed during cardiovascular development act as bridging molecules that associate with serum response factor and GATA proteins. SRF-CRP-GATA complexes strongly activated smooth muscle gene targets. CRP2 was found in the nucleus during early stages of coronary smooth muscle differentiation from proepicardial cells. A dominant-negative CRP2 mutant blocked proepicardial cells from differentiating into smooth muscle cells. Together with SRF and GATA proteins, CRP1 and CRP2 converted pluripotent 10T1/2 fibroblasts into smooth muscle cells, while muscle LIM protein CRP3 inhibited the conversion. Thus, LIM-only proteins of the CRP family play important roles in organizing multiprotein complexes, both in the cytoplasm, where they participate in cytoskeletal remodeling, and in the nucleus, where they strongly facilitate smooth muscle differentiation.
Vascular progenitors were previously isolated from blood and bone marrow; herein, we define the presence, phenotype, potential, and origin of vascular progenitors resident within adult skeletal muscle. Two distinct populations of cells were simultaneously isolated from hindlimb muscle: the side population (SP) of highly purified hematopoietic stem cells and non-SP cells, which do not reconstitute blood. Muscle SP cells were found to be derived from, and replenished by, bone marrow SP cells; however, within the muscle environment, they were phenotypically distinct from marrow SP cells. Non-SP cells were also derived from marrow stem cells and contained progenitors with a mesenchymal phenotype. Muscle SP and non-SP cells were isolated from Rosa26 mice and directly injected into injured muscle of genetically matched recipients. SP cells engrafted into endothelium during vascular regeneration, and non-SP cells engrafted into smooth muscle. Thus, distinct populations of vascular progenitors are resident within skeletal muscle, are derived from bone marrow, and exhibit different cell fates during injury-induced vascular regeneration.
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