Use of an alpha-smooth muscle actin GFP reporter to identify an osteoprogenitor population

Abstract

Identification of a reliable marker of skeletal precursor cells within calcified and soft tissues remains a major challenge for the field. To address this, we used a transgenic model in which osteoblasts can be eliminated by pharmacological treatment. Following osteoblast ablation a dramatic increase in a population of alpha-smooth muscle actin (alpha-SMA) positive cells was observed. During early recovery phase from ablation we have detected cells with the simultaneous expression of alpha-SMA and a preosteoblastic 3.6GFP marker, indicating the potential for transition of alpha-SMA+ cells towards osteoprogenitor lineage. Utilizing alpha-SMAGFP transgene, alpha-SMAGFP+ positive cells were detected in the microvasculature and in the osteoprogenitor population within bone marrow stromal cells. Osteogenic and adipogenic induction stimulated expression of bone and fat markers in the alpha-SMAGFP+ population derived from bone marrow or adipose tissue. In adipose tissue, alpha-SMA+ cells were localized within the smooth muscle cell layer and in pericytes. After in vitro expansion, alpha-SMA+/CD45-/Sca1+ progenitors were highly enriched. Following cell sorting and transplantation of expanded pericyte/myofibroblast populations, donor-derived differentiated osteoblasts and new bone formation was detected. Our results show that cells with a pericyte/myofibroblast phenotype have the potential to differentiate into functional osteoblasts.

Early fracture callus displays smooth muscle‐like viscoelastic properties ex vivo: Implications for fracture healing

“…4 Despite this knowledge, the smooth muscle composition of early callus has yet to be quantified. In the present study, early callus displayed viscoelastic characteristics of SR, RSR, and hysteresis in a similar manner to the urinary bladder, which is predominantly comprised of smooth muscle.…”

“…[1][2][3][4] This early callus appears to produce force ex vivo, 1 however the exact nature of this force production is yet to be established. In smooth muscle, force has both active and passive components, with the passive component defined as the portion of total force produced when cross bridges are not cycling.…”

Skeletogenesis and the Hematopoietic Niche

“…These plastic adherent colonies have been thought to contain mesenchymal progenitor cells, and likely mesodermal progenitor cells as well (Petrini et al 2009). This would account for recent data indicating that marrow derived progenitor cells generate adipocytes, chondrocytes and osteoblasts, traditional mesenchymal cell types, as well as fibroblasts, smooth muscle cells, endothelial cells, and pericytes/subendothelial cells (Bentley and Foidart 1980;Muguruma et al 2006;Sacchetti et al 2007;Crisan et al 2008;Kalajzic et al 2008;Augello et al 2010;Mendez-Ferrer et al 2010). Thus, isolated marrow stromal cells will be referred to as multipotent stromal cells (MSC) throughout (Horwitz et al 2005).…”

Visualizing OsteogenesisIn VivoWithin a Cell–Scaffold Construct for Bone Tissue Engineering Using Two-Photon Microscopy

“…We used the reporters SMAA 43 (osteoprogenitors), Col3.6 44 (early osteoblasts), and Col2.3 42,44 (mature osteoblasts and osteocytes) (Fig. 1a), to describe their baseline expression in the cellular microenvironment before use in later experiments.…”