In Vivo Fate Mapping Identifies Mesenchymal Progenitor Cells

Abstract

Adult mesenchymal progenitor cells have enormous potential for use in regenerative medicine. However, the true identity of the progenitors in vivo and their progeny has not been precisely defined. We hypothesize that cells expressing a smooth muscle α-actin promoter (αSMA) directed Cre transgene represent mesenchymal progenitors of adult bone tissue. By combining complementary colors in combination with transgenes activating at mature stages of the lineage we characterized the phenotype and confirmed the ability of isolated αSMA+ cells to progress from a progenitor to fully mature state. In vivo lineage tracing experiments using a new bone formation model confirmed the osteogenic phenotype of αSMA+ cells. In vitro analysis of the in vivo labeled SMA9+ cells supported their differentiation potential into mesenchymal lineages. Utilizing a fracture-healing model, αSMA+ cells served as a pool of fibrocartilage and skeletal progenitors. Confirmation of the transition of αSMA+ progenitor cells to mature osteoblasts during fracture healing was assessed by activation of bone specific Col2.3emd transgene. Our findings provide a novel in vivo identification of defined population of mesenchymal progenitor cells with active role in bone remodeling and regeneration.

The rational use of animal models in the evaluation of novel bone regenerative therapies

“…Although most studies were conducted with bone marrow derived mesenchymal progenitor cells (MPCs), other tissues have been described to contain osteoprogenitor cells with similar regenerative potential including adipose tissue, muscle, umbilical cord blood, periosteum, dental pulp and periodontal ligament [4,[39][40][41][42][43][44][45]. The multilineage differentiation ability, paracrine effects and immunomodulatory properties of MPCs make them an ideal for tissue engineering and regenerative purposes [5,7,[46][47][48].…”

Wnts produced by Osterix-expressing osteolineage cells regulate their proliferation and differentiation

“…Descendants of Wnt-Responding Osteolineage Cells Contribute to Bone Injury Repair. Recent studies have shown that progenitors of the osteolineage can participate in bone tissue repair (18)(19)(20)22). Thus, in addition to lineage tracing during homeostasis, we probed for progenitor activity in the AXCT2-traced population by asking if the progeny of neonatal AXCT2-labeled cells could contribute to bone injury repair in adulthood.…”

“…Osteolineage cells arise from multipotent mesenchymal progenitors, which subsequently give rise to osteolineage-restricted progenitors (18)(19)(20)(21)(22)(23). In perinatal mice, Osterix (Osx) appears to be expressed by both populations (20,21,24) and continues to be expressed as the cells divide and differentiate into osteoblasts.…”

Determining the Role of Sost and Sostdc1 During Fracture Healing

“…We compared LacZ expression in Sostdc1 -/-and Sostdc1 -/+ calluses using an antibody specific for its gene product, β-galactosidase. Nestin is a mesenchymal cell marker used in flow cytometry to identify mesenchymal stem cell populations [191] and α-SMA marks progenitor cells that can differentiate into chondrocytes and osteoblasts [174]. β-galactosidase antibody stain ( Fig.…”

“…Optimal fracture repair requires contribution from surrounding tissues, yet we know very little about the interactions between bone, muscle, vasculature, and the periosteum [173][174][175]. In particular the periosteum, a thin tissue that covers the outer cortical bone surface, contains a reservoir of progenitor cells that contribute to bone repair; further, periosteal grafts and alpha-smooth muscle actin (α-SMA)-positive cells integrate into the callus after fracture [105,175].…”