Osteogenic potential of alpha smooth muscle actin expressing muscle resident progenitor cells

Abstract

Heterotopic ossification (HO) is a pathological process where bone forms in connective tissues such as skeletal muscle. Previous studies have suggested that muscle-resident non-myogenic mesenchymal progenitors are the likely source of osteoblasts and chondrocytes in HO. However, the previously identified markers of muscle-resident osteoprogenitors label up to half the osteoblasts within heterotopic lesions, suggesting other cell populations are involved. We have identified alpha smooth muscle actin (αSMA) as a marker of osteoprogenitor cells in bone and periodontium, and of osteo-chondro progenitors in the periosteum during fracture healing. We therefore utilized a lineage tracing approach to evaluate whether αSMACreERT2 identifies osteoprogenitors in the muscle. We show that in the muscle, αSMACreERT2 labels both perivascular cells, and satellite cells. αSMACre-labeled cells undergo osteogenic differentiation in vitro and form osteoblasts and chondrocytes in BMP2-induced HO in vivo. In contrast, Pax7CreERT2-labeled muscle satellite cells were restricted to myogenic differentiation in vitro, and rarely contributed to HO in vivo. Our data indicate that αSMACreERT2 labels a large proportion of osteoprogenitors in skeletal muscle, and therefore represents another marker of muscle-resident cells with osteogenic potential under HO-inducing stimulus. In contrast, muscle satellite cells make minimal contribution to bone formation in vivo.

Murine supraspinatus tendon injury model to identify the cellular origins of rotator cuff healing

“…6C). tdTom+ muscle fibers were also seen in the SMA-9 mice because this model is known to label a satellite cell population [25]. While the epimysium thickened in response to the sham procedure, there was no evidence of the capsule-like healing tissue in the subacromial space as seen in the limbs that underwent supraspinatus detachment (Fig.…”

“…Cre recombinase fused to a modified estrogen receptor ligand binding domain (ERT2) allowed for temporal activation of the enzyme by tamoxifen injection [22]. The three CreERT2 transgenic mouse models used in this study used DNA transcriptional regulatory elements derived from the following genes: 1) PRG4-CreERT2 (detailed description of this mouse is detailed in another manuscript currently under review), 2) αSMA-CreERT2 [11,23–25], and 3) Aggrecan (AGC)-CreERT2 [17]. The three Cre driver mice were crossed with Ai9 Rosa26-tdTomato reporter mice [26] to generate dual transgenic offspring (PRG4-9, SMA-9, and AGC-9, respectively) that would allow the activation of Cre reporter expression upon Tamoxifen injection to label cells tdTomato+ (tdTom+) at the time of surgery and then trace their contribution to tendon healing over time.…”

Skeletal and cardiac muscle pericytes: Functions and therapeutic potential

“…In skeletal muscle, pericytes appear to play additional roles in tissue regeneration, including differentiation into myofibers (Dellavalle et al, 2007). Pericytes are however also implicated in the development of fibrosis, heterotopic ossification, atherosclerosis, and tumor angiogenesis, diseases that represent some of the most frequent causes of morbidity and mortality in the western world (Collett & Canfield, 2005; Fang & Salven, 2011; Henderson et al, 2013; Matthews et al, 2016). Despite these critical roles in tissue physiology and disease, relatively little is known about skeletal muscle and cardiac pericytes (Armulik et al, 2011).…”

Visual reporters for study of the osteoblast lineage

“…Col2.3-GFP in particular has been widely used in lineage tracking studies to identify osteoblasts derived from various cell populations during development, adulthood, or following injury [19, 21, 63–65]. They are also useful to track differentiation following transplantation of cells.…”