Improved Mobilization of Exogenous Mesenchymal Stem Cells to Bone for Fracture Healing and Sex Difference

Abstract

Mesenchymal stem cell (MSC) transplantation has been tested in animal and clinical fracture studies. We have developed a bone-seeking compound, LLP2A-Alendronate (LLP2A-Ale) that augments MSC homing to bone. The purpose of this study was to determine whether treatment with LLP2A-Ale or a combination of LLP2A-Ale and MSCs would accelerate bone healing in a mouse closed fracture model and if the effects are sex dependent. A right mid-femur fracture was induced in two-month-old osterix-mCherry (Osx-mCherry) male and female reporter mice. The mice were subsequently treated with placebo, LLP2A-Ale (500 µg/kg, IV), MSCs derived from wild-type female Osx-mCherry adipose tissue (ADSC, 3 × 105, IV) or ADSC + LLP2A-Ale. In phosphate buffered saline-treated mice, females had higher systemic and surface-based bone formation than males. However, male mice formed a larger callus and had higher volumetric bone mineral density and bone strength than females. LLP2A-Ale treatment increased exogenous MSC homing to the fracture gaps, enhanced incorporation of these cells into callus formation, and stimulated endochondral bone formation. Additionally, higher engraftment of exogenous MSCs in fracture gaps seemed to contribute to overall fracture healing and improved bone strength. These effects were sex-independent. There was a sex-difference in the rate of fracture healing. ADSC and LLP2A-Ale combination treatment was superior to on callus formation, which was independent of sex. Increased mobilization of exogenous MSCs to fracture sites accelerated endochondral bone formation and enhanced bone tissue regeneration.

Acceleration of Fracture Healing by Overexpression of Basic Fibroblast Growth Factor in the Mesenchymal Stromal Cells

“…However, it is difficult to precisely distinguish the contribution of various sources of progenitors during fracture healing. Our transgenic lineage tracking attempt in combination with microCT scans and histology showed that the fracture callus was initially formed from the periosteum, which was consistent with other reports . ADSC bFGF treatment showed a similar degree of bone formation from the periosteal surface.…”

“…The cells were maintained in Mesencult mouse MSC proliferation medium (Stem Cell Technologies Inc., Vancouver, BC, Canada, https://www.stemcell.com/) and used at passage 2. These cells were 99.99% CD45 negative and positive for CD105 (>70%), CD29 (>99%) and Sca1 (>98%) .…”

Self‐assembled biomimetic Nano‐Matrix for stem cell anchorage

“…Even worse, about 8.9 million suffer from fractures worldwide (Johnell & Kanis, 2006). Activation and migration of mesenchymal stem cells (MSCs) have been shown to play an important role in fracture healing (Yao et al, 2016) and are also decreased with age (Sui, Hu, Zheng, & Jin, 2016). The older the patient, the lower activity of the osteoblast.…”

“…MSCs have been proven to have strong immunosuppressive properties with the ability for self-renewal and self-differentiation (Yao et al, 2016). The presence of MSCs has been shown to promote angiogenesis, increase tissue repair and reduce inflammation, which is important in wound healing (Hadjiargyrou & O'Keefe, 2014).…”

Repair Effect of Mesenchymal Stem Cells on Fracture Model Animals

“…Generally it is divided into inflammatory response period, repair period and plastic period. The three stages are intertwined with each other [3]. Fracture healing requires the processes of hematoma formation, fibrous callus formation, bone callus formation and callus remodeling.…”