Different Effects of Intramedullary Injection of Mesenchymal Stem Cells During the Acute vs. Chronic Inflammatory Phase on Bone Healing in the Murine Continuous Polyethylene Particle Infusion Model

Abstract

Chronic inflammation is a common feature in many diseases of different organ systems, including bone. However, there are few interventions to mitigate chronic inflammation and preserve host tissue. Previous in vitro studies demonstrated that preconditioning of mesenchymal stem cells (pMSCs) using lipopolysaccharide and tumor necrosis factor-α polarized macrophages from a pro-inflammatory to an anti-inflammatory phenotype and increased osteogenesis compared to unaltered MSCs. In the current study, we investigated the local injection of MSCs or pMSCs during the acute versus chronic inflammatory phase in a murine model of inflammation of bone: the continuous femoral intramedullary polyethylene particle infusion model. Chronic inflammation due to contaminated polyethylene particles decreased bone mineral density and increased osteoclast-like cells positively stained with leukocyte tartrate resistant acid phosphatase (TRAP) staining, and resulted in a sustained M1 pro-inflammatory macrophage phenotype and a decreased M2 anti-inflammatory phenotype. Local injection of MSCs or pMSCs during the chronic inflammatory phase reversed these findings. Conversely, immediate local injection of pMSCs during the acute inflammatory phase impaired bone healing, probably by mitigating the mandatory acute inflammatory reaction. These results suggest that the timing of interventions to facilitate bone healing by modulating inflammation is critical to the outcome. Interventions to facilitate bone healing by modulating acute inflammation should be prudently applied, as this phase of bone healing is temporally sensitive. Alternatively, local injection of MSCs or pMSCs during the chronic inflammatory phase may be a potential intervention to mitigate the adverse effects of contaminated particles on bone.

Mesenchymal Stem Cells and NF-κB Sensing Interleukin-4 Over-Expressing Mesenchymal Stem Cells Are Equally Effective in Mitigating Particle-Associated Chronic Inflammatory Bone Loss in Mice

“…The increased pro-inflammatory M1 macrophage proportion and the decreased anti-inflammatory M2 macrophage proportion caused by cPE over a 3-week period was subsequently reduced by the local injection of MSCs and NF-κB sensing IL-4 over-expressing MSCs at harvest 3 weeks later. The increased TRAP positive osteoclast-like cell number, the lower ALP positive osteoblast-like area and BMD trend in the presence of cPE infusion further confirmed that the cPE could induce bone loss ( Lin et al, 2016 , 2017a ; Pajarinen et al, 2017 ; Utsunomiya et al, 2021a , b ). The injection of MSCs and NF-κB sensing IL-4 over-expressing MSCs reversed these findings in part.…”

“…The presence of cPE significantly reduced BMD in the control groups. Previous reports showed that injection of MSCs and preconditioning of MSCs during the chronic inflammation stage could increase the BMD in the presence of cPE ( Utsunomiya et al, 2021a ). In the current study, local injection of MSCs and NF-κB sensing IL-4 over-expressing MSCs also tended to increase BMD in the presence of cPE.…”

“…is still a major an unsolved problem. We have demonstrated that local delivery of contaminated polyethylene particles (cPE) can induce acute or chronic inflammation and polarize macrophages to a pro-inflammatory M1 rather than an anti-inflammatory M2 macrophage phenotype in different in vitro and in vivo models ( Utsunomiya et al, 2021a , b ). Macrophages are the characteristic cell type involved in chronic inflammation ( Allison et al, 1978 ; Maruyama et al, 2020 ); furthermore modulation of macrophage phenotype at an appropriate time can optimize osteogenic differentiation of MSCs ( Lin et al, 2019 ) and the enhancement of the bone regeneration ( Chow et al, 2019 ; Niu et al, 2021 ).…”

“…For the detection of osteoblast-like cells, anti-alkaline phosphatase staining (1-stepTM NBT/BCIP Substrate Solution, Thermo Fisher Scientific, Rockford, IL) was used. The TRAP positive cell number of 6 randomly selected areas in each section and the percentage of ALP positive area of the entire area of each section were quantified using Image J software (National Institutes of Health, United States) according to our previous protocol ( Utsunomiya et al, 2021a ). The color threshold of each parameter was determined by consensus of three of the investigators.…”

“…Mesenchymal stem cells (MSCs) have shown great potential in skeletal tissue regeneration ( Caplan, 1991 ; Zhang et al, 2021 ). Previously we showed an intervention using unaltered MSCs during the chronic inflammatory phase could mitigate the adverse effects of contaminated particles on bone ( Utsunomiya et al, 2021a ). Furthermore, specific properties of MSCs, such as differentiation capability and immunomodulation potential can be further refined by genetic modification to optimize MSC-based therapy ( Wei et al, 2018 ; Zhang et al, 2021 ).…”