Preconditioned or IL4-Secreting Mesenchymal Stem Cells Enhanced Osteogenesis at Different Stages

Chronic inflammation-associated bone diseases involve continuous destruction and impaired regeneration of bone. Mesenchymal stem cell (MSC)-based therapy has great potential to modulate inflammatory responses and enhance tissue regeneration. We previously showed that lipopolysaccharide (LPS) plus tumor necrosis factor alpha (TNFα)-preconditioned MSCs or genetically modified inflammation-sensing (driven by nuclear factor kappa-light-chain-enhancer of activated B cells [NFκB] activation) IL4-secreting MSCs enhanced immunomodulation of macrophages to the more desired tissue repaired M2 type. In the current study, the paracrine regulation of therapeutic MSCs on the proinflammatory response and osteogenesis of macrophage–MSC cocultures (representing endogenous cells) was examined using an in vitro transwell system. In the cocultures, IL4-secreting MSCs decreased TNFα and inducible nitric oxide synthase expression, and increased Arginase 1 and CD206 expression in the presence of LPS-contaminated polyethylene particles. The preconditioned MSCs decreased TNFα and CD206 expression in the bottom MSC–macrophage cocultures in the presence of contaminated particles. In osteogenesis assays, IL4-secreting MSCs decreased alkaline phosphatase (ALP) expression, but increased Alizarin Red staining in the presence of contaminated particles. The preconditioned MSCs increased ALP and osteocalcin expression, and had no significant effect on Alizarin Red staining. These results suggest that potential treatments using preconditioned MSCs at an earlier stage, or IL4-secreting MSCs at a later stage could enhance bone regeneration in inflammatory conditions, including periprosthetic osteolysis. Pathogen-associated molecular patterns, damage-associated molecular patterns, and other noxious stimuli activate macrophages to induce the proinflammatory responses. Modulation of inflammatory macrophages (M1) into an anti-inflammatory tissue repair macrophage (M2) phenotype at the appropriate time optimizes bone remodeling and regeneration. Simulating the proinflammatory stimuli by using preconditioned mesenchymal stem cells (MSCs) at an earlier stage, and alleviate the inflammation by using IL4-secreting MSCs at a later stage could further optimize bone regeneration in chronic inflammatory conditions, including periprosthetic osteolysis.