Intra‐articular Injection of PDGF-BB Explored in a Novel in Vitro Model Mobilizes Mesenchymal Stem Cells From the Synovium Into Synovial Fluid in Rats

Abstract

BackgroundDrugs that can induce mesenchymal stem cell (MSC) mobilization from synovium into synovial uid will enable regenerative medicine in joints without use of exogenous MSCs. An in vitro synovial MSC migration model had previously been developed for screening but had problems in practical application. We herein developed a novel in vitro model, explored cytokines for synovial MSC mobilization with this model, and veri ed whether MSCs in synovial uid increase following intra-articular injection of the cytokine. MethodsHuman synovial MSCs embedded in a mixture of Matrigel and type 1 collagen hydrogel were placed on a culture insert and then put in medium containing migration factor. Of the six cytokines, we identi ed the one that mobilizes the highest number of MSCs. PDGF-BB or PBS was injected into rat knees, and 48 h later, synovial uid was collected and cultured. The cells were examined for MSC properties. ResultsPDGF-BB was the most effective for synovial MSC mobilization among six cytokines. The effect of PDGF-BB was inhibited by a PRGFR inhibitor. Injection of PDGF-BB into rat knees increased colonyforming cells in the synovial uid. These cells had surface epitopes and multipotency comparable to MSCs and a higher capacity for proliferation, colony formation, and chondrogenesis. ConclusionsThis novel in vitro model recapitulated the migration of MSCs from synovium into synovial uid. Our exploration of cytokines revealed that PDGF-BB strongly induced in vitro synovial MSC migration, while intra-articular injection of PDGF-BB increased in vivo MSC numbers in synovial uid in rats.

Mesenchymal stem cells in synovial fluid increase in number in response to synovitis and display more tissue-reparative phenotypes in osteoarthritis

“…Histological evaluation of the rat knee joints revealed that synovitis was most strongly correlated with colony number. This nding was consistent with our previous ndings that in ammatory cytokines enhanced the migration ability of synovial MSCs and that synovium-resident MSCs appeared to mobilize into the SF in response to synovitis [17]. Immunostaining of the synovium to identify events responsible for changes in SF-MSCs demonstrated a signi cant correlation between the CD68-positive area in the synovium and the SF-MSC colony number and area.…”

“…The numbers of endogenous MSCs will need to be increased to achieve endogenous tissue regeneration. We previously demonstrated that intraarticular injection of PDGF-BB effectively mobilized synovial MSCs into the SF [17]. Baboolal et al reported a mechanical method to increase SF-MSCs that involved agitation of the synovium during arthroscopy [40].…”

“…SF was collected from rat knee joints by pumping the joints twice with 50 µL of phosphate-buffered saline (PBS) [17]. The collected uid was plated in a 145 cm 2 dish (Thermo Fisher Scienti c, Waltham, MA, USA) and cultured in growth medium consisting of α-modi ed essential medium (α-MEM; Thermo Fisher Scienti c), 10% fetal bovine serum (FBS; Thermo Fisher Scienti c), and 1% antibiotic-antimycotic (Thermo Fisher Scienti c) at 37°C in 5% humidi ed CO 2 .…”

Comparing the immunomodulatory properties of equine BM-MSCs culture expanded in autologous platelet lysate, pooled platelet lysate, equine serum and fetal bovine serum supplemented culture media

“…In addition to suppressing T cell proliferation, PDGF also increases MSC migration and proliferation. Endo et al ( 53 ) found that cell migration was increased in vitro when synovial MSCs were cultured in media supplemented with PDGF-BB. They also found that intra-articular PDGF-BB treatment increased MSC proliferation and colony-forming potential ( 53 ).…”

“…Endo et al ( 53 ) found that cell migration was increased in vitro when synovial MSCs were cultured in media supplemented with PDGF-BB. They also found that intra-articular PDGF-BB treatment increased MSC proliferation and colony-forming potential ( 53 ). Although beyond the scope of this study, increased levels of PDGF-BB in PL containing medias could provide an advantage when injecting MSCs intra-articularly by not only improving the function of injected MSCs but also recruitment and proliferation of endogenous MSCs already present within the joint.…”