Enhanced mesenchymal stromal cell recruitment via natural killer cells by incorporation of inflammatory signals in biomaterials

Abstract

An exacerbated inflammatory response questions biomaterial biocompatibility, but on the other hand, inflammation has a central role in the regulation of tissue regeneration. Therefore, it may be argued that an 'ideal' inflammatory response is crucial to achieve efficient tissue repair/regeneration. Natural killer (NK) cells, being one of the first populations arriving at an injury site, can have an important role in regulating bone repair/regeneration, particularly through interactions with mesenchymal stem/stromal cells (MSCs). Here, we studied how biomaterials designed to incorporate inflammatory signals affected NK cell behaviour and NK cell-MSC interactions. Adsorption of the pro-inflammatory molecule fibrinogen (Fg) to chitosan films led to a 1.5-fold increase in adhesion of peripheral blood human NK cells, without an increase in cytokine secretion. Most importantly, it was found that NK cells are capable of stimulating a threefold increase in human bone marrow MSC invasion, a key event taking place in tissue repair, but did not affect the expression of the differentiation marker alkaline phosphatase (ALP). Of significant importance, this NK cell-mediated MSC recruitment was modulated by Fg adsorption. Designing novel biomaterials leading to rational modulation of the inflammatory response is proposed as an alternative to current bone regeneration strategies.

Macrophage interactions with polylactic acid and chitosan scaffolds lead to improved recruitment of human mesenchymal stem/stromal cells: a comprehensive study with different immune cells

“…PBMC, NK cells and monocytes were obtained from buffy coats of healthy human donors, kindly provided by Centro Hospitalar de São João after patient informed consent and ethics committee approval. Briefly, a PBMC suspension was prepared by density gradient centrifugation and NK cells were purified by negative selection using the EasySep human NK cell enrichment kit (StemCell Technologies), as detailed elsewhere [12]. Human monocytes were isolated by negative selection using a RosetteSep human monocyte enrichment cocktail (StemCell Technologies), as previously described [14].…”

“…Macrophages are master regulators of the foreign body response and tissue regeneration through secretion of bioactive molecules, which can impact inflammation, angiogenesis, extracellular matrix remodelling and stem cell recruitment and differentiation [2]. And indeed, macrophages are potent inducers of MSC recruitment, mainly through the production of the chemokine RANTES [12,13]. The remarkable plasticity of macrophages allows them to adopt a dynamic profile between M1 pro-inflammatory and M2 pro-regenerative functional programmes, which can shift the regenerative outcome.…”

“…NK cells are lymphocytes crucial for remodelling of the endometrium during pregnancy, and which can promote MSC recruitment, possibly through secretion of different chemokines [12]. Monocyte recruitment from the blood to the implant site thrives under its inflammatory environment, where they gradually differentiate into macrophages that replace the short-lived neutrophils and NK cells.…”

Adsorbed Fibrinogen Enhances Production of Bone- and Angiogenic-Related Factors by Monocytes/Macrophages

“…This suggests that when triggered by Fg, macrophages influence different key steps, are able to modulate the inflammatory response, and also contribute to new bone formation and angiogenesis, both of which were stimulated with Fg-adsorbed Ch scaffolds in vivo. 33 Furthermore, Fg has also been shown to improve recruitment of mesenchymal stem/stromal cells by NK cells 36 and to promote resorption of Ch by osteoclasts. 77 Taken together, these findings support the view that biomaterials combining Ch and Fg may constitute a complementary strategy for bone tissue engineering, by modulating the behavior of different cell populations and influencing diverse events, ranging from inflammation to biomaterial resorption.…”

“…The amount of adsorbed Fg was quantified by protein radiolabeling with 125 I and found to be 501 -63 ng of protein/cm 2 . 36 The RGD peptide (Fibronectinlike Protein Polymer, F5022 from Sigma-Aldrich) was reconstituted according to the manufacturer's instructions and used at 25 mg/mL to adsorb (20 min at RT) glass coverslips on 24-well culture plates (Fisher Scientific). Before cell culture, wells were washed twice.…”