Poster V1 - miR-146a is a Novel Regulator of Foreign Body Response to Biomaterials

Introduction: The implantation of biomaterials or medical devices often leads to the development of a foreign body response (FBR), an inflammatory condition that can lead to implant failure, which may cause harm to or death of the patient. Hallmarks of the FBR include accumulation of macrophages and destructive foreign body giant cells (FBGCs), and development of fibrous scar tissue encompassing the implant. There are no effective medical treatments for FBR, although improved fundamental understanding of the molecular mechanisms underlying the development of FBR may lead to novel strategies for the amelioration of FBR. MicroRNAs (miRs) are endogenous, small, non-coding RNAs that have emerged as powerful regulators of gene expression in numerous cellular processes including macrophage activation, inflammation, and fibrosis. Thus, it is important to determine the function of specific miRs in regulation of FBR to biomaterials.

Materials and

Methods: To induce FBGC formation in vitro, bone marrow-derived macrophages (BMDMs) were isolated, and cultured in 10% fetal bovine serum (FBS)-supplemented DMEM, treated with MCSF (25ng/ml) every 48 hours for 7-8 days to generate mature BMDMs. These mature BMDMs were seeded on polystyrene or polyacrylamide hydrogels with stiffness levels of 1kPa and 50kPa cultured in DMEM supplemented with 10% FBS for 8-10days, with continued treatment using IL4 plus GM-CSF (25ng/ml) every 48 hours for 10days and were fixed using 4% paraformaldehyde.
For the generation of FBR in vivo, subcutaneous implantation of cellulose esters was performed. 4 weeks post-implantation the implants were surgically removed along with the surrounding skin tissue and embedded in Optimal Cutting Temperature compound (OCT). A cryostat was used to make tissue sections from these tissue samples, which were subjected to staining, to observe and quantify collagen deposition and macrophage accumulation.

Results, Conclusions, and Discussions: In our subcutaneous implantation mouse model, we found that: 1) miR-146a expression levels decreased in the implant-adhered tissues, and the decrease correlated with increased macrophage accumulation, FBGC formation, and collagen accumulation; 2) miR-146a deletion in mice exacerbated in vivo macrophage accumulation, FBGC formation, and collagen accumulation; and 3) deficiency of miR-146a function exacerbated key macrophage functions including adhesion on stiff matrix, and FBGC formation in primary mouse macrophages. In essence, our findings suggest that miR-146a might act as a suppressor of FBR. We expect that the results of this study may provide invaluable information and insight regarding the molecular mechanisms mediating the FBR to biomaterials, which may lead to the development of a novel microRNA-based therapeutic strategy for the amelioration of the poorly understood FBR to biomaterials.

Acknowledgements (Optional): Support or Funding Information:
NIH (R01 AI172086) grant to Shaik O. Rahaman.