Gene Expression Profiling of Peri-Implant Healing of PLGA-Li+ Implants Suggests an Activated Wnt Signaling Pathway In Vivo

Abstract

Bone development and regeneration is associated with the Wnt signaling pathway that, according to literature, can be modulated by lithium ions (Li+). The aim of this study was to evaluate the gene expression profile during peri-implant healing of poly(lactic-co-glycolic acid) (PLGA) implants with incorporated Li+, while PLGA without Li+ was used as control, and a special attention was then paid to the Wnt signaling pathway. The implants were inserted in rat tibia for 7 or 28 days and the gene expression profile was investigated using a genome-wide microarray analysis. The results were verified by qPCR and immunohistochemistry. Histomorphometry was used to evaluate the possible effect of Li+ on bone regeneration. The microarray analysis revealed a large number of significantly differentially regulated genes over time within the two implant groups. The Wnt signaling pathway was significantly affected by Li+, with approximately 34% of all Wnt-related markers regulated over time, compared to 22% for non-Li+ containing (control; Ctrl) implants. Functional cluster analysis indicated skeletal system morphogenesis, cartilage development and condensation as related to Li+. The downstream Wnt target gene, FOSL1, and the extracellular protein-encoding gene, ASPN, were significantly upregulated by Li+ compared with Ctrl. The presence of β-catenin, FOSL1 and ASPN positive cells was confirmed around implants of both groups. Interestingly, a significantly reduced bone area was observed over time around both implant groups. The presence of periostin and calcitonin receptor-positive cells was observed at both time points. This study is to the best of the authors' knowledge the first report evaluating the effect of a local release of Li+ from PLGA at the fracture site. The present study shows that during the current time frame and with the present dose of Li+ in PLGA implants, Li+ is not an enhancer of early bone growth, although it affects the Wnt signaling pathway.

Periostin action in bone

“…Periostin has been demonstrated to be involved in various phases of bone repair: (1) early on during inflammation and angiogenesis; (2) on the recruitment of osteoprogenitors into the callus; 3in the early stages of osteoblast differentiation and bone formation. In a calvarial bone defect model, periostin has been shown to increase numbers of CD-31-positive endothelial cells and α-SMA-positive arterioles within the defect, indicating an effect on angiogenesis (22,23).…”

Proteomic and Transcriptomic Approaches for Studying Bone Regeneration in Health and Systemically Compromised Conditions

“…While it is beyond the remit of this review to discuss in details studies on implant osseointegration, it is worth mentioning that animal and human studies applying whole‐genome analyses on peri‐implant tissues and cells have also contributed to elucidate the sequence of gene activation during bone formation and they have confirmed that, while immuno‐inflammatory response‐ and ECM‐associated genes are the ones most highly expressed during the early days, the later stages of organization of the granulation tissue and formation of woven bone involve the upregulation of angiogenesis, osteogenesis and neurogenesis genes. [ 84–91 ] We previously published transcriptomic data from trephine bone core specimens retrieved together with cylindrical titanium implants from the retromolar areas of healthy volunteers at different time points (4, 7, and 14 days). Our results indicated that immune‐inflammatory pathways, such as the I‐kB kinase/nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐kB) cascade, were upregulated during the first healing days, whilst TGF‐β/BMP, Notch and Wnt signaling pathways were significantly expressed at the later healing time.…”

Fibrotic Response to Biomaterials and all Associated Sequence of Fibrosis

“…Activation of the Wnt pathway has been shown to promote fibrosis in the lung, kidneys, liver, and other organ systems, and in experimental models of fibrosis (Akhmetshina et al, 2012) and has been shown in response to biomaterial implants (e.g., Thorfve et al, 2014). Wnt ligands can be released by a variety of different cells including fibroblasts and adipocytes (Wei et al, 2011).…”