Antimicrobial Peptide Combined with BMP2-Modified Mesenchymal Stem Cells Promotes Calvarial Repair in an Osteolytic Model

Abstract

Repair and regeneration of inflammation-induced bone loss remains a clinical challenge. LL37, an antimicrobial peptide, plays critical roles in cell migration, cytokine production, apoptosis, and angiogenesis. Migration of stem cells to the affected site and promotion of vascularization are essential for tissue engineering therapy, including bone regeneration. However, it is largely unknown whether LL37 affects mesenchymal stem cell (MSC) behavior and bone morphogenetic protein 2 (BMP2)-mediated bone repair during the bone pathologic remodeling process. By performing in vitro and in vivo studies with MSCs and a lipopolysaccharide (LPS)-induced mouse calvarial osteolytic bone defect model, we found that LL37 significantly promotes cell differentiation, migration, and proliferation in both unmodified MSCs and BMP2 gene-modified MSCs. Additionally, LL37 inhibited LPS-induced osteoclast formation and bacterial activity in vitro. Furthermore, the combination of LL37 and BMP2 markedly promoted MSC-mediated angiogenesis and bone repair and regeneration in LPS-induced osteolytic defects in mouse calvaria. These findings demonstrate for the first time that LL37 can be a potential candidate drug for promoting osteogenesis and for inhibiting bacterial growth and osteoclastogenesis, and that the combination of BMP2 and LL37 is ideal for MSC-mediated bone regeneration, especially for inflammation-induced bone loss.

Influence of inflammatory conditions provided by macrophages on osteogenic ability of mesenchymal stem cells

“…The early step of bone formation involves the migration of mesenchymal stem cells (MSC), which undergo proliferation and differentiation along the osteoblastic lineage. Indeed, MSC implantation has emerged as a promising strategy for promoting bone regeneration in several clinical conditions, including delayed unions and non-unions, critical-sized bone defects, periprosthetic osteolysis, osteonecrosis, and inflammatory bone disorders [6][7][8][9][10]. The benefits of MSC therapy are mainly attributed to paracrine effects via soluble factors, exerting both immunoregulatory and regenerative actions [11].…”

Anti-Microbial Peptides and Their Speculative Role in Periodontitis

“…Thus, a dual approach is mandatory to comprehend the task of hosts' immunity in response to, against periodontitis [37]. This involves more comprehensive statistics about HNP and hBD, LL-37, and other oral antimicrobial peptides and proteins, along with their mode of action and clinical significance [38][39][40][41][42][43][44][45][46][47][48][49][50]. These peptides are peculiar in keeping the level of bacteria in control, having distinctive as well as dual roles in maintaining oral health.…”

Combating Implant Infections: Shifting Focus from Bacteria to Host

“…[175,207] In line with these findings, it was found that LL-37 can restore LPS-induced bone loss in vivo. [208] Moreover, LL-37 is thought to stabilize the defective functions of neutrophils that normally are observed around the biomaterial. [28,89] In view of the "frustrated" inflammatory state around the biomaterial, [27] there is evidence to support that LL-37 favors the differentiation of macrophages toward a wound healing and prorepair phenotype, [100,209] without impairing their ability to perform antimicrobial functions ( Figure 3B).…”

“…[199] The immunomodulation by LL-37 could also promote the required macrophage-osteoblast crosstalk around the biomaterial needed for osseointegration. [208,210,211] This is a combinatorial advantage of LL-37 that could further imply its use to improve the functionality of orthopedic implants.…”