Human cathelicidin antimicrobial peptide LL-37 promotes lymphangiogenesis in lymphatic endothelial cells through the ERK and Akt signaling pathways

Antimicrobial peptides in bone regeneration: mechanism and potential

INTRODUCTION

Antimicrobial peptides (AMPs) are small-molecule peptides with a unique antimicrobial mechanism. Other notable biological activities of AMPs, including anti-inflammatory, angiogenesis, and bone formation effects, have recently received widespread attention. These remarkable bioactivities, combined with the unique antimicrobial mechanism of action of AMPs, have led to their increasingly important role in bone regeneration.

AREAS COVERED

In this review, on the one hand, we aimed to summarize information about the AMPs that are currently used for bone regeneration by reviewing published literature in the PubMed database. On the other hand, we also highlight some AMPs with potential roles in bone regeneration and their possible mechanisms of action.

EXPERT OPINION

The translation of AMPs to the clinic still faces many problems, but their unique antimicrobial mechanisms and other conspicuous biological activities suggest great potential. An in-depth understanding of the structure and mechanism of action of AMPs will help us to subsequently combine AMPs with different carrier systems and perform structural modifications to reduce toxicity and achieve stable release, which may be a key strategy for facilitating the translation of AMPs to the clinic.

Evaluation of biocompatibility and angiogenic potential of extracellular matrix hydrogel biofunctionalized with the LL-37 peptide

BACKGROUND

Biomaterials must allow revascularization for a successful tissue regeneration process. Biomaterials formulated from the extracellular matrix (ECM) have gained popularity in tissue engineering because of their superior biocompatibility, and due to their rheological properties, ECM-hydrogels can be easily applied in damaged areas, allowing cell colonization and integration into the host tissue. Porcine urinary bladder ECM (pUBM) retains functional signaling and structural proteins, being an excellent option in regenerative medicine. Even some small molecules, such as the antimicrobial cathelicidin-derived LL-37 peptide have proven angiogenic properties.

OBJECTIVE

The objective of this study was to evaluate the biocompatibility and angiogenic potential of an ECM-hydrogel derived from the porcine urinary bladder (pUBMh) biofunctionalized with the LL-37 peptide (pUBMh/LL37).

METHODS

Macrophages, fibroblasts, and adipose tissue-derived mesenchymal stem cells (AD-MSC) were exposed pUBMh/LL37, and the effect on cell proliferation was evaluated by MTT assay, cytotoxicity by quantification of lactate dehydrogenase release and the Live/Dead Cell Imaging assays. Moreover, macrophage production of IL-6, IL-10, IL-12p70, MCP-1, INF-γ, and TNF-α cytokines was quantified using a bead-based cytometric array. pUBMh/LL37 was implanted directly by dorsal subcutaneous injection in Wistar rats for 24 h to evaluate biocompatibility, and pUBMh/LL37-loaded angioreactors were implanted for 21 days for evaluation of angiogenesis.

RESULTS

We found that pUBMh/LL37 did not affect cell proliferation and is cytocompatible to all tested cell lines but induces the production of TNF-α and MCP-1 in macrophages. In vivo, this ECM-hydrogel induces fibroblast-like cell recruitment within the material, without tissue damage or inflammation at 48 h. Interestingly, tissue remodeling with vasculature inside angioreactors was seen at 21 days.

CONCLUSIONS

Our results showed that pUBMh/LL37 is cytologically compatible, and induces angiogenesis in vivo, showing potential for tissue regeneration therapies.

Piper retrofractum extract and its component piperine promote lymphangiogenesis via an AKT- and ERK-dependent mechanism

Administration of Piper retrofractum extract (PRE) has been reported to alleviate edema, but the mechanism underlying this effect is unknown. Promotion of lymphangiogenesis is known to improve lymphedema, but the effect of PRE on lymphangiogenesis remains unclear. In the present study, we investigated whether PRE and specifically, piperine, the main component of PRE, can induce lymphangiogenesis. Treatments with PRE and piperine significantly promoted the proliferation, migration, and tube formation in human dermal lymphatic microvascular endothelial cells (HDLECs) but had no effect on the expression of lymphangiogenic factors. Furthermore, PRE and piperine significantly promoted the phosphorylation of the AKT and ERK proteins in HDLECs, and pretreatment with AKT and ERK inhibitors significantly attenuated the PRE- and piperine-induced lymphangiogenesis. These results indicate that PRE and piperine promote lymphangiogenesis via an AKT- and ERK-dependent mechanism. PRACTICAL APPLICATIONS: The lymphatic system plays various roles such as maintaining tissue fluid homeostasis, immune defense, and metabolism. Disruption of the lymphatic system results in insufficient fluid drainage, which causes edema. Currently, there are no effective treatments for lymphedema; therefore, the development of novel treatment strategies is desirable. In this study, we showed that PRE and its main component piperine promote lymphangiogenesis in lymphatic endothelial cells. Therefore, PRE has the potential to be used as a novel functional food for relieving lymphedema.

Extracellular Vesicles Derived From Hypoxia-Conditioned Adipose-Derived Mesenchymal Stem Cells Enhance Lymphangiogenesis

Extracellular vesicles from adipose-derived mesenchymal stem cells (ADSCs) play an important role in lymphangiogenesis; however, the underlying mechanisms are not fully understood. In this study, we aimed to investigate the function of extracellular vesicles secreted by hypoxia-conditioned ADSCs in lymphangiogenesis and explore the potential molecular mechanisms. Extracellular vesicles were extracted from ADSCs cultured under hypoxia or normoxia conditions. The uptake of extracellular vesicles by lymphatic endothelial cells (LECs) was detected by immunofluorescence staining. The effects of extracellular vesicles on the viability, migration, and tube formation of LECs were determined by CCK-8 assay, migration assay, and tube formation assay, respectively. Molecules and pathway involved in lymphangiogenesis mediated by ADSC-derived extracellular vesicles were analyzed by luciferase reporter assay, qRT-polymerase chain reaction (PCR), and Western blot. Hypoxia ADSC-derived extracellular vesicles (H-ADSC/evs) significantly enhanced the proliferation, migration, and tube formation of LECs. Hypoxia decreased the expression of miR-129 in ADSC-derived extracellular vesicles. Overexpression of miR-129 counteracted the promoting effect of H-ADSC/evs on lymphangiogenesis. In addition, decreased exosomal miR-129 expression resulted in upregulation of HMGB1 in LECs, which led to AKT activation and lymphangiogenesis enhancement. Our data reveal that extracellular vesicles derived from hypoxia-conditioned ADSCs induce lymphangiogenesis, and this effect is mediated by miR-129/HMGB1/AKT signaling. Our findings imply that hypoxia ADSC-isolated extracellular vesicles may represent as a valuable target for the treatment of diseases associated with lymphatic remodeling.