Histatin-1 is a novel osteogenic factor that promotes bone cell adhesion, migration, and differentiation

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.

Hst1/Gel-MA Scaffold Significantly Promotes the Quality of Osteochondral Regeneration in the Temporomandibular Joint

OBJECTIVE

Our aim was to evaluate the capacity of the human salivary histatin-1-functionalized methacrylic gelatin scaffold to control osteochondral tissue regeneration and repair in vivo in rabbits with major temporomandibular joint dimensional abnormalities.

MATERIALS AND METHODS

In order to compare human salivary histatin-1-functionalized methacrylic gelatin scaffolds to the Blank and Gel-MA hydrogel groups, scaffolds were implanted into osteochondral lesions of a critical size (3 × 3 mm) in the anterior region of the condyle of the temporomandibular joint in New Zealand white rabbits. At 4 weeks after implantation, the repair was evaluated using macroscopic examination, histology, and micro-CT analysis.

RESULTS

In the comparison of the composite scaffold group with the Blank and Gel-MA groups, analysis of the healed tissue revealed an improved macroscopic appearance in the composite scaffold group. Regeneration was induced by host cell migration in the Hst1/Gel-MA scaffold group.

CONCLUSIONS

The current study offers a viable method for in vivo cartilage repair that does not require cell transplantation. Future clinical applications of this strategy's optimization have many potential advantages.

The salivary peptide histatin-1 enhances bone repair in vivo

The salivary peptide histatin-1 was recently described as a novel osteogenic factor that stimulates cell adhesion, migration, and differentiation in bone-lineage cells. Since these cell responses collectively contribute to bone regeneration, we hypothesized that histatin-1 harbors the capacity to enhance bone tissue repair at the preclinical level. By using a model of monocortical bone defect, we explored the effects of histatin-1 in tibial mineralization and organic matrix formation in vivo. To this end, different amounts of histatin-1 were embedded in one-mm3 collagen sponges and then applied to tibial monocortical defects in C57bl/6 mice. After seven days, mice were euthanized, and samples were processed for subsequent analysis. Micro-computed tomography screening showed that histatin-1 increased intraosseous mineralization, and this phenomenon was accompanied by augmented collagen matrix deposition and closure of cortical defect edges, as determined by Hematoxylin-Eosin and Masson's Trichrome staining. Moreover, immunohistochemical analyses showed that histatin-1 increased the expression of the osteogenic marker alkaline phosphatase, which was accompanied by augmented blood vessel formation. Collectively, our findings show that histatin-1 itself promotes bone regeneration in an orthotopic model, proposing this molecule as a therapeutic candidate for use in bone regenerative medicine.

Sigma-2 Receptors—From Basic Biology to Therapeutic Target: A Focus on Age-Related Degenerative Diseases

There is a large unmet medical need to develop disease-modifying treatment options for individuals with age-related degenerative diseases of the central nervous system. The sigma-2 receptor (S2R), encoded by TMEM97, is expressed in brain and retinal cells, and regulates cell functions via its co-receptor progesterone receptor membrane component 1 (PGRMC1), and through other protein–protein interactions. Studies describing functions of S2R involve the manipulation of expression or pharmacological modulation using exogenous small-molecule ligands. These studies demonstrate that S2R modulates key pathways involved in age-related diseases including autophagy, trafficking, oxidative stress, and amyloid-β and α-synuclein toxicity. Furthermore, S2R modulation can ameliorate functional deficits in cell-based and animal models of disease. This review summarizes the current evidence-based understanding of S2R biology and function, and its potential as a therapeutic target for age-related degenerative diseases of the central nervous system, including Alzheimer’s disease, α-synucleinopathies, and dry age-related macular degeneration.

Aging envisage imbalance of the periodontium: A keystone in oral disease and systemic health

Aging is a gradual and progressive deterioration of integrity across multiple organ systems that negatively affects gingival wound healing. The cellular responses associated with wound healing, such as collagen synthesis, cell migration, proliferation, and collagen contraction, have been shown to be lower in gingival fibroblasts (the most abundant cells from the connective gingival tissue) in aged donors than young donors. Cellular senescence is one of the hallmarks of aging, which is characterized by the acquisition of a senescence-associated secretory phenotype that is characterized by the release of pro-inflammatory cytokines, chemokines, growth factors, and proteases which have been implicated in the recruitment of immune cells such as neutrophils, T cells and monocytes. Moreover, during aging, macrophages show altered acquisition of functional phenotypes in response to the tissue microenvironment. Thus, inflammatory and resolution macrophage-mediated processes are impaired, impacting the progression of periodontal disease. Interestingly, salivary antimicrobial peptides, such as histatins, which are involved in various functions, such as antifungal, bactericidal, enamel-protecting, angiogenesis, and re-epithelization, have been shown to fluctuate with aging. Several studies have associated the presence of Porphyromonas gingivalis, a key pathogen related to periodontitis and apical periodontitis, with the progression of Alzheimer's disease, as well as gut, esophageal, and gastric cancers. Moreover, herpes simplex virus types 1 and 2 have been associated with the severity of periodontal disease, cardiovascular complications, and nervous system-related pathologies. This review encompasses the effects of aging on periodontal tissues, how P. gingivalis and HSV infections could favor periodontitis and their relationship with other pathologies.

GPCR/endocytosis/ERK signaling/S2R is involved in the regulation of the internalization, mitochondria-targeting and -activating properties of human salivary histatin 1

Human salivary histatin 1 (Hst1) exhibits a series of cell-activating properties, such as promoting cell spreading, migration, and metabolic activity. We recently have shown that fluorescently labeled Hst1 (F-Hst1) targets and activates mitochondria, presenting an important molecular mechanism. However, its regulating signaling pathways remain to be elucidated. We investigated the influence of specific inhibitors of G protein-coupled receptors (GPCR), endocytosis pathways, extracellular signal-regulated kinases 1/2 (ERK1/2) signaling, p38 signaling, mitochondrial respiration and Na+/K+-ATPase activity on the uptake, mitochondria-targeting and -activating properties of F-Hst1. We performed a siRNA knockdown (KD) to assess the effect of Sigma-2 receptor (S2R) /Transmembrane Protein 97 (TMEM97)—a recently identified target protein of Hst1. We also adopted live cell imaging to monitor the whole intracellular trafficking process of F-Hst1. Our results showed that the inhibition of cellular respiration hindered the internalization of F-Hst1. The inhibitors of GPCR, ERK1/2, phagocytosis, and clathrin-mediated endocytosis (CME) as well as siRNA KD of S2R/TMEM97 significantly reduced the uptake, which was accompanied by the nullification of the promoting effect of F-Hst1 on cell metabolic activity. Only the inhibitor of CME and KD of S2R/TMEM97 significantly compromised the mitochondria-targeting of Hst1. We further showed the intracellular trafficking and targeting process of F-Hst1, in which early endosome plays an important role. Overall, phagocytosis, CME, GPCR, ERK signaling, and S2R/TMEM97 are involved in the internalization of Hst1, while only CME and S2R/TMEM97 are critical for its subcellular targeting. The inhibition of either internalization or mitochondria-targeting of Hst1 could significantly compromise its mitochondria-activating property.

Conditioned medium of amniotic fluid-derived stromal cells exerts a bone anabolic effect by enhancing progenitor population and angiogenesis

A cell-free approach utilizing the paracrine effects of mesenchymal stromal cells is receiving attention in regenerative medicine. In the present study, we evaluated the effects of a conditioned medium of amniotic fluid-derived stromal cells (AFSC-CM) on bone metabolism. In mice, intraperitoneal injections of AFSC-CM increased bone mass and enhanced bone turnover. The precursor populations of myeloid and mesenchymal lineages, as well as endothelial cells in bone marrow, were also augmented by AFSC-CM administration. In an in vitro culture experiment, AFSC-CM increased osteoclast differentiation of bone marrow-derived macrophages, but had no significant effect on the osteogenic differentiation of preosteoblasts. However, AFSC-CM administration dramatically accelerated the migration and tube formation of endothelial cells, and a cytokine array showed that AFSC-CM contained many angiogenic factors. These results indicate that AFSC-CM exerts a bone anabolic effect by changing the bone marrow microenvironment, including angiogenesis and precursor expansion. Therefore, ameliorating marrow angiogenesis is a potential therapeutic strategy for bone regeneration, for which AFSCs can be a good cellular source.

Comprehensive analysis of lncRNA-miRNA-mRNA networks during osteogenic differentiation of bone marrow mesenchymal stem cells

Background

Long non-coding RNA (lncRNA) plays crucial role in osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs), involving in regulation of competing endogenous RNA (ceRNA) mechanisms and conduction of signaling pathways. However, its mechanisms are poorly understood. This study aimed to investigate lncRNAs, miRNAs and mRNAs expression profiles in rat BMMSCs (rBMMSCs) osteogenic differentiation, screen the potential key lncRNA-miRNA-mRNA networks, explore the putative functions and identify the key molecules, as the basis of studying potential mechanism of rBMMSCs osteogenic differentiation driven by lncRNA, providing molecular targets for the management of bone defect.

Methods

High-throughput RNA sequencing (RNA-seq) was used to determine lncRNAs, miRNAs, and mRNAs expression profiles at 14-day rBMMSCs osteogenesis. The pivotal lncRNA-miRNA and miRNA-mRNA networks were predicted from sequencing data and bioinformatic analysis, and the results were exported by Cytoscape 3.9.0 software. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used for functional exploration. Real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed to validate lncRNAs, miRNAs and mRNAs.

Results

rBMMSCs were identified, and the osteogenic and adipogenic differentiation ability were detected. A total of 8634 lncRNAs were detected by RNA-seq, and 1524 differential expressed lncRNAs, of which 812 up-regulated and 712 down-regulated in osteo-inductive groups compared with control groups. 30 up-regulated and 61 down-regulated miRNAs, 91 miRNAs were differentially expressed in total. 2453 differentially expressed mRNAs including 1272 up-expressed and 1181 down-expressed were detected. 10 up-regulated lncRNAs were chosen to predict 21 down-regulated miRNAs and 650 up-regulated mRNAs. 49 lncRNA-miRNA and 1515 miRNA–mRNA interactive networks were constructed. GO analysis showed the most important enrichment in cell component and molecular function were “cytoplasm” and “protein binding”, respectively. Biological process related to osteogenic differentiation such as “cell proliferation”, “wound healing”, “cell migration”, “osteoblast differentiation”, “extracellular matrix organization” and “response to hypoxia” were enriched. KEGG analysis showed differentially expressed genes were mainly enriched in “PI3K-Akt signaling pathway”, “Signaling pathway regulating pluripotency of stem cells”, “cGMP-PKG signaling pathway”, “Axon guidance” and “Calcium signaling pathway”. qRT-PCR verified that lncRNA Tug1, lncRNA AABR07011996.1, rno-miR-93-5p, rno-miR-322-5p, Sgk1 and Fzd4 were consistent with the sequencing results, and 4 lncRNA-miRNA-mRNA networks based on validations were constructed, and enrichment pathways were closely related to “PI3K-Akt signaling pathway”, “Signaling pathway regulating pluripotency of stem cells” and “Wnt signaling pathway”.

Conclusions

lncRNAs, miRNAs and mRNAs expression profiles provide clues for future studies on their roles for BMMSCs osteogenic differentiation. Furthermore, lncRNA–miRNA–mRNA networks give more information on potential new mechanisms and targets for management on bone defect.

Supplementary information

The online version contains supplementary material available at 10.1186/s12864-022-08646-x.

Identification of VEGFR2 as the Histatin-1 receptor in endothelial cells

Histatin-1 is a salivary peptide with antimicrobial and wound healing promoting activities, which was previously shown to stimulate angiogenesis in vitro and in vivo via inducing endothelial cell migration. The mechanisms underlying the proangiogenic effects of Histatin-1 remain poorly understood and specifically, the endothelial receptor for this peptide, is unknown. Based on the similarities between Histatin-1-dependent responses and those induced by the prototypical angiogenic receptor, vascular endothelial growth factor receptor 2 (VEGFR2), we hypothesized that VEGFR2 is the Histatin-1 receptor in endothelial cells. First, we observed that VEGFR2 is necessary for Histatin-1-induced endothelial cell migration, as shown by both pharmacological inhibition studies and siRNA-mediated ablation of VEGFR2. Moreover, Histatin-1 co-immunoprecipitated and co-localized with VEGFR2, associating spatial proximity between these proteins with receptor activation. Indeed, pulldown assays with pure, tagged and non-tagged proteins showed that Histatin-1 and VEGFR2 directly interact in vitro. Optical tweezers experiments permitted estimating kinetic parameters and rupture forces, indicating that the Histatin-1-VEGFR2 interaction is transient, but specific and direct. Sequence alignment and molecular modeling identified residues Phe26, Tyr30 and Tyr34 within the C-terminal domain of Histatin-1 as relevant for VEGFR2 binding and activation. This was corroborated by mutation and molecular dynamics analyses, as well as in direct binding assays. Importantly, these residues were required for Histatin-1 to induce endothelial cell migration and angiogenesis in vitro. Taken together, our findings reveal that VEGFR2 is the endothelial cell receptor of Histatin-1 and provide insights to the mechanism by which this peptide promotes endothelial cell migration and angiogenesis.

Human Salivary Histatin-1-Functionalized Gelatin Methacrylate Hydrogels Promote the Regeneration of Cartilage and Subchondral Bone in Temporomandibular Joints

The avascular structure and lack of regenerative cells make the repair of osteochondral defects in the temporomandibular joint (TMJ) highly challenging in the clinic. To provide a viable treatment option, we developed a methacrylated gelatin (Gel-MA) hydrogel functionalized with human salivary histatin-1 (Hst1). Gel-MA is highly biocompatible, biodegradable, and cost-effective. Hst1 is capable of activating a series of cell activities, such as adhesion, migration, differentiation, and angiogenesis. To evaluate the efficacy of Hst1/Gel-MA, critical-size osteochondral defects (3 mm in diameter and 3 mm in depth) of TMJ in New Zealand white rabbits were surgically created and randomly assigned to one of the three treatment groups: (1) control (no filling material); (2) Gel-MA hydrogel; (3) Hst1/Gel-MA hydrogel. Samples were retrieved 1, 2, and 4 weeks post-surgery and subjected to gross examination and a series of histomorphometric and immunological analyses. In comparison with the control and Gel-MA alone groups, Hst1/Gel-MA hydrogel was associated with significantly higher International Cartilage Repair Society score, modified O’Driscoll score, area percentages of newly formed bone, cartilage, collagen fiber, and glycosaminoglycan, and expression of collagen II and aggrecan. In conclusion, Hst1/Gel-MA hydrogels significantly enhance bone and cartilage regeneration, thus bearing promising application potential for repairing osteochondral defects.