The effects of hypoxia-inducible factor (HIF)-1α protein on bone regeneration during distraction osteogenesis: an animal study

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Hsp20 Promotes Endothelial Progenitor Cell Angiogenesis via Activation of PI3K/Akt Signaling Pathway under Hypoxia

BACKGROUND

Mandibular distraction osteogenesis (MDO) is a kind of endogenous tissue engineering technology that lengthens the jaw and opens airway so that a patient can breathe safely and comfortably on his or her own. Endothelial progenitor cells (EPCs) are crucial for MDO-related angiogenesis. Moreover, emerging evidence suggests that heat shock protein 20 (Hsp20) modulates angiogenesis under hypoxic conditions. However, the specific role of Hsp20 in EPCs, in the context of MDO, is not yet known. The aim of this study was to explore the expression of Hsp20 during MDO and the effects of Hsp20 on EPCs under hypoxia.

METHODS

Mandibular distraction osteogenesis and mandibular bone defect (MBD) canine model were established. The expression of CD34, CD133, HIF-1α, and Hsp20 in callus was detected by immunofluorescence on day 14 after surgery. Canine bone marrow EPCs were cultured, with or without optimal cobalt chloride (CoCl2) concentration. Hypoxic effects, caused by CoCl2, were evaluated by means of the cell cycle, cell apoptosis, transwell cell migration, and tube formation assays. The Hsp20/KDR/PI3K/Akt expression levels were evaluated via immunofluorescence, RT-qPCR, and western blot. Next, EPCs were incorporated with either Hsp20-overexpression or Hsp20-siRNA lentivirus. The resulting effects were evaluated as described above.

RESULTS

CD34, CD133, HIF-1α, and Hsp20 were displayed more positive in the callus of MDO compared with MBD. In addition, hypoxic conditions, generated by 0.1 mM CoCl2, in canine EPCs, accelerated cell proliferation, migration, tube formation, and Hsp20 expression. Hsp20 overexpression in EPCs significantly stimulated cell proliferation, migration, and tube formation, whereas Hsp20 inhibition produced the opposite effect. Additionally, the molecular mechanism was partly dependent on the KDR/PI3K/Akt pathway.

CONCLUSION

In summary, herein, we present a novel mechanism of Hsp20-mediated regulation of canine EPCs via Akt activation in a hypoxic microenvironment.

Promotion of osteogenesis in BMSC under hypoxia by ATF4 via the PERK-eIF2α signaling pathway

Mandibular distraction osteogenesis (MDO) is an endogenous tissue engineering technology in which bone marrow mesenchymal stem cells (BMSC) play a key role in MDO-related osteogenesis. Activating transcription factor 4 (ATF4) is involved in osteogenesis through activation of PERK (Protein kinase R-like endoplasmic reticulum kinase) in endoplasmic reticulum stress (ERS) condition under hypoxia. However, the specific role of ATF4 in MDO with BMSC remains unknown. The aim of this study was to explore the effects of ATF4 in MDO with BMSC under hypoxia. Briefly, canine BMSCs were cultured in a hypoxic chamber, and effects of hypoxia were evaluated using cell migration assay and Alizarin Red S staining. Expression levels of protein kinase R-like endoplasmic reticulum kinase, eukaryotic translation initiation factor 2α, ATF4, osteocalcin, and bone sialoprotein were evaluated using quantitative polymerase chain reaction and western blotting. BMSCs were transduced with the ATF4-small interfering RNA lentivirus. The effects were evaluated using all the aforementioned experiments. The results showed that hypoxia promoted migration, osteoblast differentiation, and ATF4 expression in BMSC. ATF4 knockdown in BMSC significantly inhibited migration and osteoblast differentiation abilities, while hypoxia reversed these effects to some extent. In addition, the molecular mechanism partly depended on the ERS signaling pathway, with ATF4 as the key factor. In summary, we presented a novel mechanism of ATF4-mediated regulation of BMSC under hypoxia.

The effect of topical administration of simvastatin on entochondrostosis and intramembranous ossification: An animal experiment

Background

Simvastatin, a drug for lowering serum cholesterol, has been shown to enhance bone regeneration, but few studies have qualitatively and quantitatively tested its effect when used topically in different animal models. This study aims to investigate topical administration of simvastatin as a bone regeneration inducer by testing its effect on bone formation in both long tubular bone and flat bone defect, and the mechanism involved.

Methods

Two animal models were used for testing the effect of simvastatin on entochondrostosis and intramembranous ossification respectively. Simvastatin of different dosages combined with poly lactic acid were implanted in extreme radial defects of 12 adult male New Zealand rabbits. Bone formation was monitored using x-ray and CT-scan and measured using x-ray scales, pixel values and spiral CT-scan for 16 weeks before being subject to histological and immunohistochemistry examination. The result was compared with that of autograft and blank control groups. Simvastatin with thrombin and fibrin sealant were implanted in calvarial defects of three Rhesus monkeys and monitored for 18 weeks. Bone formation was compared between the simvastatin and the blank control group using spiral CT-scan and histological examination.

Results

Both visual and quantitative measurements by x-ray and spiral CT-scan indicated significant bone formation in radial defects in all simvastatin groups and the autograft group whereas no bone formation was found in control groups. There was no significant difference in bone formation quantity between 100 ​mg simvastatin and autograft. Histological and immunohistochemistry examination indicated entochondrostosis in association with positive expression of BMP-2 and HIF-1 alpha. Spiral CT-scan and histological examination of calvarial defects of monkeys showed intramembranous ossification after simvastatin implantation. No change was found in the control group.

Conclusions

Topical administration of simvastatin induces entochondrostosis and intramembranous ossification by enhancing expression of BMP-2 and HIF-1 alpha. The effect of simvastatin on bone regeneration is comparable to autograft.

The translational potential of this article

Topical administration of simvastatin can repair bone defect in both long tubular bones and flat bones of rabbits and monkeys as effectively as autograft. Given that it is cheap, safe and already in clinical use, simvastatin might be considered as a bone regeneration inducer with great potential.

The assessment of new bone formation induced by unfocused extracorporeal shock wave therapy applied on pre-surgical phase of distraction osteogenesis

Purpose:

This study aims to evaluate the effects of extracorporeal shock wave therapy applied before and/or immediately after the osteotomy on the maturation during the consolidation phase.

Materials and methods:

21 female New Zealand rabbits were used in the study. Subjects were divided randomly into three groups: Control (Distraction without ESWT), A (Distraction +ESWT After Osteotomy), AB (Distraction+ESWT After and Before Osteotomy). ESWT (500 pulses, 5 Hz, 0.19 mJ/mm2 energy flux density) was applied to group A and group AB after 5, 12 and 19 days after osteotomy and group AB only on days 7,14 and 21 before osteotomy. On the 28th day of the consolidation period, all subjects were sacrificed. Dual-energy x-ray absorptiometry (DEXA) was used to determine bone mineral density (BMD) and bone mineral content (BMC), and stereological methods were used to determine the new bone, connective tissue and neovascularization volumes.

Results:

As a result of DEXA examinations made on the 1st and 4th week of consolidation, there was no significant difference between groups regarding BMD and BMC values. According to the results of stereological examination, when the connective tissue and new bone tissue were evaluated, higher values were observed in AB when compared to A, and in AB and A compared to the control group, but the differences are not statistically significant. There was no difference between the groups in terms of neovascularization.

Conclusion:

ESWT in these parameters was not positively effective in bone maturation during consolidation when applied before osteotomy or both before and after osteotomy.

Effects of NSAIDs and environmental oxygen pressure on bone regeneration

Objective: To evaluate the effects of administering diclofenac and ketoprofen, as well as the effects of environmental oxygen pressure variation on mandibular bone regeneration. Methods: Thirty-six guinea pigs were distributed into two equal groups. Mandibular bone defects were performed on both groups. Group A was monitored under oxygen pressure at altitude (3320msl, 107mm Hg). Group B was monitored at sea level oxygen pressure (150msl, 157mm Hg). Each group was subdivided into 3 equal groups (A1, A2, A3 and B1, B2, B3). Subgroups A1 and B1 were given diclofenac; subgroups A2 and B2 ketoprofen; subgroups A3 and B3 NaCl. Bone regeneration was evaluated histologically on days 15 and 30. Results: After 15 days in the group controlled at sea level, the level of osteoblasts presented by the control subgroup was significantly higher (28.00±2.65) compared to the diclofenac subgroup (16.00±6.25) and to the ketoprofen subgroup (18.00±4.36); (p=0.041). After 15 days in the group controlled at altitude, the level of osteoblasts was significantly higher in the control subgroup (38.00±5.29) compared to the diclofenac subgroup (21.67±6.35) and to the ketoprofen subgroup (19.33±2.52); p=0.007. After 30 days in the group at sea level there was no difference found in the cell counting; p>0.05. After 30 days in the group controlled at altitude, the level of osteoblast was significantly higher in the control subgroup (58.00±4.58) compared to the diclofenac subgroup (34.33±4.73) and the ketoprofen subgroup (34.00±11.14); (p=0.003). Conclusion: The administration of diclofenac and ketoprofen produced lower mandibular bone regeneration, the effect being significantly more negative at sea level.

Effect of microRNA-21 on hypoxia-inducible factor-1α in orthodontic tooth movement and human periodontal ligament cells under hypoxia

Orthodontic tooth movement can lead to temporary hypoxia of periodontal tissues. Periodontal ligament cells (PDLCs) react to hypoxia, releasing various biological factors to promote periodontal tissue reconstruction. Hypoxia-inducible factor-1α (HIF-1α) is one of the most sensitive factors involved in the response to hypoxia. HIF-1α has been identified to be involved in osteogenic and osteoclast differentiation in vitro; however, few studies have investigated the expression of HIF-1α in the periodontal ligament (PDL) during orthodontic movement in vivo. In a previous study, microRNA-21 (miR-21) was demonstrated to be highly expressed in a rat model of orthodontic tooth movement. Additionally, miR-21 can increase the expression of HIF-1α in certain tumor cell types and is involved in tumor bioactivities. In the present study, HIF-1α exhibited expression patterns in a similar way to miR-21 in PDL samples from a rat model of orthodontic tooth movement, with expression initially increased and followed by a decrease over time. Furthermore, human PDLCs were exposed to a hypoxic environment in vitro, which induced significant upregulation of HIF-1α and miR-21 expression. Furthermore, miR-21 mimics increased HIF-1α expression and promoted osteogenic differentiation, indicated by upregulated expression of the osteogenic markers osteopontin, runt-related gene-2 and alkaline phosphatase. miR-21 inhibitors suppressed HIF-1α expression and downregulated the osteogenic markers. In conclusion, the results revealed that miR-21 has a positive effect on HIF-1α expression in PDLCs under hypoxia and has important roles in osteogenic differentiation during orthodontic tooth movement. These findings provide a theoretical basis by which to promote tissue reconstruction during orthodontic tooth movement.

[Effect of "accordion" technique on bone consolidation during distraction osteogenesis]

Objective

To investigate the effect, right timing, and mechanism of "accordion" technique on bone regeneration in rat distraction osteogenesis model.

Methods

Fifty-four 12-week-old male Sprague Dawley rats underwent right tibial distraction osteogenesis procedure. After a 5-day latency, the distraction was performed for 7 days followed by 6-week consolidation. All animals were randomly divided into 4 groups based on different periods of "accordion" maneuvers in consolidation phase: control group ( n=18) with no manipulation, and three experimental groups including early-phase group ( n=18), mid-phase group ( n=12), and late-phase group ( n=6) with "accordion" maneuvers applied at 1, 3, and 5 weeks, respectively. The duration of the "accordion" maneuver was 7 days consisting of a 3.5-day compression and 3.5-day distraction. Rats in control group and early-phase group were sacrificed at 2, 4, and 6 weeks of the consolidation phase; rats in mid-phase group were sacrificed at 4 and 6 weeks of the consolidation phase; and rats in late-phase group were sacrificed at 6 weeks of the consolidation phase. Bilateral tibias from 6 rats in each group at each time point were obtained. Callus formation was monitored by X-ray radiography every week; new bone was reconstructed by Micro-CT three-dimensional reconstruction. The change of bone structure was evaluated, and parameters containing bone volume (BV)/tissue volume (TV) ratio (BV/TV) and bone mineral density (BMD) in three thresholds (158-211, 211-1 000, 158-1 000) were recorded and calculated at 6 weeks. Mechanical test consisting of ultimate load, modulus of elasticity, and energy to failure was performed. Histological analysis, such as Von Kossa staining, Safranin O staining, and HE staining, was done. Immunohistochemical staining using markers of osterix (OSX), osteocalcin (OCN), and vascular endothelial growth factor (VEGF) was analyzed.

Results

Images of X-ray showed that callus formation increased significantly in the mid-phase group. Micro-CT three-dimensional reconstruction demonstrated the mid-phase group owned fastest reconstructed speed among 4 groups, the cortical bone was continual at 6 weeks. At 6 weeks, the BMD and BV/TV in thresholds 158-1 000 and 211-1 000 in mid-phase group were higher than those in other groups. The results of mechanical test showed that ultimate load, modulus of elasticity, and energy to failure in mid-phase group were significantly higher than those in other groups ( P<0.05). Histological testing showed that the continuity of bone marrow cavity in mid-phase group was evident at 6 weeks after distraction. Immunohistochemical analyses confirmed the expression levels of osteogenesis (OCN, OSX) and angiogenesis (VEGF) elevated remarkably and then returned to normal in mid-phase group.

Conclusion

The "accordion" technique is beneficial for new callus formation in distraction area. Applying the maneuver during the middle phase of the consolidation period was effective to accelerate new bone formation in rat distraction osteogenesis model.

Redox regulation in regenerative medicine and tissue engineering: The paradox of oxygen

One of the biggest challenges in tissue engineering and regenerative medicine is to incorporate a functioning vasculature to overcome the consequences of a lack of oxygen and nutrients in the tissue construct. Otherwise, decreased oxygen tension leads to incomplete metabolism and the formation of the so‐called reactive oxygen species (ROS). Cells have many endogenous antioxidant systems to ensure a balance between ROS and antioxidants, but if this balance is disrupted by factors such as high levels of ROS due to long‐term hypoxia, there will be tissue damage and dysfunction. Current attempts to solve the oxygen problem in the field rarely take into account the importance of the redox balance and are instead centred on releasing or generating oxygen. The first problem with this approach is that although oxygen is necessary for life, it is paradoxically also a highly toxic molecule. Furthermore, although some oxygen‐generating biomaterials produce oxygen, they also generate hydrogen peroxide, a ROS, as an intermediate product. In this review, we discuss why it would be a superior strategy to supplement oxygen delivery with molecules to safeguard the important redox balance. Redox sensor proteins that can stimulate the anaerobic metabolism, angiogenesis, and enhancement of endogenous antioxidant systems are discussed as promising targets. We propose that redox regulating biomaterials have the potential to tackle some of the challenges related to angiogenesis and that the knowledge in this review will help scientists in tissue engineering and regenerative medicine realize this aim.

Effect of Hypoxia-Inducible Factor 1α on Early Healing in Extraction Sockets

The aim of the present study was to investigate the effect of hypoxia-inducible factor 1α (HIF1A) on the early healing (4 weeks) of extraction sockets exhibiting partial loss of the labial bone. Two extraction sockets of the maxillary incisors from each of six dogs were assigned to two treatment modalities: deproteinized bovine bone mineral (i) with 10% collagen (DBBM-C) soaked with HIF1A and covered by a collagen membrane (CM) (HIF group) or (ii) treated with DBBM-C only and covered by a CM (control group). Microcomputed tomography revealed some degree of collapse of the labial contour. The totally augmented volume and new bone volume did not differ significantly between two groups (P > 0.05). The histological analysis revealed that the apical area of the socket was mostly filled with newly formed bone, while there was less newly formed bone in the coronal area and incomplete cortex formation. The histomorphometric analysis revealed that the area of newly formed bone was significantly larger in the HIF group than the control group (12.16 ± 3.04 versus 9.48 ± 2.01 mm², P < 0.05), while there was no significant intergroup difference in the total augmented area. In conclusion, even though DBBM-C soaked with HIF1A enhanced histomorphometric bone formation, this intervention did not demonstrate superiority in preventing ridge shrinkage compared to DBBM-C alone. Clinical relevance of these findings should be further studied.

Nephropreventing effect of hypoxia-inducible factor 1α in a rat model of ischaemic/reperfusion acute kidney injury

Acute kidney injury (AKI) occurs in 5% of hospitalized patients and in 50% of sepsis patients with acute renal dysfunction. However, there have been no safe and effective therapeutic strategies. The hypoxia condition is closely related to renal injury and function under AKI. As hypoxia-inducible factor 1α (HIF-1α) is critical for the cellular response to hypoxia, we investigated the protective effect of HIF-1α in a rat AKI model. We found that HIF-1α injection improved the survival of rat with AKI, and the level of creatinine and blood urea nitrogen (BUN) was also increased. Our data showed that HIF-1α treatment significantly alleviated ischaemic/reperfusion injury to kidney tubules and nephrocytes. We also found the downstream factors, such as EPOR, VEGF, and PHD3, were also upregulated by HIF-1α. Finally, it was observed that HIF-1α treatment also increased the percentage of adult resident progenitor cells (ARPC) in vitro and in vivo. In conclusion, HIF-1α plays a protective role in the ischaemic AKI model through stimulating the proliferation of ARPC, and our study provided a potential therapeutic strategy for AKI.

QSAR modeling and in silico design of small-molecule inhibitors targeting the interaction between E3 ligase VHL and HIF-1α

Protein-protein interactions (PPIs) have attracted much attention recently because of their preponderant role in most biological processes. The prevention of the interaction between E3 ligase VHL and HIF-1[Formula: see text] may improve tolerance to hypoxia and ameliorate the prognosis of many diseases. To obtain novel potent inhibitors of VHL/HIF-1[Formula: see text] interaction, a series of hydroxyproline-based inhibitors were investigated for structural optimization using a combination of QSAR modeling and molecular docking. Here, 2D- and 3D-QSAR models were developed by genetic function approximation (GFA) and comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) methods, respectively. The top-ranked models with strict validation revealed satisfactory statistical parameters (CoMFA with [Formula: see text], 0.637; [Formula: see text], 0.955; [Formula: see text], 0.944; CoMSIA with [Formula: see text], 0.649; [Formula: see text], 0.954; [Formula: see text], 0.911; GFA with [Formula: see text], 0.721; [Formula: see text], 0.801; [Formula: see text], 0.861). The selected five 2D-QSAR descriptors were in good accordance with the 3D-QSAR results, and contour maps gave the visualization of feature requirements for inhibitory activity. A new diverse molecular database was created by molecular fragment replacement and BREED techniques for subsequent virtual screening. Eventually, 31 novel hydroxyproline derivatives stood out as potential VHL/HIF-1[Formula: see text] inhibitors with favorable predictions by the CoMFA, CoMSIA and GFA models. The reliability of this protocol suggests that it could also be applied to the exploration of lead optimization of other PPI targets.

[Research progress of mechanism of hypoxia-inducible factor-1α signaling pathway in condylar cartilage growth and remodeling]

The condylar cartilage was adapted to hypoxic conditions in vivo. However, condylar cartilage cells exposed in normoxia in vitro affect the chondrocyte phenotype and cartilage matrix formation. This condition also resulted in great difficulty in chondrocyte research. Culturing chondrocyte should be simulated in in vivo hypoxia environment as much as possible. The hypoxia-inducible factor-1α (HIF-1α) demonstrates an important transcription factor of adaptive response to hypoxic conditions. HIF-1α also plays an active role in maintaining homeostasis and function of chondrocytes. This review summarized current knowledge of the HIF-1α structure, signaling pathway, and mechanism of HIF-1α in the condylar cartilage repair.

Targeting P38 Pathway Regulates Bony Formation via MSC Recruitment during Mandibular Distraction Osteogenesis in Rats

Distraction osteogenesis (DO) is a widely used self-tissue engineering. However, complications and discomfort due to the long treatment period are still the bottleneck of DO. Novel strategies to accelerate bone formation in DO are still needed. P38 is capable of regulating the osteogenic differentiation of both mesenchymal stem cells (MSCs) and osteoblasts, which are crucial to bone regeneration. However, it is not clear whether targeting p38 could regulate bony formation in DO. The purpose of the current work was to investigate the effects of local application of either p38 agonist anisomycin or p38 inhibitor SB203580 in a rat model of DO. 30 adult rats were randomly divided into 3 groups: (A) rats injected with DMSO served as the control group; (B) rats injected with p38 agonist anisomycin; (C) rats injected with p38 inhibitor SB203580. All the rats were subjected to mandibular distraction and the injection was performed daily during this period. The distracted mandibles were harvested on days 15 and 30 after surgery and subjected to the following analysis. Micro-computed tomography and histological evaluation results showed that local application of p38 agonist anisomycin increased new bone formation in DO, whereas p38 inhibitor SB203580 decreased it. Immunohistochemical analysis suggested that anisomycin promoted MSC recruitment in the distraction gap. In conclusion, this study demonstrated that local application of p38 agonist anisomycin can increase new bone formation during DO. This study may lead to a novel cell-based strategy for the improvement of bone regeneration.