Expression of HIF‑1α in cycling stretch‑induced osteogenic differentiation of bone mesenchymal stem cells

Priming mesenchymal stem cells to develop "super stem cells"

The stem cell pre-treatment approaches at cellular and sub-cellular levels encompass physical manipulation of stem cells to growth factor treatment, genetic manipulation, and chemical and pharmacological treatment, each strategy having advantages and limitations. Most of these pre-treatment protocols are non-combinative. This editorial is a continuum of Li et al's published article and Wan et al's editorial focusing on the significance of pre-treatment strategies to enhance their stemness, immunoregulatory, and immunosuppressive properties. They have elaborated on the intricacies of the combinative pre-treatment protocol using pro-inflammatory cytokines and hypoxia. Applying a well-defined multi-pronged combinatorial strategy of mesenchymal stem cells (MSCs), pre-treatment based on the mechanistic understanding is expected to develop "Super MSCs", which will create a transformative shift in MSC-based therapies in clinical settings, potentially revolutionizing the field. Once optimized, the standardized protocols may be used with slight modifications to pre-treat different stem cells to develop "super stem cells" with augmented stemness, functionality, and reparability for diverse clinical applications with better outcomes.

Mechanical Force Modulates Alveolar Bone Marrow Mesenchymal Cells Characteristics for Bone Remodeling during Orthodontic Tooth Movement through Lactate Production

Orthodontic tooth movement (OTM) relies on mechanical force-induced bone remodeling. As a metabolic intermediate of glycolysis, lactate has recently been discovered to participate in bone remodeling by serving as a signaling molecule. However, whether lactate could respond to mechanical stimulus during OTM, as well as whether lactate has an impact on the alveolar bone remodeling during orthodontics, remain to be further elucidated. In the current study, we observed physiologically elevated production of lactate along with increased osteogenic differentiation, proliferation, and migration of alveolar bone marrow mesenchymal cells (ABMMCs) under mechanical force. Inhibition of lactate, induced by cyclic mechanical stretch by GNE-140, remarkably suppressed the osteogenic differentiation, proliferation, and migration, yet enhanced apoptosis of ABMMCs. Mechanistically, these regulatory effects of lactate were mediated by histone lactylation. Taken together, our results suggest that force-induced lactate is involved in controlling bone remodeling-related cellular activities in ABMMCs and plays a vital role in the alveolar bone remodeling during OTM. Our findings indicate that lactate might be a critical modulator for alveolar bone remodeling during OTM, providing a novel therapeutic target for the purpose of more effectively controlling tooth movement and improving the stability of orthodontic results.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

How the mechanical microenvironment of stem cell growth affects their differentiation: a review

Stem cell differentiation is of great interest in medical research; however, specifically and effectively regulating stem cell differentiation is still a challenge. In addition to chemical factors, physical signals are an important component of the stem cell ecotone. The mechanical microenvironment of stem cells has a huge role in stem cell differentiation. Herein, we describe the knowledge accumulated to date on the mechanical environment in which stem cells exist, which consists of various factors, including the extracellular matrix and topology, substrate stiffness, shear stress, hydrostatic pressure, tension, and microgravity. We then detail the currently known signalling pathways that stem cells use to perceive the mechanical environment, including those involving nuclear factor-kB, the nicotinic acetylcholine receptor, the piezoelectric mechanosensitive ion channel, and hypoxia-inducible factor 1α. Using this information in clinical settings to treat diseases is the goal of this research, and we describe the progress that has been made. In this review, we examined the effects of mechanical factors in the stem cell growth microenvironment on stem cell differentiation, how mechanical signals are transmitted to and function within the cell, and the influence of mechanical factors on the use of stem cells in clinical applications.

ANGPTL4 regulates the osteogenic differentiation of periodontal ligament stem cells

The molecular mechanism of mechanical force regulating the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) has not been clearly elucidated. In this study, two mRNA-seqs, GSE106887 and GSE109167, which contained several samples of PDLSCs under mechanical force, were downloaded from Gene Expression Omnibus. Differential expression analysis was firstly taken between GSE106887 and GSE109167, then the common 84 up-regulated genes and 26 down-regulated genes were selected. Function enrichment analysis was used to identify the key genes and pathways in PDLSCs subjected to the tension and compression force. PDLSCs were isolated from human periodontal ligament tissues. The effects of ANGPTL4 knockdown with shRNA on the osteogenic differentiation of PDLSCs were studied in vitro. Then, the orthodontic tooth movement (OTM) rat model was used to study the expression of HIF-1α and ANGPTL4 in alveolar bone remodeling in vivo. ANGPTL4 and the HIF-1 pathway were identified in PDLSCs subjected to the tension and compression force. alizarin red staining, alcian blue staining, and oil red O staining verified that PDLSCs had the ability of osteogenic, chondrogenic, and adipogenic differentiation, respectively. Verification experiment revealed that the expression of ANGPTL4 in PDLSCs significantly increased when cultured under osteogenic medium in vitro. While ANGPTL4 was knocked down by shRNA, the levels of ALPL, RUNX2, and OCN decreased significantly, as well as the protein levels of COL1A1, ALPL, RUNX2, and OCN. During the OTM, the expression of HIF-1α and ANGPTL4 in periodontal ligament cells increased on the tension and compression sides. We concluded the positive relationship between ANGPTL4 and osteogenic differentiation of PDLSCs.

Demethylase FTO promotes mechanical stress induced osteogenic differentiation of BMSCs with up-regulation of HIF-1α

BACKGROUND

In orthodontics, mechanical stress plays an important role in the process of bone remodeling. Mechanical stress has an effect on osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). However, the mechanism remains to be studied. The aim of this study is to investigate the effects of demethyltransferase fat mass and obesity-associated (FTO) on osteogenic differentiation of BMSCs under mechanical stress condition.

METHODS AND RESULTS

The rat BMSCs were cultured in vitro, followed by flow cytometry to identify the cell surface antigens. Osteogenic differentiation of BMSCs was induced by mechanical stress by using the flexcell tension system for 6 h every day and 3 days in total. BMSCs were transfected by using plasmid for FTO knockdown. The expression level of FTO, hypoxia-inducible factor (HIF)-1α, runt-related transcription factor 2 (RUNX2), bone morphogenetic proteins (BMPs) and alkaline phosphatase (ALP) were measured by real-time qPCR, western blotting. ALP activity were determined by ALP staining assays. The expression of FTO and HIF-1α in BMSCs with mechanical stress were significantly higher than BMSCs without mechanical stress, also, the expression of osteogenic differentiation markers were higher in BMSCs with mechanical stress. Knockdown of FTO decreased expression of osteogenic differentiation marker and ALP activity in stretched BMSCs. In addition, the expression of HIF-1α was decreased after knocking down FTO.

CONCLUSIONS

FTO promotes the expression of HIF-1α and osteogenic differentiation under the condition of mechanical stress. This finding may facilitate the clinical application of orthodontics and the mechanism research of mechanical stress-induced osteogenesis.

Integrins in the Regulation of Mesenchymal Stem Cell Differentiation by Mechanical Signals

Mesenchymal stem cells (MSCs) can sense and convert mechanical stimuli signals into a chemical response. Integrins are involved in the mechanotransduction from inside to outside and from outside to inside, and ultimately affect the fate of MSCs responding to different mechanical signals. Different integrins participate in different signaling pathways to regulate MSCs multi-differentiation. In this review, we summarize the latest advances in the effects of mechanical signals on the differentiation of MSCs, the importance of integrins in mechanotransduction, the relationship between integrin heterodimers and different mechanical signals, and the interaction among mechanical signals. We put forward our views on the prospect and challenges of developing mechanical biology in tissue engineering and regenerative medicine.

A Novel Tension Machine Promotes Bone Marrow Mesenchymal Stem Cell Osteoblastic and Fibroblastic Differentiation by Applying Cyclic Tension

Bone marrow mesenchymal stem cells (BMSCs) are intraosseous stem cells, and the effects of tensile strain on BMSC differentiation mediate several bone-related treatments. To study the response of BMSCs under tension, we designed and developed a small cellular tension instrument, iStrain. When iStrain applied tension on BMSCs, these cells exhibited convergence in the alignment direction and lengthening of the cell processes and cell body. Real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting demonstrated that iStrain-mediated cyclic tension promotes the differentiation of BMSCs toward osteogenesis and fibrogenesis. And the mRNA and protein expression of differentiation-related genes changes with the extension of tension time.

Mechanical stimulation induced osteogenic differentiation of BMSCs through TWIST/E2A/p21 axis

The relationship between mechanical force and alveolar bone remodeling is an important issue in orthodontics because tooth movement is dependent on the response of bone tissue to the mechanical force induced by the appliances used. Mechanical cyclical stretch plays an essential role in the cell osteogenic differentiation involved in bone remodeling. However, the underlying mechanisms are unclear, particularly the molecular pathways regulated by mechanical stimulation. In the present study, we reported a dynamic change of p21 level in response to mechanical cyclical stretch, and shRNA-p21 in bone marrow mesenchymal stem cells (BMSCs) induced osteogenic differentiation. The mechanism was mediated through TWIST/E2A/p21 axis. These results supported the mechanical stimulation-induced osteogenic differentiation is negatively regulated by p21.

microRNA-155-3p attenuates intervertebral disc degeneration via inhibition of KDM3A and HIF1α

OBJECTIVE

Intervertebral disc degeneration (IDD) is a key element resulting in low back pain, but the mechanisms underlying IDD remain largely unknown. The purpose of the study was to investigate the influence of microRNA-155-3p (miR-155-3p) on proliferation and autophagy of nucleus pulposus (NP) cells in IDD with the involvement of hypoxia-inducible factor 1 α (HIF1α)/histone lysine demethylase 3A (KDM3A) axis.

METHODS

IDD NP tissues of patients with lumbar disc herniation and traumatic intervertebral disc NP tissues from patients with traumatic lumbar fracture were collected. Apoptosis in NP tissues was observed, and autophagy marker proteins in NP tissues were detected. NP cells in IDD were transfected with miR-155-3p mimic or KDM3A-siRNA to explore their roles in cell proliferation, autophagy and apoptosis. MiR-155-3p, KDM3A and HIF1α expression in NP tissues and cells were detected.

RESULTS

Decreased miR-155-3p, and elevated HIF1α and KDM3A were presented in NP tissues and cells of IDD. Elevated miR-155-3p or silenced KDM3A promoted the proliferation and autophagy, and inhibited the apoptosis of NP cells of IDD. Moreover, elevated miR-155-3p decreased KDM3A and HIF1α expression, while silenced KDM3A decreased HIF1α expression in NP cells with IDD.

CONCLUSION

The study concludes that up-regulated miR-155-3p or silenced KDM3A promotes the proliferation, autophagy, and restrains the apoptosis of NP cells of IDD via inhibition of HIF1α, which may be a promising approach for the treatment of IDD.

MiR-935/HIF1α Feedback Loop Inhibits the Proliferation and Invasiveness of Glioma

Objective

The biological functions and molecular mechanisms of miR-935 have been widely investigated in various types of cancer. The aim of the present study was to explore the function of miR-935 in glioma.

Methods

Bioinformatic analysis and quantitative real-time fluorescent PCR (qRT-PCR) were used to determine the expression of miR-935 in glioma tissues and glioma cell lines. Chi-square test was performed to analyze the relationship between the expression of miR-935 and clinical traits. CCK-8 assay, colony formation assay, cell cycle analysis and subcutaneous tumorigenesis model in nude mice were conducted to determine the effects of miR-935 on the proliferation of glioma cells both in vitro and in vivo. Wound healing and transwell assays were used to detect the effects of miR-935 on the migration and invasion of glioma cells in vitro. The relationship between miR-935 and HIF1α was analyzed using bioinformatics, luciferase reporter assay and Western blotting.

Results

The expression of miR-935 was lower in glioma tissues than in the adjacent tissues, and in cell lines than in the normal human astrocytes (NHAs), and the low expression levels of miR-935 predicted a poor outcome. Exogenous overexpression of miR-935 inhibited the proliferation of glioma cells both in vitro and in vivo, and suppressed the migration and invasion of glioma cells in vitro. HIF1α was identified as the target of miR-935, whereas miR-935 overexpression decreased the expression of HIF1α and its target genes VEGF, MCL1 and GLUT1. Strikingly, overexpression of HIF1α significantly decreased the expression of miR-935, whereas silencing HIF1α increased the expression of miR-935. Similarly, HIF1α overexpression remarkably reversed the inhibitory effects of miR-935 on the proliferation, migration and invasion of glioma cells.

Conclusion

Overall, present study reveals the presence of miR-935/HIF1α feedback loop in glioma, which inhibits the development of glioma. This feedback loop may be a potential target for the treatment of glioma.