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Lin G, Pan W, He Y, Yi X, Zhou P, Lu J. Opportunities and Perspectives for Three Dimensional Culture of Mesenchymal Stem Cell-Derived Exosomes. TISSUE ENGINEERING. PART B, REVIEWS 2024; 30:462-476. [PMID: 38265004 DOI: 10.1089/ten.teb.2023.0253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2024]
Abstract
Exosomes are nanosized extracellular vesicles (EVs) that participate in intercellular communication through surface proteins and the delivery of internal cargo. The exosomes have gained attention for their potential as disease biomarkers and therapeutic agents. The therapeutic ability of exosomes has been verified by copious previous studies. Effective methods for extensive clinical applications are being researched for exosome-based regenerative therapies, including the application of 3D cultures to enhance exosome production and secretion, which can resolve limited exosome secretion from the parent cells. Cell culture has emerged as a crucial approach for biomedical research because of its many benefits. Both well-established continuous cell lines and primary cell cultures continue to be invaluable for basic research and clinical application. Previous studies have shown that three-dimensional cultured exosomes (3D-Exo) improve therapeutic properties and yields compared with traditional culture systems. Since the majority of studies have focused on exosomes derived from mesenchymal stem cells (MSC-Exo), this review will also concentrate on MSC-Exo. In this review, we will summarize the advantages of 3D-Exo and introduce the 3D culture system and methods of exosome isolation, providing scientific strategies for the diagnosis, treatment, and prognosis of a wide variety of diseases.
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Affiliation(s)
- Guanyi Lin
- Southern Medical University, Guangzhou, China
| | - Wennuo Pan
- Southern Medical University, Guangzhou, China
| | - Yinde He
- Southern Medical University, Guangzhou, China
| | - Xiao Yi
- Department of Obstetrics & Gynecology, Zhujiang Hospital, Southern Medical University, Guangzhou, China
- Cancer Research Institute, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Immune Regulation and Immunotherapy, Southern Medical University, Guangzhou, China
| | - Pengyu Zhou
- Department of Cardiovascular Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Jun Lu
- Department of Cardiovascular Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
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Tepe U, Aslanbay Guler B, Imamoglu E. Applications and sensory utilizations of magnetic levitation in 3D cell culture for tissue Engineering. Mol Biol Rep 2023; 50:7017-7025. [PMID: 37378748 DOI: 10.1007/s11033-023-08585-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 06/07/2023] [Indexed: 06/29/2023]
Abstract
3D cell culture approaches are cell culture methods that provide good visualization of interactions between cells while preserving the natural growth pattern. In recent years, several studies have managed to implement magnetic levitation technology on 3D cell culture applications by either combining cells with magnetic nanoparticles (positive magnetophoresis) or applying a magnetic field directly to the cells in a high-intensity medium (negative magnetophoresis). The positive magnetophoresis technique consists of integrating magnetic nanoparticles into the cells, while the negative magnetophoresis technique consists of levitating the cells without labelling them with magnetic nanoparticles. Magnetic levitation methods can be used to manipulate 3D culture, provide more complex habitats and custom control, or display density data as a sensor.The present review aims to show the advantages, limitations, and promises of magnetic 3D cell culture, along with its application methods, tools, and capabilities as a density sensor. In this context, the promising magnetic levitation technique on 3D cell cultures could be fully utilized in further studies with precise control.
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Affiliation(s)
- Ugur Tepe
- Faculty of Engineering, Department of Bioengineering, Ege University, Izmir, Turkey
| | - Bahar Aslanbay Guler
- Faculty of Engineering, Department of Bioengineering, Ege University, Izmir, Turkey
| | - Esra Imamoglu
- Faculty of Engineering, Department of Bioengineering, Ege University, Izmir, Turkey.
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Park JH, Lee JR, Park S, Kim YJ, Yoon JK, Park HS, Hyun J, Joung YK, Lee TI, Bhang SH. Subaqueous 3D stem cell spheroid levitation culture using anti-gravity bioreactor based on sound wave superposition. Biomater Res 2023; 27:51. [PMID: 37208764 DOI: 10.1186/s40824-023-00383-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 04/19/2023] [Indexed: 05/21/2023] Open
Abstract
BACKGROUND Recently, various studies have revealed that 3D cell spheroids have several advantages over 2D cells in stem cell culture. However, conventional 3D spheroid culture methods have some disadvantages and limitations such as time required for spheroid formation and complexity of the experimental process. Here, we used acoustic levitation as cell culture platform to overcome the limitation of conventional 3D culture methods. METHODS In our anti-gravity bioreactor, continuous standing sonic waves created pressure field for 3D culture of human mesenchymal stem cells (hMSCs). hMSCs were trapped and aggerated in pressure field and consequently formed spheroids. The structure, viability, gene and protein expression of spheroids formed in the anti-gravity bioreactor were analyzed by electron microscope, immunostaining, polymerase chain reaction, and western blot. We injected hMSC spheroids fabricated by anti-gravity bioreactor into the mouse hindlimb ischemia model. Limb salvage was quantified to evaluate therapeutic efficacy of hMSC spheroids. RESULTS The acoustic levitation in anti-gravity bioreactor made spheroids faster and more compact compared to the conventional hanging drop method, which resulted in the upregulation of angiogenic paracrine factors of hMSCs, such as vascular endothelial growth factor and angiopoietin 2. Injected hMSCs spheroids cultured in the anti-gravity bioreactor exhibited improved therapeutic efficacy, including the degree of limb salvage, capillary formation, and attenuation of fibrosis and inflammation, for mouse hindlimb ischemia model compared to spheroids formed by the conventional hanging drop method. CONCLUSION Our stem cell culture system using acoustic levitation will be proposed as a new platform for the future 3D cell culture system.
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Affiliation(s)
- Jung Hwan Park
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Ju-Ro Lee
- Center for Biomaterials, Biomedical Research Institute, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Sungkwon Park
- Department of Food Science and Biotechnology, College of Life Science, Sejong University, Seoul, 05006, Korea
| | - Yu-Jin Kim
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Jeong-Kee Yoon
- Department of Systems Biotechnology, Chung-Ang University, Gyeonggi-Do, Anseong-Si, 17540, Republic of Korea
| | - Hyun Su Park
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Jiyu Hyun
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Yoon Ki Joung
- Center for Biomaterials, Biomedical Research Institute, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Division of Bio-Medical Science and Technology, University of Science and Technology, Republic of Korea, Seoul, 02792, Republic of Korea
| | - Tae Il Lee
- Department of Materials Science and Engineering, Gachon University, Gyeonggi-Do, Seongnam-Si, 13120, Republic of Korea.
| | - Suk Ho Bhang
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
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Wang J, Shang P. Static magnetic field: A potential tool of controlling stem cells fates for stem cell therapy in osteoporosis. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2023; 178:91-102. [PMID: 36596343 DOI: 10.1016/j.pbiomolbio.2022.12.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 12/10/2022] [Accepted: 12/29/2022] [Indexed: 01/01/2023]
Abstract
Osteoporosis is a kind of bone diseases characterized by dynamic imbalance of bone formation and bone absorption, which is prone to fracture, and seriously endangers human health. At present, there is a lack of highly effective drugs for it, and the existing measures all have some side effects. In recent years, mesenchymal stem cell therapy has brought a certain hope for osteoporosis, while shortcomings such as homing difficulty and unstable therapeutic effects limit its application widely. Therefore, it is extremely urgent to find effective and reliable means/drugs for adjuvant stem cell therapy or develop new research techniques. It has been reported that static magnetic fields(SMFs) has a certain alleviating and therapeutic effect on varieties of bone diseases, also promotes the proliferation and osteogenic differentiation of mesenchymal stem cells derived from different tissues to a certain extent. Basing on the above background, this article focuses on the key words "static/constant magnetic field, mesenchymal stem cell, osteoporosis", combined literature and relevant contents were studied to look forward that SMFs has unique advantages in the treatment of osteoporosis with mesenchymal stem cells, which can be used as an application tool to promote the progress of stem cell therapy in clinical application.
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Affiliation(s)
- Jianping Wang
- School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China; Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China
| | - Peng Shang
- Research & Development Institute of Northwestern Polytechnical University in Shenzhen, Shenzhen, 518057, China; School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China; Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China.
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The Effects of Combined Exposure to Simulated Microgravity, Ionizing Radiation, and Cortisol on the In Vitro Wound Healing Process. Cells 2023; 12:cells12020246. [PMID: 36672184 PMCID: PMC9857207 DOI: 10.3390/cells12020246] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 12/23/2022] [Accepted: 12/30/2022] [Indexed: 01/11/2023] Open
Abstract
Human spaceflight is associated with several health-related issues as a result of long-term exposure to microgravity, ionizing radiation, and higher levels of psychological stress. Frequent reported skin problems in space include rashes, itches, and a delayed wound healing. Access to space is restricted by financial and logistical issues; as a consequence, experimental sample sizes are often small, which limits the generalization of the results. Earth-based simulation models can be used to investigate cellular responses as a result of exposure to certain spaceflight stressors. Here, we describe the development of an in vitro model of the simulated spaceflight environment, which we used to investigate the combined effect of simulated microgravity using the random positioning machine (RPM), ionizing radiation, and stress hormones on the wound-healing capacity of human dermal fibroblasts. Fibroblasts were exposed to cortisol, after which they were irradiated with different radiation qualities (including X-rays, protons, carbon ions, and iron ions) followed by exposure to simulated microgravity using a random positioning machine (RPM). Data related to the inflammatory, proliferation, and remodeling phase of wound healing has been collected. Results show that spaceflight stressors can interfere with the wound healing process at any phase. Moreover, several interactions between the different spaceflight stressors were found. This highlights the complexity that needs to be taken into account when studying the effect of spaceflight stressors on certain biological processes and for the aim of countermeasures development.
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Hazrati A, Malekpour K, Soudi S, Hashemi SM. Mesenchymal stromal/stem cells spheroid culture effect on the therapeutic efficacy of these cells and their exosomes: A new strategy to overcome cell therapy limitations. Biomed Pharmacother 2022; 152:113211. [PMID: 35696942 DOI: 10.1016/j.biopha.2022.113211] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Revised: 05/22/2022] [Accepted: 05/25/2022] [Indexed: 11/02/2022] Open
Abstract
Cell therapy is one of the new treatment methods in which mesenchymal stem/stromal cell (MSCs) transplantation is one of the cells widely used in this field. The results of MSCs application in the clinic prove their therapeutic efficacy. For this reason, many clinical trials have been designed based on the application of MSCs for various diseases, especially inflammatory disease and regenerative medicine. These cells perform their therapeutic functions through multiple mechanisms, including the differentiative potential, immunomodulatory properties, production of therapeutic exosomes, production of growth factors and cytokines, and anti-apoptotic effects. Exosomes are nanosized extracellular vesicles (EVs) that change target cell functions by transferring different cargos. The therapeutic ability of MSCs-derived exosomes has been demonstrated in many studies. However, some limitations, such as the low production of exosomes by cells and the need for large amounts of them and also their limited therapeutic ability, have encouraged researchers to find methods that increase exosomes' therapeutic potential. One of these methods is the spheroid culture of MSCs. Studies show that the three-dimensional culture (3DCC) of MSCs in the form of multicellular spheroids increases the therapeutic efficacy of these cells in laboratory and animal applications. In addition, the spheroid culture of MSCs leads to enhanced therapeutic properties of their exosomes and production rate. Due to the novelty of the field of using 3DCC MSCs-derived exosomes, examination of their properties and the results of their therapeutic application can increase our view of this field. This review discussed MSCs and their exosomes enhanced properties in spheroid culture.
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Affiliation(s)
- Ali Hazrati
- Department of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
| | - Kosar Malekpour
- Department of Immunology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
| | - Sara Soudi
- Department of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
| | - Seyed Mahmoud Hashemi
- Medical Nanotechnology and Tissue Engineering Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran; Department of Immunology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Kouroupis D, Correa D. Increased Mesenchymal Stem Cell Functionalization in Three-Dimensional Manufacturing Settings for Enhanced Therapeutic Applications. Front Bioeng Biotechnol 2021; 9:621748. [PMID: 33644016 PMCID: PMC7907607 DOI: 10.3389/fbioe.2021.621748] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 01/07/2021] [Indexed: 12/23/2022] Open
Abstract
Mesenchymal stem/stromal cell (MSC) exist within their in vivo niches as part of heterogeneous cell populations, exhibiting variable stemness potential and supportive functionalities. Conventional extensive 2D in vitro MSC expansion, aimed at obtaining clinically relevant therapeutic cell numbers, results in detrimental effects on both cellular characteristics (e.g., phenotypic changes and senescence) and functions (e.g., differentiation capacity and immunomodulatory effects). These deleterious effects, added to the inherent inter-donor variability, negatively affect the standardization and reproducibility of MSC therapeutic potential. The resulting manufacturing challenges that drive the qualitative variability of MSC-based products is evident in various clinical trials where MSC therapeutic efficacy is moderate or, in some cases, totally insufficient. To circumvent these limitations, various in vitro/ex vivo techniques have been applied to manufacturing protocols to induce specific features, attributes, and functions in expanding cells. Exposure to inflammatory cues (cell priming) is one of them, however, with untoward effects such as transient expression of HLA-DR preventing allogeneic therapeutic schemes. MSC functionalization can be also achieved by in vitro 3D culturing techniques, in an effort to more closely recapitulate the in vivo MSC niche. The resulting spheroid structures provide spatial cell organization with increased cell–cell interactions, stable, or even enhanced phenotypic profiles, and increased trophic and immunomodulatory functionalities. In that context, MSC 3D spheroids have shown enhanced “medicinal signaling” activities and increased homing and survival capacities upon transplantation in vivo. Importantly, MSC spheroids have been applied in various preclinical animal models including wound healing, bone and osteochondral defects, and cardiovascular diseases showing safety and efficacy in vivo. Therefore, the incorporation of 3D MSC culturing approach into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved without requiring ex vivo stimulatory regimes. In the present review, we discuss the MSC functionalization in 3D settings and how this strategy can contribute to an improved MSC-based product for safer and more effective therapeutic applications.
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Affiliation(s)
- Dimitrios Kouroupis
- Department of Orthopedics, UHealth Sports Medicine Institute, University of Miami, Miller School of Medicine, Miami, FL, United States.,Diabetes Research Institute & Cell Transplantation Center, University of Miami, Miller School of Medicine, Miami, FL, United States
| | - Diego Correa
- Department of Orthopedics, UHealth Sports Medicine Institute, University of Miami, Miller School of Medicine, Miami, FL, United States.,Diabetes Research Institute & Cell Transplantation Center, University of Miami, Miller School of Medicine, Miami, FL, United States
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NAD +/NADH redox alterations reconfigure metabolism and rejuvenate senescent human mesenchymal stem cells in vitro. Commun Biol 2020; 3:774. [PMID: 33319867 PMCID: PMC7738682 DOI: 10.1038/s42003-020-01514-y] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 11/17/2020] [Indexed: 02/06/2023] Open
Abstract
Human mesenchymal stem cells (hMSCs) promote endogenous tissue regeneration and have become a promising candidate for cell therapy. However, in vitro culture expansion of hMSCs induces a rapid decline of stem cell properties through replicative senescence. Here, we characterize metabolic profiles of hMSCs during expansion. We show that alterations of cellular nicotinamide adenine dinucleotide (NAD + /NADH) redox balance and activity of the Sirtuin (Sirt) family enzymes regulate cellular senescence of hMSCs. Treatment with NAD + precursor nicotinamide increases the intracellular NAD + level and re-balances the NAD + /NADH ratio, with enhanced Sirt-1 activity in hMSCs at high passage, partially restores mitochondrial fitness and rejuvenates senescent hMSCs. By contrast, human fibroblasts exhibit limited senescence as their cellular NAD + /NADH balance is comparatively stable during expansion. These results indicate a potential metabolic and redox connection to replicative senescence in adult stem cells and identify NAD + as a metabolic regulator that distinguishes stem cells from mature cells. This study also suggests potential strategies to maintain cellular homeostasis of hMSCs in clinical applications. Yuan et al. characterise metabolic profiles of human mesenchymal stem cells (hMSCs) during cell expansion in culture. They find that late passage hMSCs exhibit a NAD + /NADH redox cycle imbalance and that adding NAD + precursor nicotinamide restores mitochondrial fitness and cellular homeostasis in senescent hMSCs indicating a possible route to preserve hMSC homeostasis for therapeutic use.
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Stem Cell Culture Under Simulated Microgravity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1298:105-132. [PMID: 32424490 DOI: 10.1007/5584_2020_539] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Challenging environment of space causes several pivotal alterations in living systems, especially due to microgravity. The possibility of simulating microgravity by ground-based systems provides research opportunities that may lead to the understanding of in vitro biological effects of microgravity by eliminating the challenges inherent to spaceflight experiments. Stem cells are one of the most prominent cell types, due to their self-renewal and differentiation capabilities. Research on stem cells under simulated microgravity has generated many important findings, enlightening the impact of microgravity on molecular and cellular processes of stem cells with varying potencies. Simulation techniques including clinostat, random positioning machine, rotating wall vessel and magnetic levitation-based systems have improved our knowledge on the effects of microgravity on morphology, migration, proliferation and differentiation of stem cells. Clarification of the mechanisms underlying such changes offers exciting potential for various applications such as identification of putative therapeutic targets to modulate stem cell function and stem cell based regenerative medicine.
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Spheroid Culture System Methods and Applications for Mesenchymal Stem Cells. Cells 2019; 8:cells8121620. [PMID: 31842346 PMCID: PMC6953111 DOI: 10.3390/cells8121620] [Citation(s) in RCA: 256] [Impact Index Per Article: 51.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 12/09/2019] [Accepted: 12/09/2019] [Indexed: 12/16/2022] Open
Abstract
Owing to the importance of stem cell culture systems in clinical applications, researchers have extensively studied them to optimize the culture conditions and increase efficiency of cell culture. A spheroid culture system provides a similar physicochemical environment in vivo by facilitating cell–cell and cell–matrix interaction to overcome the limitations of traditional monolayer cell culture. In suspension culture, aggregates of adjacent cells form a spheroid shape having wide utility in tumor and cancer research, therapeutic transplantation, drug screening, and clinical study, as well as organic culture. There are various spheroid culture methods such as hanging drop, gel embedding, magnetic levitation, and spinner culture. Lately, efforts are being made to apply the spheroid culture system to the study of drug delivery platforms and co-cultures, and to regulate differentiation and pluripotency. To study spheroid cell culture, various kinds of biomaterials are used as building forms of hydrogel, film, particle, and bead, depending upon the requirement. However, spheroid cell culture system has limitations such as hypoxia and necrosis in the spheroid core. In addition, studies should focus on methods to dissociate cells from spheroid into single cells.
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Effects of BMP-2 and FGF2 on the osteogenesis of bone marrow-derived mesenchymal stem cells in hindlimb-unloaded rats. Cell Biochem Biophys 2015; 70:1127-36. [PMID: 24880437 DOI: 10.1007/s12013-014-0032-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Hindlimb unloading, as a simulation of microgravity, decreases the osteogenic potential of mesenchymal stem cells (MSCs) from hindlimb femur of rat. We simulated the microgravity by 28-day of hindlimb unloading for male Sprague-Dawley rat, and performed intramuscular injection of BMP-2 and FGF2 at a given interval during hindlimb unloading. Then, the bone marrow (BM) was collected from hindlimb femur of rat. MSCs were isolated from BM, cultured for four passages, and then induced for osteogenesis. The results revealed that the hindlimb unloading decreased the osteogenic potential of MSCs and also the expression of osteoblast gene marker mRNAs in cells induced by osteogenic conditions. Hindlimb unloading for 28 days resulted in the decrease of vinculin-containing focal adhesion in MSCs. During hindlimb unloading, the interval intramuscular injection of BMP-2 or FGF2 alone could increase the osteogenic potential of MSCs and the expression of osteoblast gene marker mRNA. However, the effect of BMP-2 or FGF2 injection alone was significantly lower than that of combination injection of both factors. The further examination showed that the intramuscular injection of BMP-2 promoted the expression of Runx2 mRNA and that the intramuscular injection of FGF2 increased the phosphorylation of ERK and Runx2. Nevertheless, the intramuscular injection of any factor could not increase the formation of vinculin-containing focal adhesions in MSCs. This suggests that BMP-2 should increase the expression of Runx2, and that the activation of Runx2 should be promoted by the FGF2 signaling pathway which activated ERK/Runx2. The activation of this signaling pathway should not lie on the formation of vinculin-containing focal adhesions.
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Wang Y, Chen ZH, Yin C, Ma JH, Li DJ, Zhao F, Sun YL, Hu LF, Shang P, Qian AR. GeneChip expression profiling reveals the alterations of energy metabolism related genes in osteocytes under large gradient high magnetic fields. PLoS One 2015; 10:e0116359. [PMID: 25635858 PMCID: PMC4312085 DOI: 10.1371/journal.pone.0116359] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Accepted: 12/05/2014] [Indexed: 12/31/2022] Open
Abstract
The diamagnetic levitation as a novel ground-based model for simulating a reduced gravity environment has recently been applied in life science research. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. Osteocyte, as the most important mechanosensor in bone, takes a pivotal position in mediating the mechano-induced bone remodeling. In this study, the effects of LG-HMF on gene expression profiling of osteocyte-like cell line MLO-Y4 were investigated by Affymetrix DNA microarray. LG-HMF affected osteocyte gene expression profiling. Differentially expressed genes (DEGs) and data mining were further analyzed by using bioinfomatic tools, such as DAVID, iReport. 12 energy metabolism related genes (PFKL, AK4, ALDOC, COX7A1, STC1, ADM, CA9, CA12, P4HA1, APLN, GPR35 and GPR84) were further confirmed by real-time PCR. An integrated gene interaction network of 12 DEGs was constructed. Bio-data mining showed that genes involved in glucose metabolic process and apoptosis changed notablly. Our results demostrated that LG-HMF affected the expression of energy metabolism related genes in osteocyte. The identification of sensitive genes to special environments may provide some potential targets for preventing and treating bone loss or osteoporosis.
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Affiliation(s)
- Yang Wang
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Zhi-Hao Chen
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Chun Yin
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Jian-Hua Ma
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Di-Jie Li
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Fan Zhao
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Yu-Long Sun
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Li-Fang Hu
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
| | - Peng Shang
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
- * E-mail: (PS); (ARQ)
| | - Ai-Rong Qian
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi’an 710072, China
- * E-mail: (PS); (ARQ)
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RhoGTPases as key players in mammalian cell adaptation to microgravity. BIOMED RESEARCH INTERNATIONAL 2015; 2015:747693. [PMID: 25649831 PMCID: PMC4310447 DOI: 10.1155/2015/747693] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 08/14/2014] [Accepted: 09/09/2014] [Indexed: 01/03/2023]
Abstract
A growing number of studies are revealing that cells reorganize their cytoskeleton when exposed to conditions of microgravity. Most, if not all, of the structural changes observed on flown cells can be explained by modulation of RhoGTPases, which are mechanosensitive switches responsible for cytoskeletal dynamics control. This review identifies general principles defining cell sensitivity to gravitational stresses. We discuss what is known about changes in cell shape, nucleus, and focal adhesions and try to establish the relationship with specific RhoGTPase activities. We conclude by considering the potential relevance of live imaging of RhoGTPase activity or cytoskeletal structures in order to enhance our understanding of cell adaptation to microgravity-related conditions.
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Rocca A, Marino A, Rocca V, Moscato S, de Vito G, Piazza V, Mazzolai B, Mattoli V, Ngo-Anh TJ, Ciofani G. Barium titanate nanoparticles and hypergravity stimulation improve differentiation of mesenchymal stem cells into osteoblasts. Int J Nanomedicine 2015; 10:433-45. [PMID: 25609955 PMCID: PMC4294648 DOI: 10.2147/ijn.s76329] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Background Enhancement of the osteogenic potential of mesenchymal stem cells (MSCs) is highly desirable in the field of bone regeneration. This paper proposes a new approach for the improvement of osteogenesis combining hypergravity with osteoinductive nanoparticles (NPs). Materials and methods In this study, we aimed to investigate the combined effects of hypergravity and barium titanate NPs (BTNPs) on the osteogenic differentiation of rat MSCs, and the hypergravity effects on NP internalization. To obtain the hypergravity condition, we used a large-diameter centrifuge in the presence of a BTNP-doped culture medium. We analyzed cell morphology and NP internalization with immunofluorescent staining and coherent anti-Stokes Raman scattering, respectively. Moreover, cell differentiation was evaluated both at the gene level with quantitative real-time reverse-transcription polymerase chain reaction and at the protein level with Western blotting. Results Following a 20 g treatment, we found alterations in cytoskeleton conformation, cellular shape and morphology, as well as a significant increment of expression of osteoblastic markers both at the gene and protein levels, jointly pointing to a substantial increment of NP uptake. Taken together, our findings suggest a synergistic effect of hypergravity and BTNPs in the enhancement of the osteogenic differentiation of MSCs. Conclusion The obtained results could become useful in the design of new approaches in bone-tissue engineering, as well as for in vitro drug-delivery strategies where an increment of nanocarrier internalization could result in a higher drug uptake by cell and/or tissue constructs.
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Affiliation(s)
- Antonella Rocca
- Istituto Italiano di Tecnologia, Center for Micro-BioRobotics @ SSSA, Pontedera, Italy ; Scuola Superiore Sant'Anna, The BioRobotics Institute, Pontedera, Italy
| | - Attilio Marino
- Istituto Italiano di Tecnologia, Center for Micro-BioRobotics @ SSSA, Pontedera, Italy ; Scuola Superiore Sant'Anna, The BioRobotics Institute, Pontedera, Italy
| | - Veronica Rocca
- Università di Pisa, Dipartimento di Ingegneria dell'Informazione, Pisa, Italy, Noordwijk, the Netherlands
| | - Stefania Moscato
- Università di Pisa, Dipartimento di Medicina Clinica e Sperimentale, Pisa, Italy
| | - Giuseppe de Vito
- Istituto Italiano di Tecnologia, Center for Nanotechnology Innovation @NEST, Pisa, Italy ; Scuola Normale Superiore, NEST, Pisa, Italy
| | - Vincenzo Piazza
- Istituto Italiano di Tecnologia, Center for Nanotechnology Innovation @NEST, Pisa, Italy
| | - Barbara Mazzolai
- Istituto Italiano di Tecnologia, Center for Micro-BioRobotics @ SSSA, Pontedera, Italy
| | - Virgilio Mattoli
- Istituto Italiano di Tecnologia, Center for Micro-BioRobotics @ SSSA, Pontedera, Italy
| | - Thu Jennifer Ngo-Anh
- Directorate of Human Spaceflight and Operations, European Space Agency, Noordwijk, the Netherlands
| | - Gianni Ciofani
- Istituto Italiano di Tecnologia, Center for Micro-BioRobotics @ SSSA, Pontedera, Italy
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15
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Sun YL, Chen ZH, Chen XH, Yin C, Li DJ, Ma XL, Zhao F, Zhang G, Shang P, Qian AR. Diamagnetic levitation promotes osteoclast differentiation from RAW264.7 cells. IEEE Trans Biomed Eng 2014; 62:900-8. [PMID: 25398175 DOI: 10.1109/tbme.2014.2370039] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The superconducting magnet with a high magnetic force field can levitate diamagnetic materials. In this study, a specially designed superconducting magnet with large gradient high magnetic field (LGHMF), which provides three apparent gravity levels (μg, 1 g, and 2 g), was used to study its influence on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation from preosteoclast cell line RAW264.7. The effects of LGHMF on the viability, nitric oxide (NO) production, morphology in RAW264.7 cells were detected by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method, the Griess method, and the immunofluorescence staining, respectively. The changes induced by LGHMF in osteoclast formation, mRNA expression, and bone resorption were determined by tartrate-resistant acid phosphatase staining, semiquantity PCR, and bone resorption test, respectively. The results showed that: 1) LGHMF had no lethal effect on osteoclast precursors but attenuated NO release in RAW264.7 cells. 2) Diamagnetic levitation (μg) enhanced both the formation and bone resorption capacity of osteoclast. Moreover, diamagnetic levitation up-regulated mRNA expression of RANK, Cathepsin K, MMP-9, and NFATc1, while down-regulated RunX2 in comparison with controls. Furthermore, diamagnetic levitation induced obvious morphological alterations in osteoclast, including active cytoplasmic peripheral pseudopodial expansion, formation of pedosome belt, and aggregation of actin ring. 3) Magnetic field produced by LGHMF attenuated osteoclast resorption activity. Collectively, LGHMF with combined effects has multiple effects on osteoclast, which attenuated osteoclast resorption with magnetic field, whereas promoted osteoclast differentiation with diamagnetic levitation. Therefore, these findings indicate that diamagnetic levitation could be used as a novel ground-based microgravity simulator, which facilitates bone cell research of weightlessness condition.
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16
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Arfat Y, Xiao WZ, Iftikhar S, Zhao F, Li DJ, Sun YL, Zhang G, Shang P, Qian AR. Physiological effects of microgravity on bone cells. Calcif Tissue Int 2014; 94:569-79. [PMID: 24687524 DOI: 10.1007/s00223-014-9851-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Accepted: 03/12/2014] [Indexed: 01/07/2023]
Abstract
Life on Earth developed under the influence of normal gravity (1g). With evidence from previous studies, scientists have suggested that normal physiological processes, such as the functional integrity of muscles and bone mass, can be affected by microgravity during spaceflight. During the life span, bone not only develops as a structure designed specifically for mechanical tasks but also adapts for efficiency. The lack of weight-bearing forces makes microgravity an ideal physical stimulus to evaluate bone cell responses. One of the most serious problems induced by long-term weightlessness is bone mineral loss. Results from in vitro studies that entailed the use of bone cells in spaceflights showed modification in cell attachment structures and cytoskeletal reorganization, which may be involved in bone loss. Humans exposed to microgravity conditions experience various physiological changes, including loss of bone mass, muscle deterioration, and immunodeficiency. In vitro models can be used to extract valuable information about changes in mechanical stress to ultimately identify the different pathways of mechanotransduction in bone cells. Despite many in vivo and in vitro studies under both real microgravity and simulated conditions, the mechanism of bone loss is still not well defined. The objective of this review is to summarize the recent research on bone cells under microgravity conditions based on advances in the field.
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Affiliation(s)
- Yasir Arfat
- Key Laboratory for Space Biosciences & Biotechnology, Institute of Special Environmental Biophysics, Faculty of Life Sciences, Northwestern Polytechnical University, 127 Youyi Xilu, Xi'an, 710072, People's Republic of China
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17
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Grimm D, Wehland M, Pietsch J, Aleshcheva G, Wise P, van Loon J, Ulbrich C, Magnusson NE, Infanger M, Bauer J. Growing tissues in real and simulated microgravity: new methods for tissue engineering. TISSUE ENGINEERING PART B-REVIEWS 2014; 20:555-66. [PMID: 24597549 DOI: 10.1089/ten.teb.2013.0704] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Tissue engineering in simulated (s-) and real microgravity (r-μg) is currently a topic in Space medicine contributing to biomedical sciences and their applications on Earth. The principal aim of this review is to highlight the advances and accomplishments in the field of tissue engineering that could be achieved by culturing cells in Space or by devices created to simulate microgravity on Earth. Understanding the biology of three-dimensional (3D) multicellular structures is very important for a more complete appreciation of in vivo tissue function and advancing in vitro tissue engineering efforts. Various cells exposed to r-μg in Space or to s-μg created by a random positioning machine, a 2D-clinostat, or a rotating wall vessel bioreactor grew in the form of 3D tissues. Hence, these methods represent a new strategy for tissue engineering of a variety of tissues, such as regenerated cartilage, artificial vessel constructs, and other organ tissues as well as multicellular cancer spheroids. These aggregates are used to study molecular mechanisms involved in angiogenesis, cancer development, and biology and for pharmacological testing of, for example, chemotherapeutic drugs or inhibitors of neoangiogenesis. Moreover, they are useful for studying multicellular responses in toxicology and radiation biology, or for performing coculture experiments. The future will show whether these tissue-engineered constructs can be used for medical transplantations. Unveiling the mechanisms of microgravity-dependent molecular and cellular changes is an up-to-date requirement for improving Space medicine and developing new treatment strategies that can be translated to in vivo models while reducing the use of laboratory animals.
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Affiliation(s)
- Daniela Grimm
- 1 Institute of Biomedicine, Pharmacology, Aarhus University , Aarhus, Denmark
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18
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Meng R, Xie L. Gap junction mediated regulation of osteocytes to osteoblastic alkaline phosphatase activity is independent of microgravity. Anim Cells Syst (Seoul) 2014. [DOI: 10.1080/19768354.2013.870092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
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19
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Vorselen D, Roos WH, MacKintosh FC, Wuite GJL, van Loon JJWA. The role of the cytoskeleton in sensing changes in gravity by nonspecialized cells. FASEB J 2013; 28:536-47. [PMID: 24249634 DOI: 10.1096/fj.13-236356] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A large body of evidence indicates that single cells in vitro respond to changes in gravity, and that this response might play an important role for physiological changes at the organism level during spaceflight. Gravity can lead to changes in cell proliferation, differentiation, signaling, and gene expression. At first glance, gravitational forces seem too small to affect bodies with the size of a cell. Thus, the initial response to gravity is both puzzling and important for understanding physiological changes in space. This also offers a unique environment to study the mechanical response of cells. In the past 2 decades, important steps have been made in the field of mechanobiology, and we use these advances to reevaluate the response of single cells to changes in gravity. Recent studies have focused on the cytoskeleton as initial gravity sensor. Thus, we review the observed changes in the cytoskeleton in a microgravity environment, both during spaceflight and in ground-based simulation techniques. We also evaluate to what degree the current experimental evidence supports the cytoskeleton as primary gravity sensor. Finally, we consider how the cytoskeleton itself could be affected by changed gravity. To make the next step toward understanding the response of cells to altered gravity, the challenge will be to track changes quantitatively and on short timescales.
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Affiliation(s)
- Daan Vorselen
- 1Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), Office 11N15, Gustav Mahler Laan 3004, 1081LA, Amsterdam, the Netherlands.
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20
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SHANG PENG, ZHANG JIAN, QIAN AIRONG, LI JINGBAO, MENG RUI, DI SHENGMENG, HU LIFANG, GU ZHONGZE. BONE CELLS UNDER MICROGRAVITY. J MECH MED BIOL 2013. [DOI: 10.1142/s021951941340006x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Weightlessness environment (also microgravity) during the exploration of space is the major condition which must be faced by astronauts. One of the most serious adverse effects on astronauts is the weightlessness-induced bone loss due to the unbalanced bone remodeling. Bone remodeling of human beings has evolved during billions of years to make bone tissue adapt to the gravitational field of Earth (1g) and maintain skeleton structure to meet mechanical loading on Earth. However, under weightlessness environment the skeleton system no longer functions against the pull of gravity, so there is no necessity to keep bone strong enough to support the body's weight. Therefore, the balance of bone remodeling is disrupted and bone loss occurs, which is extremely deleterious to an astronaut's health during long-term spaceflight. Bone remodeling is mainly orchestrated by bone mesenchymal stem cells, osteoblasts, osteocytes, and osteoclasts. Here, we review how these bone cells respond to microgravity environment.
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Affiliation(s)
- PENG SHANG
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
- The State Key Laboratory of Bioelectonics, Southeast University, 210096, P. R. China
| | - JIAN ZHANG
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - AIRONG QIAN
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - JINGBAO LI
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - RUI MENG
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - SHENGMENG DI
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - LIFANG HU
- Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, 710072, Xi'an, P. R. China
| | - ZHONGZE GU
- The State Key Laboratory of Bioelectonics, Southeast University, 210096, P. R. China
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21
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Large gradient high magnetic fields affect osteoblast ultrastructure and function by disrupting collagen I or fibronectin/αβ1 integrin. PLoS One 2013; 8:e51036. [PMID: 23382804 PMCID: PMC3558520 DOI: 10.1371/journal.pone.0051036] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Accepted: 10/29/2012] [Indexed: 11/19/2022] Open
Abstract
The superconducting magnet generates a field and field gradient product that can levitate diamagnetic materials. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. The effects of LG-HMF on the ultrastructure and function of osteoblast-like cells (MG-63 and MC3T3-E1) and the underlying mechanism were investigated by transmission electromicroscopy (TEM), MTT, and cell western (ICW) assays. Under LG-HMF significant morphologic changes in osteoblast-like cells occurred, including expansion of endoplasmic reticulum and mitochondria, an increased number of lysosomes, distorted microvilli, and aggregates of actin filaments. Compared to controls, cell viability and alkaline phosphatase (ALP) secretion were significantly increased, and collagen I (col I), fibronectin (FN), vinculin, integrin α3, αv, and β1 expression were changed under LG-HMF conditions. In conclusion, LG-HMF affects osteoblast ultrastructure, cell viability, and ALP secretion, and the changes caused by LG-HMF may be related to disrupting col I or FN/αβ1 integrin.
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22
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On the nature and shape of tubulin trails: implications on microtubule self-organization. Acta Biotheor 2012; 60:55-82. [PMID: 22331498 DOI: 10.1007/s10441-012-9149-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Accepted: 01/23/2012] [Indexed: 10/28/2022]
Abstract
Microtubules, major elements of the cell skeleton are, most of the time, well organized in vivo, but they can also show self-organizing behaviors in time and/or space in purified solutions in vitro. Theoretical studies and models based on the concepts of collective dynamics in complex systems, reaction-diffusion processes and emergent phenomena were proposed to explain some of these behaviors. In the particular case of microtubule spatial self-organization, it has been advanced that microtubules could behave like ants, self-organizing by 'talking to each other' by way of hypothetic (because never observed) concentrated chemical trails of tubulin that are expected to be released by their disassembling ends. Deterministic models based on this idea yielded indeed like-looking spatio-temporal self-organizing behaviors. Nevertheless the question remains of whether microscopic tubulin trails produced by individual or bundles of several microtubules are intense enough to allow microtubule self-organization at a macroscopic level. In the present work, by simulating the diffusion of tubulin in microtubule solutions at the microscopic scale, we measure the shape and intensity of tubulin trails and discuss about the assumption of microtubule self-organization due to the production of chemical trails by disassembling microtubules. We show that the tubulin trails produced by individual microtubules or small microtubule arrays are very weak and not elongated even at very high reactive rates. Although the variations of concentration due to such trails are not significant compared to natural fluctuations of the concentration of tubuline in the chemical environment, the study shows that heterogeneities of biochemical composition can form due to microtubule disassembly. They could become significant when produced by numerous microtubule ends located in the same place. Their possible formation could play a role in certain conditions of reaction. In particular, it gives a mesoscopic basis to explain the collective dynamics observed in excitable microtubule solutions showing the propagation of concentration waves of microtubules at the millimeter scale, although we doubt that individual microtubules or bundles can behave like molecular ants.
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