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Sun Z, Li Y, Zhou H, Cai M, Liu J, Gao S, Yang J, Tong L, Wang J, Zhou S, Hu Z, Wang Y, Wang K, Zhang L, Wang H, Zhang L, Shi F, Cao X, Zhang S, Ji Y, Zhao J. Simulated microgravity reduces intracellular-free calcium concentration by inhibiting calcium channels in primary mouse osteoblasts. J Cell Biochem 2018; 120:4009-4020. [PMID: 30260002 DOI: 10.1002/jcb.27685] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 08/27/2018] [Indexed: 12/11/2022]
Abstract
Calcium homeostasis in osteoblasts plays fundamental roles in the physiology and pathology of bone tissue. Various types of mechanical stimuli promote osteogenesis and increase bone formation elicit increases in intracellular-free calcium concentration in osteoblasts. However, whether microgravity, a condition of mechanical unloading, exerts an influence on intracellular-free calcium concentration in osteoblasts or what mechanisms may underlie such an effect are unclear. Herein, we show that simulated microgravity reduces intracellular-free calcium concentration in primary mouse osteoblasts. In addition, simulated microgravity substantially suppresses the activities of L-type voltage-sensitive calcium channels, which selectively allow calcium to cross the plasma membrane from the extracellular space. Moreover, the functional expression of ryanodine receptors and inositol 1,4,5-trisphosphate receptors, which mediate the release of calcium from intracellular storage, decreased under simulated microgravity conditions. These results suggest that simulated microgravity substantially reduces intracellular-free calcium concentration through inhibition of calcium channels in primary mouse osteoblasts. Our study may provide a novel mechanism for microgravity-induced detrimental effects in osteoblasts, offering a new avenue to further investigate bone loss induced by mechanical unloading.
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Affiliation(s)
- Zhongyang Sun
- Department of Orthopedics, Jinling Hospital, Medical School of Nanjing University, Nanjing, China.,Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China.,The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Ying Li
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Hua Zhou
- Department of Emergency, First Affiliated Hospital, Xi'an Medical University, Xi'an, China
| | - Min Cai
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China.,Medical Services Section, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Jing Liu
- Department of Pharmacy, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Shanshan Gao
- Medical Services Section, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Junsheng Yang
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Liangcheng Tong
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Jianling Wang
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Sheng Zhou
- Department of Orthopedics, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Zebing Hu
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Yixuan Wang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Ke Wang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Lijun Zhang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Han Wang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Lianchang Zhang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Fei Shi
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Xinsheng Cao
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Shu Zhang
- The Key Laboratory of Aerospace Medicine, Chinese Ministry of Education, Fourth Military Medical University, Xi'an, China
| | - Yongzhang Ji
- Medical Services Section, No. 454 Hospital of PLA, Anhui Medical University, Nanjing, China
| | - Jianning Zhao
- Department of Orthopedics, Jinling Hospital, Medical School of Nanjing University, Nanjing, China
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Abstract
In the past decade, automated microscopy has become an important tool for the drug discovery and development process. The establishment of imaging modalities as screening tools depended on technological breakthroughs in the domain of automated microscopy and automated image analysis. These types of assays are often referred to as high content screening or high content analysis (HCS/HCA). The driving force to adopt imaging for drug development is the quantity and quality of cellular information that can be collected and the enhanced physiological relevance of cellular screening compared to biochemical screening. Most imaging in drug development is performed on fixed cells as this allows uncoupling the preparation of the cells from the acquisition of the images. Live-cell imaging is technically challenging, but is very useful for many aspects of the drug development pipeline such as kinetic studies of compound mode of action or to analyze the motion of cellular components. Most vendors of HCS microscopy systems offer the option of environmental chambers and onboard pipetting on their platforms. This reflects the wish and desire of many customers to have the ability to perform live-cell assays on their HCS automated microscopes. This book chapter summarizes the challenges and advantages of live-cell imaging in drug discovery. Examples of applications are presented and the motivation to perform these assays in kinetic mode is discussed.
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Affiliation(s)
- Milan Esner
- High Throughput Technology Development Studio (HT-TDS), Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307, Dresden, Germany
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Kamenice 3, 625 00, Brno, Czech Republic
| | - Felix Meyenhofer
- High Throughput Technology Development Studio (HT-TDS), Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307, Dresden, Germany
- Département de Médecine, Faculté des Sciences, University of Fribourg, 1, Rte., Albert Gockel, Fribourg, 1700, Switzerland
| | - Marc Bickle
- High Throughput Technology Development Studio (HT-TDS), Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307, Dresden, Germany.
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Firing frequency and entrainment maintained in primary auditory neurons in the presence of combined BDNF and NT3. Sci Rep 2016; 6:28584. [PMID: 27335179 PMCID: PMC4917828 DOI: 10.1038/srep28584] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 06/07/2016] [Indexed: 12/16/2022] Open
Abstract
Primary auditory neurons rely on neurotrophic factors for development and survival. We previously determined that exposure to brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) alters the activity of hyperpolarization-activated currents (Ih) in this neuronal population. Since potassium channels are sensitive to neurotrophins, and changes in Ih are often accompanied by a shift in voltage-gated potassium currents (IK), this study examined IK with exposure to both BDNF and NT3 and the impact on firing entrainment during high frequency pulse trains. Whole-cell patch-clamp recordings revealed significant changes in action potential latency and duration, but no change in firing adaptation or total outward IK. Dendrotoxin-I (DTX-I), targeting voltage-gated potassium channel subunits KV1.1 and KV1.2, uncovered an increase in the contribution of DTX-I sensitive currents with exposure to neurotrophins. No difference in Phrixotoxin-1 (PaTX-1) sensitive currents, mediated by KV4.2 and KV4.3 subunits, was observed. Further, no difference was seen in firing entrainment. These results show that combined BDNF and NT3 exposure influences the contribution of KV1.1 and KV1.2 to the low voltage-activated potassium current (IKL). Whilst this is accompanied by a shift in spike latency and duration, both firing frequency and entrainment to high frequency pulse trains are preserved.
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Abstract
Many studies of Ca2+ signaling use PC12 cells, yet the balance of Ca2+ clearance mechanisms in these cells is unknown. We used pharmacological inhibition of Ca2+ transporters to characterize Ca2+ clearance after depolarizations in both undifferentiated and nerve growth factor-differentiated PC12 cells. Sarco-endoplasmic reticulum Ca2+ ATPase (SERCA), plasma membrane Ca2+ ATPase (PMCA), and Na+/Ca2+ exchanger (NCX) account for almost all Ca2+ clearance in both cell states, with NCX and PMCA making the greatest contributions. Any contribution of mitochondrial uniporters is small. The ATP pool in differentiated cells was much more labile than that of undifferentiated cells in the presence of agents that dissipated mitochondrial proton gradients. Differentiated PC12 cells have a small component of Ca2+ clearance possessing pharmacological characteristics consistent with secretory pathway Ca2+ ATPase (SPCA), potentially residing on Golgi and/or secretory granules. Undifferentiated and differentiated cells are similar in overall Ca2+ transport and in the small transport due to SERCA, but they differ in the fraction of transport by PMCA and NCX. Transport in neurites of differentiated PC12 cells was qualitatively similar to that in the somata, except that the ER stores in neurites sometimes released Ca2+ instead of clearing it after depolarization. We formulated a mathematical model to simulate the observed Ca2+ clearance and to describe the differences between these undifferentiated and NGF-differentiated states quantitatively. The model required a value for the endogenous Ca2+ binding ratio of PC12 cell cytoplasm, which we measured to be 268 ± 85. Our results indicate that Ca2+ transport in undifferentiated PC12 cells is quite unlike transport in adrenal chromaffin cells, for which they often are considered models. Transport in both cell states more closely resembles that of sympathetic neurons, for which differentiated PC12 cells often are considered models. Comparison with other cell types shows that different cells emphasize different Ca2+ transport mechanisms.
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Affiliation(s)
- Joseph G Duman
- Department of Physiology and Biophysics University of Washington School of Medicine, Seattle, WA 98195, USA
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Ford CP, Wong KV, Lu VB, Posse de Chaves E, Smith PA. Differential neurotrophic regulation of sodium and calcium channels in an adult sympathetic neuron. J Neurophysiol 2008; 99:1319-32. [PMID: 18216230 DOI: 10.1152/jn.00966.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adult neuronal phenotype is maintained, at least in part, by the sensitivity of individual neurons to a specific selection of neurotrophic factors and the availability of such factors in the neurons' environment. Nerve growth factor (NGF) increases the functional expression of Na(+) channel currents (I(Na)) and both N- and L-type Ca(2+) currents (I(Ca,N) and I(Ca,L)) in adult bullfrog sympathetic ganglion (BFSG) B-neurons. The effects of NGF on I(Ca) involve the mitogen-activated protein kinase (MAPK) pathway. Prolonged exposure to the ganglionic neurotransmitter luteinizing hormone releasing hormone (LHRH) also increases I(Ca,N) but the transduction mechanism remains to be elucidated as does the transduction mechanism for NGF regulation of Na(+) channels. We therefore exposed cultured BFSG B-neurons to chicken II LHRH (0.45 microM; 6-9 days) or to NGF (200 ng/ml; 9-10 days) and used whole cell recording, immunoblot analysis, and ras or rap-1 pulldown assays to study effects of various inhibitors and activators of transduction pathways. We found that 1) LHRH signals via ras-MAPK to increase I(Ca,N), 2) this effect is mediated via protein kinase C-beta (PKC-beta-IotaIota), 3) protein kinase A (PKA) is necessary but not sufficient to effect transduction, 4) NGF signals via phosphatidylinositol 3-kinase (PI3K) to increase I(Na), and 5) long-term exposure to LHRH fails to affect I(Na). Thus downstream signaling from LHRH has access to the ras-MAPK pathway but not to the PI3K pathway. This allows for differential retrograde and anterograde neurotrophic regulation of sodium and calcium channels in an adult sympathetic neuron.
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Affiliation(s)
- Christopher P Ford
- Centre for Neuroscience and Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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Andrade A, de León MB, Hernández-Hernández O, Cisneros B, Felix R. Myotonic dystrophy CTG repeat expansion alters Ca2+channel functional expression in PC12 cells. FEBS Lett 2007; 581:4430-8. [PMID: 17719582 DOI: 10.1016/j.febslet.2007.08.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 08/07/2007] [Accepted: 08/08/2007] [Indexed: 12/22/2022]
Abstract
We previously reported that expression of myotonic dystrophy (DM1) expanded CUG repeats impedes NGF-induced differentiation in a PC12 clone (CTG90 cells). Here, we present evidence for changes in the fractional contribution of distinct voltage-gated Ca(2+) channels, key elements in neurotrophin-promoted differentiation, to the total Ca(2+) current in the CTG90 cells. Patch-clamp recordings showed that the relative proportion of pharmacologically isolated Ca(2+) channel types differed between control and CTG90 cells. Particularly, the functional expression of N-type channels was significantly reduced. Though quantitative real-time RT-PCR revealed that transcripts for the pore-forming subunit encoding the N-type channels remained unchanged, the protein level analyzed by semi-quantitative Western blotting was down-regulated in the CTG90 cells. These data suggest modifications in the processing of N-type Ca(2+) channels in PC12 cells expressing the DM1 mutation.
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Affiliation(s)
- Arturo Andrade
- Department of Physiology, Biophysics and Neuroscience, Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav-IPN), Mexico City, Mexico
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López-Domínguez AM, Espinosa JL, Navarrete A, Avila G, Cota G. Nerve growth factor affects Ca2+ currents via the p75 receptor to enhance prolactin mRNA levels in GH3 rat pituitary cells. J Physiol 2006; 574:349-65. [PMID: 16690703 PMCID: PMC1817754 DOI: 10.1113/jphysiol.2006.110791] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
In clonal pituitary GH(3) cells, spontaneous action potentials drive the opening of Ca(v)1 (L-type) channels, leading to Ca(2+) transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH(3) cells, but the underlying mechanisms are unknown. Here we studied whether NGF influences prolactin gene expression and Ca(2+) currents. By using RT-PCR, NGF (50 ng ml(-1)) was found to augment prolactin mRNA levels by approximately 80% when applied to GH(3) cells for 3 days. A parallel change in the prolactin content was detected by Western blotting. Both NGF-induced responses were mimicked by an agonist (Bay K 8644) and prevented by a blocker (nimodipine) of L-type channels. In whole-cell patch-clamp experiments, NGF enhanced the L-type Ca(2+) current by approximately 2-fold within 60 min. This effect reversed quickly upon growth factor withdrawal, but was maintained for days in the continued presence of NGF. In addition, chronic treatment (>or= 24 h) with NGF amplified the T-type current, which flows through Ca(v)3 channels and is thought to support pacemaking activity. Thus, NGF probably increases the amount of Ca(2+) that enters per action potential and may also induce a late increase in spike frequency. MC192, a specific antibody for the p75 neurotrophin receptor, but not tyrosine kinase inhibitors (K252a and lavendustin A), blocked the effects of NGF on Ca(2+) currents. Overall, the results indicate that NGF activates the p75 receptor to cause a prolonged increase in Ca(2+) influx through L-type channels, which in turn up-regulates the prolactin mRNA.
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Affiliation(s)
- Adriana M López-Domínguez
- Department of Physiology, Biophysics and Neurosciences, Cinvestav-IPN, AP 14-740, Mexico, DF 07000, Mexico
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