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Gong S, Ma J, Tian A, Lang S, Luo Z, Ma X. Effects and mechanisms of microenvironmental acidosis on osteoclast biology. Biosci Trends 2021; 16:58-72. [PMID: 34732613 DOI: 10.5582/bst.2021.01357] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Due to continuous bone remodeling, the bone tissue is dynamic and constantly being updated. Bone remodeling is precisely regulated by the balance between osteoblast-induced bone formation and osteoclast-induced bone resorption. As a giant multinucleated cell, formation and activities of osteoclasts are regulated by macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor-kappaB ligand (RANKL), and by pathological destabilization of the extracellular microenvironment. Microenvironmental acidosis, as the prime candidate, is a driving force of multiple biological activities of osteoclast precursor and osteoclasts. The mechanisms involved in these processes, especially acid-sensitive receptors/channels, are of great precision and complicated. Recently, remarkable progress has been achieved in the field of acid-sensitive mechanisms of osteoclasts. It is important to elucidate the relationship between microenvironmental acidosis and excessive osteoclasts activity, which will help in understanding the pathophysiology of diseases that are associated with excess bone resorption. This review summarizes physiological consequences and in particular, potential mechanisms of osteoclast precursor or osteoclasts in the context of acidosis microenvironments.
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Affiliation(s)
- Shuwei Gong
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China.,Graduate School, Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Jianxiong Ma
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China
| | - Aixian Tian
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China
| | - Shuang Lang
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China.,Graduate School, Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Zhiheng Luo
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China
| | - Xinlong Ma
- Tianjin Key Laboratory of Orthopedic Biomechanics and Medical Engineering, Orthopedic Research Institute, Tianjin Hospital, Tianjin, China.,Department of Orthopedics, Tianjin Hospital, Tianjin, China
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2
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Abstract
Skeletal involvement is a frequent and troublesome complication in advanced cancers. In the process of tumor cells homing to the skeleton to form bone metastases (BM), different mechanisms allow tumor cells to interact with cells of the bone microenvironment and seed in the bone tissue. Among these, tumor acidosis has been directly associated with tumor invasion and aggressiveness in several types of cancer although it has been less explored in the context of BM. In bone, the association of local acidosis and cancer invasiveness is even more important for tumor expansion since the extracellular matrix is formed by both organic and hard inorganic matrices and bone cells are used to sense protons and adapt or react to a low pH to maintain tissue homeostasis. In the BM microenvironment, increased concentration of protons may derive not only from glycolytic tumor cells but also from tumor-induced osteoclasts, the bone-resorbing cells, and may influence the progression or symptoms of BM in many different ways, by directly enhancing cancer cell motility and aggressiveness, or by modulating the functions of bone cells versus a pro-tumorigenic phenotype, or by inducing bone pain. In this review, we will describe and discuss the cause of acidosis in BM, its role in BM microenvironment, and which are the final effectors that may be targeted to treat metastatic patients.
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Affiliation(s)
- Sofia Avnet
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy.
| | - Gemma Di Pompo
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
| | - Silvia Lemma
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
| | - Nicola Baldini
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
- Department of Biomedical and Neuromotor Sciences, University of Bologna, 40123, Bologna, Italy
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3
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Kong L, Smith W, Hao D. Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli. J Cell Mol Med 2019; 23:3077-3087. [PMID: 30892789 PMCID: PMC6484317 DOI: 10.1111/jcmm.14277] [Citation(s) in RCA: 89] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 02/13/2019] [Accepted: 02/16/2019] [Indexed: 12/25/2022] Open
Abstract
Bone homeostasis is preserved by the balance of maintaining between the activity of osteogenesis and osteoclastogenesis. However, investigations for the osteoclastogenesis were hampered by considerable difficulties associated with isolating and culturing osteoclast in vivo. As the alternative, stimuli‐induced osteoclasts formation from RAW264.7 cells (RAW‐OCs) have gain its importance for extensively osteoclastogenic study of bone diseases, such as rheumatoid arthritis, osteoporosis, osteolysis and periodontitis. However, considering the RAW‐OCs have not yet been well‐characterized and RAW264.7 cells are polymorphic because of a diverse phenotype of the individual cells comprising this cell linage, and different fate associated with various stimuli contributions. Thus, in present study, we provide an overview for current knowledge of the phenotype of RAW264.7 cells, as well as the current understanding of the complicated interactions between various stimuli and RAW‐OCs in the light of the recent progress.
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Affiliation(s)
- Lingbo Kong
- Department of Spine, School of Medicine, Honghui-hospital, Xi'an Jiaotong University, Xi'an, China
| | - Wanli Smith
- Department of Neuroscience, Johns Hopkins University, Baltimore, Maryland
| | - Dingjun Hao
- Department of Spine, School of Medicine, Honghui-hospital, Xi'an Jiaotong University, Xi'an, China
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4
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Petkus DL, Murray-Kolb LE, De Souza MJ. The Unexplored Crossroads of the Female Athlete Triad and Iron Deficiency: A Narrative Review. Sports Med 2018; 47:1721-1737. [PMID: 28290159 DOI: 10.1007/s40279-017-0706-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Despite the severity and prevalence of iron deficiency in exercising women, few published reports have explored how iron deficiency interacts with another prevalent and severe condition in exercising women: the 'female athlete triad.' This review aims to describe how iron deficiency may interact with each component of the female athlete triad, that is, energy status, reproductive function, and bone health. The effects of iron deficiency on energy status are discussed in regards to thyroid function, metabolic fuel availability, eating behaviors, and energy expenditure. The interactions between iron deficiency and reproductive function are explored by discussing the potentially impaired fertility and hyperprolactinemia due to iron deficiency and the alterations in iron metabolism due to menstrual blood loss and estrogen exposure. The interaction of iron deficiency with bone health may occur via dysregulation of the growth hormone/insulin-like growth factor-1 axis, hypoxia, and hypothyroidism. Based on these discussions, several future directions for research are presented.
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Affiliation(s)
- Dylan L Petkus
- Department of Kinesiology, The Pennsylvania State University, 104 Noll Laboratory, University Park, PA, 16802, USA
| | - Laura E Murray-Kolb
- Department of Nutritional Sciences, The Pennsylvania State University, University Park, PA, USA
| | - Mary Jane De Souza
- Department of Kinesiology, The Pennsylvania State University, 104 Noll Laboratory, University Park, PA, 16802, USA.
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5
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Cooperative electrogenic proton transport pathways in the plasma membrane of the proton-secreting osteoclast. Pflugers Arch 2018; 470:851-866. [PMID: 29550927 DOI: 10.1007/s00424-018-2137-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Revised: 02/13/2018] [Accepted: 03/06/2018] [Indexed: 02/05/2023]
Abstract
A proton is a ubiquitous signaling ion. Many transmembrane H+ transport pathways either maintain pH homeostasis or generate acidic compartments. The osteoclast is a bone-resorbing cell, which degrades bone tissues by secreting protons and lysosomal enzymes into the resorption pit. The plasma membrane facing bone tissue (ruffled border), generated partly by fusion of lysosomes, may mimic H+ flux mechanisms regulating acidic vesicles. We identified three electrogenic H+-fluxes in osteoclast plasma membranes-a vacuolar H+-ATPase (V-ATPase), a voltage-gated proton channel (Hv channel) and an acid-inducible H+-leak-whose electrophysiological profiles and regulation mechanisms differed. V-ATPase and Hv channel, both may have intracellular reservoirs, but the recruitment/internalization is regulated independently. V-ATPase mediates active H+ efflux, acidifying the resorption pit, while acid-inducible H+ leak, activated at an extracellular pH < 5.5, diminishes pit acidification, possibly to protect bone from excess degradation. The two-way H+ flux mechanisms in opposite directions may have advantages in fine regulation of pit pH. Hv channel mediates passive H+ efflux. Although its working ranges are limited, the amount of H+ extrusion is 100 times larger than those of the V-ATPase and may support reactive oxygen species production during osteoclastogenesis. Extracellular Ca2+, H+ and inorganic phosphate, which accumulate in the resorption pit, will either stimulate or inhibit these H+ fluxes. Skeletal integration is disrupted by too much or too less of bone resorption. Diversities in plasma membrane H+ flux pathways, which may co-operate or compete, are essential to adjust osteoclast functions in variable conditions.
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6
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Alexander RT, Cordat E, Chambrey R, Dimke H, Eladari D. Acidosis and Urinary Calcium Excretion: Insights from Genetic Disorders. J Am Soc Nephrol 2016; 27:3511-3520. [PMID: 27468975 DOI: 10.1681/asn.2016030305] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabolic acidosis is associated with increased urinary calcium excretion and related sequelae, including nephrocalcinosis and nephrolithiasis. The increased urinary calcium excretion induced by metabolic acidosis predominantly results from increased mobilization of calcium out of bone and inhibition of calcium transport processes within the renal tubule. The mechanisms whereby acid alters the integrity and stability of bone have been examined extensively in the published literature. Here, after briefly reviewing this literature, we consider the effects of acid on calcium transport in the renal tubule and then discuss why not all gene defects that cause renal tubular acidosis are associated with hypercalciuria and nephrocalcinosis.
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Affiliation(s)
- R Todd Alexander
- Departments of Pediatrics and .,Physiology, University of Alberta, Edmonton, Canada
| | | | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark; and
| | - Dominique Eladari
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.,Department of Physiologie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
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7
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Yuan FL, Xu MH, Li X, Xinlong H, Fang W, Dong J. The Roles of Acidosis in Osteoclast Biology. Front Physiol 2016; 7:222. [PMID: 27445831 PMCID: PMC4919343 DOI: 10.3389/fphys.2016.00222] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 05/27/2016] [Indexed: 12/21/2022] Open
Abstract
The adverse effect of acidosis on the skeletal system has been recognized for almost a century. Although the underlying mechanism has not been fully elucidated, it appears that acidosis acts as a general stimulator of osteoclasts derived from bone marrow precursors cells and enhances osteoclastic resorption. Prior work suggests that acidosis plays a significant role in osteoclasts formation and activation via up-regulating various genes responsible for its adhesion, migration, survival and bone matrix degradation. Understanding the role of acidosis in osteoclast biology may lead to development of novel therapeutic approaches for the treatment of diseases related to low bone mass. In this review, we aim to discuss the recent investigations into the effects of acidosis in osteoclast biology and the acid-sensing molecular mechanism.
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Affiliation(s)
- Feng-Lai Yuan
- Department of Orthopaedics and Central Laboratory, The Third Hospital Affiliated to Nantong University Wuxi, China
| | - Ming-Hui Xu
- Department of Orthopaedics and Central Laboratory, The Third Hospital Affiliated to Nantong University Wuxi, China
| | - Xia Li
- Department of Orthopaedics and Central Laboratory, The Third Hospital Affiliated to Nantong University Wuxi, China
| | - He Xinlong
- Department of Orthopaedics and Central Laboratory, The Third Hospital Affiliated to Nantong University Wuxi, China
| | - Wei Fang
- Department of Neurosurgery, Wuxi Ninth People's Hospital Affiliated to Soochow University Liangxi Road Wuxi, China
| | - Jian Dong
- Department of Orthopedic Surgery, Zhongshan Hospital, Fudan University Shanghai, China
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8
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Morethson P. Extracellular fluid flow and chloride content modulate H(+) transport by osteoclasts. BMC Cell Biol 2015; 16:20. [PMID: 26271334 PMCID: PMC4536797 DOI: 10.1186/s12860-015-0066-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 07/28/2015] [Indexed: 11/18/2022] Open
Abstract
Background Bone resorption takes place within the basic multicellular units (BMU), and the surface to be resorbed is isolated from adjacent bone surfaces by a sealing zone between osteoclast membrane and bone matrix, which defines the limits of the resorption lacuna. Considering that the extracellular fluid (ECF) in both BMU and the resorption lacuna can be isolated from its surroundings, I hypothesize that flow and ion composition of the bone ECF in these sites might contribute to the regulation of osteoclast H+ secretion. To investigate this hypothesis, I evaluated the H+ secretion properties of individual osteoclasts and osteoclast-like cells (OCL-cells) and investigated whether changes in flow or chloride content of the extracellular solution modify the H+ secretion properties in vitro. Results The results show that 1) osteoclasts are unable to secrete H+ and regulate intracellular pH (pHi) under continuous flow conditions and exhibit progressive intracellular acidification; 2) the cessation of flow coincides with the onset of H+ secretion and subsequent progressive intracellular alkalinization of osteoclasts and OCL-cells; 3) osteoclasts exhibit spontaneous rhythmic oscillations of pHi in non-flowing ECF, 4) pHi oscillations are not abolished by concanamycin, NPPB, or removal of extracellular Na+ or Cl−; 5) extracellular Cl− removal modifies the pattern of oscillations, by diminishing H+ secretion; 6) pHi oscillations are abolished by continuous flowing of ECF over osteoclasts and OCL-cells. Conclusions The data suggest, for the first time, that ECF flow and Cl− content have direct effects on osteoclast H+ secretion and could be part of a mechanism determining the onset of osteoclast H+ secretion required for bone resorption. Electronic supplementary material The online version of this article (doi:10.1186/s12860-015-0066-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Priscilla Morethson
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil. .,Department of Biosciences, Federal University of São Paulo - Unifesp, R. Silva Jardim 136 Vila Mathias, Santos, 11065-201, SP, Brazil.
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9
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Involvement of the G-protein-coupled receptor 4 in RANKL expression by osteoblasts in an acidic environment. Biochem Biophys Res Commun 2015; 458:435-40. [DOI: 10.1016/j.bbrc.2015.01.142] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2015] [Accepted: 01/30/2015] [Indexed: 11/20/2022]
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10
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Laurent J, Venn A, Tambutté É, Ganot P, Allemand D, Tambutté S. Regulation of intracellular pH in cnidarians: response to acidosis in Anemonia viridis. FEBS J 2013; 281:683-95. [PMID: 24256552 DOI: 10.1111/febs.12614] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 11/07/2013] [Accepted: 11/11/2013] [Indexed: 11/28/2022]
Abstract
The regulation of intracellular pH (pHi) is a fundamental aspect of cell physiology that has received little attention in studies of the phylum Cnidaria, which includes ecologically important sea anemones and reef-building corals. Like all organisms, cnidarians must maintain pH homeostasis to counterbalance reductions in pHi, which can arise because of changes in either intrinsic or extrinsic parameters. Corals and sea anemones face natural daily changes in internal fluids, where the extracellular pH can range from 8.9 during the day to 7.4 at night. Furthermore, cnidarians are likely to experience future CO₂-driven declines in seawater pH, a process known as ocean acidification. Here, we carried out the first mechanistic investigation to determine how cnidarian pHi regulation responds to decreases in extracellular and intracellular pH. Using the anemone Anemonia viridis, we employed confocal live cell imaging and a pH-sensitive dye to track the dynamics of pHi after intracellular acidosis induced by acute exposure to decreases in seawater pH and NH₄Cl prepulses. The investigation was conducted on cells that contained intracellular symbiotic algae (Symbiodinium sp.) and on symbiont-free endoderm cells. Experiments using inhibitors and Na⁺-free seawater indicate a potential role of Na⁺/H⁺ plasma membrane exchangers (NHEs) in mediating pHi recovery following intracellular acidosis in both cell types. We also measured the buffering capacity of cells, and obtained values between 20.8 and 43.8 mM per pH unit, which are comparable to those in other invertebrates. Our findings provide the first steps towards a better understanding of acid-base regulation in these basal metazoans, for which information on cell physiology is extremely limited.
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11
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DeCoursey TE. Voltage-gated proton channels: molecular biology, physiology, and pathophysiology of the H(V) family. Physiol Rev 2013; 93:599-652. [PMID: 23589829 PMCID: PMC3677779 DOI: 10.1152/physrev.00011.2012] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Voltage-gated proton channels (H(V)) are unique, in part because the ion they conduct is unique. H(V) channels are perfectly selective for protons and have a very small unitary conductance, both arguably manifestations of the extremely low H(+) concentration in physiological solutions. They open with membrane depolarization, but their voltage dependence is strongly regulated by the pH gradient across the membrane (ΔpH), with the result that in most species they normally conduct only outward current. The H(V) channel protein is strikingly similar to the voltage-sensing domain (VSD, the first four membrane-spanning segments) of voltage-gated K(+) and Na(+) channels. In higher species, H(V) channels exist as dimers in which each protomer has its own conduction pathway, yet gating is cooperative. H(V) channels are phylogenetically diverse, distributed from humans to unicellular marine life, and perhaps even plants. Correspondingly, H(V) functions vary widely as well, from promoting calcification in coccolithophores and triggering bioluminescent flashes in dinoflagellates to facilitating killing bacteria, airway pH regulation, basophil histamine release, sperm maturation, and B lymphocyte responses in humans. Recent evidence that hH(V)1 may exacerbate breast cancer metastasis and cerebral damage from ischemic stroke highlights the rapidly expanding recognition of the clinical importance of hH(V)1.
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Affiliation(s)
- Thomas E DeCoursey
- Dept. of Molecular Biophysics and Physiology, Rush University Medical Center HOS-036, 1750 West Harrison, Chicago, IL 60612, USA.
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12
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Brisson L, Reshkin SJ, Goré J, Roger S. pH regulators in invadosomal functioning: proton delivery for matrix tasting. Eur J Cell Biol 2012; 91:847-60. [PMID: 22673002 DOI: 10.1016/j.ejcb.2012.04.004] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 04/18/2012] [Accepted: 04/19/2012] [Indexed: 12/20/2022] Open
Abstract
Invadosomes are actin-rich finger-like cellular structures sensing and interacting with the surrounding extracellular matrix (ECM) and involved in its proteolytic remodeling. Invadosomes are structures distinct from other adhesion complexes, and have been identified in normal cells that have to cross tissue barriers to fulfill their function such as leukocytes, osteoclasts and endothelial cells. They also represent features of highly aggressive cancer cells, allowing them to escape from the primary tumor, to invade surrounding tissues and to reach systemic circulation. They are localized to the ventral membrane of cells grown under 2-dimensional conditions and are supposed to be present all around cells grown in 3-dimensional matrices. Indeed invadosomes are key structures in physiological processes such as inflammation and the immune response, bone remodeling, tissue repair, but also in pathological conditions such as osteopetrosis and the development of metastases. Invadosomes are subdivided into podosomes, found in normal cells, and into invadopodia specific for cancer cells. While these two structures exhibit differences in organization, size, number and half-life, they share similarities in molecular composition, participation in cell-matrix adhesion and promoting matrix degradation. A key determinant in invadosomal function is the recruitment and release of proteases, such as matrix metalloproteinases (MMPs), serine proteases and cysteine cathepsins, together with their activation in a tightly controlled and highly acidic microenvironment. Therefore numerous pH regulators such as V-ATPases and Na(+)/H(+) exchangers, are found in invadosomes and are directly involved in their constitution as well as their functioning. This review focuses on the participation of pH regulators in invadosome function in physiological and pathological conditions, with a particular emphasis on ECM remodeling by osteoclasts during bone resorption and by cancer cells.
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Affiliation(s)
- Lucie Brisson
- Nutrition, Growth and Cancer, Université François-Rabelais de Tours, Inserm U, France
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13
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Extracellular acidosis accelerates bone resorption by enhancing osteoclast survival, adhesion, and migration. Biochem Biophys Res Commun 2012; 418:144-8. [PMID: 22244876 DOI: 10.1016/j.bbrc.2011.12.149] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Accepted: 12/30/2011] [Indexed: 01/30/2023]
Abstract
Acidic extracellular pH promotes osteoporotic bone loss by osteoclast activation. However, the change of osteoclastic cell behavior in acidosis-stimulated bone resorption process is unknown. We found that lowering extracellular pH induced an increase in the survival, adhesion, and migration of mature osteoclasts with a full actin ring, leading to enhanced pit formation on dentine slices. Acidosis upregulated osteopontin, which is an Arg-Gly-Asp (RGD) motif-containing matrix protein secreted from osteoclasts and acts as a common modulator for their survival, adhesion, and migration. A synthetic RGD peptide treatment blocked acidosis-induced osteoclast adhesion and migration, likely by competing with the RGD motif-containing extracellular matrix proteins for cell surface integrin binding. We finally observed that acidosis was associated with activation of osteoclast survival/adhesion/migration-related Pyk2, Cbl-b, and Src signals. Collectively, the findings indicate that extracellular acidosis stimulates bone resorption by extending osteoclast survival and facilitating osteoclast adhesion and migration.
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14
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Gramoun A, Azizi N, Sodek J, Heersche JN, Nakchbandi I, Manolson MF. Fibronectin inhibits osteoclastogenesis while enhancing osteoclast activity via nitric oxide and interleukin-1β-mediated signaling pathways. J Cell Biochem 2010; 111:1020-34. [DOI: 10.1002/jcb.22791] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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15
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Arnett TR. Acidosis, hypoxia and bone. Arch Biochem Biophys 2010; 503:103-9. [PMID: 20655868 DOI: 10.1016/j.abb.2010.07.021] [Citation(s) in RCA: 186] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2010] [Revised: 07/17/2010] [Accepted: 07/20/2010] [Indexed: 10/19/2022]
Abstract
Bone homeostasis is profoundly affected by local pH and oxygen tension. It has long been recognised that the skeleton contains a large reserve of alkaline mineral (hydroxyapatite), which is ultimately available to neutralise metabolic H(+) if acid-base balance is not maintained within narrow limits. Bone cells are extremely sensitive to the direct effects of pH: acidosis inhibits mineral deposition by osteoblasts but it activates osteoclasts to resorb bone and other mineralised tissues. These reciprocal responses act to maximise the availability of OH(-) ions from hydroxyapatite in solution, where they can buffer excess H(+). The mechanisms by which bone cells sense small pH changes are likely to be complex, involving ion channels and receptors in the cell membrane, as well as direct intracellular effects. The importance of oxygen tension in the skeleton has also long been known. Recent work shows that hypoxia blocks the growth and differentiation of osteoblasts (and thus bone formation), whilst strongly stimulating osteoclast formation (and thus bone resorption). Surprisingly, the resorptive function of osteoclasts is unimpaired in hypoxia. In vivo, tissue hypoxia is usually accompanied by acidosis due to reduced vascular perfusion and increased glycolytic metabolism. Thus, disruption of the blood supply can engender a multiple negative impact on bone via the direct actions of reduced pO(2) and pH on bone cells. These observations may contribute to our understanding of the bone disturbances that occur in numerous settings, including ageing, inflammation, fractures, tumours, anaemias, kidney disease, diabetes, respiratory disease and smoking.
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Affiliation(s)
- Timothy R Arnett
- Department of Cell & Developmental Biology, University College London, London WC1E 6BT, UK.
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16
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Gramoun A, Goto T, Nordström T, Rotstein OD, Grinstein S, Heersche JN, Manolson MF. Bone matrix proteins and extracellular acidification: Potential co-regulators of osteoclast morphology. J Cell Biochem 2010; 111:350-61. [DOI: 10.1002/jcb.22705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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17
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DeCoursey TE. Voltage-gated proton channels find their dream job managing the respiratory burst in phagocytes. Physiology (Bethesda) 2010; 25:27-40. [PMID: 20134026 PMCID: PMC3023998 DOI: 10.1152/physiol.00039.2009] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The voltage-gated proton channel bears surprising resemblance to the voltage-sensing domain (S1-S4) of other voltage-gated ion channels but is a dimer with two conduction pathways. The proton channel seems designed for efficient proton extrusion from cells. In phagocytes, it facilitates the production of reactive oxygen species by NADPH oxidase.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois, USA.
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18
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Shin L, Basi N, Jeremic A, Lee JS, Cho WJ, Chen Z, Abu-Hamdah R, Oupicky D, Jena BP. Involvement of vH(+)-ATPase in synaptic vesicle swelling. J Neurosci Res 2010; 88:95-101. [PMID: 19610106 DOI: 10.1002/jnr.22180] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Secretory vesicle swelling is central to cell secretion, but the underlying mechanism of vesicle swelling, particularly synaptic vesicles, is not completely understood. The G(alphai3)-PLA2-mediated involvement of water channel AQP-1 in the regulation of secretory vesicle swelling in exocrine pancreas and the G(alphao)-mediated AQP-6 involvement in synaptic vesicle swelling in neurons have previously been reported. Furthermore, the role of vH(+)-ATPase in neurotransmitter transport into synaptic vesicles has also been shown. Using nanometer-scale precision measurements of isolated synaptic vesicles, the present study reports for the first time the involvement of vH(+)-ATPase in GTP-G(alphao)-mediated synaptic vesicle swelling. Results from this study demonstrate that the GTP-G(alphao)-mediated vesicle swelling is vH(+)-ATPase dependent and pH sensitive. Zeta potential measurements of isolated synaptic vesicles further demonstrate a bafilomycin-sensitive vesicle acidification, following the GTP-G(alphao)-induced swelling stimulus. Water channels are bidirectional and the vH(+)-ATPase inhibitor bafilomycin decreases both the volume of isolated synaptic vesicles and GTP-mastoparan stimulated swelling, suggesting that vH(+)-ATPase is upstream of AQP-6, in the pathway leading from G(alphao)-stimulated swelling of synaptic vesicles. Vesicle acidification is therefore a prerequisite for AQP-6-mediated gating of water into synaptic vesicles.
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Affiliation(s)
- Leah Shin
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan, USA
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Mandel S, Tas AC. Brushite (CaHPO 4 ·2H 2 O) to octacalcium phosphate (Ca 8 (HPO 4 ) 2 (PO 4 ) 4 ·5H 2 O) transformation in DMEM solutions at 36.5 °C. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2010; 30:245-254. [PMID: 30011614 DOI: 10.1016/j.msec.2009.10.009] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Accepted: 10/26/2009] [Indexed: 10/20/2022]
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Abstract
This review is an attempt to identify and place in context some of the many questions about voltage-gated proton channels that remain unsolved. As the gene was identified only 2 years ago, the situation is very different than in fields where the gene has been known for decades. For the proton channel, most of the obvious and less obvious structure-function questions are still wide open. Remarkably, the proton channel protein strongly resembles the voltage-sensing domain of many voltage-gated ion channels, and thus offers a novel approach to study gating mechanisms. Another surprise is that the proton channel appears to function as a dimer, with two separate conduction pathways. A number of significant biological questions remain in dispute, unanswered, or in some cases, not yet asked. This latter deficit is ascribable to the intrinsic difficulty in evaluating the importance of one component in a complex system, and in addition, to the lack, until recently, of a means of performing an unambiguous lesion experiment, that is, of selectively eliminating the molecule in question. We still lack a potent, selective pharmacological inhibitor, but the identification of the gene has allowed the development of powerful new tools including proton channel antibodies, siRNA and knockout mice.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 W. Harrison, Chicago, IL 60612, USA.
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Calcium homeostasis, acid–base balance, and health status in periparturient Holstein cows fed diets with low cation–anion difference. Livest Sci 2008. [DOI: 10.1016/j.livsci.2007.11.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Abstract
The history of research on voltage-gated proton channels is recounted, from their proposed existence in dinoflagellates by Hastings in 1972 and their demonstration in snail neurons by Thomas and Meech in 1982 to the discovery in 2006 (after a decade of controversy) of genes that unequivocally code for proton channels. Voltage-gated proton channels are perfectly selective for protons, conduct deuterons half as well, and the conductance is strongly temperature dependent. These properties are consistent with a conduction mechanism involving hydrogen-bonded-chain transfer, in which the selectivity filter is a titratable amino acid residue. Channel opening is regulated stringently by pH such that only outward current is normally activated. Main functions of proton channels include acid extrusion from cells and charge compensation for the electrogenic activity of the phagocyte NADPH oxidase. Genetic approaches hold the promise of rapid progress in the near future.
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Affiliation(s)
- T E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 W. Harrison, Chicago, Illinois 60612, USA.
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Ehrlich H, Koutsoukos PG, Demadis KD, Pokrovsky OS. Principles of demineralization: modern strategies for the isolation of organic frameworks. Part II. Decalcification. Micron 2008; 40:169-93. [PMID: 18804381 DOI: 10.1016/j.micron.2008.06.004] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Accepted: 06/30/2008] [Indexed: 12/15/2022]
Abstract
This is the second paper on principles of demineralization. The initial paper is dedicated to the common definitions and the history of demineralization. In present work we review the principles and mechanisms of decalcification, i.e., removing the mineral Ca-containing compounds (phosphates and carbonates) from the organic matrix in its two main aspects: natural and artificial. Natural chemical erosion of biominerals (cavitation of biogenic calcareous substrata by bacteria, fungi, algae, foraminifera, sponges, polychaetes, and mollusks) is driven by production of mineral and organic acids, acidic polysaccharides, and enzymes (cabonic anhydrase, alkaline and phosphoprotein phosphataes, and H(+)-ATPase). Examples of artifical decalcification includes demineralization of bone, dentin and enamel, and skeletal formations of corals and crustacean. The mechanism and kinetics of Ca-containing biomineral dissolution is analyzed within the framework of (i) diffusion-reaction theory; (ii) surface-reaction controlled, morphology-based theories, and (iii) phenomenological surface coordination models. The application of surface complexation model for describing and predicting the effect of organic ligands on calcium and magnesium dissolution kinetics is also described. Use of the electron microscopy-based methods for observation and visualization of the decalcification phenomenon is discussed.
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Affiliation(s)
- Hermann Ehrlich
- Max Bergmann Center of Biomaterials, Institute of Materials Science, Dresden University of Technology, Budapester Str. 27, D-01069 Dresden, Germany.
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Abstract
The skeletons of land vertebrates contain a massive reserve of alkaline mineral (hydroxyapatite), which is ultimately available to buffer metabolic H+ if acid-base balance is not maintained within narrow limits. The negative impact of acidosis on the skeleton has long been known but was thought to result from passive, physicochemical dissolution of bone mineral. This brief, selective review summarizes what is now known of the direct functional responses of bone cells to extracellular pH. We discovered that bone resorption by cultured osteoclasts is stimulated directly by acid. The stimulatory effect is near-maximal at pH 7.0, whereas above pH 7.4, resorption is switched off. In bone organ cultures, H+-stimulated bone mineral release is almost entirely osteoclast-mediated, with a negligible physicochemical component. Acidification is the key requirement for osteoclasts to excavate resorption pits in all species studied to date, and extracellular H+ may thus be regarded as the long-sought osteoclast activation factor. Acid-activated osteoclasts can be stimulated further by agents such as parathyroid hormone, 1,25-dihydroxycholecalciferol, and receptor activator of nuclear factor kappaB ligand. Osteoclasts may respond to pH changes via H+-sensing ion channels such as transient receptor potential vanilloid 1, a nociceptor that is also activated by capsaicin. Acidosis also exerts a powerful, reciprocal inhibitory effect on the mineralization of bone matrix by cultured osteoblasts. This is caused by increased hydroxyapatite solubility at low pH, together with selective inhibition of alkaline phosphatase, which is required for mineralization. Diets or drugs that shift acid-base balance in the alkaline direction may provide useful treatments for bone loss disorders.
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Affiliation(s)
- Timothy R Arnett
- Department of Anatomy and Developmental Biology, University College London, London WC1E 6BT, UK.
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Margolis DS, Szivek JA, Lai LW, Lien YHH. Phenotypic characteristics of bone in carbonic anhydrase II-deficient mice. Calcif Tissue Int 2008; 82:66-76. [PMID: 18175028 DOI: 10.1007/s00223-007-9098-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Accepted: 12/04/2007] [Indexed: 02/04/2023]
Abstract
Carbonic anhydrase II (CAII)-deficient mice were created to study the syndrome of CAII deficiency in humans including osteopetrosis, renal tubular acidosis, and cerebral calcification. Although CAII mice have renal tubular acidosis, studies that analyzed only cortical bones found no changes characteristic of osteopetrosis. Consistent with previous studies, the tibiae of CAII-deficient mice were significantly smaller than those of wild-type (WT) mice (28.7 +/- 0.9 vs. 43.6 +/- 3.7 mg; p < 0.005), and the normalized cortical bone volume of CAII-deficient mice (79.3 +/- 2.2%) was within 5% of that of WT mice (82.7 +/- 2.3%; p < 0.05), however, metaphyseal widening of the tibial plateau was noted in CAII-deficient mice, consistent with osteopetrosis. In contrast to cortical bone, trabecular bone volume demonstrated a nearly 50% increase in CAII-deficient mice (22.9 +/- 3.5% in CAII, compared to 15.3 +/- 1.6% in WT; p < 0.001). In addition, histomorphometry demonstrated that bone formation rate was decreased by 68% in cortical bone (4.77 +/- 1.65 microm3/microm2/day in WT vs. 2.07 +/- 1.71 microm3/microm2/day in CAII mice; p < 0.05) and 55% in trabecular bone (0.617 +/- 0.230 microm3/microm2/day in WT vs. 0.272 +/- 0.114 microm3/microm2/day in CAII mice; p < 0.05) in CAII-deficient mice. The number of osteoclasts was significantly increased (67%) in CAII-deficient mice, while osteoblast number was not different from that in WT mice. The metaphyseal widening and changes in the trabecular bone are consistent with osteopetrosis, making the CAII-deficient mouse a valuable model of human disease.
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Affiliation(s)
- David S Margolis
- Orthopaedic Research Lab, Department of Orthopaedic Surgery, University of Arizona, Tucson, AZ 85721, USA.
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Muzylak M, Arnett TR, Price JS, Horton MA. The in vitro effect of pH on osteoclasts and bone resorption in the cat: implications for the pathogenesis of FORL. J Cell Physiol 2007; 213:144-50. [PMID: 17477347 PMCID: PMC7167146 DOI: 10.1002/jcp.21103] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Dental disease due to osteoclast over‐activity reaches epidemic proportions in older domestic cats and has also been reported in wild cats. Feline osteoclastic resorptive lesions (FORL) involve extensive resorption of the tooth leaving it liable to root fracture and subsequent tooth loss. The aetio‐pathogenesis of FORL is not known. Recent work has shown that systemic acidosis causes increased osteoclast activation and that loci of infection or inflammation in cat mouth are likely to be acidotic. To investigate this, we generated osteoclasts from cat blood and found that they formed in large numbers (∼400) in cultures on bovine cortical bone slices. Acidosis caused an increase in the size of cells—in cultures maintained up to 14 days at basal pH 7.25, mean osteoclast area was 0.01 ± 0.003 mm2, whereas an 8.6‐fold increase was observed in cells cultured between 11 and 14 days at pH 7.15 (0.086 ± 0.004 mm2). Acidosis caused a modest increase in the number of osteoclasts. Exposure to pH 6.92 exhibited a 5‐fold increase in the area of bone slices covered by resorption lacunae (∼70% bone slice resorbed). In line with this finding, significant increases were observed in the expression of cathepsin K and proton pump enzymes (both approximately 3‐fold) that are key enzymes reflective of resorptive activity in osteoclasts. These results demonstrate that acidosis is a major regulator of osteoclast formation and functional activation in the cat, and suggest that local pH changes may play a significant role in the pathogenesis of FORL. J. Cell. Physiol. 213: 144–150, 2007. © 2007 Wiley‐Liss, Inc.
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Affiliation(s)
- Mariusz Muzylak
- Department of Veterinary Basic Sciences, The Royal Veterinary College, London, UK
| | | | - Joanna S. Price
- Department of Veterinary Basic Sciences, The Royal Veterinary College, London, UK
| | - Michael A. Horton
- Department of Medicine, Rayne Building, University College London, London, UK
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Ambühl PM. Posttransplant metabolic acidosis: a neglected factor in renal transplantation? Curr Opin Nephrol Hypertens 2007; 16:379-87. [PMID: 17565282 DOI: 10.1097/mnh.0b013e3281bd8860] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE OF REVIEW The occurrence and pathogenesis of metabolic acidosis after renal transplantation is reviewed. Posttransplant acidosis is shown to be a key mechanism for major metabolic complications in mineral and muscle metabolism, and for anemia, discussed in the context of both acidosis and renal transplantation. RECENT FINDINGS Continuous improvement in kidney transplant survival has shifted attention to long-term outcomes, specifically to disorders linked to cardiovascular disease, physical capacity and quality of life. Metabolic acidosis is gaining growing acceptance as a clinical entity and has occasionally come into focus in the context of renal transplantation. The possible link to metabolic disturbances resulting in impairment of musculoskeletal disorders and physical limitations, however, has not been considered specifically. SUMMARY Available evidence suggests a high prevalence of (compensated) metabolic acidosis after renal transplantation, presenting as low serum bicarbonate and impaired renal acid excretion. This condition is associated with relevant disorders in mineral metabolism and muscle function. Current knowledge about the effects of acidosis on renal electrolyte handling, mineral metabolism and protein synthesis suggests that acid/base derangements contribute to the muscle and bone pathology, as well as anemia, encountered after kidney transplantation. Consequently, posttransplant acidosis may be a relevant factor in the causal pathway of impaired physical capacity observed in this patient group.
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Affiliation(s)
- Patrice M Ambühl
- Department of Nephrology, University Hospital, Zurich, Switzerland.
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Wang D, Miller SC, Liu XM, Anderson B, Wang XS, Goldring SR. Novel dexamethasone-HPMA copolymer conjugate and its potential application in treatment of rheumatoid arthritis. Arthritis Res Ther 2007; 9:R2. [PMID: 17233911 PMCID: PMC1860059 DOI: 10.1186/ar2106] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Revised: 12/04/2006] [Accepted: 01/18/2007] [Indexed: 11/10/2022] Open
Abstract
Rheumatoid arthritis (RA) is a chronic autoimmune disease of unknown etiology. Effective treatment of this disorder has been hampered by the lack of availability of agents that selectively target affected joint tissue. We developed a novel pH-sensitive drug delivery system of dexamethasone (Dex) based on an N-(2-hydroxypropyl)methacrylamide copolymer (P-Dex) and have shown that the delivery system specifically accumulates in inflamed joints in an animal model of arthritis. We hypothesize that the arthrotropism of the delivery system and the local acidosis-mediated drug release provide superior therapeutic efficacy and potentially reduced side effects in RA treatment. The initial in vitro drug-release study confirmed that the Dex release is indeed dependent upon the environmental pH. At pH 5, 37°C, the conjugate shows the highest level of drug release. When administered systemically in an adjuvant-induced arthritis rat model, P-Dex offers superior and longer-lasting anti-inflammatory effects compared with systemically administered free Dex. In addition, greater bone and cartilage preservation was observed with the P-Dex treatment compared with free Dex treatment. Our data indicate that the differential effect of the conjugate is related to its selective accumulation, potential macrophage-mediated retention, and pH-sensitive drug release (extracellular and intracellular) in arthritic joints. This newly developed drug delivery system provides a unique method for selective targeting of glucocorticoids to inflamed joints which may potentially reduce systemic side effects.
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Affiliation(s)
- Dong Wang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, 986025 Nebraska Medical Center, COP 3026, Omaha, NE 68198-6025, USA
- Department of Pharmaceutics and Pharmaceutical Chemistry, University of Utah, 30 South 2000 East, Salt Lake City, UT 84112, USA
| | - Scott C Miller
- Department of Radiology/Radiobiology Division, University of Utah, 729 Arapeen Dr., Salt Lake City, UT 84108, USA
| | - Xin-Ming Liu
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, 986025 Nebraska Medical Center, COP 3026, Omaha, NE 68198-6025, USA
| | - Brian Anderson
- Department of Radiology/Radiobiology Division, University of Utah, 729 Arapeen Dr., Salt Lake City, UT 84108, USA
| | - Xu Sherry Wang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, 986025 Nebraska Medical Center, COP 3026, Omaha, NE 68198-6025, USA
- Washington University in St. Louis, 6515 Wydown Blvd., Campus Box 3519, St. Louis, MO 63105, USA
| | - Steven R Goldring
- Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA
- New England Baptist Bone and Joint Institute, Harvard Institutes of Medicine, 4 Blackfan Circle, Boston, MA 02115, USA
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Ntrivalas E, Gilman-Sachs A, Kwak-Kim J, Beaman K. The N-terminus domain of the a2 isoform of vacuolar ATPase can regulate interleukin-1beta production from mononuclear cells in co-culture with JEG-3 choriocarcinoma cells. Am J Reprod Immunol 2007; 57:201-9. [PMID: 17295899 DOI: 10.1111/j.1600-0897.2006.00463.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
PROBLEM a2V-ATPase is the a2 isoform of vacuolar ATPase and is expressed in human trophoblast cells. a2V-ATPase resides as a 70-kDa molecule in intracellular vesicles. Upon cell stimulation, it migrates to the surface as a 50-kDa molecule, after a 20-kDa portion [N-terminus domain of the a2V-ATPase (a2NTD)] is cleaved and secreted to the extracellular environment. Previous studies showed that a2NTD-regulated cytokine production from stimulated T cells. The aim of this study was to determine if a2NTD can regulate cytokine production from immune cells that were in contact with JEG-3 cells. METHOD OF STUDY Peripheral blood mononuclear cells (PBMC) from females were co-cultured with JEG-3 cells in the presence or absence of a2NTD, and supernatants were analyzed by enzyme-linked immunosorbent assay for interleukin (IL)-1beta. Additionally, PBMC cultured with JEG-3 cells, in the presence or absence of a2NTD, were analyzed for cytokine gene expression by gene arrays. RESULTS There was an increased secretion of IL-1beta and a decrease in type I and II IL-1 receptors (IL1RA and IL-1R2) gene expression in PBMC that were co-cultured with JEG-3 cells in the presence of a2NTD. CONCLUSION These data suggest a role for a2NTD in the regulation of IL-1beta pro-inflammatory cytokine production at the fetal-maternal interface.
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Affiliation(s)
- Evangelos Ntrivalas
- Clinical Immunology Laboratory, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, N. Chicago, IL 60064, USA
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Ntrivalas E, Derks R, Gilman-Sachs A, Kwak-Kim J, Levine R, Beaman K. Novel role for the N-terminus domain of the a2 isoform of vacuolar ATPase in interleukin-1beta production. Hum Immunol 2007; 68:469-77. [PMID: 17509446 DOI: 10.1016/j.humimm.2007.02.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Revised: 02/16/2007] [Accepted: 02/26/2007] [Indexed: 10/23/2022]
Abstract
Interleukin-1beta (IL-1beta) is a mediator cytokine that is released by macrophages and epithelial cells in pregnancy and tumorigenesis before antigen recognition. a2V-ATPase is a protein expressed during pregnancy and tumorigenesis and has a novel role in immune regulation. It is expressed as a 70 kDa molecule in intracellular vesicles. Upon cell stimulation it migrates to the surface followed by the cleavage of a 20 kDa portion (a2 N-terminus domain, a2NTD). This study aimed to determine whether a2NTD could induce IL-1beta production in immune cells. Peripheral blood mononuclear cells (PMBC) were stimulated with a2NTD and analyzed for cytokine gene expression by gene arrays. Supernatants were analyzed for IL-1beta by enzyme-linked immunosorbent assay, and cells were analyzed for intracellular expression of IL-1alpha, IL-1beta, and TNF-alpha by flow cytometry. When PBMC were cultured with a2NTD, there was a 2.5-fold increase in IL1A and IL1B gene expression and no induction of TNF gene expression. There was a 72-fold increase in IL-1beta in supernatants of PBMC cultured with a2NTD. Finally, there was a 204-fold increase in intracellular expression of IL-1beta in monocytes incubated with a2NTD. These results indicate a regulatory role for a2NTD in IL-1 cytokine production and suggest a unique role for this molecule in inflammation.
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Affiliation(s)
- Evangelos Ntrivalas
- Clinical Immunology Laboratory, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
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Abstract
Bone growth and turnover results from the coordinated activities of two key cell types. Bone matrix is deposited and mineralised by osteoblasts and it is resorbed by osteoclasts, multinucleate cells that excavate pits on bone surfaces. It has been known since the early 20th century that systemic acidosis causes depletion of the skeleton, an effect assumed to result from physico-chemical dissolution of bone mineral. However, our own work has shown that resorption pit formation by cultured osteoclasts was absolutely dependent on extracellular acidification; these cells are inactive at pH levels above about 7·3 and show maximum stimulation at a pH of about 6·9. Bone resorption is most sensitive to changes in H+concentration at a pH of about 7·1 (which may be close to the interstitial pH in bone). In this region pH shifts of <0·05 units can cause a doubling or halving of pit formation. In whole-bone cultures, chronic HCO3-acidosis results in similar stimulations of osteoclast-mediated Ca2+release, with a negligible physico-chemical component.In vivo, severe systemic acidosis (pH change of about –0·05 to –0·20) often results from renal disease; milder chronic acidosis (pH change of about –0·02 to –0·05) can be caused by excessive protein intake, acid feeding, prolonged exercise, ageing, airway diseases or the menopause. Acidosis can also occur locally as a result of inflammation, infection, wounds, tumours or diabetic ischaemia. Cell function, including that of osteoblasts, is normally impaired by acid; the unusual stimulatory effect of acid on osteoclasts may represent a primitive ‘fail-safe’ that evolved with terrestrial vertebrates to correct systemic acidosis by ensuring release of alkaline bone mineral when the lungs and kidneys are unable to remove sufficient H+equivalent. The present results suggest that even subtle chronic acidosis could be sufficient to cause appreciable bone loss over time.
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Affiliation(s)
- Tim Arnett
- Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
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Trebec DP, Chandra D, Gramoun A, Li K, Heersche JNM, Manolson MF. Increased expression of activating factors in large osteoclasts could explain their excessive activity in osteolytic diseases. J Cell Biochem 2007; 101:205-20. [PMID: 17216600 DOI: 10.1002/jcb.21171] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Large osteoclasts (>or=10 nuclei) predominate at sites of pathological bone resorption. We hypothesized this was related to increased resorptive activity of large osteoclasts and have demonstrated previously that larger osteoclasts are 8-fold more likely to be resorbing than small osteoclasts (2-5 nuclei). Here we ask whether these differences in resorptive activity can be explained by differences in expression of factors involved in osteoclast signaling, fusion, attachment, and matrix degradation. Authentic rabbit osteoclasts and osteoclasts derived from RAW264.7 cells showed similar increases in c-fms expression (1.7- to 1.8-fold) in large osteoclasts suggesting that RAW cells are a viable system for further analysis. We found 2- to 4.5-fold increases in the expression of the integrins alpha(v) and beta(3), the proteases proMMP9, matMMP9 and pro-cathepsinK, and in activating receptors RANK, IL-1R1, and TNFR1 in large osteoclasts. In contrast, small osteoclasts had higher expression of the fusion protein SIRPalpha1 and the decoy receptor IL-1R2. The higher expression of activation receptors and lower expression of IL-1R2 in large osteoclasts suggest they are hyperresponsive to extracellular factors. This is supported by the observation that the resorptive activity in large osteoclasts was more responsive to IL-1beta, and that this increased activity was inhibited by the IL-1 receptor antagonist, IL-1ra. This increased responsiveness of large osteoclasts to IL-1 may, in part, explain the pathological bone loss noted in inflammatory diseases. The heterogeneity in receptor expression and the differential response to cytokines and their antagonists could prove useful for selective inhibition of large osteoclasts actively engaged in pathological bone loss.
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Affiliation(s)
- Diana P Trebec
- Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
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Abstract
Cathepsins play important roles in the development of joint and bone diseases such as osteoporosis, rheumatoid arthritis (RA) and osteoarthritis (OA). Cathepsin inhibitors are presently in development and clinical testing for use as novel disease-modifying drugs for the improved treatment of osteoporosis. They may also be applicable for the treatment of joint diseases. However, some barriers still hamper their clinical applications in these indications. Based on pathophysiological features of RA and OA, the authors discuss six potential drug delivery strategies for the effective delivery of cathepsin inhibitors or other antiarthritic drugs to the arthritic joint tissue. Successful application of these strategies may significantly contribute to a more effective and safe treatment of RA and OA.
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Affiliation(s)
- Dong Wang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA.
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Kajiya H, Okamoto F, Li JP, Nakao A, Okabe K. Expression of mouse osteoclast K-Cl Co-transporter-1 and its role during bone resorption. J Bone Miner Res 2006; 21:984-92. [PMID: 16813519 DOI: 10.1359/jbmr.060407] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
UNLABELLED To assess the role of Cl- transport during osteoclastic bone resorption, we studied the expression and function of K+/Cl- co-transporters (KCCs). KCC1 and chloride channel-7 were found to be expressed in mouse osteoclasts. The KCC inhibitor, R(+)-butylindazone (DIOA), KCC1 antisense oligo-nucleotides, and siRNA suppressed osteoclastic pit formation. DIOA also decreased Cl- extrusion and reduced H+ extrusion activity. These results show that KCC1 provides a Cl- extrusion mechanism accompanying the H+ extrusion during bone resorption. INTRODUCTION Mice with deficient chloride (Cl-) channels, ClC7, show severe osteopetrosis, resulting from impairment of Cl- extrusion during osteoclastic bone resorption. However, the expression and functional role of Cl- transporters other than ClC7 in mammalian osteoclasts is unknown. The aim of this study was to determine expression of K+/Cl- co-transporters (KCCs) and their functional role for bone resorption in mouse osteoclasts. MATERIALS AND METHODS Mouse osteoclasts were derived from cultured bone marrow cells with macrophage-colony stimulating factor (M-CSF) and RANKL or from co-culture of bone marrow cells and primary osteoblasts. We examined the expression of Cl- transporters using RT-PCR, immunochemical, and Western blot methods. The effects of Cl- transport inhibitors on H+ and Cl- extrusion were assessed by measuring intracellular H+ ([H+]i) and Cl- ([Cl-]i). The effects of inhibitors, antisense oligo-nucleotides, and siRNA for Cl- transporters on bone resorption activities were evaluated using a pit formation assay. RESULTS AND CONCLUSIONS Mouse osteoclasts express not only ClC7 but also K+/Cl- co-transporter mRNA. The existence of KCC1 in the cell membrane of mouse osteoclasts was confirmed by immunochemical staining and Western blot analysis. KCC inhibitors and Cl- channels blockers increased [Cl-]i and [H+]i in resorbing osteoclasts, suggesting that the suppression of Cl- extrusion through KCC and Cl- channels leads to reduced H+ extrusion activity. The combination of both inhibitors greatly suppressed these extrusion activities. KCC inhibitors and Cl- channel blockers also decreased osteoclastic bone resorption in our pit area essay. Furthermore, KCC1 antisense oligo-nucleotides and siRNA suppressed osteoclastic pit formation as well as treatment of ClC7 inhibitors. These results indicate that K+/Cl- co-transporter-1 expressed in mouse osteoclasts acts as a Cl- extruder and plays an important role for H+ extrusion during bone resorption.
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Affiliation(s)
- Hiroshi Kajiya
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Tamura, Japan.
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Komarova SV, Pereverzev A, Shum JW, Sims SM, Dixon SJ. Convergent signaling by acidosis and receptor activator of NF-kappaB ligand (RANKL) on the calcium/calcineurin/NFAT pathway in osteoclasts. Proc Natl Acad Sci U S A 2005; 102:2643-8. [PMID: 15695591 PMCID: PMC548977 DOI: 10.1073/pnas.0406874102] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Systemic acidosis has detrimental effects on the skeleton, and local acidosis coincides with bone destruction in inflammatory and metastatic diseases. Acidification dramatically enhances osteoclastic resorption, although the underlying mechanism has remained elusive. We investigated the effect of acidosis on the osteoclastogenic transcription factor NFATc1, which upon dephosphorylation translocates from the cytoplasm to nuclei. Lowering extracellular pH dramatically increased accumulation of NFATc1 in nuclei of rat and rabbit osteoclasts to levels comparable with those induced by the proresorptive cytokine receptor activator of NF-kappaB ligand (RANKL). Activation of NFATc1 by RANKL was mediated by means of prolonged stimulation of the Ca2+/calmodulin-dependent protein phosphatase, calcineurin. In contrast, NFATc1 activation by acidosis involved stimulation of calcineurin and suppression of NFATc1 inactivation. Acidosis, like RANKL, induced transient elevation of cytosolic free Ca2+ concentration ([Ca2+]i), which persisted in Ca2+-free media and was abolished by inhibition of phospholipase C or depletion of intracellular Ca2+ stores. Real-time-PCR of osteoclast-like cells generated from RAW 264.7 cells revealed high levels of expression of ovarian cancer G protein-coupled receptor 1, which links extracellular acidification to elevation of [Ca2+]i. In addition, the calcineurin inhibitor cyclosporin A suppressed the stimulatory effect of acidification on resorption, implicating NFAT in mediating the actions of acidosis on osteoclast activity. In summary, acidification and RANKL induce signals in osteoclasts that converge on the Ca2+/calcineurin/NFAT pathway. Acidosis acts directly on osteoclasts to activate NFATc1 and stimulate resorption.
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Affiliation(s)
- Svetlana V Komarova
- Canadian Institutes of Health Research Group in Skeletal Development and Remodeling, Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 5C1
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Schilling AF, Linhart W, Filke S, Gebauer M, Schinke T, Rueger JM, Amling M. Resorbability of bone substitute biomaterials by human osteoclasts. Biomaterials 2004; 25:3963-72. [PMID: 15046886 DOI: 10.1016/j.biomaterials.2003.10.079] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2003] [Accepted: 10/22/2003] [Indexed: 11/30/2022]
Abstract
Third generation biomaterials are being designed with the aim that once implanted they will help the body to heal itself. One desirable characteristic of these materials in bone is their ability to be remodeled, i.e. that osteoclasts resorb the material and it is subsequently replaced by newly formed bone through osteoblastic activity. So far the only way to test this biological property of bone substitutes are animal experiments with all their limitations like ethics, costs and limited transferability to man. The present study was designed, to develop a human in vitro assay, allowing to generate human osteoclasts directly on the biomaterial. The assay was validated using calcium phosphate cement and PMMA as biomaterials. Quantification was performed by raster electron microscopy and computer assisted image analysis. Dentin was used as internal standard. Our assay shows iso-bone resorbability of calcium phosphate cement in comparison to unresorbable PMMA cement. Both current clinical orthopedic practice and future skeletal engineering may profit from the availability and use of a test system for the assessment of resorption quality. The assay presented here allows to address this question of resorbability and to select the best materials for the use as bone substitutes in specific patients.
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Affiliation(s)
- Arndt F Schilling
- Department of Trauma, Hand, and Reconstructive Surgery, Center for Biomechanics, Hamburg University School of Medicine, Martinistrasse 52, Hamburg 20246, Germany.
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Horiuchi-Suzuki K, Konno A, Ueda M, Fukuda Y, Nishio S, Hashimoto K, Saji H. Skeletal affinity of Tc(V)-DMS is bone cell mediated and pH dependent. Eur J Nucl Med Mol Imaging 2003; 31:388-98. [PMID: 14647982 DOI: 10.1007/s00259-003-1364-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2003] [Accepted: 09/16/2003] [Indexed: 10/26/2022]
Abstract
In spite of recent advances in bone cellular and molecular biology, there is still a poor correlation between these parameters and data obtained from bone scintigraphy. Diphosphonate derivatives radiolabelled with technetium-99m (Tc-BPs) have long been recognised as bone-seeking agents with an affinity for areas of active mineralisation. However, during clinical trials with a pH-sensitive tumour agent, the pentavalent technetium complex of dimercaptosuccinic acid [Tc(V)-DMS] showed a noticeable osteotropic character only in bone pathologies (bone metastases, Paget's diseases) and lacked accumulation in normal mature bone. To decipher the osteotropic character of Tc(V)-DMS, a study at the cellular level was considered necessary. Moreover, to learn more about the role of Tc bone agents, acid-base regulation by bone tissue or cells was studied. First, biological parameters in body fluid were measured under systemic acidosis, induced by glucose administration, in normal and Ehrlich ascites tumour (EAT)-bearing mice. Then, in vivo biodistribution studies using Tc(V)-DMS or a conventional Tc-BP agent were carried out. The effect of glucose-mediated acidification on the skeletal distribution of the Tc agents in the mice provided valuable hints regarding the differential mediation of bone cells in skeletal tissue affinity for the agents. Thereafter, in vitro studies on osteoblast and osteoclast cells were performed and the comparative affinity of Tc(V)-DMS and Tc-BP was screened under diverse acidification conditions. Moreover, studies were also carried out on acid-base parameters related to the cellular uptake mechanism. Very specific pH-sensitive Tc(V)-DMS accumulation only in the osteoclastic system was detected, and use of Tc(V)-DMS in the differential detection of osteoblastic and osteoclastic metastases is discussed.
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Affiliation(s)
- Kazuko Horiuchi-Suzuki
- Development Bureau, Hamamatsu Photonics K.K., Hirakuchi 500, 434-8601, Hamakita City, Japan.
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Abstract
Proton channels exist in a wide variety of membrane proteins where they transport protons rapidly and efficiently. Usually the proton pathway is formed mainly by water molecules present in the protein, but its function is regulated by titratable groups on critical amino acid residues in the pathway. All proton channels conduct protons by a hydrogen-bonded chain mechanism in which the proton hops from one water or titratable group to the next. Voltage-gated proton channels represent a specific subset of proton channels that have voltage- and time-dependent gating like other ion channels. However, they differ from most ion channels in their extraordinarily high selectivity, tiny conductance, strong temperature and deuterium isotope effects on conductance and gating kinetics, and insensitivity to block by steric occlusion. Gating of H(+) channels is regulated tightly by pH and voltage, ensuring that they open only when the electrochemical gradient is outward. Thus they function to extrude acid from cells. H(+) channels are expressed in many cells. During the respiratory burst in phagocytes, H(+) current compensates for electron extrusion by NADPH oxidase. Most evidence indicates that the H(+) channel is not part of the NADPH oxidase complex, but rather is a distinct and as yet unidentified molecule.
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Affiliation(s)
- Thomas E Decoursey
- Department of Molecular Biophysics and Physiology, Rush Presbyterian St. Luke's Medical Center, Chicago, Illinois 60612, USA.
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Kajiya H, Okamoto F, Fukushima H, Okabe K. Calcitonin inhibits proton extrusion in resorbing rat osteoclasts via protein kinase A. Pflugers Arch 2003; 445:651-8. [PMID: 12632184 DOI: 10.1007/s00424-002-0989-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2002] [Revised: 10/09/2002] [Accepted: 11/05/2002] [Indexed: 10/22/2022]
Abstract
Although calcitonin is well known to be a potent inhibitor of bone resorption, it remains unknown how it regulates osteoclastic H(+) transport. In this study, we examined the effects of calcitonin on H(+) extrusion in cultured rat resorbing osteoclasts using an intracellular pH (pHi) indicator, BCECF [2'7'-bis-(2-carboxyethyl)- 5-carboxyfluorescein]. Resorbing osteoclasts were identified by their formation of resorbing pits on calcium phosphate-coated quartz coverslips. Both basal pHi and H(+) extrusion activity were significantly higher compared to non-resorbing osteoclasts. Two types of H(+)-extruding systems were identified by pharmacological and immunocytochemical means: a bafilomycin-A(1)-sensitive and an amiloride-sensitive system [H(+) extrusion mediated by a vacuolar type proton pump (V-ATPase) and by a Na(+)/H(+) exchanger (NHE), respectively]. Calcitonin inhibited both H(+) extrusion activities in a dose-dependent manner and this action was mimicked by protein kinase A (PKA) activators, but not by protein kinase C (PKC) activators. Pretreatment with PKA inhibitors completely suppressed calcitonin-induced inhibition, whereas neither PKC inhibitors nor calcium chelators suppressed it. These results indicate that calcitonin inhibits H(+) extrusion generated by V-ATPase and NHE via PKA activation. These inhibitory mechanisms of H(+) transport by calcitonin are important for the regulation of bone resorption.
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Affiliation(s)
- Hiroshi Kajiya
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Tamura 2-15-1, 814-0193, Sawara-ku, Fukuoka, Japan.
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Maurer M, Riesen W, Muser J, Hulter HN, Krapf R. Neutralization of Western diet inhibits bone resorption independently of K intake and reduces cortisol secretion in humans. Am J Physiol Renal Physiol 2003; 284:F32-40. [PMID: 12388390 DOI: 10.1152/ajprenal.00212.2002] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A Western-type diet is associated with osteoporosis and calcium nephrolithiasis. On the basis of observations that calcium retention and inhibition of bone resorption result from alkali administration, it is assumed that the acid load inherent in this diet is responsible for increased bone resorption and calcium loss from bone. However, it is not known whether the dietary acid load acts directly or indirectly (i.e., via endocrine changes) on bone metabolism. It is also unclear whether alkali administration affects bone resorption/calcium balance directly or whether alkali-induced calcium retention is dependent on the cation (i.e., potassium) supplied with administered base. The effects of neutralization of dietary acid load (equimolar amounts of NaHCO(3) and KHCO(3) substituted for NaCl and KCl) in nine healthy subjects (6 men, 3 women) under metabolic balance conditions on calcium balance, bone markers, and endocrine systems relevant to bone [glucocorticoid secretion, IGF-1, parathyroid hormone (PTH)/1,25(OH)(2) vitamin D and thyroid hormones] were studied. Neutralization for 7 days induced a significant cumulative calcium retention (10.7 +/- 0.4 mmol) and significantly reduced the urinary excretion of deoxypyridinoline, pyridinoline, and n-telopeptide. Mean daily plasma cortisol decreased from 264 +/- 45 to 232 +/- 43 nmol/l (P = 0.032), and urinary excretion of tetrahydrocortisol (THF) decreased from 2,410 +/- 210 to 2,098 +/- 190 microg/24 h (P = 0.027). No significant effect was found on free IGF-1, PTH/1,25(OH)(2) vitamin D, or thyroid hormones. An acidogenic Western diet results in mild metabolic acidosis in association with a state of cortisol excess, altered divalent ion metabolism, and increased bone resorptive indices. Acidosis-induced increases in cortisol secretion and plasma concentration may play a role in mild acidosis-induced alterations in bone metabolism and possibly in osteoporosis associated with an acidogenic Western diet.
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Affiliation(s)
- Marc Maurer
- Medizinische Universitätsklinik und Zentrallabor, Kantonsspital Bruderholz, CH-4101 Bruderholz/Basel, Switzerland
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Sakuta K, Sakai H, Mori H, Morihata H, Kuno M. Na+ dependence of extracellular Ca2+-sensing mechanisms leading to activation of an outwardly rectifying Cl- channel in murine osteoclasts. Bone 2002; 31:374-80. [PMID: 12231409 DOI: 10.1016/s8756-3282(02)00838-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
An elevation in the extracellular Ca(2+) concentration ([Ca(2+)](o)) is a key signal for bone remodeling by inhibiting the resorbing activity of osteoclasts. The [Ca(2+)](o)-sensing responses include a variety of morphological and functional changes, but the underlying mechanisms are yet to be defined. This study was aimed at investigating the [Ca(2+)](o)-sensing mechanisms leading to the activation of the Cl(-) channel in murine osteoclasts. A rise in either Ca(2+) or Gd(3+) activated an outwardly rectifying Cl(-) (OR(cl)) channel reversibly and dose-dependently, which was characterized by rapid activation kinetics, little inactivation, and blockage by DIDS. The concentration required for a half-maximal response was estimated to be >20-30 mmol/L for Ca(2+). Intracellular dialysis with an ATP-free pipette solution or application of an actin destabilizer, cytochalasin D, decreased the [Ca(2+)](o)-activated OR(cl) current. Substitution of extracellular Na(+) by an impermeable cation, N-methyl-D-glucamine(+), inhibited the [Ca(2+)](o)-activated OR(cl) channel, suggesting that the activation depended on extracellular Na(+). A blocker for the Na(+)-Ca(2+) exchanger, 2'4'-dichlorobenzamil hydrochloride (DCB), inhibited the [Ca(2+)](o)-activated OR(cl) channel as well. Although 10 mmol/L Ca(2+) activated the OR(cl) current only slightly at a standard intracellular pH (7.3), decreasing pH by dialyzing cells with an acidic pipette solution (pH 6.6) enhanced the [Ca(2+)](o)-activated OR(cl) current. This potentiation by cell acidosis was eliminated by amiloride, a blocker for the Na(+)-H(+) exchanger. Zinc ion (0.1 mmol/L) and a polycation, neomycin (0.2 mmol/L), activated the OR(cl) current at intracellular pH 6.6, whereas the effects of those cations were negligible at intracellular pH 7.3. These results suggest that [Ca(2+)](o)-sensing mechanisms, leading to activation of the OR(cl) channel in murine osteoclasts, are regulated by ATP and actin cytoskeletal organization, and are sensitized greatly by cell acidosis. Contributions of Na(+)-dependent transporters in this activating process are examined in the context of a possible intermediate signal of cell swelling caused by Na(+) influx.
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Affiliation(s)
- K Sakuta
- Department of Physiology, Osaka City University Graduate School of Medicine, Osaka, Japan
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Lees RL, Sabharwal VK, Heersche JN. Resorptive state and cell size influence intracellular pH regulation in rabbit osteoclasts cultured on collagen-hydroxyapatite films. Bone 2001; 28:187-94. [PMID: 11182377 DOI: 10.1016/s8756-3282(00)00433-6] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Diseases exhibiting excessive bone loss are often characterized by an increase in the size and number of osteoclasts in affected areas, suggesting that osteoclast size is associated with increased resorptive activity or efficiency. Because osteoclastic bone resorption depends on proton extrusion via a bafilomycin A1-sensitive vacuolar type H+ ATPase (V-ATPase), we investigated the relationship between osteoclast size and state of activity on the one hand, and proton-extruding mechanisms (bafilomycin A1-sensitive V-ATPase and amiloride-sensitive Na+/H+ exchange) on the other. In determining resorptive activities of individual osteoclasts, osteoclast-containing cell suspensions obtained from newborn rabbit long bones were cultured on apatite-collagen complex (ACC)-coated coverslips. Large osteoclasts resorbed 2.5 times more per cell than small osteoclasts, but the amount resorbed per nucleus was the same for the two categories. However, a much larger percentage of large osteoclasts was resorbing compared with small osteoclasts. To study pH regulatory mechanisms in individual large and small osteoclasts, the cells were loaded with the pH-sensitive indicator BCECF and analyzed by single-cell fluorescence. Small and large resorbing osteoclasts had significantly higher basal pH(i) than their nonresorbing counterparts. Also, small nonresorbing osteoclasts were insensitive to bafilomycin A1 addition or Na+ removal from the medium, large nonresorbing osteoclasts responded slightly, and all resorbing osteoclasts (small and large) responded strongly. Differences were also seen in the recovery from an acid load: both small and large nonresorbing osteoclasts were more sensitive to amiloride inhibition, while large resorbing cells were more sensitive to bafilomycin A1 inhibition. Small resorbing cells were inhibited equally by bafilomycin A1 and amiloride. These results clearly show that a greater proportion of large osteoclasts are active in resorption and that pH(i) regulation is associated with enhanced proton pump activity in actively resorbing osteoclasts. Thus, large and small osteoclasts differ in the proportion of cells that are resorbing, while pH regulatory mechanisms differ mainly between resorbing and nonresorbing cells.
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Affiliation(s)
- R L Lees
- Department of Pharmacology, Faculty of Medicine, Toronto, Ontario, Canada
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Lees RL, Heersche JN. Differences in regulation of pH(i) in large (>/=10 nuclei) and small (</=5 nuclei) osteoclasts. Am J Physiol Cell Physiol 2000; 279:C751-61. [PMID: 10942726 DOI: 10.1152/ajpcell.2000.279.3.c751] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Osteoclasts are multinucleated cells that resorb bone by extrusion of protons and proteolytic enzymes. They display marked heterogeneity in cell size, shape, and resorptive activity. Because high resorptive activity in vivo is associated with an increase in the average size of osteoclasts in areas of greater resorption and because of the importance of proton extrusion in resorption, we investigated whether the activity of the bafilomycin A(1)-sensitive vacuolar-type H(+)-ATPase (V-ATPase) and amiloride-sensitive Na(+)/H(+) exchanger differed between large and small osteoclasts. Osteoclasts were obtained from newborn rabbit bones, cultured on glass coverslips, and loaded with the pH-sensitive indicator 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Intracellular pH (pH(i)) was recorded in single osteoclasts by monitoring fluorescence. Large (>/=10 nuclei) and small (</=5 nuclei) osteoclasts differed in that large osteoclasts had a higher basal pH(i), their pH(i) was decreased by bafilomycin A(1) addition or removal of extracellular Na(+), and the realkalinization upon readdition of Na(+) was bafilomycin A(1) sensitive. After acid loading, a subpopulation of large osteoclasts (40%) recovered by V-ATPase activity alone, whereas all small osteoclasts recovered by Na(+)/H(+) exchanger activity. Interestingly, in 60% of the large osteoclasts, pH(i) recovery was mediated by both the Na(+)/H(+) exchanger and V-ATPase activity. Our results show a striking difference between pH(i) regulatory mechanisms of large and small osteoclasts that we hypothesize may be associated with differences in the potential resorptive activity of these cells.
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Affiliation(s)
- R L Lees
- Department of Pharmacology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada M5G 1G6
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46
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Abstract
Osteoclasts are the primary cell type responsible for bone resorption. This paper reviews many of the known regulators of osteoclast activity, including hormones, cytokines, ions, and arachidonic acid metabolites. Most of the hormones and cytokines that inhibit osteoclast activity act directly on the osteoclasts. In contrast, most of the hormones and cytokines that stimulate osteoclast activity act indirectly through osteoblasts. Particularly interesting in this regard are agents that directly inhibit activity of highly purified osteoclasts yet stimulate activity of osteoclasts that are co-cultured with osteoblasts. Recent studies have demonstrated that the primary mechanism by which bone resorptive agents stimulate osteoclast activity indirectly is likely to be up-regulation of production of osteoclast differentiation factor/osteoprotegerin ligand (ODF/OPGL) by the osteoblasts. In addition to discussing regulators of osteoclast activity per se, this paper also reviews the role of osteoclast apoptosis to limit the extent of bone resorption.
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Affiliation(s)
- E M Greenfield
- Department of Orthopaedics, Case Western Reserve University, Cleveland, OH 44106-5000, USA.
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Altan N, Chen Y, Schindler M, Simon SM. Tamoxifen inhibits acidification in cells independent of the estrogen receptor. Proc Natl Acad Sci U S A 1999; 96:4432-7. [PMID: 10200279 PMCID: PMC16349 DOI: 10.1073/pnas.96.8.4432] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Tamoxifen has been reported to have numerous physiological effects that are independent of the estrogen receptor, including sensitization of resistant tumor cells to many chemotherapeutic agents. Drug-resistant cells sequester weak base chemotherapeutics in acidic organelles away from their sites of action in the cytosol and nucleus. This work reports that tamoxifen causes redistribution of weak base chemotherapeutics from acidic organelles to the nucleus in drug-resistant cells. Agents that disrupt organelle acidification (e.g., monensin, bafilomycin A1) cause a similar redistribution. Measurement of cellular pH in several cell lines reveals that tamoxifen inhibits acidification of endosomes and lysosomes without affecting cytoplasmic pH. Similar to monensin, tamoxifen decreased the rate of vesicular transport though the recycling and secretory pathways. Organellar acidification is required for many cellular functions, and its disruption could account for many of the side effects of tamoxifen.
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Affiliation(s)
- N Altan
- Laboratory of Cellular Biophysics, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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Laitala-Leinonen T, Väänänen HK. Decreased bone resorption, osteoclast differentiation, and expression of vacuolar H+-ATPase in antisense DNA-treated mouse metacarpal and calvaria cultures ex vivo. ANTISENSE & NUCLEIC ACID DRUG DEVELOPMENT 1999; 9:155-69. [PMID: 10355822 DOI: 10.1089/oli.1.1999.9.155] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Expression and function of vacuolar H(+)-ATPase, a key enzyme in bone resorption, were monitored in antisense DNA-treated bone organ cultures ex vivo. A novel fluoroimmunoassay was used to quantitate mRNA levels after treatment with various antisense, sense, or random DNA oligonucleotides. Conventional slot blots and in vitro translation experiments were used to monitor the efficiency of the antisense molecules. In cell cultures, the used antisense molecules were transported into osteoclasts and a population of mononuclear cells. A significant decrease in bone resorption and in the expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase was seen after antisense treatment. Also, osteoclast differentiation was decreased in antisense-treated mouse metacarpal cultures. These data show that the proper function of V-ATPase in osteoclasts requires expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase. Antisense DNA molecules can be used to inhibit osteoclast differentiation and function in tissue cultures, in which the physical and chemical cellular environment resembles that in vivo. However, more studies are needed to learn if antisense DNA molecules can be used for inhibiting bone resorption also in vivo.
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Affiliation(s)
- T Laitala-Leinonen
- Department of Anatomy, Institute of Biomedicine, University of Turku, Finland
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Sakai H, Nakamura F, Kuno M. Synergetic activation of outwardly rectifying Cl- currents by hypotonic stress and external Ca2+ in murine osteoclasts. J Physiol 1999; 515 ( Pt 1):157-68. [PMID: 9925886 PMCID: PMC2269141 DOI: 10.1111/j.1469-7793.1999.157ad.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. An outwardly rectifying Cl- (ORCl) current of murine osteoclasts was activated by hypotonic stimulation. The current was characterized by rapid activation, little inactivation, strong outward rectification, blockage by DIDS and permeability to organic acids (pyruvate and glutamate). 2. The hypotonically activated ORCl current was inhibited by intracellular dialysis with an ATP-free pipette solution, but not by replacement of ATP with a poorly hydrolysable ATP analogue adenosine 5'-O-(3-thiotriphosphate). The current amplitude was reduced when intracellular alkalinity increased over the pH range 6.6-8.0. 3. Intracellular application of cytochalasin D occasionally activated the ORCl current without hypotonic stress, but inhibited activation of the ORCl current by hypotonic stimulation. The hypotonically activated ORCl current was unaffected by a non-actin-depolymerizing cytochalasin, chaetoglobosin C, but partially inhibited by deoxyribonuclease I. 4. Removal of extracellular Ca2+ inhibited activation of the ORCl current by hypotonic shock, but did not reduce the current once activated. The hypotonically activated ORCl current was partially decreased by intracellular dialysis with 20 mM EGTA. 5. With 10 mM Ca2+ in the extracellular medium, the ORCl current was activated in response to more minor decreases in osmolarity than with 1 mM Ca2+. The increased sensitivity to hypotonicity was mimicked by increasing the intracellular Ca2+ level (pCa 6.5). 6. These results suggest that hypotonic stimulation and a rise in the extracellular Ca2+ level synergistically activate the ORCl channel of murine osteoclasts, and that the activating process is modified by multiple intracellular factors (pH, ATP and actin cytoskeletal organization).
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Affiliation(s)
- H Sakai
- Department of Physiology, Osaka City University Medical School, Abeno-ku, Osaka 545-8585, Japan
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50
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Roussa E, Thévenod F, Sabolic I, Herak-Kramberger CM, Nastainczyk W, Bock R, Schulz I. Immunolocalization of vacuolar-type H+-ATPase in rat submandibular gland and adaptive changes induced by acid-base disturbances. J Histochem Cytochem 1998; 46:91-100. [PMID: 9405498 DOI: 10.1177/002215549804600112] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Using antibodies against the 31-kD and 70-kD subunits of vacuolar type H+-ATPase (V-ATPase) and light microscopic immunocytochemistry, we have demonstrated the presence of this V-ATPase in rat submandibular gland. We have also investigated the adaptive changes of this transporter during acid-base disturbances such as acute and chronic metabolic acidosis or alkalosis. Our results show intracellularly distributed V-ATPase in striated, granular, and main excretory duct cells in controls, but no V-ATPase immunoreaction in acinar cells. Both acute and chronic metabolic acidosis caused a shift in V-ATPase away from diffuse distribution towards apical localization in striated and granular duct cells, suggesting that a V-ATPase could be involved in the regulation of acid-base homeostasis. In contrast, during acidosis the main excretory duct cells showed no changes in the V-ATPase distribution compared to controls. With acute and chronic metabolic alkalosis, no changes in the V-ATPase distribution occurred. (J Histochem Cytochem 46:91-100, 1998)
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Affiliation(s)
- E Roussa
- Anatomisches Institut, Medizinische Fakultät, Universität des Saarlandes, Homburg/Saar, Germany
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