Stephen M. Sims
University of Western Ontario
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Featured researches published by Stephen M. Sims.
Nature | 2006
D. Holstead Jones; Tomoki Nakashima; Otto Sanchez; Ivona Kozieradzki; Svetlana V. Komarova; Ildiko Sarosi; Sean Morony; Evelyn Rubin; Carlo V. Hojilla; Vukoslav Komnenovic; Young-Yun Kong; Martin Schreiber; S. Jeffrey Dixon; Stephen M. Sims; Rama Khokha; Teiji Wada; Josef M. Penninger
Bone metastases are a frequent complication of many cancers that result in severe disease burden and pain. Since the late nineteenth century, it has been thought that the microenvironment of the local host tissue actively participates in the propensity of certain cancers to metastasize to specific organs, and that bone provides an especially fertile ‘soil’. In the case of breast cancers, the local chemokine milieu is now emerging as an explanation for why these tumours preferentially metastasize to certain organs. However, as the inhibition of chemokine receptors in vivo only partially blocks metastatic behaviour, other factors must exist that regulate the preferential metastasis of breast cancer cells. Here we show that the cytokine RANKL (receptor activator of NF-κB ligand) triggers migration of human epithelial cancer cells and melanoma cells that express the receptor RANK. RANK is expressed on cancer cell lines and breast cancer cells in patients. In a mouse model of melanoma metastasis, in vivo neutralization of RANKL by osteoprotegerin results in complete protection from paralysis and a marked reduction in tumour burden in bones but not in other organs. Our data show that local differentiation factors such as RANKL have an important role in cell migration and the tissue-specific metastatic behaviour of cancer cells.
The Journal of Physiology | 1992
L J Janssen; Stephen M. Sims
1. Membrane currents activated by acetylcholine (ACh) were investigated in isolated canine and guinea‐pig tracheal myocytes using the nystatin perforated patch configuration of whole‐cell recording. ACh caused depolarization accompanied by a membrane conductance increase. 2. When cells were held under voltage clamp (holding potential, Vh = ‐60 mV), ACh elicited inward current (IACh) of up to 3900 pA, with a reversal potential (Erev) of approximately ‐20 mV. 3. Removal of extracellular Na+ (Na+o) reduced but did not eliminate IACh. IACh remaining in the absence of Na+ reversed direction close to the predicted equilibrium potential for Cl‐. Erev shifted 32 +/‐ 4 mV per 10‐fold change of [Cl‐]i. Increasing external [K+] caused Erev to shift in the positive direction. These results suggest that ACh activated chloride and non‐selective cation conductances. 4. In the absence of Na+o, the Cl‐ channel blockers SITS or niflumic acid reversibly antagonized IACh. 5. Caffeine and ryanodine elicited currents both in the presence and absence of Na+o; these currents had a reversal potential similar to that of IACh. Caffeine applied before ACh occluded the response to ACh. 6. We also observed two types of spontaneous membrane currents. Spontaneous transient outward currents (STOCs) may represent Ca(2+)‐activated K+ currents. Spontaneous inward currents were also observed which were reduced in magnitude (but not eliminated) by removal of Na+o and reversed direction at approximately the Cl‐ equilibrium potential. The spontaneous inward currents and STOCs were coincident and were reversibly suppressed by ACh. 7. ACh elicited contractions of cells under voltage clamp at ‐60 mV, an effect also observed in the absence of extracellular Ca2+ or when IACh was reduced by omission of Na+o and exposure to Cl‐ channel blockers. The number of cells which did contract in response to ACh decreased, however, when the concentration of internal Cl‐ decreased. 8. All effects of ACh on contraction and membrane currents were antagonized by atropine. 9. We conclude that activation of muscarinic receptors in mammalian tracheal myocytes causes release of Ca2+ from intracellular stores and subsequent activation of Cl‐ and non‐selective cation conductances. This is the first direct demonstration of these conductances in tracheal smooth muscle cells. Activation of these conductances does not appear to be required for contraction. However, regulation of cytosolic Cl‐ levels may be important for release and uptake of Ca2+ from internal stores.
The Journal of Physiology | 1998
Ronghua ZhuGe; Stephen M. Sims; Richard A. Tuft; Kevin E. Fogarty; John V. Walsh
1 Local changes in cytosolic [Ca2+] were imaged with a wide‐field, high‐speed, digital imaging system while membrane currents were simultaneously recorded using whole‐cell, perforated patch recording in freshly dissociated guinea‐pig tracheal myocytes. 2 Depending on membrane potential, Ca2+ sparks triggered ‘spontaneous’ transient inward currents (STICs), ‘spontaneous’ transient outward currents (STOCs) and biphasic currents in which the outward phase always preceded the inward (STOICs). The outward currents resulted from the opening of large‐conductance Ca2+‐activated K+ (BK) channels and the inward currents from Ca2+‐activated Cl− (ClCa) channels. 3 A single Ca2+ spark elicited both phases of a STOIC, and sparks originating from the same site triggered STOCs, STICs and STOICs, depending on membrane potential. 4 STOCs had a shorter time to peak (TTP) than Ca2+ sparks and a much shorter half‐time of decay. In contrast, STICs had a somewhat longer TTP than sparks but the same half‐time of decay. Thus, the STIC, not the STOC, more closely reflected the time course of cytosolic Ca2+ elevation during a Ca2+ spark. 5 These findings suggest that ClCa channels and BK channels may be organized spatially in quite different ways in relation to points of Ca2+ release from intracellular Ca2+ stores. The results also suggest that Ca2+ sparks may have functions in smooth muscle not previously suggested, such as a stabilizing effect on membrane potential and hence on the contractile state of the cell, or as activators of voltage‐gated Ca2+ channels due to depolarization mediated by STICs.
Bone | 2003
Svetlana V. Komarova; Robert Smith; S. Jeffrey Dixon; Stephen M. Sims; Lindi M. Wahl
Bone remodeling occurs asynchronously at multiple sites in the adult skeleton and involves resorption by osteoclasts, followed by formation of new bone by osteoblasts. Disruptions in bone remodeling contribute to the pathogenesis of disorders such as osteoporosis, osteoarthritis, and Pagets disease. Interactions among cells of osteoblast and osteoclast lineages are critical in the regulation of bone remodeling. We constructed a mathematical model of autocrine and paracrine interactions among osteoblasts and osteoclasts that allowed us to calculate cell population dynamics and changes in bone mass at a discrete site of bone remodeling. The model predicted different modes of dynamic behavior: a single remodeling cycle in response to an external stimulus, a series of internally regulated cycles of bone remodeling, or unstable behavior similar to pathological bone remodeling in Pagets disease. Parametric analysis demonstrated that the mode of dynamic behavior in the system depends strongly on the regulation of osteoclasts by autocrine factors, such as transforming growth factor beta. Moreover, simulations demonstrated that nonlinear dynamics of the system may explain the differing effects of immunosuppressants on bone remodeling in vitro and in vivo. In conclusion, the mathematical model revealed that interactions among osteoblasts and osteoclasts result in complex, nonlinear system behavior, which cannot be deduced from studies of each cell type alone. The model will be useful in future studies assessing the impact of cytokines, growth factors, and potential therapies on the overall process of remodeling in normal bone and in pathological conditions such as osteoporosis and Pagets disease.
Journal of Cell Biology | 2008
Nattapon Panupinthu; Joseph T. Rogers; Lin Zhao; Luis Pastor Solano-Flores; Fred Possmayer; Stephen M. Sims; S. Jeffrey Dixon
Nucleotides are released from cells in response to mechanical stimuli and signal in an autocrine/paracrine manner through cell surface P2 receptors. P2rx7-/- mice exhibit diminished appositional growth of long bones and impaired responses to mechanical loading. We find that calvarial sutures are wider in P2rx7-/- mice. Functional P2X7 receptors are expressed on osteoblasts in situ and in vitro. Activation of P2X7 receptors by exogenous nucleotides stimulates expression of osteoblast markers and enhances mineralization in cultures of rat calvarial cells. Moreover, osteogenesis is suppressed in calvarial cell cultures from P2rx7-/- mice compared with the wild type. P2X7 receptors couple to production of the potent lipid mediators lysophosphatidic acid (LPA) and prostaglandin E2. Either an LPA receptor antagonist or cyclooxygenase (COX) inhibitors abolish the stimulatory effects of P2X7 receptor activation on osteogenesis. We conclude that P2X7 receptors enhance osteoblast function through a cell-autonomous mechanism. Furthermore, a novel signaling axis links P2X7 receptors to production of LPA and COX metabolites, which in turn stimulate osteogenesis.
Circulation Research | 1999
Shaohua Li; Stephen M. Sims; Yang Jiao; Lawrence H. Chow; J. Geoffrey Pickering
Smooth muscle cells (SMCs) perform diverse functions that can be categorized as contractile and synthetic. A traditional model holds that these distinct functions are performed by the same cell, by virtue of its capacity for bidirectional modulation of phenotype. However, this model has been challenged, in part because there is no physiological evidence that an adult synthetic SMC can acquire the ability to contract. We sought evidence for this by cloning adult SMCs from human internal thoracic artery. One clone, HITB5, expressed smooth muscle alpha-actin, smooth myosin heavy chains, heavy caldesmon, and calponin and showed robust calcium transients in response to histamine and angiotensin II, which confirmed intact transmembrane signaling cascades. On serum withdrawal, these cells adopted an elongated and spindle-shaped morphology, random migration slowed, extracellular matrix protein production fell, and cell proliferation and [(3)H]thymidine incorporation fell to near 0. Cell viability was not compromised, however; in fact, apoptosis rate fell significantly. In this state, agonist-induced elevation of cytoplasmic calcium was even more pronounced and was accompanied by SMC contraction. Readdition of 10% serum completely returned HITB5 cells to a noncontractile, proliferative phenotype. Contractile protein expression increased after serum withdrawal, although modestly, which suggested that the switch to contractile function involved reorganization or sensitization of existing contractile structures. To our knowledge, the physiological properties of HITB5 SMCs provide the first direct demonstration that cultured human adult SMCs can convert between a synthetic, noncontracting state and a contracting state. HITB5 cells should be valuable for characterizing the basis of this critical transition.
Journal of Bone and Mineral Research | 2004
Jasminka Korcok; Lin Raimundo; Hua Z. Ke; Stephen M. Sims; S. Jeffrey Dixon
Nucleotides, released in response to mechanical and other stimuli, act on P2 receptors in osteoclasts and other cell types. In vitro studies of osteoclasts from rabbits and P2X7 receptor‐deficient mice revealed that P2X7 receptors couple to activation of the key transcription factor NF‐κB.
Journal of Biological Chemistry | 2007
Nattapon Panupinthu; Lin Zhao; Fred Possmayer; Hua Z. Ke; Stephen M. Sims; S. Jeffrey Dixon
Extracellular nucleotides, released in response to mechanical or inflammatory stimuli, signal through P2 receptors in many cell types, including osteoblasts. P2X7 receptors are ATP-gated cation channels that can induce formation of large membrane pores. Disruption of the gene encoding the P2X7 receptor leads to decreased periosteal bone formation and insensitivity of the skeleton to mechanical stimulation. Our purpose was to investigate signaling pathways coupled to P2X7 activation in osteoblasts. Live cell imaging showed that ATP or 2 ′,3 ′-O-(4-benzoylbenzoyl)-ATP (BzATP), but not UTP, UDP, or 2-methylthio-ADP, induced dynamic membrane blebbing in calvarial osteoblasts. Blebbing was observed in calvarial cells from wildtype but not P2X7 knock-out mice. P2X7 receptors coupled to activation of phospholipase D and A2, inhibition of which suppressed BzATP-induced blebbing. Activation of these phospholipases leads to production of lysophosphatidic acid (LPA). LPA caused dynamic blebbing in osteoblasts from both wild-type and P2X7 knock-out mice, similar to that induced by BzATP in wildtype cells. However, LPA-induced blebbing was more rapid in onset and was not affected by inhibition of phospholipase D or A2. Blockade or desensitization of LPA receptors suppressed blebbing in response to LPA and BzATP, without affecting P2X7-stimulated pore formation. Thus, LPA functions downstream of P2X7 receptors to induce membrane blebbing. Furthermore, inhibition of Rho-associated kinase abolished blebbing induced by both BzATP and LPA. In summary, we propose a novel signaling axis that links P2X7 receptors through phospholipases to production of LPA and activation of Rho-associated kinase. This pathway may contribute to P2X7-stimulated osteogenesis during skeletal development and mechanotransduction.
Biomaterials | 2013
Daniel O. Costa; Paul Prowse; Tom Chrones; Stephen M. Sims; Douglas W. Hamilton; Amin S. Rizkalla; S. Jeffrey Dixon
The behavior of bone cells is influenced by the surface chemistry and topography of implants and scaffolds. Our purpose was to investigate how the topography of biomimetic hydroxyapatite (HA) coatings influences the attachment and differentiation of osteoblasts, and the resorptive activity of osteoclasts. Using strategies reported previously, we directly controlled the surface topography of HA coatings on polycaprolactone discs. Osteoblasts and osteoclasts were incubated on HA coatings having distinct isotropic topographies with submicrometer and micro-scale features. Osteoblast attachment and differentiation were greater on more complex, micro-rough HA surfaces (Ra ~2 μm) than on smoother topographies (Ra ~1 μm). In contrast, activity of the osteoclast marker tartrate-resistant acid phosphatase was greater on smoother than on micro-rough surfaces. Furthermore, scanning electron microscopy revealed the presence of resorption lacunae exclusively on smoother HA coatings. Inhibition of resorption on micro-rough surfaces was associated with disruption of filamentous actin sealing zones. In conclusion, HA coatings can be prepared with distinct topographies, which differentially regulate responses of osteoblasts, as well as osteoclastic activity and hence susceptibility to resorption. Thus, it may be possible to design HA coatings that induce optimal rates of bone formation and degradation specifically tailored for different applications in orthopedics and dentistry.
The Journal of Physiology | 1992
Stephen M. Sims
1. The effects of acetylcholine on membrane electrical properties of single smooth muscle cells dissociated from the circular layer of the canine gastric corpus were investigated using the nystatin perforated patch technique. Cells retained their ability to contract during recording, making it possible to correlate changes in membrane potential and membrane currents with contractions. 2. Acetylcholine caused depolarization from ‐59 +/‐ 8 mV to ‐18 +/‐ 7 mV (means +/‐ S.D., n = 12) with no generation of action potentials. The depolarization was associated with a membrane conductance increase, consistent with acetylcholine activating an inward current. In addition, acetylcholine caused contraction of cells to 58% of initial length. Both depolarization and contraction were reversible and were antagonized by atropine. 3. Under voltage clamp, acetylcholine activated inward current associated with increased current noise. The current‐voltage relationship of the acetylcholine‐induced current was studied at steady‐state voltages and with voltage ramp commands. The inward current was largest between ‐40 and ‐20 mV and reversed direction to outward close to 0 mV (reversal potential, Erev = +3 +/‐ 9 mV). Reduction of external Na+ concentration to 21 mM shifted Erev to ‐42 +/‐ 5 mV, as predicted for a non‐selective cation current. The conductance activated by acetylcholine (gACh) increased sigmoidally with depolarization, with about 2.5 nS activated at 0 mV. 4. Cells consistently contracted upon stimulation with acetylcholine, even when studied under voltage clamp at potentials as negative as ‐100 mV. This was consistent with muscarinic receptor activation causing release of Ca2+ from internal stores. When cells were bathed in Ca(2+)‐free solutions, the first application of acetylcholine elicited normal inward current and contraction. Thereafter, both inward current and contractions were greatly diminished or absent, suggesting that the stores of Ca2+ had been depleted. 5. Caffeine caused reversible contraction and activation of inward current similar to that elicited by acetylcholine. 6. It is concluded that muscarinic stimulation of canine gastric smooth muscle cells involves activation of a non‐selective cation conductance and is consistently accompanied by contraction. The release of Ca2+ from internal stores may be a common trigger for both events.