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S A Goldstein

Publications and source records attributed to S A Goldstein.

At least 37 records · Page 2Linked to original sources
PubMed2001

Chondrocyte differentiation is modulated by frequency and duration of cyclic compressive loading.

As part of a program of research aimed at determining the role of mechanical forces in connective tissue differentiation, we have developed a model for investigating the effects of dynamic compressive loading on chondrocyte differentiation in vitro. In the current study, we examined the influence of cyclic compressive loading of chick limb bud mesenchymal cells to a constant peak stress of 9.25 kPa during each of the first 3 days in culture. Cells embedded in agarose gel were subjected to uniaxial, cyclic compression at 0.03, 0.15, or 0.33 Hz for 2 h. In addition, load durations of 12, 54, or 120 min were evaluated while holding frequency constant at 0.33 Hz. For a 2 h duration, there was no response to loading at 0.03 Hz. A significant increase in chondrocyte differentiation was associated with loading at 0.15 Hz, and an even greater increase with loading at 0.33 Hz. Holding frequency constant at 0.33 Hz, a loading duration of 12 min elicited no response, whereas chondrocyte differentiation was enhanced by loading for either 54 or 120 min. Although not statistically significant from the 120 min response, average cartilage nodule density and glycosaminoglycan synthesis rate were highest in the 54 min duration group. This result suggests that cells may be sensitive to the level of cumulative (nonrecoverable) compressive strain, as well as to the dynamic strain history.

Animals↗
PubMed2001

Functional tissue engineering: the role of biomechanics in articular cartilage repair.

Articular cartilage shows little or no intrinsic capacity for repair in response to injury or disease, and even minor lesions or injuries may lead to progressive damage and joint degeneration. Tissue engineering is a relatively new but rapidly growing field that has sought to use combinations of implanted cells, biomaterials, and biologically active molecules to repair or regenerate injured or diseased tissues. Despite many advances, tissue engineers have faced significant challenges in repairing or replacing tissues that serve a predominantly biomechanical function, such as articular cartilage. An evolving discipline termed functional tissue engineering seeks to address these challenges by emphasizing and evaluating the role of biomechanical factors in the intrinsic and engineered repair of tissues and organs. In the current study, the authors describe some of the fundamental issues involving the interaction of biomechanical stresses in vivo and in vitro with native and repair articular cartilage and with other biomechanically functional tissues. A more thorough and formal investigation of these issues may provide a basis for developing rational design principles for tissue engineered replacement or repair of load-bearing structures in the body.

Animals↗
PubMed2001

Potassium channel subunits encoded by the KCNE gene family: physiology and pathophysiology of the MinK-related peptides (MiRPs).

Voltage-gated potassium channels provide tightly Controlled, ion-specific pathways across membranes and are key to the normal function of nerves muscles. They arise from the assembly of four pore-forming proteins called alpha-subunits. To attain the properties of native currents, alpha-subunits interact with additional molecules such as the mink-related peptides (MiRPs), single-transmembrane subunits encoded by the KCNE genes. Significantly, mutations in KCNE 1, 2 and 3 have been linked either to life-threatening cardiac arrhythmia or a disorder of skeletal muscle, familial periodic paralysis. The capacity of MiRPs to partner with multiple alpha-subunits in experimental cells appears to reflect still undiscovered roles for the KCNE-encoded peptides in vivo. Here, we consider these unique peptides in health disease and discuss future research directions.

Amino Acid Sequence↗
PubMed2000

Genomic organization and chromosomal localization of the murine 2 P domain potassium channel gene Kcnk8: conservation of gene structure in 2 P domain potassium channels.

A 2 P domain potassium channel expressed in eye, lung, and stomach, Kcnk8, has recently been identified. To initiate further biochemical and genetic studies of this channel, we assembled the murine Kcnk8 cDNA sequence, characterized the genomic structure of the Kcnk8 gene, determined its chromosomal localization, and analyzed its activity in a Xenopus laevis oocyte expression system. The composite cDNA has an open reading frame of 1029 bp and encodes a protein of 343 amino acids with a predicted molecular mass of 36 kDa. Structure analyses predict 2 P domains and four potential transmembrane helices with a potential single EF-hand motif and four potential SH3-binding motifs in the COOH-terminus. Cloning of the Kcnk8 chromosomal gene revealed that it is composed of three exons distributed over 4 kb of genomic DNA. Genome database searching revealed that one of the intron/exon boundaries identified in Kcnk8 is present in other mammalian 2 P domain potassium channels genes and many C. elegans 2P domain potassium channel genes, revealing evolutionary conservation of gene structure. Using fluorescence in situ hybridization, the murine Kcnk8 gene was mapped to chromosome 19, 2B, the locus of the murine dancer phenotype, and syntenic to 11q11-11q13, the location of the human homologue. No significant currents were generated in a Xenopus laevis oocyte expression system using the composite Kcnk8 cDNA sequence, suggesting, like many potassium channels, additional channel subunits, modulator substances, or cellular chaperones are required for channel function.

Amino Acid Sequence↗
PubMed2000

A common polymorphism associated with antibiotic-induced cardiac arrhythmia.

Drug-induced long QT syndrome (LQTS) is a prevalent disorder of uncertain etiology that predisposes to sudden death. KCNE2 encodes MinK-related peptide 1 (MiRP1), a subunit of the cardiac potassium channel I(Kr) that has been associated previously with inherited LQTS. Here, we examine KCNE2 in 98 patients with drug-induced LQTS, identifying three individuals with sporadic mutations and a patient with sulfamethoxazole-associated LQTS who carried a single-nucleotide polymorphism (SNP) found in approximately 1.6% of the general population. While mutant channels showed diminished potassium flux at baseline and wild-type drug sensitivity, channels with the SNP were normal at baseline but inhibited by sulfamethoxazole at therapeutic levels that did not affect wild-type channels. We conclude that allelic variants of MiRP1 contribute to a significant fraction of cases of drug-induced LQTS through multiple mechanisms and that common sequence variations that increase the risk of life-threatening drug reactions can be clinically silent before drug exposure.

Amino Acid Sequence↗
PubMed2000

Proton block and voltage gating are potassium-dependent in the cardiac leak channel Kcnk3.

Potassium leak conductances were recently revealed to exist as independent molecular entities. Here, the genomic structure, cardiac localization, and biophysical properties of a murine example are considered. Kcnk3 subunits have two pore-forming P domains and unique functional attributes. At steady state, Kcnk3 channels behave like open, potassium-selective, transmembrane holes that are inhibited by physiological levels of proton. With voltage steps, Kcnk3 channels open and close in two phases, one appears to be immediate and one is time-dependent (tau = approximately 5 ms). Both proton block and gating are potassium-sensitive; this produces an anomalous increase in outward flux as external potassium levels rise because of decreased proton block. Single Kcnk3 channels open across the physiological voltage range; hence they are "leak" conductances; however, they open only briefly and rarely even after exposure to agents that activate other potassium channels.

Amino Acid Sequence↗
PubMed2000

Effect of compressive loading on chondrocyte differentiation in agarose cultures of chick limb-bud cells.

It is well established that mechanical loading is important to homeostasis of cartilage tissue, and growing evidence suggests that it influences cartilage differentiation as well. Whereas the effect of mechanical forces on chondrocyte biosynthesis and gene expression has been vigorously investigated, the effect of the mechanical environment on chondrocyte differentiation has received little attention. The long-term objective of this research is to investigate the regulatory role of mechanical loading in cell differentiation. The goal of this study was to determine if mechanical compression could modulate chondrocyte differentiation in vitro. Stage 23/24 chick limb-bud cells, embedded in agarose gel, were subjected to either static (constant 4.5-kPa stress) or cyclic (9.0-kPa peak stress at 0.33 Hz) loading in unconfined compression during the initial phase of commitment to a phenotypic lineage. Compared with nonloaded controls, cyclic compressive loading roughly doubled the number of cartilage nodules and the amount of sulfate incorporation on day 8, whereas static compression had little effect on these two measures. Neither compression protocol significantly affected overall cell viability or the proliferation of cells within nodules. Since limb-bud mesenchymal cells were seeded directly into agarose, an assessment of cartilage nodules in the agarose reflects the proportion of the original cells that had given rise to chondrocytes. Thus, the results indicate that about twice as many mesenchymal cells were induced to enter the chondrogenic pathway by cyclic mechanical compression. The coincidence of the increase in sulfate incorporation and nodule density indicates that the primary effect of mechanical compression on mesenchymal cells was on cellular differentiation and not on their subsequent metabolism. Further studies are needed to identify the primary chondrogenic signal associated with cyclic compressive loading and to determine the mechanism by which it influences commitment to or progression through the chondrogenic lineage, or both.

Animals↗
PubMed2000

Vertebral trabecular bone microscopic tissue elastic modulus and hardness do not change in ovariectomized rats.

Ovariectomized rats have been used extensively and have received substantial acceptance as animal models for postmenopausal osteoporosis. However, little is known about the microscopic tissue properties of rat vertebral bone, especially during osteoporosis caused by estrogen depletion. This study applied a new nanoindentation technique to quantify the microscopic mechanical properties of vertebral trabecular bone tissue in ovariectomized rats. Seventeen-week-old Sprague-Dawley rats underwent an ovariectomy. After death at 37 weeks, the fraction of the trabecular bone area of the lumbar vertebrae (L4) was measured with scanning electron microscopy and the elastic modulus and hardness were determined with the nanoindentation technique. The bone area fraction was reduced significantly after the ovariectomy. However, the elastic modulus and hardness did not change significantly at the microscopic level. The results indicate that estrogen-dependent osteoporosis in rats manifests in a loss of bone mass whereas the elastic and hardness properties of the surviving bone tissue remain relatively unchanged.

Animals↗
PubMed2000

Age, gender, and bone lamellae elastic moduli.

To enhance preventative and therapeutic strategies for metabolic bone diseases and bone fragility disorders, we began to explore the physical properties of bone tissue at the cellular level. Proximal femurs were harvested from 27 cadavera (16 male and 11 female) for in vitro measurement of the mechanical properties. We measured the variations in lamellar-level elastic modulus and hardness in human bone as a function of age and gender to identify microstructural properties responsible for age and gender-related reductions in the mechanical integrity. The lateral femoral necks were examined, and age, gender, height, body mass, and body mass index were not found to correlate with lamellar-level elastic modulus or hardness. This result was consistent for osteonal, interstitial, and trabecular tissue. These data suggest that increased bone mass maintenance, known to occur in heavier individuals, is not accompanied by increases in the lamellar-level elastic modulus or hardness. The independence of elastic modulus and hardness from age and gender suggests that age and gender-related decreases in mechanical integrity do not involve alterations in elastic modulus or hardness of the extracellular matrix. Lamellar-level ultimate, fatigue, and fracture toughness properties should also be investigated. Other factors, such as tissue mass and organization, may also contribute to age and gender-related decreases in the mechanical integrity.

Adult↗
PubMed2000

MinK endows the I(Ks) potassium channel pore with sensitivity to internal tetraethylammonium.

I(Ks) channels are heteromeric complexes of pore-forming KvLQT1 subunits and pore-associated MinK subunits. Channels formed only of KvLQT1 subunits vary from I(Ks) channels in their gating kinetics, single-channel conductance, and ion selectivity. Here we show that I(Ks) channels are more sensitive to blockade by internal tetraethylammonium ion (TEA) than KvLQT1 channels. Inhibition by internal TEA is shown to proceed by a simple bimolecular interaction in the I(Ks) conduction pathway. Application of a noise-variance strategy suggests that MinK enhances blockade by increasing the dwell time of TEA on its pore site from approximately 70 to 370 micros. Mutation of consecutive residues across the single transmembrane segment of MinK identifies positions that alter TEA blockade of I(Ks) channels. MinK is seen to determine the pharmacology of I(Ks) channels in addition to establishing their biophysical attributes.

Amino Acid Sequence↗
PubMed2000

Heterogeneity of bone lamellar-level elastic moduli.

Advances in our ability to assess fracture risk, predict implant success, and evaluate new therapies for bone metabolic and remodeling disorders depend on our understanding of anatomically specific measures of local tissue mechanical properties near and surrounding bone cells. Using nanoindentation, we have quantified elastic modulus and hardness of human lamellar bone tissue as a function of tissue microstructures and anatomic location. Cortical and trabecular bone specimens were obtained from the femoral neck and diaphysis, distal radius, and fifth lumbar vertebra of ten male subjects (aged 40-85 years). Tissue was tested under moist conditions at room temperature to a maximum depth of 500 nm with a loading rate of 10 nm/sec. Diaphyseal tissue was found to have greater elastic modulus and hardness than metaphyseal tissues for all microstructures, whereas interstitial elastic modulus and hardness did not differ significantly between metaphyses. Trabecular bone varied across locations, with the femoral neck having greater lamellar-level elastic modulus and hardness than the distal radius, which had greater properties than the fifth lumbar vertebra. Osteonal, interstitial, and primary lamellar tissues of compact bone had greater elastic moduli and hardnesses than trabecular bone when comparing within an anatomic location. Only femoral neck interstitial tissue had a greater elastic modulus than its osteonal counterpart, which suggests that microstructural distinctions can vary with anatomical location and may reflect differences in the average tissue age of cortical bone or mineral and collagen organization.

Adult↗
PubMed2000

Opening and closing of KCNKO potassium leak channels is tightly regulated.

Potassium-selective leak channels control neuromuscular function through effects on membrane excitability. Nonetheless, their existence as independent molecular entities was established only recently with the cloning of KCNKO from Drosophila melanogaster. Here, the operating mechanism of these 2 P domain leak channels is delineated. Single KCNKO channels switch between two long-lived states (one open and one closed) in a tenaciously regulated fashion. Activation can increase the open probability to approximately 1, and inhibition can reduce it to approximately 0.05. Gating is dictated by a 700-residue carboxy-terminal tail that controls the closed state dwell time but does not form a channel gate; its deletion (to produce a 300-residue subunit with two P domains and four transmembrane segments) yields unregulated leak channels that enter, but do not maintain, the closed state. The tail integrates simultaneous input from multiple regulatory pathways acting via protein kinases C, A, and G.

Animals↗
PubMed2000

In vivo nonviral delivery factors to enhance bone repair.

The purpose of the current study was to provide a review of a method for the nonviral delivery of genes into a skeletal defect for the purpose of promoting bone repair. To treat fractures at risk for delayed unions or nonunions, the delivery of plasmid deoxyribonucleic acid by a three-dimensional structural matrix is described. When these gene activated matrices are placed within a wound site, repair fibroblasts are observed migrating into the matrix where they encounter the plasmid deoxyribonucleic acid, take it up, and produce the protein that was defined by the plasmid. In varied animal models including rats, dogs, and sheep, the delivery of plasmids for parathyroid hormone or bone morphogenetic protein promoted bone formation and the healing of critical size defects. These studies show that the delivery of deoxyribonucleic acid to wound repair cells by three-dimensional matrix creates a persistent expression of factors that can promote bone formation.

Animals↗
PubMed2000

Immediate effect of Biosense guided percutaneous direct myocardial revascularization with holmium:yttrium aluminium garnet laser on myocardial contractility assessed by transesophageal echocardiography.

OBJECTIVE: To evaluate immediate changes in left ventricular wall motion in patients treated using Biosense direct myocardial revascularization laser system. METHODS: Regional wall motion in 10 patients undergoing catheter-based direct myocardial revascularization using a holmium:yttrium aluminium garnet laser was assessed by transesophageal echocardiography before and immediately after the procedure. RESULTS: Mild deterioration in wall-motion score occurred rarely for only three of 160 (1.9%) segments and did not induce clinical heart failure. CONCLUSION: With the current catheter-based laser myocardial revascularization strategy, mild deterioration in wall motion of treated segments was rarely observed and did not effect overall left ventricular function or induce clinical congestive heart failure.

Aged↗
PubMed2000

Functional tissue engineering: the role of biomechanics.

"Tissue engineering" uses implanted cells, scaffolds, DNA, protein, and/or protein fragments to replace or repair injured or diseased tissues and organs. Despite its early success, tissue engineers have faced challenges in repairing or replacing tissues that serve a predominantly biomechanical function. An evolving discipline called "functional tissue engineering" (FTE) seeks to address these challenges. In this paper, the authors present principles of functional tissue engineering that should be addressed when engineering repairs and replacements for load-bearing structures. First, in vivo stress/strain histories need to be measured for a variety of activities. These in vivo data provide mechanical thresholds that tissue repairs/replacements will likely encounter after surgery. Second, the mechanical properties of the native tissues must be established for subfailure and failure conditions. These "baseline data" provide parameters within the expected thresholds for different in vivo activities and beyond these levels if safety factors are to be incorporated. Third, a subset of these mechanical properties must be selected and prioritized. This subset is important, given that the mechanical properties of the designs are not expected to completely duplicate the properties of the native tissues. Fourth, standards must be set when evaluating the repairs/replacements after surgery so as to determine, "how good is good enough?" Some aspects of the repair outcome may be inferior, but other mechanical characteristics of the repairs and replacements might be suitable. New and improved methods must also be developed for assessing the function of engineered tissues. Fifth, the effects of physical factors on cellular activity must be determined in engineered tissues. Knowing these signals may shorten the iterations required to replace a tissue successfully and direct cellular activity and phenotype toward a desired end goal. Finally, to effect a better repair outcome, cell-matrix implants may benefit from being mechanically stimulated using in vitro "bioreactors" prior to implantation. Increasing evidence suggests that mechanical stress, as well as other physical factors, may significantly increase the biosynthetic activity of cells in bioartificial matrices. Incorporating each of these principles of functional tissue engineering should result in safer and more efficacious repairs and replacements for the surgeon and patient.

Biocompatible Materials↗
PubMed2000

Variations in three-dimensional cancellous bone architecture of the proximal femur in female hip fractures and in controls.

Cubes of cancellous bone were obtained from proximal femora of women with hip fractures (n = 26) and from female cadaveric controls (n = 32) to compare architecture and mechanics between groups. Specimens were scanned on a microcomputed tomography system. Stereologic algorithms and model-based estimates were applied to the data to characterize the three-dimensional cancellous microstructure. Cubes were mechanically tested to failure to obtain mechanical properties. Specimens from control subjects had significantly higher bone volume fraction, trabecular number, and connectivity than specimens from patients with hip fractures; no difference in trabecular thickness was observed between groups. Both maximum modulus and ultimate stress were significantly higher in the control than in the fracture group, consistent with the higher bone volume found in the control group. No statistical differences in any of these architectural or mechanical variables were found when groups were matched for bone volume. Specimens from both patients with hip fractures and controls demonstrated strong relationships between trabecular number and bone volume fraction that were statistically equivalent, suggesting that for a given bone mass, both groups have the same overall number of trabeculae. However, there was an architectural difference between fracture and control groups in terms of the three-dimensional spatial arrangement of trabeculae. Fracture specimens had a significantly more anisotropic (oriented) structure than control specimens, with proportionately fewer trabecular elements transverse to the primary load axis, even when matched for bone volume. Relationships between mechanical and architectural parameters were significantly different between groups, suggesting that fracture and control groups have different structure-mechanics relationships, which we hypothesize may be a consequence of the altered three-dimensional structure between groups.

Algorithms↗
PubMed2000

Increased marrow-derived osteoprogenitor cells and endosteal bone formation in mice lacking thrombospondin 2.

The phenotype of thrombospondin 2 (TSP2)-null mice includes abnormalities in collagen fibrils and increases in ligamentous laxity, vascular density, and bleeding time. In this study, analyses by computerized tomography (CT) revealed that cortical density was increased in long bones of TSP2-null mice. Histomorphometric analysis showed that the mid-diaphyseal endosteal bone formation rate (BFR) of TSP2-null mice was increased in comparison with that of wild-type (WT) animals. Although microgeometric analysis showed that periosteal and endosteal radii were reduced, the mechanical properties of femurs from TSP2-null mice were not significantly different from those of controls, presumably because of the concomitant increase in endosteal bone mass. Bone loss in ovariectomized mice was equivalent for WT and mutant mice, a finding that indicates that TSP2-null animals are capable of normal bone resorption. To further explore the cellular basis for the increased endosteal BFR in TSP2-null mice, marrow stromal cells (MSCs) were isolated and examined in vitro. These cells were found to be present in increased numbers in a colony forming unit (CFU) assay and showed an increased rate of proliferation in vitro. We conclude that TSP2 regulates the proliferation of osteoblast progenitors, directly or indirectly, and that in its absence endosteal bone formation is increased.

Animals↗