Search PubMed⌕ Search

Biomedical subjects

K Schwartz

Publications and source records attributed to K Schwartz.

At least 127 records · Page 7Linked to original sources
PubMed1996

Structures of class A macrophage scavenger receptors. Electron microscopic study of flexible, multidomain, fibrous proteins and determination of the disulfide bond pattern of the scavenger receptor cysteine-rich domain.

Structures of secreted forms of the human type I and II class A macrophage scavenger receptors were studied using biochemical and biophysical methods. Proteolytic analysis was used to determine the intramolecular disulfide bonds in the type I-specific scavenger receptor cysteine-rich (SRCR) domain: Cys2-Cys7, Cys3-Cys8, and Cys5-Cys6. This pattern is likely to be shared by the highly homologous domains in the many other members of the SRCR domain superfamily. Electron microscopy using rotary shadowing and negative staining showed that the type I and II receptors are extended molecules whose contour lengths are approximately 440 A. They comprised two adjacent fibrous segments, an alpha-helical coiled-coil ( approximately 230 A, including a contribution from the N-terminal spacer domain) and a collagenous triple helix ( approximately 210 A). The type I molecules also contained a C-terminal globular structure ( approximately 58 x 76 A) composed of three SRCR domains. The fibrous domains were joined by an extremely flexible hinge. The angle between these domains varied from 0 to 180 degrees and depended on the conditions of sample preparation. Unexpectedly, at physiologic pH, the prevalent angle seen using rotary shadowing was 0 degrees , resulting in a structure that is significantly more compact than previously suggested. The apparent juxtaposition of the fibrous domains at neutral pH provides a framework for future structure-function studies of these unusual multiligand receptors.

Amino Acid Sequence↗
PubMed1996

Apoptosis in pressure overload-induced heart hypertrophy in the rat.

Pressure overload induces cardiac growth in the rat, which implies the hypertrophy of cardiac muscle cells and proliferation of nonmuscle cells. The cardiac cell loss observed in parallel has generally been attributed to necrosis. Using an in situ assay, we demonstrated a phase of apoptosis or programmed cell death during the first 7 d after pressure overload with a peak at day 4 while cardiac growth continued for over 30 d. The increase in apoptosis was confirmed by quantification of 180-1500-bp DNA oligonucleosomes with agarose gel electrophoresis and in situ labeling via 3'-terminal deoxynucleotidyl transferase assay. While some apoptosis was observed in the basal state in nonmuscle cells, pressure overload induced apoptosis mainly in cardiomyocytes. These data suggest that cardiac hypertrophy is initiated by a wave of apoptosis of cardiomyocytes. Thus, apoptosis may be involved in the pathogenesis of heart remodeling.

Adaptation, Physiological↗
PubMed1996

A randomized, double-blind, placebo-controlled study to evaluate botulinum toxin type A in essential hand tremor.

Twenty-five patients with hand tremor of 2+ (moderate) to 4+ (severe) on the tremor severity rating scale were randomized to receive either 50 U of botulinum toxin (BTX) type A (Allergan, Irvine, CA) or placebo injections into the wrist flexors and extensors of the dominant limb. If patients failed to respond to the initial injection, they were eligible to receive another injection of 100 U 4 weeks later. Rest, postural, and kinetic tremors were evaluated at 2- to 4-week intervals over a 16-week study period using tremor severity rating scales, accelerometry, and assessments of improvement and disability. A significant improvement (p < 0.05) was observed on the tremor severity rating scale 4 weeks after injection in patients treated with BTX as compared with placebo, and this effect was maintained for the duration of the study. Four weeks after injection, 75% of BTX-treated patients vs. 27% of placebo-treated patients (p < 0.05) reported mild to moderate improvement (peak effect rating > or = 2). There were no significant improvements in functional rating scales, although trends were observed for some items. Postural accelerometry measurements showed a > or = 30% reduction in amplitude in nine of 12 BTX-treated subjects and in one of nine placebo-treated subjects (p < 0.05). Although all patients treated with BTX reported some degree of finger weakness, no severe, irreversible, or unexpected adverse events occurred. Chemodenervation with BTX may significantly ameliorate essential hand tremor in patients who fail to improve with conventional pharmacologic therapy.

Aged↗
PubMed1996

A mutation in HERG associated with notched T waves in long QT syndrome.

Long QT syndrome (LQT) is a genetically heterogeneous inherited disorder that causes sudden death from cardiac arrhythmia. Four loci have been mapped to chromosomes 3, 4, 7 and 11 and three specific mutated genes for LQT syndrome have been identified. LQT2 results from mutations in the human ether-a-gogo-related gene, HERG, a cardiac potassium channel, whose protein product likely underlies Ikd the rapidly activating delayed rectifier current. By SSCP analysis and direct sequencing, we determined a new missense mutation in the HERG coding sequence, a G to A transition at position 1681 resulting in the substitution of threonine for a highly conserved alanine at codon 561. This mutation, Ala561Thr, in the coding sequence of the fifth membrane-spanning domain (S5) of the HERG protein seems to convey a risk of cardiac events in affected family members. In addition to a prolonged T wave of low amplitude on the surface ECG, a distinctive biphasic T-wave pattern was found in the left precordial leads of all affected subjects with the Ala561Thr mutation regardless of age, gender and beta blocking therapy.

Adolescent↗
PubMed1996

Molecular cloning and analysis of the human cardiac sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2) gene promoter.

The sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2) plays a critical role in regulating Ca2+ movements in myocardium. In cardiac hypertrophy and human heart failure, the decrease in mRNA and protein levels of SERCA2 might account for the reduced diastolic Ca2+ re-uptake seen in these conditions. To investigate the regulation of human SERCA2 gene expression, an 18.6-kb human genomic clone that contains exons 1,2 and 3 of the SERCA2 gene has been isolated, and 13 kb of 5' upstream flanking sequence of which the proximal 2.5 kb of the promoter have been sequenced. Similar to the rabbit gene, the human SERCA2 promoter possesses a TATA-like box (-25 bp), a CAAT-box (-78 bp) and a number of consensus cis-regulatory elements including three Sp1 sites, a CACCC-box, and an OTF-1 binding sequence. No CArG box (present in the rabbit SERCA2 promoter) was identified in the human proximal promoter. Two putative thyroid response elements (TRE) are also present, suggesting that the human SERCA2 gene is also regulated by thyroid hormone as are the rat and rabbit genes. To study transcriptional activity of the human SERCA2 promoter in vitro, luciferase reporter plasmids containing a series of 5' deleted promoter constructs from -2577 bp to +170 bp were transfected into neonatal rat cardiomyocytes and C2C12 myotubes. The results suggest that: (a) the sequences from the transcription start site to -263 bp are necessary to obtain maximal transcriptional activity; (b) sequences from the transcription start site to -125 bp are essential for basal transcriptional activity; (c) at least one positive regulatory element is located between -263 bp and -125 bp; and (d) at least one negative regulatory element is present between -1741 bp and -412 bp.

Animals↗
PubMed1996

Molecular and cellular biology of heart failure.

In recent years, the striking development of molecular biology and molecular genetic has brought completely new insights into the understanding of heart failure. Two aspects for which significant progress has been made in 1995 are discussed in this review: the genetic mechanisms of inherited cardiomyopathies and the molecular basis of heart failure due to chronic hemodynamic overload. In familial hypertrophic cardiomyopathy, a novel disease gene was found. It encodes myosin binding protein C, whose structure and function are poorly understood. Contractile deficits associated with the myosin mutations were demonstrated, and all this strengthened the hypothesis that hypertrophy is a compensatory mechanism that occurs in presence of a sarcomeric defect. These studies have important prognostic and clinical implications, but new and unexpected concerns have arisen, because a widespread difference in phenotype can be seen in patients harboring similar genotypes. In familial dilated cardiomyopathy, the main findings were the identification of four disease loci, but the genes are still unknown. With respect to the consequences of chronic hemodynamic overload on myocyte function and phenotype, recent data gave rise to lively discussions in the fields of reexpression of fetal troponin T isoforms and of decreased function and expression of the sarco(endo)plasmic reticulum Ca2+ ATPase in the failing human heart; at the moment it is difficult to draw definitive conclusions. Interestingly, three new concepts emerged in the understanding of the pathogenesis of heart failure: the increased contribution of the Na(+)-Ca2+ exchange, the possible recruitment of an inositol phosphate-sensitive calcium pool for myofibrillar activation, and the involvement of apoptotic myocyte and nonmyocyte cell death in myocardial remodeling.

Apoptosis↗
PubMed1996

Substitution of a conserved cysteine-996 in a cysteine-rich motif of the laminin alpha2-chain in congenital muscular dystrophy with partial deficiency of the protein.

Congenital muscular dystrophies (CMDs) are autosomal recessive muscle disorders of early onset. Approximately half of CMD patients present laminin alpha2-chain (merosin) deficiency in muscle biopsies, and the disease locus has been mapped to the region of the LAMA2 gene (6q22-23) in several families. Recently, two nonsense mutations in the laminin alpha2-chain gene were identified in CMD patients exhibiting complete deficiency of the laminin alpha2-chain in muscle biopsies. However, a subset of CMD patients with linkage to LAMA2 show only partial absence of the laminin alpha2-chain around muscle fibers, by immunocytochemical analysis. In the present study we have identified a homozygous missense mutation in the alpha2-chain gene of a consanguineous Turkish family with partial laminin alpha2-chain deficiency. The T-->C transition at position 3035 in the cDNA sequence results in a Cys996-->Arg substitution. The mutation that affects one of the conserved cysteine-rich repeats in the short arm of the laminin alpha2-chain should result in normal synthesis of the chain and in formation and secretion of a heterotrimeric laminin molecule. Muscular dysfunction is possibly caused either by abnormal disulfide cross-links and folding of the laminin repeat, leading to the disturbance of an as yet unknown binding function of the laminin alpha2-chain and to shorter half-life of the muscle-specific laminin-2 and laminin-4 isoforms, or by increased proteolytic sensitivity, leading to truncation of the short arm.

Amino Acid Sequence↗
PubMed1995

The recurring evolution of lipoprotein(a). Insights from cloning of hedgehog apolipoprotein(a).

The lipoprotein Lp(a), a major inherited risk factor for atherosclerosis, consists of a low density lipoprotein-like particle containing apolipoprotein B-100 plus the distinguishing component apolipoprotein(a) (apo(a)). Human apo(a) contains highly repeated domains related to plasminogen kringle four plus single kringle five and protease-like domains. Apo(a) is virtually confined to primates, and the gene may have arisen during primate evolution. One exception is the occurrence of an Lp(a)-like particle in the hedgehog. Cloning of the hedgehog apo(a)-like gene shows that it is distinctive in form and evolutionary history from human apo(a), but that it has acquired several common features. It appears that the primate and hedgehog apo(a) genes evolved independently by duplication and modification of different domains of the plasminogen gene, providing a novel type of "convergent" molecular evolution.

Amino Acid Sequence↗
PubMed1995

Calcium transport proteins in the nonfailing and failing heart: gene expression and function.

In heart failure alterations of intracellular Ca2+ handling are thought to be a major reason for impaired contraction and relaxation. Peak Ca2+ transients are reduced, resting Ca2+ levels elevated, and the time course of diastolic Ca2+ decline is markedly prolonged in failing hearts. The proteins of the sarcoplasmic reticulum and the sarcolemmal Na+/Ca2+ exchanger are the most important tools for Ca2+ homeostasis in the cardiomyocyte, and their molecular cloning has allowed prediction of structure/function analysis. The investigation of function and gene expression of these proteins in failing myocardium has been an area of intensive research in recent years in order to provide a more detailed understanding of the pathophysiology of heart failure. Quantitative changes in expression of the sarcoplasmic reticulum Ca(2+)-ATPase, the ryanodine receptor, and the Na+/Ca2+ exchanger with correlations to functional alterations have been reported both in experimental animal models and in the human failing heart. However, in human heart failure these findings are currently the subject of a lively discussion because observations have apparently been in part contradictory. This review discusses the proteins involved in myocardial Ca2+ handling and describes the current state of research on expressional and functional alterations and their potential implication in the pathomechanism of heart failure.

Animals↗
PubMed1995

Characterization of a novel transcript of retroviral origin expressed in rat heart and liver.

Eleven cDNA clones of retroviral origin (SORO) have been isolated and characterized from a rat cardiac cDNA library that are highly homologous to the RAL-element family of rat retroviral endogenous sequences. SORO-1, the largest of the clones isolated at approximately 3.5 kb, contains a characteristic long terminal repeat (LTR) that is unique to previously identified retroposons. Its LTR contains elements homologous to the CAAT box, a TATA box, a core enhancer sequence, and potential binding sites for GATA. SORO-1 hybridizes to a mRNA of approximately 7 kb, that is present both in rat heart and liver. This transcript was not, however, detected in other tissues (fast and slow skeletal muscles, brain, kidney, testis, lung, intestine, spleen) or from any other species (man, monkey, mouse, dog, rabbit, chicken, cow, yeast) examined. During postnatal cardiac development, the expression of the transcript appears to be down-regulated and is present at levels 10-fold greater in neonates than in adults. The function of this retroposon that is expressed in rat heart and liver has not yet been determined, but the sequence analysis of its LTR and its expression pattern suggest that it may be regulated by specific trans-acting factors that are present in both rat heart and liver.

Animals↗
PubMed1995

Removal of the financial barrier to health care: does it impact on prostate cancer at presentation and survival? A comparative study between black and white men in a Veterans Affairs system.

OBJECTIVES: African-American men are known to have a higher incidence and mortality rate from prostate cancer than American-Caucasian men. It is also known that African Americans have a higher incidence of advanced stage disease at diagnosis. One hypothesis for the latter is a delay in diagnosis due to lack of financial access to health care. Because eligibility for medical care in Veterans Affairs Medical Centers (VAMCs) is similar for both black and white patients, less disparity of stage at diagnosis, and therefore survival between blacks and whites, would be expected. METHODS: Cases for this study included only those histologically confirmed, newly diagnosed prostate cancers at the Allen Park VAMC in Wayne County, Michigan, between 1973 and 1992. Trained Surveillance, Epidemiology, and End Result (SEER) abstractors determined the stage at diagnosis, according to SEER criteria. Data analyses include descriptive statistics and survival analysis. RESULTS: The distribution of race and annual income of all male patients seen at the VAMC in Allen Park is similar. Over the entire 20-year period (1973 to 1992), there were a total of 358 prostate cancers in white patients and 383 in black patients. The ages of black and white patients were comparable. The proportion of white and black men presenting with localized disease is similar (57% and 54%, respectively). A significantly greater proportion of black patients with prostate cancer were classified as having distant disease compared with white patients (25% versus 19%; P = 0.045). A racial "crossover" effect in survival occurred around age 70 years, with white men demonstrating improved survival under 70 years of age, and black men 70 years and older tending to have better survival. CONCLUSIONS: These data suggest that financial access to care has no apparent influence on the higher proportion of distant disease and poorer survival of African-American patients with prostate cancer compared with American-Caucasian men.

Black or African American↗