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Biomedical subjects

Scott A Rivkees

Publications and source records attributed to Scott A Rivkees.

At least 19 recordsLinked to original sources
PubMed2006

Sphingosine-1-phosphate inhibits cell migration and endothelial to mesenchymal cell transformation during cardiac development.

Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid metabolite that exerts important effects on numerous cellular events via cell surface receptors, S1P(1-5). S1P influences differentiation, proliferation, and migration during vascular development. However, the effects of S1P signaling on early cardiac development are not well understood. To address this issue, we examined the expression of S1P regulatory enzymes and S1P receptors during cardiac development. We observed that enzymes that regulate S1P levels, sphingosine kinase and sphingosine-1-phosphate phosphatase, are expressed in the developing heart. In addition, RT-PCR revealed that four of the five known S1P receptors (S1P(1-4)) are also expressed in the developing heart. Next, effects of altered S1P levels on whole embryo and atrioventricular (AV) canal cultures were investigated. We demonstrate that inactivation of the S1P producing enzyme, sphingosine kinase, leads to cell death in cardiac tissue which is rescued by exogenous S1P treatment. Other experiments reveal that increased S1P concentration prevents alterations in cell morphology that are required for cell migration. This effect results in reduced cell migration and inhibited mesenchymal cell formation in AV canal cushion tissue. These data indicate that S1P, locally maintained within a specific concentration range, is an important and necessary component of early heart development.

Animals↗
PubMed2006

Hypoglycemia influences oligodendrocyte development and myelin formation.

Damage to central nervous system white matter is observed following hypoglycemia, raising the possibility that hypoglycemia influences oligodendrocytes and myelination. To examine effects of hypoglycemia on oligodendrocytes and myelin formation, we studied cultured oligodendrocyte precursor cells and cerebellar slice cultures. We observed that with decreasing concentrations of glucose, oligodendrocyte precursor cell proliferation, maturation, and migration decreased. We also observed that hypoglycemia induced apoptotic cell death and activation of caspase-3 in oligodendrocyte precursor cells. Slice culture studies showed that glucose is required for myelinated fiber formation, as with reduction in the glucose concentration, the density of myelinated fibers decreased. Collectively, these data show that hypoglycemia inhibits oligodendrocyte development and myelination and that hypoglycemia triggers apoptotic cell death in oligodendrocyte precursor cells.

Animals↗
PubMed2006

Protective effects of caffeine on chronic hypoxia-induced perinatal white matter injury.

OBJECTIVE: Periventricular white matter injury (PWMI) is the major cause of cerebral palsy and cognitive impairment in prematurely born infants. PWMI is characterized by reductions in cerebral myelination and cerebrocortical volumes and is associated with secondary ventriculomegaly. In neonatal rodents, these features of PWMI can be induced by rearing in chronic hypoxia or by activation of A1 adenosine receptors. We determined: (1) whether altered maturation or development of one or more oligodendrocyte (OL) lineage stages plays a role in the pathogenesis of the myelination disturbances associated with exposure to chronic hypoxia, and (2) whether blockade of A1 adenosine receptor action with the adenosine antagonist caffeine can prevent hypoxia-induced white matter injury. METHODS: Ventriculomegaly and reduced cerebral myelination were generated in mice reared in hypoxia (10% oxygen) from postnatal days 3 (P3) through 12. RESULTS: Hypomyelination was related to abnormal OL lineage progression and a reduction in the OL progenitor pool. Myelination was enhanced and ventriculomegaly reduced in hypoxia-exposed neonatal pups treated with caffeine from P3 to P12. INTERPRETATION: These observations support that hypoxia inhibits OL maturation and that caffeine administration during early postnatal development may have utility in the prevention of PWMI.

Adenosine↗
PubMed2006

The treatment of Graves' disease in children.

Graves' disease is the most common form of hyperthyroidism in childhood. Current treatment options include antithyroid medications, surgery, and radioactive iodine. Medical therapy is generally associated with long-term remission rates of less than 25% and a small risk of serious adverse reactions that include hepatic failure and bone marrow suppression. Total thyroidectomy is associated with very high cure rates and a small risk of hypoparathyroidism and recurrent laryngeal nerve damage. When radioactive iodine is used at appropriate doses, there is a very high cure rate without increased risks of thyroid cancer or genetic damage. Clinicians caring for the child or adolescent with Graves' disease are thus faced with using medications with potential short-term and long-term toxicity, for a condition in which spontaneous remission occurs in the minority of pediatric patients. Definitive therapy in the form of surgery or radioactive iodine is necessary and unavoidable for the majority of pediatric patients with Graves' disease.

Antithyroid Agents↗
PubMed2005

Detection of Turner syndrome using high-throughput quantitative genotyping.

CONTEXT: Turner syndrome (TS) is the most common genetic problem affecting women and occurs when an X chromosome is completely deleted, portions of an X chromosome are deleted, or chromosomal mosaicism occurs. Girls with TS may also have occult Y chromosome sequences. Whereas some girls with TS are identified in infancy or early childhood, many girls with TS are not detected until after 10 yr of age, resulting in delayed evaluation and treatment. OBJECTIVE: To prevent the delayed recognition and treatment of TS, a quantitative method of genotyping that can be performed as part of newborn screening is needed. DESIGN: To screen for sex chromosome abnormalities, we assembled a panel of informative single nucleotide polymorphism (SNP) markers that span the X chromosome from the dbSNP database. Pyrosequencing assays suitable for quantitative assessment of signal strength from single nucleotides were designed and used to genotype 46,XX; 46,XY; 45,X; and TS mosaics, examining zygosity and signal strength for individual alleles. Pyrosequencing assays were also designed for the detection of Y chromosome material. RESULTS: With just four informative SNP markers for the X chromosome, all TS girls with 45,X, partial X chromosome deletions, or mosaicism were identified with 100% sensitivity. In mosaic individuals, Y chromosomal material was detected with 100% sensitivity. CONCLUSION: These results suggest that inexpensive high-throughput screening is possible for TS and other sex chromosome disorders using quantitative genotyping approaches.

Chromosomes, Human, X↗
PubMed2005

A "locked-on," constitutively active mutant of the adenosine A1 receptor.

We studied the wild-type human adenosine A1 receptor and three mutant receptors, in which the glycine at position 14 had been changed into an alanine, a leucine, or a threonine residue. All receptors were characterized in radioligand binding experiments, the wild-type and the Gly14Thr mutant receptor in greater detail. Both receptors were allosterically modulated by sodium ions and PD81,723 (2-amino-4,5-dimethyl-3-thienyl-[3(trifluoromethyl)-phenyl]methanone), although in a different way. All mutant receptors appeared to be spontaneously or "constitutively" active in a [35S]GTPgammaS binding assay, the first demonstration of the existence of such CAM (constitutively active mutant) receptors for the adenosine A1 receptor. The Gly14Thr mutant receptor was also constitutively active in another functional assay, i.e., the inhibition of forskolin-induced cAMP production in intact cells. Importantly, this mutant displayed a peculiar "locked-on" phenotype, i.e., neither agonist nor inverse agonist was capable of modulating the basal activity in both the GTPgammaS and the cAMP assay, unlike the wild-type and the two other mutant receptors.

Adenosine↗
PubMed2005

Susceptibility of the developing brain to acute hypoglycemia involving A1 adenosine receptor activation.

It has been suggested that the developing brain is less vulnerable to the adverse effects of hypoglycemia than the mature brain; however, this issue remains controversial. We also do not know the magnitude or duration of hypoglycemia needed to trigger hypoglycemic brain injury during development. To address this issue a series of in vivo and in vitro studies were performed. First, we established an acute model of insulin-induced hypoglycemia in mice by administering 3 U/kg of neutral-protamine Hagadorn insulin subcutaneously. When we examined degenerating neurons in hippocampus and striatum by TUNEL labeling, injury was observed after 4 h of hypoglycemia in postnatal day (P)7 mice, and we observed more cell injury in animals rendered hypoglycemic at P7 than at P21. Studies of hippocampal slice cultures revealed that reduction in glucose concentration induced more neuronal injury in slices prepared from P3 and P7 than from P14 and P21 mice. Treatment of slices with an adenosine A(1) receptor (A(1)AR) antagonist reduced the hypoglycemic damage, whereas agonists increased damage, particularly in slices prepared from very young pups. This suggests a critically important role for A(1)ARs, which was further demonstrated by the reduction of hypoglycemic damage in hippocampal slices prepared from A(1)AR(-/-) mice. Furthermore, insulin-induced hypoglycemia in P7 A(1)AR(-/-) mice did not increase TUNEL-positive cells, but a major increase was seen in A(1)AR(+/-) mice. These observations show that the developing nervous system is indeed sensitive to acute hypoglycemic injury and that A(1)AR activation contributes to damage induced by hypoglycemia, particularly in immature mouse brain.

Animals↗
PubMed2004

Rho-associated kinases play a role in endocardial cell differentiation and migration.

Development of the endocardial cushions in the heart involves cell migration and cell differentiation, which is known as epithelial-mesenchymal transformation (EMT). These processes are regulated by cell signaling systems. Yet, the roles of intracellular GTPases and their effectors on these cellular activities remain to be addressed. This study investigated the role Rho GTPase-associated kinases (ROCKs) in endocardial cushion development. Using reverse transcription (RT) and polymerase chain reaction (PCR), expression of the rock1 and rock2 genes was found in the endocardial cushions during development. To investigate the role of ROCKs in development, the ROCK inhibitor Y27632 and adenoviruses containing a dominant negative form of the rock gene were used to treat cultured endocardial cushions and cells. In monolayer cell culture and three-dimensional tissue culture, blockade of ROCK inhibited EMT development. Using three-dimensional collagen gel assays and confocal microscopy, we also observed inhibition of cell migration with ROCK inhibition. Examination of cell morphology and actin cytoskeleton revealed that inhibition of ROCK activity disturbed cytoskeletal organization and blocked the formation of lamellipodia and filopodia. Collectively, these data show that ROCKs play an essential role in endothelial cell differentiation and migration during endocardial cushion development.

Adenoviridae↗
PubMed2004

Putative tumor suppressor protein 4.1B is differentially expressed in kidney and brain via alternative promoters and 5' alternative splicing.

Protein 4.1B has been reported as a tumor suppressor in brain, but not in kidney, despite high expression in both tissues. Here we demonstrate that N-terminal variability in kidney and brain 4.1B isoforms arises through an unusual coupling of RNA processing events in the 5' region of the gene. We describe two transcriptional promoters at far upstream alternative exons 1A and 1B, and show that their respective transcripts splice differentially to exon 2'/2 in a manner that determines mRNA coding capacity. The consequence of this unique processing is that exon 1B transcripts initiate translation at AUG1 (in exon 2') and encode larger 4.1B isoforms with an N-terminal extension; exon 1A transcripts initiate translation at AUG2 (in exon 4) and encode smaller 4.1B isoforms. Tissue-specific differences in promoter utilization may thus explain the abundance of larger 4.1B isoforms in brain but not in kidney. In cell studies, differentiation of PC12 cells was accompanied by translocation of large protein 4.1B isoforms into the nucleus. We propose that first exon specification is coupled to downstream splicing events, generating 4.1B isoforms with diverse roles in kidney and brain physiology, and potentially unique functions in cell proliferation and tumor suppression.

Alternative Splicing↗
PubMed2004

Cytoskeletal protein 4.1G is a binding partner of the metabotropic glutamate receptor subtype 1 alpha.

Recent evidence suggests that cytoskeletal proteins play important roles in the clustering and anchoring of glutamate receptors to the cell surface membrane. To examine further this issue, we tested for direct interactions between the metabotropic glutamate receptor subtype 1alpha (mGlu1alpha) and 4.1G, which is a member of the erythrocyte membrane, cytoskeletal protein 4.1 family. First, co-localization of 4.1G and mGlu1alpha was observed in cultured hippocampal neurons. Second, in transiently transfected HEK 293 cells and in whole rat brain tissue, direct interactions between mGlu1alpha and 4.1G were observed. Third, we were able to identify the C-terminal tail of mGlu1alpha as an essential region for mGlu1alpha-4.1G interactions. Fourth, 4.1 G influences mGlu1alpha-mediated cAMP accumulation. Finally, we found that 4.1G increases the ligand-binding ability of mGlu1alpha and alters its cellular distribution. These observations identify 4.1G as a novel binding partner of mGlu1alpha that can regulate the action of mGlu1alpha.

Animals↗
PubMed2004

Cytoskeletal protein 4.1G binds to the third intracellular loop of the A1 adenosine receptor and inhibits receptor action.

To identify binding partners of the A1AR (A1 adenosine receptor), yeast two-hybrid screening of a rat embryonic cDNA library was performed. This procedure led to the identification of erythrocyte membrane cytoskeletal protein (represented as 4.1G) as an A1AR-binding partner. Truncation studies revealed that the C-terminal domain of 4.1G was essential for binding to A1ARs and that the C-terminal domain of 4.1G and the third intracellular loop of A1ARs interacted. A1AR-4.1G interaction was also confirmed in studies using brain tissue. Studies in HEK-293 (human embryonic kidney 293) cells and Chinese-hamster ovary cells showed that 4.1G interfered with A1AR signal transduction, as 4.1G reduced A1AR-mediated inhibition of cAMP accumulation and intracellular calcium release. 4.1G also altered cell-surface A1AR expression. These observations identify 4.1G as a novel A1AR-binding partner that can regulate adenosine action.

Animals↗
PubMed2004

Emergence and influences of circadian rhythmicity in infants.

Recent evidence shows that the circadian system of primate infants is responsive to light at very premature stages and that low intensity lighting can regulate the developing clock. After birth, there is progressive maturation of the circadian system outputs, with pronounced rhythms in sleep-wake and hormone secretion generally developing after 2 months of age. Showing the importance of photic regulation of circadian phase in infants, exposure of premature infants to low-intensity cycled lighting results in the early establishment of rest-activity patterns that are in phase with the 24-hour light-dark cycle. With the continued elucidation of circadian system development and influences on human physiology and illness, it is anticipated that consideration of circadian biology will become an increasingly important component of neonatal care.

Circadian Rhythm↗
PubMed2004

Emerging concepts in periventricular white matter injury.

Approximately 10% of newborns are born prematurely. Of these children, more than 10% will sustain neurological injuries leading to significant learning disabilities, cerebral palsy, or mental retardation, with very low birth weight infants having an even higher incidence of brain injury. Whereas intraventricular hemorrhage was the most common form of serious neurological injury a decade ago, periventricular white matter injury (PWMI) is now the most common cause of brain injury in preterm infants. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia; PVL) and diffuse myelination disturbances. Recent neuroimaging studies support that the incidence of PVL is declining, whereas diffuse cerebral white matter injury is emerging as the predominant lesion. Factors that predispose to PVL include prematurity, hypoxia, ischemia, and inflammation. It is believed that injury to oligodendrocyte (OL) progenitors contributes to the pathogenesis of myelination disturbances in PWMI by disrupting the maturation of myelin-myelin-forming oligodendrocytes. Other potential mechanisms of injury include activation of microglia and axonal damage. Chemical mediators that may contribute to white matter injury include reactive oxygen (ROS) and nitrogen species (RNS), glutamate, cytokines, and adenosine. As our understanding of the pathogenesis of PWMI improves, it is anticipated that new strategies for directly preventing brain injury in premature infants will evolve.

Adenosine↗
PubMed2004

Rest-activity patterns of premature infants are regulated by cycled lighting.

OBJECTIVES: Many hospitalized premature infants are exposed to continuous dim lighting rather than to cycled lighting. However, we do not know whether dim lighting or low-intensity cycled lighting is more conducive to the development of rest-activity patterns that are in phase with the solar light-dark cycle. Thus, we examined the effects of nursery lighting conditions on the development of activity patterns in premature infants. METHODS: Premature infants who were born at <32 weeks' postmenstrual age and were medically stable in neonatal intensive care unit rooms were randomly assigned between 32 and 34 weeks' postmenstrual age to either continuous dim lighting (<25 lux; duration 24 days; control group; n = 29) or cycled lighting (239 +/- 29 lux, 7:00 AM to 7:00 PM; <25 lux, 7:00 PM to 7:00 AM; duration: 25 days; experimental group; n = 33). Activity was continuously monitored from enrollment until approximately 1 month after discharge from the hospital. Weight and head circumference were also assessed up to 6 months after discharge from the hospital. RESULTS: Over the first 10 days at home, distinct day-night differences in activity were not seen in control subjects (D day-night: N 1.07 +/- 0.02), but experimental group infants were more active during the day than at night (day-night: 1.25 +/- 0.03). It was not until 21 to 30 days after discharge that day-night activity ratios in control infants matched those seen in experimental group infants shortly after discharge, yet even at this age, experimental group infants (day-night: 2.13 +/- 0.19) were considerably more active during the day than at night as compared with control subjects (day-night: 1.43 +/- 0.09). CONCLUSION: Exposure of premature infants to low-intensity cycled lighting in the hospital nursery induces distinct patterns of rest-activity that are apparent within 1 week after discharge. In comparison, the appearance of distinct patterns of rest and activity are delayed in infants who are exposed to continuous dim lighting in the hospital. These observations show that day-night rhythms in activity patterns can be detected shortly after discharge to home in premature infants and that the circadian clock of developing infants is entrained by cycled lighting.

Activity Cycles↗
PubMed2003

A1 adenosine receptors mediate hypoxia-induced ventriculomegaly.

Periventricular leukomalacia is characterized by a reduction in brain matter and secondary ventriculomegaly and is a major cause of developmental delay and cerebral palsy in prematurely born infants. Currently, our understanding of the pathogenesis of this condition is limited. In animal models, features of periventricular leukomalacia can be induced by hypoxia and activation of A1 adenosine receptors (A1ARs). Using mice that are deficient in the A1AR gene (A1AR-/-), we show that A1ARs play a prominent role in the development of hypoxia-induced ventriculomegaly in neonates. Supporting a role for adenosine in the pathogenesis of developmental brain injury, ventriculomegaly was also observed in mice lacking the enzyme adenosine deaminase, which degrades adenosine. Thus, adenosine acting on A1ARs appears to mediate hypoxia-induced brain injury ventriculomegaly during early postnatal development.

Animals↗
PubMed2003

Rho-associated kinases play an essential role in cardiac morphogenesis and cardiomyocyte proliferation.

Rho-associated coiled-coil kinases (ROCKs), initially identified as effectors for Rho GTPases, play a role in cardiac cell physiology and are also expressed in the developing heart. However, their role in cardiac development is not known. To investigate the role of these kinases in cardiac development, we examined cardiac development in cultured murine embryos treated with the ROCK inhibitor Y27632. After inhibition of ROCK activity, we found disturbed cardiac chamber formation and trabeculation. To further examine the mechanisms by which ROCK blockade causes cardiac hypoplasia, we assessed programmed cell death and cell proliferation in the hearts. We found decreased cell proliferation in the Y27632-treated hearts, but no changes in programmed cell death. We further observed that ROCK inhibition decreased cardiac myocyte proliferation, suggesting that ROCK kinases regulate cardiomyocyte division. To identify factors involved in ROCK action in regulation of cardiac cell division, we examined expression of cell cycle proteins by using Western blot analysis. We found that ROCK blockade decreased expression of cell cycle proteins, cyclin D3, CDK6, and p27(KIP1) in the hearts and cardiomyocytes, which are required for initiation of cell cycle and G1/S phase transition. These observations show that ROCK kinases play a role in cardiac development and that ROCK kinases regulate cardiac cell proliferation and cell cycle protein expression.

Amides↗