Biomedical subjects

Kaie Ojamaa

Publications and source records attributed to Kaie Ojamaa.

10 recordsLinked to original sources

PubMed2006

Cytokine response in children undergoing surgery for congenital heart disease.

Pediatric cardiac surgery with cardiopulmonary bypass (CPB) induces a complex inflammatory response that may cause multiorgan dysfunction. The objective of this study was to measure postoperative cytokine production and correlate the magnitude of this response with intraoperative variables and postoperative outcomes. Serum samples from 20 children (median age, 15 months) undergoing cardiac surgery with CPB were obtained preoperatively and on postoperative days (POD) 1-3. Serum levels of interleukin (IL)-6, IL-8, and IL-10 increased significantly on POD 1 (p < 0.01) vs pre-op values to 271 +/- 68, 44 +/- 9, 7.5 +/- 0.8 pg/ml, respectively, whereas serum IL-1beta, IL-12, and tumor neurosis factor -alpha were not significantly changed. The serum IL-6 and IL-8 levels correlated positively (p < 0.01) with the degree of postoperative medical intervention as measured by the Therapeutic Interventional Scoring System and indicated a greater need for inotropic support (p = 0.057). A negative correlation (p < 0.01) between IL-6, IL-8, and mixed venous oxygen saturation suggested compromised cardiopulmonary function. Patients with single ventricle anatomy had the highest levels of IL-6 and IL-8 (629 +/- 131 and 70 +/- 17 pg/ml, respectively), with a mean CPB time of 106 +/- 23 minutes. Thus, the proinflammatory response after surgery with CPB was associated with postoperative morbidity with increased need for medical intervention.

Adolescent↗

PubMed2006

Thyroid hormone stimulates protein synthesis in the cardiomyocyte by activating the Akt-mTOR and p70S6K pathways.

Thyroid hormones affect cardiac growth and phenotype; however, the mechanisms by which the hormones induce cardiomyocyte hypertrophy remain uncharacterized. Tri-iodo-L-thyronine (T3) treatment of cultured cardiomyocytes for 24 h resulted in a 41 +/- 5% (p < 0.001) increase in [(3)H]leucine incorporation into total cellular protein. This response was abrogated by the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin. Co-immunoprecipitation studies showed a direct interaction of cytosol-localized thyroid hormone receptor TRalpha1 and the p85alpha subunit of PI3K. T3 treatment rapidly increased PI3K activity by 52 +/- 3% (p < 0.005), which resulted in increased phosphorylation of downstream kinases Akt and mammalian target of rapamycin (mTOR). This effect was abrogated by pretreatment with wortmannin or LY294002. Phosphorylation of p70(S6K), a known target of mTOR, occurred rapidly following T3 treatment and was inhibited by rapamycin and wortmannin. In contrast, phosphorylation of the p85 variant of S6K in response to T3 was not blocked by LY294002, wortmannin, or rapamycin, thus supporting a T3-activated pathway independent of PI3K and mTOR. 40 S ribosomal protein S6, a target of p70(S6K), and 4E-BP1, a target of mTOR, were both phosphorylated within 15-25 min of T3 treatment and could be inhibited by wortmannin and rapamycin. Thus, rapid T3-mediated activation of PI3K by cytosolic TRalpha1 and subsequent activation of the Akt-mTOR-S6K signaling pathway may underlie one of the mechanisms by which thyroid hormone regulates physiological cardiac growth.

Animals↗

PubMed2005

Nuclear localization of protein kinase C-alpha induces thyroid hormone receptor-alpha1 expression in the cardiomyocyte.

Maladaptive cardiac hypertrophy results in phenotypic changes in several genes that are thyroid hormone responsive, suggesting that thyroid hormone receptor (TR) function may be altered by cellular kinases, including protein kinase C (PKC) isozymes that are activated in pathological hypertrophy. To investigate the role of PKC signaling in regulating TR function, cultured neonatal rat ventricular myocytes were transduced with adenovirus (Ad) expressing wild-type (wt) or kinase-inactive (dn) PKC alpha or constitutively active (ca) PKC delta and PKC epsilon. Overexpression of wtPKC alpha, but not caPKC delta or caPKC epsilon, induced a 28-fold increase (P < 0.001) in TR alpha1 protein in the nuclear compartment and a smaller increase in the cytosol. Furthermore, TR alpha1 mRNA was increased 55-fold (P < 0.001). This effect of PKC alpha was dependent on its kinase activity because dnPKC alpha was without effect. Phorbol 12-myristate 13-acetate (PMA) induced nuclear translocation of endogenous PKC alpha and Ad-wtPKC alpha concomitantly with an increase in nuclear TR alpha1 protein. In contrast, PMA-induced nuclear translocation of dnPKC alpha resulted in a decrease of TR alpha1. The increase in TR alpha1 protein in Ad-wtPKC alpha-transduced cardiomyocytes was not the result of a reduced rate of protein degradation, nor was the half-life of TR alpha1 mRNA prolonged, suggesting a PKC alpha-mediated effect on TR alpha transcription. Although phosphorylation of ERK1/2 was increased in Ad-wtPKC alpha-transduced cells, inhibition of phospho-ERK did not change TR alpha1 expression. PKC alpha overexpression in cardiomyocytes caused marked repression of triiodothyronine (T3)-responsive genes, alpha-myosin heavy chain, and the sarcoplasmic reticulum calcium-activated adenosinetriphosphatase SERCA2. Treatment with T3 for 4 h resulted in significant reductions of PKC alpha in nuclear and cytosolic compartments, and decreased TR alpha1 mRNA and protein, with normalization of phenotype. These results implicate PKC alpha as a regulator of TR function and suggest that nuclear localization of PKC alpha may control transcription of the TR alpha gene, and consequently, affect cardiac phenotype.

Adenoviridae↗

PubMed2005

Macrophage migration inhibitory factor within the alveolar spaces induces changes in the heart during late experimental sepsis.

Respiratory dysfunction during sepsis is common. However, although lung function can often be adequately supported, death frequently results from cardiovascular collapse. Despite intense investigation, the mechanism underlying the myocardial dysfunction of sepsis remains unclear. Macrophage migration inhibitory factor (MIF), an important cytokine released in sepsis and the acute respiratory distress syndrome, is a known cardiac depressant. We hypothesized that MIF released from the lung results in myocardial dysfunction during sepsis. In murine models of polymicrobial sepsis, we demonstrate a significant increase in the lungs of total and lavagable MIF between 20 and 30 h post induction of sepsis. At 30 h post sepsis, the lungs released MIF into the pulmonary circulation, increasing the plasma concentration by up to 51% in a single pass. Exogenous MIF, instilled into the lungs, increased alveolar keratinocyte-derived chemokine (KC), Macrophage inflammatory protein-2 (MIP2), and tumor necrosis factor alpha (TNFalpha) at 3 h, and plasma KC and MIP2 at 6 h postinstillation. This was associated with an increase in p38 mitogen-activated protein kinase and c-Jun N-terminal kinase phosphorylation. Because changes in mitogen-activated protein kinase activation can lead to myocardial depression, these data suggest that MIF released from the lungs may be responsible, at least in part, for the cardiac dysfunction seen in the late stages of sepsis.

Animals↗

PubMed2004

Ligand-mediated decrease of thyroid hormone receptor-alpha1 in cardiomyocytes by proteosome-dependent degradation and altered mRNA stability.

Tri-iodo-L-thyronine (T3) is essential for maintaining normal cardiac contractile function by regulating transcription of numerous T3-responsive genes. Both hormone availability and relative amounts of nuclear thyroid hormone receptor isoforms (TRalpha1, TRbeta1) determine T3 effectiveness. Cultured neonatal rat ventricular myocytes grown in T3-depleted medium expressed predominantly TRalpha1 protein, but within 4 h of T3 treatment, TRbeta1 protein increased significantly, whereas TRalpha1 was decreased by 46 +/- 5%. Using replication-defective adenoviruses to overexpress TRalpha1 in cardiomyocytes, we studied the mechanisms by which T3 mediated the decrease in TRalpha1 protein. Inhibitors of the proteosome pathway resulted in an accumulation of ubiquitylated TRalpha1 in the nucleus and prevented T3-induced degradation of ubiquitylated TRalpha1, suggesting that T3 induced proteosome-mediated degradation of TRalpha1; however, TR ubiquitylation was T3 independent. TRalpha1 transcriptional activity, measured using transient transfection of a thyroid hormone-responsive element (TRE) reporter plasmid, was T3 dose dependent and inversely proportional to nuclear TRalpha1 content, with 10 nM T3 having maximum effect. Quantitative RT-PCR showed that both endogenous and adenovirus-expressed TRalpha1 mRNAs were significantly decreased to 54 +/- 11 and 25 +/- 5%, respectively, within 4 h of T3 treatment. Measurements of TRalpha1 mRNA half-life in actinomycin D-treated cardiomyocytes showed that T3 treatment significantly decreased TRalpha1 mRNA half-life from 4 h to less than 2 h, whereas it had no effect of TRbeta1 mRNA half-life. These data support a role for both the proteosome degradation pathway and altered mRNA stability in T3-induced decrease of nuclear TRalpha1 in the cardiomyocyte and provide novel cellular targets for therapeutic development.

Adenoviridae↗

PubMed2004

Altered myocardial Ca2+ cycling after left ventricular assist device support in the failing human heart.

OBJECTIVES: The objective of the present study was to determine whether improved contractility after left ventricular assist device (LVAD) support reflects altered myocyte calcium cycling and changes in calcium-handling proteins. BACKGROUND: Previous reports demonstrate that LVAD support induces sustained unloading of the heart with regression of pathologic hypertrophy and improvements in contractile performance. METHODS: In the human myocardium of subjects with heart failure (HF), with non-failing hearts (NF), and with LVAD-supported failing hearts (HF-LVAD), intracellular calcium ([Ca(2+)](i)) transients were measured in isolated myocytes at 0.5 Hz, and frequency-dependent force generation was measured in multicellular preparations (trabeculae). Abundance of sarcoplasmic reticulum Ca(2+) adenosine triphosphatase (SERCA), Na(+)/Ca(2+) exchanger (NCX), and phospholamban was assessed by Western analysis. RESULTS: Compared with NF myocytes, HF myocytes exhibited a slowed terminal decay of the Ca(2+) transient (DT(terminal), 376 +/- 18 ms vs. 270 +/- 21 ms, HF vs. NF, p < 0.0008), and HF-LVAD myocytes exhibited a DT(terminal) that was much shorter than that observed in HF myocytes (278 +/- 10 ms, HF vs. HF-LVAD, p < 0.0001). Trabeculae from HF showed a negative force-frequency relationship, compared with a positive relationship in NF, whereas a neutral relationship was observed in HF-LVAD. Although decreased SERCA abundance in HF was not altered by LVAD support, improvements in [Ca(2+)](i) transients and frequency-dependent contractile function were associated with a significant decrease in NCX abundance and activity from HF to HF-LVAD. CONCLUSIONS: Improvement in rate-dependent contractility in LVAD-supported failing human hearts is associated with a faster decay of the myocyte calcium transient. These improvements reflect decreases in NCX abundance and transport capacity without significant changes in SERCA after LVAD support. Our results suggest that reverse remodeling may involve selective, rather than global, normalization of the pathologic patterns associated with the failing heart.

Blotting, Western↗

PubMed2003

Triiodothyronine-mediated myosin heavy chain gene transcription in the heart.

We developed an RT-PCR assay to study both the time course and the mechanism for the triiodothyronine (T(3))-induced transcription of the alpha- and beta-myosin heavy chain (MHC) genes in vivo on the basis of the quantity of specific heterogeneous nuclear RNA (hnRNA). The temporal relationship of changes in transcriptional activity to the amount of alpha-MHC mRNA and the coordinated regulation of transcription of more than one gene in response to T(3) are demonstrated here for the first time. Quantitation of alpha-MHC hnRNA demonstrated that T(3) induced alpha-MHC transcription in hypothyroid rats within 30 min of a single injection of T(3) (0.5 microg/100 g body wt). Maximal transcription rates (135% +/- 15.8 of euthyroid values) occurred 6 h after injection and subsequently declined in parallel with serum T(3) levels. The transcription of beta-MHC was reduced to 86% of peak hypothyroid levels 6 h after a single T(3) injection and reached a nadir of 59% of hypothyroid levels at 36 h. Analysis of the time course of T(3)-mediated induction of alpha-MHC hnRNA and repression of beta-MHC hnRNA indicates that separate molecular mechanisms are involved in the coordinated regulation of these genes.

Animals↗

PubMed2003

Acute exposure to thyroid hormone increases Na+ current and intracellular Ca2+ in cat atrial myocytes.

Whole-cell recording methods and fluorescence microscopy were used to study the effects of acute exposure to thyroid hormone (T(3)) on cat atrial myocytes. Acute exposure ( approximately 5 min) to 10 nM T(3) significantly increased tetrodotoxin (TTX)-sensitive inward Na(+) current (I(Na)) at voltages between -40 and +20 mV. At maximal I(Na) activation (-40 mV) T(3) increased peak I(Na) by 32 %. T(3) had no effect on the time course of I(Na) decay, voltage dependence of activation, inactivation, or recovery from inactivation. Comparable exposures to reverse T(3) (rT(3)) or T(4) had no effect on I(Na). L-type Ca2+ current was unaffected by acute exposure to T(3). T(3)-induced increases in I(Na) were unaffected by 50 microM nickel, a blocker of T-type Ca2+ current. T(3) significantly increased cell shortening (+62 %) and could elicit spontaneous action potentials arising from Ca2+ -mediated after-depolarizations. T(3) (but not rT(3)) significantly increased baseline intracellular Ca2+, release of Ca2+ from sarcoplasmic reticulum (SR) and caffeine (10 mM)-induced release of SR Ca2+. We conclude that acute T(3) exposure increases Na(+) influx via I(Na) and thereby stimulates reverse-mode Na(+)-Ca2+ exchange to increase intracellular Ca2+ content and release. As a result, T(3) increases contraction strength, and can initiate Ca2+ -mediated arrhythmic activity. Acute non-genomic effects of T(3) can contribute to the positive inotropy and sinus (atrial) tachycardia traditionally attributed to chronic, genomic effects of elevated thyroid hormone on atrial muscle.

Action Potentials↗

PubMed2003

Interleukin-6 and thyroid hormone metabolism in pediatric cardiac surgery patients.

Pediatric patients undergoing cardiac surgery have been reported to have low serum triiodothyronine (T(3)) levels in the postoperative period. The cause of this dysfunction is not known, although proinflammatory cytokines such as interleukin-6 (IL-6) have been implicated in the inhibition of hepatic conversion of thyroxine (T(4)) to T(3). This study measured serum levels of IL-6 and T(3) during the first 4 postoperative days in 16 children (mean age, 28 +/- 7 days) undergoing cardiopulmonary bypass surgery. The mean preoperative serum total T(3) level was 164 +/- 30 ng/dL (2.5 +/- 0.5 nmol/L) that decreased significantly to a nadir of 43 +/- 8 ng/dL (0.6 +/- 0.01 nmol/L) within 48 hours after surgery. Serum IL-6 levels increased significantly from 16 +/- 7 pg/mL preoperatively to a peak value of 374 +/- 134 pg/mL measured 2-3 hours after surgery. A positive correlation (r(2) = 0.507) was found between the peak serum level of IL-6 and the lowest serum T(3) level in each patient attained during the 4 postoperative days. Potential treatments directed toward diminishing the rise in proinflammatory cytokines in the immediate postoperative period may prove effective in preventing the low serum T(3) in children undergoing cardiac surgery, and thus diminish the associated postoperative morbidity.

Aortic Valve↗

PubMed2002

Role of USF1 phosphorylation on cardiac alpha-myosin heavy chain promoter activity.

Contractile activity of the cardiac myocyte is required for maintaining cell mass and phenotype, including expression of the cardiac-specific alpha-myosin heavy chain (alpha-MHC) gene. An E-box hemodynamic response element (HME) located at position -47 within the alpha-MHC promoter is both necessary and sufficient to confer contractile responsiveness to the gene and has been shown to bind upstream stimulatory factor-1 (USF1). When studied in spontaneously contracting cardiac myocytes, there is enhanced binding of USF1 to the HME compared with quiescent cells, which correlates with a threefold increase in alpha-MHC promoter activity. A molecular mechanism by which contractile function modulates alpha-MHC transcriptional activity may involve signaling via phosphorylation of USF1. The present studies showed that purified rat USF1 was phosphorylated in vitro by protein kinase C (PKC) and cAMP-dependent protein kinase (PKA) but not casein kinase II. Phosphorylated USF1 by either PKC or PKA had increased DNA binding activity to the HME. PKC-mediated phosphorylation also leads to the formation of USF1 multimers as assessed by gel shift assay. Analysis of in vivo phosphorylated nuclear proteins from cultured ventricular myocytes showed that USF1 was phosphorylated, and resolution by two-dimensional gel electrophoresis identified at least two distinct phosphorylated USF1 molecules. These results suggest that endogenous kinases can covalently modify USF1 and provide a potential molecular mechanism by which the contractile stimulus mediates changes in myocyte gene transcription.

Animals↗