Results of a collaborative study of the EDNAP group regarding mitochondrial DNA heteroplasmy and segregation in hair shafts

A collaborative exercise was carried out by the European DNA Profiling Group (EDNAP) in order to evaluate the distribution of mitochondrial DNA (mtDNA) heteroplasmy amongst the hairs of an individual who displays point heteroplasmy in blood and buccal cells. A second aim of the exercise was to study reproducibility of mtDNA sequencing of hairs between laboratories using differing chemistries, further to the first mtDNA reproducibility study carried out by the EDNAP group. Laboratories were asked to type 2 sections from each of 10 hairs, such that each hair was typed by at least two laboratories. Ten laboratories participated in the study, and a total of 55 hairs were typed. The results showed that the C/T point heteroplasmy observed in blood and buccal cells at position 16234 segregated differentially between hairs, such that some hairs showed only C, others only T and the remainder, C/T heteroplasmy at varying ratios. Additionally, differential segregation of heteroplasmic variants was confirmed in independent extracts at positions 16093 and the poly(C) tract at 302-309, whilst a complete A-G transition was confirmed at position 16129 in one hair. Heteroplasmy was observed at position 16195 on both strands of a single extract from one hair segment, but was not observed in the extracts from any other segment of the same hair. Similarly, heteroplasmy at position 16304 was observed on both strands of a single extract from one hair. Additional variants at positions 73, 249 and the HVII poly(C) region were reported by one laboratory; as these were not confirmed in independent extracts, the possibility of contamination cannot be excluded. Additionally, the electrophoresis and detection equipment used by this laboratory was different to those of the other laboratories, and the discrepancies at position 249 and the HVII poly(C) region appear to be due to reading errors that may be associated with this technology. The results, and their implications for forensic mtDNA typing, are discussed in the light of the biology of hair formation.

Overexpression of beta 1 and beta 2 adrenergic receptors in rat atrial myocytes. Differential coupling to G protein-gated inward rectifier K(+) channels via G(s) and G(i)/o

G protein-activated inwardly rectifying K(+) (GIRK) channels, expressed in atrial myocytes, various neurons, and endocrine cells, represent the paradigmatic target of beta gamma subunits released from activated heterotrimeric G proteins. These channels contribute to physiological slowing of cardiac frequency and synaptic inhibition. They are activated by beta gamma dimers released upon stimulation of receptors coupled to pertussis toxin-sensitive G proteins (G(i/o)), whereas beta gamma released from G(s) do not converge on the channel subunits. This is in conflict with the finding that dimeric combinations of various beta and gamma subunits can activate GIRK channels with little specificity. In the present study, we have overexpressed the major subtypes of cardiac beta-adrenergic receptors (beta(1)-AR and beta(2)-AR) in atrial myocytes by transient transfection. Whereas in native cells beta-adrenergic stimulation with isoproterenol failed to induce measurable GIRK current, robust currents were recorded from myocytes overexpressing either beta(1)-AR or beta(2)-AR. Whereas the beta(2)-AR-induced current showed the same sensitivity to pertussis toxin as the current evoked by the endogenous G(i/o)-coupled muscarinic M(2) receptor, isoproterenol-activated currents were insensitive to pertussis toxin treatment in beta(1)-AR-overexpressing myocytes. In contrast to a recent publication (Leaney, J. L., Milligan, G., and Tinker, A. (2000) J. Biol. Chem. 275, 921-929), sizable GIRK currents could also be activated by isoproterenol when the signaling pathway was reconstituted by transient transfection in two different standard cell lines (Chinese hamster ovary and HEK293). These results demonstrate that specificity of receptor-G protein signaling can be disrupted by overexpression of receptors. Moreover, the alpha subunit of heterotrimeric G proteins does not confer specificity to G beta gamma-mediated signaling.

Overexpression of monomeric and multimeric GIRK4 subunits in rat atrial myocytes removes fast desensitization and reduces inward rectification of muscarinic K(+) current (I(K(ACh))). Evidence for functional homomeric GIRK4 channels

K(+) channels composed of G-protein-coupled inwardly rectifying K(+) channel (GIRK) (Kir3.0) subunits are expressed in cardiac, neuronal, and various endocrine tissues. They are involved in inhibiting excitability and contribute to regulating important physiological functions such as cardiac frequency and secretion of hormones. The functional cardiac (K((ACh))) channel activated by G(i)/G(o)-coupled receptors such as muscarinic M(2) or purinergic A(1) receptors is supposed to be composed of the subunits GIRK1 and GIRK4 in a heterotetrameric (2:2) fashion. In the present study, we have manipulated the subunit composition of the K((ACh)) channels in cultured atrial myocytes from hearts of adult rats by transient transfection of vectors encoding for GIRK1 or GIRK4 subunits or GIRK4 concatemeric constructs and investigated the effects on properties of macroscopic I(K(ACh)). Transfection with a GIRK1 vector did not cause any measurable effect on properties of I(K(ACh)), whereas transfection with a GIRK4 vector resulted in a complete loss in desensitization, a reduction of inward rectification, and a slowing of activation. Transfection of myocytes with a construct encoding for a concatemeric GIRK4(2) subunit had similar effects on desensitization and inward rectification. Following transfection of a tetrameric construct (GIRK4(4)), these changes in properties of I(K(ACh)) were still observed but were less pronounced. Heterologous expression in Chinese hamster ovary cells and human embryonic kidney 293 cells of monomeric, dimeric, and tetrameric GIRK4 resulted in robust currents activated by co-expressed A(1) and M(2) receptors, respectively. These data provide strong evidence that homomeric GIRK4 complexes form functional G(beta)gamma gated ion channels and that kinetic properties of GIRK channels, such as activation rate, desensitization, and inward rectification, depend on subunit composition.

Sphingosylphosphocholine is a naturally occurring lipid mediator in blood plasma: a possible role in regulating cardiac function via sphingolipid receptors

Blood plasma and serum contain factors that activate inwardly rectifying GIRK1/GIRK4 K+ channels in atrial myocytes via one or more non-atropine-sensitive receptors coupled to pertussis-toxin-sensitive G-proteins. This channel is also the target of muscarinic M(2) receptors activated by the physiological release of acetylcholine from parasympathetic nerve endings. By using a combination of HPLC and TLC techniques with matrix-assisted laser desorption ionization-time-of-flight MS, we purified and identified sphingosine 1-phosphate (SPP) and sphingosylphosphocholine (SPC) as the plasma and serum factors responsible for activating the inwardly rectifying K+ channel (I(K)). With the use of MS the concentration of SPC was estimated at 50 nM in plasma and 130 nM in serum; those concentrations exceeded the 1.5 nM EC(50) measured in guinea-pig atrial myocytes. With the use of reverse-transcriptase-mediated PCR and/or Western blot analysis, we detected Edg1, Edg3, Edg5 and Edg8 as well as OGR1 sphingolipid receptor transcripts and/or proteins. In perfused guinea-pig hearts, SPC exerted a negative chronotropic effect with a threshold concentration of 1 microM. SPC was completely removed after perfusion through the coronary circulation at a concentration of 10 microM. On the basis of their constitutive presence in plasma, the expression of specific receptors, and a mechanism of ligand inactivation, we propose that SPP and SPC might have a physiologically relevant role in the regulation of the heart.

Depletion of phosphatidylinositol 4,5-bisphosphate by activation of phospholipase C-coupled receptors causes slow inhibition but not desensitization of G protein-gated inward rectifier K+ current in atrial myocytes

G protein-gated inwardly rectifier K+ current in atrial myocytes (I(K(ACh))) upon stimulation with acetylcholine (ACh) shows a fast desensitizing component (t(1/2) approximately 5 s). After washout of ACh, I(K(ACh)) recovers from fast desensitization within < 30 s. A recent hypothesis suggests that fast desensitization is caused by depletion of phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P(2)), resulting from costimulation of phospholipase C (PLC)-coupled M3 receptors (M3AChR). The effects of stimulating two established PLC-coupled receptors, alpha-adrenergic and endothelin (ET(A)), on I(K(ACh)) were studied in rat atrial myocytes. Stimulation of these receptors caused activation of I(K(ACh)) and inhibition of the M2AChR-activated current. In myocytes loaded with GTPgammaS (guanosine 5'-3-O-(thio)triphosphate), causing stable activation of I(K(ACh)), inhibition via alpha-agonists and ET-1 was studied in isolation. Stimulation of either type of receptor under this condition, via G(q/11), caused a slow inhibition (t(1/2) approximately 50 s) by about 70%. No comparable effect on GTPgammaS-activated I(K(ACh)) was induced by ACh, suggesting that PLC-coupled M3AChRs are not functionally expressed in rat myocytes, which was supported by the finding that M3AChR transcripts were not detected by reverse transcriptase-polymerase chain reaction in identified atrial myocytes. Supplementing the pipette solution with PtIns(4,5)P(2) significantly reduced inhibition of I(K(ACh)) but had no effect on fast desensitization. From these data it is concluded that stimulation of PLC-coupled receptors causes slow inhibition of I(K(ACh)) by depletion of PtIns(4,5)P(2), whereas fast desensitization of I(K(ACh)) is not related to PtIns(4,5)P(2) depletion. As muscarinic stimulation by ACh does not exert inhibition of I(K(ACh)) comparable to stimulation of alpha(1)- and ET(A) receptors, expression of functional PLC-coupled muscarinic receptors in rat atrial myocytes is unlikely.

Uncoupling of ATP-sensitive potassium current from cell metabolism due to antisense oligonucleotides against sulfonylurea receptor in guinea-pig atrial myocytes

ATP-sensitive K+ current (IK(ATP)) plays an important role in the regulation of cardiac electrical activity. In the myocardium, IK(ATP) is regulated by the sulfonylurea receptor (SURIIA) which mediates the inhibition of IK(ATP) due to glibenclamide (Gli). The role played by SURIIA in the sensitivity of IK(ATP) to metabolic inhibition is unclear. We studied the effect of SURIIA antisense oligonucleotides (ODNs) on the properties of IK(ATP) in cultured guinea-pig atrial myocytes. IK(ATP) was measured by the whole-cell voltage clamp method and was activated with cromakalim (Cro; 200 microns) and dinitrophenole (DNP; 100 microns). Mean IK(ATP) density activated by DNP and Cro in nonincubated cells was 117 +/- 12 pA/pF (n = 17) and 17 +/- 9 pA/pF (n = 16) respectively. No significant difference was observed after incubation with nODN [DNP: 121 +/- 13 pA/pF (n = 20); Cro:19 +/- 4 pA/pF (n = 8)]. Cells incubated with ODNs showed a significant reduction of IK(ATP) due to DNP (19 +/- 13 pA/pF; P < 0.05, n = 6), whereas Cro-induced IK(ATP) was unaffected (16 +/- 8 pA/pF, n = 8). The effectiveness of DNP-induced metabolic inhibition was apparent in a concomitant reduction of the nucleotide-phosphate dependent muscarinic K+ current (inhibition of IK(ACh) in ODN incubated myocytes without activation of IK(ATP)). The ATP sensitivity of IK(ATP) appears mediated by SURIIA. Activation of this current by Cro seems to be SURIIA-independent. ODN-induced metabolic uncoupling of IK(ATP) may be a useful experimental tool. A reduced sensitivity of IK(ATP) to intracellular ATP concentrations may be of clinical interest.

Tetranucleotide short tandem repeat polymorphisms and their possible mode of origin

An analysis of three autosomal, one X-chromosomal, and one Y-chromosomal tetranucleotide short tandem repeat loci in a large southern German population sample (including family studies) and in several nonhuman primate species revealed remarkable similarities in structure of already known and some newly detected alleles and in allele frequency distributions. These similarities, which are briefly discussed, can best be explained by transspecific evolution, followed by gene-conversion-like mutational events.

Application of mtDNA sequence analysis in forensic casework for the identification of human remains

In four forensic cases of unidentified skeletal remains investigated in the last year, we were able to attach three to missing persons. In one case we could show that the discovered bone sample did not fit to a missing child. The method for mitochondrial DNA analysis for the routine identification of skeletal remains was established in our institute by typing bone samples of defined age obtained from Frankfurt's cemetery. Reproducible results were obtained for bones up to 75 years old. For analysis the bone samples were pulverised to fine powder, decalcified and DNA was extracted. From the DNA we amplified a 404-bp fragment from HV-1 and a 379-bp fragment from HV-2 of the mtDNA control region. After sequencing of the PCR products, the results were compared to the Anderson reference sequence and to putative maternal relatives.

The role of states in ensuring essential public health services: development of state-level performance measures

The Association of State and Territorial Health Officials (ASTHO) has worked with other public health partners across the country to develop National Public Health Performance Standards, nationally recognized measures by which state public health systems can compare themselves with similar systems across the country. The lead federal agency is the Centers for Disease Control and Prevention (CDC), and other partners include the Public Health Foundation, the American Public Health Association, the National Association of City and County Health Officials, and the National Association of Local Boards of Health. Both challenges and opportunities emerged during the development of the state public health system standards.

UV-Induced stabilization of c-fos and other short-lived mRNAs

Irradiation of cells with short-wavelength ultraviolet light (UVC) changes the program of gene expression, in part within less than 15 min. As one of the immediate-early genes in response to UV, expression of the oncogene c-fos is upregulated. This immediate induction is regulated at the transcriptional level and is transient in character, due to the autocatalyzed shutoff of transcription and the rapid turnover of c-fos mRNA. In an experiment analyzing the kinetics of c-fos mRNA expression in murine fibroblasts irradiated with UVC, we found that, in addition to the initial transient induction, c-fos mRNA accumulated in a second wave starting at 4 to 5 h after irradiation, reaching a maximum at 8 h, and persisting for several more hours. It was accompanied by an increase in Fos protein synthesis. The second peak of c-fos RNA was caused by an UV dose-dependent increase in mRNA half-life from about 10 to 60 min. With similar kinetics, the mRNAs of other UV target genes (i.e., the Kin17 gene, c-jun, IkappaB, and c-myc) were stabilized (e.g., Kin17 RNA from 80 min to more than 8 h). The delayed response was not due to autocrine cytokine secretion with subsequent autostimulation of the secreting cells or to UV-induced growth factor receptor activation. Cells unable to repair UVC-induced DNA damage responded to lower doses of UVC with an even greater accumulation of c-fos and Kin17 mRNAs than repair-proficient wild-type cells, suggesting that a process in which a repair protein is involved regulates mRNA stability. Although resembling the induction of p53, a DNA damage-dependent increase in p53 was not a necessary intermediate in the stabilization reaction, since cells derived from p53 knockout mice showed the same pattern of c-fos and Kin17 mRNA accumulation as wild-type cells. The data indicate that the signal flow induced by UV radiation addresses not only protein stability (p53) and transcription but also RNA stability, a hitherto-unrecognized level of UV-induced regulation.

Overexpressed A(1) adenosine receptors reduce activation of acetylcholine-sensitive K(+) current by native muscarinic M(2) receptors in rat atrial myocytes

In adult rat atrial myocytes, muscarinic acetylcholine (ACh)-sensitive K(+) current activated by a saturating concentration of adenosine (I(K(ACh),(Ado))) via A(1) receptors (A(1)Rs) amounts to only 30% of the current activated by a saturating concentration of ACh (I(K(ACh),(ACh))) via muscarinic M(2) receptors. The half-time of activation of I(K(ACh),(Ado)) on a rapid exposure to agonist was approximately 4-fold longer than that of I(K(ACh),(ACh)). Furthermore, I(K(ACh),(Ado)) never showed fast desensitization. To study the importance of receptor density for A(1)R-I(K(ACh),(Ado)) signaling, adult atrial myocytes in vitro were transfected with cDNA encoding for rat brain A(1)R and enhanced green fluorescent protein (EGFP) as a reporter. Whole-cell current was measured on days 3 and 4 after transfection. Time-matched cells transfected with only the EGFP vector served as controls. In approximately 30% of EGFP-positive cells (group I), the density of I(K(ACh),(Ado)) was increased by 72%, and its half-time of activation was reduced. Density and kinetic properties of I(K(ACh),(ACh)) were not affected in this fraction. In approximately 70% of transfection-positive myocytes (group II), the density of I(K(ACh),(ACh)) was significantly reduced, its activation was slowed, and the fast desensitizing component was lost. Adenosine-induced currents were larger in group II than in group I, their activation rate was further increased, and a fast desensitizing component developed. These data indicate that in native myocytes the amplitude and activation kinetics of I(K(ACh),(Ado)) are limited by the expression of A(1)R. Overexpression of A(1)R negatively interferes with signal transduction via the muscarinic M(2) receptor-linked pathway, which might reflect a competition of receptors with a common pool of G proteins. Negative interference of an overexpressed receptor with physiological regulation of a target protein by a different receptor should be considered in attempts to use receptor overexpression for gene therapy.

Antisense oligonucleotides against receptor kinase GRK2 disrupt target selectivity of beta-adrenergic receptors in atrial myocytes

K+ channels composed of GIRK subunits are predominantly expressed in the heart and various regions of the brain. They are activated by betagamma-subunits released from pertussis toxin-sensitive G-proteins coupled to different seven-helix receptors. In rat atrial myocytes, activation of K(ACh) channels is strictly limited to receptors coupled to pertussis toxin-sensitive G-proteins. Upon treatment of myocytes with antisense oligodesoxynucleotides against GRK2, a receptor kinase with Gbetagamma binding sites, in a fraction of cells, K(ACh) channels can be activated by beta-adrenergic receptors. Sensitivity to beta-agonist is insensitive to pertussis toxin treatment. These findings demonstrate a potential role of Gbetagamma binding proteins for target selectivity of G-protein-coupled receptors.

Radiation-induced signal transduction. Mechanisms and consequences

Over a dose range up to 50 Gy of low-LET (linear energy transfer) ionizing radiation and up to 5 kJ/m2 UVB, mammalian cells convert molecular damage into productive response (mostly gain of function). By inactivation of negative regulatory components, such as protein tyrosine phosphatases as one mechanism discovered, the balance between restraining and stimulating influences is disturbed and an increase in signal flow results. Also DNA damage causing transcriptional arrest produces a signalling cascade of as yet unknown details. Such stimulation of the intracellular communication network can lead to apoptosis, elevated cell cycling and differentiation processes possibly including repair and recombination. The outcome likely depends on integration of all signals received which is as yet ill-understood. Although accurate determinations of low-dose inductions have not been achieved for technical reasons, the dose-response curves of induced signal transduction likely show threshold characteristics, in contrast to the direct consequences of DNA damage.

The role of the health care team in the implementation of the National Kidney Foundation-Dialysis Outcomes Quality Initiative: a case study

The National Kidney Foundation-Dialysis Outcomes Quality Initiative (NKF-DOQI) provides an opportunity to review multidisciplinary practice in end-stage renal disease settings across the country. The role of the nephrology nurse, nephrology technician, renal dietitian, and nephrology social worker are reviewed through a case presentation referencing NKF-DOQI Guidelines. Each discipline provides an overview of its respective assessments and interventions focused on improving the patient's outcome.

Activation of muscarinic K+ current by beta-adrenergic receptors in cultured atrial myocytes transfected with beta1 subunit of heterotrimeric G proteins

Muscarinic K+ channels (IK(ACh)) in native atrial myocytes are activated by betagamma subunits of pertussis toxin (Ptx)-sensitive heterotrimeric G proteins coupled to different receptors. betagamma subunits of Ptx-insensitive Gs, coupled to beta-adrenergic receptors, do not activate native IK(ACh). In atrial myocytes from adult rats transfected with rat brain beta1 subunit IK(ACh) can be activated by stimulation of beta-adrenergic receptors using isoprenaline. This effect is insensitive to Ptx. These findings demonstrate for the first time promiscuous (Ptx-insensitive) coupling of Gsbetagamma to GIRK channels in their native environment.

Sequential DNA damage-independent and -dependent activation of NF-kappaB by UV

NF-kappaB activation in response to UV irradiation of HeLa cells or of primary human skin fibroblasts occurs with two overlapping kinetics but totally different mechanisms. Although both mechanisms involve induced dissociation of NF-kappaB from IkappaBalpha and degradation of IkappaBalpha, targeting for degradation and signaling are different. Early IkappaBalpha degradation at 30 min to approximately 6 h is not initiated by UV-induced DNA damage. It does not require IkappaB kinase (IKK), as shown by introduction of a dominant-negative kinase subunit, and does not depend on the presence of the phosphorylatable substrate, IkappaBalpha, carrying serines at positions 32 and 36. Induced IkappaBalpha degradation requires, however, intact N- (positions 1-36) and C-terminal (positions 277-287) sequences. IkappaB degradation and NF-kappaB activation at late time points, 15-20 h after UV irradiation, is mediated through DNA damage-induced cleavage of IL-1alpha precursor, release of IL-1alpha and autocrine/paracrine action of IL-1alpha. Late-induced IkappaBalpha requires the presence of Ser32 and Ser36. The late mechanism indicates the existence of signal transfer from photoproducts in the nucleus to the cytoplasm. The release of the 'alarmone' IL-1alpha may account for some of the systemic effects of sunlight exposure.

Photoproducts in transcriptionally active DNA induce signal transduction to the delayed U.V.-responsive genes for collagenase and metallothionein

Mammalian cells in culture react to ultraviolet irradiation with the massive transcriptional activation of several genes and with the stabilization of the p53 protein. While U.V.-induced transcription of several immediate-response genes depends on U.V.-induced activation of signal transduction generated by non-nuclear mechanisms, stabilization of p53 and the transcription of several delayed-response genes are triggered by U.V.-induced DNA damage. By comparing dose responses for the activation by U.V. of delayed-responsive genes (collagenase 1, metallothionein IIA) in cells from patients with different DNA repair deficiencies (complementation groups of Xeroderma pigmentosum, Cockayne's syndrome and Trichothiodystrophy), we show here that U.V.-induced transcription of these genes does depend on pyrimidine dimers in transcribed regions of the genome (but not on damage in its silent part). Since all cells with defects in DNA repair that had been tested and which lack different enzymes, respond to U.V. with expression of these same genes, functional repair does not appear to be required for the induction of expression, and repair intermediates (which would not be identical in cells of different repair deficiency) cannot be responsible for signal generation.