Biomedical subjects

Norbert Hübner

Publications and source records attributed to Norbert Hübner.

10 recordsLinked to original sources

PubMed2006

Evaluation of myocardial metabolism with microdialysis during bypass surgery with cold blood- or Calafiore cardioplegia.

BACKGROUND: For the first time, microdialysis was used to investigate in vivo and online the myocardial metabolism during and after cardiac surgery in patients treated with two different methods of myocardial protection. METHODS: Thirty patients underwent standard CABG with one of two different methods of myocardial protection. The patients were randomised to receive either cold blood (COLD group) or warm modified Calafiore cardioplegia (WARM group). Microdialysis probes were implanted into the myocardium of left ventricular apical region of the heart. Cardioplegia was given antegrade only. Microdialysis measurements were performed at time intervals before, during and 24 h after cardiopulmonary bypass and analysed for glucose, lactate, pyruvate and glycerol. RESULTS: Myocardial lactate concentrations were significantly higher in the WARM group compared with that of the COLD group, while serum lactate was comparable. Glycerol was significantly higher at the end of the clamping time in the WARM group. At the same time the glucose-lactate ratio as a marker of nutritional disorder had significantly lower levels in the WARM group. The cumulative CK-MB release over 24 h was significantly higher in those hearts protected with warm blood. CONCLUSIONS: The oxidative stress measured was significantly higher in patients undergoing CABG using modified Calafiore cardioplegia, whereas the cold cardioplegia minimised the effects of aortic clamping. The results indicate that cold cardioplegia offers superior protection of the heart, in terms of more rapid normalisation of myocardial metabolism. In elective myocardial revascularisation, intermittent antegrade warm blood cardioplegia is a comparable safe method of myocardial protection. However, in patients referring to a long clamping time, advantages of cold cardioplegia for myocardial revascularisation may be magnified.

Aged↗

PubMed2004

Integrated and sequence-ordered BAC- and YAC-based physical maps for the rat genome.

As part of the effort to sequence the genome of Rattus norvegicus, we constructed a physical map comprised of fingerprinted bacterial artificial chromosome (BAC) clones from the CHORI-230 BAC library. These BAC clones provide approximately 13-fold redundant coverage of the genome and have been assembled into 376 fingerprint contigs. A yeast artificial chromosome (YAC) map was also constructed and aligned with the BAC map via fingerprinted BAC and P1 artificial chromosome clones (PACs) sharing interspersed repetitive sequence markers with the YAC-based physical map. We have annotated 95% of the fingerprint map clones in contigs with coordinates on the version 3.1 rat genome sequence assembly, using BAC-end sequences and in silico mapping methods. These coordinates have allowed anchoring 358 of the 376 fingerprint map contigs onto the sequence assembly. Of these, 324 contigs are anchored to rat genome sequences localized to chromosomes, and 34 contigs are anchored to unlocalized portions of the rat sequence assembly. The remaining 18 contigs, containing 54 clones, still require placement. The fingerprint map is a high-resolution integrative data resource that provides genome-ordered associations among BAC, YAC, and PAC clones and the assembled sequence of the rat genome.

Animals↗

PubMed2003

Genome-wide linkage reveals a locus for human essential (primary) hypertension on chromosome 12p.

Essential (primary) hypertension is an important risk factor for cardiovascular morbidity and mortality. Blood pressure is largely heritable; however, the genetic factors contributing to essential hypertension are mostly unknown. We examined a large Chinese kindred (n=387) and selected a subset of 94 individuals for genotyping. An additional 32 Chinese nuclear families with essential hypertension were also recruited. Genome-wide parametric linkage analysis identified a new locus for primary hypertension on chromosome 12p (parametric LOD score 3.44). This locus overlaps with the assigned locus that causes severe autosomal-dominant hypertension and brachydactyly, the only form of monogenic hypertension known to date that resembles primary hypertension. We suggest that this genomic region, spanning 18 annotated genes, will be of great relevance in elucidating new mechanisms for primary hypertension.

Adult↗

PubMed2003

The role of Wnk4 in polygenic hypertension: a candidate gene analysis on rat chromosome 10.

Linkage analyses in experimental crosses of stroke-prone spontaneously hypertensive (SHRSP) and normotensive Wistar-Kyoto (WKY) rats have strongly suggested the presence of quantitative trait loci (QTL) influencing blood pressure and ACE levels on rat chromosome 10, which have been confirmed in multiple independent studies. Analysis of the orthologous region on human chromosome 17 also revealed significant linkage to blood pressure in several populations. Wnk4, a gene previously identified to cause pseudohypoaldosteronism type II, a rare mendelian form of arterial hypertension, is located on human chromosome 17. The hypothesis has been advanced that molecular variants of this gene might contribute to common polygenic forms of hypertension, since Wnk4 is located in a region of conserved synteny that demonstrates an overlap between quantitative trait loci for primary hypertension in humans and rats. In this report, we describe the confirmation of the blood pressure QTL on rat chromosome 10 by congenic approaches, spanning the Wnk4 locus. Comparative analysis of the complete coding sequence of Wnk4 in SHRSP and WKY strains revealed no mutation and demonstrated high conservation between rat and human proteins. Furthermore, comparison of mRNA levels in the kidney showed no differences between SHRSP and WKY. Additionally, we excluded a secondary effect of blood pressure on the transcriptional regulation of Wnk4. Our results fail to support a material contribution of Wnk4 to blood pressure regulation in this model of polygenic hypertension. Thus, Wnk4 is likely not to represent the underlying disease gene for the QTL captured in chromosome 10 congenic animals.

Amino Acid Sequence↗

PubMed2003

Interaction between blood pressure quantitative trait loci in rats in which trait variation at chromosome 1 is conditional upon a specific allele at chromosome 10.

We have used inbred and congenic rat strains in F(2) segregation studies to discover epistasis in a polygenic model of hypertension. Previously, we have found evidence that the presence of a blood pressure quantitative trait locus (QTL) on chromosome 1 is conditional upon the allele status of chromosome 10. To prove the existence of an epistatic interaction we have analyzed congenic strains for chromosome 1 and 10 carrying high blood pressure QTL alleles from the spontaneously hypertensive rat on a normotensive background of the Wistar-Kyoto (WKY) rat. Additionally, a double congenic strain was developed with both chromosome 1 and 10 high blood pressure QTL alleles on the WKY background. Analysis of variance for blood pressure phenotypes as determined by radiotelemetry showed a significant effect for chromosome 10 but not chromosome 1 QTL alleles and demonstrated a significant interaction between the two loci (P<0.05). The interaction accounted for 5 mmHg of blood pressure. Thus, the identification of epistasis is critical to the understanding of the quantitative nature of blood pressure genetics.

Alleles↗

PubMed2002

Conditional expression of mutant M-line titins results in cardiomyopathy with altered sarcomere structure.

Titin is a giant protein responsible for muscle elasticity and provides a scaffold for several sarcomeric proteins, including the novel titin-binding protein MURF-1, which binds near the titin M-line region. Another unique feature of titin is the presence of a serine/threonine kinase-like domain at the edge of the M-line region of the sarcomere, for which no physiological catalytic function has yet been shown. To investigate the role(s) of the titin M-line segment, we have conditionally deleted the exons MEx1 and MEx2 (encoding the kinase domain plus flanking sequences) at different stages of embryonic development. Our data demonstrate an important role for MEx1 and MEx2 in early cardiac development (embryonic lethality) as well as postnatally when disruption of M-line titin leads to muscle weakness and death at approximately 5 weeks of age. Myopathic changes include pale M-lines devoid of MURF-1, and gradual sarcomeric disassembly. The animal model presented here indicates a critical role for the M-line region of titin in maintaining the structural integrity of the sarcomere.

Actins↗

PubMed2002

Conditional mutation of the ErbB2 (HER2) receptor in cardiomyocytes leads to dilated cardiomyopathy.

The ErbB2 (Her2) proto-oncogene encodes a receptor tyrosine kinase, which is frequently amplified and overexpressed in human tumors. ErbB2 provides the target for a novel and effective antibody-based therapy (Trastuzumab/Herceptin) used for the treatment of mammary carcinomas. However, cardiomyopathies develop in a proportion of patients treated with Trastuzumab, and the incidence of such complications is increased by combination with standard chemotherapy. Gene ablation studies have previously demonstrated that the ErbB2 receptor, together with its coreceptor ErbB4 and the ligand Neuregulin-1, are essential for normal development of the heart ventricle. We use here Cre-loxP technology to mutate ErbB2 specifically in ventricular cardiomyocytes. Conditional mutant mice develop a severe dilated cardiomyopathy, with signs of cardiac dysfunction generally appearing by the second postnatal month. We infer that signaling from the ErbB2 receptor, which is enriched in T-tubules in cardiomyocytes, is crucial for adult heart function. Conditional ErbB2 mutant mice provide a model of dilated cardiomyopathy. In particular, they will allow a rigorous assessment of the role of ErbB2 in the heart and provide insight into the molecular mechanisms that underlie the adverse effects of anti-ErbB2 antibodies.

Animals↗

PubMed2002

Congenic rat strains are important tools for the genetic dissection of essential hypertension.

The identification of mutated genes and the characterization of disease pathways in monogenetic forms of human arterial hypertension has been very successful during the past decade, although only little progress has been made with regard to the genetic analysis of essential hypertension. Inbred rat strains that display hypertension as an inherited trait represent an attractive substitute for the dissection of the polygenetic basis of human essential hypertension. The power of studying these inbred models with natural allelic variation is that each strain can be thought of as a different subtype of essential hypertension. Thus, to study the genetics of hypertension using a potpourri of inbred hypertensive rat strains may help to identify a set of genes that can give rise to hypertension in the heterogeneous clinical situation of essential hypertension. Indeed, multiple blood pressure quantitative trait loci (QTL) have been identified in the rat genome and a few of those have been implicated in the human disease by homology mapping already. Here, we discuss the role of congenic breeding strategies to further dissect the genetics of hypertension in the rat. Based on recent accomplishments it can be anticipated that by using congenic strains, the genetic sifting of the collection of blood pressure QTLs identified so far will lead to the identification of additional and new candidate genes. This will open the possibility for the development of new diagnostic and therapeutic means contributing to a better control of human essential hypertension.

Animals↗

PubMed2002

A gene expression analysis in rat kidney following high and low salt intake.

BACKGROUND: The effects of salt intake on renal regulation have been investigated for decades. To find new pathways and to demonstrate the utility of oligonucleotide expression arrays, we studied whole kidneys. METHODS: Eight Sprague-Dawley rats were divided into two groups. One group received a 6% salt (by weight) diet, while the other group received a 0.3%, otherwise identical, salt diet for 7 days. The rats were sacrificed after 7 days and the left kidney was subjected to RNA extraction. Oligonucleotide expression arrays (Affymetrix) were used to determine downregulation and upregulation, comparing high with low salt intake. Four rats from each group were studied separately. RESULTS: The experiments were reproducible. Thirty genes were downregulated with the high-salt diet, while 35 genes were upregulated. The renin gene, beta-2 glycoprotein-1, retinol binding protein, annexin VI, and the PTP2C protein tyrosine phosphatase were among the downregulated genes. The angiotensin II receptor type 1B receptor, HMG-CoA reductase, B7 antigen, and the rat calcium channel beta subunit III were among the upregulated genes. Differentially regulated were the p55 subunit (upregulated) and the p50 subunit (downregulated) of the phosphatidyl inositol 3-kinase enzyme complex. We verified our results by selecting a high-salt downregulated gene (renin) and an upregulated gene (B7 antigen) and subjecting these genes to real-time polymerase chain reaction. The results were consistent. CONCLUSION: Oligonucleotide expression arrays can detect novel genes encoding for proteins not generally associated with responses to varied salt intake. Experiments of this nature have substantial limitations and require detailed verification. However, overall, the utility is promising.

Animals↗

PubMed2002

Conserved synteny in rat and mouse for a blood pressure QTL on human chromosome 17.

Evidence for blood pressure quantitative trait loci (QTLs) on rat chromosome 10 has been found in multiple independent studies. Analysis of the homologous region on human chromosome 17 revealed significant linkage to blood pressure. The critical segment on human chromosome 17 spans a large interval containing the genes Itga2b, Gfap, and Itgb3. Therefore, findings in the rat may help to refine the position of blood pressure-regulating loci, assuming a common molecular cause across species. However, it has recently been suggested that the gene order in human, rat, and mouse is not conserved in this region, leaving uncertainty about the overlap of the blood pressure- regulating region between human chromosome 17 and rat chromosome 10. We have performed a detailed comparative analysis among human, mouse, and rat, defining the segment in question, by obtaining gene structure information in silico and by radiation hybrid mapping. It is of interest that this region also contains Wnk4, a gene previously identified to cause pseudohypoaldosteronism type II and human hypertension. Our results definitively show that the conserved synteny extends among human chromosome 17, rat chromosome 10, and mouse chromosome 11, demonstrating an overlap between previously localized blood pressure QTLs in humans and rats.

Animals↗