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Biomedical subjects

C N Hahn

Publications and source records attributed to C N Hahn.

28 records · Page 2Linked to original sources
PubMed1997

Generalized CNS disease and massive GM1-ganglioside accumulation in mice defective in lysosomal acid beta-galactosidase.

Human GM1-gangliosidosis is caused by a genetic deficiency of lysosomal acid beta-galactosidase (beta-gal). The disease manifests itself either as an infantile, juvenile or adult form and is primarily a neurological disorder with progressive brain dysfunction. A mouse model lacking a functional beta-gal gene has been generated by homologous recombination and embryonic stem cell technology. Tissues from affected mice are devoid of beta-gal mRNA and totally deficient in GM1-ganglioside-hydrolyzing capacity. Storage material was already conspicuous in the brain at 3 weeks. By 5 weeks, extensive storage of periodic acid Schiff-positive material was observed in neurons throughout the brain and spinal cord. Consistent with the neuropathology, abnormal accumulation of GM1-ganglioside in the brain progressed from twice to almost five times the normal amount during the period from 3 weeks to 3.5 months. Despite the accumulation of brain GM1-ganglioside at the level equal to or exceeding that seen in gravely ill human patients, these mice show no overt clinical phenotype up to 4-5 months. However, tremor, ataxia and abnormal gait become apparent in older mice. Thus, the beta-gal-deficient mice appear to mimic closely the pathological, biochemical and clinical abnormalities of the human disease.

Animals↗
PubMed1996

Transcriptional synergism between vitamin D-responsive elements in the rat 25-hydroxyvitamin D3 24-hydroxylase (CYP24) promoter.

Transcription of the CYP24 gene is induced by 1,25-(OH)2D3 through a vitamin D receptor-dependent process. The functional activities of three possible vitamin D response elements (VDREs), located on the antisense strand of the rat CYP24 promoter, were investigated by transient expression of native and mutant promoter constructs in COS-1, JTC-12, and ROS 17/2.8 cells. A putative VDRE with a half-site spacing of 6 base pairs at -249/-232 (VDRE-3) did not contribute to 1,25-(OH)2D3 induced expression in the native promoter, although activity has been reported when the element was fused to the heterologous thymidine kinase promoter. Two VDREs with half-site spacings of 3 base pairs at -150/-136 and -258/-244 (VDRE-1 and VDRE-2, respectively), showed transcriptional synergism in COS-1 cells when treated with 1,25-(OH)2D3 (10(-7) to 10(-11) M). The contribution of both VDREs was hormone-concentration dependent from 10(-10) to 10(-12) M, with VDRE-1 demonstrating greatest sensitivity to 1,25-(OH)2D3. Transactivation by VDRE-1 was always greater than VDRE-2, but the converse was observed for the binding of vitamin D receptor-retinoid X receptor complex by each VDRE in gel mobility shift assays. The synergy observed between VDRE-1 and VDRE-2 may have important implications in cellular responses to different circulating levels of 1,25-(OH)2D3.

Animals↗
PubMed1994

Identification of a vitamin D responsive element in the promoter of the rat cytochrome P450(24) gene.

Mitochondrial cytochrome P450(24) expression in the vitamin D-degradation pathway is induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. The molecular basis of this enzyme regulation was investigated by isolating the rat P450(24) gene and examining the 5'-flanking region for possible cis-acting regulatory elements involved in the induction process. Constructs containing different lengths of 5'-flanking region of the gene were linked to a luciferase reporter gene and transiently co-transfected with a human vitamin D receptor (hVDR) expression vector (pRSV-hVDR) into COS-1 cells. These experiments showed that the flanking region from -298 to -122 directed a 24-fold increase in luciferase activity in response to 1,25-(OH)2D3 provided that the cells were co-transfected with pRSV-hVDR. Within this region, the sequence from position -171 to -123 conferred 1,25-(OH)2D3 responsiveness to both the native P450(24) promoter and the heterologous thymidine kinase promoter. Mutagenesis revealed that the sequence from position -150 to -136 is required for induction by 1,25-(OH)2D3 and that this sequence shares similarity to other vitamin D responsive elements (VDREs) reported for other genes. Gel shift mobility assays showed this region specifically bound a nuclear protein complex from 1,25-(OH)2D3 treated COS-1 cells that had been co-transfected with pRSV-hVDR. The retarded band was specifically competed with the well characterized VDRE from the mouse osteopontin gene. A VDRE at position -150 to -136 in the promoter of the rat P450(24) gene is identified in this study and found to be important in mediating the enhanced expression of the gene by 1,25-(OH)2D3.

Animals↗
PubMed1993

Superinduction by cycloheximide of cytochrome P4502H1 and 5-aminolevulinate synthase gene transcription in chick embryo liver.

The present study examines the effect of inhibiting protein synthesis with cycloheximide on the induction of the genes for cytochrome P4502H1 (CYP2H1) and 5-aminolevulinate synthase (ALAS) in phenobarbital-treated chick embryo livers. Phenobarbital administration caused a 10- to 15-fold increase in the levels of mRNAs for both CYP2H1 and ALAS. Cycloheximide treatment alone also induced the levels of mRNA for CYP2H1 and ALAS by 7- and 3-fold, respectively, but in combination, cycloheximide and phenobarbital elicited an additional effect resulting in a 33- and 40-fold increase, respectively. To investigate whether these effects were due to transcriptional activation or a post-transcriptional mechanism, nuclear transcription run-on experiments were conducted. The observed changes in mRNA levels for CYP2H1 and ALAS were shown to be predominantly due to changes in the rate of transcription of the respective genes. These findings establish that drug induction of the CYP2H1 and ALAS genes can proceed in the almost complete absence of protein synthesis and also imply that a labile repressor protein may be involved in modulating expression of these genes. In addition, these results indicate that drug induction of ALAS does not require concomitant synthesis of P450 apoprotein.

5-Aminolevulinate Synthetase↗
PubMed1991

Transcriptional regulation of the chicken CYP2H1 gene. Localization of a phenobarbital-responsive enhancer domain.

The mechanism by which the drugs phenobarbital and 2-allyl-2-isopropylacetamide induce levels of chicken cytochrome P-450 (CYP) mRNAs has been investigated in primary hepatocyte cultures from 17-day-old chick embryos. It has been demonstrated that three CYP mRNAs of 3.5, 2.5, and 2.2 kilobases (kb) are strongly induced by phenobarbital in primary hepatocytes, as found previously in chick embryo liver in ovo (Hansen, A. J., Elferink, L. A., and May, B. K. (1989) DNA (NY) 8, 179-191), and that, at least for the 3.5-kb mRNA, this is predominantly a result of enhanced transcription of the corresponding gene, CYP2H1. Transient transfection assays were carried out in primary cultures using constructs containing different lengths of CYP2H1 gene 5'-flanking sequence fused to the reporter chloramphenicol acetyl-transferase (CAT) gene. These experiments established that cis-acting elements located in the first 0.5 kb of the CYP2H1 gene 5'-flanking region direct high basal expression of the CAT gene, but do not mediate phenobarbital inducibility. When constructs containing more than 1.1 kb of CYP2H1 gene 5'-flanking sequence were examined, phenobarbital induction of CAT expression was observed, and a drug-responsive domain between positions -5.9 and -1.1 kb was identified. This domain has the properties of an enhancer, since it is able to confer phenobarbital responsiveness to the enhancerless SV40 promoter when tested in either orientation or at different distances from the promoter. The enhancer domain also responds to 2-allyl-2-isopropylacetamide, but whether the action of the two drugs is mediated by a single nuclear receptor interacting with common DNA elements in the domain remains to be established.

Animals↗
PubMedDate not supplied

Measurement of the lateral thoracic reflex latency in ponies.

Lateral thoracic nerve reflex latencies values were measured in ponies using a simple, non-invasive technique. The reflex was elicited using an external triggering hammer attached to an electrodiagnostic unit. The resulting evoked, compound muscle action potentials were recorded with electrodes, which were placed over the 6th ribs or 11th rib level with the axilla. Two superimposed repeats of 4 signal-averaged sweeps of 50 or 100 milliseconds were recorded and the estimated reflex pathway was measured for each subject in order to calculate the reflex latencies and latency velocities. Mean left and right 6th rib peak latencies were not significantly different from each other (P = .609), but left 6th rib latencies were shorter than those recorded from the 11th rib (P < .0001), substantiating the existence of an indirect (central) pathway to the reflex. The calculated left and right 6th rib latency velocities were not significantly different from each other (P = .58) but left 6th rib latency velocities were different from left 11th rib (P = .009). The calculated latency velocities were within the broad range for corticospinal tract motor conduction velocities and comparable to magnetic motor evoked latency velocities. The use of lateral thoracic reflex latency measurements to objectively identify the site of spinal cord lesions is discussed.

Animals↗