Biomedical subjects

U B Jensen

Publications and source records attributed to U B Jensen.

21 records · Page 2Linked to original sources

PubMed1993

Correction of steroid sulfatase deficiency by gene transfer into basal cells of tissue-cultured epidermis from patients with recessive X-linked ichthyosis.

To develop an experimental model for somatic gene therapy we have tried to correct the steroid sulfatase (STS) deficiency in tissue-cultured primary epidermal keratinocytes from patients suffering from recessive X-linked ichthyosis. An efficient Epstein-Barr virus-based vector was constructed, in which full-length steroid sulfatase cDNA is located between an SV40 early promotor and processing signals. After STS gene transfer into cultured basal cells from ichthyotic skin, the cells produce large amounts of enzymatically active steroid sulfatase protein. The subpopulation of transfected cells can be made to produce approximately 100 times more STS activity than normal keratinocytes. Keratinocytes from patients suffering from recessive X-linked ichthyosis display an abnormal phenotype when developing a multilayered tissue in culture: Initially an extensive burst of keratinization is observed, followed by rapid, premature shedding and degradation of most suprabasal cell layers, leaving a culture with hyperproliferative relatively immature keratinocytes. Transfection of these immature ichthyotic cells with the functional STS construct led to an increase in the amount of retained cell material in the culture medium, indicating an increased cell maturation. It is possible to genetically label individual transfected epidermal cells with a reporter gene. Cotransfection experiments with STS and reporter gene vectors show that the cohort of transfected cells had a tendency to develop less rapidly since they became overrepresented in the smaller size classes at the same time the total population was somewhat shifted toward higher cell sizes. We interpret these results as an indication that restoration of the enzymatic activity induces a more normal maturation of the transfected keratinocytes.

Arylsulfatases↗

PubMed1993

A rare disease-associated mutation in the medium-chain acyl-CoA dehydrogenase (MCAD) gene changes a conserved arginine, previously shown to be functionally essential in short-chain acyl-CoA dehydrogenase (SCAD).

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a serious and potentially fatal inherited defect in the beta-oxidation of fatty acids. Approximately 80% of patients with MCAD deficiency are homozygous for a single disease-causing mutation (G985). The remaining patients (except for a few cases worldwide) are compound heterozygous with G985 in one allele. By sequencing of cloned PCR-amplified MCAD cDNA from a G985 compound heterozygous patient, we identified a C-to-T transition at position 157 as the only change in the entire coding sequence of the non-G985 allele. The presence of the T157 mutation was verified in genomic DNA from the patient and her mother by a PCR-based assay. The mutation changes conserved arginine at position 28 (R28C) of the mature MCAD protein. The effect of the T157 mutation on MCAD protein was investigated by expression of mutant MCAD cDNA in COS-7 cells. On the basis of knowledge about the three-dimensional structure of the MCAD protein, we suggest that the mutation destroys a salt bridge between arginine28 and glutamate86, thereby affecting the formation of enzymatically active protein. Twenty-two additional families with compound heterozygous patients were tested in the PCR-based assay. The T157 mutation was identified in one of these families, which had an MCAD-deficient child who died unexpectedly in infancy. Our results indicate that the mutation is rare. It is, however, noteworthy that a homologous mutation has previously been identified in the short-chain acyl-CoA dehydrogenase (SCAD) gene of a patient with SCAD deficiency, suggesting that the conserved arginine is crucial for formation of active enzyme in the straight-chain acyl-CoA dehydrogenases.

Acyl-CoA Dehydrogenase↗

PubMed1992

Expression of wild-type and mutant medium-chain acyl-CoA dehydrogenase (MCAD) cDNA in eucaryotic cells.

An effective EBV-based expression system for eucaryotic cells has been developed and used for the study of the mitochondrial enzyme medium-chain acyl-CoA dehydrogenase (MCAD). 1325 bp of PCR-generated MCAD cDNA, containing the entire coding region, was placed between the SV40 early promoter and polyadenylation signals in the EBV-based vector. Both wild-type MCAD cDNA and cDNA containing the prevalent disease-causing mutation A to G at position 985 of the MCAD cDNA were tested. In transfected COS-7 cells, the steady state amount of mutant MCAD protein was consistently lower than the amount of wild-type human enzyme. The enzyme activity in extracts from cells harbouring the wild-type MCAD cDNA was dramatically higher than in the controls (harbouring the vector without the MCAD gene) while only a slightly higher activity was measured with the mutant MCAD. The mutant MCAD present behaves like wild-type MCAD with respect to solubility, subcellular location, mature protein size and tetrameric structure. In immunoblot comparisons, the MCAD protein was present in normal fibroblasts, but essentially undetectable in patient fibroblasts homozygous for the prevalent mutation. We suggest that the MCAD protein carrying this mutation has an impaired ability to form correct tetramers, leading to instability and subsequent degradation of the enzyme. This finding is discussed in relation to the results from expression of human MCAD in Escherichia coli, where preliminary results show that production of mutant MCAD leads to the formation of aggregates.

Acyl-CoA Dehydrogenase↗