Osmoregulation of GPC:choline phosphodiesterase in MDCK cells: different effects of urea and NaCl

The organic osmolyte, glycerophosphocholine (GPC), accumulates in renal cells in response to high concentrations of either NaCl or urea, despite the very different effects of these solutes on cell function and volume. Together, high levels of these solutes increase GPC amount in Madin-Darby canine kidney cells by inhibiting its enzymatic degradation. The present study tests the effects of NaCl and urea, individually, on GPC accumulation and its degradation. A technique was developed to determine the absolute rate of GPC degradation by measuring the initial rate of disappearance of [3H]GPC (pulsed into the cells by hypotonic shock) and the specific activity of GPC in the cells. The mass of GPC in the cells was measured by another newly developed method, a sensitive chemiluminescent assay. We find that exposure to high NaCl or urea decreases the absolute rate of cellular GPC degradation by approximately one-half during the first 20.5 h. Reductions in GPC degradation are accompanied by commensurate decreases in the activity of GPC:choline phosphodiesterase (GPC:PDE; EC 3.1.4.2), an enzyme that catalyzes degradation of GPC. Activity of GPC:PDE falls > 50% in cells exposed for 2 h to high osmolality. Inhibition is sustained for 7 days with high urea alone. In contrast, with high NaCl alone, GPC:PDE activity reverts to control values by 7 days, by which time synthesis of GPC is increased, accounting for sustained GPC accumulation. Collectively, these data suggest that GPC accumulation in response to either high NaCl or urea occurs initially by inhibition of its degradation but that the effect of NaCl on degradation differs, in that it is transient, while that of urea is sustained.

Osmotic regulation of synthesis of glycerophosphocholine from phosphatidylcholine in MDCK cells

Glycerophosphocholine (GPC) is osmotically regulated in renal medullary cells and in cultured Madin-Darby canine kidney (MDCK) cells. Previously, it was shown that a high extracellular concentration of urea or NaCl causes these cells to accumulate large amounts of GPC. GPC is known to be a product of phosphatidylcholine (PC) catabolism. The purpose of the present experiments was to examine the role of changes in the rate of GPC synthesis from PC in hyperosmotically induced GPC accumulation. When 1-palmitoyl-2-lysophosphatidyl-[methyl-3H]choline ([3H]LPC) is added to the medium, it is taken up by the cells and most of it is rapidly converted to PC. During a chase, 3H lost from PC appears almost exclusively in GPC and sphingomyelin. The rate of catabolism of PC is twofold greater in cells exposed to high NaCl (200 mosmol/kgH2O, added for 2 days) than in control or high-urea medium. Increased PC catabolism in NaCl-treated cells is associated with a 2.6-fold increase in GPC synthesis from PC; sphingomyelin synthesis decreases, and total cell PC does not change. Also, neither total mass nor specific radioactivity of lysophosphatidylcholine changes. PC catabolism is unaffected by short (2 h) exposure to high NaCl or urea. To investigate the enzymatic basis for the increased PC catabolism in response to high NaCl, phospholipase activity was measured in cell homogenates with 1-palmitoyl-2-[1-14C]palmitoyl-PC as a substrate. Exposure of cells to high NaCl for 2 days (but not 2 h) increases activity 2.8-fold compared with control or high-urea medium. Lysophospholipase activity (measured with [3H]LPC as the substrate) is unchanged. The increased phospholipase activity occurs with dipalmitoyl PC, but not sn-2-arachidonyl PC, as a substrate. Collectively, these data suggest a role for a phospholipase, unrelated to the arachidonyl-selective enzyme, in the regulation of PC catabolism during accumulation of GPC induced by prolonged exposure to high extracellular NaCl.

Cloning, genomic organization, and osmotic response of the aldose reductase gene

Diverse organisms accumulate organic osmolytes to adapt to hyperosmotic stress. The molecular basis of eukaryotic gene osmoregulation remains obscure. Aldose reductase [AR; alditol:NAD(P)+ 1-oxidoreductase, EC 1.1.1.21], which catalyzes the conversion of glucose to sorbitol (an organic osmolyte), is induced in renal medullary cells under hyperosmotic conditions. Elevated extracellular NaCl increases AR mRNA transcription in PAP-HT25 cells, a cell line derived from the rabbit renal papilla. We have cloned and characterized the rabbit AR gene to determine how it is regulated by hyperosmolality. The length of the gene, not including 5' or 3' flanking regions, is approximately 14.7 kilobases (kb) organized into 10 exons and 9 introns. The transcription start site is 36 base pairs upstream of the initiator methionine codon. A 5-kb fragment containing approximately 3.5 kb of 5' flanking region was isolated. The 3.5-kb sequence was examined for basal promoter activity and hyperosmotic response in luciferase reporter gene constructs. A 235-base-pair fragment (base pairs -208 to +27) was able to drive the downstream reporter gene in transfected PAP-HT25 cells under isoosmotic conditions (300 mosmol/kg of H2O). When this fragment plus the remaining upstream sequence (from approximately base pair -3429 to base pair +27) was used, cells in hyperosmotic medium (500 mosmol/kg of H2O) showed about 40-fold induction of luciferase expression compared with cells in isoosmotic medium. The upstream fragment (from approximately base pair -3429 to base pair -192) also conferred osmotic response to a heterologous promoter (B19). This finding evidences putative osmotic response element(s) (OREs) within a specific DNA fragment in a eukaryotic genome. Identification and characterization of OREs within this fragment and their associated trans-acting factors should reveal the molecular mechanisms of gene regulation in osmotic stress.

Induction of gene expression by heat shock versus osmotic stress

Elevated temperature rapidly increases expression of genes for heat shock proteins (HSP), including HSP-70. The response is presumably triggered by denaturation of cell proteins and helps in their renaturation. Hypertonicity may also denature proteins, but the protective response, which is accumulation of compatible organic osmolytes [including betaine and inositol in Madin-Darby canine kidney (MDCK) cells], apparently differs and is slow. Recently, hypertonicity was found also to increase expression of HSP-70 in MDCK cells, a response proposed to provide protection until organic osmolytes can accumulate. Our purpose was to examine whether 1) a gene involved in accumulation of organic osmolytes also responds to heat stress and 2) whether accumulation of organic osmolytes affects expression of HSP-70. We find that 1) the betaine transporter mRNA, which is greatly increased by hypertonicity (515 vs. 315 mosmol), is unaffected by high temperature (42 degrees C vs. 37 degrees C); 2) hypertonicity-induced increases in HSP-70 and betaine transporter mRNA are much greater when the medium (and cell) contain no betaine and no inositol than when high concentrations of these are present; and 3) high betaine greatly inhibits the increase in HSP-70 mRNA at high temperature. We conclude the following. 1) Although heat shock and betaine transporter genes both respond to hypertonicity, the betaine transporter is not a HSP. 2) Accumulation of organic osmolytes attenuates the HSP-70 response to hypertonicity, as it might if the HSP-70 expression were a temporizing response. 3) Betaine inhibits HSP-70 response to elevated temperature, presumably by its known effect of stabilizing proteins.

Neuropsychological evaluation of children with intracranial tumors: impact of treatment modalities

Antineoplastic treatment has a deleterious effect on intellectual functions, which is mainly attributable to radiotherapy. With the object of determining the neuropsychological disturbances associated with brain irradiation in the child, and to try to differentiate them from the effects caused by the other types of treatment (surgical and chemotherapy) as well as from the effects of the tumor itself, a cross-sectional study was carried out in 25 survivors of medial edge intracranial tumors. In order to monitor the effect of systemic chemotherapy on the cognitive functions, and the effect of prolonged absence from school, two control groups were formed, one made up of subjects treated with chemotherapy for extracranial tumors, and the other of patients with non-malignant chronic disease. Neuropsychological functions were measured using the Spanish version of the Wechsler scale, as well as the following tests: Spreen-Benton, ITPA and TALE scales, Yuste Memory Test, Thurstone Attention Test, and the Rey Complex Figure. In addition to a progressive decline found in the full scale intelligence quotient in children irradiated for intracranial tumors, variance analysis showed that these patients deteriorate mainly in visual attention and memory, but also significantly in verbal fluency and in the Performance Intelligence Quotient and all its subtests, when compared to the control groups. Visual attention and the Wechsler Picture Arrangement and Block Designs, were the tests whose decline correlated with the total radiation administered. The article relates this specific neuropsychological injury with the total brain irradiation dose but also with the structures located in the cone-down fields of irradiation to boost regions in the middle edge intracranial content.

Self-inflicted tongue ulcer: an unusual form of factitious disorder

Factitious disorders in the buccal cavity are infrequent. A 9-year-old boy with a 5-year history of an artefact ulcer of the tongue is described. Psychiatric evaluation revealed an altered personality structure with a background of psychotic traits. Complete remission was observed with psychiatric management.

[Familial chronic mucocutaneous candidiasis. Study of 2 families]

Four cases of familial mucocutaneous candidiasis corresponding to two families were studied. In two of the cases (Family I), there were lesions in the mouth, vaginal mucosa, nails, palms and soles, with no other associated infections. In the other two cases (Family II) there were oral (glossitis with macroglossia), genital and inguinal folds lesions, associated to frequent bacterial infections (recurring forunculosis , pneumonia). The immunological study in the four cases showed overlapping results: anti-candida circulating antibodies at high dilutions, a negative or weakly positive candidine a negative TTL to candida in some of the cases, and not other abnormalities in T. lymphocytes. All of the cases became sensitive to DNCB. In two of them, there were low figures of ferritin (Family II); however, no improvement was obtained with an iron treatment. There were no endocrinological abnormalities in any case. All of the cases were cured with ketoconazole in a few months, and no relapse was found six months after the end of the treatment in one of them. A follow up could not be performed on the other three cases.

Pretibial epidermolysis bullosa: report of two families and review of the literature

Two pretibial epidermolysis bullosa families, with a total of four cases directly examined and another eight cases known from references, were studied. Both families showed an autosomal dominant inheritance. In one family there was a case of "bullous epidermolysis albo-papular of Pasini". All cases were compared with those of the literature.