Contribution of estrogen receptors alpha and beta to the effects of estradiol in the brain.

Clinical and experimental studies show a modulatory role of estrogens in the brain and suggest their beneficial action in mental and neurodegenerative diseases. The estrogen receptors ERalpha and ERbeta are present in the brain and their targeting could bring selectivity and reduced risk of cancer. Implication of ERs in the effect of estradiol on dopamine, opiate and glutamate neurotransmission is reviewed. The ERalpha agonist, PPT, is shown as estradiol to modulate hippocampal NMDA receptors and AMPA receptors in cortex and striatum of ovariectomized rats whereas the ERbeta agonist DPN is inactive. Striatal DPN activity suggests implication of ERbeta in estradiol modulation of D2 receptors and transporters in ovariectomized rats and is supported by the lack of effect of estradiol in ERbeta knockout (ERKObeta) mice. Both ERalpha and ERbeta agonists modulate striatal preproenkephalin (PPE) gene expression in ovariectomized rats. In male mice PPT protects against MPTP toxicity to striatal dopamine; this implicates Akt/GSK3beta signaling and the apoptotic regulators Bcl2 and Bad. This suggests a role for ERalpha in striatal dopamine neuroprotection. ERKOalpha mice are more susceptible to MPTP toxicity and not protected by estradiol; differences in ERKObeta mice are subtler. These results suggest therapeutic potential for the brain of ER specific agonists.

Structural and functional analysis of missense mutations in fumarylacetoacetate hydrolase, the gene deficient in hereditary tyrosinemia type 1.

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease caused by a deficiency of the enzyme involved in the last step of tyrosine degradation, fumarylacetoacetate hydrolase (FAH). Thus far, 34 mutations in the FAH gene have been reported in various HT1 patients. Site-directed mutagenesis of the FAH cDNA was used to investigate the effects of eight missense mutations found in HTI patients on the structure and activity of FAH. Mutated FAH proteins were expressed in Escherichia coli and in mammalian CV-1 cells. Mutations N16I, F62C, A134D, C193R, D233V, and W234G lead to enzymatically inactive FAH proteins. Two mutations (R341W, associated with the pseudo-deficiency phenotype, and Q279R) produced proteins with a level of activity comparable to the wild-type enzyme. The N16I, F62C, C193R, and W234G variants were enriched in an insoluble cellular fraction, suggesting that these amino acid substitutions interfere with the proper folding of the enzyme. Based on the tertiary structure of FAH, on circular dichroism data, and on solubility measurements, we propose that the studied missense mutations cause three types of structural effects on the enzyme: 1) gross structural perturbations, 2) limited conformational changes in the active site, and 3) conformational modifications with no significant effect on enzymatic activity.

Hepatocellular carcinoma despite long-term survival in chronic tyrosinaemia I.

Tyrosinaemia I (fumarylacetoacetate hydrolase deficiency) is an autosomal recessive inborn error of tyrosine metabolism that produces liver failure in infancy or a more chronic course of liver disease with cirrhosis, often complicated by hepatocellular carcinoma, in childhood or early adolescence. We studied a 37-year-old woman with tyrosinaemia I whose severe liver disease in infancy and rickets during childhood resolved with dietary therapy. From 14 years of age she resumed an unrestricted diet with the continued presence of the biochemical features of tyrosinaemia, yet maintained normal liver function. In adult years she accumulated only small amounts of succinylacetone. Despite this evolution to a mild biochemical and clinical phenotype, she eventually developed hepatocellular carcinoma. Her fumarylacetoacetate hydrolase genotype consists of a splice mutation, IVS6-1g>t, and a novel missense mutation, Q279R. Studies of resected liver demonstrated the absence of hydrolytic activity and of immunological expression of fumarylacetoacetate hydrolase in liver tumour. In nontumoral areas, however, 53% of normal hydrolytic activity and immunologically present fumarylacetoacetate hydrolase was found. This case demonstrates the high risk of liver cancer in tyrosinaemia I even in a seemingly favourable biological environment.