The odyssey of a young gene: structure-function studies in human glutamate dehydrogenases reveal evolutionary-acquired complex allosteric regulation mechanisms.

Mammalian glutamate dehydrogenase (GDH) catalyzes the reversible inter-conversion of glutamate to α-ketoglutarate and ammonia, interconnecting carbon skeleton and nitrogen metabolism. In addition, it functions as an energy switch by its ability to fuel the Krebs cycle depending on the energy status of the cell. As GDH lies at the intersection of several metabolic pathways, its activity is tightly regulated by several allosteric compounds that are metabolic intermediates. In contrast to other mammals that have a single GDH-encoding gene, humans and great apes possess two isoforms of GDH (hGDH1 and hGDH2, encoded by the GLUD1 and GLUD2 genes, respectively) with distinct regulation pattern, but remarkable sequence similarity (they differ, in their mature form, in only 15 of their 505 amino-acids). The GLUD2 gene is considered a very young gene, emerging from the GLUD1 gene through retro-position only recently (<23 million years ago). The new hGDH2 iso-enzyme, through random mutations and natural selection, is thought to have conferred an evolutionary advantage that helped its persistence through primate evolution. The properties of the two highly homologous human GDHs have been studied using purified recombinant hGDH1 and hGDH2 proteins obtained by expression of the corresponding cDNAs in Sf21 cells. According to these studies, in contrast to hGDH1 that maintains basal activity at 35-40 % of its maximal, hGDH2 displays low basal activity that is highly responsive to activation by rising levels of ADP and/or L-leucine which can also act synergistically. While hGDH1 is inhibited potently by GTP, hGDH2 shows remarkable GTP resistance. Furthermore, the two iso-enzymes are differentially inhibited by estrogens, polyamines and neuroleptics, and also differ in heat-lability. To elucidate the molecular mechanisms that underlie these different regulation patterns of the two iso-enzymes (and consequently the evolutionary adaptation of hGDH2 to a new functional role), we have performed mutagenesis at sites of difference in their amino acid sequence. Results showed that the low basal activity, heat-lability and estrogen sensitivity of hGDH2 could be, at least partially, ascribed to the Arg443Ser evolutionary change, whereas resistance to GTP inhibition has been attributed to the Gly456Ala change. Other amino acid substitutions studied thus far cannot explain all the remaining functional differences between the two iso-enzymes. Also, the Arg443Ser/Gly456Ala double mutation in hGDH1 approached the properties of wild-type hGDH2, without being identical to it. The insights into the structural mechanism of enzymatic regulation and the implications in cell biology provided by these findings are discussed.

The Cretan Aging Cohort: Cohort Description and Burden of Dementia and Mild Cognitive Impairment.

Our aim was to explore the burden of dementia in the Cretan Aging Cohort, comprised of 3140 persons aged ≥60 years (56.8% women, 5.8 ± 3.3 years formal education, 86.2% living in rural areas) who attended selected primary health-care facilities on the island of Crete, Greece. In the first study phase, a formal diagnosis of dementia had been reached in 4.0% of the participants. However, when selected 505 participants underwent thorough neuropsychiatric evaluation in the second phase of this study (344 with Mini-Mental State Examination [MMSE] <24 and 161 with MMSE ≥24), and results were extrapolated to the entire cohort, the prevalence of dementia and mild cognitive impairment was estimated at 10.8% (9.7%-11.9%) and 32.4% (30.8%-34.0%), respectively. Using both the field diagnostic data and the extrapolated data, the highest dementia prevalence (27.2%) was found in the 80- to 84-year-old group, who also showed the lowest educational level, apparently due to lack of schooling during World War II.

Cerebrovascular events in inflammatory bowel disease patients treated with anti-tumour necrosis factor alpha agents.

BACKGROUND AND AIMS: Cerebrovascular accidents [CVA] have rarely been reported in inflammatory bowel disease [IBD] patients treated with anti-tumour necrosis alpha [anti-TNF alpha] agents. Our aim here was to describe the clinical course of CVA in these patients. METHODS: This was a European Crohn's and Colitis Organisation [ECCO] retrospective observational study, performed as part of the CONFER [COllaborative Network For Exceptionally Rare case reports] project. A call to all ECCO members was made to report on IBD patients afflicted with CVA during treatment with anti-TNF alpha agents. Clinical data were recorded in a standardised case report form and analysed for event association with anti-TNF alpha treatment. RESULTS: A total of 19 patients were identified from 16 centres: 14 had Crohn's disease, four ulcerative colitis and one IBD colitis unclassified [median age at diagnosis: 38.0 years, range: 18.6-62.5]. Patients received anti-TNF alpha for a median duration of 11.8 months [range: 0-62] at CVA onset; seven had previously been treated with at least one other anti-TNF alpha agent. Complete neurological recovery was observed in 16 patients. Anti-TNF alpha was discontinued in 16/19 patients. However, recurrent CVA or neurological deterioration was not observed in any of the 11 patients who received anti-TNF alpha after CVA [eight resumed after temporary cessation, three continued without interruption] for a median follow-up of 39.8 months [range: 5.6-98.2]. CONCLUSION: These preliminary findings do not unequivocally indicate a causal role of anti-TNF alpha in CVA complicating IBD. Resuming or continuing anti-TNF alpha in IBD patients with CVA may be feasible and safe in selected cases, but careful weighing of IBD activity versus neurological status is prudent.