We examined the hypothesis that senescence represents a proximate mechanism by which the kidney is damaged in type 2 diabetic nephropathy (DN). As a first step, we studied whether the senescence-associated ␤-galactosidase (SA-␤-Gal) and the cell cycle inhibitor p16INK4A are induced in renal biopsies from patients with type 2 DN. SA-␤-Gal staining was approximately threefold higher (P Ͻ 0.05) than in controls in the tubular compartment of diabetic kidneys and correlated directly with body mass index and blood glucose. P16INK4A expression was significantly increased in tubules (P Ͻ 0.005) and in podocytes (P ϭ 0.04). Nuclear p16 INK4A in glomeruli was associated with proteinuria (P Ͻ 0.002), while tubular p16INK4A was directly associated with body mass index, LDL cholesterol, and HbA1c (P Ͻ 0.001-0.05). In a parallel set of experiments, proximal tubule cells passaged under high glucose presented a limited life span and an approximately twofold increase in SA-␤-Gal and p16INK4A protein. Mean telomere lengths decreased ϳ20% as an effect of replicative senescence. In addition, mean telomere decreased further by ϳ30% in cells cultivated under high glucose. Our results show that the kidney with type 2 diabetic nephropathy displays an accelerated senescent phenotype in defined renal cell types, mainly tubule cells and, to a lesser extent, podocytes. A similar senescent pattern was observed when proximal tubule cell cultures where incubated under highglucose media. These changes are associated with shortening tubular telomere length in vitro. These findings indicate that diabetes may boost common pathways involving kidney cell senescence, thus reinforcing the role of the metabolic syndrome on biological aging of tissues. tubular cells; telomeres; p16 INK4A ; senescence-associated ␤-galactosidase AGING has been proposed to represent the failure or success of tumor-suppressor mechanisms that depend on the activities of the cyclin-dependent kinase inhibitor p16INK4A and of telomere shortening (2). It has been theorized that the high frequency of end-stage renal disease in the elderly results from an interaction between somatic cell senescence and age-associated diseases, such as hypertension and type 2 diabetes mellitus, which could hinder the limited ability of aged kidney to repair and maintain epithelial functions (24, 25). Cell senescence is characterized by an irreversible growth arrest and functional and morphological changes (2), including enhanced expression of senescence markers, such as senescence-associated ␤-galactosidase (SA-␤-Gal), and different sets of genes, including negative regulators of the cell cycle (2, 17, 18). In vitro studies support the hypothesis that diabetes may accelerate cell and organ senescence in humans. Hyperglycemia induces premature replicative senescence in human skin fibroblasts, an effect that is tightly coupled to larger cell volume in skin fibroblasts from patients with diabetic nephropathy (3, 21). In addition, a role of hyperglycemia in kidney cell senescence has been observed in ...

Purified enzymes were mixed to form a cell-free system that simulated the conditions for removal of hydrogen peroxide within human erythrocytes. Human glutathione peroxidase disposed of hydrogen peroxide (H2O2) at a rate that was only 17% of the rate at which human catalase simultaneously removed hydrogen peroxide. The relative rates observed were in agreement with the relative rates predicted from the kinetic constants of the two enzymes. These results confirm two earlier studies on intact erythrocytes, which refuted the notion that glutathione peroxidase is the primary enzyme for removal of hydrogen peroxide within erythrocytes. The present findings differ from the results with intact cells, however, in showing that glutathione peroxidase accounts for even less than 50% of the removal of hydrogen peroxide. A means is proposed for calculating the relative contribution of glutathione peroxidase and catalase in other cells and species. The present results raise the possibility that the major function of glutathione peroxidase may be the disposal of organic peroxides rather than the removal of hydrogen peroxide.

Mutations of the presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer disease (FAD). PS1 mutations alter the activity of the ␥-secretase on the ␤-amyloid precursor protein (APP), leading to selective overproduction of ␤-amyloid (A␤) 42 peptides, the species that forms oligomers that may exert toxic effects on neurons. Here we show that PS1 mutations, expressed both transiently and stably, in non-neuronal and neuronal cell lines increase the expression and the activity of the ␤-secretase (BACE1), the rate-limiting step of A␤ production. Also, BACE1 expression and activity are elevated in brains of PS1 mutant knock-in mice compared with wild type littermates as well as in cerebral cortex of FAD cases bearing various PS1 mutations compared with in sporadic AD cases and controls. The up-regulation of BACE1 by PS1 mutations requires the ␥-secretase cleavage of APP and is proportional to the amount of secreted A␤42. A␤42, and not AICD (APP intracellular domain), is indeed the APP derivative that mediates the overexpression of BACE1. The effect of PS1 mutations on BACE1 may contribute to determine the wide clinical and pathological phenotype of early onset FAD.The ␤-amyloid peptide (A␤) 2 that accumulates in vulnerable brain regions in Alzheimer disease (AD) is released from the ␤-amyloid precursor protein (APP) by sequential cleavages by ␤-secretase and ␥-secretase. A single protein called BACE1 is responsible for ␤-secretase activity, whereas ␥-secretase involves at least four proteins including a catalytic subunit called presenilin-1 (PS1) (1, 2). Mutations of PS1 are the most common cause of early onset familial AD (FAD). The known effect of PS1 mutations on APP processing is the increased production of A␤ species ending at residue 42, which aggregates faster than the A␤40 isoform and accumulates in the brain in the state of soluble low molecular weight oligomers (3, 4). Small, soluble, and diffusible aggregates composed of a mixture of full-length and N-terminal-truncated A␤42 species appear early in the cerebral cortex of subjects at risk of Alzheimer disease pathology (5). The rate of accumulation as well as the properties of aggregation and toxicity of cerebral soluble A␤ depend on the ratio of the three major A␤ species, 1-42, pyroglutamate 3-42, and pyroglutamate 11-42 (6). We have shown that, in the cerebral cortex of FAD cases with mutations of PS1, the relative percentage of the two N-terminal-truncated A␤ species is significantly increased in comparison to sporadic AD cases (7). A relative increase of N-terminal-truncated A␤ peptides also occurs in the brain of transgenic mice bearing a double PS1 mutation (8). When overexpressed in cell lines, BACE1 increases the production of A␤ 11-x (9) and A␤ 3-x peptides (10) in vitro. BACE1 has been found to be transcriptionally regulated by several different mechanisms involving various transcription factors and pathways (11)(12)(13)(14)(15), and given the complexity and richness in transcription factor recognition sites of its gene p...

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Influenza vaccine is effective and well tolerated in patients with CLPD and MM. No contraindications exist for its use, and it should become a routine practice, in order to prevent serious complications during the influenza epidemic season.

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

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