Diabetic nephropathy is the most common cause of endstage renal disease in the U.S. Recent studies demonstrate that loss of podocytes is an early feature of diabetic nephropathy that predicts its progressive course. Cause and consequences of podocyte loss during early diabetic nephropathy remain poorly understood. Here, we demonstrate that podocyte apoptosis increased sharply with onset of hyperglycemia in Ins2Akita (Akita) mice with type 1 diabetes and Lepr db/db (db/db) mice with obesity and type 2 diabetes. Podocyte apoptosis coincided with the onset of urinary albumin excretion (UAE) and preceded significant losses of podocytes in Akita (37% reduction) and db/db (27% reduction) mice. Increased extracellular glucose (30 mmol/l) rapidly stimulated generation of intracellular reactive oxygen species (ROS) through NADPH oxidase and mitochondrial pathways and led to activation of proapoptotic p38 mitogen-activated protein kinase and caspase 3 and to apoptosis of conditionally immortalized podocytes in vitro. Chronic inhibition of NADPH oxidase prevented podocyte apoptosis and ameliorated podocyte depletion, UAE, and mesangial matrix expansion in db/db mice. In conclusion, our results demonstrate for the first time that glucose-induced ROS production initiates podocyte apoptosis and podocyte depletion in vitro and in vivo and suggest that podocyte apoptosis/depletion represents a novel early pathomechanism(s) leading to diabetic nephropathy in murine type 1 and type 2 diabetic models. Diabetes 55: [225][226][227][228][229][230][231][232][233] 2006

The HIR/HPC (histone regulation/histone periodic control) negative regulators play important roles in the transcription of six of the eight core histone genes during the Saccharomyces cerevisiae cell cycle. The phenotypes of hir1 and hir2 mutants suggested that the wild-type HIR1 and HIR2 genes encode transcriptional repressors that function in the absence of direct DNA binding. When Hir1p and Hir2p were artificially tethered to yeast promoters, each protein repressed transcription, suggesting that they represent a new class of transcriptional corepressors. The two proteins might function as a complex in vivo: Hir2p required both Hir1p and another Hir protein, Hir3p, to repress transcription when it was tethered to an HTA1-lacZ reporter gene, and Hir1p and Hir2p could be coimmunoprecipitated from yeast cell extracts. Tethered Hir1p also directed the periodic transcription of the HTA1 gene and repressed HTA1 transcription in response to two cell cycle regulatory signals. Thus, it represents the first example of a transcriptional corepressor with a direct role in cell cycle-regulated transcription.Histone synthesis is tightly regulated in eukaryotes to ensure that the components for nucleosome assembly are present both at the correct time during the cell cycle and in the proper stoichiometric levels (39). Regulation at the level of transcription plays an important role in the synthesis of the core histones in Saccharomyces cerevisiae, and negative regulation has emerged as a significant mechanism in the transcription of six of the eight histone genes (HTA1-HTB1, HHT1-HHF1, and HHT2-HHF2) in this organism (39). A negative site has been identified in the promoters of each of the negatively regulated histone genes in close proximity to upstream activation sequence (UAS) elements (14, 41). The HTA1-HTB1 negative site has been shown to play a key role in cell cycle-regulated transcription: deletion of this site derepresses HTA1 and HTB1 transcription early in G 1 phase, late in S phase, and in G 2 /M phase, points in the cell cycle when the two genes are usually not expressed (41), and prevents the same genes from being repressed in S-phase cells when DNA replication has been interrupted (29). The same site is also required for a feedback repression pathway that is triggered by the overproduction of histones H2A and H2B (32). In its absence, HTA1 and HTB1 transcription is insensitive to the intracellular levels of these two histone proteins.Two related genetic screens have identified seven HIR and HPC (histone regulation and histone periodic control) genes whose products are postulated to encode repressors of HTA1-HTB1, HHT1-HHF1, and HHT2-HHF2 transcription (43, 64). Four of these genes (HIR1, HIR2, HIR3, and HPC2) have been isolated and extensively characterized (51,54,64). None of the genes is essential, and each appears to encode a novel polypeptide. Interestingly, the HIR1 and HIR2 genes have been evolutionarily conserved; the human homolog, HIRA, encodes a protein that encompasses structural features from both ye...

SummaryBackground and objectives Metabolic acidosis contributes to muscle breakdown in patients with CKD, but whether its treatment improves functional outcomes is unknown. The choice of dose and tolerability of high doses remain unclear. In CKD patients with mild acidosis, this study evaluated the dose-response relationship of alkali with serum bicarbonate, its side effect profile, and its effect on muscle strength. Conclusions NaHCO 3 supplementation produces a dose-dependent increase in serum bicarbonate and improves lower extremity muscle strength after a short-term intervention in CKD patients with mild acidosis. Long-term studies are needed to determine if this finding translates into improved functional status.

Mortality in ESRD remains unacceptably high. It is hoped that as knowledge emerges on the causes and consequences of uremia, we are embarking on an era not only of new insights but also new and effective treatments for patients with the ill effects of uremia.