It has been hypothesized that insulin resistance is mediated by a deficiency of mitochondria in skeletal muscle. In keeping with this hypothesis, high-fat diets that cause insulin resistance have been reported to result in a decrease in muscle mitochondria. In contrast, we found that feeding rats high-fat diets that cause muscle insulin resistance results in a concomitant gradual increase in muscle mitochondria. This adaptation appears to be mediated by activation of peroxisome proliferator-activated receptor (PPAR)␦ by fatty acids, which results in a gradual, posttranscriptionally regulated increase in PPAR ␥ coactivator 1␣ (PGC-1␣) protein expression. Similarly, overexpression of PPAR␦ results in a large increase in PGC-1␣ protein in the absence of any increase in PGC-1␣ mRNA. We interpret our findings as evidence that raising free fatty acids results in an increase in mitochondria by activating PPAR␦, which mediates a posttranscriptional increase in PGC-1␣. Our findings argue against the concept that insulin resistance is mediated by a deficiency of muscle mitochondria.I t has been hypothesized that insulin resistance in patients with impaired or diabetic glucose tolerance is mediated by a deficiency of mitochondria in skeletal muscle (1, 2). The mechanism by which a decrease in mitochondria is proposed to cause insulin resistance is accumulation of intramyocellular lipids caused by a decrease in the capacity to oxidize fat (2). This hypothesis is based on the finding that type 2 diabetics and insulin-resistant individuals with impaired glucose tolerance have Ϸ30% less mitochondria in their muscles than insulinsensitive control subjects (3-7). In support of this concept, recent studies have reported that raising serum free fatty acids (FFA) by a high-fat diet in humans (8), or by feeding mice or rats high-fat diets (8-10), results in decreases in skeletal muscle peroxisome proliferator-activated receptor ␥ coactivator-1␣ (PGC-1␣) mRNA (8-10) and the mRNA levels of various mitochondrial constituents (8). In contrast, a number of earlier studies provided evidence that high-fat diets induce increases in mitochondrial marker enzymes (11-14), and Turner et al. (15) recently reported that a high-fat diet resulted in increases in mitochondrial biogenesis and fatty acid oxidative capacity in skeletal muscle of mice.We have found that raising serum FFA in rats by feeding them a high-fat diet and giving them daily heparin injections results in an increase in muscle mitochondria (16). The initial purpose of the present study was to determine whether the more modest increase in FFA induced by a high-fat diet also results in increased mitochondrial biogenesis with an increase in the capacity of muscle to oxidize fat. We found that a high-fat diet does induce an increase in muscle mitochondria. This finding made it possible to evaluate whether a high-fat diet causes muscle insulin resistance despite increases in mitochondria and fat oxidative capacity.Overexpression of peroxisome proliferator-activated receptor (PPAR)␦ i...

The ABO blood group is of great importance in blood transfusion and organ transplantation. However, the mechanisms regulating human ABO gene expression remain obscure. On the basis of DNase I-hypersensitive sites in and upstream of ABO in K562 cells, in the present study, we prepared reporter plasmid constructs including these sites. Subsequent luciferase assays indicated a novel positive regulatory element in intron 1. This element was shown to enhance ABO promoter activity in an erythroid cellspecific manner. Electrophoretic mobilityshift assays demonstrated that it bound to the tissue-restricted transcription factor GATA-1. Mutation of the GATA motifs to abrogate binding of this factor reduced the regulatory activity of the element. Therefore, GATA-1 appears to be involved in the cell-specific activity of the element.

In the single radial enzyme-diffusion (SRED) method for assay of deoxyribonuclease I, a precisely measured volume of the enzyme solution is dispensed into a circular well in an agarose gel layer in which DNA and ethidium bromide are uniformly distributed. A circular dark zone is formed as the enzyme diffuses from the well radially into the gel and digests substrate DNA. The diameter of the dark circle of hydrolyzed DNA increases in size with time and correlates linearly with the amount of enzyme applied to the well. Thus, the SRED can be used for quantitation of deoxyribonuclease I with a limit of detection of 2 x 10(-6) unit. This corresponds to 1 pg of purified urine deoxyribonuclease I. We measured the deoxyribonuclease I activity of 17 different human tissues and body fluids from healthy donors. Urine samples showed the greatest activity, 6.0 +/- 2.2 kilo-units/g protein (mean +/- SD). Serum deoxyribonuclease I activity was 4.4 +/- 1.8 units/L.

A deoxyribonuclease I was purified from the urine of a 46-year-old male (a single individual) by using a series of column chromatographies to a homogeneous state as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme was found to be a glycoprotein, containing 1 fucose, 7 galactose, 10 mannose, 6 glucosamine, and 2 sialic acid residues per molecule. The N-terminal amino acid sequence up to the 27th residue of the enzyme was similar to that of pancreatic deoxyribonuclease I from bovine and other species. The catalytic properties of the enzyme derived from a single individual closely resembled those of deoxyribonuclease I purified from human urine collected from several volunteers [Ito, K. et al. (1984) J. Biochem. 95, 1399-1406]. The purified enzyme was found to consist of multiple forms with different pI values. These findings are compatible with the existence of genetic polymorphism of deoxyribonuclease I in human urine previously reported [Kishi, K. et al. (1989) Hum. Genet. 81, 295-297]. This multiplicity of the urine enzyme might be due to variations in the primary structure and/or differences in the content of sialic acid.

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These observations suggest that the mutation in the GATA motif of the erythroid-specific regulatory element may diminish the binding of GATA transcription factors and down regulate transcriptional activity of the element on the B allele, leading to reduction of B antigen expression in erythroid lineage cells of the Bm individual.

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