In extrahepatic tissues lipoprotein lipase (LPL) hydrolyzes triglycerides thereby generating FFA for tissue uptake and metabolism. To study the effects of increased FFA uptake in muscle tissue, transgenic mouse lines were generated with a human LPL minigene driven by the promoter of the muscle creatine kinase gene. In these mice human LPL was expressed in skeletal muscle and cardiac muscle, but not in other tissues. In proportion to the level of LPL overexpression, decreased plasma triglyceride levels, elevated FFA uptake by muscle tissue, weight loss, and premature death were observed in three independent transgenic mouse lines. The animals developed a severe myopathy characterized by muscle fiber degeneration, fiber atrophy, glycogen storage, and extensive proliferation of mitochondria and peroxisomes. This degree of proliferation suggests that FFA play an important role in the biogenesis of these organelles. Our experiments indicate that LPL is rate limiting for the supply of muscle tissue with triglyceride-derived FFA. Improper regulation of muscle LPL can lead to major pathological changes and may be important in the pathogenesis of some human myopathies. Muscle-specific LPL transgenic mouse lines will serve as a useful animal model for the investigation of myopathies and the biogenesis of mitochondria and peroxisomes. (J. Clin. Invest. 1995. 96:976-986.)

Lp(a) is a plasma lipoprotein particle consisting of a plasminogenlike protein [apo(a)

Plasma Lp(a) levels correlate with atherosclerosis susceptibility. This lipoprotein consists of an LDL-like particle attached to a large glycoprotein called apo(a). Apo(a) is a complex glycoprotein containing multiple Kringle domains, found to be highly homologous to plasminogen Kringle IV, and a single Kringle domain homologous to plasminogen Kringle V. Lp(a) levels appear to be inversely correlated with apo(a) size in a given individual. In this study, we have used probes specific to the Kringles IV and V domains of apo(a) cDNA in quantitative Southern blotting analysis. By this method, we have determined the ratio of Kringle IV/Kringle V encoding domains in the apo(a) gene of 53 unrelated individuals with different plasma concentrations of Lp(a). This ratio was found to be inversely correlated with log Lp(a) levels (r = -0.90, P < 0.0001) and directly correlated with apo(a) apparent molecular weight (Mr) (r = 0.79, P < 0.0001). In summary, by showing that Lp(a) concentrations and apo(a) apparent size are highly correlated with the ratio of Kringle IV/Kringle V encoding domains in the apo(a) gene, we provide a DNA marker for this atherosclerosis risk factor as well as an important insight into the genetic mechanism regulating Lp(a) levels.

We have isolated cDNA clones encoding human apolipoprotein (apo) A-I. Twenty putative apo A-I cDNA clones were selected by screening 10,000 clones of an adult human liver cDNA library with an oligonucleotide probe. The probe was a mixture of synthetic 14-base-long DNA oligomers constructed to correspond to the codons for apo A-I amino acids 105-109. Four of these clones were examined further and showed 600-to 800-base-pair (bp) inserts. Preliminary restriction mapping and partial DNA sequence analysis indicated that the shorter inserts were a subset of the longer DNA inserts. DNA sequence analysis of the clone with an insert of -600 bp, designated pAl-113, revealed that it contained a DNA sequence corresponding to apo A-I amino acids 94-243. The DNA base sequence of this clone also contained a standard termination codon, polyadenylylation signal, and poly(A) tail. Partial DNA sequence ofa second clone that contained an 800-bp insert, designated pAI-107, showed that it corresponded to apo A-I amino acids 18-243 and also included the 3' untranslated region. Isolation of these cDNA clones will facilitate molecular analyses of apolipoproteins in normal and disease states.

A method for analyzing individual mammalian cells with electron probe microanalysis has been developed using human diploid fibroblasts. Cells were grown on the same support that is used for experimental manipulations and analysis. Steady-state cation and anion concentrations and kinetic processes during experimental perturbations could be measured on populations of less than 1,000 cells. Human diploid fibroblasts in normal tissue culture medium had the following intracellular concentrations (in mM): K, 168; Na, 25.0; Cl, 51.2; P, 84.1; S, 16.5; Ca, 6.04; and Mg, 10.0. The ratios of K to Na were equivalent when measured in the nuclear or cytoplasmic area of the cells. Serum in the incubation medium was found to increase the cellular effective permeability to Na by a factor of 2.5, while leaving the effective permeability to K unchanged. When returned to control medium after 7 h of incubation in K-free medium, the cells recovered normal K/Na in less than 1 h. In some experiments the coupling ratio of the ouabain-inhibitable cellular transport of Na to K was 3:2 and the ratio of Cl to K was 1:2. The sum of intracellular content (Na + K) (an estimate of cellular volume) did not change when the cells were placed in K-free medium and increased by less than 30% after ouabain treatment. After 5-7 h of ouabain treatment or of incubation in K-free medium, long after the intracellular K had been replaced by Na, the cellular chloride content had not changed significantly.