The full induction of human apoprotein A-I gene expression by the experimental nephrotic syndrome in transgenic mice depends on cis-acting elements in the proximal 256 base-pair promoter region and the trans-acting factor early growth response factor 1

AMPK signaling pathway regulated the expression of the ApoA1 gene via the transcription factor Egr1 during G. parasuis stimulation

Glaesserella parasuis (G. parasuis) is the causative agent of porcine Glässer's disease, resulting in high mortality rates in pigs due to excessive inflammation-induced tissue damage. Previous studies investigating the protective effects of G. parasuis vaccination indicated a possible role of ApoA1 in reflecting disease progression following G. parasuis infection. However, the mechanisms of ApoA1 expression and its role in these infections are not well understood. In this investigation, newborn porcine tracheal (NPTr) epithelial cells infected with G. parasuis were used to elucidate the molecular mechanism and role of ApoA1. The study revealed that the AMPK pathway activation inhibited ApoA1 expression in NPTr cells infected with G. parasuis for the first time. Furthermore, Egr1 was identified as a core transcription factor regulating ApoA1 expression using a CRISPR/Cas9-based system. Importantly, it was discovered that APOA1 protein significantly reduced apoptosis, pyroptosis, necroptosis, and inflammatory factors induced by G. parasuis in vivo. These findings not only enhance our understanding of ApoA1 in response to bacterial infections but also highlight its potential in mitigating tissue damage caused by G. parasuis infection.

Analysis of the zebrafish sox9b promoter: Identification of elements that recapitulate organ-specific expression of sox9b

The SRY-related high-mobility box 9 (SOX9) gene is expressed in many different tissues. To better understand the DNA elements that control tissue-specific expression, we cloned and sequenced a 2.5 kb fragment lying 5' to the zebrafish sox9b gene transcriptional start site. Three regions of this clone contained stable secondary structures that hindered cloning, sequencing, and amplification. This segment and smaller fragmentswere inserted 5' of an EGFP reporter and transgenic fish were raised with the different reporters. Reporter expression was also observed in embryos directly injected with the constructs to transiently express the reporter. Heart expression required only a very short 5' sequence, as a 0.6 kb sox9b fragment produced reporter expression in heart in transgenic zebrafish, and transient experiments showed heart expression from a minimal sox9b promoter region containing a conserved TATA box and an EGR2 element (-74/+29 bp). Reporter expression in transgenic skeletal muscle was consistently lower than in other tissues. Jaw, brain, and notochord expression was strong with the full-length clone, but was dramatically reduced as the size of the fragment driving the reporter decreased from approximately 1.8 to 0.9 kb. The 2.5 kb region 5' of the sox9b contained 7 conserved non-coding elements (CNEs) that included putative hypoxia inducible factor 1α (HIF1α), CAAT box (CCAAT), early growth response protein 2 (EGR2), and core promoter elements. While a synthetic fragment containing all 7 CNEs produced some degree of reporter expression in muscle, jaw, heart and brain, the degree of reporter expression was considerably lower than that produced by the full length clone. These results can account for the tissue-specific expression of sox9b in the developing zebrafish.

Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational

HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.

RAGE: developmental expression and positive feedback regulation by Egr-1 during cigarette smoke exposure in pulmonary epithelial cells

The receptor for advanced glycation end-products (RAGE) is a member of the immunoglobin superfamily of multiligand receptors. Following ligand binding, mechanisms associated with host defense, tissue remodeling, and inflammation are activated. RAGE is highly expressed in pulmonary epithelium transitioning from alveolar type (AT) II to ATI cells and is upregulated in the presence of ligand; however, the regulation and function of RAGE during development are less clear. Herein, immunohistochemistry demonstrated a temporal-spatial pattern of RAGE expression in pulmonary epithelial cells from embryonic day 17.5 to postnatal day 10. Cotransfection experiments revealed that the mouse RAGE promoter was activated by early growth response gene 1 (Egr-1) and inhibited by thyroid transcription factor-1 (TTF-1) via interaction with specific regulatory elements. A rat ATI cell line (R3/1) with endogenous RAGE expression also differentially regulated RAGE when transfected with TTF-1 or Egr-1. Because Egr-1 is markedly induced in pulmonary epithelial cells exposed to cigarette smoke extract (CSE; Reynolds PR, Hoidal JR. Am J Respir Cell Mol Biol 35: 314-319, 2006.), we sought to investigate RAGE induction by CSE. Employing RT-PCR and Western blotting, RAGE and common ligands (amphoterin and S100A12) were upregulated in epithelial (R3/1 and A549) and macrophage (RAW) cell lines following exposure to CSE. Immunostaining for RAGE in cells similarly exposed and in lungs from mice exposed to cigarette smoke for 6 mo revealed elevated RAGE expression in pulmonary epithelium. After the addition of glyoxylated BSA, an advanced glycation end-product that binds RAGE, real-time RT-PCR detected a 200-fold increase in Egr-1. These results indicate that Egr-1 regulates RAGE expression during development and the likelihood of positive feedback involving Egr-1 and RAGE in cigarette smoke-related disease.

Cigarette smoke-induced Egr-1 upregulates proinflammatory cytokines in pulmonary epithelial cells

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death worldwide and is a progressive and irreversible disorder. Cigarette smoking is associated with 80-90% of COPD cases; however, the genes involved in COPD-associated emphysema and chronic inflammation are poorly understood. It was recently demonstrated that early growth response gene 1 (Egr-1) is significantly upregulated in the lungs of smokers with COPD (Ning W and coworkers, Proc Natl Acad Sci 2004;101:14895-14900). We hypothesized that Egr-1 is activated in pulmonary epithelial cells during exposure to cigarette smoke extract (CSE). Using immunohistochemistry, we demonstrated that pulmonary adenocarcinoma cells (A-549) and primary epithelial cells lacking basal Egr-1 markedly induce Egr-1 expression after CSE exposure. To evaluate Egr-1-specific effects, we used antisense (alphaS) oligodeoxynucleotides (ODN) to knock down Egr-1 expression. Incorporation of Egr-1 alphaS ODN significantly decreased CSE-induced Egr-1 mRNA and protein, while sense ODN had no effect. Via Egr-1-mediated mechanisms, IL-1beta and TNF-alpha were significantly upregulated in pulmonary epithelial cells exposed to CSE or transfected with Egr-1. To investigate the relationship between Egr-1 induction by smoking and susceptibility to emphysema, we determined Egr-1 expression in strains of mice with different susceptibilities for the development of smoking-induced emphysema. Egr-1 was markedly increased in the lungs of emphysema-susceptible AKR/J mice chronically exposed to cigarette smoke, but only minimally increased in resistant NZWLac/J mice. In conclusion, Egr-1 is induced by cigarette smoke and functions in proinflammatory mechanisms that likely contribute to the development of COPD in the lungs of smokers.

Glomerular and tubular epithelial defects in kd/kd mice lead to progressive renal failure

BACKGROUND/AIM

The kd/kd mouse spontaneously develops severe and progressive nephritis leading to renal failure, characterized by cellular infiltration, tubular destruction and glomerular sclerosis. Recent identification of the mutant gene and the observation that podocytes are affected, led to the hypothesis that there are primary renal epithelial cell defects in this strain.

METHODS

Clinical and pathological signs of disease in a large cohort of kd/kd mice were studied by light microscopy, electron microscopy, and biochemical analyses of serum and urine at early stages of disease. Special attention was paid to mice under 140 days of age that had normal blood urea nitrogen (BUN) levels, but had developed albuminuria.

RESULTS

Although overt glomerular abnormalities are commonly observed either coincident with or after tubulointerstitial nephritis, we now report that albuminuria and visceral epithelial abnormalities, including hyperplasia and podocyte effacement may occur before the onset of either elevated BUN levels or severe interstitial nephritis, and this is accompanied by biochemical perturbations in serum typical of the nephrotic syndrome.

CONCLUSIONS

The results suggest that the defect in kd/kd mice primarily affects both the tubular and glomerular visceral epithelium. The tubular epithelial defect triggers autoimmune interstitial nephritis, whereas a defect in podocytes leads to proteinuria and glomerulosclerosis. Thus, a single mitochondrial abnormality may result in differences in disease expression that vary with the type of epithelial cells. It is likely that the mitochrondrial perturbations in glomerular and tubular epithelia act in concert, through activation of different pathologic pathways, to accelerate disease progression leading to renal failure.

Regulation of apoA-I gene expression: mechanism of action of estrogen and genistein

We have previously shown that 17-beta-estradiol (E2) and genistein increase the expression of apolipoprotein A-I (apoA-I), the major protein component of HDL, in Hep G2 cells. To elucidate the mechanism mediating the increase in apoA-I gene expression by these compounds, plasmid constructs containing serial deletions of the apoA-I promoter region were generated. The smallest region maintaining response to E2 and genistein spanned the -220 to -148 sequence, and the estrogen antagonist ICI182,780 completely inhibited the E2 and genistein effect. Nuclear extracts from cells treated with E2 and genistein showed increased binding to site B oligonucleotide (-169 to -146), and nuclear extracts from genistein-treated cells showed increased binding to an early growth response factor 1 (Egr-1) oligonucleotide compared to control cells. An increase in the concentrations of Egr-1 and hepatocyte nuclear factor-3beta was observed in nuclear extracts of cells treated with both compounds compared to control cells. Treatment with a specific inhibitor of mitogen-activated protein (MAP) kinase, but not with other inhibitors, abolished the stimulation of apoA-I gene expression by E2 and genistein. These results indicate that the MAP kinase pathway is involved in the regulation of apoA-I gene expression by genistein and E2, possibly through downstream regulation of transcription factors binding to the promoter region.

Zinc depletion reduced Egr-1 and HNF-3beta expression and apolipoprotein A-I promoter activity in Hep G2 cells

We examined the influence of zinc status on expression of certain transcription factors involved in regulation of apolipoprotein A-I (apoAI) expression in human hepatoblastoma Hep G2 cells. A low zinc basal medium (zinc deficient, ZD) consisting of DMEM and 10% Chelex100-treated fetal bovine serum was used to deplete cellular zinc over one passage. Cells were also cultured for one passage in medium supplemented with 0.4 (ZD0.4), 4.0 (zinc normal, ZN), 16.0 (zinc adequate, ZA), or 32.0 microM zinc (zinc supplemented, ZS). Compared with ZN cells, cellular zinc levels were 43 and 31% lower in ZD and ZD0.4 cells but 70 and 146% higher in ZA and ZS cells, respectively. Supplementation of 0.4 microM zinc significantly increased DNA contents per plate, from 65% in ZD cells to 83% in ZD0.4 cells compared with ZN cells. Addition of >4 microM zinc in medium did not further increase DNA contents. The proportion of cells in G(1)/S and S phase was about fourfold higher and threefold lower, respectively, in ZD cells compared with ZN and other groups. Nuclear Egr-1 protein was markedly decreased in ZD and ZD0.4 cells. Moreover, hepatocyte nuclear factor (HNF)-3beta was severely degraded in ZD and ZD0.4 cells. In contrast, HNF-4alpha remained stable in all groups and was not significantly lower in ZD and ZD0.4 cells. Furthermore, downregulation of trans-acting factor Egr-1 and cleavage of HNF-3beta were associated with reduction of apoAI promoter activity in zinc-deficient Hep G2 cells. Thus zinc is critical in transcriptional regulation of apoAI gene expression in hepatocytes.

Transcriptional profiling reveals global defects in energy metabolism, lipoprotein, and bile acid synthesis and transport with reversal by leptin treatment in ob/ob mouse liver

Leptin, a hormone secreted by adipose tissue, has been shown to have a major influence on hepatic lipid and lipoprotein metabolism. To characterize changes in lipid and lipoprotein gene expression in mouse liver, suppression subtractive hybridization and cDNA microarray analysis were used to identify mRNAs differentially expressed after leptin treatment of ob/ob mice. Ob/ob mice showed a profound decrease in mRNAs encoding genes controlling bile acid synthesis and transport as well as a variety of apolipoprotein genes and hepatic lipase with reversal upon leptin administration, suggesting that leptin coordinately regulates high density lipoprotein and bile salt metabolism. Leptin administration also resulted in decreased expression of genes involved in fatty acid and cholesterol synthesis, glycolysis, gluconeogenesis, and urea synthesis, and increased expression of genes mediating fatty acid oxidation, ATP synthesis, and oxidant defenses. The changes in mRNA expression are consistent with a switch in energy metabolism from glucose utilization and fatty acid synthesis to fatty acid oxidation and increased respiration. The latter changes may produce oxidant stress, explaining the unexpected finding that leptin induces a battery of genes involved in antioxidant defenses. Expression cluster analysis revealed responses of several sets of genes that were kinetically linked. Thus, the mRNA levels of genes involved in fatty acid and cholesterol synthesis are rapidly (<1 h) repressed by leptin administration, in association with an acute decrease in plasma insulin levels and decreased sterol regulator element-binding protein-1 expression. In contrast, genes participating in fatty acid oxidation and ketogenesis were induced more slowly (24 h), following an increase in expression of their common regulatory factor, peroxisome proliferator-activated receptor alpha. However, the regulation of genes involved in high density lipoprotein and bile salt metabolism shows complex kinetics and is likely to be mediated by novel transcription factors.

Diminished molecular response to doxorubicin and loss of cardioprotective effect of dexrazoxane inEgr-1deficient female mice

Doxorubicin (DOX) and VP16 are DNA topoisomerase II inhibitors yet only DOX induces an irreversible cardiotoxicity, likely through DOX-induced oxidative stress. Egr-1 is overexpressed after many stimuli that increase oxidative stress in vitro and after DOX-injection into adult mice in vivo. To investigate Egr-1 function in the heart, we compared the molecular and histological responses of wild type (+/+) and Egr-1 deficient (–/–) female mice to saline, DOX, VP16, the cardioprotectant dexrazoxane (DZR), or DOX+DZR injection. DOX, and to a lesser extent VP16, induced characteristic increases in cardiac muscle and non-muscle genes typical of cardiac damage in +/+ mice, whereas only β-MHC and Sp1 were increased in –/– mice. DZR-alone treated +/+ mice showed increased cardiomyocyte transnuclear width without a change to the heart to body weight (HW/BW) ratio. However, DZR-alone treated –/– mice had an increased HW/BW, increased cardiomyocyte transnuclear width, and gene expression changes similar to DOX-injected +/+ mice. DZR pre-injection alleviated DOX-induced gene changes in +/+ mice; in DZR+DOX injected –/– mice the increases in cardiac and non-muscle gene expression were equal to, or exceeded that, detected after DOX-alone or DZR-alone injections. We conclude that Egr-1 is required for DOX-induced molecular changes and for DZR-mediated cardioprotection.Key words: mice, gene expression, doxorubicin, DNA topoisomerase II inhibitors, cardioprotection.

Transcriptional regulatory mechanisms of the human apolipoprotein genes in vitro and in vivo

The present review summarizes recent advances in the transcriptional regulation of the human apolipoprotein genes, focusing mostly, but not exclusively, on in-vivo studies and signaling mechanisms that affect apolipoprotein gene transcription. An attempt is made to explain how interactions of transcription factors that bind to proximal promoters and distal enhancers may bring about gene transcription. The experimental approaches used and the transcriptional regulatory mechanisms that emerge from these studies may also be applicable in other gene systems that are associated with human disease. Understanding extracellular stimuli and the specific mechanisms that underlie apolipoprotein gene transcription may in the long run allow us to selectively switch on antiatherogenic genes, and switch off proatherogenic genes. This may have beneficial effects and may confer protection from atherosclerosis to humans.

Grb-2-associated binder-1 is involved in insulin-induced egr-1 gene expression through its phosphatidylinositol 3'-kinase binding site

The Grb2-associated binder-1 (Gab1) is one of the major adapter molecules downstream of growth factor receptor signaling. Even though insulin causes tyrosine phosphorylation of Gab1, its role in insulin signaling has not been identified yet. We have demonstrated that insulin increased expression of early growth response gene-1 (egr-1), which is one of the most important transcription factors involved in cell proliferation and differentiation. In the present study, the possible role of Gab1 in insulin-induced egr-1 expression was studied using Rat1 fibroblasts expressing human insulin receptors and wildtype Gab1 (HIRc/Gab1(WT)), Gab1 with three tyrosines in the phosphatidylinositol (PI) 3'-kinase binding domain mutated to phenylalanine (HIRc/Gab1(DeltaPI3K)), or histidinol resistance only (HIRc/HIS). Insulin-induced egr-1 expression in HIRc/Gab1(DeltaPI3K) cells was much lower than in the other cells, as determined by Northern blot analysis. These results suggest that Gab1 is involved in the signaling pathway for insulin-induced egr-1 expression through increasing PI3'-kinase activity. The MAP kinase activity increased less with insulin treatment in HIRc/Gab1(DeltaPI3K) cells than in other cells. Inhibition of MAP kinase by the MEK inhibitor completely abolished insulin-induced egr-1 expression. These results suggest that Gab1 increases MAP kinase activity through its PI3'-kinase binding site, which then leads to egr-1 expression. Our results indicate that Gab1 is involved in the control of egr-1 expression regulated by insulin.

The transcription factor early growth-response factor 1 modulates tumor necrosis factor-alpha, immunoglobulin E, and airway responsiveness in mice

Early growth-response factor 1 (Egr-1) is a sequence-specific transcription factor that plays a regulatory role in the expression of many genes important in inflammation, cell growth, apoptosis, and the pathogenesis of disease. In vitro studies suggest that Egr-1 is capable of regulating the expression of tumor necrosis factor-alpha (TNF-alpha) and other genes involved in airway inflammation and reactivity following allergen stimulation. On the basis of these data, we hypothesized that in the absence of Egr-1, the TNF-alpha response and subsequent downstream inflammatory events that usually follow allergen challenge would be diminished. To test our hypothesis Egr-1 knock-out (KO) mice were examined in an ovalbumin (OVA)-induced model of airway inflammation and reactivity, and compared with identically treated wild-type (WT) control mice. In response to OVA sensitization and airway challenge, KO mice had diminished TNF-alpha mRNA and protein in the lungs and mast cells compared with WT mice. Interestingly, the KO mice had elevated IgE levels at baseline and after allergen challenge compared with WT mice. Furthermore, the airways of KO mice were hyporesponsive to methacholine challenge at baseline and after allergen challenge. These data indicate that Egr-1 modulates TNF-alpha, IgE, and airway responsiveness in mice.

Expression of Egr-1 in late stage emphysema

The transcription factor early growth response (Egr)-1 is an immediate-early gene product rapidly and transiently expressed after acute tissue injury. In contrast, in this report we demonstrate that lung tissue from patients undergoing lung reduction surgery for advanced emphysema, without clinical or anatomical evidence of acute infection, displays a selective and apparently sustained increase in Egr-1 transcripts and antigen, compared with a broad survey of other genes, including the transcription factor Sp1, whose levels were not significantly altered. Enhanced Egr-1 expression was especially evident in smooth muscle cells of bronchial and vascular walls, in alveolar macrophages, and some vascular endothelium. Gel shift analysis with (32)P-labeled Egr probe showed a band with nuclear extracts from emphysematous lung which was supershifted with antibody to Egr-1. Egr-1 has the capacity to regulate genes relevant to the pathophysiology of emphysema, namely those related to extracellular matrix formation and remodeling, thrombogenesis, and those encoding cytokines/chemokines and growth factors. Thus, we propose that further analysis of Egr-1, which appears to be up-regulated in a sustained fashion in patients with late stage emphysema, may provide insights into the pathogenesis of this destructive pulmonary disease, as well as a new facet in the biology of Egr-1.

Pulmonary expression of early growth response-1: biphasic time course and effect of oxygen concentration

Hypoxia induces complex adaptive responses. In this report, induction of early growth response-1 (Egr-1) transcripts in lungs of mice subjected to hypoxia is shown to be dose and time dependent. Within 30 min of hypoxia, Egr-1 transcripts were approximately 20-fold elevated in 6% oxygen, approximately 5.2-fold increased by 10% oxygen, and returned to the normoxic baseline by 12% oxygen. Time course studies up to 48 h showed a biphasic profile with an initial steep rise in Egr-1 transcripts after 0.5 h of hypoxia and a second elevation beginning after 20-24 h. Hypoxic induction of Egr-1 was paralleled by enhanced expression of the downstream target gene tissue factor. Egr-1 and tissue factor antigen were visualized in bronchial and vascular smooth muscle and in alveolar macrophages. Egr-1 has the capacity to modulate expression of genes involved in the remodeling of the extracellular matrix and properties of smooth muscle, thus possibly contributing to the pulmonary response to chronic hypoxia.

Coordinate augmentation in expression of genes encoding transcription factors and liver secretory proteins in hypo-oncotic states

BACKGROUND

In the nephrotic syndrome (NS) proteins of intermediate size (40 to 200 kD) are lost into the urine resulting in a decrease in plasma albumin concentration and as a consequence a reduction in plasma colloid osmotic pressure (pi). Plasma pi has also been reported to be reduced in the condition of hereditary analbuminemia. The liver, in an apparent compensatory response, increases synthesis of a group of secreted proteins defending plasma pi. Regulation of several of these proteins, including both positive and negative acute phase proteins, is at the transcriptional level. This is the only known condition in which transcription of both positive and negative acute phase proteins (APPs) are increased simultaneously. The specific transcription factor(s) that might regulate this cascade is not defined.

METHODS

RNA was extracted from livers of 5 rats with hereditary analbuminemia (the Nagase analbuminemic rat, NAR), 5 rats with NS induced by adriamycin (Adria), 5 rats with NS caused by passive Heymann nephritis (NS) and 5 control animals. The concentrations of mRNAs encoding four secreted proteins (albumin, transferrin, fibrinogen, and apo A-1), five transcription factors, early growth response factor 1 (EGRF-1), HNF-4, NGFI-C, EGR-3, and Krox20 relative to two housekeeping genes, beta actin and GAPDH were determined simultaneously using kinetic reverse transcriptase polymerase chain methodology (kRT-PCR).

RESULTS

The levels of all mRNAs encoding secreted proteins except for albumin (which was reduced in NAR) were increased in NS and NAR and correlated significantly with one another. mRNA encoding EGRF 1 was increased fivefold in NS and NAR, and correlated significantly with mRNAs encoding Apo A-1, transferrin and albumin in the two NS groups. HNF-4 mRNA was increased approximately twofold in both NS groups and correlated with albumin (R = 0.881, P < 0.001), transferrin (R = 0.563, P = 0.012) and apo A-1 (R = 0.644, P = 0. 003). While fibrinogen mRNA correlated with that of each of the other secreted proteins, it did not correlate with either HNF-4 or EGRF-1 mRNA. Krox20, EGR3 and NGF1C were expressed at nearly undetectable levels.

CONCLUSIONS

The hepatic response in conditions characterized by reduced plasma pi include increased levels of mRNAs encoding a group of secreted proteins, including the negative APPs albumin, transferrin and apo A-1, and the positive APP fibrinogen. Levels of mRNAs encoding negative APPs and fibrinogen correlate with one another, suggesting that they are coordinately controlled. Both EGRF-1 and HNF-4 may regulate the expression of the negative APPs, which have increased transcription in hypo-oncotic states.

Lipoprotein(a) levels in relation to albumin concentration in childhood nephrotic syndrome

BACKGROUND

Lipoprotein(a) [Lp(a)] is a lipoprotein consisting of a low-density lipoprotein (LDL) particle linked to a polymorphic glycoprotein, apoprotein(a) [apo(a)]. Prior studies have reported high Lp(a) levels in the nephrotic syndrome, but it is still controversial whether this is due to the degree of hypoalbuminemia or proteinuria.

METHODS

To investigate a model of nephrotic syndrome in the absence of renal failure, we studied a group of 84 children in different clinical stages of the disease for a period of five years. We evaluated the direct relationships between lipoproteins, including Lp(a), and/or plasma albumin and proteinuria.

RESULTS

Lp(a) levels were significantly higher in the subjects with the active disease compared with patients in remission, and were also significantly different when subjects were ranked by albumin quartiles. Multiple regression analysis revealed that Lp(a) levels were inversely correlated with apo(a) isoform size and plasma albumin levels but not with the proteinuria/creatinine clearance ratio. Among subjects in complete remission, Lp(a) levels were different in patients with albumin levels below or above the fifth percentile. After the improvement of the clinical stage of the disease, the Delta% variation of albumin levels was related to the Delta% of apoB and LDL cholesterol (LDL-C), but not with the Delta% variation of Lp(a), whereas the Delta% variation of LDL-C was, in turn, related to the Delta% of Lp(a) levels.

CONCLUSIONS

These results suggest that in the childhood nephrotic syndrome, the increased Lp(a) levels are mainly related to hypoalbuminemia, probably through a mechanism involving apoB overproduction, which leads to an increased number of LDL particles to be converted into Lp(a).

Increased high density lipoprotein (HDL), defective hepatic catabolism of ApoA-I and ApoA-II, and decreased ApoA-I mRNA in ob/ob mice. Possible role of leptin in stimulation of HDL turnover

Abnormalities of plasma high density lipoprotein (HDL) levels commonly reflect altered metabolism of the major HDL apolipoproteins, apoA-I and apoA-II, but the regulation of apolipoprotein metabolism is poorly understood. Two mouse models of obesity, ob/ob and db/db, have markedly increased plasma HDL cholesterol levels. The purpose of this study was to evaluate mechanisms responsible for increased HDL in ob/ob mice and to assess potential reversibility by leptin administration. ob/ob mice were found to have increased HDL cholesterol (2-fold), apoA-I (1.3-fold), and apoA-II (4-fold). ApoA-I mRNA was markedly decreased (to 25% of wild-type) and apoA-II mRNA was unchanged, suggesting a defect in HDL catabolism. HDL apoprotein turnover studies using nondegradable radiolabels confirmed a decrease in catabolism of apoA-I and apoA-II and a 4-fold decrease in hepatic uptake in ob/ob mice compared with wild-type, but similar renal uptake. Low dose leptin treatment markedly lowered HDL cholesterol and apoA-II levels in both ob/ob mice and in lean wild-type mice, and it restored apoA-I mRNA to normal levels in ob/ob mice. These changes occurred without significant alteration in body weight. Moreover, ob/ob neuropeptide Y-/- mice, despite marked attenuation of diabetes and obesity phenotypes, showed no change in HDL cholesterol levels relative to ob/ob mice. Thus, increased HDL levels in ob/ob mice reflect a marked hepatic catabolic defect for apoA-I and apoA-II. In the case of apoA-I, this is offset by decreased apoA-I mRNA, resulting in apoA-II-rich HDL particles. The studies reveal a specific HDL particle catabolic pathway that is down-regulated in ob/ob mice and suggest that HDL apolipoprotein turnover may be regulated by obesity and/or leptin signaling.