Hepatic Lipase: Regulation at the post-transcriptional level

Hepatic lipase is synthesized and constitutively secreted by liver parenchymal cells (1-3), and is subsequently bound extracellularly in the space of Disse of the liver (4-6). The protein is also found in adrenals, ovaries and testes (7-10). However, in adrenals and ovaries an altered, shorter mRNA is expressed and no mature HL protein is synthesized (3, 9, 11, 12). Thus, liver parenchymal cells may uniquely synthesize and secrete a fully active HL. HL affects the metabolism of several lipoproteins and is thought to protect against the development of atherosclerosis (Chapter 1.1.1). Therefore it is of importance to understand the mechanisms which regulate HL expression. Several cell types serve as a model system for secretion ofHL (13-17). The studies described herein were performed with the human-derived HepG2 cell-line and freshly isolated rat hepatocytes

Intracellular activation of rat hepatic lipase requires transport to the Golgi compartment and is associated with a decrease in sedimentation velocity

Hepatic lipase (HL) is an N-glycoprotein that acquires triglyceridase activity somewhere during maturation and secretion. To determine where and how HL becomes activated, the effect of drugs that interfere with maturation and intracellular transport of HL protein was studied using freshly isolated rat hepatocytes. Carbonyl cyanide m-chlorophenyl hydrazone (CCCP), castanospermine, monensin, and colchicin all inhibited secretion of HL without affecting its specific enzyme activity. The specific enzyme activity of intracellular HL was decreased by 25-50% upon incubation with CCCP or castanospermine, and increased 2-fold with monensin and colchicin. Glucose trimming of HL protein was not affected by CCCP, as indicated by diges

Analysis of KLF transcription factor family gene variants in type 2 diabetes

<p>Abstract</p> <p>Background</p> <p>The Krüppel-like factor (<it>KLF</it>) family consists of transcription factors that can activate or repress different genes implicated in processes such as differentiation, development, and cell cycle progression. Moreover, several of these proteins have been implicated in glucose homeostasis, making them candidate genes for involvement in type 2 diabetes (T2D).</p> <p>Methods</p> <p>Variants of nine <it>KLF </it>genes were genotyped in T2D cases and controls and analysed in a two-stage study. The first case-control set included 365 T2D patients with a strong family history of T2D and 363 normoglycemic individuals and the second set, 750 T2D patients and 741 normoglycemic individuals, all of French origin. The SNPs of six <it>KLF </it>genes were genotyped by Taqman^®SNP Genotyping Assays. The other three <it>KLF </it>genes (KLF2, -15 and -16) were screened and the identified frequent variants of these genes were analysed in the case-control studies.</p> <p>Results</p> <p>Three of the 28 SNPs showed a trend to be associated with T2D in our first case-control set (P < 0.10). These SNPs, located in the <it>KLF2, KLF4 </it>and <it>KLF5 </it>gene were then analysed in our second replication set, but analysis of this set and the combined analysis of the three variants in all 2,219 individuals did not show an association with T2D in this French population. As the <it>KLF2</it>, -15 and -16 variants were representative for the genetic variability in these genes, we conclude they do not contribute to genetic susceptibility for T2D.</p> <p>Conclusion</p> <p>It is unlikely that variants in different members of the <it>KLF </it>gene family play a major role in T2D in the French population.</p

GAD2 on chromosome 10p12 is a candidate gene for human obesity

The gene GAD2 encoding the glutamic acid decarboxylase enzyme (GAD65) is a positional candidate gene for obesity on Chromosome 10p11&ndash;12, a susceptibility locus for morbid obesity in four independent ethnic populations. GAD65 catalyzes the formation of &gamma;-aminobutyric acid (GABA), which interacts with neuropeptide Y in the paraventricular nucleus to contribute to stimulate food intake. A case-control study (575 morbidly obese and 646 control subjects) analyzing GAD2 variants identified both a protective haplotype, including the most frequent alleles of single nucleotide polymorphisms (SNPs) +61450 C&gt;A and +83897 T&gt;A (OR = 0.81, 95% CI [0.681&ndash;0.972], p = 0.0049) and an at-risk SNP (&minus;243 A&gt;G) for morbid obesity (OR = 1.3, 95% CI [1.053&ndash;1.585], p = 0.014). Furthermore, familial-based analyses confirmed the association with the obesity of SNP +61450 C&gt;A and +83897 T&gt;A haplotype (&chi;2 = 7.637, p = 0.02). In the murine insulinoma cell line &beta;TC3, the G at-risk allele of SNP &minus;243 A&gt;G increased six times GAD2 promoter activity (p &lt; 0.0001) and induced a 6-fold higher affinity for nuclear extracts. The &minus;243 A&gt;G SNP was associated with higher hunger scores (p = 0.007) and disinhibition scores (p = 0.028), as assessed by the Stunkard Three-Factor Eating Questionnaire. As GAD2 is highly expressed in pancreatic &beta; cells, we analyzed GAD65 antibody level as a marker of &beta;-cell activity and of insulin secretion. In the control group, &minus;243 A&gt;G, +61450 C&gt;A, and +83897 T&gt;A SNPs were associated with lower GAD65 autoantibody levels (p values of 0.003, 0.047, and 0.006, respectively). SNP +83897 T&gt;A was associated with lower fasting insulin and insulin secretion, as assessed by the HOMA-B% homeostasis model of &beta;-cell function (p = 0.009 and 0.01, respectively). These data support the hypothesis of the orexigenic effect of GABA in humans and of a contribution of genes involved in GABA metabolism in the modulation of food intake and in the development of morbid obesity.<br /