Mutation-function Analysis In The Lipoprotein Lipase Gene In Hypertriglyceridemic Members Of Type 2 Diabetic Pedigrees

1. Molecular screening of the lipoprotein Iipase gene in hypertriglyceridemic members of type 2 diabetic pedigreesAim: To investigate the lipoprotein lipase(LPL) gene mutations in hypertriglyceridemic members of type 2 diabetic pedigrees in a Chinese population in Chengdu.Methods: Members of type 2 diabetic pedigrees were chosen for analysis of LPL gene if fasting triglyceride(TG) levels exceeded 2.25mmol/L. Fifty-three individuals met the criteria, including 31 individuals with type 2 diabetes mellitus(T2DM), 11 individuals with impaired glucose tolerance(IGT), and 11 individuals with normal glucose tolerance(NGT). These subjects represented 26 type 2 diabetic pedigrees. TG levels ranged from 2.3mmol/L to 13.0mmol/L. The control population consisted of 118 healthy individuals chosen from non-diabetic families. Polymerase chain reaction(PCR)-single strand conformation polymorphism (SSCP), PCR-denaturing high performance liquid chromatography(DHPLC) and direct DNA sequencing were applied for analysis of LPL gene.Results: 1. A total of 7 different LPL variants were detected among 53 individuals of type 2 diabetic pedigrees. Four of the variants were previously detected in exon 3 (Ala71Thr and VaI108Val), and exon 6 (Leu286Pro and Asn291Ser). Three novel variants were detected in exon6 (Lys312 insertion C) and in exon 8 (Thr361 insertion A and Leu376Leu). 2. The LPL gene in the family members of the novel Lys312insC and Thr361insA mutations pedigrees were further analyzed. In 8# family, 6 individuals who carried Lys312insC mutation had a high triglyceridemia, and three of them also carried the Asn291Ser mutation had a much higher triglyceridemia, so maybe there was a strong linkage disequilibrium between the Lys312insC mutation and the Asn291Ser mutation; In 14# and 28# family, the Thr361insA mutation cosegregated with the phenotype (hypertriglyceridemia) and was thus suggested to have a pathophysiological effect; No individual carried with Lys312insC and Thr361insA mutations in control group. 3. In new 1# pedigree, the proband whose TG was 11.9mmol/L was found carrying the Leu286Pro mutation; and in new 3# pedigree, the proband whose TG was 13.0mmol/L was found carrying the Ala71Thr mutation. The mutation, Leu286Pro and Ala71Thr, reported previously, had a significant association with hypertriglyceridemia, so we think the mutation contribute to the hypertriglyceridemia in this two pedigrees.Conclusion: The genetic variants at the LPL gene occurcommonly in hypertriglyceridemic members of type 2 diabetic pedigrees in a Chinese population in Chengdu. LPL variants contribute to the hypertriglyceridemia in some families.2. Construction, clone and identification of recombinantwild lipoprotein lipase gene plasmidAim: To obtain the recombinant wild lipoprotein lipase(LPL) gene plasmid.Methods: The total RNA was isolated from the human epiploon adipose tissue. According to the reported cDNA sequence of the LPL, primers were designed and synthesized. By means of RT-PCR,the LPL cDNA was obtained. The LPL cDNA was cloned into the pcDNA3.1Zeo (+) vector. The recombinant pcDNA3.1Zeo (+) /LPL cDNA was identified by endonucleases, PCR and DNA sequencing.Results: The LPL gene had been cloned into the pcDNA3.1Zeo (+) plasmid identified by endonucleases and PCR. The sequence of the LPL gene was the same to the sequence of the Gene Bank identified by DNA sequencing.Conclusion: The recombinant plasmid pcDNA3.1Zeo (+)/LPL cDNA was successfully constructed.3. Site-directed mutation and expression in vitro of recombinant LPL gene plasmidAim: To obtain the recombinant mutant LPL gene plasmid and to investigate the function of the mutant LPL gene.Methods: Mutant LPL cDNAs with the desired mutations were generated from the pcDNA3.1Zeo(+)-wild type LPL cDNA using the Site-directed Kit (Takara, Japan). COS-1 cells were transfecteed with the recombinant LPL gene plasmid using LIPOFECTAMINE 2000?(LF2000, Gibco BRL, Life Technologies, USA). The LPL mass in cells and the culture medium were determined by a Markit-M LPL Kit (Dainippon Pharmaceutical Co., Ltd, Japan). Spectrophotometry was used to measure the LPL activity.Results: 1. Mutant pcDNA3.1Zeo(+)/LPLcDNA plasmids with the mutations Asn291Ser, Lys312insC, Thr361insA and Asn291 Ser + Lys312insC were generated and transformed into the COS-1 cells. 2. LPL mass and enzyme activity in both culture medium and cell lysate were measured. COS-1 cells and pcDNA3.1Zeo(+) plasmid themselves expressed no LPL. The COS-1 cells expressed LPL mass and activity when transfected with wild type LPL cDNA. All mutations transfected COS-1 cells produced significantly decreased LPL activities in both cell lysates and medium. The LPL activities were undetectable in cell lysates and medium of the Asn291Ser+Lys312insC transfected cells. The LPL mass of all mutant types was also significantly lower in culture medium compared to the mass of the wildtype, but all mutant types had LPL mass similar to that of the wild type in cell lysates.Conclusion: the mutations Asn291Ser, Lys312insC, Thr361insA and Asn291Ser+Lys312insC did not influence the transcription and translation of LPL, but affected the secretion and activity of the enzyme to various degrees.