Biochemical Analysis of the Lipoprotein Lipase Truncation Variant, LPL^S447X, Reveals Increased Lipoprotein Uptake

Lipoprotein lipase (LPL) is responsible for the hydrolysis of triglycerides from circulating lipoproteins. Whereas most identified mutations in the LPL gene are deleterious, one mutation, LPL^S447X, causes a gain of function. This mutation truncates two amino acids from LPL’s C-terminus. Carriers of LPL^S447X have decreased VLDL levels and increased HDL levels, a cardioprotective phenotype. LPL^S447X is used in Alipogene tiparvovec, the gene therapy product for individuals with familial LPL deficiency. It is unclear why LPL^S447X results in a serum lipid profile more favorable than that of LPL. <i>In vitro</i> reports vary as to whether LPL^S447X is more active than LPL. We report a comprehensive, biochemical comparison of purified LPL^S447X and LPL dimers. We found no difference in specific activity on synthetic and natural substrates. We also did not observe a difference in the <i>K</i>_i for ANGPTL4 inhibition of LPL^S447X relative to that of LPL. Finally, we analyzed LPL-mediated uptake of fluorescently labeled lipoprotein particles and found that LPL^S447X enhanced lipoprotein uptake to a greater degree than LPL did. An LPL structural model suggests that the LPL^S447X truncation exposes residues implicated in LPL binding to uptake receptors

Genotypic association of 5 SNPs in Study 3

<p>Genotypic association of 5 SNPs in Study 3</p

Twenty four SNPs associated with MI in Study 1 and Study 2

*<p>1 sided P value</p

Risk factors for MI in three case–control studies

†<p>Data available for 254 cases.</p>‡<p>Individuals with diabetes were excluded from control group.</p>§<p>Dyslipidemia was defined in Study 1 and Study 2 to be self-reported history of a physician diagnosis of dyslipidemia or the use of lipid lowering prescription medication(s) and defined in Study 3 to be the use of lipid lowering prescription medication(s), LDL cholesterol >129 mg/dL, triglycerides >149 mg/dL or HDL cholesterol <45 mg/dL .</p>||<p>Hypertension was defined in Study 1 and Study 2 to be a self–reported history of a physician diagnosis of hypertension or use of antihypertensive prescription medication(s) and defined in Study 3 to be the use of antihypertensive prescription medication(s), systolic blood pressure >160 mmHg, or diastolic blood pressure >90 mmHg.</p><p>NA; not applicable.</p