Apolipoprotein A-V deficiency results in marked hypertriglyceridemia attributable to decreased lipolysis of triglyceride-rich lipoproteins and removal of their remnants

Objective - ApoAV, a newly discovered apoprotein, affects plasma triglyceride level. To determine how this occurs, we studied triglyceride-rich lipoprotein (TRL) metabolism in mice deficient in apoAV. Methods and Results - No significant difference in triglyceride production rate was found between apoa5^-/- mice and controls. The presence or absence of apoAV affected TRL catabolism. After the injection of ¹⁴C-palmitate and ³H-cholesterol labeled chylomicrons and ¹²⁵I-labeled chylomicron remnants, the disappearance of ¹⁴C, ³H, and ¹²⁵I was significantly slower in apoa5^-/- mice relative to controls. This was because of diminished lipolysis of TRL and the reduced rate of uptake of their remnants in apoa5^-/- mice. Observed elevated cholesterol level was caused by increased high-density lipoprotein (HDL) cholesterol in apoa5^-/- mice. VLDL from apoa5^-/- mice were poor substrate for lipoprotein lipase, and did not bind to the low-density lipoprotein (LDL) receptor as well as normal very-low-density lipoprotein (VLDL). LDL receptor levels were slightly elevated in apoa5^-/- mice consistent with lower remnant uptake rates. These alterations may be the result of the lower apoE-to-apoC ratio found in VLDL isolated from apoa5^-/- mice. Conclusions - These results support the hypothesis that the absence of apoAV slows lipolysis of TRL and the removal of their remnants by regulating their apoproteins content after secretion.