Directly Measuring Atherogenic Lipoprotein Kinetics in Zebrafish With the Photoconvertible LipoTimer Reporter

Lipoprotein kinetics are a crucial factor in understanding lipoprotein metabolism because a prolonged time in circulation can contribute to the atherogenic character of B-lps (ApoB-containing lipoproteins).

We developed a genetically encoded B-Lp reporter, LipoTimer, in which the zebrafish endogenous apoBb.1 (apolipoprotein Bb.1) gene was modified to produce a fusion with the photoconvertible fluorophore Dendra2, that shifts its emission profile from green to red on UV (ultraviolet radiation) exposure.

By quantifying the red population of ApoB-Dendra2 over time, we found that B-lp turnover in wild-type larvae becomes faster as development proceeds. Mutants with impaired B-lp uptake or lipolysis present with increased B-lp levels and half-life. In contrast, mutants with impaired B-lp triglyceride loading display slightly fewer and smaller B-lps, which have a significantly shorter B-lp half-life. Furthermore, we showed that chronic high-cholesterol feeding is associated with a longer B-lp half-life in wild-type juveniles but does not lead to changes in B-lp half-life in lipolysis-deficient apoC2 (apolipoprotein C2) mutants. These data support the hypothesis that B-lp lipolysis is suppressed by the flood of intestinal-derived B-lps that follow a high-fat meal.

In conclusion, the new LipoTimer reporter allows for direct in vivo examination of B-lp kinetics, which can be used to better understand the role of lipoprotein modifier genes and environmental factors (eg, diet) on B-lp lifetime.