Key Points
- To determine whether the uncleaved hydrophobic signal peptide of apolipoprotein M functions as a structural anchor that binds the protein to lipoproteins and prevents rapid renal clearance.
- Generated transgenic mice expressing wild-type human apoM or mutant apoM(Q22A), which undergoes cleavage of its NH2-terminal signal peptide prior to secretion.
- Injected recombinant apoM lacking a signal peptide into wild-type mice to monitor lipoprotein binding and systemic clearance kinetics.
- Performed renal artery ligation in apoM(Q22A) transgenic mice to verify the pathway responsible for rapid plasma clearance.
- apoM(Q22A) transgenic mice showed normal hepatic mRNA levels and hepatocyte secretion, but human apoM was undetectable in plasma compared with high levels in wild-type apoM transgenic mice.
- Recombinant apoM lacking the signal peptide failed to associate with plasma lipoproteins and cleared rapidly through the kidneys upon injection.
- Ligation of renal arteries in apoM(Q22A) transgenic mice led to rapid plasma accumulation of human apoM, confirming that absence of the anchor leads to rapid kidney filtration.
Structured PICO
PPopulationMice expressing mutated apoM(Q22A) cDNA in the liver (apoM(Q22A)-Tg mice) and wild-type mice
IInterventionExpression of mutated apoM(Q22A) lacking the signal peptide, or injection of recombinant apoM lacking the signal peptide
CComparatorMice expressing wild-type human apoM (apoM-Tg mice)
OOutcomePlasma levels of human apoM and lipoprotein associationsurrogate
The hydrophobic signal peptide sequence anchors apolipoprotein M in plasma lipoproteins, preventing its rapid clearance by kidney filtration.