Origin of apolipoprotein A-I polymorphism in plasma

Area of Science:

• Biochemistry
• Molecular Biology
• Human Physiology

Background:

• Apolipoprotein A-I (apo-A-I) is a key component of high-density lipoproteins (HDL).
• Plasma contains multiple apo-A-I isoforms, including proapo-A-I and mature forms.
• The origin and functional significance of apo-A-I polymorphism require further investigation.

Purpose of the Study:

• To investigate the origin and functional significance of apo-A-I polymorphism in humans.
• To determine the relationship between different mature apo-A-I isoforms.
• To elucidate the catabolic pathways of apo-A-I isoforms.

Main Methods:

• In vitro incubation of apo-A-I isoforms (A-I3, A-I4) with and without HDL.
• Analysis of apo-A-I isoprotein conversion and ammonia liberation.
• In vivo turnover studies in normal volunteers to determine plasma residence times and degradation rates.

Main Results:

• Mature apo-A-I isoforms (A-I2 to A-I5) are derived from apo-A-I3 via stepwise deamidation.
• Deamidation occurs at similar rates in vitro and in vivo.
• Apo-A-I3 exhibits a longer plasma residence time and higher degradation rate compared to apo-A-I4.

Conclusions:

• Apo-A-I3 is the direct precursor to more acidic mature apo-A-I isoforms in plasma.
• Apo-A-I3 is the major isoform through which apo-A-I is eliminated from plasma.
• Deamidation is a key post-translational modification influencing apo-A-I catabolism.