Phospholipid transfer protein can transform reconstituted discoidal HDL into vesicular structures

Area of Science:

• Lipid Metabolism and Transport
• Lipoprotein Biochemistry
• Cardiovascular Research

Background:

• High-density lipoprotein (HDL) exists in various forms, including discoidal (d-HDL) and spherical (vesicular) structures.
• Phospholipid transfer protein (PLTP) is implicated in HDL remodeling and cholesterol transport.
• Understanding HDL transformation is crucial for elucidating lipid and lipoprotein metabolism.

Purpose of the Study:

• To investigate the effect of PLTP on the transformation of discoidal HDL (d-HDL) into vesicular structures.
• To elucidate the mechanism by which PLTP mediates this structural conversion.
• To explore the implications of d-HDL transformation in lipid transport.

Main Methods:

• Reconstituted d-HDL with apo-AI incubated with PLTP.
• KBr density gradient centrifugation to analyze hydrated densities.
• Non-denaturing gradient gel electrophoresis for size determination.
• Electron microscopy for structural visualization.

Main Results:

• PLTP induced the formation of vesicular structures from d-HDL, with size and density dependent on PLTP concentration and incubation time.
• Significant transformation occurred rapidly, with ~80% conversion to 1.07 g/mL vesicles within 8 hours at plasma PLTP concentrations.
• Transformation was triggered by PLTP-mediated displacement of apo-AI, suggesting apo-AI deficient particle fusion.
• Cross-linking or adding free apo-AI inhibited transformation, confirming apo-AI's role.
• PLTP also influenced the conversion of smaller to larger vesicles.

Conclusions:

• PLTP actively transforms d-HDL into vesicular structures, a process dependent on apo-AI displacement.
• This transformation mechanism may be significant for lipid and lipoprotein transport in physiological and pathological states.
• The study provides insights into HDL remodeling and its functional consequences.