Cholesterol-mediated membrane surface area dynamics in neuroendocrine cells

Area of Science:

• Cell Biology
• Membrane Biophysics

Background:

• Cholesterol is a vital membrane component, but its precise role in secretory cell membrane surface area dynamics remains unclear.
• Understanding cholesterol's function is key to comprehending cellular processes like exocytosis and endocytosis.

Purpose of the Study:

• To investigate how cholesterol depletion impacts membrane surface area dynamics in secretory cells.
• To elucidate the role of cholesterol in regulating exocytosis and membrane replenishment.

Main Methods:

• Real-time imaging of melanotrophs from male Wistar rats.
• Monitoring membrane capacitance (C(m)) changes using methyl-beta-cyclodextrin (MbetaCD) for cholesterol depletion.
• Cytosolic dialysis and acute extracellular application of MbetaCD.
• Assessing endocytosis using Dyngo 4a and dextran uptake.

Main Results:

• MbetaCD treatment dose-dependently reduced cellular cholesterol and attenuated calcium-evoked C(m) increase, indicating impaired exocytosis.
• Cytosolic MbetaCD application further enhanced exocytosis attenuation, suggesting intracellular cholesterol sites are involved.
• Acute MbetaCD application caused an immediate C(m) decline correlating with surface area loss, highlighting cholesterol's role in membrane dynamics.
• The rate of C(m) decline was slower than cholesterol decay, implying exocytosis is a primary mechanism for membrane cholesterol replenishment.
• Endocytosis blockade did not affect the MbetaCD-induced C(m) decline.

Conclusions:

• Acute cholesterol removal by MbetaCD leads to a C(m) decline not compensated by exocytosis.
• Cholesterol plays a primary role in regulating membrane surface area dynamics, mainly through its involvement in regulated exocytosis.
• Exocytosis is likely the physiological pathway for replenishing plasma membrane cholesterol.