Lamellar body membrane turnover is stimulated by secretagogues

Area of Science:

• Cell Biology
• Pulmonary Medicine
• Biochemistry

Background:

• Lamellar bodies are crucial organelles in lung alveolar type II cells, storing pulmonary surfactant.
• Understanding lamellar body trafficking is key to comprehending surfactant secretion and lung function.

Purpose of the Study:

• To investigate the trafficking dynamics of lamellar bodies in alveolar type II cells.
• To utilize a novel monoclonal antibody (MAb 3C9) as a reporter for lamellar body membrane turnover.
• To explore the mechanisms involved in lamellar body uptake and secretion.

Main Methods:

• Utilized iodinated monoclonal antibody (MAb) 3C9, targeting an 180 kDa lamellar body membrane protein.
• Assessed MAb 3C9 binding and internalization in type II cells and the L2 cell line.
• Investigated the effects of secretagogues (ATP, PMA, cAMP) and inhibitors (Calphostin C, phenylarsine oxide, cytochalasin D) on MAb 3C9 trafficking.

Main Results:

• MAb 3C9 binding and uptake by type II cells were time-, concentration-, and antibody-dependent.
• Internalized MAb 3C9 remained undegraded for 4 hours.
• Secretagogues enhanced MAb 3C9 binding and uptake, while Calphostin C inhibited both secretion and MAb uptake.
• Clathrin-mediated endocytosis was not involved in MAb 3C9 uptake, but actin-mediated processes were important.
• L2 cells lacking lamellar bodies did not bind MAb 3C9.

Conclusions:

• Lamellar body membrane turnover is enhanced during surfactant secretion.
• The MAb 3C9 reporter system effectively monitors lamellar body trafficking and membrane dynamics.
• These findings provide insights into the cellular mechanisms regulating surfactant homeostasis in the lungs.