Cell shape and organelle modification in apoptotic U937 cells

Area of Science:

• Cell Biology
• Apoptosis Research
• Biochemistry

Background:

• Apoptosis is a crucial process for cellular homeostasis and development.
• Morphological changes during apoptosis, including blebbing, are key indicators of programmed cell death.
• Understanding the mechanisms of apoptosis in U937 monocytic cells provides insights into immune system regulation.

Purpose of the Study:

• To investigate the dynamic morphological alterations in U937 cells during puromycin-induced apoptosis.
• To analyze the ultrastructural changes in the nucleus, mitochondria, and cytoplasm during blebbing.
• To determine the role of actin polymerization in blebbing and its necessity for apoptosis.

Main Methods:

• Induction of apoptosis in U937 cells using puromycin, an inhibitor of protein synthesis.
• Time-course analysis of cellular morphology, focusing on blebbing and apoptotic body formation.
• Ultrastructural examination using electron microscopy to observe nuclear and cytoplasmic modifications.
• Inhibition of actin polymerization to assess its role in blebbing and apoptosis.

Main Results:

• Puromycin treatment induced progressive and dramatic cell shape changes, characterized by intense blebbing and apoptotic body production.
• Blebbing evolved over time, with early stages affecting cortical cytoplasm and later stages involving the whole cell body.
• Ultrastructural analysis revealed nuclear fragmentation and cytoplasmic modifications, with blebs lacking organelles like ribosomes and mitochondria.
• Inhibition of actin polymerization demonstrated that blebbing is a dispensable event in puromycin-induced apoptosis.

Conclusions:

• Puromycin effectively induces apoptosis in U937 cells, accompanied by significant blebbing and apoptotic body formation.
• Blebbing is a dynamic process during apoptosis but is not essential for cell death, as evidenced by actin polymerization inhibition.
• The study provides a comprehensive analysis of morphological changes during apoptosis, highlighting the dispensable nature of blebbing.