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Spontaneous human monocyte apoptosis utilizes a caspase-3-dependent pathway that is blocked by endotoxin and is

R J Fahy1, A I Doseff, M D Wewers

  • 1Department of Internal Medicine, Division of Pulmonary and Critical Care, The Heart and Lung Institute, Ohio State University, Columbus, OH 43210, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|August 10, 1999
PubMed

Insights

Spontaneous monocyte apoptosis involves caspase-3 activation, not caspase-1. Inhibiting caspase-3 prevents monocyte cell death, while lipopolysaccharide blocks both apoptosis and caspase-3 activation.

Area of Science:

  • Cell Biology
  • Immunology
  • Biochemistry

Background:

  • Apoptosis regulates monocyte and macrophage populations.
  • Caspases (cysteine-aspartate-specific proteases) are crucial for apoptosis, requiring prodomain removal for activation.
  • Caspase-1 and caspase-3 are implicated in apoptosis in various models.

Purpose of the Study:

  • To investigate the specific roles of caspase-1 and caspase-3 in spontaneous monocyte apoptosis.
  • To determine the molecular mechanisms underlying monocyte cell death in serum-free conditions.

Main Methods:

  • Monocytes were cultured in serum-free conditions.
  • Apoptosis was assessed by DNA fragmentation and caspase activity assays.
  • Specific caspase inhibitors (z-VAD-FMK, z-DEVD-FMK, YVAD-CMK) were used.
  • Immunoblots and fluorogenic substrates (DEVD-AFC, YVAD-AFC) identified caspase activity.
  • Lipopolysaccharide (LPS) was used to modulate monocyte apoptosis and caspase activation.

Main Results:

  • Monocytes initiated apoptosis within 4 hours, marked by caspase-3-like activity.
  • Apoptosis was inhibited by caspase inhibitors z-VAD-FMK and z-DEVD-FMK, confirming caspase involvement.
  • Caspase-3 activation was confirmed by procaspase-3 cleavage and DEVD-AFC substrate cleavage.
  • Caspase-1 inhibition did not prevent apoptosis, and caspase-1 activity did not increase.
  • Lipopolysaccharide prevented monocyte apoptosis and caspase-3 activation but did not alter baseline caspase-1 activity.

Conclusions:

  • Spontaneous monocyte apoptosis is directly linked to the proteolytic activation of caspase-3.
  • Caspase-1 does not appear to play a significant role in spontaneous monocyte apoptosis.
  • Lipopolysaccharide exerts an anti-apoptotic effect on monocytes by inhibiting caspase-3 activation.

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