apoptosis

Examples of apoptosis in the following topics:

• Programmed Cell Death

  • Apoptosis is the process of PCD that may occur in multicellular organisms.
  • Apoptosis can also be initiated via external signaling.
  • Apoptosis is also essential for normal embryological development.
  • It is hypothesized that necroptosis can serve as a cell-death backup to apoptosis when the apoptosis signaling is blocked by endogenous or exogenous factors, such as viruses or mutations.
  • This video describes the process of apoptosis, or programmed cell death.

• Cell Signaling and Cell Death

  • When a cell is damaged, unnecessary, or dangerous to an organism, a cell can initiate the mechanism for cell death known as apoptosis.
  • External signaling can also initiate apoptosis.
  • Another example of external signaling that leads to apoptosis occurs in T-cell development.
  • Apoptosis is also essential for normal embryological development.
  • A cell signaling mechanism triggers apoptosis, which destroys the cells between the developing digits.

• Natural Killer Cells

  • NK cells use wo cytolytic granule-mediated apoptosis to destroy abnormal and infected cells.
  • Apoptosis is a form of "programmed cell death" in which the cell is stimulated by the cytotoxic mechanisms to destroy itself.
  • Unlike with lysis, apoptosis does not degrade DNA, and cells are destroyed cleanly and completely on their own.
  • In apoptosis, these virus particles are destroyed.
  • However, cancer cells often develop genetic mechanisms to prevent apoptosis signals from occurring, so cell lysis is generally more effective.

• Tumor Suppressor Genes

  • At this point, a functional p53 will deem the cell unsalvageable and trigger programmed cell death (apoptosis).
  • The damaged version of p53 found in cancer cells, however, cannot trigger apoptosis.
  • If repairs are unsuccessful, p53 signals apoptosis.
  • A cell with an abnormal p53 protein cannot repair damaged DNA and cannot signal apoptosis.

• Natural Killer Cells

  • Typically immune cells detect MHC that is present on infected cell surfaces, triggering cytokine release and causing lysis or apoptosis.
  • The granzymes then break down the target cell, inducing death by either apoptosis or osmotic cell lysis.
  • Natural cytotoxicity receptors directly induce apoptosis after binding to ligands that directly indicate infection of a cell.
  • The MHC dependent receptors (described above) use an alternate pathway to induce apoptosis in infected cells.
  • Functions of NK cells include: Cytolytic Granule Mediated Cell Apoptosis; Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC); Cytokine induced NK and CTL activation; Missing 'self' hypothesis; Tumor cell surveillance; NK cell function in adaptive response; NK cell function in pregnancy; and NK cell evasion by tumor cells .

• Cartilaginous Joints: Synchodroses

  • In puberty, increasing levels of estrogen, in both females and males, leads to increased apoptosis of chondrocytes in the epiphyseal plate.
  • Depletion of chondrocytes due to apoptosis leads to less ossification, and growth slows down and later stops when the cartilage has been completely replaced by bone.

• WBC Function

  • When pathogens are encountered, granule dependent apoptosis (a mechanism of cytotoxicity) may be induced in the pathogen by releasing perforins, granzymes, and proteaseases from their granules.
  • Pathogens that bear the T cell's antigen are destroyed through cytotoxic induced apoptosis and protease activity.

• Type IV (Delayed Cell-Mediated) Reactions

  • Cytotoxic T cells cause death by apoptosis without using cytokines.
  • 1. activating antigen-specific cytotoxic T-lymphocytes that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens

• Cancer Viruses

  • This can result from having control of their own growth signals, losing sensitivity to anti-growth signals, and losing the ability to undergo apoptosis, or programmed cell death.

• Damage to the Cell Wall

  • Damage to the cell wall disturbs the state of cell electrolytes, which can activate death pathways (apoptosis or programmed cell death).