Pyroptosis

What is pyroptosis and how does it occur

The term pyroptosis comes from the combination of two Latin words: piros, meaning "fire" and symbolizing a prominent inflammatory response, and ptosis, meaning "to fall" or death. Thus, it is a form of cell death that is always coupled with inflammation.

The mechanism of this process represents a strict sequence of pathophysiological events:

1. Cytokine activation. At the initial stage, hydrolytic activation of key pro-inflammatory mediators occurs. This primarily involves the interleukins IL-1$\beta$ and IL-18.
2. Membrane damage. Specific pores begin to form in the cytoplasmic membrane of the affected cell.
3. Release of cellular contents. Through the formed pores, the internal contents of the cell are rapidly released outward. It is important to note that this release occurs specifically into the interstitium (intercellular space), rather than into the cytosol, vascular lumen, or synovial fluid.
4. Inflammatory response. The release of intracellular components into the interstitium naturally triggers the development of a powerful perifocal inflammation around the dead cell.

Biological role of pyroptosis

Despite the fact that the cell dies, this process is of immense biological importance for the body's defense. Pyroptosis acts as a crucial tool of the innate immune system.

Its main objectives are as follows:

• Pathogen destruction. The process ensures the reliable death of microbes that have managed to penetrate inside the cell.
• Halting replication. By destroying the cellular habitat, the intracellular proliferation of infectious agents is effectively inhibited. The cell literally sacrifices itself to stop the further spread of the infection.

Ferroptosis — an iron-dependent alternative

In addition to pyroptosis, there is another variant of cell death — ferroptosis (from Latin ferrum — iron and ptosis — falling). This is a specific, iron-dependent form of death whose mechanism differs radically from inflammatory pyroptosis.

Stages of ferroptosis development:

• Initiation. The process is triggered by the iron-dependent and excessive generation of reactive oxygen species (ROS).
• Progression. There is a sharp intensification of lipid peroxidation (LPO), which is implemented with the direct participation of iron ions ($Fe$).
• Biochemical basis. A key link in the pathogenesis is a critical decrease in intracellular glutathione content and complete blockade of the protective enzyme — glutathione peroxidase.
• Outcome. The process culminates in the fatal activation of lipid peroxidation, which inevitably leads to the destruction of cellular structures.

General patterns of cell damage

Any cell damage, regardless of whether it ends in pyroptosis, ferroptosis, or another outcome, causes two large groups of changes. The first group comprises changes characteristic of various damaging factors and different cell types. The second group consists of specific changes characteristic of a given pathogenic factor when acting on various cells, or inherent to a specific (given) cell.

Examples of specific factor action:

• Uncouplers of oxidation and phosphorylation. These include an excess of higher fatty acids (HFAs) and calcium ions ($Ca^{2+}$). They reduce or completely block the coupling of oxidation and phosphorylation processes. As a result, the efficiency of biological oxidation drops, and ATP levels decrease critically.
• Excess aldosterone. An increase in the effects of this adrenal cortex hormone leads to the pathological intracellular accumulation of excess sodium ions ($Na^+$).
• Cellular specificity. The action of various agents on strictly defined types of cells causes changes specific only to these particular cells.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• The role of reactive oxygen species (ROS) in initiating cell death.
• Mechanisms of lipid peroxidation (LPO) involving iron ions.
• Uncouplers of oxidation and phosphorylation: effect on ATP levels.
• Cellular specificity upon exposure to various pathogenic agents.

Other topics in "Chapter 4: Cell Injury as the Basis for the Development of Various Forms of Human Pathology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.