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Revision as of 19:26, 25 May 2009

Cell Death: Necrosis

Introduction

Necrosis, derived from the Greek word neckros for ‘corpse’, is a type of irreversible cell death. It is mainly caused by early plasma membrane rupture , mitochondrial dysfunction, cell injury, infarction, inflammation and lysosomal rupture . Unlike apoptosis, it is considered as uncontrolled. Necrosis is irreversible and can be fatal. There are several types of necrosis classified based on morphological criteria.


History


  • 1858 – cell death was first discussed by in the lecture given by Rudolf Virchow, a German pathologist and biologist, he termed it “necrobiosis” which is described as “degeneration, softening,necrosis, and mortification”
  • 1877 – Carl Weigert and Julius Cohnheim identified coagulation necrosis which is a white infract produced in cell death.
  • Up until 1971, the term “necrosis” was used for all types of cell death.


  • 1971 – the definition of cell death is modified to include a distinction between pathological and non-pathological forms.
    • In 1971 Kerr et al. first observed a form of non-pathologic cell death in certain tissues,terming it ‘shrinkage necrosis’. ‘Necrosis’ now refers to pathological forms of cell death.


  • 1972 - ‘Shrinkage necrosis’ is renamed ‘apoptosis’ as it became implicated in the control of organ homeostasis (Kerr et al. 1972). The two basic types of cell death were now termed apoptosis, defined as a non-pathological, ‘programmed’ form of cell death, and necrosis, defined as a pathological, non-programmed form of cell death.


  • Nomenclature Committee on Cell Death 2009: necrosis is defined as being ‘morphologically characterized by a gain in cell volume (oncosis), swelling of organelles, plasma membrane rupture and subsequent loss of intracellular contents’


  • Today there is increasing evidence to suggest that necrosis may not be just an accidental uncontrolled form of cell death. It is thought that necrosis may in fact controlled by various signal transduction pathways and catabolic mechanisms eg Toll-like receptors and death domain receptors



Apoptosis vs Necrosis

There are distant morphological and biochemical differences in apoptosis and necrosis. Apoptosis is considered as a physiological event while necrosis is a pathological event.

Apoptosis is classified as programmed cell death and called “cell suicide”, the process is under genetic control and regulated by a variety of cellular signaling pathways. In Apoptosis, cell is shrinking and become denser. Condensation of chromatin to form sharply circumscribed, uniformly dense, cresentic masses that abut the nuclear envelope. Karyohexis takes place which mean the nucleus will break up. There is DNA degeneration and cleavage of chromosomal DNA into internucleosomal fragments. The cell becomes divided in apoptotic bodies by "budding". Apoptotic bodies consist of cell organelles and nuclear material surrounded by an intact plasma membrane. These bodies are mostly engulfed by neighbouring cells and in particular by macrophages. Caspase-1 and caspase-3 are the main ptroteases to mediate apoptosis. Cell death caused by apoptosis requires energy in the form of ATP.


Different from apoptosis, necrosis is not a programmed cell death and considered to be uncontrolled. It is initiated accidentally by ischemia, trauma or ATP depletion. Swelling cells can be found in the case of necrosis but no apoptotic bodies or DNA fragment is present. The plasma membrane integrity is not maintained in necrosis, necrotic cell released cellular contents including lysosomal enzymes due to the breakdown of of the plasma membrane into the extracellular fluid and this cellular leakage will promote a inflammatory responses.Unlike apoptosis, there is no ATP is required for the process of necrosis. Necrosis is also known as caspase-independent cell death that caspase is not involved in this type of cell death.

Apoptosis vs Necrosis
Apoptosis Necrosis
Regulation genetic programmed ischemia,trauma and ATP depletion
Control controlled uncontrolled
Cell sharp skrinkage, condensed swelling
Plasma membrane integrity maintained collasped
Cellular process budding blebbing
Cellular content packaged in apoptoic bodies leakage to extracellular fluid
DNA fragmentation, chromatin condensation no fragmentation
Energy ATP required not required
Inflammatory response absent present
Mediator caspase caspase-independent



Cellular Processes

The term ‘necrosis’ is used for the presence of dead tissues or cells and is the total of the transformations which have occurred in cells after they have died. It is currently thought to be a type of cell death that is accidental as opposed to programmed. Necrosis this therefore thought of as a passive form of cell death because it does not require the complex regulatory mechanisms such as protein synthesis that are characteristic of programmed cell death. In addition to this, the process of necrosis has minimal energy requirements, whereas cell death by apoptosis requires energy in the form of ATP.


The full process of necrosis is complete only after 12-24 hours. Therefore, cells are dead long before any necrotic changes can be seen through a light microscope. Necrosis, therefore, refers to morphological features noticed after a cell has already died and attained equilibrium with its surroundings. Necrosis is typified by rapid cell swelling and eventually lysis of the cell. It’s associated with loss of cell membrane integrity and the subsequent leakage of cytoplasmic contents and generation of an inflammatory response. This specific form of cell death is also characterised morphologically by intracellular swelling and condensed nuclear chromatin, which are associated with loss of membrane integrity.

Indicators of Necrosis

Light microscopy level

  • Early mitochondrial swelling
  • Loss of plasma membrane
  • Nuclear membrane preserved


Ultrastructural level

  • Proliferation of the endoplasmic reticulum
  • Disaggregation of polyribosomes
  • Dilation of organelles
  • Intranuclear vacuoles
  • Breakdown of cell membrane (plasmalemma)


Changes in the nucleus

  • Clumping and swelling of chromatin
  • Pyknosis
  • Kayorrhexis
  • Karyolysis

In general, the death of a cell is accompanied by severe swelling, distension of organelles, clumping of nuclear DNA, “plasma membrane endocytosis and autophagy”[1]. The morphological changes that occur within the nucleus can be observed over time.

Nuclear changes

Appear in three patterns (as indicated above) and all due to nonspecific breakdown of DNA. The first pattern identified as karyolysis. This is essentially the fading of basophilia of the chromatin which results in the dissolution of the nucleus by action of deoxyribonucleases. The second pattern is pyknosis, characterised by nuclear shrinkage and condensation of the nucleus which is mainly due to increased basophilia. In the third pattern, karyorrhexis, the nucleus which has already undergone pyknosis then undergoes fragmentation. Over time, the nucleus eventually disappears.

[1] Death by necrosis. Uncontrollable catastrophe, or is there order behind the chaos? Syntichaki P, Tavernarakis N. EMBO Rep. 2002 Jul;3(7):604-9. PMID: 12101090


Causes

(IN PROGRESS) Necrosis is best understood when compared to apoptosis. Necrotic cells have distinct morphological features. • Cells first swell (oncosis) • Plasma membrane collapses • Cells are rapidly lysed and cytotoxic components are released from the plasma membrane causing inflammation

These morphological features differ from apoptotic cells. Apoptotic cells undergo regulated catabolism where enzymes digest the cytosolic components and nuclear DNA. The cells shrink into fragmented apoptotic bodies which are phagocytized by neighboring cells. Apoptosis has a regulated mechanism leading to death of the cell and necrosis has been long accepted to be an unregulated series of events leading to the death of the cell. However, recent research shows that the cell does undergo a regulated series of events leading to necrosis. Cells can die through unregulated processes of membrane and cytosolic destruction under extreme conditions. These extreme conditions tend to me physico-chemical stresses and thus necrosis is said to be accidental and uncontrolled. These stresses arise from various bacterial toxins and viruses, inadequate secretions of cytokines, nitric oxide and reactive oxygen species and calcium. A cell may undergo two different processes leading to necrosis. The first, primary necrosis, is characterized by external chemical and physical damage to the cell. The second, secondary necrosis occurs in late apoptotic cells which fail to be engulfed by macrophages. Cells undergoing this process are not phagocytosed and thus lose membrane integrity, cease to be metabolically active and release their cytoplasmic content out into the extracellular matrix, or if in vitro, into the culture medium. Double staining procedures are used to identify cells that are undergoing seondary necrosis. [1]

Cytokines

Cytokines are secreted by affected tissues during infection and inflammation and are capable of initiating necrosis. This is demonstrated in the pancreatic cells of diabetic patients where exposure to cytokines such as TNF-α caused both apoptotic and necrotic cell death.

Mitochondria and ROS

Mitochondrial Dysfunction: It is one of the major causes of necrosis due to ATP depletion. The mitochondria is site of cellular oxygen consumption and responsible for generating ATP by oxidative phosphorylation. When there are insufficient oxygen supply to the cell, it causes the uncoupling of oxidative phosphorylation that makes the mitochondria cannot generate ATP and this may lead to cell death. At the early stage of oxygen deprivation, there is a formation of protrusion of the plasma membrane called blebs, it casuse the mitochrondria cell start to swell. If this condition persists, the growth of blebs accelerated and the mitochrodrial membrane continues to swell. Once the plasma membrane of blebs ruptures, this cell injury is irreversible and lead to necrosis.[2]

Signal transduction cascades

cytoskeleton

Ischemia

Spiders

--Gurkiran Flora 20:48, 17 May 2009 (EST)




Patterns of Necrosis

As a result of necrotic cell death, the affected tissues or organs display morphological changes. Based on this morphology, necrosis can be categorized into several distinct types or patterns. Such types, when observed at both the gross and microscopic level, can provide pathologists and clinicians with clues about its underlying cause.


Coagulative necrosis

Figure 1: Coagulative necrosis in the liver

Coagulative necrosis is the most common pattern of necrosis occurring in tissues or organs. Its morphological pattern is primarily a consequence of protein degradation frequently caused by ischemia where lack of oxygen causes cell death in a localized area. Coagulative necrosis can occur in all tissues, except the brain (liquefactive necrosis is the pattern observed here) and is characteristic of infarcts in solid organs, for example a myocardial infarction in the heart or a renal infarct in the kidney.

The gross morphology of an area of coagulative necrosis is observed as being a pale yellow-whitish colour with diminished transparency compared to the surrounding non-affected areas which have a good vascular supply. Initially foci may be swollen due to an inflammatory response elicited by the necrotic cells which release inflammatory factors such as cytokines and interleukin-2. Later the tissue becomes very firm.

When observed under a light microscope, the microscopic morphology of coagulative necrosis shows that despite the cells are dead and anucleate their basic cell shape, or ‘ghost’ outline (a term commonly used to describe their appearance), remains preserved for several days. An acute inflammatory response develops and this too is observable under the microscope with an influx of phagocytic leukocytes such as macrophages which remove the necrotic cells.

Provided there is an adequate amount of labile cells around the affected tissue, regeneration of this tissue can occur. Labile cells which are constantly dividing can replicate and replace the cells that were killed to restore the tissue back to normal. This is in contrast to stable or permanent cells (eg cardiac myocytes) which are not constantly replicating and so will not replace the affected tissue. Healing by fibrosis therefore follows, first with granulation tissue which is eventually replaced by fibrosis after a few months. During this time, fibroblasts can be microscopically observed in the affected tissue and the fibrosis is attributable to the firm gross appearance observed on the organ.

Thus the end result of this necrosis is a whitish-yellow area of firm tissue and a histological structure barely recognizable to the original.



Liquefactive necrosis

Figure 2: Liquefactive necrosis in the brain

Liquefactive necrosis is a pattern of necrosis which occurs as a consequence of enzymatic degradation. This is in contrast to coagulative necrosis which occurs as a result of protein degradation.

Liquefactive necrosis typically occurs in tissues which have a high lipid content, particularly the brain. Mentioned previously, whilst hypoxic cell death in most tissues normally results in coagulative necrosis, this pattern of necrosis is not usually typical to tissue in the central nervous system. Because these tissues have little structural framework, hypoxic cell death as in a cerebral infarct for example, results in disintegration of the necrotic cells and ultimately, transformation of the affected tissue into a liquid viscous mass. By taking a section through the brain, the macroscopic appearance of the liquefactive necrosis typically reveals the affected tissue to be gelatinous-looking. Microscopically, the tissue is edematous, with the neurons undergoing chromatolysis, with loss of cytological detail. An infiltrate of neutrophils, shortly replaced by macrophages, can also be observed, as well as microglia, phagocytes of the central nervous system. Removal of the necrotic cells is usually seen after two weeks concurrent with the repair process which is termed gliosis. A gross examination of the brain will now show destruction where the necrosis was and surrounding gliosis.

Liquefactive necrosis is also observed in within abscesses caused by focal bacterial, and sometimes fungal, infections. Such bacterial or fungal infections result in the migration of polymorphonuclear leukocytes, specifically neutrophils and macrophages, to the site of insult. The leukocytes release enzymes to eliminate the offending microbes; however this comes to the detriment of the surrounding tissue which is also enzymatically digested, and the tissue is transformed into a viscous liquid material. Whenever liquefactive necrosis is caused by acute inflammation, the ‘liquefied’ tissue characteristically has a creamy-yellow colour and is called pus.



Caseous necrosis

Figure 3: Caseous necrosis in the kidney

Caseous necrosis is a form of necrosis characteristic of mycobaterial infections and is most commonly observed in tuberculosis lesions. The term ‘caseous’ (meaning cheese-like) arises from the gross morphology of the necrotic tissue, described to resemble crumbly yellow-white cottage cheese.

A microscopic examination of the necrotic area shows the architecture of the affected tissue to be completely destroyed: the cells are fragmented or lysed and have an amorphous and granular appearance. This is in contrast to the microscopic morphology of coagulative necrosis, where despite the cells being dead, the tissue architecture is preserved. Often the lesion is observed microscopically as a granuloma whereby there a focal area of necrosis is surrounded by a distinct inflammatory border. The granuloma comprises four recognisable layers; it has a centre of caseous necrosis which is surrounded by a layer of giant and epithelioid cells (activated macrophages). The third layer consists of leucocytes and the outer layer is a layer of fibrosis.



Fibrinoid necrosis

Figure 4: Fibrinoid necrosis of polyarteritis nodosa in arteries of the kidney

Fibrinoid necrosis is a type of necrosis that occurs specifically in blood vessels. It is associated with injury often caused by immunologically mediated reactions to blood vessels by the formation of immune complexes in the circulation. Immune complexes, which are essentially complexes of an antigen and an antibody, are deposited on the walls of blood vessels, along with fibrin, which leaks out from the blood vessels. These depositions result in its characteristic fibrinoid (or ‘fibrin-like’) appearance when viewed under the light microscope. Fibrin is easily identified by the fact it stains brightly with eosin. Following deposition of the immune complexes, an inflammatory response ensues with attempted phagocytosis of the immune complexes. The immune complexes can in addition cause platelet aggregation which enhances the inflammatory response and also initiates the formation of microthrombi contributing to local ischemia. This process can consequently culminate in the characteristic fibrinoid necrosis.

Polyarteritis nodosa, manifested by systemic vasculitis, is an example of a disease in which fibrinoid necrosis is observed.



Fat necrosis

Figure 5: Fat necrosis of the mesentery

Fat necrosis is another type of necrosis, which like fibrinoid necrosis, occurs in specific tissues. As the name suggests, fat necrosis occurs in tissues with a high lipid content and is primarily characterised by focal areas of fat destruction. It is usually caused by acute pancreatitis (inflammation of the pancreas) or by direct physical trauma to fat (for example as a result of surgery or by a physical blow).

The necrosis is ultimately due to the release of pancreatic lipases (enzymes that digest fat) out of the acinar cells and ducts of the pancreas and into the peritoneum. Here the lipases act on adipose tissue, particularly fat cell membranes, splitting triglyceride esters and causing free fatty acids to be released. The fatty acids may then combine with calcium to produce white-chalky deposits. This is called fat saponification and is visible at a gross level. A microscopic view of fat necrosis shows the shadowy outline of the adipocytes (fat cells) with a surrounding inflammatory reaction that is similar to coagulative necrosis but has the extra addition of calcium deposits.

Glossary

Abscess - a localised collection of pus


Eosinophilia - increased numbers of eosinophils circulating in the blood


Fibrosis - the extensive deposition of connective tissue, particularly collagen, in an organ or tissue, that occurs as a part of the reparative process after substantial tissue destruction


Gliosis - the process of repair and scar formation in the brain


Granuloma - a focal collection of chronic inflammatory immune cells which forms when the immune system tries to wall of foriegn material but cannot eliminate. Necrosis is often found within the centre of a granuloma


Hypoxic - an oxygen deficiency to the tissues or organs of the body


Infarct - a circumscribed area of necrosis in a tissue or organ resulting from obstruction to blood flow


Inflammation - a local response to cellular injury that serves as a mechanism to eliminate noxious agents and of damaged tissue and protect from further injury; may be acute or chronic - however when unqualified the term usually tends to refer to acute inflammation which is characterised by vascular dilatation, leukocyte infiltration, redness, heat, pain, swelling, and often loss of function


Ischaemia - a state occurring when there is an insufficient supply of blood to a tissue or organ


Karyolysis – dissolution of the nucleus by action of deoxyribonecleases


Kayorrhexis – fragmentation of the nucleus


Leukocyte - a white blood cell


Macrophages - phagocytic white blood cells that function in the destruction of foreign antigens, including microbes, as well as the removal of necrotic debris. They also function as antigen-presenting cells


Microthrombi - small thrombi. A thrombus is a solid or semi-solid mass derived from the constituents of blood within a blood vessel and remains attached to the place in which it was formed


Morphology - the structure of a tissue or organ; can be described at macroscopic(gross) and microscopic levels


Necrosis - a type of cell death 'morphologically characterized by a gain in cell volume (oncosis), swelling of organelles, plasma membrane rupture and subsequent loss of intracellular contents'


Neutrophils - are described as polymorphonuclear granulocytic white blood cells, in that they have a multi-lobed nucleus and a granulocytic cytoplasm. These cells function as phagocytes, capable of ingesting microbes and particulate matter. They are also one of the first cell types to be seen at a site of acute inflammation


Phagocytosis - the engulfment, ingestion and usually destruction of particulate or foreign matter by phagocytic cells


Pus - a thick yellowish white semi-fluid matter consisting of both necrotic and living neutrophils, exudate, microbes and tissue debris


Pyknosis – condensation and skrinkage of the nucleus



References

Apoptosis, oncosis, and necrosis. An overview of cell death. Majno G, Joris I. Am J Pathol. 1995 Jan;146(1):3-15. Review. PMID: 7856735

Death by necrosis. Uncontrollable catastrophe, or is there order behind the chaos? Syntichaki P, Tavernarakis N. EMBO Rep. 2002 Jul;3(7):604-9. PMID: 12101090

Morphological and biochemical aspects of apoptosis, oncosis and necrosis. Van Cruchten S, Van Den Broeck W. Anat Histol Embryol. 2002 Aug;31(4):214-23. Review. PMID: 12196263

Necrosis: a specific form of programmed cell death? Proskuryakov SY, Konoplyannikov AG, Gabai VL. Exp Cell Res. 2003 Feb 1;283(1):1-16. Review. PMID: 12565815

Ultrastructural characteristics of necrotic and apoptotic mode of neuronal cell death ina model of anoxia in vitro, Nagańska E, Matyja E. Folia Neuropathol. 2001;39(3):129-39. PMID: 11770123

http://www.copewithcytokines.de/cope.cgi?key=necrosis

Kroemer G, Galluzzi L, Vandenabeele P, Abrams J, Alnemri ES, Baehrecke EH, Blagosklonny MV, El-Deiry WS, Golstein P, Green DR, Hengartner M, Knight RA, Kumar S, Lipton SA, Malorni W, Nuñez G, Peter ME, Tschopp J, Yuan J, Piacentini M, Zhivotovsky B, Melino G; Nomenclature Committee on Cell Death 2009. Classification of cell death: recommendations of the Nomenclature Committee on Cell Death 2009. Cell Death Differ. 2009 Jan;16(1):3-11. Epub 2008 Oct 10. PMID: 18846107

Kumar, V., Abbas, A., Fausto, N. & Mitchell, R., ‘Robbins Basic Pathology’, 8th Edition, Saunders Elsevier, China, 2007.


2009 Group Projects

--Mark Hill 14:02, 19 March 2009 (EST) Please leave these links to all group projects at the bottom of your project page.

Group 1 Meiosis | Group 2 Cell Death - Apoptosis | Group 3 Cell Division | Group 4 Trk Receptors | Group 5 The Cell Cycle | Group 6 Golgi Apparatus | Group 7 Mitochondria | Group 8 Cell Death - Necrosis | Group 9 Nucleus | Group 10 Cell Shape