MAJOR CREDIT SEMINAR ON

MOLECULAR MECHANISM OF PARENCHYMAL CELL INJURY AND THEIR ULTRASTRUCTURE

PRESENTED BY- SWATI CHAUDHARY M VSc SCHOLAR IVRI

M 5429

Introduction

Rudolph Virchow , “father of cellular pathology” , put forward the concept that disease begins at the cellular level.

METHODS OF STUDYING PATHOLOGY

• Gross examination• Light microscopy• Immunochemistry• Electron microscopy• Molecular biology

Organ Parenchymal cells

Brain Neurons and glial cells

Heart Myocyte

Kidney Nephron

Liver Hepatocyte

Lungs

 Alveolar tissue with respiratory

bronchioles, alveolar ducts and terminal

bronchioles

Ovary Follicles with egg cells

PancreasIslets of

Langerhans and Pancreatic acini

Spleen White pulp and red pulp

Ultrastructure of a typical animal cell

Plasma membrane

Ultrastructure of different organelles of the cell

Cell injury

Cell injury is a sequence of events that occur if the limits of adaptive capability are exceeded or no adaptive response is possible.

The capacity for adaptation and the sensitivity to different types of injury varies according to cell type.

+ Stress

Injury+Stress

Apoptosis

Necrosis

- Stress

- Stress

Overview of cell injury

AdaptedCell

Normal cell

Reversiblyinjured cell

Irreversibly Injured cell

AdaptedCell

Dead cell

CausesCauses of cell injury of cell injury

Hypoxia Ischemia Physical agents Chemical agents Infective agents Immunologic reaction Genetic injury Nutrition imbalance

Common bio molecular mechanism of cell injury1. ATP depletion

2. Loss of calcium homeostasis

3. Oxidative stress

4. Damage to mitochondria

5. Defect in membrane permeability

Cell injury caused by ATP depletion /hypoxia

Neurons and cardiac myocytes are rapidly injured by ATP decrease

The Na+/K+ ATPase Pump Almost one-third of all the energy generated by the

mitochondria in animal cells is used to run this pump.

Formation of lactic acid during Formation of lactic acid during ATP depletionATP depletion

lactate and H+, causes cytosolic acidosislactate and H+, causes cytosolic acidosis Interferes with the functions of the intracellular Interferes with the functions of the intracellular

enzymes, thus resulting in the inhibition of the enzymes, thus resulting in the inhibition of the glycolysis so that this last source of ATP dries upglycolysis so that this last source of ATP dries up

Change in conformation of protein moleculesChange in conformation of protein molecules Increase of Permeability of cellular membranesIncrease of Permeability of cellular membranes Activating enzymes of lysosomes.Activating enzymes of lysosomes.

Ca2+ Mg ATPase pump

It uses the energy provided by one molecule of ATP to pump one Ca2+ ion out of the cell.

Increased ICF Ca+2 in cell due to reduced ATP production

Sustained rise in Ca level is initial step of irreversible injury.

Increased Cytosolic Calcium in Cell Injury

Uncoupling of gap junction

Mitochondrial damage

• Phospholipase damage to membrane

• Formation of high conductance channels c/d as MPT

• Loss of the H+ gradient , preventing ATP generation.

• Swelling due to ionic shifts• Deposition of amorphous substance• Finally, rupture of membrane

followed by progressing increased calcification.

Swollen mitochondria and endoplasmic reticulum

Loss of cristae

Rupture of mitochondria

MEMBRANE DAMAGE

SOME PORE-FORMING BACTERIAL TOXINS

Toxins Bacterial source

Hemolysin Escherichia coli

Listeriolysin Listeria monocytogenes

Anthrax EF Bacillus anthracis

Alpha toxin Staphylococcus aureus

Pneumolysin Streptococcus pneumoniae

Streptolysin O Streptococcus pyogenes

Leukocidin Staphylococcus aureus

Perfringiolysin O Clostridium perfringens

Ultra structural changes in plasma membrane

Cellular swelling Formation of cytoplasmic blebs Blunting and distortion of microvilli Creation of myelin figures Deterioration and loosening of intercellular

attachments

Ultra structural changes in Endoplasmic reticulum

Free Radicals in Injury

Radiation-Induced Cellular Injury

Direct DNA damageDNA directly absorbs the UV radiationCauses thymine dimer formation.

Indirect damage Absorption of radiant energy (ultraviolet light & x-rays): H2O OH* & H*

Chemical injury

A very large number of chemicals can produce reversible and irreversible injury. Hepatic cells is the most common target for toxic chemical injury

(REYNOLD.E.S., 1963)

Liver injury by CCl4

Dilatation of golgi

Dilatation of mitochondria

Dilatation of ER

(Jeffrey H. Teckman) 2002 

 

Effects of viruses• Inhibition of Host Macromolecular Biosynthesis• Changes in the Regulation of Gene Expression• Appearance of New Antigenic Determinants on the Cell Surface. • Cell Fusion

Infectious agentsInfectious agents

virus infection, Liver 

H&E EM

Reversible Injury

Caused by mild injury of short duration characterized by

• Cell Swelling• Hydropic or Vacular

Degeneration• Intracellular

accumulation

REVERSIBLE CELL INJURY

Mitochondrial swelling in acute ischemic cell injury

Renal tubular epithelium –reversible ischemic injury

• Loss of microvilli • Surface blebbing • Slight swelling of

mitochondria• Clumping of

nuclearchromatin

(http://www.studyblue.com)

PCT cell

Irreversible injury

The transition to irreversible injury depends on the extent of ATP depletion and membrane dysfunction especially of mitochondria

Enzymatic digestion of dead cellular elements

Denaturation of proteins Cytoplasm - increased eosinophilia

Epithelial cell proximal kidney tubule A. NormalB. Reversible ischemic changesC. Irreversible ischemic changesc changes

http://www.studyblue.com

Autophagic vacuoles (a) containing

damaged mitochondria after induced hypoxia of

15 mins

(Decker R.S. and Wildenthal (1979)

Myocyte after 1h of hypoxia. Display many

feature of irreversible cell injury ,severely condensed

chromatin (N), relaxed myofibril (S) , rupture of

sarcolemma is also observed(SL)

Decker et al., 1980

Death of cells occurs in three ways

Necrosis

Apoptosis

pyro ptosis

Necrosis

Necrosis is accidental, uncontrolled, un-programmed cell death

Pyknosis

Karyorrhexis

Karyolysis 

Normal Pyknosis Karyorrhexis Karyolysis

Histological changes in necrosis

(Jerome niquet 2003)

Necrosis in neuronal cell due to hypoxia

Apoptosis

An internally programmed series of events effected by dedicate gene products

In necrotic neurons, the mitochondrial structure is irreversibly damaged, but appears functional in apoptotic cells. because apoptosis needs energy for it’s own cellular destruction.

 info@nf.mpg.de

Pyroptosis 

Is a form of programmed cell death associated with antimicrobial responses during inflammation

 Immune cells that recognize certain danger signals within themselves , produce cytokines, swell, burst and die.

Releases the cytokines, attracts other immune cells , contributes to inflammation.

Pyroptosis occurs for example in salmonella infected macrophages and in HIV-infected T helper cells.

Characteristics Apoptosis Pyroptosis necrosis

Morphology

Cell lysis NO YES YES

Cell swelling NO YES YES

Pore formation NO YES YES

Membrane blebbing

YES NO NO

DNA fragmentation

YES YES YES

Mechanism

Caspase-1 NO YES NO

Caspase-3 YES NO NO

Cytochome-c release

YES NO NO

OutcomeInflammation NO(anti) YES YES

Programmed cell death

YES YES NO

CONCLUSION Cell is the structural and functional unit of tissue

or organ Normal cell has to remain live with in narrow

range of structure and function Cell try to escape from injury by adaptive

responses like hypertrophy, hyperplasia If adaptive capability exceeded cell suffer from

injury it may be reversible or irreversible . Necrosis and apoptosis are main mechanisms of

cell death. Apoptosis can be a physiological and pathological process

Knowledge about injury at the sub cellular organelle and molecular levels is essential for development of new therapeutic strategies.

References McGavin.D.M.,and Zachary.J.F.,(2012) Pathologic Basis of

Veterinary Disease,, 4th ed. chapter 1. Mosby Elsevier

Cheville. N.F., (2007) Introduction to veterinary pathology , ,third ed

Decker .R.S.Wildenthal K.(1979) Lysosomal alterations in hypoxic and reoxygenated heart vol98.no.2 1980 American journal of pathology

Tamara Hirsch, Philippe Marchetti, Santos A Susin, Bruno Dallaporta, Naoufal Zamzami, Isabel Marzo, Maurice Geuskens

and Guido Kroemer The apoptosis-necrosis paradox. Apoptogenic proteases activated after mitochondrial permeability transition determine the mode of cell death

Reynold Edward S (1963) vol.19 1963 liver parenchymal cell injury with ccl4 The journal of cell biology

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