Cell Injury 4: Apoptosis, Cellular & Extracellular Accumulations & Metabolic Derangements

What is apoptosis?

• programmed cell death

• highly coordinated sequence of events

• active process (energy dependent)

What are examples of physiological apoptosis?

• involution of tissues during embryonic development

• involution of tissue related to functional phases

• age related involution/atrophy of the thymus

What are examples of pathological apoptosis?

irreversible cell injury with different underlying causes

infectious agents, ionising radiation, chemicals, growth factors withdrawal

What specific enzymes are involved in apoptosis?

• Capases

• Nucleases

Describe how the following features differ between necrosis and apoptosis:

• Cell Size

• Nucleus

• Plasma Membrane

• Cellular Contents

• Adjacent Inflammation

• Physiologic or pathologic role & significance

Necrosis

• Cell Size: Increase

• Nucleus

  • Pyknosis

  • Karyorrhexis

  • Karyolysis

• Plasma Membrane: disrupted, destruction

• Cellular Contents: enzymatic digestion may leak out of cell

• Adjacent Inflammation: frequent, including neutrophils and macrophages

• Physiologic or pathologic role & significance: pathologic (culmination of irreversible cell injury)

Apoptosis

• Cell Size: decrease

• Nucleus

  • Fragmentation into nucleosome-size fragments

• Plasma Membrane: intact, altered structure, especially orientation of lipids

• Cellular Contents: intact, may be released in apoptotic bodies

• Adjacent Inflammation: NO (only macrophages clearing apoptotic debris)

• Physiologic or pathologic role & significance: DNA damage, cell mediated cytotoxicity

What are the two routes of apoptosis?

1.) Mitochondrial (Intrinsic) Pathway

• Cell Injury

• (GF withdrawal, DNA damage, protein misfolding)

• Release of cytochrome C + pro-apoptotic proteins which activate initiator caspases, and executioner caspases

• Leading to nuclear fragmentation + breakdown of cytoskeleton

2.) Death Receptor (Extrinsic) Pathway

• Receptor-ligand interactions (Fas + TNF)

• Downstream cascade of adaptor proteins → initiatior caspases… same as above

What are intracellular accumulations?

Provide examples.

• intracellular accumulations are degenerative changes due to metabolic alterations

- excessive normal cellular component

• water, lipids, proteins, carbohydrates

- abnormal exogenous or endogenous substances

• mineral or product of infectious agent

• product of abnormal synthesis or metabolism

- pigment accumulation

What are examples of extracellular accumulations?

- amyloid

- calcification

- urates (gout)

What are some causes of intracellular accumulations?

• decreased rate of metabolism

• build-up of a normal endogenous substance

• eg triglycerides → fatty change in the liver (Hepatic lipidosis / fatty liver)

• genetic or acquired defects in metabolism, packaging, transport or secretion

• eg lysosomal storage diseases

• failure of enzymatic machinery to degrade or transport an abnormal exogenous substance

• eg carbon, silica

Is a manifestation of metabolic derangement in cells.

Describe the intracellular accumulation of hyaline proteins.

Defect in protein folding, transport within cell

• Protein resorption droplets (e.g. proximal renal tubule epithelium)

• Russell bodies in plasma cells, accumulation of immunoglobulins

• Defective protein folding

  • Some forms of amyloidosis

  • More often extracellular in veterinary medicine

Describe the intracellular accumulation - lysosomal storage diseases.

• Lack of enzyme to convert complex substrate to soluble products, accumulate within the lysosomes

What is Suffolk Sheep GM1 Gangliosidosis?

Intracellular Accumulation Disease

• B1-galactosidase + a-neuraminidase (Enzymes) deficiency

• Defect in catabolism of glycosphingolipids (Normal components of cell membranes)

• Leads to intracellular accumulation (Particularly in neurons)

What is lipofuscin accumulation?

• Intracellular accumulation disease

  • Accumulation of brown pigment

  • “Wear and tear” pigment

• Accumulated in post-mitotic (permanent) cells

  • Neurons, cardiomyocytes & stable (slowly-dividing) cells (hepatocytes)

  • Final undegradable residual product of autophagocytosis

  • proteins + lipids + carbohydrate

  • Indigestible

    - Thus accumulates in lysosomes

What is an exogenous material accumulation?

Intracellular accumulation disease

• For example carbon pigment, uptake by cells, non-digestible and accumulate in lysosomes

What is an hemosiderin accumulation?

Intracellular accumulation disease

• Golden, yellow or brown granular pigment

• Contains iron

  • Histological confirmation with Perls blue special stain

• Involved with organs involved in red cell breakdown (spleen, liver)

  • Brownish color

• Local hemosiderosis

  • Bruising

• Generalized hemosiderosis

  • Hemolytic anemia

  • hemocromatosis

What is “formalin pigment” and how may it affect histology?

• Commonly observed in H&E stained histological sections

• “Fixation artifact”

  • acid formalin haematin

  • brown to black fine granular spicules of haematin lie between and on the red cells

  • worse if fixation of blood-rich tissues in unbuffered (acid) 10% formalin

What is a glycogen accumulation?

Intracellular accumulation disease

• Normally found in hepatocytes and myocytes

• Hepatocyte level of glycogen is dependent on feeding to sampling interval

  • no glycogen if starved

  - increased levels with corticosteroids

  • endogenous steroids

    • Cushing's disease

  • exogenous steroids

• Diabetes mellitus

  • Accumulation of glycogen

What is an amyloid accumulation?

Extracellular proteinaceous material

- diverse group of glycoproteins

• B pleated sheet configuration

• apple green birefringence with Congo red

- histologically: eosinophilic, amorphous hyaline substance

• resistant to normal proteolytic mechanisms

• compresses tissue cells

• causing atrophy or even cell death and loss

What is secondary amyloidosis?

• secondary (reactive systemic) amyloidosis

• secondary to chronic inflammation / neoplasia

  • sustained antigenic stimulation with cell breakdown

- most common form in animals

- deposits in kidney (proteinuria), liver, spleen & lymph nodes

What is primary amyloidosis?

- plasma cell tumours [AL amyloid form Ig light chains]

- important in humans but RARE in domestic animals

- pancreatic islets of cats with non-insulin dependent diabetes

mellitus [Islet amyloid polypeptide (IAPP)-derived]

- Familial AA amyloidosis

• Dogs: Beagle, Shar-Pei, gray Collie, English Foxhound

• Cats: Abyssinian, Siamese and Oriental

Describe the pathology of secondary (reactive systemic) amyloidosis.

• Composed of serum amyloid A (SAA)

• sustained production of acute phase lipoprotein produced the liver (stimulated by IL-1 and IL-6)

• Under stimulation in chronic inflammatory processes

Under what circumstances do we observe animals suffering from secondary amyloidosis?

→ cattle

chronic suppurative pneumonia, hoof abscesses, traumatic reticulopericarditis, visceral abscesses

→ horse

visceral abscesses

What is renal amyloidosis?

AKA where are the desposits found?

Deposition in the…

• glomerular capillary basement membrane

• glomerular mesangium

• interstitium of medulla and/or cortex

What are the gross findings of renal amyloidosis?

• Large, pale, waxy kidneys with swollen cortex

What are the functional implications of renal amyloidosis?

protein-losing nephropathy (nephrotic syndrome)

subcutaneous oedema, brisket oedema, "bottle jaw", due to reduced oncotic pressure

What are clinical correlates of renal amyloidosis?

Anasarca = generalised oedema

Ascites = serous fluid in peritoneal cavity

What is a pathologic calcification?

Extracellular Accumulation

• Calcium salts deposited in tissues (Necrotic or normal)

• Indication of a previous injury

• Affected areas are white and gritty

• Calcium salts stain blue (Basophilic) with H&E

What two ways do we distinguish types of calcification?

Dystrophic or metastatic

What is dystrophic calcification?

• associated with necrosis

• most prominent in coagulative and caseous necrosis and in fat necrosis

• dead / dying cells cannot regulate cytoplasmic Calcium influx

• THUS Calcium accumulates in the mitochondria

What vitamins and minerals are associated with causing dystrophic calcification?

• Vitamin E and Selenium

• Affecting hearts - causing irregular whiteish gritty areas of dystrophic calcification associated with myocardial degeneration and necrosis

What is metastatic calcification?

• Occurring in normal tissues secondary to hypercalcaemia

• Entry of large amounts of calcium ions into cells

• Calcium ions precipitate on organelles (Particularly mitochondria)

What are the most common causes of metastatic calcification?

1) Renal failure

2) Vitamin D toxicosis

3) Parathyroid hormone [PTH] Increase

• hyperparathyroidism (primary or secondary)

4) PTH-related protein [PTH-rp]

• paraneoplastic hypercalcaemia

5) Destruction of bone from primary or metastatic neoplasms

Describe how renal failure may lead to metastatic calcification.

Renal failure → retention of phosphates = secondary renal

hyperparathyroidism and hypercalcemia

• caIcium deposits in gastric mucosa, kidney, and alveolar septa

Describe how vitamin D toxicosis may lead to metastatic calcification.

Vitamin D toxicosis - ingestion of calcinogenic plants (Cestrum diurnum) by herbivores → severe soft tissue mineralisation chiefly involving the aorta, heart*, and lungs

• *atrial and left ventricular endocardium most affected

How does acute Vit D toxicosis in dogs and cats most often occur?

ingestion of rodenticides containing cholecalciferol

• Intestinal mucosa, vessel walls, lung, and kidneys mineralised

Describe how an increase in parathyroid hormone and PTH-related protein may lead to metastatic calcification.

• Increase in PTH and PTH-related hormone

• Primary hyperparathyroidism is rare

• Secondary (Renal) hyperparathryoidism is most common

Describe how paraneoplastic hypercalcemia may lead to metastatic calcification.

• Caused by PTH-rp release by malignant tumors

• Common in canine lymphomas

• and Canine adenocarcinoma of the apocrine glands of the anal sac

• Calcification in: Intestinal mucosa, vessel walls, lung, and kidneys are mineralised

What is Gout?

Extracellular Accumulation

• Deposits of sodium urate crystals (tophi)

• Birds, reptiles, and humans

  • Birds and reptiles excrete uric acid as semisolid urates

  • Humans lack uricase enzyme

Describe the types of gout, causes and the gross appearance.

visceral gout and articular gout (rare)

• Visceral gout common in birds and reptiles

  • vitamin A deficiency, high-protein diet, renal injury

• Gross

  • grey/white granules on the visceral serosae