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Question

Difficulty: HardCellular Injury and Adaptation

A 42-year-old man presents to the clinic with progressive shortness of breath on exertion and a chronic daily cough. He has a 10-pack-year smoking history but quit 5 years ago. Pulmonary function testing demonstrates an obstructive pattern with a decreased diffusing capacity of the lungs for carbon monoxide (DLCO). Routine laboratory evaluation reveals mildly elevated serum aminotransferases. A subsequent liver biopsy is performed, revealing periodic acid-Schiff (PAS)-positive, diastase-resistant globules in the cytoplasm of periportal hepatocytes. If the accumulated substance in this patient's hepatocytes continues to overwhelm the cellular degradative capacity, which of the following mechanisms will most likely mediate the subsequent cell death?

  1. Activation of the intrinsic apoptotic pathway due to endoplasmic reticulum stressAnswer
  2. B
    Disruption of the plasma membrane caused by massive cytosolic calcium influx
  3. C
    Depletion of intracellular glutathione leading to reactive oxygen species accumulation
  4. D
    Activation of the extrinsic apoptotic pathway via death receptor-ligand binding
  5. E
    Lipid peroxidation of cellular membranes by Fenton reaction products

Answer

Activation of the intrinsic apoptotic pathway due to endoplasmic reticulum stress
The correct answer identifies that the intrinsic apoptotic pathway is activated by endoplasmic reticulum (ER) stress. This patient has alpha-1 antitrypsin (AAT) deficiency, characterized by early-onset panacinar emphysema and liver disease. The mutation causes the AAT protein to misfold. Because it cannot be secreted normally, it accumulates within the rough ER of hepatocytes, forming the characteristic PAS-positive, diastase-resistant globules seen on biopsy. This massive accumulation of misfolded protein triggers the unfolded protein response (UPR) to alleviate ER stress. When the UPR is overwhelmed and the degradative capacity of the cell is exceeded, the cell undergoes apoptosis. This is mediated by the intrinsic pathway, involving the release of cytochrome c from the mitochondria and the activation of caspase-9.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient is a young male with early-onset obstructive lung disease (emphysema, indicated by decreased DLCO) and concomitant liver involvement.
To formulate an initial differential diagnosis for combined pulmonary and hepatic disease in a young adult.
2
Interpret the specific liver biopsy findings.
PAS-positive, diastase-resistant globules in periportal hepatocytes are identified.
To confirm the specific etiology of the patient's condition.
3
Synthesize the findings to establish a diagnosis.
The combination of early-onset panacinar emphysema and PAS-positive, diastase-resistant hepatocyte inclusions is diagnostic of alpha-1 antitrypsin (AAT) deficiency.
To establish the underlying disease process before identifying the cellular mechanism of injury.
4
Identify the cellular mechanism of liver injury in AAT deficiency.
In AAT deficiency, a genetic mutation (most commonly PiZZ) causes the AAT protein to misfold. Because it cannot be secreted, it accumulates within the rough endoplasmic reticulum (RER) of hepatocytes.
To understand the subcellular location of the pathology.
5
Determine the cellular adaptation and subsequent injury pathway.
Severe accumulation of misfolded proteins causes endoplasmic reticulum (ER) stress. If the compensatory unfolded protein response (UPR) is overwhelmed, the intrinsic (mitochondrial) pathway of apoptosis is activated, leading to cell death.
To answer the specific question asked in the stem regarding the mechanism of subsequent cell death.

Key Concept

In alpha-1 antitrypsin deficiency, misfolded proteins accumulate in the hepatocyte rough endoplasmic reticulum, leading to ER stress. If unmitigated, this stress activates the intrinsic apoptotic pathway.
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Topics

Cellular Injury and Adaptation

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