Questions: Pathological Fibrosis and Excessive Scarring

Question 1

A patient with chronic hepatitis C has had repeated episodes of hepatic injury over 20 years. Biopsy shows dense collagen deposits replacing hepatocytes. Why is this fibrosis so difficult to reverse, even if antiviral therapy now eliminates the virus?

• A. Antiviral drugs cannot penetrate fibrotic liver tissue to reach remaining hepatocytes
• B. Once established, fibrosis creates a self-sustaining loop: matrix stiffness mechanically activates TGF-β via integrin signaling independently of the original viral stimulus, so removing the virus does not fully reset the profibrotic program
• C. Hepatocytes that have undergone EMT have permanently altered their genome and cannot revert to a hepatocyte identity
• D. The immune system develops autoantibodies against collagen during fibrosis, which continue attacking liver tissue even after viral clearance

Answer: (B)

This is the critical insight about irreversibility: fibrosis becomes self-sustaining because the stiffened ECM itself is a mechanical signal. Integrins on myofibroblasts sense matrix rigidity and activate TGF-β, perpetuating myofibroblast activation and collagen deposition even after the initial injurious stimulus is removed. This biomechanical feedback loop is why current anti-fibrotic strategies aim to both block TGF-β and target the mechanical properties of the matrix.

Question 2

What is the fundamental difference between normal wound repair and pathological fibrosis at the level of cellular events?

• A. Normal repair uses collagen type III (temporary), while fibrosis deposits collagen type I (permanent) — the pathology lies in which collagen type is produced
• B. In normal repair, myofibroblasts undergo apoptosis and MMPs degrade excess collagen during the remodeling phase; in fibrosis, unresolved TGF-β signaling keeps myofibroblasts activated, preventing this resolution
• C. Fibrosis is caused by excessive neutrophil infiltration during the inflammatory phase, while normal repair uses predominantly macrophages
• D. Normal repair is driven by growth factors; fibrosis is driven by cytokines — the pathology is a change in the signaling molecule class

Answer: (B)

The distinction is about resolution, not initiation. Both normal healing and fibrosis begin with myofibroblast activation and collagen deposition. The difference is that normal healing resolves: myofibroblasts apoptose, MMPs degrade excess matrix, and the scar matures. Fibrosis is wound healing that cannot stop — TGF-β continues to signal, myofibroblasts persist, and MMP production is suppressed. The collagen type distinction (option 0) is a secondary detail, not the core distinction.

Question 3

TGF-β1 is self-amplifying in fibrosis: it promotes myofibroblast differentiation, suppresses matrix metalloproteinases (blocking collagen degradation), and stimulates its own further secretion, creating a positive feedback loop.

• T. True
• F. False

Answer: True

This autocrine and paracrine amplification is why TGF-β is the 'central villain' of fibrosis. TGF-β induces myofibroblast differentiation from fibroblasts, drives those myofibroblasts to secrete more TGF-β, and simultaneously blocks the enzymes (MMPs) that would degrade the accumulating collagen. Additionally, the stiffened matrix that results mechanically activates more TGF-β, adding a biomechanical amplification loop. Therapeutic strategies targeting TGF-β (pirfenidone, nintedanib in IPF) aim to break this cycle.

Question 4

Pathological fibrosis is effectively reversible if the underlying injurious stimulus is removed early enough, because eliminating the trigger will cause myofibroblasts to naturally undergo apoptosis and the tissue to remodel back toward normal.

• T. True
• F. False

Answer: False

This is the key misconception. Once fibrosis is established, it is largely irreversible with current treatments. The biomechanical feedback loop — matrix stiffness activating integrin signaling → TGF-β → more collagen — operates independently of the original injury. Even if the hepatitis virus is cleared or the toxic exposure eliminated, established fibrosis persists and may progress. Some regression is possible with early intervention (e.g., antiviral therapy in early hepatic fibrosis), but advanced fibrosis (cirrhosis) is considered irreversible with current therapies.

Question 5

Why is pathological fibrosis described as 'wound healing that doesn't stop'? What cellular and molecular events prevent the normal resolution phase from occurring?

Model answer: Normal healing resolves because TGF-β signaling declines once the wound is closed, triggering myofibroblast apoptosis and MMP-mediated matrix remodeling. In pathological fibrosis, a persistent injurious stimulus (chronic infection, repeated toxin exposure, ischemia) keeps TGF-β elevated. This maintains myofibroblasts in an activated, collagen-secreting state while suppressing MMPs that would clear excess matrix. Additionally, once collagen accumulates and the matrix stiffens, integrin-mediated mechanical signals activate more TGF-β, creating an autonomous feedback loop. The wound can no longer 'sense' that repair is complete — the resolution switch cannot be flipped.

The molecular heart of the answer is TGF-β's role as both a driver of fibrosis and a suppressor of resolution, combined with the biomechanical feedback from matrix stiffness. Understanding both the chemical (TGF-β) and mechanical (integrin-matrix rigidity) amplification loops explains why fibrosis, once established, persists even when the original trigger is removed.