01. Gene therapy Boulikas.pdf - Gene therapy & Molecular Biology

F. Wound healing and plasminogen
A number of diseases including cancer, cancer
metastasis, atherosclerosis, arthritis, hepatitis, dermatitis,
inflammatory bowel disease, sickle cell anemia, and
autoimmune disease result in severe tissue damage.
Plasminogen has a profound importance in wound healing
and might play a central role in many of these diseases
(Rømer et al, 1996). Plasminogen is an inactive precursorprotease
synthesized and secreted by the liver and
converted into plasmin (trypsin-like serine protease) by
the action of two different proteases: (i) tissue-type
plasminogen activator (tPA) and (ii) urokinase-type
plasminogen activator (uPA); in addition to uPA- and tPAregulation,
the activity of plasminogen is also controlled
by plasminogen-specific cell surface receptors, by
inhibitors of plasminogen activation (PAI-1 and PAI-2),
and by the receptor of uPA (uPAR). Angiostatin is a 38
kDa plasminogen fragment generated by cancer-mediated
proteolysis of plasminogen (O'Reilly et al, 1994, 1996, see
angiostatin). Endostatin is a 20 kDa C-terminal fragment
of collagen XVIII (O'Reilly et al, 1997); both angiostatin
and endostatin inhibit angiogenesis and tumor growth.
Plasmin passes to extravascular fluids and stimulates
proteolytic activity in the extracellular matrix (such as
degradation of fibrin) but also contributes to the activation
of growth factors and other proteases (see Rømer et al,
1996). Fibrin is an important component of the wound
healing and reepithelization process and is formed from
fibrinogen by the action of the protease thrombin (see
Rade et al, 1996). These processes take place during
wound healing but also during the process of
atherosclerosis, restenosis, response to vascular injury, and
in tumorigenesis during formation of the tumor stroma.
Plasminogen-deficient mice (transgenic animals
produced by targeted disruption in the plasminogen gene)
completed embryonic development and survived to
adulthood but were predisposed to spontaneous thrombotic
lesions in many tissues and displayed fibrin deposition in
the liver (Bugge et al, 1995). These animals showed
severe impairment in the healing of skin wounds; thus,
plasminogen plays a central role in extracellular matrix
degradation during wound healing in rodents in vivo and
most likely also in humans (Rømer et al, 1996). Fibrin
dissolution allows keratinocyte migration from incisional
wound edges; detriment in fibrin degradation slows down
wound repair by the limited ability of epidermis cells to
dissect their way through the extracellular matrix beneath
the wound crust (Rømer et al, 1996). Fibrin is a major
component of the extracellular matrix in wounds and solid
tumors but not in normal embryonic or adult tissue.
G. TGF-β in injury and wound healing
Transforming growth factor-β (TGF-β) is a cytokine
implicated in the pathogenesis of impaired wound healing
Boulikas: An overview on gene therapy
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but also in autoimmune disease, malignancy, and
atherosclerosis (Grainger et al, 1995). TGF-β has gained
interest for the treatment of autoimmune disease, multiple
sclerosis (autoimmune encephalomyelitis), and arthritis;
however, prolonged overproduction of TGF-β may lead to
tissue fibrosis by overproduction of extracellular cell
matrix affecting kidney, liver, lung and other organs.
TGF-β1 is involved in the pathogenesis of fibrosis by its
matrix-inducing effects on stromal cells such as in
activation of the pulmonary fibrotic process (Sime et al,
1997). Overexpression of TGF-β1 in the heart is thought
to contribute to the development of cardiac hypertrophy
and fibrosis (Villarreal et al, 1996). TGF-β can activate
and then suppress T cells, macrophages, and leukocytes;
transgenic mice with targeted disruption of the TGF-β
gene die with autoimmune symptoms (reviewed by Border
and Noble, 1995).
The preservation and architectural design of the
extracellular matrix depends on the action of cytokine
polypeptides. TGF-β controls the mitogenic action of
platelet-derived growth factor (PDGF); in response to
injury or disease, the production of TGF-β and PDGF are
increased stimulating extracellular matrix production; this
is accomplished by inhibition of proteases and stimulation
of synthesis of extracellular matrix proteins by TGF-β.
Failure of cells to produce enough TGF-β has been
proposed to result in impaired wound healing in the
elderly, glucocorticoid-treated individuals, and in
diabetics; a single injection of TGF-β has been shown to
accelerate wound healing (reviewed by Border and Noble,
1995).
TGF-β inhibits epithelial and smooth cell proliferation;
it is believed that one of the factors contributing to the
unrestricted growth of cancer cells is their
nonresponsiveness to TGF-β because of loss of functional
TGF-β receptors; microsatellite instability in colon cancer
cells inactivates the type II TGF-β receptors (Markowitz et
al, 1995). Tamoxifen, an anticancer drug, stimulates TGFβ
thus inhibiting cancer cell proliferation. Restoration of
the TGF-β receptor genes might constitute a strategy for
treating human cancers (Border and Noble, 1995).
Transfer of the cDNA of porcine TGF-β1 to rat lung
induced prolonged and severe interstitial and pleural
fibrosis characterized by extensive deposition of the
extracellular matrix (ECM) proteins collagen, fibronectin,
and elastin (Sime et al, 1997). Particle-mediated delivery
of mutant porcine constitutively active TGF-β1 cDNA to
rat skin at the site of skin incisions increased tensile
strength up to 80% for 14-21 days (Benn et al, 1996).
Neurodegeneration associated with Alzheimer's disease is
believed to involve toxicity to β-amyloid and related
peptides; this neurotoxicity was significantly attenuated by
single treatments with TGF-β1 and was prevented by
repetitive treatments, a process associated with a
preservation of mitochondrial potential and function