The Role of Autocrine Growth Factors in Radiation Damage to the Epiphyseal Growth Plate

Division of General Medicine, University of Rochester, Rochester, New York, United States
Radiation Research (Impact Factor: 2.91). 07/2001; 155(6):847-57. DOI: 10.1667/0033-7587(2001)155[0847:TROAGF]2.0.CO;2
Source: PubMed


Radiation therapy plays an important role as part of the multimodality treatment for a number of childhood malignancies. Dose-limiting complications of radiotherapy include skeletal abnormalities and disturbances in skeletal development within the irradiated field. The current study was undertaken to investigate the molecular mechanisms involved in radiation-induced arrest of bone growth. Our hypotheses were: (1) Expression of autocrine growth factors that regulate chondrocyte proliferation is inhibited by radiation in a specific pattern; (2) the disparity in radiosensitivity of growth plate chondrocytes and epiphyseal chondrocytes is due to differential modulation of autocrine growth factor expression by radiation. Given the important role these cells play in skeletal growth and development, we examined the comparative effects of radiation on expression of specific mitogenic growth factors in growth plate chondrocytes. The effect of radiation on the expression of autocrine/paracrine growth factors was examined in an established avian model of epiphyseal growth plate maturation. Exposure of growth plate chondrocytes to radiation resulted in a specific pattern of biochemical and morphological alterations that were dependent on dose and were progressive over time. While radiation did not affect the mRNA expression of some of the autocrine and paracrine factors important in endochondral ossification (such as FGF2 and TGFB isoforms), it did lead to a decrease in the mRNA expression of PTHrP, a critically important mitogen in growth plate chondrocytes, and a dose-dependent decrease in the PTH/PTHrP receptor mRNA. Interestingly, PTHrP mRNA levels were not affected in irradiated epiphyseal chondrocytes, the main source of PTHrP. Given evidence indicating a role for intracellular calcium levels in regulating PTHrP expression, basal calcium levels in irradiated growth plate chondrocytes and epiphyseal chondrocytes were examined 24 h after treatment. While cytosolic calcium levels were significantly higher in irradiated growth plate chondrocytes, they were not significantly affected in irradiated epiphyseal chondrocytes. The importance of calcium in mediating radiation damage to growth plate chondrocytes was further demonstrated by the finding that the addition of 4.0 mM EGTA (a calcium chelator) to the cell cultures before irradiation prevented the decrease in PTHrP mRNA levels. Since PTHrP up-regulates BCL2 levels and prevents growth plate chondrocyte maturation and apoptosis, BCL2 mRNA levels were examined in irradiated growth plate chondrocytes, and a dose-dependent decrease was found. An increase in apoptosis was further confirmed by a fivefold increase in caspase 3 levels in irradiated growth plate chondrocytes. The results of the current study suggest that radiation may interfere with proliferation of growth plate chondrocytes in part by causing an increase in cytosolic calcium levels which in turn leads to a decrease in PTHrP mRNA. Growth plate chondrocyte PTHrP receptor mRNA expression is also inhibited by radiation, further decreasing PTHrP signaling. Despite subtle differences between the chick and mammalian growth plates, further studies should provide an enhanced understanding of the mechanism(s) of radiation injury to the growth plate, as well as possibilities for new therapeutic strategies to protect the growing skeleton from the detrimental effects of radiotherapy.

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    • "Growth plate is situated at both ends of long bones, which is composed of three distinct zones: the resting, proliferative, and hypertrophic zones. Bone growth begins as progenitor cells at resting zone are activated and enter the cell cycle at the proliferative zone [2] and produce extracellular matrix rich in collagen-II and aggrecan [1]. The hypertrophic chondrocytes secrete matrix rich in collagen-X and direct mineralisation of their surrounding matrix while undergoing apoptosis [3]. "
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    ABSTRACT: The advancement and intensive use of chemotherapy in treating childhood cancers has led to a growing population of young cancer survivors who face increased bone health risks. However, the underlying mechanisms for chemotherapy-induced skeletal defects remain largely unclear. Methotrexate (MTX), the most commonly used antimetabolite in paediatric cancer treatment, is known to cause bone growth defects in children undergoing chemotherapy. Animal studies not only have confirmed the clinical observations but also have increased our understanding of the mechanisms underlying chemotherapy-induced skeletal damage. These models revealed that high-dose MTX can cause growth plate dysfunction, damage osteoprogenitor cells, suppress bone formation, and increase bone resorption and marrow adipogenesis, resulting in overall bone loss. While recent rat studies have shown that antidote folinic acid can reduce MTX damage in the growth plate and bone, future studies should investigate potential adjuvant treatments to reduce chemotherapy-induced skeletal toxicities.
    Full-text · Article · Mar 2011 · BioMed Research International
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    • "Once it has been traumatized either by accidents, radiation (Bakker et al. 2003, Pateder et al. 2001) or unknown, internal regulating incidents, it hardly ever recovers (Davis and Green 1976, Farnum et al. 2000). This generally leads to premature closure of the growth plate such that ossification sets in and longitudinal growth is abruptly stopped (Bakker et al. 2003, Canadell and de Pablos 1985, Davis and Green 1976). "
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    • "In addition to phosphate, adverse effects have been seen by glucocorticoids and radiation, which yields and increase in apoptosis [52] [53] [54] [55]. In animals treated with a ten-day course of glucocorticoids, an increase of apoptosis in the hypertrophic chondrocytes yields a growth plate with a reduced width was revealed [53]. Both, PTHrH and parathyroid hormone are the main stimulators of the perichondrium. "
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