Immunolocalization of basic fibroblastic growth factor in avian tibial dyschondroplastic cartilage

Identification of differentially expressed genes in the growth plate of broiler chickens with thiram-induced tibial dyschondroplasia

Tibial dyschondroplasia (TD) is characterized by expansion of the proximal growth plates of the tibiotarsus that fail to form bone, lack blood vessels, and contain non-viable cells. Thiram (a carbamate pesticide), when fed to young broiler chicks, induces TD with high regularity and precision. We used this experimental model to understand the cause of the defects associated with TD by selecting and identifying the genes differentially expressed in the TD growth plate of broiler chickens. Broiler chicks at 7 days of age were randomly divided into two groups. After fasting overnight, they were fed with regular diet (control) or the same diet containing 100 mg/kg thiram for 96 h to induce TD (thiram-fed). mRNA was purified from the growth plates of control and thiram-fed broilers. Forward and reverse-subtracted cDNA libraries were generated by suppression subtractive hybridization technology. Ten selected genes from cDNA libraries were identified by real-time quantitative polymerase chain reaction. All were differentially expressed in TD growth plates (P<0.05 or P<0.01). The levels of collagen type X (Col X), pro-alpha-1 collagen type I (Col I alpha1), collagen type IX (Col IX), NADH dehydrogenase (NADH DH), cytochrome C oxidase subunit III (COX III), enolase 1, alpha (ENO1), carbonic anhydrase II (CA2) and heat shock protein 90 (Hsp90) mRNA transcripts were up-regulated, while the expression levels of Matrilin 3 (MATN3) and chondromodulin-I (ChM-I) were down-regulated. Col I and Hsp90 were detected by immunohistochemistry at different stages. Given that these genes are involved in matrix formation, endochondral ossification, developmental regulation, electron transport in the mitochondrial respiratory chain and vascularization, our findings may provide new insights into understanding the pathogenesis of TD.

Tibial dyschondroplasia 40 years later

Tibial dyschondroplasia is a disease of rapid growth rate that occurs in many avian species. It is characterized by an avascular lesion in which the life span of the growth plate chondrocyte is essentially doubled. A characteristic pattern of gene expression and gene product localization has emerged that mimics the pattern observed with endoplasmic reticulum (ER) stress in growth plate chondrocytes. This activates a cell-survival mechanism called autophagy. The initial phases of this mechanism appear to originate in the avascular transition zone of the growth plate. Because specific genes and gene products are associated with autophagy and ER stress, it should now be possible to identify the mechanisms involved in the development of this cartilage abnormality. The potential biochemical pathways responsible for initiating ER stress are discussed.

Decreased proliferation precedes growth factor changes after physeal irradiation

The effects of irradiation on growth plate chondrocytes and mediators of chondrocytic differentiation are poorly understood. In earlier work on rat growth plate changes 1/2 to 4 weeks after irradiation, a nadir was identified at 1 week in proliferation and growth factor expression coincident with maximal histomorphometric derangement. The purpose of this study was to determine the earlier sequential relationship of proliferative, growth factor, and histomorphometric changes after irradiation leading to the 1-week nadir. Twenty-four weanling 5-week-old male Sprague-Dawley rats had right knee irradiation with single fraction 17.5 Gy whereas the left leg served as an internal control. The earliest change identified was a significant decrease in BrdU evidence of proliferative activity between 6 and 12 hours after irradiation, which persisted through 48 hours. Twelve to 24 hours after irradiation, caspase-3 staining for apoptosis was higher than that in growth plates not having received radiotherapy. Histomorphometric changes after irradiation were observed as early as 24 hours. Growth factors and their downstream antiapoptotic and proapoptotic mediators did not differ significantly between limbs through 48 hours. The current study suggests that decreased proliferation and apoptosis precede any change in histomorphometric features of the growth plate after irradiation and that decreased growth factor expression occurs later.

Temporal changes in PTHrP, Bcl-2, Bax, caspase, TGF-beta, and FGF-2 expression following growth plate irradiation with or without radioprotectant

This study examined temporal changes in growth plate apoptosis molecules and growth factors in an animal model of radiation injury with and without a radioprotectant. Thirty weanling 5-week Sprague-Dawley rats underwent right knee irradiation with single-fraction 17.5 Gy while the left served as internal control. Six animals each were sacrificed at 0.5, 1, 2, 3, or 4 weeks after irradiation. Half of the animals received pretreatment with amifostine (WR-2721) radioprotectant. Immunohistochemical staining for PTHrP, Bcl-2, Bax, caspase-3, FGF-2, and TGF-beta was performed. PTHrP decreased to a nadir at 1 week after irradiation but rebounded to above control levels at 2 weeks in the reserve and transitional zones. The radioprotectant amifostine blunted the decrease in PTHrP but kept PTHrP expression lower than controls during the rebound phase in untreated irradiated animals. Hypertrophic zone Bax expression was decreased by amifostine in both irradiated and non-irradiated limbs at 1 and 2 weeks. FGF, TGF-beta, Bcl-2, and caspase levels generally decreased at 1 week and returned thereafter toward control levels. These findings underscore the importance of PTHrP in response to growth plate irradiation and show the novel finding of a decrease in Bax expression with amifostine pretreatment.

Chondrocytes and longitudinal bone growth: the development of tibial dyschondroplasia

Growth plate cartilage is central to the process of bone elongation. Chondrocytes originating within the resting zone of the growth plate proceed through a series of intermediate phenotypes: proliferating, prehypertrophic and hypertrophic, before reaching a terminally differentiated state. Disruption of this chondrocyte maturational sequence causes many skeletal abnormalities in poultry such as tibial dyschondroplasia (TD), which is a common cause of deformity and lameness in the broiler chicken. Cell and matrix components of the growth plate have been studied in order to determine the cause(s) of the premature arrest of chondrocyte differentiation and retention of prehypertrophic chondrocytes observed in TD. Chondrocyte proliferation proceeds normally in TD, but markers of the differentiated phenotype, local growth factors, and the vitamin D receptor are abnormally expressed within the prehypertrophic chondrocytes above, and within, the lesion. Tibial dyschondroplasia is also associated with a reduced incidence of apoptosis, suggesting that the lesion contains an accumulation of immature cells that have outlived their normal life span. Immunolocalization studies of matrix components suggest an abnormal distribution within the TD growth plate that is consistent with a failure of the chondrocytes to fully hypertrophy. In addition, the collagen matrix of the TD lesion is highly crosslinked, which may make the formed lesion more impervious to vascular invasion and osteoclastic resorption. Recent studies have applied the techniques of differential display and semiquantitative reverse transcriptase-polymerase chain reaction to RNA obtained from discrete populations of growth plate chondrocytes of different maturational phenotypes. This strategy has allowed us to compare phenotypically identical cell fractions from normal and TD growth plates in an attempt to identify possible candidate genes for TD.

Gene expression and tibial dyschondroplasia

Tibial dyschondroplasia (TD) is a skeletal deformity associated with rapid growth in a number of avian species. The disease is the result of a disruption in the cascade of events that occur in the epiphyseal growth plate. Whereas the incidence of TD is susceptible to genetic selection, no specific genetic defect has been identified. Although there are extensive data describing the morphological and biochemical characteristics of the lesion, the mechanism of lesion formation is unknown. However, naturally occurring or induced genetic mutations in other species can provide important clues to possible mechanisms responsible for lesion development. Disruption of normal chondrocyte differentiation by constitutive activation of the parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) receptor, inactivation of the fibroblast growth factor receptor-3 (FGFR-3) receptor, and blocking vascular endothelial growth factor (VEGF) signaling all result in lesions that resemble TD. Impairment of vascular penetration due to the ablation of matrix metalloproteinase-9 (MMP-9) or tartrate-resistant acid phosphatase (TRAP) activity also results in similar cartilage abnormalities. We have integrated these observations with our current knowledge of TD to describe a hypothesis for the sequence of events responsible for the development of tibial dyschondroplastic lesions.

Expression patterns of chondrocyte genes cloned by differential display in tibial dyschondroplasia

Tibial dyschondroplasia (TD) appears to involve a failure of the growth plate chondrocytes within growing long bones to differentiate fully to the hypertrophic stage, resulting in a mass of prehypertrophic chondrocytes which form the avascular TD lesion. Many biochemical and molecular markers of chondrocyte hypertrophy are absent from the lesion, or show reduced expression, but the cause of the disorder remains to be identified. As differentiation to the hypertrophic state is impaired in TD, we hypothesised that chondrocyte genes that are differentially expressed in the growth plate should show altered expression in TD. Using differential display, four genes, B-cadherin, EF2, HT7 and Ex-FABP were cloned from chondrocytes stimulated to differentiate to the hypertrophic stage in vitro, and their differential expression confirmed in vivo. Using semi-quantitative RT-PCR, the expression patterns of these genes were compared in chondrocytes from normal and TD growth plates. Surprisingly, none of these genes showed the pattern of expression that might be expected in TD lesion chondrocytes, and two of them, B-cadherin and Ex-FABP, were upregulated in the lesion. This indicates that the TD phenotype does not merely reflect the absence of hypertrophic marker genes, but may be influenced by more complex developmental mechanisms/defects than previously thought.

Parathyroid receptor gene expression by epiphyseal growth plates in rickets and tibial dyschondroplasia

PTH/PTHrP receptor gene expression was evaluated in situ in avian epiphyseal growth plates taken from normal, rachitic and tibial dyschondroplasia (TD) afflicted chicks induced by thiram or by genetic selection. In the normal growth plates, PTH/PTHrP receptor gene expression was localized to the maturation zone as demonstrated by the expression of collagen type II (col II), osteopontin (OPN) genes and alkaline phosphatase activity (AP). In TD, either induced by thiram or by genetic selection, normal levels of PTH/PTHrP receptor gene expression were observed up to 21 days post-hatch. In rickets, on the other hand, no PTH/PTHrP receptor gene expression was observed in the growth plate from day 8 of a vitamin D-deficient diet. In cultured chondrocytes, PTH caused time-dependent down-regulation of its own receptor. These results suggest that alterations in the PTH/PTHrP receptor gene expression are associated with rickets but not with TD. The reduction in the PTH/PTHrP receptor gene expression in rickets may be due to the high plasma levels of PTH.

Matrix metalloproteinase activities in avian tibial dyschondroplasia

Tibial dyschondroplasia (TD) in poultry is a disorder of growth plate cartilage that fails to resorb and consequently prevents bone formation. Matrix metalloproteinases (MMP) contribute to the process of resorption through the degradation of extracellular matrices and facilitating vascularization, growth plate remodeling, and maturation. In order to understand the cause of the failure of cartilage degradation in TD, the gelatinase and collagenase activities, and the levels of collagen and glycosaminoglycans of conditioned media derived from cartilage-explant cultures of normal and TD growth plates were measured. Substrate zymography exhibited two prominent gelatinolytic and collagenolytic bands corresponding to MW 63, 59, and a broad but fuzzy band of activity between 100 and 200 kDa. On treatment with 4-aminophenylmercuric acetate, a compound that converts proenzyme forms of MMP, the 63 kDa MW gelatinolytic band migrated as a approximately 60 kDa band and contributed to the broadening of the 59 kDa band. The TD-growth plate-conditioned media had significantly lower collagenolytic-gelatinolytic activities. The sulfated glycosaminoglycans, but not the collagen contents of the conditioned media from TD-explant cultures, were also reduced significantly. It is likely that the decreased matrix metalloproteinase activities of growth plate chondrocyte may contribute to a reduced turnover of extracellular matrices (ECM), leading to the retention of cartilage and its lack of vascularity in TD-affected growth plates.