EFFECTS OF ZINC DEFICIENCY ON LONGITUDINAL BONE GROWTH IN JUVENILE CHICKENS AND YOUNG GROWING RATS
Open Access
- Author:
- Wang, Xibin
- Graduate Program:
- Nutrition
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 19, 2000
- Committee Members:
- Gary J Fosmire, Committee Member
Ronald Scott Kensinger, Committee Member
Sally E Johnson, Committee Member
Carol V Gay, Committee Member
Roland M Leach, Committee Chair/Co-Chair - Keywords:
- bone
zinc deficiency
cell proliferation
apoptosis
growth plate
in situ hybridization
immunohistochemistry - Abstract:
- Zinc is essential for endochondral bone formation. Zinc deficiency affects the epiphyseal growth plate and thereby impairs longitudinal bone growth in humans and animals. In a zinc deficient state, the width of the growth plate is narrowed and the structure is histologically abnormal. However, the cellular and molecular mechanisms for the effects of zinc deficiency on bone formation have not been well-defined. The first objective of this thesis was to investigate the effects of zinc deficiency on chondrocyte proliferation, differentiation and apoptosis in the epiphyseal growth plate of juvenile chickens. Newly hatched broiler chickens were fed either a low zinc (10 mg per kg diet, or 10 ppm) or a zinc adequate (68 ppm) soy protein-based purified diet. Cell proliferation in the growth plate was evaluated with BrdU labeling technique. Apoptosis was assessed using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method. The results showed that, as early as day 3 of the study, zinc deficiency significantly inhibited chondrocyte proliferation in the growth plate. Premature differentiation also occurred in chondrocytes of the proliferative zone, as indicated by immunostaining for osteonectin, a marker for chondrocyte maturation. Furthermore, zinc deficiency caused apoptosis of growth plate chondrocytes. These effects were primarily manifested in the areas remote from the blood supply. In addition, in situ hybridization showed that collagen II mRNA was uniformly decreased in the growth plate due to zinc deficiency. Immunostaining of local growth factors PTHrP and IGF-1 did not reveal any differences between zinc deficient and adequate tissues at the early stage. By day 7 of the study, severe growth plate lesions, characterized by reduced cellularity, abnormally shaped cells and apoptotic bodies, were formed in areas remote from blood vessels. Collagen II mRNA, PTHrP and IGF-1 were greatly reduced in the lesion. However, the growth rate and food intake of zinc deficient chickens were not different from that of the controls during the 7 day experiment period. Therefore, zinc deficiency affected chondrocyte proliferation, differentiation, and apoptosis independently from long-term effects on nutrient intake. The second objective of this thesis was to investigate the influence of maternal zinc deficiency during lactation and dietary zinc treatment after weaning on the longitudinal bone growth of young growing rats. Sprague-Dawley dams were fed either a zinc-adequate (34 ppm zinc) or a low zinc (4 ppm zinc) purified diet throughout lactation. After weaning at 22 days postpartum, pups received dietary treatment for another 16 days. Pups from zinc-sufficient dams were fed the zinc-adequate diet (Control), while pups from zinc-deficient dams were divided into 3 groups: one group received a low zinc diet (2 ppm zinc) and the other two groups were fed the zinc-adequate diet with (pair-fed) or without (ad libitum-fed) food restriction. Maternal zinc deficiency significantly affected the growth of suckling pups. At age of 21days, the average body weight, femur length, and femur dry weight were 30.1 g, 16.0 mm, and 47.4 mg for the pups from zinc-deficient dams, respectively, and 56.5 g, 18.9 mm, and 76.3 mg for the pups from zinc-sufficient dams, respectively (p<0.05). Furthermore, dietary zinc deficiency after weaning completely prevented growth in pups from zinc-deficient dams. Growth of pair-fed animals was also severely impaired. In contrast, the growth rate of ad libitum-fed animals was similar to that of the control animals. At the end of the study, femur length, femur dry weight, and the width of tibial growth pate were significantly lower in zinc-deficient and pair-fed rats as compared to ad libitum-fed and control animals. No histological differences were observed in growth plates between zinc-deficient and pair-fed rats. In conclusion, maternal zinc deficiency during lactation and dietary zinc restriction after weaning severely impaired the longitudinal bone growth of young growing rats. However, this effect was largely attributable to the inanition associated with zinc deficiency as the effect could be duplicated with food restriction. In summary, zinc deficiency decreased proliferation, promoted differentiation and induced apoptosis in growth plate chondrocytes of juvenile chickens. These effects were responsible for the disrupted structure and formation of pathological lesions in the chicken growth plate. In young growing rats, maternal zinc deficiency and dietary zinc restriction also severely reduced the width of the growth plate and impaired longitudinal bone growth.