Vitamin A effects on vertebral bone tissue homeostasis in gilthead sea bream (Sparus aurata) juveniles

Abstract

Summary Vertebral deformities constitute a recurrent problem in farmed teleost fish species. Potential causes of skeletal deformities are associated with genetic, environmental and nutritional factors. Considering nutritional factors, previous studies have shown that nutritional vitamin A (VA) imbalance implied the appearance of vertebral deformities in marine fish larvae; however, information about the effects of VA on bone homeostasis in juveniles is scarce. A study of vertebral bone tissue homeostasis in gilthead sea bream (Sparus aurata) juveniles fed with two dietary VA levels was performed by means of histological (Haematoxylin‐Eosin, Alcian blue – PAS, Haematoxylin – VOF and Picrosirius red staining) and histochemical (immunostaining for bone and matrix Gla protein; OC and MGP, respectively) approaches. Fish were fed with two diets containing 2.5 × 104 (control) and 2.3 × 106 (hypervitaminosis A group) IU total VA kg−1 during 6 months. Results showed that gilthead sea bream juveniles were not affected in terms of growth or survival rate by nutritional hypervitaminosis A, whereas the homeostasis of the vertebral bone was altered. Vertebral bodies from the control and VA fed fish showed differences in their morphological and biochemical composition at the growth zone of the vertebral end‐plates. Picrosirius red staining revealed that vertebral end‐plates and the trabecular bone layer from control and VA fed fish presented different diameter in collagen fibers. In addition, immunohistochemical analysis revealed increased protein levels of MGP and BGP in the notochord from gilthead sea bream juveniles fed hypervitaminosis A. Results suggest that hypervitaminosis A alter bone homeostasis through an accelerated bone mineralization, which might increase mechanical load between adjacent vertebrae and induce vertebral compression/fusion through a bone remodelling process.

Normal and histopathological organization of the opercular bone and vertebrae in gilthead sea bream Sparus aurata

“…Concerning MGP, a preferential deposition was detected in notochordal cells of non-deformed vertebrae compared with deformed ones. Higher levels of OC and MGP deposition in notochordal tissue of deformed vertebrae were similar to those reported by Fernández et al (2012) in gilthead sea bream juveniles fed hypervitaminosis A. These results are in agreement with previous studies in which an increased co-transcription of both chondrogenic and osteogenic markers were found in the notochord of Atlantic salmon displaying spinal fusions (Ytteborg et al 2010(Ytteborg et al , 2012.…”

“…Another major histomorphological change in lordotic gilthead sea bream vertebrae was the disorganization of the intervertebral region, which lead to a complete loss of notochordal sheath integrity. These results were in concordance with those reported by other authors for Atlantic salmon Salmon salar reared at high temperatures (Ytteborg et al 2010), gilthead sea bream fed hypervitaminosis A (Fernández et al 2012) and guppy Poecilia reticulata displaying a curveback syndrome (Gorman et al 2010). Major histomorphological changes of lordotic vertebrae in gilthead sea bream specimens from this study were linked to the loss of the integrity of notochordal cells, which was associated with the presence of modified chordocytes in which calcium deposition was noticeable.…”

“…A comparison between normal and deformed opercula revealed differences in collagen fiber thickness and in their 3-dimensional arrangement, consisting of reduced and scattered areas of orange dye (fewer big collagen fibers) in deformed opercular bones (opercle and subopercle). This fact has been suggested as a bone remodelling process linked to changes in bone composition and degradation of collagen fibers (Fernández et al 2012). Considering that the mechanical properties of the opercular bone depend on the composition and structure of its matrix (Totland et al 2011), the thickness of collagen fibers in deformed opercula might indicate a weakness and vulnerability to mechanical disturbances of this skeletal structure, since collagen content confers certain tissue elasticity (Prades et al 2010), and therefore changes in its proportion could reduce tissue flexibility and plasticity (Canavese & Colitti 1996, Ytteborg et al 2012.…”

“…Various procedures have been used as simple and rapid diagnostic tools for studying skeletal deformities in fish, such as X-rays, double staining or even computer tomography; allowing the identification of abnormal growth in different skeletal structures (see reviews in Witten et al 2009, Koumoundouros 2010, Boglione et al 2013b. Although there is a great variety of research in fish skeletal histology (reviewed in Meunier 2011), there is limited information about the histological organization of skeletal tissues in gilthead sea bream (Galeotti et al 2000, Beraldo et al 2003, Fernández et al 2012. The use of histological procedures is considered a valuable tool for providing basic knowledge on bone formation, as well as providing new insights into the structural changes oc curring in deformed skeletal structures (Ytteborg et al 2012).…”

Interdisciplinary approaches in fish skeletal biology

“…How epigenetic factors, such as nutrition, vaccination or temperature, influence skeletal development is often explored by scientist that aim to improve skeletal development in farmed fish. The same factors may, however, influence skeletal development in zebrafish and medaka and in other vertebrates including humans (Berg et al., 2012; Boglino et al., 2012; Dionísio et al., 2012; Fernández et al., 2012; de Vareilles et al., 2012). The extend of skeletal plasticity and its fundamental function for development and evolution is shown by Levin et al.…”