Molecular pathology of vertebral deformities in hyperthermic Atlantic salmon (Salmo salar)

Abstract

BackgroundHyperthermia has been shown in a number of organisms to induce developmental defects as a result of changes in cell proliferation, differentiation and gene expression. In spite of this, salmon aquaculture commonly uses high water temperature to speed up developmental rate in intensive production systems, resulting in an increased frequency of skeletal deformities. In order to study the molecular pathology of vertebral deformities, Atlantic salmon was subjected to hyperthermic conditions from fertilization until after the juvenile stage.ResultsFish exposed to the high temperature regime showed a markedly higher growth rate and a significant higher percentage of deformities in the spinal column than fish reared at low temperatures. By analyzing phenotypically normal spinal columns from the two temperature regimes, we found that the increased risk of developing vertebral deformities was linked to an altered gene transcription. In particular, down-regulation of extracellular matrix (ECM) genes such as col1a1, osteocalcin, osteonectin and decorin, indicated that maturation and mineralization of osteoblasts were restrained. Moreover, histological staining and in situ hybridization visualized areas with distorted chondrocytes and an increased population of hypertrophic cells. These findings were further confirmed by an up-regulation of mef2c and col10a, genes involved in chondrocyte hypertrophy.ConclusionThe presented data strongly indicates that temperature induced fast growth is severely affecting gene transcription in osteoblasts and chondrocytes; hence change in the vertebral tissue structure and composition. A disrupted bone and cartilage production was detected, which most likely is involved in the higher rate of deformities developed in the high intensive group. Our results are of basic interest for bone metabolism and contribute to the understanding of the mechanisms involved in development of temperature induced vertebral pathology. The findings may further conduce to future molecular tools for assessing fish welfare in practical farming.

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

“…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. Furthermore, bone tissue with lower levels of OC might demineralize more easily than that with higher OC content (Krossøy et al 2009), suggesting that lordotic vertebrae may be more fragile than non-deformed ones.…”

“…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.…”

“…Several studies in higher vertebrates have suggested that changes in the balance between cell death and cell proliferation are involved in bone and cartilage defects, which could ultimately lead to skeletal deformities (Cockroft & New 1978, Miura et al 2004. In this sense, the above-mentioned imbalanced cell cycling detected in lordotic vertebrae might also explain the presence of dense packaged chordocytes, occupying most of the intervertebral space without vacuolation, as was described by Ytteborg et al (2010) in Atlantic salmon vertebral fusions. Regarding the bone homeostasis measured by ALP and TRAP immunostaining, although this procedure may not be considered to be a quantitative assessment of bone formation and resorption, the present data might indicate that lordotic vertebrae were subjected to a more localized bone resorption process than non-deformed ones, since TRAP activity was only found in the chondrocytic areas of deformed vertebrae but was homogeneously distributed in the trabecular spaces of normal vertebrae.…”

“…The first 2 cell types secrete the extracellular matrix proteins of the cartilage and bone, respectively, while the third type produces cathepsins, matrix metalloproteinases and tartrate-resistant acid phosphatase (TRAP), providing an acidic environment in which the mineralized matrix is broken down (Ytteborg et al 2010). In addition, skeletogenesis involves a fourth type of cell: the osteocytes, which are involved in maintaining bone matrix and acting as mechanical load receptors.…”

Spinal deformities in a wild line of Poecilia wingei bred in captivity: report of cases and review of the literature

“…Several chemical/physical water parameters are known to be responsible for spinal malformations in fish [19] , including pH and heat shock [12,20] , low dissolved oxygen [21] , herbicides, organophosphate and organochlorine pesticides [22] , heavy metals [11,[23][24][25][26][27][28] and other pollutants [11,[29][30][31][32] . These potential causes do not seem to be related to our cases since the water of the farm was previously filtered in a reverse osmotic system in order to block heavy metals and other potential dangerous chemical agents, and then added with specific salts and water conditioner (Sera Aquatan 襆 ).…”