GLUCOSE USE IN FISH

Carbohydrate utilization by the working muscle of rainbow trout

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 Obiettivo del progetto (Objective)

'Carbohydrate-rich diets are frequently used in the commercial farming of fish. However, fish do not appear to have an elevated capacity to clear a high load of glucose from their circulation. Special attention has been directed towards the study of the physiological responses to such carbohydrate-rich feeding. Skeletal muscles play a key role in glucose homeostasis in mammals, and exercise has a noticeable effect in lowering plasma glucose. This effect is caused by an up-regulation of glucose transport mediated by GLUT4 in skeletal muscles in response to exercise. However, the exact mediating mechanism in the modulation of glucose transport in skeletal muscle has not been entirely characterized in vertebrates. Moreover, fish are an excellent model for the research of mechanisms involved in changes of the GLUT glucose transporters produced by exercise because they have anatomically separated red and white muscle masses, which allow the measurement of fibre-type-specific responses. I hypothesize that sustained exercise can be used to enhance carbohydrate expenditure in fish, increasing their natural capacity to clear and utilize plasma glucose by the contracting muscle. I will investigate this possibility, placing a special emphasis on the study of the cellular and molecular mechanisms regulating the GLUT-1 and -4 glucose transporters in white and red muscles. Changes in patterns for gene expression using a microarray platform and key biochemical parameters will also be measured in red and white muscles of rainbow trout after four weeks of sustained swimming. I expect that the results obtained from this research will help us to understand how glucose is regulated in fish. This knowledge could be transferred to European companies, leading to more efficient and environmentally conscious feeding practices in the rapidly growing and economic important aquaculture sector.'

Introduzione (Teaser)

A high carbohydrate diet may seem like a nightmare to a carnivore but researchers have investigated how exercise can make all the difference, particularly in fish farming.

Descrizione progetto (Article)

Commercial fish diets in farming enterprises may contain a high proportion of carbohydrates which could pose problems due to the fish's lack of ability to utilise the carbs. The EU-funded 'Carbohydrate utilization by the working muscle of rainbow trout' (Glucose USE IN FISH) project has studied the effects of exercise in trout to see exactly how carbohydrate utilisation can be increased.

Trout are a carnivorous group and are cultured worldwide. The team used a multi-tissue genomic approach, a whole organism physiological assessment and a cellular mechanistic analysis to study the effects of exercise on the fish.

After 40 days of exercise, trout metabolism recreated the spawning migration period where the fish mobilise lipid reserves that sustain the metabolic demands of endurance exercise. Using next generation sequencing, genes transcripted from red muscle were shown to be more involved in induced sustained swimming than those from the white. The scientists suggest that the white muscle may switch to a more aerobic phenotype.

After 30 days of high carbs and exercise, GLUT1 and GLUT4 glucose transporters were both upregulated in red muscle. Microarray analysis showed an increase in gene expression related to the immune response and muscle development.

To perform some of the molecular assays, the project team developed an in vitro model that mimics the exercise condition by delivering electric pulses to trout muscle myotubes. The process is modulated by adenosine monophosphate-activated protein kinase (MAPK) and, not only that but GLUT1 and GLUT4 transcription increases with exercise.

A first in research, the trout scientists have shown an important role for MAPK, a master metabolic switch that mediates the observed increase of glucose uptake in mammal muscle during exercise in non-mammalian vertebrates. Results showed that MAPK is involved in stimulating glucose uptake in fish muscle cells.

Transcript databases from the research may form a valuable data pool that can be used in research on red and white muscle functioning. The main applications of the research, however, rest with its significance for the aquaculture sector.

Glucose USE IN FISH has produced important evidence for swimming-enhanced carbohydrate utilisation in fish which may contribute to growth improvement. Farming a fitter fish may prove profitable and be more sustainable as well as humane.