Short-Days Induce Weight Loss in Siberian Hamsters Despite Overexpression of the Agouti-Related Peptide Gene

Authors

  • P. H. Jethwa,

    1. School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham, UK.
    2. Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Loughborough, UK.
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    • 1

      These authors contributed equally to this work.

  • A. Warner,

    1. School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham, UK.
    2. Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Loughborough, UK.
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    • 1

      These authors contributed equally to this work.

  • M. J. Fowler,

    1. School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham, UK.
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  • M. Murphy,

    1. School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham, UK.
    2. Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Loughborough, UK.
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  • M. W. De Backer,

    1. Rudolf Magnus Institute of Neuroscience, Department of Neuroscience and Pharmacology, University Medical Center Utrecht, Utrecht, Netherlands.
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  • R. A. H. Adan,

    1. Rudolf Magnus Institute of Neuroscience, Department of Neuroscience and Pharmacology, University Medical Center Utrecht, Utrecht, Netherlands.
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  • P. Barrett,

    1. Molecular Endocrinology Group, University of Aberdeen Rowett Institute of Nutrition and Health, Aberdeen, UK.
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  • J. M. Brameld,

    1. Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Loughborough, UK.
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  • F. J. P. Ebling

    1. School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham, UK.
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Correspondence to: Francis J. P. Ebling, School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham NG7 2UH, UK
(e-mail: fran.ebling@nottingham.ac.uk).

Abstract

Many vertebrates express profound annual cycles of body fattening, although it is not clear whether these represent differential activity of the central pathways known to mediate homeostatic control of food intake and energy expenditure, or whether the recent discovery of a major role for pars tuberalis-ependymal signalling points towards novel mechanisms. We examined this in the Siberian hamster (Phodopus sungorus) by using gene transfection to up-regulate a major orexigenic peptide, agouti-related peptide (AgRP), and then determined whether this increased anabolic drive could prevent the short-day induced winter catabolic state. Infusions of a recombinant adeno-associated virus encoding an AgRP construct into the hypothalamus of hamsters in the long-day obese phase of their seasonal cycle produced a 20% gain in body weight over 6 weeks compared to hamsters receiving a control reporter construct, reflecting a significant increase in food intake and a significant decrease in energy expenditure. However, all hamsters showed a significant, prolonged decrease in body weight when exposed to short photoperiods, despite the hamsters expressing the AgRP construct maintaining a higher food intake and lower energy expenditure relative to the control hamsters. Visualisation of the green fluorescent protein reporter and analysis of AgRP-immunoreactivity confirmed widespread expression of the construct in the hypothalamus, which was maintained for the 21-week duration of the study. In conclusion, the over-expression of AgRP in the hypothalamus produced a profoundly obese state but did not block the seasonal catabolic response, suggesting a separation of rheostatic mechanisms in seasonality from those maintaining homeostasis of energy metabolism.

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