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Tups, A. et al.

Alexander Tups, Sigrid Stöhr, Michael Helwig, Perry Barrett, Elżbieta Krol, Joachim Schachtner, Julian G. Mercer, Martin Klingenspor,

Seasonal leptin resistance is associated with impaired signalling via JAK2-STAT3 but not ERK, possibly mediated by reduced hypothalamic GRB2 protein.

The Siberian hamster, Phodopus sungorus, undergoes a striking seasonal cycle of leptin sensitivity and body weight regulation, but the molecular mechanism and relevance to human leptin insensitivity are unknown. Here we show that nuclear translocation of phospho-STAT3 in the hypothalamus is rapidly stimulated by leptin to a greater extent in hamsters held in short-day length (SD) as compared to long-day length (LD). Intriguingly, effects of leptin on STAT3 appeared to be in part limited to nuclear translocation of phospho-STAT3 associated with the cell surface rather than phosphorylation of STAT3. The number of phospho-ERK cells within the hypothalamus was unaffected by either photoperiod or leptin. However, proximal to ERK phosphorylation, hypothalamic SH2-containing tyrosine phosphatase (SHP2) and the small growth factor receptor-binding protein (GRB2), which act as competitive negative modulators on binding of SOCS3 to leptin receptor (LRb)-associated Tyr(985), were increased in SD compared to LD. Our findings suggest that activation of STAT3 by leptin may be dependent on interaction of stimulatory SHP2/GRB2 as well as inhibitory SOCS3 on the level of competitive binding to LRb-associated Tyr(985). This hypothetical mechanism may represent the molecular identity of seasonally induced adjustments in leptin sensitivity and may be applied to investigating leptin sensitivity in other rodent models.[1]

References

Seasonal leptin resistance is associated with impaired signalling via JAK2-STAT3 but not ERK, possibly mediated by reduced hypothalamic GRB2 protein. Tups, A., Stöhr, S., Helwig, M., Barrett, P., Krol, E., Schachtner, J., Mercer, J.G., Klingenspor, M. J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol. (2012) [Pubmed]

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