Endocrine Abstracts

Aims/hypothesis: Resistin could be implicated in the mechanism of insulin resistance and recent evidence suggests this occurs, in part, via a brain-dependent pathway. Given the emerging role of hypothalamic AMP-activated protein kinase (AMPK) in the modulation of appetite and glucose levels, we hypothesized that its activity would be modulated by resistin. To verify such a pathway, we employed the N-1 hypothalamic neuronal cell line, which expresses a variety of neuropeptides relevant to central energy metabolism. We also performed parallel studies using differentiated 3T3-L1 adipocytes, which are known to be sensitive to resistin.

Methods: The two cell lines were: (a) treated with recombinant resistin (100 ng/ml or 1000 ng/ml; 45 min); (b) transfected with a resistin (rstn) overexpression vector (24 h) or (c) transfected with a rstn-specific siRNA (100 nM; 24 h).The phosphorylation of AMPKα (pAMPKα), relative to total AMPKα, was determined by Western blotting with rabbit polyclonal antibodies (Cellsignal.com) and used to assess AMPK activation.

Results: Treatment of either cell line with resistin induced a significant increase in the ratio of pAMPKα/total AMPK( (30–122%, P<0.05). Rstn overexpression induced a similar increase in the ratio of pAMPKα in N-1 cells (+46%, P<0.001), but not in 3T3-L1 adipocytes. However silencing of rstn expression using a specific siRNA induced a significant reduction in the ratio of pAMPKα (−40%, P<0.001 and −30%, P<0.01) in N-1 and 3T3-L1 cells respectively.

Conclusions: These data suggest that resistin can modulate AMPK activity by either an endocrine or autocrine/paracrine mechanism in both N-1 hypothalamic neurons or 3T3-L1 adipocytes. These results provide a potential mechanism by which resistin might impact the hypothalamic-dependent regulation of appetite and glucose homeostasis.

Financial support was received from IWK Health Centre, UIMRF/Capital Health, and NSHRF.We acknowledge the generous gift of N-1 cells by Dr D Belsham (Toronto).