AbstractBackground and PurposeLeptin, an important regulator of the energy balance, acts on the brain to inhibit feeding. However, the mechanisms involved in leptin signalling have not yet been fully elucidated. Heat shock protein 90 (HSP90) is a molecular chaperone that is involved in regulating cellular homeostasis. In the present study, we investigated the possible involvement of HSP90 in leptin signal transduction.Experimental ApproachHEK293 and SH‐SY5Y cell lines stably transfected with the Ob‐Rb leptin receptor (HEK293 Ob‐Rb, SH‐SY5Y Ob‐Rb) were used in the present study. Phosphorylation of JAK2 and STAT3 was analysed by western blotting. An HSP90 inhibitor was administered i.c.v. into rats and their food intake was analysed.Key ResultsThe knock‐down of HSP90 in the HEK293 Ob‐Rb cell line attenuated leptin‐induced JAK2 and STAT3 signalling. Moreover, leptin‐induced JAK2/STAT3 phosphorylation was markedly attenuated by the HSP90 inhibitors geldanamycin, radicicol and novobiocin. However, these effects were not mediated through previously known factors, which are known to be involved in the development of leptin resistance, such as suppressor of cytokine signalling 3 or endoplasmic reticulum stress. The infusion of an HSP90 inhibitor into the CNS blunted the anorexigenic actions of leptin in rats (male Wister rat).Conclusions and ImplicationsHSP90 may be a novel factor involved in leptin‐mediated signalling that is linked to anorexia.