Resistin differentially modulates neuropeptide gene expression and AMP-activated protein kinase activity in N-1...

Intraventricular resistin is known to reduce food intake, modify hypothalamic gene expression (e.g. NPY, POMC) and influence the activity of novel metabolic enzymes (e.g. 5'AMP-activated protein kinase; AMPK) in the rodent brain. Previously we demonstrated that the hypothalamus, and the N-1 hypothalamic neuronal cell line, also expressed several adipokines, including resistin and adiponectin (ADPN). These data suggested that they might also impact brain function and metabolism. We used the N-1 hypothalamic neuronal cell line to examine NPY, AgRP, POMC, and ADPN expression following acute resistin treatment (45 min; 100 ng/mL and 1000 ng/mL). The total and phosphorylated levels of AMPKalpha and acetyl-CoA carboxylase (ACC) were subsequently assessed using Western blot analysis. Parallel investigations were also conducted following a) resistin overexpression, or b) after the RNAi-mediated attenuation of resistin mRNA in N-1 neurons. Resistin overexpression lowered POMC (-35%, p<0.01), ADPN (-23%, p<0.05) and NPY (-36%, p<0.05) mRNA as evaluated using realtime RT-PCR, although AgRP remained unchanged, and significant increases in pAMPKalpha and pACC were detected (+47% and +34% respectively, p<0.001). In contrast recombinant resistin only significantly increased the level of pAMPKalpha (+31%; p<0.05), but failed to significantly modify gene expression, in N-1 neurons. Conversely the RNAi-mediated silencing of resistin expression increased AgRP (+37%, p<0.05), POMC (+66%, p<0.0001), ADPN (+87%, p<0.0001), whereas NPY was reduced (-22%, p<0.01) along with pAMPKalpha and pACC (-43% and -35% respectively, p<0.001). In summary, these in vitro data suggest that endogenous resistin might be capable of fine-tuning the expression and enzymatic activity of various hypothalamic targets previously implicated in the delicate homeostatic control of food intake. As such, resistin may be part of an autocrine/paracrine loop, which may in turn contribute to some of the reported effects of resistin on energy metabolism.