Suppressor of cytokine signaling 3 knockdown in the mediobasal hypothalamus: counterintuitive effects on energy balance M W A de Backer 1 , M A D Brans 1 , A J van Rozen 1 , E M van der Zwaal 1 , M C M Luijendijk 1 , K G Garner 1 , M de Krom 1 , O van Beekum 1 , S E la Fleur 1,2 * and R A H Adan 1 * 1 Department of Neuroscience and Pharmacology, Rudolf Magnus Institute of Neuroscience, Utrecht University Medical Centre Utrecht, Universiteitsweg 100, Stratenum 5.203, 3584 CG Utrecht, The Netherlands 2 Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands (Correspondence should be addressed to R A H Adan; Email: r.a.h.adan@umcutrecht.nl) (S E la Fleur and R A H Adan contributed equally to this work) Abstract An increase in brain suppressor of cytokine signaling 3 (SOCS3) has been implicated in the development of both leptin and insulin resistance. Socs3 mRNA is localized throughout the brain, and it remains unclear which brain areas are involved in the effect of SOCS3 levels on energy balance. We investigated the role of SOCS3 expressed in the mediobasal hypothalamus (MBH) in the development of diet-induced obesity in adult rats. Socs3 mRNA was down- regulated by local injection of adeno-associated viral vectors expressing a short hairpin directed against Socs3, after which we determined the response to high-fat high-sucrose choice diet. In contrast to neuronal Socs3 knockout mice, rats with SOCS3 knockdown limited to the MBH showed increased body weight gain, larger amounts of white adipose tissue, and higher leptin concentrations at the end of the experiment. These effects were partly due to the decrease in locomotor activity, as 24 h food intake was comparable with controls. In addition, rats with Socs3 knockdown in the MBH showed alterations in their meal patterns: average meal size in the light period was increased and was accompanied by a compensatory decrease in meal frequency in the dark phase. In addition, neuropeptide Y (Npy) mRNA levels were significantly increased in the arcuate nucleus of Socs3 knockdown rats. Since leptin is known to stimulate Npy transcription in the absence of Socs3, these data suggest that knockdown of Socs3 mRNA limited to the MBH increases Npy mRNA levels, which subsequently decreases locomotor activity and alters feeding patterns. Journal of Molecular Endocrinology (2010) 45, 341–353 Introduction Obesity has been associated with leptin resistance in both humans and rodents. Although leptin normally reduces food intake, obese humans and rodents still overconsume calories despite increased leptin levels (Frederich et al. 1995, Maffei et al. 1995, Considine et al. 1996). In addition, after injection of exogenous leptin, obese humans and rodents do not respond with the decrease in food intake, which is normally observed in lean subjects and rodents (Cusin et al. 1996, Seeley et al. 1996, Halaas et al. 1997, Heymsfield et al. 1999). Several mechanisms have been proposed to mediate this leptin resistance such as impaired transport of leptin over the blood–brain barrier, impaired leptin receptor b (LEPRb) expression, and impaired LEPRb signaling (see review Morris & Rui (2009)). When leptin binds to the LEPRb, one of the pathways activated is the JAK2–STAT3 cascade (Bjorbaek et al. 1999). Phosphorylated STAT3 enters the nucleus and serves as a transcription factor, increasing the transcription of several genes including suppressor of cytokine signaling 3 (Socs3). In turn, SOCS3 inhibits leptin signaling through binding to JAK2 and phosphorylated tyrosine 985 on the LEPRb (Bjorbaek et al. 1999, Bjorbak et al. 2000). Thus, SOCS3 appears to act as a negative feedback regulator to prevent overactivation of leptin signaling. It has been shown that administration of leptin increases Socs3 mRNA in lean animals and that Socs3 mRNA levels are elevated in hypothalami of obese animals (Bjorbaek et al. 1998, Emilsson et al. 1999, Peiser et al. 2000, Munzberg et al. 2004, Tups et al. 2004, Krol et al. 2007). Together, these data suggest that SOCS3 plays an important role in the develop- ment of leptin resistance and obesity. The importance of SOCS3 in leptin resistance and diet-induced obesity is supported by studies that examined the phenotype of mice with altered Socs3 alleles. Although Socs3 knockout mice die at 341 Journal of Molecular Endocrinology (2010) 45, 341–353 DOI: 10.1677/JME-10-0057 0952–5041/10/045–341 q 2010 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology-journals.org