Rho-kinase signaling in energy balance

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The melanocortin signaling pathway has emerged as a key signaling system regulating normal body-weight homeostasis and energy balance. Activation of melanocortin-4 receptor (MC4R) by ?-MSH reduces fat stores by decreasing food intake and increasing energy expenditure. Yet, the cellular mechanism(s) underlying melanocortin actions remains poorly understood. Our preliminary data point to the importance of ROCK1 action in MC4R-expressing neurons that is significant for the development of obesity in mice and humans. We found that selective deletion of ROCK1 in MC4R-expressing or Sim1-expressing neurons significantly increases body weight and adiposity. Interestingly, we found that ROCK1 activation in MC4R-containing neurons is required for the anorexigenic action of melanocortin through suppressing AMPK. Evidence demonstrates that UBE2O is an upstream mediator of AMPK that targets ?2AMPK for ubiquitination and degradation. Furthermore, we observed that human ROCK1 variant (2824G<A, E942K) from a consanguineous population in Pakistan displays severe obesity, and the mutant mice carrying the human ROCK1 mutation (E942K) are obese. We therefore hypothesize that ROCK1 in MC4R-expressing neurons is necessary for the metabolic regulation of normal body-weight homeostasis and energy balance and is linked with the UBE2O-AMPK signaling cascade for anorexigenic action of melanocortin. Thus, an impaired ROCK1 signaling axis leads to energy imbalance, causing obesity. To this end, we will (i) elucidate the functional importance of ROCK1 in MC4R-expressing neurons in the control of energy balance; (ii) establish the mechanism(s) by which ROCK1 mediates the effect of melanocortin on feeding; and (iii) explore the significance of the human ROCK1 mutation (E942K) in regulating energy balance. To accomplish these goals, we will employ state-of-the-art biochemical, molecular, cellular, and metabolic physiological techniques, including genetically engineered tissue-specific transgenic mouse models, mutant mice carrying the human ROCK1-E942K mutation, Cre-inducible AAV, DREADD, and the rAAV-FlexON switch system. These studies will provide a unique opportunity to establish a novel mechanism implicating ROCK1 as a key determinant of hypothalamic energy balance. The data generated from these timely studies may offer further insights into the pathogenesis of obesity-linked metabolic diseases and lead to new therapeutic targets for the treatment of obesity.