Hypothalamic mTORC2 is essential for metabolic health and longevity.

The mechanistic target of rapamycin (mTOR) is an evolutionarily conserved protein kinase that regulates growth and metabolism. mTOR is found in two protein complexes, mTORC1 and mTORC2, that have distinct components and substrates and are both inhibited by rapamycin, a macrolide drug that robustly extends lifespan in multiple species including worms and mice. Although the beneficial effect of rapamycin on longevity is generally attributed to reduced mTORC1 signaling, disruption of mTORC2 signaling can also influence the longevity of worms, either positively or negatively depending on the temperature and food source. Here, we show that loss of hypothalamic mTORC2 signaling in mice decreases activity level, increases the set point for adiposity, and renders the animals susceptible to diet-induced obesity. Hypothalamic mTORC2 signaling normally increases with age, and mice lacking this pathway display higher fat mass and impaired glucose homeostasis throughout life, become more frail with age, and have decreased overall survival. We conclude that hypothalamic mTORC2 is essential for the normal metabolic health, fitness, and lifespan of mice. Our results have implications for the use of mTORC2-inhibiting pharmaceuticals in the treatment of brain cancer and diseases of aging.

Activation of AMPK by metformin improves withdrawal signs precipitated by nicotine withdrawal.

Cigarette smoking is the leading cause of preventable disease and death in the United States, with more persons dying from nicotine addiction than any other preventable cause of death. Even though smoking cessation incurs multiple health benefits, the abstinence rate remains low with current medications. Here we show that the AMP-activated protein kinase (AMPK) pathway in the hippocampus is activated following chronic nicotine use, an effect that is rapidly reversed by nicotine withdrawal. Increasing pAMPK levels and, consequently, downstream AMPK signaling pharmacologically attenuate anxiety-like behavior following nicotine withdrawal. We show that metformin, a known AMPK activator in the periphery, reduces withdrawal symptoms through a mechanism dependent on the presence of the AMPKα subunits within the hippocampus. This study provides evidence of a direct effect of AMPK modulation on nicotine withdrawal symptoms and suggests central AMPK activation as a therapeutic target for smoking cessation.

Normal sleep requires the astrocyte brain-type fatty acid binding protein FABP7.

Sleep is found widely in the animal kingdom. Despite this, few conserved molecular pathways that govern sleep across phyla have been described. The mammalian brain-type fatty acid binding protein (Fabp7) is expressed in astrocytes, and its mRNA oscillates in tandem with the sleep-wake cycle. However, the role of FABP7 in regulating sleep remains poorly understood. We found that the missense mutation FABP7.T61M is associated with fragmented sleep in humans. This phenotype was recapitulated in mice and fruitflies bearing similar mutations: Fabp7-deficient mice and transgenic flies that express the FABP7.T61M missense mutation in astrocytes also show fragmented sleep. These results provide novel evidence for a distinct molecular pathway linking lipid-signaling cascades within astrocytes in sleep regulation among phylogenetically disparate species.

The effect of glycomimetic functionalized collagen on peripheral nerve repair.

Increasing evidence suggests that the improper synaptic reconnection of regenerating axons is a significant cause of incomplete functional recovery following peripheral nerve injury. In this study, we evaluate the use of collagen hydrogels functionalized with two peptide glycomimetics of naturally occurring carbohydrates-polysialic acid (PSA) and human natural killer cell epitope epitope (HNK-1)-that have been independently shown to encourage nerve regeneration and axonal targeting. Our novel biomaterial was used to bridge a critical gap size (5 mm) in a mouse femoral nerve injury model. Functional recovery was assessed using gait and hind limb extension, and was significantly better in all glycomimetic peptide-coupled collagen conditions versus non-functional scrambled peptide-coupled collagen, native collagen, and saline controls. Analysis of cross-sections of the regenerated nerve demonstrated that hydrogels coupled with the PSA glycomimetic, but not HNK, had significant increases in the number of myelinated axons over controls. Conversely, hydrogels coupled with HNK, but not PSA, showed improvement in myelination. Additionally, significantly more correctly projecting motoneurons were observed in groups containing coupled HNK-1 mimicking peptide, but not PSA mimicking peptide. Given the distinct morphological outcomes between the two glycomimetics, our study indicates that the enhancement of recovery following peripheral nerve injury induced by PSA- and HNK-functionalized collagen hydrogels likely occurs through distinct mechanisms.

Neural cell type-specific responses to glycomimetic functionalized collagen.

Despite their noted functional role, glycans have had limited therapeutic use due to difficulties in synthesis and quick degradation in vivo. The recent discovery of glycomimetics has provided new opportunities for their application. In this study, we have functionalized type I collagen with peptide mimics of two glycans: (1) polysialic acid (PSA) and (2) an epitope first discovered on human natural killer cells (HNK-1). These glycans and their glycomimetic counterparts have been shown to be important regulators of repair following injury through their unique and phenotypically specific effects on neural behavior. We show that these molecules retain their bioactivity following functionalization to the collagen backbone. Grafted HNK-1 encouraged motor neuron outgrowth, while grafted PSA encouraged sensory and motor neuron outgrowth and enhanced Schwann cell proliferation and process extension. These data support the potential of glycomimetic-functionalized collagen as a biomaterial strategy to increase the efficiency of synaptic reconnection following nervous system injury.