Dysregulation of lipid metabolism in individual tissues can lead to systemic disruption of insulin action and glucose metabolism. Utilizing a comprehensive lipidomic platform and mice deficient in adipose tissue lipid chaperones aP2 and mal1, we explored how metabolic alterations in adipose tissue are linked to whole-body metabolism through lipid signals. A robust increase in de novo lipogenesis rendered the adipose tissue of these mice resistant to the deleterious systemic effects of dietary lipid exposure. Systemic lipid profiling also led to identification of C16:1n7-palmitoleate as an adipose tissue-derived lipid hormone that strongly stimulates muscle insulin action and suppresses hepatosteatosis. Our data reveal a novel, lipid-mediated endocrine network and demonstrate that adipose tissue uses lipokines such as C16:1n7-palmitoleate to communicate with distant organs and regulate systemic metabolic homeostasis.

SUMMARYItch, the unpleasant sensation that evokes a desire to scratch, accompanies numerous skin and nervous system disorders. In many cases, pathological itch is insensitive to antihistamine treatment. Recent studies have identified members of the Mas-related GPCR (Mrgpr) family that are activated by mast cell mediators and promote histamine-independent itch. MrgprA3 and MrgprC11 act as receptors for the pruritogens chloroquine and BAM8–22, respectively. However, the signaling pathways and transduction channels activated downstream of these pruritogens are largely unknown. We found that TRPA1 is the downstream target of both MrgprA3 and MrgprC11, in cultured sensory neurons and heterologous cells. TRPA1 is required for Mrgpr-mediated signaling, as sensory neurons from TRPA1-deficient mice exhibited profoundly diminished responses to chloroquine and BAM8–22. Likewise, TRPA1-deficient mice displayed little to no scratching in response to these pruritogens. Our findings demonstrate that TRPA1 is an essential component of the signaling pathways that promote histamine-independent itch.

The cAMP-dependent protein kinase (PKA) has been shown to play an important role in long-term potentiation (LTP) in the hippocampus, but little is known about the function of PKA in long-term depression (LTD). We have combined pharmacologic and genetic approaches to demonstrate that PKA activity is required for both homosynaptic LTD and depotentiation and that a specific neuronal isoform of type I regulatory subunit (RI,B) is essential. Mice carrying a null mutation in the gene encoding RI.8 were established by use of gene targeting in embryonic stem cells. Hippocampal slices from mutant mice show a severe deficit in LTD and depotentiation at the Schaffer collateral-CAl synapse. This defect is also evident at the lateral perforant path-dentate granule cell synapse in RIp mutant mice. Despite a compensatory increase in the related RIa protein and a lack of detectable changes in total PKA activity, the hippocampal function in these mice is not rescued, suggesting a unique role for RID. Since the late phase of CAl LTP also requires PKA but is normal in RI,8 mutant mice, our data further suggest that different forms of synaptic plasticity are likely to employ different combinations of regulatory and catalytic subunits.Little is known about the molecular mechanisms underlying homosynaptic long-term depression (LTD), an electrophysiological phenomenon thought to reflect some of the biochemical processes used in mammalian learning (1, 2). Like longterm potentiation (LTP), LTD requires an increase in intraneuronal calcium (3-5). However, in LTD a low level of calcium influx is believed to preferentially activate phosphatases (6-10), whereas in LTP a larger influx of calcium is thought to activate kinases, including (indirectly) the cAMPdependent protein kinase (PKA) w_hich is critical for the late phase of LTP (11)(12)(13)(14).In addition to mediating use-dependent changes in synaptic efficacy, PKA may be important for certain forms of learning and is specifically involved in the switch from short-to long-term memory (15). Si-nce several isoforms of PKA exist, its involvement in synaptic plasticity and learning raises a question: Do different types of learning-related neuronal changes require specific regulatory (R) or catalytic (C) subunits? In the mouse, there are four R subunits (RIa, RIP3, RIIa, RIIP) that bind cAMP and two C subunits (Ca, C13) that phosphorylate substrate proteins when released from the R subunits upon cAMP binding. In the nervous system, RI13 appears to be specific to neurons (16) and is expressed in many regions including the neocortex, the pyramidal layer of the hippocampus, and the Purkinje and granular layers of the cerebellum (17). To elucidate the role of PKA in synaptic plasticity and to determine whether specific subunits serve unique intracellular signaling functions, we used homologous recombination in embryonic stem cells to generate mice carrying a null mutation in RIP3. MATERIALS AND METHODSGeneration of Mutant Mice. The targeting of embryonic stem cells and the establishment ...

Three sensory systems, olfaction, taste, and somatosensation, are dedicated to the detection of chemicals in the environment. Trigeminal somatosensory neurons enable us to detect a wide range of environmental stimuli, including pressure, temperature, and chemical irritants, within the oral and nasal mucosa. Natural plant-derived irritants have served as powerful pharmacological tools for identifying receptors underlying somatosensation. This is illustrated by the use of capsaicin, menthol, and wasabi to identify the heat-sensitive ion channel TRPV1, the cold-sensitive ion channel TRPM8, and the irritant receptor TRPA1, respectively. In addition to TRP channels, members of the two-pore potassium channel family have also been implicated in trigeminal chemosensation. KCNK18 was recently identified as a target for hydroxy-α-sanshool, the tingling and numbing compound produced in Schezuan peppers and other members of the Xanthoxylum genus. The role of these channels in trigeminal thermosensation and pain will be discussed.

Little is known about the molecular mechanisms underlying mammalian touch transduction. To identify novel candidate transducers, we examined the molecular and cellular basis of touch in one of the most sensitive tactile organs in the animal kingdom, the star of the star-nosed mole. Our findings demonstrate that the trigeminal ganglia innervating the star are enriched in tactile-sensitive neurons, resulting in a higher proportion of light touch fibers and lower proportion of nociceptors compared to the dorsal root ganglia innervating the rest of the body. We exploit this difference using transcriptome analysis of the star-nosed mole sensory ganglia to identify novel candidate mammalian touch and pain transducers. The most enriched candidates are also expressed in mouse somatosesensory ganglia, suggesting they may mediate transduction in diverse species and are not unique to moles. These findings highlight the utility of examining diverse and specialized species to address fundamental questions in mammalian biology.