Disorders of pain neural systems are frequently chronic and, when recalcitrant to treatment, can severely degrade the quality of life. The pain pathway begins with sensory neurons in dorsal root or trigeminal ganglia and the neuronal subpopulations that express the TRPV1 ion channel transduce sensations of painful heat and inflammation, and play a fundamental role in clinical pain arising from cancer and arthritis. In the present study we elucidate the complete transcriptomes of neurons from the TRPV1 lineage and a non-TRPV1 neuro-glial population in sensory ganglia through the combined application of next-gen deep RNA-Seq, genetic neuronal labeling with fluorescence-activated cell sorting, or neuron-selective chemoablation. RNA-Seq accurately quantitates gene expression, a difficult parameter to determine with most other methods especially for very low and very high expressed genes. Differentially expressed genes are present at every level of cellular function from the nucleus to the plasma membrane. We identified many ligand receptor pairs in the TRPV1 population suggesting that autonomous presynaptic regulation maybe a major regulatory mechanism in nociceptive neurons. The data define, in a quantitative, cell population specific fashion, the molecular signature of a distinct and clinically important group of pain-sensing neurons and provide an overall framework for understanding the transcriptome of TRPV1 nociceptive neurons.

Inherited sensory neuropathies are caused by mutations in genes affecting either primary afferent neurons, or the Schwann cells that myelinate them. Using RNA-Seq, we analyzed the transcriptome of human and rat DRG and peripheral nerve, which contain sensory neurons and Schwann cells, respectively. We subdivide inherited sensory neuropathies based on expression of the mutated gene in these tissues, as well as in mouse TRPV1 lineage DRG nociceptive neurons, and across 32 human tissues from the Human Protein Atlas. We propose that this comprehensive approach to neuropathy gene expression leads to better understanding of the involved cell types in patients with these disorders. We also characterize the genetic “fingerprint” of both tissues, and present the highly tissue-specific genes in DRG and sciatic nerve that may aid in the development of gene panels to improve diagnostics for genetic neuropathies, and may represent specific drug targets for diseases of these tissues.

BackgroundThree neuropeptides, gastrin releasing peptide (GRP), natriuritic precursor peptide B (NPPB), and neuromedin B (NMB) have been proposed to play roles in itch sensation. However, the tissues in which these peptides are expressed and their positions in the itch circuit has recently become the subject of debate. Here we used next-gen RNA-Seq to examine the expression of transcripts coding for GRP, NPPB, NMB, and other peptides in DRG, trigeminal ganglion, and the spinal cord as well as expression levels for their cognate receptors in these tissues.ResultsRNA-Seq demonstrates that GRP is not transcribed in mouse, rat, or human sensory ganglia. NPPB, which activates natriuretic peptide receptor 1 (NPR1), is well expressed in mouse DRG and less so in rat and human, whereas NPPA, which also acts on the NPR1 receptor, is expressed in all three species. Analysis of transcripts expressed in the spinal cord of mouse, rat, and human reveals no expression of Nppb, but unambiguously detects expression of Grp and the GRP-receptor (Grpr). The transcripts coding for NMB and tachykinin peptides are among the most highly expressed in DRG. Bioinformatics comparisons using the sequence of the peptides used to produce GRP-antibodies with proteome databases revealed that the C-terminal primary sequence of NMB and Substance P can potentially account for results from previous studies which showed GRP-immunostaining in the DRG.ConclusionsRNA-Seq corroborates a primary itch afferent role for NPPB in mouse and potentially NPPB and NPPA in rats and humans, but does not support GRP as a primary itch neurotransmitter in mouse, rat, or humans. As such, our results are at odds with the initial proposal of Sun and Chen (2007) that GRP is expressed in DRG. By contrast, our data strongly support an itch pathway where the itch-inducing actions of GRP are exerted through its release from spinal cord neurons.

Escherichia coli nucleoside-diphosphate kinase (Ndk) catalyzes nucleoside triphosphate synthesis and maintains intracellular triphosphate pools. Mutants of E. coli lacking Ndk exhibit normal growth rates but show a mutator phenotype that cannot be entirely attributed to the absence of Ndk catalytic activity or to an imbalance in cellular triphosphates. It has been suggested previously that Ndk, similar to its human counterparts, possesses nuclease and DNA repair activities, including the excision of uracil from DNA, an activity normally associated with the Ung and Mug uracil-DNA glycosylases (UDGs) in E. coli. Here we have demonstrated that recombinant Ndk purified from wild-type E. coli contains significant UDG activity that is not intrinsic, but rather, is a consequence of a direct physical and functional interaction between Ung and Ndk, although a residual amount of intrinsic UDG activity exists as well. Co-purification of Ung and Ndk through multicolumn low pressure and nickel-nitrilotriacetic acid affinity chromatography suggests that the interaction occurs in a cellular context, as was also suggested by co-immunoprecipitation of endogenous Ung and Ndk from cellular extracts. Glutathione S-transferase pulldown and far Western analyses demonstrate that the interaction also occurs at the level of purified protein, suggesting that it is specific and direct. Moreover, significant augmentation of Ung catalytic activity by Ndk was observed, suggesting that the interaction between the two enzymes is functionally relevant. These findings represent the first example of Ung interacting with another E. coli protein and also lend support to the recently discovered role of nucleoside-diphosphate kinases as regulatory components of multiprotein complexes. Escherichia coli nucleoside-diphosphate (NDP)3 kinase (NDK, EC 2.7.4.6) belongs to a large family of highly conserved oligomeric phosphate transfer enzymes consisting of 4 -6 identically folded subunits of 16 -20 kDa, each containing an active site. NDP kinases catalyze the reversible transfer of ␥-phosphates between nucleoside di-and triphosphates at very high efficiencies through an evolutionarily conserved active site histidine residue (1-3). E. coli NDP kinase is encoded by a single gene, ndk (4), whereas the genetically distinct forms of human NDP kinases are encoded by multiple genes termed NM23-H1 through H8 (5). The name NM (nonmetastatic)23 was initially accorded to the matriarch of the family, NM23-H1, on the basis of its reported action as a tissue-specific metastasis inhibitor (6). Moreover, there is evidence that NM23/NDK proteins promote tumor formation and play various roles in normal development and cellular proliferation (7,8).NM23/NDP kinases are also multifunctional in vitro. In addition to the phosphoryl transfer reactions, they can catalyze various types of DNA cleavage (9 -12) and activate transcription (13-15). The involvement of NM23 in DNA repair was initially proposed on the basis of a covalent, lysine-mediated mechanism by which NM23-H2/NDK-B ...

No abstract