Molecular Signatures of Mouse TRPV1-Lineage Neurons Revealed by RNA-Seq Transcriptome Analysis

Abstract

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.

Dual action of neurokinin-1 antagonists on Mas-related GPCRs

“…The similar number of SP-induced scratching bouts reported in WT and mast cell-deficient mice (17) can now be explained as follows: MrgprB2 is expressed on mast cells and thus absent in mast cell-deficient mice (16). MrgprA1 is expressed at functional levels on nerves and MrgprB2 is not (11,16).…”

“…MrgprA1 is expressed at functional levels on nerves and MrgprB2 is not (11,16). As mouse MrgprA1 is 10-fold more sensitive to SP than mouse MrgprB2, scratching in WT and mast cell-deficient mice is driven by the interaction between SP and mouse MrgprA1.…”

“…This line of reasoning leads to the suggestion that a distinct Mrgpr on mouse sensory nerves may also serve as an ortholog to human MRGPRX2. Previous studies revealed that MrgprA1 is exclusively expressed at functional levels (16) on mouse DRGs but not mast cells (8,11,16). We evaluated the interaction of SP with several mouse Mrgprs and found that SP activates mouse MrgprA1 (Figure 1 and Supplemental Figure 1; supplemental material available online with this article; doi:10.1172/jci.insight.89362DS1).…”

Somatosensory neuron types identified by high-coverage single-cell RNA-sequencing and functional heterogeneity

“…The "NP subset" and "PEP subset" are no longer suitable for defining neuron types because transcriptome analysis clearly shows that IB4-positive (NP) neurons express neuropeptides at various levels, and expression of neuropeptides such as substance P and CGRP is not limited to C1 (PEP) neurons. The transcriptional profiles of TRPV1-lineage DRG neurons and Na v 1.8 channel-expressing nociceptors [23,24] could be shared by several neuron types. Interestingly, some C1 neurons express high levels of both Trpa1 and Trpv1, whereas C4, C5 and C6 express relatively lower levels of Trpa1.…”

“…The transcriptional profiles of TRPV1 lineage and Na v 1.8 channel-expressing DRG neurons have been examined by RNA-seq [23,24]. By single-cell PCR, Chiu et al identified six subgroups of DRG neurons [25].…”