Transmembrane protein TMEM184B is necessary for interleukin-31-induced itch.

ABSTRACT: Nociceptive and pruriceptive neurons in the dorsal root ganglia (DRG) convey sensations of pain and itch to the spinal cord, respectively. One subtype of mature DRG neurons, comprising 6% to 8% of neurons in the ganglia, is responsible for sensing mediators of acute itch and atopic dermatitis, including the cytokine IL-31. How itch-sensitive (pruriceptive) neurons are specified is unclear. Here, we show that transmembrane protein 184B (TMEM184B), a protein with roles in axon degeneration and nerve terminal maintenance, is required for the expression of a large cohort of itch receptors, including those for interleukin 31 (IL-31), leukotriene C4, and histamine. Male and female mice lacking TMEM184B show reduced responses to IL-31 but maintain normal responses to pain and mechanical force, indicating a specific behavioral defect in IL-31-induced pruriception. Calcium imaging experiments indicate that a reduction in IL-31-induced calcium entry is a likely contributor to this phenotype. We identified an early failure of proper Wnt-dependent transcriptional signatures and signaling components in Tmem184b mutant mice that may explain the improper DRG neuronal subtype specification. Accordingly, lentiviral re-expression of TMEM184B in mutant embryonic neurons restores Wnt signatures. Together, these data demonstrate that TMEM184B promotes adult somatosensation through developmental Wnt signaling and promotion of proper pruriceptive gene expression. Our data illuminate a new key regulatory step in the processes controlling the establishment of diversity in the somatosensory system.

Acute pain alters P-glycoprotein-containing protein complexes in rat cerebral microvessels: Implications for P-glycoprotein trafficking.

P-glycoprotein (PgP) is the major drug efflux pump in human cerebral microvessels. PgP prevents pathogens, toxins and therapeutic drugs from entering the CNS. Understanding the molecular regulation of PgP activity will suggest novel mechanisms to improve CNS drug delivery. Previously, we found that during peripheral inflammatory pain (PIP) (3 h after λ carrageenan injection in the rat paw), PgP traffics to the cortical microvessel endothelial cell plasma membrane concomitant with increased PgP activity. In the current study, we measured the changes in composition of PgP-containing protein complexes after PIP in rat microvessel isolates. We found that a portion of the PgP is contained in a multi-protein complex that also contains the caveolar proteins CAV1, SDPR, PTRF and PRKCDBP. With PIP, total CAV1 bound to PgP was unchanged; however, phosphorylated CAV1 (Y14P-CAV1) in the complex increased. There were few PgP/CAV1 complexes relative to total PgP and CAV1 in the microvessels suggesting CAV1 bound to PgP is unlikely to affect total PgP activity. However, both PgP and CAV1 trafficked away from the nucleus in response to PIP. These data suggest that P-CAV1 bound to PgP potentially regulates PgP trafficking and contributes to the acute PgP activity increase after a PIP stimulus.

Chronic morphine exposure potentiates p-glycoprotein trafficking from nuclear reservoirs in cortical rat brain microvessels.

The rates of opioid prescription and use have continued to increase over the last few decades resulting in a greater number of opioid tolerant patients. Treatment of acute pain from surgery and injury is a clinical challenge for these patients. Several pain management strategies including prescribing increased opioids are used clinically with limited success; all currently available strategies have significant limitations. Many opioids are a substrate for p-glycoprotein (p-gp), an efflux transporter at the blood-brain barrier (BBB). Increased p-gp is associated with a decreased central nervous system uptake and analgesic efficacy of morphine. Our laboratory previously found that acute peripheral inflammatory pain (PIP) induces p-gp trafficking from the nucleus to the luminal surface of endothelial cells making up the BBB concomitant with increased p-gp activity and decreased morphine analgesic efficacy. In the current study, we tested whether PIP-induced p-gp trafficking could contribute to decreased opioid efficacy in morphine tolerant rats. A 6-day continuous dosing of morphine from osmotic minipumps was used to establish morphine tolerance in female rats. PIP induced p-gp trafficking away from nuclear stores showed a 2-fold increase in morphine tolerant rats. This observation suggests that p-gp trafficking contributes to the decreased morphine analgesic effects in morphine tolerant rats experiencing an acute pain stimulus. Attenuating p-gp trafficking during an acute pain stimulus could improve pain management by increasing the amount of opioid that could reach CNS analgesic targets and decrease the need for the dose escalation that is a serious challenge in pain management.

P-glycoprotein traffics from the nucleus to the plasma membrane in rat brain endothelium during inflammatory pain.

P-glycoprotein (PgP), a drug efflux pump in blood-brain barrier endothelial cells, is a major clinical obstacle for effective central nervous system drug delivery. Identifying PgP regulatory pathways that can be exploited clinically is critical for improving central nervous system drug delivery. We previously found that PgP activity increases in rat brain microvessels concomitant with decreased central nervous system drug delivery in response to acute peripheral inflammatory pain. In the current study, we tested the hypothesis that PgP traffics to the luminal plasma membrane of the microvessel endothelial cells from intracellular stores during peripheral inflammatory pain. Using immunofluorescence microscopy, we detected PgP in endothelial cell nuclei and in the luminal plasma membrane in control animals. Following peripheral inflammatory pain, luminal PgP staining increased while staining in the nucleus decreased. Biochemical analysis of nuclear PgP content confirmed our visual observations. Peripheral inflammatory pain also increased endothelial cell luminal staining of polymerase 1 and transcript release factor/cavin1 and serum deprivation response protein/cavin2, two caveolar scaffold proteins, without changing caveolin1 or protein kinase C delta binding protein/cavin3 location. Our data (a) indicate that PgP traffics from stores in the nucleus to the endothelial cell luminal membrane in response to peripheral inflammatory pain; (b) provide an explanation for our previous observation that peripheral inflammatory pain inhibits central nervous system drug uptake; and (c) suggest a novel regulatory mechanism for PgP activity in rat brain.