Pax3 expression enhances PDGF-B-induced brainstem gliomagenesis and characterizes a subset of brainstem glioma.

High-grade Brainstem Glioma (BSG), also known as Diffuse Intrinsic Pontine Glioma (DIPG), is an incurable pediatric brain cancer. Increasing evidence supports the existence of regional differences in gliomagenesis such that BSG is considered a distinct disease from glioma of the cerebral cortex (CG). In an effort to elucidate unique characteristics of BSG, we conducted expression analysis of mouse PDGF-B-driven BSG and CG initiated in Nestin progenitor cells and identified a short list of expression changes specific to the brainstem gliomagenesis process, including abnormal upregulation of paired box 3 (Pax3). In the neonatal mouse brain, Pax3 expression marks a subset of brainstem progenitor cells, while it is absent from the cerebral cortex, mirroring its regional expression in glioma. Ectopic expression of Pax3 in normal brainstem progenitors in vitro shows that Pax3 inhibits apoptosis. Pax3-induced inhibition of apoptosis is p53-dependent, however, and in the absence of p53, Pax3 promotes proliferation of brainstem progenitors. In vivo, Pax3 enhances PDGF-B-driven gliomagenesis by shortening tumor latency and increasing tumor penetrance and grade, in a region-specific manner, while loss of Pax3 function extends survival of PDGF-B-driven;p53-deficient BSG-bearing mice by 33%. Importantly, Pax3 is regionally expressed in human glioma as well, with high PAX3 mRNA characterizing 40% of human BSG, revealing a subset of tumors that significantly associates with PDGFRA alterations, amplifications of cell cycle regulatory genes, and is exclusive of ACVR1 mutations. Collectively, these data suggest that regional Pax3 expression not only marks a novel subset of BSG but also contributes to PDGF-B-induced brainstem gliomagenesis.

TRPV4 is necessary for trigeminal irritant pain and functions as a cellular formalin receptor.

Detection of external irritants by head nociceptor neurons has deep evolutionary roots. Irritant-induced aversive behavior is a popular pain model in laboratory animals. It is used widely in the formalin model, where formaldehyde is injected into the rodent paw, eliciting quantifiable nocifensive behavior that has a direct, tissue-injury-evoked phase, and a subsequent tonic phase caused by neural maladaptation. The formalin model has elucidated many antipain compounds and pain-modulating signaling pathways. We have adopted this model to trigeminally innervated territories in mice. In addition, we examined the involvement of TRPV4 channels in formalin-evoked trigeminal pain behavior because TRPV4 is abundantly expressed in trigeminal ganglion (TG) sensory neurons, and because we have recently defined TRPV4's role in response to airborne irritants and in a model for temporomandibular joint pain. We found TRPV4 to be important for trigeminal nocifensive behavior evoked by formalin whisker pad injections. This conclusion is supported by studies with Trpv4(-/-) mice and TRPV4-specific antagonists. Our results imply TRPV4 in MEK-ERK activation in TG sensory neurons. Furthermore, cellular studies in primary TG neurons and in heterologous TRPV4-expressing cells suggest that TRPV4 can be activated directly by formalin to gate Ca(2+). Using TRPA1-blocker and Trpa1(-/-) mice, we found that both TRP channels co-contribute to the formalin trigeminal pain response. These results imply TRPV4 as an important signaling molecule in irritation-evoked trigeminal pain. TRPV4-antagonistic therapies can therefore be envisioned as novel analgesics, possibly for specific targeting of trigeminal pain disorders, such as migraine, headaches, temporomandibular joint, facial, and dental pain, and irritation of trigeminally innervated surface epithelia.

UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling.

At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.

Temporomandibular joint pain: a critical role for Trpv4 in the trigeminal ganglion.

Temporomandibular joint disorder (TMJD) is known for its mastication-associated pain. TMJD is medically relevant because of its prevalence, severity, chronicity, the therapy-refractoriness of its pain, and its largely elusive pathogenesis. Against this background, we sought to investigate the pathogenetic contributions of the calcium-permeable TRPV4 ion channel, robustly expressed in the trigeminal ganglion sensory neurons, to TMJ inflammation and pain behavior. We demonstrate here that TRPV4 is critical for TMJ-inflammation-evoked pain behavior in mice and that trigeminal ganglion pronociceptive changes are TRPV4-dependent. As a quantitative metric, bite force was recorded as evidence of masticatory sensitization, in keeping with human translational studies. In Trpv4(-/-) mice with TMJ inflammation, attenuation of bite force was significantly less than in wildtype (WT) mice. Similar effects were seen with systemic application of a specific TRPV4 inhibitor. TMJ inflammation and mandibular bony changes were apparent after injections of complete Freund adjuvant but were remarkably independent of the Trpv4 genotype. It was intriguing that, as a result of TMJ inflammation, WT mice exhibited significant upregulation of TRPV4 and phosphorylated extracellular-signal-regulated kinase (ERK) in TMJ-innervating trigeminal sensory neurons, which were absent in Trpv4(-/-) mice. Mice with genetically-impaired MEK/ERK phosphorylation in neurons showed resistance to reduction of bite force similar to that of Trpv4(-/-) mice. Thus, TRPV4 is necessary for masticatory sensitization in TMJ inflammation and probably functions upstream of MEK/ERK phosphorylation in trigeminal ganglion sensory neurons in vivo. TRPV4 therefore represents a novel pronociceptive target in TMJ inflammation and should be considered a target of interest in human TMJD.