5in paw-pad skin of gene expression by TRPV4 in response to UVB
5in paw-pad skin of gene expression by TRPV4 in response to UVB. In culture, UVB causes a direct, TRPV4-dependent Ca2+ 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. The surface epithelium (epidermis) of skin provides barrier protection against dehydration LPA antibody and the potentially harmful external environment (1). Accordingly, skin is the site of first conversation between ambient environment and immunologically qualified organismal structures, and also the site for sentient responses (2). Sensory neurons in the dorsal root ganglia (DRG) and trigeminal ganglia (TG) are endowed with sensory transduction capacity for heat, cold, mechanical cues, itch, and pain, and their axons directly interface with skin epithelium (2C4). Against a background of suggestive findings (2, 5C7), we wondered whether the epidermis as a forefront of sensory signaling may function in sensitizing pain transduction in response to naturally occurring irritating cues. To elucidate mechanisms, we used a mouse sunburn model and induced a state of lowered sensory thresholds associated with tissue injury caused by UV radiation (8C10). UV-sunburn-evoked lowering of sensory thresholds shares major hallmarks of pathological pain, a valuable feature of this model. Skin tissue injury caused by UVB has been elucidated to be mediated by cytokines and chemokines, known from immunological responses, such as IL-1 and IL-6, which are also known to cause and facilitate pain (11C19). Another more recent study recognized a proinflammatory chemokine, CXCL5, as proalgesic in response to UVB overexposure of rat and human skin (20). An exciting new arena pertaining to molecular mechanisms of the skins response to noxious UV was recently opened by an elegant study that FadD32 Inhibitor-1 reported the role of UVB-mediated damage to noncoding RNA molecules in FadD32 Inhibitor-1 the skin (21). Unraveling a molecular mechanism, the gene was found crucial in signaling the proinflammatory actions of the UVB-damaged noncoding RNA molecules. However, this FadD32 Inhibitor-1 study focused on molecular mechanisms of acute inflammation in the skin. We intended to identify pain mechanisms that mediate the pain associated with UVB-mediated tissue injury. Pain in response to external environmental cues has been understood better because of scientific progress in the field of transient receptor potential (TRP) ion channels that have been found responsive to such cues, and which were found expressed in DRG and TG peripheral sensory neurons, which are the cells believed to be the primary transducers. Indeed, TRPV1, one of the founding users of the TRPV channel subfamily, has been identified as relevant for pain, including pathological pain, response to thermal cues, and most recently FadD32 Inhibitor-1 for itch (22C31). However, TRPA1 (transient receptor potential ion channel, ankyrin subfamily, family member #1) and TRPM8 seem to be involved in transduction of pain-inducing stimuli as well (32C36). Also a family member of the TRPV subfamily, TRPV4 is usually a multimodally activated, nonselective cation channel that is involved in physiological pain evoked by osmotic and mechanical, but not thermal, cues (37C40). For pathological pain, it is relevant for inflammation- and nerve-damage-induced pain sensitization (41C43). Of notice, gene-targeted mice, selectively inducing targeting in postnatal keratinocytes, and topically applying selective TRPV4 inhibitors, we demonstrate that FadD32 Inhibitor-1 epidermal TRPV4 plays a prominent, hitherto unrecognized role in UVB-evoked skin tissue damage and pain of sunburn. Results Epidermal-Specific, Tamoxifen-Inducible Null Mouse: Nocifensive Behavior. To circumvent developmental issues that can arise in gene-targeted mice with ubiquitous deletions, we developed an inducible conditional system to assess the functions of TRPV4 in sunburn and pain. Using mouse ES cells, we first built and expression in skin epidermis, as judged by anti-TRPV4 immunolabeling, quantitative RT (qRT)-PCR, and Western blotting (Fig. 1knockdown did not result in gross alterations of skin structure or in induction of the terminal differentiation-specific marker keratin-1 (K1), which is known to be governed by elevated Ca2+ influx suprabasally (Fig. 1and Fig. S1knockout (iKO) mice were detected. Open in a separate windows Fig. 1. Keratinocyte-specific ablation of prospects to alterations in nocifensive behavior in response to UVB. (in tam-induced iKO mice. (mRNA from paw-pad skin is shown, indicating significant knockdown in response to tam treatment vs. carrier (oil). 0.0001, test. ( 10 animals per group; ** 0.01 ANOVA. (knockdown; = 12 animals are shown for which both parameters were available and mRNA levels 0.45. Note the four vehicle-induced animals (green symbols) vs. their tam-induced counterparts (reddish symbols). (= 4 per group..