Involvement of skin TRPV3 in temperature detection regulated by TMEM79 in mice

Activation of transient receptor potential vanilloid 3 is required for keratinocyte differentiation and epidermal barrier formation

Transient receptor potential vanilloid 3 (TRPV3)-mediated Ca²+ signaling in keratinocytes plays a crucial role in epidermal keratinocyte differentiation and triggers the release of pro-inflammatory cytokines, causing inflammation and itching. However, the regulation of skin barrier recovery by TRPV3 and its expression during keratinocyte differentiation remain unexplored. This study aimed to investigate the role and expression levels of TRPV3 in keratinocyte differentiation and skin barrier recovery, focusing on the effects of varying TRPV3 activation using pharmacological agents. Differentiation of primary human keratinocytes was induced in high-calcium media, and TRPV3 activity and expression were assessed using patch-clamp, fura-2 fluorimetry, and immunoblotting. The effects of TRPV3 agonists on skin barrier recovery following tape stripping were evaluated by measuring transepidermal water loss in mice. Results showed that TRPV3 expression, current density, and agonist-induced [Ca2+]i changes increased with keratinocyte differentiation. The TRPV3 antagonist, ruthenium red, inhibited both keratinocyte differentiation and TRPV3 upregulation. TRPV3 agonists (2-APB/carvacrol) facilitated early differentiation but paradoxically downregulated TRPV3 expression at higher concentrations. Moderate TRPV3 activation by lower agonist concentrations enhanced skin barrier recovery, while higher concentrations hindered recovery and induced immune cell infiltration. These findings highlight the dual role of TRPV3 in skin homeostasis and suggest that targeted modulation of TRPV3 could be a promising strategy for treating skin disorders.

Neuro-immuno-endocrinology of the skin: how environment regulates body homeostasis

The skin, including the hypodermis, is the largest organ of the body. The epidermis, the uppermost layer, is in direct contact with the environment and is exposed to environmental stressors, including solar radiation and biological, chemical and physical factors. These environmental factors trigger local responses within the skin that modulate homeostasis on both the cutaneous and systemic levels. Using mediators in common with brain pathways, immune and neuroendocrine systems within the skin regulate these responses to activate various signal transduction pathways and influence the systemic endocrine and immune systems in a context-dependent manner. This skin neuro-immuno-endocrine system is compartmentalized through the formation of epidermal, dermal, hypodermal and adnexal regulatory units. These units can act separately or in concert to preserve skin integrity, allow for adaptation to a changing environment and prevent the development of pathological processes. Through activation of peripheral nerve endings, the release of neurotransmitters, hormones, neuropeptides, and cytokines and/or chemokines into the circulation, or by priming circulating and resident immune cells, this system affects central coordinating centres and global homeostasis, thus adjusting the body's homeostasis and allostasis to optimally respond to the changing environment.

TRPV3 in skin thermosensation and temperature responses

Human skin, as a sophisticated sensory organ, is able to detect subtle changes in ambient temperature. This thermosensory capability is primarily mediated by temperature-sensitive TRP channels expressed in both sensory neurons and keratinocytes. Among these, TRPV3, which responds to warm temperatures and plays a crucial role in various skin functions, is particularly notable. TRPV3 channels not only detect moderate warmth but are also sensitive to chemical ligands that evoke thermal sensations. The activation of TRPV3 by warm temperatures and compounds highlights its importance in the molecular mechanisms underlying skin thermosensation. This review mainly discusses the role of TRPV3, particularly its contribution to skin thermosensation and structural insights into its temperature sensitivity, providing an understanding of how TRPV3 modulates thermal perception at the molecular level.

Forty sites of TRP channel regulation

Transient receptor potential (TRP) channels are polymodal molecular sensors that integrate chemical, thermal, mechanical and electrical stimuli and convert them into ionic currents that regulate senses of taste, smell, vision, hearing, touch and contribute to perception of temperature and pain. TRP channels are implicated in the pathogenesis of numerous human diseases, including cancers, and represent one of the most ardently pursued drug targets. Recent advances in structural biology, particularly associated with the cryo-EM "resolution revolution", yielded numerous TRP channel structures in complex with ligands that might have therapeutic potential. In this review, we describe the recent progress in TRP channel structural biology, focusing on the description of identified binding sites for small molecules, their relationship to membrane lipids, and interaction of TRP channels with other proteins. The characterized binding sites and interfaces create a diversity of druggable targets and provide a roadmap to aid in the design of new molecules for tuning TRP channel function in disease conditions.

Preliminary investigation on the establishment of a new meibomian gland obstruction model and gene expression

Meibomian gland dysfunction is a chronic ocular surface disease with a complex pathogenesis, whose main clinical manifestations are meibomian gland obstruction or/and lipid abnormalities. To explore the mechanism of MGD due to meibomian gland obstruction (MGO), we established a rat model of MGO by cauterizing the meibomian gland orifice. The morphology of the lid margins and meibomian gland orifices were visualized by slit lamp. The tear production of rats was measured by phenol red cotton thread, the tear film breakup time and corneal fluorescein staining scores of rats were detected under cobalt blue light of slit lamp. Changes in the histological structure of the meibomian gland (MG) were observed by HE staining, Oil Red O staining and immunofluorescence staining (collagen IV). RNA sequencing was used to detect differentially expressed genes in MGO and normal rats, which were validated by qPCR. In the MGO group after 4, 8, and 16 weeks, the meibomian gland orifices were closed, tear film break-up time decreased and corneal fluorescein staining score increased (p < 0.05). MG acini was smaller at 8-week and 16-week MGO rats in HE staining. Oil Red O staining showed less condensed staining in the 8- and 16-week MGO groups, while more condensed staining in the 4-week MGO group. Additionally, the basement membrane was destroyed in 16-week MGO group by immunofluorescence staining of collagen IV. Meanwhile, RNA sequencing and qPCR showed that lipid peroxidation (LPO), transient receptor potential vanilloid-3 (TRPV3) and genes in PPAR signaling pathway were differentially expressed in 16-week meibomian gland obstructive rats (p < 0.05). Consequently, meibomian gland obstruction model rats were established successfully with corneal damage and lower tear film stability. Meibomian gland obstruction is a causative factor of MGD, which led to abnormal histological structure in MG, differential expression of PPAR signaling pathway and TRPV3.

Mussel-Bioinspired Lignin Adhesive for Wearable Bioelectrodes

As a natural "binder," lignin fixes cellulose in plants to foster growth and longevity. However, isolated lignin has a poor binding ability, which limits its biomedical applications. In this study, inspired by mussel adhesive proteins, acidic/basic amino acids (AAs) are introduced in alkali lignin (AL) to form ionic-π/spatial correlation interactions, followed by demethylation to create catechol residues for enhanced adhesion activity. Atomic force microscopy reveals that catechol residues are the primary adhesion structures, with basic AAs exhibiting superior synergistic effects compared to acidic AAs. Demethylated lysine-grafted AL exhibits the strongest adhesion force toward skin tissue. Molecular dynamic simulation and density functional theory calculations indicate that adhesion against skin tissue mainly results from hydrogen bonds and cation-π interactions, with the adhesion mechanism being based on the Gibbs free energy of the Schiff base reaction. In summary, a biomimetic electrode based on lignin inspired by mussel adhesive proteins is prepared; the presented method offers a straightforward strategy for the development of biomimetic adhesives. Furthermore, this mussel-inspired adhesive can be used as a wearable bioelectrode in biomedical applications.

Functional relationship between peripheral thermosensation and behavioral thermoregulation

Thermoregulation is a fundamental mechanism for maintaining homeostasis in living organisms because temperature affects essentially all biochemical and physiological processes. Effector responses to internal and external temperature cues are critical for achieving effective thermoregulation by controlling heat production and dissipation. Thermoregulation can be classified as physiological, which is observed primarily in higher organisms (homeotherms), and behavioral, which manifests as crucial physiological functions that are conserved across many species. Neuronal pathways for physiological thermoregulation are well-characterized, but those associated with behavioral regulation remain unclear. Thermoreceptors, including Transient Receptor Potential (TRP) channels, play pivotal roles in thermoregulation. Mammals have 11 thermosensitive TRP channels, the functions for which have been elucidated through behavioral studies using knockout mice. Behavioral thermoregulation is also observed in ectotherms such as the fruit fly, Drosophila melanogaster. Studies of Drosophila thermoregulation helped elucidate significant roles for thermoreceptors as well as regulatory actions of membrane lipids in modulating the activity of both thermosensitive TRP channels and thermoregulation. This review provides an overview of thermosensitive TRP channel functions in behavioral thermoregulation based on results of studies involving mice or Drosophila melanogaster.

Hypothalamic Neuromodulation and Control of the Dermal Surface Temperature of Livestock during Hyperthermia

Hyperthermia elicits several physiological and behavioral responses in livestock to restore thermal neutrality. Among these responses, vasodilation and sweating help to reduce core body temperature by increasing heat dissipation by radiation and evaporation. Thermoregulatory behaviors such as increasing standing time, reducing feed intake, shade-seeking, and limiting locomotor activity also increase heat loss. These mechanisms are elicited by the connection between peripheral thermoreceptors and cerebral centers, such as the preoptic area of the hypothalamus. Considering the importance of this thermoregulatory pathway, this review aims to discuss the hypothalamic control of hyperthermia in livestock, including the main physiological and behavioral changes that animals adopt to maintain their thermal stability.

Role of thermosensitive transient receptor potential (TRP) channels in thermal preference of male and female mice

Transient Receptor Potential (TRP) ion channels are important for sensing environmental temperature. In rodents, TRPV4 senses warmth (25-34 °C), TRPV1 senses heat (>42 °C), TRPA1 putatively senses cold (<17 °C), and TRPM8 senses cool-cold (18-26 °C). We investigated if knockout (KO) mice lacking these TRP channels exhibited changes in thermal preference. Thermal preference was tested using a dual hot-cold plate with one thermoelectric surface set at 30 °C and the adjacent surface at a temperature of 15-45 °C in 5 °C increments. Blinded observers counted the number of times mice crossed through an opening between plates and the percentage of time spent on the 30 °C plate. In a separate experiment, observers blinded as to genotype also assessed the temperature at the location on a thermal gradient (1.83 m, 4-50 °C) occupied by the mouse at 5- or 10-min intervals over 2 h. Male and female wildtype mice preferred 30 °C and significantly avoided colder (15-20 °C) and hotter (40-45 °C) temperatures. Male TRPV1KOs and TRPA1KOs, and TRPV4KOs of both sexes, were similar, while female WTs, TRPV1KOs, TRPA1KOs and TRPM8KOs did not show significant thermal preferences across the temperature range. Male and female TRPM8KOs did not significantly avoid the coldest temperatures. Male mice (except for TRPM8KOs) exhibited significantly fewer plate crossings at hot and cold temperatures and more crossings at thermoneutral temperatures, while females exhibited a similar but non-significant trend. Occupancy temperatures along the thermal gradient exhibited a broad distribution that shrank somewhat over time. Mean occupancy temperatures (recorded at 90-120 min) were significantly higher for females (30-34 °C) compared to males (26-27 °C) of all genotypes, except for TRPA1KOs which exhibited no sex difference. The results indicate (1) sex differences with females (except TRPA1KOs) preferring warmer temperatures, (2) reduced thermosensitivity in female TRPV1KOs, and (3) reduced sensitivity to cold and innocuous warmth in male and female TRPM8KOs consistent with previous studies.

Thermal gradient ring for analysis of temperature-dependent behaviors involving TRP channels in mice

There are a lot of temperature-sensitive proteins including transient receptor potential (TRP) channels. Some TRP channels are temperature receptors having specific activation temperatures in vitro that are within the physiological temperature range. Mice deficient in specific TRP channels show abnormal thermal behaviors, but the role of TRP channels in these behaviors is not fully understood. The Thermal Gradient Ring is a new apparatus that allows mice to freely move around the ring floor and not stay in a corner. The system can analyze various factors (e.g., 'Spent time', 'Travel distance', 'Moving speed', 'Acceleration') associated with temperature-dependent behaviors of TRP-deficient mice. For example, the Ring system clearly discriminated differences in temperature-dependent phenotypes between mice with diabetic peripheral neuropathy and TRPV1-/- mice, and demonstrated the importance of TRPV3 in temperature detection in skin. Studies using the Thermal Gradient Ring system can increase understanding of the molecular basis of thermal behaviors in mice and in turn help develop strategies to affect responses to different temperature conditions in humans.

Thermosensation and TRP Channels

Somatosensory neurons can sense external temperature by converting sensation of temperature information to neural activity via afferent input to the central nervous system. Various populations of somatosensory neurons have specialized gene expression, including expression of thermosensitive transient receptor potential (TRP) ion channels. Thermosensitive TRP channels are responsible for thermal transduction at the peripheral ends of somatosensory neurons and can sense a wide range of temperatures. Here we focus on several thermosensitive TRP channels including TRPV1, TRPV4, TRPM2, TRPM3, TRPM8, TRPC5, and TRPA1 in sensory neurons. TRPV3, TRPV4, and TRPC5 are also involved in somatosensation in nonneuronal cells and tissues. In particular, we discuss whether skin senses ambient temperatures through TRPV3 and TRPV4 activation in skin keratinocytes and the involvement of TRPM2 expressed by hypothalamic neurons in thermosensation in the brain.