Fine-tuning of eTRPM8 expression and activity conditions keratinocyte fate

Hemodynamics of the oral mucosa during cooling: A crossover clinical trial

Objective

Oral cryotherapy is used to prevent the onset of oral mucositis, a common and debilitating adverse effect following cancer chemotherapy. A protective mechanism associated with oral cooling is thought to be mediated through reduced tissue microcirculation. The aim of the present study was to examine the underlying mechanism associated with oral mucosal cooling by measuring oral microcirculation and tissue oxygen saturation after cooling with ice chips (IC) and an intraoral cooling device (ICD).

Study design

In a single-center randomized crossover study, 10 healthy volunteers were assigned (1:1) randomly to the order in which the two intraoral cooling procedures (IC/ICD) were to be commenced. On day 1, half of the study participants started with IC and then crossed over to intraoral cooling with the ICD on day 2, while the other half of the participants undertook the same two procedures in the reverse order. Total and functional capillary density (T/FCD) and tissue oxygen saturation (StO2) measurements were obtained at baseline and 30 min following oral cooling.

Results

Following 30 min of oral cooling, a statistically significant difference was found for FCD between IC and ICD (percentage points; +2 vs. -13; p < 0.05). A statistically significant decrease in StO2 was observed with both IC and ICD (%; 13 vs. 10) after 30 min of cooling as compared to baseline (p < 0.05). As for the participants' preference the ICD was preferred over IC by 9 out of 10 participants (p = 0.021).

Conclusions

Both microcirculation parameters and tissue oxygen saturation are altered in conjunction with oral cooling, indicating their potential mechanistic contribution towards cryoprevention of oral mucositis.

Do epidermal keratinocytes have sensory and information processing systems?

It was long considered that the role of epidermal keratinocytes is solely to construct a water-impermeable protective membrane, the stratum corneum, at the uppermost layer of the skin. However, in the last two decades, it has been found that keratinocytes contain multiple sensory systems that detect environmental changes, including mechanical stimuli, sound, visible radiation, electric fields, magnetic fields, temperature and chemical stimuli, and also a variety of receptor molecules associated with olfactory or taste sensation. Moreover, neurotransmitters and their receptors that play crucial roles in the brain are functionally expressed in keratinocytes. Recent studies have demonstrated that excitation of keratinocytes can induce sensory perception in the brain. Here, we review the sensory and information processing capabilities of keratinocytes. We discuss the possibility that epidermal keratinocytes might represent the earliest stage in the development of the brain during the evolution of vertebrates.

TRPM8 Channel Promotes the Osteogenic Differentiation in Human Bone Marrow Mesenchymal Stem Cells

Various families of ion channels have been characterized in mesenchymal stem cells (MSCs), including some members of transient receptor potential (TRP) channels family. TRP channels are involved in critical cellular processes as differentiation and cell proliferation. Here, we analyzed the expression of TRPM8 channel in human bone marrow MSCs (hBM-MSCs), and its relation with osteogenic differentiation. Patch-clamp recordings showed that hBM-MSCs expressed outwardly rectifying currents which were increased by exposure to 500 μM menthol and were partially inhibited by 10 μM of BCTC, a TRPM8 channels antagonist. Additionally, we have found the expression of TRPM8 by RT-PCR and western blot. We also explored the TRPM8 localization in hBM-MSCs by immunofluorescence using confocal microscopy. Remarkably, hBM-MSCs treatment with 100 μM of menthol or 10 μM of icilin, TRPM8 agonists, increases osteogenic differentiation. Conversely, 20 μM of BCTC, induced a decrease of osteogenic differentiation. These results suggest that TRPM8 channels are functionally active in hBM-MSCs and have a role in cell differentiation.

The effects of oscillatory temperature on HaCaT keratinocyte behaviors

BACKGROUND

Keratinocytes are exposed to a thermal gradient throughout epidermal layers in human skin depending on environmental temperatures.

OBJECTIVE

Here, the effect of cyclic temperature changes (ΔT) on HaCaT cell behaviors was explored.

METHODS

HaCaT cells were cultured at constant temperature (37 °C or 25 °C) or under ΔT conditions. The morphology, mechanics, cell cycle progression, proliferation, and lipid synthesis of HaCaT cells were determined.

RESULTS

ΔT conditions led to the inhomogeneous arrangement of the cytoskeleton in HaCaT cells, which resulted in enlarged size, rounder shape, and increased stiffness. Accumulation in the G2/M phase in the cell cycle, a decreased proliferation rate, and a delayed lipogenesis were detected in HaCaT cells cultured under ΔT conditions.

CONCLUSIONS

ΔT conditions resulted in the re-arrangement of the cytoskeleton in HaCaT cells, which showed similarity to the temperature-induced disassemble and re-assemble of cytoskeletons in keratinocyte in vivo. The altered cytoskeleton arrangement resulted in the cell enlargement and stiffening, which reflected the changes in cellular functions. The application of oscillatory temperature in the in vitro culture of keratinocytes provides a way to gain more insights into the role of skin in response to environmental stimuli and maintaining its homeostasis in vivo.

Mitochondrial energy metabolism is negatively regulated by cannabinoid receptor 1 in intact human epidermis

Epidermal energy metabolism is relevant to skin physiology, ageing and photodamage. While selected hormones stimulate epidermal keratinocyte mitochondrial activity, its negative regulation remains unknown. In several cell types, cannabinoid receptor 1 (CB₁ ) is expressed both on the cell membrane (cmCB₁ ) and on the mitochondrial outer membrane (mtCB₁ ), where its stimulation directly suppresses mitochondrial functions. In the current pilot study, we investigated if CB₁ is a negative regulator of human epidermal energy metabolism under physiological conditions. Using organ-cultured full-thickness human skin specimens of healthy individuals, we showed that antagonizing the homeostatic CB₁ signalling by the administration of the CB₁ inverse agonist AM251 increased respiratory chain complex I and II/IV activity. The effect was CB₁ -dependent, since the CB₁ -selective agonist arachidonyl-2'-chloroethylamide could prevent the effect. Moreover, the phenomenon was also reproduced by siRNA-mediated down-regulation of CB₁ . As revealed by the unaltered expression of several relevant markers (TFAM, VDAC1, MTCO1 and NDUFS4), modulation of CB₁ signalling had no effect on the epidermal mitochondrial mass. Next, by using immunoelectron microscopy, we found that human epidermal keratinocytes express both cmCB₁ and mtCB₁ . Finally, by using equipotent extracellularly restricted (hemopressin) as well as cell-permeable (AM251) inverse agonists, we found that mitochondrial activity is most likely exclusively regulated by mtCB₁ . Thus, our data identify mtCB₁ as a novel negative regulator of keratinocyte mitochondrial activity in intact human epidermis, and raise the question, whether topical therapeutic interventions capable of selectively activating mtCB₁ can reduce excessive mitochondrial ROS production resulting from dysregulated mitochondrial activity during skin ageing or photodamage.

Influence of Temperature on Motor Behaviors in Newborn Opossums (Monodelphis domestica): An In Vitro Study

External thermosensation is crucial to regulate animal behavior and homeostasis, but the development of the mammalian thermosensory system is not well known. We investigated whether temperature could play a role in the control of movements in a mammalian model born very immature, the opossum (Monodelphis domestica). Like other marsupials, at birth the opossum performs alternate and rhythmic movements with its forelimbs (FLs) to reach a teat where it attaches in order to continue its development. It was shown that FL movements can be induced by mechanical stimulation of the snout in in vitro preparations of newborns consisting of the neuraxis with skin and FLs intact. In the present study, we used puff ejections of cold, neutral (bath temperature) and hot liquid directed toward the snout to induce FL responses in such preparations. Either the responses were visually observed under a microscope or triceps muscle activity was recorded. Cold liquid systematically induced FL movements and triceps contractions, but neutral and hot temperatures were less potent to do so. Sections of the trigeminal nerves and removal of the facial skin diminished responses to cold and nearly abolished those to hot and neutral stimulations. Transient receptor potential melastatin 8 (TRPM8) being the major cold receptor cation channel in adult mammals, we employed immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) to test for its expression, but found that it is not expressed before 13 postnatal days. Overall our results indicate that cold thermosensation exerts a strong influence on motor behaviors in newborn opossums.

Characterization of human skin equivalents developed at body's core and surface temperatures

Human skin equivalents (HSEs) are in vitro developed three‐dimensional models resembling native human skin (NHS) to a high extent. However, the epidermal lipid biosynthesis, barrier lipid composition, and organization are altered, leading to an elevated diffusion rate of therapeutic molecules. The altered lipid barrier formation in HSEs may be induced by standardized culture conditions, including a culture temperature of 37°C, which is dissimilar to skin surface temperature. Therefore, we aim to determine the influence of culture temperature during the generation of full thickness models (FTMs) on epidermal morphogenesis and lipid barrier formation. For this purpose, FTMs were developed at conventional core temperature (37°C) or lower temperatures (35°C and 33°C) and evaluated over a time period of 4 weeks. The stratum corneum (SC) lipid composition was analysed using advanced liquid chromatography coupled to mass spectrometry analysis. Our results show that SC layers accumulated at a similar rate irrespective of culture temperature. At reduced culture temperature, an increased epidermal thickness, a disorganization of the lower epidermal cell layers, a delayed early differentiation, and an enlargement of granular cells were detected. Interestingly, melanogenesis was reduced at lower temperature. The ceramide subclass profile, chain length distribution, and level of unsaturated ceramides were similar in FTMs generated at 37°C and 35°C but changed when generated at 33°C, reducing the resemblance to NHS. Herein, we report that culture temperature affects epidermal morphogenesis substantially and to a lesser extent the lipid barrier formation, highlighting the importance of optimized external parameters during reconstruction of skin.

Evolution of the human cold/menthol receptor, TRPM8

Genes showing versatile functions or subjected to fast expansion and contraction during the adaptation of species to specific ecological conditions, like sensory receptors for odors, pheromones and tastes, are characterized by a great plasticity through evolution. One of the most fascinating sensory receptors in the family of TRP channels, the cold and menthol receptor TRPM8, has received significant attention in the literature. Recent studies have reported the existence of TRPM8 channel isoforms encoded by alternative mRNAs transcribed from alternative promoters and processed by alternative splicing. Since the first draft of the human genome was accomplished in 2000, alternative transcription, alternative splicing and alternative translation have appeared as major sources of gene product diversity and are thought to participate in the generation of complexity in higher organisms. In this study, we investigate whether alternative transcription has been a driving force in the evolution of the human forms of the cold receptor TRPM8. We identified 33 TRPM8 alternative mRNAs (24 new sequences) and their associated protein isoforms in human tissues. Using comparative genomics, we described the evolution of the human TRPM8 sequences in eight ancestors since the origin of Amniota, and estimated in which ancestors the new TRPM8 variants originated. In order to validate the estimated origins of this receptor, we performed experimental validations of predicted exons in mouse tissues. Our results suggest a first diversification event of the cold receptor in the Boreoeutheria ancestor, and a subsequent divergence at the origin of Simiiformes.

TRPM8 and prostate: a cold case?

While originally cloned from the prostate in 2001, transient receptor potential, melastatin member 8 (TRPM8) has since been identified as the cold/menthol receptor in the peripheral nervous system. This discovery has led to hundreds of studies regarding the role of this channel in pain and thermosensation phenomena, while relegating TRPM8 involvement in cancer to a secondary role. Despite these findings, there is growing evidence that TRPM8 should be carefully studied within the frame of carcinogenesis, especially in the prostate, where it is highly expressed and where many teams have confirmed variations in its expression during cancer progression. Its regulation by physiological factors, such as PSA and androgens, has proved that TRPM8 can exhibit an activity beyond that of a cold receptor, thus explaining how the channel can be activated in organs not exposed to temperature variations. With this review, we aim to provide a brief overview of the current knowledge regarding the complex roles of TRPM8 in prostate carcinogenesis and to show that this research path still represents a "hot" topic with potential clinical applications in the short term.

Transcriptional correlates of proximal-distal identify and regeneration timing in axolotl limbs

Cells within salamander limbs retain memories that inform the correct replacement of amputated tissues at different positions along the length of the arm, with proximal and distal amputations completing regeneration at similar times. We investigated the possibility that positional memory is associated with variation in transcript abundances along the proximal-distal limb axis. Transcripts were deeply sampled from Ambystoma mexicanum limbs at the time they were administered fore arm vs upper arm amputations, and at 19 post-amputation time points. After amputation and prior to regenerative outgrowth, genes typically expressed by differentiated muscle cells declined more rapidly in upper arms while cell cycle transcripts were expressed more highly. These and other expression patterns suggest upper arms undergo more robust tissue remodeling and cell proliferation responses after amputation, and thus provide an explanation for why the overall time to complete regeneration is similar for proximal and distal amputations. Additionally, we identified candidate positional memory genes that were expressed differently between fore and upper arms that encode a surprising number of epithelial proteins and a variety of cell surface, cell adhesion, and extracellular matrix molecules. Also, genes were discovered that exhibited different, bivariate patterns of gene expression between fore and upper arms, implicating dynamic transcriptional regulation for the first time in limb regeneration. Finally, 43 genes expressed differently between fore and upper arm samples showed similar transcriptional patterns during retinoic acid-induced reprogramming of fore arm blastema cells into upper arm cells. Our study provides new insights about the basis of positional information in regenerating axolotl limbs.

4TM-TRPM8 channels are new gatekeepers of the ER-mitochondria Ca2+ transfer

Calcium (Ca²⁺) release from the endoplasmic reticulum plays an important role in many cell-fate defining cellular processes. Traditionally, this Ca²⁺ release was associated with the ER Ca²⁺ release channels, inositol 1,4,5‑triphosphate receptor (IP₃R) and ryanodine receptor (RyR). Lately, however, other calcium conductances have been found to be intracellularly localized and to participate in cell fate regulation. Nonetheless, molecular identity and functional properties of the ER Ca²⁺ release mechanisms associated with multiple diseases, e.g. prostate cancer, remain unknown. Here we identify a new family of transient receptor potential melastatine 8 (TRPM8) channel isoforms as functional ER Ca²⁺ release channels expressed in mitochondria-associated ER membranes (MAMs). These TRPM8 isoforms exhibit an unconventional structure with 4 transmembrane domains (TMs) instead of 6 TMs characteristic of the TRP channel archetype. We show that these 4TM-TRPM8 isoforms form functional channels in the ER and participate in regulation of the steady-state Ca²⁺ concentration ([Ca²⁺]) in mitochondria and the ER. Thus, our study identifies 4TM-TRPM8 isoforms as ER Ca²⁺ release mechanism distinct from classical Ca²⁺ release channels.

Transient Receptor Potential Melastatin-8 Activation Induces Relaxation of Pulmonary Artery by Inhibition of Store-Operated Calcium Entry in Normoxic and Chronic Hypoxic Pulmonary Hypertensive Rats

Pulmonary hypertension (PH) is characterized by enhanced vasoconstriction and vascular remodeling, which are attributable to the alteration of Ca²⁺ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). It is well established that store-operated Ca²⁺ entry (SOCE) is augmented in PASMCs during PH and that it plays a crucial role in PH development. Our previous studies showed that the melastatin-related transient receptor potential 8 (TRPM8) is down-regulated in PASMCs of PH animal models, and activation of TRPM8 causes relaxation of pulmonary arteries (PAs). However, the mechanism of TRPM8-induced PA relaxation is unclear. Here we examined the interaction of TRPM8 and SOCE in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats, a model of human group 3 PH. We found that TRPM8 was down-regulated and TRPM8-mediated cation entry was reduced in CHPH-PASMCs. Activation of TRPM8 with icilin caused concentration-dependent relaxation of cyclopiazonic acid (CPA) and endothelin-1 contracted endothelium-denuded PAs, and the effect was abolished by the SOCE antagonist Gd³⁺ Application of icilin to PASMCs suppressed CPA-induced Mn²⁺ quenching and Ca²⁺ entry, which was reversed by the TRPM8 antagonist N-(3-aminopropyl)-2-([(3-methylphenyl)methyl])-oxy-N-(2-thienylmethyl)benzamide hydrochloride salt (AMTB). Moreover, the inhibitory effects of icilin on SOCE in PA and PASMCs of CHPH rats were significantly augmented due to enhanced SOCE activity in PH. Our results, therefore, demonstrated a novel mechanism of TRPM8-mediated inhibition of SOCE in pulmonary vasculature. Because SOCE is important for vascular remodeling and enhanced vasoconstriction, down-regulation of TRPM8 in PASMCs of CHPH rats may minimize its inhibitory influence to allow unimpeded SOCE activity for PH development.

Targeting of short TRPM8 isoforms induces 4TM-TRPM8-dependent apoptosis in prostate cancer cells

Since its cloning a decade ago, TRPM8 channel has emerged as a promising prognostic marker and a putative therapeutic target in prostate cancer (PCa). However, recent studies have brought to light the complexity of TRPM8 isoforms in PCa. Consequently, the respective role of each TRPM8 isoform needs to be deciphered prior to considering TRPM8 as an attractive therapeutic target. Full-length (6 transmembrane (TM)-domain) TRPM8 channel is overexpressed in early PCa and repressed in advanced prostate tumors whereas the localization of the truncated, 4TM-TRPM8 channel (4 transmembrane (TM)-domain), in the membranes of endoplasmic reticulum (ER) is independent of the pathogenic status of epithelial cells. In the same line, expression of non-channel cytoplasmic small TRPM8 isoforms (namely sM8) is conserved in cancer cells. In this study, we identify sM8s as putative regulator of PCa cell death. Indeed, suppression of sM8 isoforms was found to induce concomitantly ER stress, oxidative stress, p21 expression and apoptosis in human epithelial prostate cancer cells. We furthermore demonstrate that induction of such mechanisms required the activity of 4TM-TRPM8 channels at the ER-mitochondria junction. Our study thus suggests that targeting sM8 could be an appropriate strategy to fight prostate cancer.