The cold-sensing ion channel TRPM8 regulates central and peripheral clockwork and the circadian oscillations of body temperature

Effects of ocular hypothermia: potential perspectives in vitreoretinal surgery

PURPOSE

To summarize knowledge about the effects of experimental and iatrogenic hypothermia on ocular structures, with a specific focus on retinal consequences and therapeutical perspectives in vitreoretinal surgery.

MATERIALS AND METHODS

This review of the literature includes a section on the effects of low temperature on different ocular structures (sclera, choroid, retina, vitreous and ciliary body), a focus on the effect on retinal pigment epithelium (RPE), retinal neurons and inflammation and a section about results of vitreoretinal surgery performed at low temperature. In vitro, animal and human studies were included.

RESULTS

Temperature changes induce several regulatory responses within the eye, including modifications of intraocular pressure (IOP), local blood flow, cytokine secretion and cellular metabolism. Cooling of retinal structures has been demonstrated to induce beneficial effects including increased survival of RPE and retinal neurons. Vitreoretinal surgery performed at lower intraocular temperatures has shown positive effect on postoperative inflammation, even though the rebound effect of a sudden postoperative temperature increase seems to be detrimental.

CONCLUSIONS

Despite being a promising approach, vitreoretinal surgery performed under lower intraocular temperature conditions deserves refinement in its methodologies. Hopefully, new randomized clinical trials will provide indications on how to apply this technique in the safest and most effective way.

Systemic TRPV4 inhibition worsens retinal response to acute intraocular pressure elevation in older but not younger mice

SIGNIFICANCE

Previous evidence showed that transient receptor potential vanilloid 4 (TRPV4) inhibition was protective of retinal ganglion cell (RGC) loss after chronic intraocular pressure (IOP) elevation in young animals. However, the role of TRPV4 in mechanosensing IOP changes in the aging eye is not well understood.

PURPOSE

This study compared the recovery of retinal function and structure after acute IOP elevation in 3- and 12-month-old mouse eyes with and without TRPV4 inhibition.

METHODS

We examined retinal TRPV4 expression in 2-month-old rodent eyes using immunohistochemistry and transcript analysis of isolated macroglia and RGCs. To modulate TRPV4, mice were treated daily with either vehicle or a TRPV4 antagonist (HC-067047 10 mg/kg) delivered intraperitoneally for 7 days before and 7 days after IOP elevation (50 mmHg for 30 minutes). Retinal function and structure were assessed using dark-adapted full-field electroretinography and optical coherence tomography, respectively.

RESULTS

We showed that Müller cells strongly expressed TRPV4. Seven days after IOP elevation, RGC functional recovery was significantly poorer in older mice treated with TRPV4 antagonist compared with age-matched vehicle controls (-54 ± 7% vs. -24 ± 10%, p=0.046) and their younger TRPV4 antagonist-treated counterparts (-5 ± 5%, p<0.001).

CONCLUSIONS

This study showed that there was an age-related deficit in RGC functional recovery from IOP elevation with TRPV4 inhibition.

Transcriptomic Profile Analysis of Brain Tissue in the Absence of Functional TRPM8 Calcium Channel

Background/Objectives: Transient Receptor Potential Melastatin 8 (TRPM8) is a non-selective, Ca2+-permeable cation channel involved in thermoregulation and other physiological processes, such as basal tear secretion, cell differentiation, and insulin homeostasis. The activation and deactivation of TRPM8 occur through genetic modifications, channel interactions, and signaling cascades. Recent evidence suggests a significant role of TRPM8 in the hypothalamus and amygdala related to pain sensation and sexual behavior. Notably, TRPM8 has been implicated in neuropathic pain, migraines, and neurodegenerative diseases such as Parkinson's disease. Our laboratory has identified testosterone as a high-affinity ligand of TRPM8. TRPM8 deficiency appears to influence behavioral traits in mice, like increased aggression and deficits in sexual satiety. Here, we aim to explore the pathways altered in brain tissues of TRPM8-deficient mice using the expression and methylation profiles of messenger RNA (mRNA) and long non-coding RNA (lncRNA). Specifically, we focused on brain regions integral to behavioral and hormonal control, including the olfactory bulb, hypothalamus, amygdala, and insula. Methods: RNA was isolated and purified for microarray analysis collected from male wild-type and TRPM8 knockout mice. Results: We identified various differentially expressed genes tied to multiple signaling pathways. Among them, the androgen-estrogen receptor (AR-ER) pathway, steroidogenesis pathway, sexual reward pathway, and cocaine reward pathway are particularly worth noting. Conclusions: These results should bridge the existing gaps in the knowledge regarding TRPM8 and inform potential targets for future studies to elucidate its role in the behavior changes and pathology of the diseases associated with TRPM8 activity.

Subcutaneous administration of a novel TRPM8 antagonist reverses cold hypersensitivity while attenuating the drop in core body temperature

BACKGROUND AND PURPOSE

We extend the characterization of the TRPM8 antagonist VBJ103 with tests of selectivity, specificity and distribution, therapeutic efficacy of systemic administration against oxaliplatin-induced cold hyperalgesia and the impact of systemic administration on core body temperature (CBT).

EXPERIMENTAL APPROACH

Selectivity at human TRPA1 and TRPV1 as well as in vitro safety profiling was determined. Effects of systemic administration of VBJ103 were evaluated in a model of oxaliplatin-induced cold hyperalgesia. Both peripheral and centrally mediated effects of VBJ103 on CBT were assessed with radiotelemetry.

KEY RESULTS

VBJ103 had no antagonist activity at TRPV1 and TRPA1, but low potency TRPA1 activation. The only safety liability detected was partial inhibition of the dopamine transporter (DAT). VBJ103 delivered subcutaneously dose-dependently attenuated cold hypersensitivity in oxaliplatin-treated mice at 3, 10 and 30 mg·kg-1 (n = 7, P < 0.05). VBJ103 (30 mg·kg-1) antinociception was influenced by neither the TRPA1 antagonist HC-030031 nor the DAT antagonist GBR12909. Subcutaneous administration of VBJ103 (3, 10 and 30 mg·kg-1, but not 100 or 300 mg·kg-1, n = 7) decreased CBT (2°C). Intraperitoneal (i.p.) administration of VBJ103 (3, 10 and 30 mg·kg-1) dose-dependently decreased CBT to an extent larger than that detected with subcutaneous administration. Intracerebroventricular (i.c.v.) administration (306 nmol/1 μL; n = 5) did not alter CBT.

CONCLUSIONS AND IMPLICATIONS

We achieve therapeutic efficacy with subcutaneous administration of a novel TRPM8 antagonist that attenuates deleterious influences on CBT, a side effect that has largely prevented the translation of TRPM8 as a target.

Timing of acute cold exposure determines UCP1 and FGF21 expression - Possible interactions between the thermal environment, thermoregulatory responses, and peripheral clocks

Thermoregulation is synchronized across the circadian cycle to uphold thermal homeostasis. To test if time-of-day matters for the response to environmental cold exposure, mice were acclimated to thermoneutrality (27 °C) for 2 months were subjected acutely (8 h) to cold ambient conditions (15 °C), whereas controls were maintained at thermoneutral conditions. The thermal exposure was tested in separate groups (N = 8) at three distinct time-of-day periods: in the LIGHT phase (L); the DARK phase (D); and a mix of the two (D + L). The magnitude of UCP1 protein and mRNA induction in brown adipose tissue (BAT) in response to acute cold exposure was time-of-day sensitive, peaking in LIGHT, whereas lower induction levels were observed in D + L, and DARK. Plasma levels of FGF21 were induced 3-fold by acute cold exposure at LIGHT and D + L, compared to the time-matched thermoneutral controls, whereas cold in DARK did not cause a significant increase of FGF21 plasma levels. Cold exposure affected, in BAT, the temporal mRNA expression patterns of core circadian clock components: Bmal1, Clock, Per1, Per3, Cry1, Cry2 Nr1d1, and Nr1d2, but in the liver, none of the transcripts were modified. Behavioral assessment using the Thermal Gradient Test (TGT) showed that acute cold exposure reduced cold sensitivity in D + L, but not in DARK. RNA-seq analyses of somatosensory neurons in DRG highlighted the role of the core circadian components in these cells, as well as transcriptional changes due to acute cold exposure. This elucidates the sensory system as a gauge and potential regulator of thermoregulatory responses based on circadian physiology. In conclusion, acute cold exposure elicits time-of-day specific effects on thermoregulatory pathways, which may involve underlying changes in thermal perception. These results have implications for efforts aimed at reducing risks associated with the organization of shift work in cold environments.

Avian migration clocks in a changing world

Avian long-distance migration requires refined programming to orchestrate the birds' movements on annual temporal and continental spatial scales. Programming is particularly important as long-distance movements typically anticipate future environmental conditions. Hence, migration has long been of particular interest in chronobiology. Captivity studies using a proxy, the shift to nocturnality during migration seasons (i.e., migratory restlessness), have revealed circannual and circadian regulation, as well as an innate sense of direction. Thanks to rapid development of tracking technology, detailed information from free-flying birds, including annual-cycle data and actograms, now allows relating this mechanistic background to behaviour in the wild. Likewise, genomic approaches begin to unravel the many physiological pathways that contribute to migration. Despite these advances, it is still unclear how migration programmes are integrated with specific environmental conditions experienced during the journey. Such knowledge is imminently important as temporal environments undergo rapid anthropogenic modification. Migratory birds as a group are not dealing well with the changes, yet some species show remarkable adjustments at behavioural and genetic levels. Integrated research programmes and interdisciplinary collaborations are needed to understand the range of responses of migratory birds to environmental change, and more broadly, the functioning of timing programmes under natural conditions.

The physiological role of TRP channels in sleep and circadian rhythm

TRP channels, are non-specific cationic channels that are involved in multiple physiological processes that include salivation, cellular secretions, memory extinction and consolidation, temperature, pain, store-operated calcium entry, thermosensation and functionality of the nervous system. Here we choose to look at the evidence that decisively shows how TRP channels modulate human neuron plasticity as it relates to the molecular neurobiology of sleep/circadian rhythm. There are numerous model organisms of sleep and circadian rhythm that are the results of the absence or genetic manipulation of the non-specific cationic TRP channels. Drosophila and mice that have had their TRP channels genetically ablated or manipulated show strong evidence of changes in sleep duration, sleep activity, circadian rhythm and response to temperature, noxious odours and pattern of activity during both sleep and wakefulness along with cardiovascular and respiratory function during sleep. Indeed the role of TRP channels in regulating sleep and circadian rhythm is very interesting considering the parallel roles of TRP channels in thermoregulation and thermal response with concomitant responses in growth and degradation of neurites, peripheral nerves and neuronal brain networks. TRP channels provide evidence of an ability to create, regulate and modify our sleep and circadian rhythm in a wide array of physiological and pathophysiological conditions. In the current review, we summarize previous results and novel recent advances in the understanding of calcium ion entry via TRP channels in different sleep and circadian rhythm conditions. We discuss the role of TRP channels in sleep and circadian disorders.

Sex differences in thermoregulation in mammals: Implications for energy homeostasis

Thermal homeostasis is a fundamental process in mammals, which allows the maintenance of a constant internal body temperature to ensure an efficient function of cells despite changes in ambient temperature. Increasing evidence has revealed the great impact of thermoregulation on energy homeostasis. Homeothermy requires a fine regulation of food intake, heat production, conservation and dissipation and energy expenditure. A great interest on this field of research has re-emerged following the discovery of thermogenic brown adipose tissue and browning of white fat in adult humans, with a potential clinical relevance on obesity and metabolic comorbidities. However, most of our knowledge comes from male animal models or men, which introduces unwanted biases on the findings. In this review, we discuss how differences in sex-dependent characteristics (anthropometry, body composition, hormonal regulation, and other sexual factors) influence numerous aspects of thermal regulation, which impact on energy homeostasis. Individuals of both sexes should be used in the experimental paradigms, considering the ovarian cycles and sexual hormonal regulation as influential factors in these studies. Only by collecting data in both sexes on molecular, functional, and clinical aspects, we will be able to establish in a rigorous way the real impact of thermoregulation on energy homeostasis, opening new avenues in the understanding and treatment of obesity and metabolic associated diseases.

Validation of Six Commercial Antibodies for the Detection of Heterologous and Endogenous TRPM8 Ion Channel Expression

TRPM8 is a non-selective cation channel expressed in primary sensory neurons and other tissues, including the prostate and urothelium. Its participation in different physiological and pathological processes such as thermoregulation, pain, itch, inflammation and cancer has been widely described, making it a promising target for therapeutic approaches. The detection and quantification of TRPM8 seems crucial for advancing the knowledge of the mechanisms underlying its role in these pathophysiological conditions. Antibody-based techniques are commonly used for protein detection and quantification, although their performance with many ion channels, including TRPM8, is suboptimal. Thus, the search for reliable antibodies is of utmost importance. In this study, we characterized the performance of six TRPM8 commercial antibodies in three immunodetection techniques: Western blot, immunocytochemistry and immunohistochemistry. Different outcomes were obtained for the tested antibodies; two of them proved to be successful in detecting TRPM8 in the three approaches while, in the conditions tested, the other four were acceptable only for specific techniques. Considering our results, we offer some insight into the usefulness of these antibodies for the detection of TRPM8 depending on the methodology of choice.