Role of alpha2C-adrenoceptors in the reduction of skin blood flow induced by local cooling in mice

Rosacea in East Asian populations: Clinical manifestations and pathophysiological perspectives for accurate diagnosis

Rosacea is a chronic inflammatory disorder primarily affecting the facial skin, prominently involving the cheeks, nose, chin, forehead, and periorbital area. Cutaneous manifestations encompass persistent facial erythema, phymas, papules, pustules, telangiectasia, and flushing. The pathogenesis of rosacea is associated with various exacerbating or triggering factors, including microbial infestation, temperature fluctuations, sunlight exposure, physical exertion, emotional stress, consumption of hot beverages and spicy foods, and exposure to airborne pollen. These environmental factors interact with genetic predispositions in the development of rosacea. The roles of the lipophilic microbiome, ultraviolet radiation, nociceptive responses, and vascular alterations have been proposed as significant factors in the pathogenesis. These insights contribute to understanding the anatomical specificity of facial involvement and the progressive nature of rosacea. East Asian skin, predominantly classified as Fitzpatrick skin phototypes III to IV, is characterized by relatively diminished skin barrier function and increased sensitivity to irritants. Airborne pollen exposure may particularly act as a trigger in East Asian individuals, possibly mediated through toll-like receptors. The lack of specificity in objective clinical and histopathological findings leads to diagnostic challenges for individuals with colored skin, including East Asians, particularly when erythema is the sole objective manifestation. An alternative diagnostic scheme may thus be necessary. A diagnostic approach emphasizing vascular manifestations and nociceptive symptoms potentially holds promise for individuals with darker skin tones. More research focusing on potential variations in skin physiology across different racial groups is essential to establish more effective diagnostic schemes applicable to both dark and light skin colors.

Role of Hemigraphis alternata in wound healing: metabolomic profiling and molecular insights into mechanisms

Hemigraphis alternata (H. alternata), commonly known as Red Flame Ivy, is widely recognized for its wound healing capabilities. However, the pharmacologically active plant components and their mechanisms of action in wound healing are yet to be determined. This study presents the mass spectrometry-based global metabolite profiling of aqueous and ethanolic extract of H. alternata leaves. The analysis identified 2285 metabolites from 24,203 spectra obtained in both positive and negative polarities. The identified metabolites were classified under ketones, carboxylic acids, primary aliphatic amines, steroids and steroid derivatives. We performed network pharmacology analysis to explore metabolite-protein interactions and identified 124 human proteins as targets for H. alternata metabolites. Among these, several of them were implicated in wound healing including prothrombin (F2), alpha-2A adrenergic receptor (ADRA2A) and fibroblast growth factor receptor 1 (FGFR1). Gene ontology analysis of target proteins enriched cellular functions related to glucose metabolic process, platelet activation, membrane organization and response to wounding. Additionally, pathway enrichment analysis revealed potential molecular network involved in wound healing. Moreover, in-silico docking analysis showed strong binding energy between H. alternata metabolites with identified protein targets (F2 and PTPN11). Furthermore, the key metabolites involved in wound healing were further validated by multiple reaction monitoring-based targeted analysis.

Pharmacological effects of higenamine based on signalling pathways and mechanism of action

Higenamine (HG) is a chemical compound found in various plants, such as aconite. Recent pharmacological studies have demonstrated its effectiveness in the management of many diseases. Several mechanisms of action of HG have been proposed; however, they have not yet been classified. This review summarises the signalling pathways and pharmacological targets of HG, focusing on its potential as a naturally extracted drug. Articles related to the pharmacological effects, signalling pathways and pharmacological targets of HG were selected by searching the keyword "Higenamine" in the PubMed, Web of Science and Google Scholar databases without limiting the search by publication years. HG possesses anti-oxidant, anti-apoptotic, anti-inflammatory, electrophysiology regulatory, anti-fibrotic and lipid-lowering activities. It is a structural analogue of catecholamines and possesses characteristics similar to those of adrenergic receptor ligands. It can modulate multiple targets, including anti-inflammation- and anti-apoptosis-related targets and some transcription factors, which directly or indirectly influence the disease course. Other naturally occurring compounds, such as cucurbitacin B (Cu B) and 6-gingerol (6-GR), can be combined with HG to enhance its anti-apoptotic activity. Although significant research progress has been made, follow-up pharmacological studies are required to determine the exact mechanism of action, new signalling pathways and targets of HG and the effects of using it in combination with other drugs.

Dysfunctional TRPM8 signalling in the vascular response to environmental cold in ageing

Ageing is associated with increased vulnerability to environmental cold exposure. Previously, we identified the role of the cold-sensitive transient receptor potential (TRP) A1, M8 receptors as vascular cold sensors in mouse skin. We hypothesised that this dynamic cold-sensor system may become dysfunctional in ageing. We show that behavioural and vascular responses to skin local environmental cooling are impaired with even moderate ageing, with reduced TRPM8 gene/protein expression especially. Pharmacological blockade of the residual TRPA1/TRPM8 component substantially diminished the response in aged, compared with young mice. This implies the reliance of the already reduced cold-induced vascular response in ageing mice on remaining TRP receptor activity. Moreover, sympathetic-induced vasoconstriction was reduced with downregulation of the α_2c adrenoceptor expression in ageing. The cold-induced vascular response is important for sensing cold and retaining body heat and health. These findings reveal that cold sensors, essential for this neurovascular pathway, decline as ageing onsets.

Paradoxical effects of acidosis on the noradrenaline-induced and neurogenic constriction of the rat tail artery at low temperatures

Although vasodilatation evoked by acidosis at normal body temperature is well known, the reports regarding effect of acidosis on the reactivity of the isolated arteries at low temperatures are nonexistent. This study tested the hypothesis that the inhibitory effect of acidosis on the neurogenic vasoconstriction may be increased by cooling. Using wire myography, we recorded the neurogenic contraction of the rat tail artery segments to the electrical field stimulation in the absence and in the presence of 0.03-10.0 µmol/L noradrenaline. The experiments were conducted at 37 °C or 25 °C and pH 7.4 or 6.6 which was decreased by means of CO₂. Noradrenaline at concentration of 0.03-0.1 µmol/L significantly potentiated the neurogenic vasoconstriction at 25 °C, and the potentiation was not inhibited by acidosis. Contrary to our hypothesis, acidosis at a low temperature did not affect the noradrenaline-induced tone and significantly increased the neurogenic contraction of the artery segments in the absence and presence of noradrenaline. These effects of acidosis were partly dependent on the endothelium and L-type Ca²⁺ channels activation. The phenomenon described for the first time might be of importance for the reduction in the heat loss by virtue of decrease in the subcutaneous blood flow at low ambient temperatures.

Molecular Mechanism for Ligand Recognition and Subtype Selectivity of α2C Adrenergic Receptor

Adrenergic G-protein-coupled receptors (GPCRs) mediate different cellular signaling pathways in the presence of endogenous catecholamines and play important roles in both physiological and pathological conditions. Extensive studies have been carried out to investigate the structure and function of β adrenergic receptors (βARs). However, the structure of α adrenergic receptors (αARs) remains to be determined. Here, we report the structure of the human α_2C adrenergic receptor (α_2CAR) with the non-selective antagonist, RS79948, at 2.8 Å. Our structure, mutations, modeling, and functional experiments indicate that a α_2CAR-specific D206^ECL2-R409^ECL3-Y405^6.58 network plays a role in determining α₂ adrenergic subtype selectivity. Furthermore, our results show that a specific loosened helix at the top of TM4 in α_2CAR is involved in receptor activation. Together, our structure of human α_2CAR-RS79948 provides key insight into the mechanism underlying the α₂ adrenergic receptor activation and subtype selectivity.

Higenamine exerts an antispasmodic effect on cold-induced vasoconstriction by regulating the PI3K/Akt, ROS/α2C-AR and PTK9 pathways independently of the AMPK/eNOS/NO axis

The present study aimed to investigate the antispasmodic effect of higenamine on cold-induced cutaneous vasoconstriction and the underlying molecular mechanisms. A cold-induced cutaneous vasoconstriction rat model was established and different doses of higenamine were delivered by intravenous injection. The changes of cutaneous regional blood flow (RBF) between groups were analyzed. In vitro, the proliferation of human dermal microvascular endothelial cells was measured by MTT. The NO concentration was detected by a nitrate reductase assay. Flow cytometry was applied to measure reactive oxygen species (ROS) levels. The protein expression levels were detected by western blotting. The results demonstrated that in the model group, RBF declined compared with the normal control group, but was reversed by treatment with higenamine. The expression of endothelial nitric oxide synthase (eNOS), phosphorylated (p)-eNOS, protein kinase B (Akt1), p-Akt1, AMP-activated protein kinase (AMPK) α1 and p-AMPKα1 was upregulated by hypothermic treatment but was reversed by higenamine treatment. Treatment with higenamine significantly reduced the level of intracellular α2C-adrenoreceptor (AR) compared with the hypothermia group (P<0.05). Furthermore, the expression of twinfilin-1 (PTK9) was downregulated in the higenamine and positive control groups compared with the hypothermia group (P<0.05). Compared with the hypothermia group, the levels of ROS and α2C-AR (intracellular & membrane) were decreased in higenamine and the positive control group (P<0.05 and P<0.01, respectively). This study, to the best of our knowledge, is the first to assess the effects of higenamine on cold-induced vasoconstriction in vivo and its molecular mechanisms on the PI3K/Akt, AMPK/eNOS/nitric oxide, ROS/α2C-AR and PTK9 signaling pathways under hypothermia conditions. Higenamine may be a good therapeutic option for Raynaud's phenomenon (RP) and cold-induced vasoconstriction.

Alleviation of mechanical stress-induced allodynia by improving blood flow in chronic constriction injury mice

Reduced blood flow in the skin is observed in patients with neuropathic pain and in animal models. The aim of the present study was to elucidate the relationship between reduced skin blood flow and neuropathic pain in mice with a chronic constriction injury (CCI). Noradrenaline-induced contraction was enhanced in isolated plantar arteries ipsilateral to the CCI surgery compared to the contralateral arteries. Ten μM hydralazine, a peripheral vasodilator, at improved the enhanced contractile response in the ipsilateral arteries. The plantar blood flow in vivo was lower on the ipsilateral side of the CCI mice than on the contralateral side, and a 50% paw withdrawal threshold, as measured using the von Frey filament test, was lower on the former than on the latter side. An intraperitoneal injection (i.p.) of hydralazine (1 mg/kg) or phentolamine (5 mg/kg) improved blood flow in the skin and hyperalgesia in the ipsilateral plantar. In adrenalectomized CCI mice, plantar blood flow in the skin on the ipsilateral side was increased compared to in sham-operated mice, which was accompanied by alleviation of hyperalgesia. Moreover, the enhanced contractile response to noradrenaline was also observed in the ipsilateral plantar arteries isolated from the adrenalectomized CCI mice. Either hydralazine (1 mg/kg, i.p.) or an adrenalectomy barely affected mean arterial pressure in the CCI mice, whereas phentolamine (5 mg/kg, i.p.) lowered it. These results suggest that reduced blood flow in the skin contributes to neuropathic pain and that improving that blood flow with peripheral vasodilators, such as hydralazine, can alleviate it.

Differential contribution of calcium channels to α1-adrenoceptor-mediated contraction is responsible for diverse responses to cooling between rat tail and iliac arteries

Our previous studies have shown that α₁-adrenoceptors, in addition to α₂-adrenoceptors, are involved in enhanced contraction of cutaneous blood vessels during cooling. The present study aimed to elucidate the mechanism underlying it. In tail and iliac arteries isolated from rats, isometric contraction was measured using a myograph and the phosphorylation level of myosin phosphatase target subunit 1 (MYPT1) was quantified by western blotting. The phenylephrine-induced contraction was enhanced by cooling to 24 °C in tail arteries, but was suppressed in iliac arteries. Endothelium denudation or treatment with iberiotoxin enhanced the phenylephrine-induced contraction in tail arteries at 37 °C; however, neither affected the contraction at 24 °C. The phenylephrine-induced contraction at 37 °C was largely suppressed by nifedipine in iliac arteries, but only slightly in tail arteries. The Rho kinase inhibitor H-1152 largely suppressed the phenylephrine-induced contraction at 24 °C, but only slightly at 37 °C, in both arteries. The phosphorylation level of MYPT1 at Thr855 in tail arteries was increased by the cooling. Taken together, these results suggest the following mechanism in regard to cooling-induced enhancement of α₁-adrenoceptor-mediated contraction in tail arteries: Cooling enhances the contraction of tail arteries via α₁-adrenoceptor stimulation by reducing endothelium-dependent, large-conductance Ca²⁺-activated K⁺ channel-mediated relaxation and by inducing Rho kinase-mediated Ca²⁺ sensitization, although the latter occurs even in iliac arteries. A smaller contribution of voltage-dependent Ca²⁺ channels, which are largely suppressed by cooling, to α₁-adrenoceptor-mediated contraction in tail arteries seems to be more crucially involved in the appearance of the enhanced contractile response to cooling.

G-protein coupled estrogen receptor-mediated non-genomic facilitatory effect of estrogen on cooling-induced reduction of skin blood flow in mice

An enhanced vasoconstrictor activity of cutaneous arteries participates in the reduction of skin blood flow induced by cooling stimulation. Raynaud's phenomenon, which is characterized by intense cooling-induced constriction of cutaneous arteries, is more common in women during the period from menarche to menopause. We thus investigated the effect of 17β-estradiol (E2) on cooling-induced reduction of plantar skin blood flow (PSBF) in mouse in vivo. Ovariectomized female ddY mice, anaesthetized with pentobarbital, were treated with tetrodotoxin for eliminating the sympathetic nerve tone and artificially ventilated. The PSBF was measured by laser Doppler flowmetry. Cooling air temperature around the foot from 25 to 20, 15, or 10°C decreased the PSBF in a temperature-dependent manner, which was suppressed by the specific α_2C-adrenoceptor antagonist MK-912. When E2 was intravenously administered as a bolus followed by a constant infusion for 10min just before the cooling stimulation, the cooling-induced reduction of PSBF was facilitated by E2 in a dose-dependent manner. The facilitatory effect of E2 was not induced after the treatment with MK-912. Similar facilitatory effect was induced by an intravenous application of G-1, an agonist of G protein-coupled estrogen receptor (GPER, also termed GPR30). Moreover, the facilitatory effect of E2 was abolished by the GPER antagonist G15. These results suggest that acute administration of E2 leads to the facilitation of cooling-induced, α_2C-adrenoceptor-mediated reduction of skin blood flow via the activation of the non-genomic estrogen receptor GPER.

Vascular responses of the extremities to transdermal application of vasoactive agents in Caucasian and African descent individuals

PURPOSE

Individuals of African descent (AFD) are more susceptible to non-freezing cold injury than Caucasians (CAU) which may be due, in part, to differences in the control of skin blood flow. We investigated the skin blood flow responses to transdermal application of vasoactive agents.

METHODS

Twenty-four young males (12 CAU and 12 AFD) undertook three tests in which iontophoresis was used to apply acetylcholine (ACh 1 w/v %), sodium nitroprusside (SNP 0.01 w/v %) and noradrenaline (NA 0.5 mM) to the skin. The skin sites tested were: volar forearm, non-glabrous finger and toe, and glabrous finger (pad) and toe (pad).

RESULTS

In response to SNP on the forearm, AFD had less vasodilatation for a given current application than CAU (P = 0.027-0.004). ACh evoked less vasodilatation in AFD for a given application current in the non-glabrous finger and toe compared with CAU (P = 0.043-0.014) with a lower maximum vasodilatation in the non-glabrous finger (median [interquartile], AFD n = 11, 41[234] %, CAU n = 12, 351[451] %, P = 0.011) and non-glabrous toe (median [interquartile], AFD n = 9, 116[318] %, CAU n = 12, 484[720] %, P = 0.018). ACh and SNP did not elicit vasodilatation in the glabrous skin sites of either group. There were no ethnic differences in response to NA.

CONCLUSION

AFD have an attenuated endothelium-dependent vasodilatation in non-glabrous sites of the fingers and toes compared with CAU. This may contribute to lower skin temperature following cold exposure and the increased risk of cold injuries experienced by AFD.

A vascular mechanistic approach to understanding Raynaud phenomenon

During exposure to cold, our bodies attempt to maintain normal core temperature by restricting heat loss through cutaneous vasoconstriction, and by increasing heat production through shivering and nonshivering thermogenesis. In selected areas of human skin (including on the fingers and toes), the vascular system has specialized structural and functional features that enable it to contribute to thermoregulation. These features include arteriovenous anastomoses, which directly connect the arterial and venous systems and bypass the nutritional capillaries supplying blood to the skin tissue. Of note, Raynaud phenomenon predominantly affects the arterial territories supplying these specialized areas of skin. Indeed, Raynaud phenomenon can be considered a disorder of vascular thermoregulatory control. This Review presents an understanding of Raynaud phenomenon in the context of vascular and thermoregulatory control mechanisms, including the role of unique thermosensitive vascular structural and functional specialization, and describes the potential role of thermogenesis in this disorder. This new approach provides remarkable insight into the disease process and builds a framework to critically appraise the existing knowledge base. This paradigm also explains the deficiencies in some current therapeutic approaches, and highlights new areas of potential relevance to the pathogenesis and treatment of Raynaud phenomenon that should be expanded and explored.

TRPA1 is essential for the vascular response to environmental cold exposure

The cold-induced vascular response, consisting of vasoconstriction followed by vasodilatation, is critical for protecting the cutaneous tissues against cold injury. Whilst this physiological reflex response is historic knowledge, the mechanisms involved are unclear. Here by using a murine model of local environmental cold exposure, we show that TRPA1 acts as a primary vascular cold sensor, as determined through TRPA1 pharmacological antagonism or gene deletion. The initial cold-induced vasoconstriction is mediated via TRPA1-dependent superoxide production that stimulates α_2C-adrenoceptors and Rho-kinase-mediated MLC phosphorylation, downstream of TRPA1 activation. The subsequent restorative blood flow component is also dependent on TRPA1 activation being mediated by sensory nerve-derived dilator neuropeptides CGRP and substance P, and also nNOS-derived NO. The results allow a new understanding of the importance of TRPA1 in cold exposure and provide impetus for further research into developing therapeutic agents aimed at the local protection of the skin in disease and adverse climates.

Blood flow in the skin of mammals changes in response to cold, but the mechanisms driving this response are unclear. Aubdool et al. show that the non-selective cation channel, TRPA1, is a vascular cold sensor and required for the vascular protective response to local cold exposure.

Effects of some anesthetic agents on skin microcirculation evaluated by laser Doppler perfusion imaging in mice

Background

Anesthetic agents alter microcirculation, influencing tissue oxygenation and delivery of vital substrates. Laser Doppler perfusion imaging is a widespread technique in the field of microvascular research that can evaluate noninvasively and in real time the effects of environmental conditions, physical manipulations, diseases and treatments on peripheral perfusion. This study aims to evaluate laser Doppler perfusion imaging as a means to detect changes in skin microcirculation induced by some popular anesthetic agents in a murine model. Twenty-four age- and gender-matched healthy CD1 mice were examined by laser Doppler perfusion imaging. The skin microcirculatory response was measured at the level of plantar surfaces during isoflurane anesthesia with or without subsequent dexmedetomidine or acepromazine. At the end of the procedure, dexmedetomidine was reversed by atipamezole administration.

Results

In all mice, skin blood flow under isoflurane anesthesia did not show significant differences over time (P = 0.1). The serial perfusion pattern and values following acepromazine or dexmedetomidine administration differed significantly (P < 0.05).

Conclusions

We standardized a reliable laser Doppler perfusion imaging protocol to non-invasively assess changes in skin microcirculation induced by anesthesia in mice, considering the advantages and drawbacks of this technique and its translational value.

Local cooling reduces regional bone blood flow

Local cooling is very common after bone and joint surgery. Therefore the knowledge of bone blood flow during local cooling is of substantial interest. Previous studies revealed that hypothermia leads to vasoconstriction followed by decreased blood flow levels. The aim of this study was to characterize if local cooling is capable of inducing reduced blood flow in bone tissue using a stepwise-reduced temperature protocol in experimental rabbits. To examine bone blood flow we utilized the fluorescent microsphere (FM) method. In New Zealand white rabbits one randomly chosen hind limb was cooled stepwise from 32 to 2°C, whereas the contra lateral hind limb served as control. Injection of microspheres was performed after stabilization of bone and muscle temperature at each temperature level. Bones were removed, dissected and fluorescence intensity was determined to calculate blood flow values. We found that blood flow of all cooled regions decreased relative to the applied external temperature. At maximum cooling blood flow was almost completely disrupted, indicating local cooling as powerful regulatory mechanism for regional bone blood flow (RBBF). Postoperative cooling therefore may lead to strongly decreased bone blood flow values. As a result external cooling has capacity to both diminish bone healing and reduce bleeding complications.

A general linear model-based approach for inferring selection to climate

Background

Many efforts have been made to detect signatures of positive selection in the human genome, especially those associated with expansion from Africa and subsequent colonization of all other continents. However, most approaches have not directly probed the relationship between the environment and patterns of variation among humans. We have designed a method to identify regions of the genome under selection based on Mantel tests conducted within a general linear model framework, which we call MAntel-GLM to Infer Clinal Selection (MAGICS). MAGICS explicitly incorporates population-specific and genome-wide patterns of background variation as well as information from environmental values to provide an improved picture of selection and its underlying causes in human populations.

Results

Our results significantly overlap with those obtained by other published methodologies, but MAGICS has several advantages. These include improvements that: limit false positives by reducing the number of independent tests conducted and by correcting for geographic distance, which we found to be a major contributor to selection signals; yield absolute rather than relative estimates of significance; identify specific geographic regions linked most strongly to particular signals of selection; and detect recent balancing as well as directional selection.

Conclusions

We find evidence of selection associated with climate (P < 10^-5) in 354 genes, and among these observe a highly significant enrichment for directional positive selection. Two of our strongest 'hits’, however, ADRA2A and ADRA2C, implicated in vasoconstriction in response to cold and pain stimuli, show evidence of balancing selection. Our results clearly demonstrate evidence of climate-related signals of directional and balancing selection.

Cyclic AMP-Rap1A signaling mediates cell surface translocation of microvascular smooth muscle α2C-adrenoceptors through the actin-binding protein filamin-2

The second messenger cyclic AMP (cAMP) plays a vital role in vascular physiology, including vasodilation of large blood vessels. We recently demonstrated cAMP activation of Epac-Rap1A and RhoA-Rho-associated kinase (ROCK)-F-actin signaling in arteriolar-derived smooth muscle cells increases expression and cell surface translocation of functional α2C-adrenoceptors (α2C-ARs) that mediate vasoconstriction in small blood vessels (arterioles). The Ras-related small GTPAse Rap1A increased expression of α2C-ARs and also increased translocation of perinuclear α2C-ARs to intracellular F-actin and to the plasma membrane. This study examined the mechanism of translocation to better understand the role of these newly discovered mediators of blood flow control, potentially activated in peripheral vascular disorders. We utilized a yeast two-hybrid screen with human microvascular smooth muscle cells (microVSM) cDNA library and the α2C-AR COOH terminus to identify a novel interaction with the actin cross-linker filamin-2. Yeast α-galactosidase assays, site-directed mutagenesis, and coimmunoprecipitation experiments in heterologous human embryonic kidney (HEK) 293 cells and in human microVSM demonstrated that α2C-ARs, but not α2A-AR subtype, interacted with filamin. In Rap1-stimulated human microVSM, α2C-ARs colocalized with filamin on intracellular filaments and at the plasma membrane. Small interfering RNA-mediated knockdown of filamin-2 inhibited Rap1-induced redistribution of α2C-ARs to the cell surface and inhibited receptor function. The studies suggest that cAMP-Rap1-Rho-ROCK signaling facilitates receptor translocation and function via phosphorylation of filamin-2 Ser(2113). Together, these studies extend our previous findings to show that functional rescue of α2C-ARs is mediated through Rap1-filamin signaling. Perturbation of this signaling pathway may lead to alterations in α2C-AR trafficking and physiological function.

Cyclic AMP-Rap1A signaling activates RhoA to induce α(2c)-adrenoceptor translocation to the cell surface of microvascular smooth muscle cells

Intracellular signaling by the second messenger cyclic AMP (cAMP) activates the Ras-related small GTPase Rap1 through the guanine exchange factor Epac. This activation leads to effector protein interactions, activation, and biological responses in the vasculature, including vasorelaxation. In vascular smooth muscle cells derived from human dermal arterioles (microVSM), Rap1 selectively regulates expression of G protein-coupled α(2C)-adrenoceptors (α(2C)-ARs) through JNK-c-jun nuclear signaling. The α(2C)-ARs are generally retained in the trans-Golgi compartment and mobilize to the cell surface and elicit vasoconstriction in response to cellular stress. The present study used human microVSM to examine the role of Rap1 in receptor localization. Complementary approaches included murine microVSM derived from tail arteries of C57BL6 mice that express functional α(2C)-ARs and mice deficient in Rap1A (Rap1A-null). In human microVSM, increasing intracellular cAMP by direct activation of adenylyl cyclase by forskolin (10 μM) or selectively activating Epac-Rap signaling by the cAMP analog 8-pCPT-2'-O-Me-cAMP (100 μM) activated RhoA, increased α(2C)-AR expression, and reorganized the actin cytoskeleton, increasing F-actin. The α(2C)-ARs mobilized from the perinuclear region to intracellular filamentous structures and to the plasma membrane. Similar results were obtained in murine wild-type microVSM, coupling Rap1-Rho-actin dynamics to receptor relocalization. This signaling was impaired in Rap1A-null murine microVSM and was rescued by delivery of constitutively active (CA) mutant of Rap1A. When tested in heterologous HEK293 cells, Rap1A-CA or Rho-kinase (ROCK-CA) caused translocation of functional α(2C)-ARs to the cell surface (~4- to 6-fold increase, respectively). Together, these studies support vascular bed-specific physiological role of Rap1 and suggest a role in vasoconstriction in microVSM.

Thermoregulation in peripheral nerve injury-induced cold-intolerant rats

PURPOSE

Cold intolerance is defined as pain after exposure to non-painful cold. It is suggested that cold intolerance may be related to dysfunctional thermoregulation in upper extremity nerve injury patients. The purpose of this study was to examine if the re-warming of a rat hind paw is altered in different peripheral nerve injury models and if these patterns are related to severity of cold intolerance.

METHODS

In the spared nerve injury (SNI) and complete sciatic lesion (CSL) model, the re-warming patterns after cold stress exposure were investigated preoperatively and at 3, 6 and 9 weeks postoperatively with a device to induce cooling of the hind paws. Thermocouples were attached on the dorsal side of the hind paw to monitor re-warming patterns.

RESULTS

The Von Frey test and cold plate test indicated a significantly lower paw-withdrawal threshold and latency in the SNI compared to the Sham model. The CSL group, however, had only significantly lower paw-withdrawal latency on the cold plate test compared to the Sham group. While we found no significantly different re-warming patterns in the SNI and CSL group compared to Sham group, we did find a tendency in temperature increase in the CSL group 3 weeks postoperatively.

CONCLUSION

Overall, our findings indicate that re-warming patterns are not altered after peripheral nerve injury in these rat models despite the fact that these animals did develop cold intolerance. This suggests that disturbed thermoregulation may not be the prime mechanism for cold intolerance and that, other, most likely, neurological mechanisms may play a more important role.

CLINICAL RELEVANCE

There is no direct correlation between cold intolerance and re-warming patterns in different peripheral nerve injury rat models. This is an important finding for future developing treatments for this common problem, since treatment focussing on vaso-regulation may not help diminish symptoms of cold-intolerant patients.

Intracellular α(2C)-adrenoceptors: storage depot, stunted development or signaling domain?

G-protein coupled receptors (GPCRs) are generally considered to function as cell surface signaling structures that respond to extracellular mediators, many of which do not readily access the cell's interior. Indeed, most GPCRs are preferentially targeted to the plasma membrane. However, some receptors, including α(2C)-Adrenoceptors, challenge conventional concepts of GPCR activity by being preferentially retained and localized within intracellular organelles. This review will address the issues associated with this unusual GPCR localization and discuss whether it represents a novel sub-cellular niche for GPCR signaling, whether these receptors are being stored for rapid deployment to the cell surface, or whether they represent immature or incomplete receptor systems.

Rho kinase activation and ROS production contributes to the cooling enhanced contraction in cutaneous equine digital veins

A decrease in environmental temperature can directly affect the contractility of cutaneous vasculature, mediated in part by α2-adrenoceptors. Most of the cellular mechanisms underlying the cooling-enhanced contractility to α2-adrenoceptor agonists have been reported in cutaneous arteries but little information is available on cutaneous veins. To investigate the cellular mechanisms associated with the cooling-enhanced contraction to UK-14304 (α2-adrenoceptor agonist), isolated equine digital veins (EDVs) were studied at 30°C and 22°C. The effects of inhibitors were studied on the contractile response to UK-14304 (0.1 μM). The cooling-enhanced responses were inhibited by Rho kinase inhibitors [maximum response to UK-14304 95.2 ± 8% of response to depolarizing Krebs solution (DKS) in control vessels cooled to 22°C, compared with 31.4 ± 6% in the presence of fasudil 1 μM and 75.8 ± 6% with Y-27632 0.1 μM] and the effects of these inhibitors were considerably less at 30°C (control response 56.4 ± 5% of DKS; 34.9 ± 6% with fasudil 1 μM and 50.6 ± 9% with Y-27632 0.1 μM). Furthermore, Western blotting showed that one of the downstream targets for Rho kinase activity, ezrin/radixin/moesin, was phosphorylated after cooling and reduced by fasudil (1 μM) only at 22°C. The activation of protein kinase C contributed to the contractile response, but predominantly at 30°C (maximum response 82.3 ± 9% of DKS for control; 57.7 ± 10% in the presence of chelerythrine 10 μM) with no significant effect at 22°C. The reduction of the response at 22°C by antioxidants, rotenone (14% reduction), and tempol (21% reduction) suggested the contribution of reactive oxygen species (ROS). No evidence was obtained to support the participation of tyrosine kinase. These data demonstrate that Rho kinase activation and the production of ROS contributes to the cooling-enhanced contraction in these cutaneous digital veins.

Local response to cold in rat tail after spinal cord transection

Subjects with severe chronic spinal cord injury (SCI) are prone to hypothermia when they are exposed to relatively low environmental temperatures that are normally well tolerated by healthy individuals. This impaired thermoregulation is presumably due to disconnection of territories below the SCI from supraspinal thermoregulatory centers. However, it is not known how these territories respond to low temperatures. Using a complete transection at T11 in rats, we examined the responses of the tail to cold (6–9°C) by measuring changes in tail blood flow and skin temperature weekly for 8 wk after SCI. Despite no significant change in baseline mean flow or temperature in the tail, the transection effectively removed the sympathetically mediated supraspinal control of the tail vasculature, since the amplitude of the pulse flow was markedly increased and the natural variations of the mean flow were almost abolished. As expected, the cold challenge before SCI caused a marked drop in mean flow, pulse amplitude, and temperature of the tail. Surprisingly, the drops in mean blood flow and temperature were observed after SCI, although the decrease in flow was slower and the pulse amplitude was not reduced. The results suggest that the cutaneous vasculature of the tail is sensitive to cold and will constrict, despite disconnection from supraspinal centers. This local effect is slow but may be sufficient to maintain some level of thermoregulation to cold. Without this vascular reaction, the effects of SCI on temperature regulation to cold would probably be much worse.

Altered mechanisms of thermoregulatory vasoconstriction in aged human skin

Human exposure to cold stimulates cutaneous vasoconstriction by activating both sympathetic reflex and locally mediated pathways. Older humans are vulnerable to hypothermia because primary aging impairs thermoregulatory cutaneous vasoconstriction. This article highlights recent findings discussing how age-related decrements in sympathetic neurotransmission contribute directly to thermoregulatory impairment, whereas changes in local cold-induced intracellular signaling suggest a more generalized age-associated vascular dysfunction.

Cyclic AMP acts through Rap1 and JNK signaling to increase expression of cutaneous smooth muscle alpha2C-adrenoceptors

Cold increases cutaneous vasoconstriction by unmasking the contractile activity of alpha(2C)-adrenoceptors (alpha(2C)-ARs) in vascular smooth muscle cells (VSMCs), which is mediated by the cold-induced mobilization of alpha(2C)-ARs from the transGolgi to the cell surface. The expression of alpha(2C)-ARs in human cutaneous VSMCs is under dual regulation by cyclic AMP: gene transcription is inhibited by cyclic AMP acting through protein kinase A but is increased by cyclic AMP acting through the exchange protein directly activated by cyclic AMP (EPAC) and the GTP-binding protein Rap1. Experiments were performed to further characterize the Rap1 signaling pathway. Forskolin (10 muM), the selective EPAC activator, 8-pCPT-2'-O-Me-cyclic AMP (CMC; 100 microM), or a constitutively active mutant of Rap1 (Rap1CA) increased the activity of c-Jun NH(2)-terminal kinase (JNK) in human cutaneous VSMCs. This was associated with the increased phosphorylation of c-Jun and activation of an activator protein (AP)-1 reporter construct, which were inhibited by the JNK inhibitor SP600125 (3 microM). Rap1CA increased the activity of an alpha(2C)-AR promoter-reporter construct, which was inhibited by SP600125 (3 microM) or by the mutation of an AP-1 binding site in the alpha(2C)-AR promoter. Furthermore, forskolin (10 microM) or CMC (100 microM) increased the expression of the alpha(2C)-AR protein, and these effects were inhibited by SP600125 (3 microM). Therefore, cyclic AMP increases the expression of alpha(2C)-ARs in cutaneous VSMCs by activating a novel Rap1 signaling pathway, mediated by the activation of JNK, AP-1, and the subsequent transcriptional activation of the alpha(2C)-AR gene. By increasing the expression of cold-responsive alpha(2C)-ARs, this pathway may contribute to enhanced cold-induced vasoconstriction in the cutaneous circulation, including Raynaud's phenomenon.

Regulation of vascular reactivity in scleroderma: new insights into Raynaud's phenomenon

Because of the role of the RhoA/Rho kinase (ROCK) pathway in regulating numerous pathologic processes including vasoconstriction, vascular remodeling, and fibrosis, ROCK inhibitors may be especially beneficial in treating Raynaud's phenomenon and scleroderma.