| Popis: |
The phenomenon of cold-induced vasodilatation (CIVD) was discovered by Sir Thomas Lewis (1930) and has been extensively investigated as it is involved in protecting against local cold-induced injury. The mechanisms underlying this well-established protective response remain unclear. The non-selective cation channel, transient receptor potential ankyrin-1 (TRPA1) is expressed in a subset of sensory neurons and acts as a polymodal membrane channel for cold sensitivity, but this remains a controversial issue in the literature. Additionally, the role of TRPA1 as a vascular cold sensor is currently unknown. Previous studies in our group have shown that TRPA1 plays an important role in regulating peripheral blood vessel tone, with little information available on the downstream signalling mechanism. The aims of this PhD project were to investigate the effects of TRPA1 activation by an exogenous agonist cinnamaldehyde and local cold exposure on peripheral vascular responses in murine skin in vivo. Using a combination of pharmacological antagonists and genetically modified mice, topical application of cinnamaldehyde (10%) was shown to increase blood flow in a TRPA1-dependent manner in the mouse ear model. This response was further shown to be dependent on the release of the potent microvascular vasodilator calcitonin gene-related peptide (CGRP), highlighting the involvement of a neurogenic component. This study provides novel evidence demonstrating the relative contribution of neuronal nitric-oxide synthase (nNOS)-derived nitric oxide and reactive oxygen species, downstream of TRPA1 activation by cinnamaldehyde. These findings highlight the prominent role of TRPA1 in mediating peripheral vasodilatation. The project further progressed to the development and characterisation of a local cold model in the mouse hindpaw in vivo. Local cold exposure was shown to cause a rapid and transient vasoconstriction, followed by a prolonged vasodilatation phase to return blood flow to baseline, an essential physiological function for protecting against local cold-induced injury. The activation of TRPA1 in the peripheral vasculature was shown to drive this cold-induced vascular response at 10°C. This model enabled the determination of the relative role of sympathetic nerves, post-junctional α2-adrenergic receptors and reactive oxygen species in the local cold-induced vasoconstriction. This study provides novel evidence showing that local cold exposure causes an increase in intracellular superoxide production in a TRPA1-dependent manner, which activates the Rho-kinase-mediated pathways and induces cold-induced α2C-adrenergic vasoconstriction. The neuropeptide CGRP was subsequently shown to have a prominent role in the vasodilator phase. This study provide novel evidence of a major involvement of TRPA1 in mediating cold-induced vasoconstriction in vivo, with a new perspective of the underlying mechanisms mediating the protection against local-cold induced injury. |
