In recent yearsestradiol has emerged as a potential regulator of transient receptor potential vanilloid (TRPV) cationic channels in the peripheral tissues and sensory neurons, however, its analogous role in theCNS is poorly understood. TRPV channels modulate Ca signalling, neurotransmission and behaviour, andexpression of these ion channels and estrogen receptors show a great degree of overlap in different brain regions. Herein, we probe if TRPV1-6 genes contain estrogen receptor-binding sites and if their expression in different brain regions is modulated during estrous cycle. Bioinformatics analysis of the mouse TRPV1-6 gene sequences showed presence of putative functional estrogen response element in their promoter regions. Using qRT-PCR, TRPV1-6 mRNA expression was observed in the olfactory bulb, cortex, hypothalamus, hippocampus, brainstem, and cerebellum of mouse. In these regions, compared to estrus, metestrus, and diestrus, reduced levels of TRPV1 and TRPV5 but elevated TRPV2 and TRPV6 mRNA levels were observed during proestrus. Lower levels of TRPV3 and TRPV4 mRNAs were seen during estrus but higher expression of TRPV3 during metestrus and diestrus, and TRPV4 during proestrus was observed. Estradiol seems to regulate TRPV1/TRPV5 and TRPV2/TRPV6 mRNA expression in opposite manner. Except TRPV4 mRNA expression in the hippocampus and TRPV6 expression in the olfactory bulb, hippocampus and brainstem, expression of other member of TRPV subfamily in distinct brain regions of male mice was comparable to those in metestrus and diestrus mice. We suggest that the circulating levels of estradiol during the estrous cycle may differentially regulate the activity of TRPV1-6 ion channels in the brain.
Transient receptor potential vanilloid (TRPV) subfamily of cationic channels have emerged as novel players in neural regulation. Unlike other members of TRPV subfamily, TRPV5 and TRPV6 are highly Ca-selective. Although TRPV5/TRPV6 transcripts are expressed in mouse brain, understanding the full functional spectrum of these ion channels in the brain is however limited due to the lack of information on their neuroanatomical distribution. We have studied TRPV6 in mouse brain in further detail. In the hypothalamus, while Western blot analysis using TRPV6 specific antiserum showed a distinct ∼95 kDa band corresponding to the molecular weight of TRPV6, transcripts for TRPV6 were detected with RT-PCR. TRPV6-immunoreactive cells/fibers were observed in vascular organ of the lamina terminalis, olfactory bulb, amygdala, hippocampus, septohypothalamic, supraoptic, arcuate (ARC), dorsomedial, and subincertal nuclei. TRPV6-immunoreactive cells/fibers were also observed in the brainstem and cerebellum. Estrogen has emerged as a potential regulator of TRPV6 in peripheral tissues. TRPV6 gene promoter contains estrogen-response element, estrogen activates TRPV6 via estrogen receptor alpha (ERα), and ERα-expressing ARC neurons in mediobasal hypothalamus (MBH) serve as primary site for estradiol feedback. Using double immunofluorescence, co-expression of TRPV6 and ERα was observed in several ARC neurons. MBH of mice during different phases of estrous cycle were subjected to Western blot analysis of TRPV6. Compared to proestrus, a significant reduction (P<0.01) in intensity of TRPV6-immunoreactive band was observed in MBH during metestrus and diestrus phases. While the wide distribution of TRPV6-expressing elements in the brain suggests its role in a range of CNS functions, the ion channel may serve as novel component of the neural pathway mediating effects of estradiol in MBH.