Abstract
The molecular bases of sperm thermotaxis, the temperature-oriented cell motility, are currently under investigation. Thermal perception relies on a subclass of the transient receptor potential [TRP] channels, whose member TRPV1 is acknowledged as the heat sensing receptor. Here we investigated the involvement of TRPV1 in human sperm thermotaxis. We obtained semen samples from 16 normozoospermic subjects attending an infertility survey programme, testis biopsies from 6 patients with testicular germ cell cancer and testis fine needle aspirates from 6 patients with obstructive azoospermia undergoing assisted reproductive technologies. Expression of TRPV1 mRNA was assessed by RT-PCR. Protein expression of TRPV1 was determined by western blot, flow cytometry and immunofluorescence. Sperm motility was assessed by Sperm Class Analyser. Acrosome reaction, apoptosis and intracellular-Ca2+ content were assessed by flow cytometry. We found that TRPV1 mRNA and protein were highly expressed in the testis, in both Sertoli cells and germ-line cells. Moreover, compared to no-gradient controls at 31°C or 37°C (Ctrl 31°C and Ctrl 37°C respectively), sperm migration towards a temperature gradient of 31–37°C (T gradient) in non-capacitated conditions selected a higher number of cells (14,9 ± 4,2×106 cells T gradient vs 5,1± 0,3×106 cells Ctrl 31°C and 5,71±0,74×106 cells Ctrl 37°C; P = 0,039). Capacitation amplified the migrating capability towards the T gradient. Sperms migrated towards the T gradient showed enriched levels of both TRPV1 protein and mRNA. In addition, sperm cells were able to migrate toward a gradient of capsaicin, a specific agonist of TRPV1, whilst capsazepine, a specific agonist of TRPV1, blocked this effect. Finally, capsazepine severely blunted migration towards T gradient without abolishing. These results suggest that TRPV1 may represent a facilitating mediator of sperm thermotaxis.
Highlights
The encounter between the sperm cell and the oocyte within the female reproductive tract leads to a cascade of events, known as fertilization, consisting of sperm penetration, sperm–oocyte fusion, and zygote division
In this manuscript we show a major involvement of transient receptor potential vanilloid receptor 1 (TRPV1) in this physiological process
Few data are available about the expression of TRPV1 in the cell population of the seminiferous tubule
Summary
The encounter between the sperm cell and the oocyte within the female reproductive tract leads to a cascade of events, known as fertilization, consisting of sperm penetration, sperm–oocyte fusion, and zygote division The chance of this cell-to-cell contact is very narrow and results from a number of highly regulated attracting mechanisms that are believed to guide spermatozoa along the oviduct [1]. Chemotaxis itself may not be a sufficient drive for spermatozoa, since the peristaltic movements of the oviduct are expected to shuffle tubal fluid and prevent the formation of a long-range chemoattractant gradient in vivo [6]. This would restrict the role of chemotaxis to a short distance range from the oocyte [7]. It has been hypothesized that, in vivo, spermatozoa are first guided by thermotaxis from the reservoir towards the warmer fertilization site, at close proximity to the oocyte and within the cumulus mass, the guidance is likely carried out by chemotaxis [6]
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