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Asian Journal of Andrology (2010) 12: 490-499. doi: 10.1038/aja.2010.40; published online 21 June 2010.
Aquaporins in spermatozoa and testicular germ cells: identification and potential role
Ching-Hei Yeung11
1 Centre of Reproductive Medicine and Andrology, University Clinic, Muenster D48149, Germany
Correspondence: Dr Ching-Hei Yeung, Centre of Reproductive Medicine and Andrology, University Clinic, Domagkstrasse 11, Muenster D48149, Germany. E-mail: yeungchinghei@yahoo.co.uk
Received 19 April 2010; Revised 5 May 2010; Accepted 10 May 2010; Published online 21 June 2010.
| Abstract |
Mammalian spermatozoa have relatively high water permeability and swell readily, as in the hypo-osmotic swelling test used in the andrology clinic. Physiologically, spermatozoa experience changes in the osmolality of the surrounding fluids in both the male and the female tracts on their journey from the testis to the ovum. Sperm volume regulation in response to such osmotic challenges is important to maintain a stable cell size for the normal shape and function of the sperm tail. Alongside ion channels for the fluxes of osmolytes, water channels would be crucial for sperm volume regulation. In contrast to the deep knowledge and numerous studies on somatic cell aquaporins (AQPs), the understanding of sperm AQPs is limited. Among the 13 AQPs, convincing evidence for their presence in spermatozoa has been confined to AQP7, AQP8 and AQP11. Overall, current findings indicate a major role of AQP8 in water influx and efflux for sperm volume regulation, which is required for natural fertilization. The preliminary data suggestive of a role for AQP7 in sperm glycerol metabolism needs further substantiation. The association of AQP11 with the residual cytoplasm of elongated spermatids and the distal tail of spermatozoa supports the hypothesis of more than just a role in conferring water permeability and also in the turnover and recycling of surplus cellular components made redundant during spermiogenesis and spermiation. This would be crucial for the maintenance of a germinal epithelium functioning efficiently in the production of spermatozoa.
Keywords: fertility; sperm volume regulation; spermatid residual cytoplasm; spermiogenesis; water channels |
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