Prostasomes: Their Characterisation: Implications for Human Reproduction: Prostasomes and Human Reproduction

Abstract

The prostate is a principal accessory genital gland that is vital for normal fertility. Epithelial cells lining the prostate acini release in a defined fashion (exocytosis) organellar nanosized structures named prostasomes. They are involved in the protection of sperm cells against immune response in the female reproductive tract by modulating the complement system and by inhibiting monocyte and neutrophil phagocytosis and lymphocyte proliferation. The immunomodulatory function most probably involves small non-coding RNAs present in prostasomes. Prostasomes have also been proposed to regulate the timing of sperm cell capacitation and induction of the acrosome reaction, since they are rich in various transferable bioactive molecules (e.g. receptors and enzymes) that promote the fertilising ability of sperm cells. Antigenicity of sperm cells has been well documented and implicated in involuntary immunological infertility of human couples, and antisperm antibodies (ASA) occur in several body fluids. The propensity of sperm cells to carry attached prostasomes suggests that they are a new category of sperm antigens. Circulating human ASA recognise prostasomes, and among 12 identified prostasomal antigens, prolactin- inducible protein (95 %) and clusterin (85 %) were immunodominant at the expense of the other 10 that were sporadically occurring.

Fig. 9.1

Ultrastructure of prostasomes. (a) Thin-section transmission electron microscopy (EM) image of human prostasomes isolated from seminal plasma. Prostasomes display rounded structures with varied sizes more or less filled with electron-dense material. (b) Ultrastructural appearance of prostasomes by cryo-EM. The samples have been vitrified in liquid ethane to prevent the formation of perturbating ice crystals. The rounded prostasomes are surrounded by classical biological membranes (Brisson A & Ronquist G, unpublished 2013)

Fig. 9.2

Highly reproducible SDS-PAGE pattern of preparations from different pools of seminal prostasomes (1–5) over a 2-year period. The three marked bands, a–c, in the high molecular weight range have been identified as follows: (a) CD13—aminopeptidase N (approximately 110 kDa), (b) CD26—dipeptidylpeptidase 4 (approximately 88 kDa), (c) CD10—neprilysin (approximately 86 kDa) (Reprinted from Ronquist et al. (2011) with permission of the publisher. Copyright 2014 John Wiley & Sons A/S)