Phosphatidylcholine-binding proteins of bovine seminal plasma modulate capacitation of spermatozoa by heparin

Abstract

Bovine seminal plasma (BSP) contains four similar acidic proteins, previously designated as BSP-A1, BSP-A2, BSP-A3, and BSP-30-kDa. These proteins are secreted by the seminal vesicles and coat the surface of the spermatozoa after ejaculation. The binding site of BSP proteins on the sperm surface has been identified as choline phospholipids on the plasma membrane. This study was undertaken to determine whether BSP proteins modulate capacitation of bovine spermatozoa induced by heparin. Bovine epididymal spermatozoa were washed and incubated in buffer containing BSP proteins and then washed and incubated with heparin. The percentage of capacitated spermatozoa was determined under the microscope after the acrosome reaction has been initiated with the addition of lysophosphatidylcholine. The results demonstrated that epididymal sperm undergo the acrosome reaction only in the presence of BSP proteins. This effect was concentration-dependent and reached a maximum level of a 3-5-fold increase at 20-40 micrograms/ml BSP protein concentrations. In contrast, ribonuclease (purified from bovine seminal fluid) or seminal fluid proteins depleted of BSP proteins (by sequential absorption of BSP proteins on gelatin-Agarose and DEAE-Sephadex columns) showed no significant potentiating activity. The purified BSP proteins were more active than crude alcohol precipitates of bovine seminal plasma. These results indicate that BSP proteins are regulatory factors of capacitation.

Functional aspects of seminal plasma and sperm proteins and their potential as molecularmarkers of fertility

“…This outcome may be the result of BSP1-induced damage on sperm, given the exposure period during fertilization (18 h). In agreement with such results, studies show that excess of BSP proteins and time exposure are harmful to cryopreserved sperm because of membrane destabilization and excessive phospholipid and cholesterol efflux (Therien et al, 1995;1998;Manjunath and Therien, 2002). Also, an earlier investigation claimed that the content of BSP5 in accessory sex gland fluid has a quadratic association with bull fertility (Moura et al, 2006), suggesting that too much BSP is detrimental to sperm physiology and/or embryo development.…”

Binding patterns of seminal plasma plasma proteins on bovine epididymal and ejaculated sperm membrane

“…This protein originates from the vesicular glands (Manjunath et al, 1988) and interacts with the sperm during ejaculation, more specifically with membrane choline-containing phospholipids (Desnoyers and Manjunath, 1992), a step that initiates sperm capacitation (Thérien et al, 1995). Identically to the other BSPs, BSP-A3 might remain attached to the sperm membrane until the oviduct (Souza et al, 2008), where it is involved in the formation of the sperm reservoir (Gwathmey et al, 2006).…”

“…Seminal plasma proteins have been implicated in several sperm functions, including capacitation and acrosome reaction (Thérien et al, 1995;Siciliano et al, 2008). The intensity of selected protein spots in 2-D maps of seminal plasma (Killian et al, 1993), accessory sex gland fluid (Moura et al, 2006a) and cauda epididymal fluid (Moura et al, 2006b) is related to the fertility of dairy bulls as well.…”

Discovery, Primary, and Crystal Structures and Capacitation-related Properties of a Prostate-derived Heparin-binding Protein WGA16 from Boar Sperm

“…However, the molecular basis of in vivo capacitation remains unclear. In the case of bovines, it has been clearly demonstrated that heparin induces capacitation (48), and heparin-binding proteins have been shown to modulate capacitation (49). The presence of heparin, heparan sulfate, and other sulfated glycosaminoglycans has been demonstrated in follicular fluid of sows (50).…”