HDL mediates reverse cholesterol transport from ram spermatozoa and induces hyperactivated motility

Abstract

Reverse Cholesterol Transport or cholesterol efflux is part of an extensive plasma membrane remodelling process in spermatozoa that is imperative for fertilisation. For ram spermatozoa, sheep serum is well known to support in vitro fertilisation (IVF), but knowledge of its explicit role is limited. Though, it is postulated to elicit cholesterol efflux owing to the presence of high density lipoproteins (HDLs) that interact with transmembrane cholesterol transporters, such as ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B, type I (SR-BI). In this study, we report that both sheep serum and HDLs were able to elicit cholesterol efflux alone by up to 20–40% (as measured by the BODIPY-cholesterol assay). Furthermore, when the antagonists glibenclamide and valspodar were used to inhibit the function of ABCA1 and SR-BI or ABCA1 alone, respectively, cholesterol efflux was only marginally reduced (8–15)%. Nevertheless, it is likely that in ram spermatozoa, a specific facilitated pathway of cholesterol efflux is involved in the interaction between cholesterol acceptors and transporters. Interestingly, exposure to HDLs also induced hyperactivated motility, another critical event required for successful fertilisation. Taken together, this study details the first report of the dual action of HDLs on ram spermatozoa, providing both an insight into the intricacy of events leading up to fertilisation in vivo as well as demonstrating the possible application of HDL supplementation in media for IVF.

Does Better Post-Thaw Motility of Dog Sperm Frozen with CLC Mean Better Zona Pellucida Binding Ability?

“…The TOPFLUOR ® Cholesterol kit (Avanti Polar Lipids, Alabaster, AL, USA) is a quite new tool and can be used to measure cholesterol efflux in variable cells [48][49][50]. Recently, it was proven that the cholesterol balance can also be assessed in mammalian spermatozoa [29,51]. In studies conducted on dog spermatozoa, different concentrations of probucol were assessed for inhibition of ABCA1.…”

Increasing the Yield and Cryosurvival of Spermatozoa from Rhinoceros Ejaculates Using the Enzyme Papain

“…The viability reported post-thaw is similar to the 48% reported in 2009 [ 6 ] which assessed the percentage of live cells using a hypo-osmotic swelling (HOS) test prior to artificial insemination. Lipid membrane disorder or membrane fluidity, as measured by median M540 fluorescence, is considered an early indication of capacitation and apoptotic-like changes [ 55 ], a sperm maturation step which occurs within the female and is crucial for fertilisation (for a review please see [ 56 ]). Premature capacitation of spermatozoa is a common artifact of freezing and can lead to early apoptosis of the cell [ 57 ].…”