Organization of lipids in the artificial outer membrane of bull spermatozoa reconstructed at the air–water interface

Miscibility of hBest1 and sphingomyelin in surface films - A prerequisite for interaction with membrane domains

Human bestrophin-1 (hBest1) is a transmembrane Ca²⁺- dependent anion channel, associated with the transport of Cl^-, HCO^3- ions, γ-aminobutiric acid (GABA), glutamate (Glu), and regulation of retinal homeostasis. Its mutant forms cause retinal degenerative diseases, defined as Bestrophinopathies. Using both physicochemical - surface pressure/mean molecular area (π/A) isotherms, hysteresis, compressibility moduli of hBest1/sphingomyelin (SM) monolayers, Brewster angle microscopy (BAM) studies, and biological approaches - detergent membrane fractionation, Laurdan (6-dodecanoyl-N,N-dimethyl-2-naphthylamine) and immunofluorescence staining of stably transfected MDCK-hBest1 and MDCK II cells, we report: 1) Ca²⁺, Glu and GABA interact with binary hBest1/SM monolayers at 35 °C, resulting in changes in hBest1 surface conformation, structure, self-organization and surface dynamics. The process of mixing in hBest1/SM monolayers is spontaneous and the effect of protein on binary films was defined as "fluidizing", hindering the phase-transition of monolayer from liquid-expanded to intermediate (LE-M) state; 2) in stably transfected MDCK-hBest1 cells, bestrophin-1 was distributed between detergent resistant (DRM) and detergent-soluble membranes (DSM) - up to 30 % and 70 %, respectively; in alive cells, hBest1 was visualized in both liquid-ordered (L_o) and liquid-disordered (L_d) fractions, quantifying protein association up to 35 % and 65 % with L_o and L_d. Our results indicate that the spontaneous miscibility of hBest1 and SM is a prerequisite to diverse protein interactions with membrane domains, different structural conformations and biological functions.

Sequestration of bovine seminal plasma proteins by different assemblies of phosphatidylcholine: A new technical approach

Binder of SPerm (BSP) proteins, the main proteins from bovine seminal plasma, are known to partially intercalate into the outer leaflet of the spermatozoa membrane and bind to choline-containing lipids being present therein. This insertion generates a negative effect on semen quality after cryopreservation by inducing an early-stage capacitation of spermatozoa. The assumption of surface properties exhibited by BSP proteins was checked by tensiometry measurements: BSP proteins are highly surface active. This suggests that BSP proteins can reach the interface covered by phospholipids not only by interactions between one and each other but also due to their own surface activity. The insertion of BSP proteins into the lipid domains outer leaflet of spermatozoa was reproduced on a biomimetic system such as Langmuir monolayers. The insertion of BSP proteins can be performed in the compressible fluid domains which contain choline-bearing lipids. Monolayer films were used as well to study the complexation of BSP proteins by two phospholipid assemblies: low density lipoprotein (LDLs) from egg yolk or liposomes produced from egg phospholipids. Irrespective of the phospholipid structure (lipoprotein or liposome), BSP was hindered to alter the structure of the membrane. Only the overall ratio BSP proteins:phosphatidylcholine was important. The difference between the two sequestering agents lies on their surface properties: LDL have a strong tendency to merge with the outer layer whereas liposomes mainly remain in the bulk on the same time scale.

The benefits of liposomes for chilling canine sperm for 4 days at 4°C

This study comprises 3 experiments exploring the possible benefits and mechanism of action of liposomes for chilling (4°C) canine sperm over a period of 4 days. In the first experiment, 20 ejaculates collected from 5 Beagle dogs were chilled in an extender containing 6% low density lipoproteins (LDL) (Control), or one of 7 extenders containing different concentrations (2, 4, 6, 8, 10, 15, 20%) of liposomes (LIPO). These ejaculates were chilled over 4 days and motility was assessed daily using a Hamilton Thorne analyzer (HTM-IVOS, 14.0). The 2% LIPO obtained the best results (p=0.038) after four days (72.55% motile spermatozoa and 31.4% progressive spermatozoa). In experiment 2, 10 ejaculates were collected from same 5 dogs and chilled in 6% LDL or 2% LIPO-based extenders. Sperm integrity characteristics were assessed prior to refrigeration and every 48h for four days (D0, D2, and D4). Acrosome integrity was assessed using the FITC-PSA test (Fluorescein IsoThiocyanate-Pisum Sativum Agglutinin), plasma membrane (PM) integrity using both the hypo-osmotic swelling test (HOSt) and SYBR14/Propidium Iodide test (SYBR14/PI), and DNA integrity using the Acridine-Orange test (AO). The 2% LIPO extender provided equivalent preservation of sperm integrity parameters to the reference extender (6% LDL). In experiment 3, a Langmuir-Blodgett trough was used to evaluate the mechanistic interactions between LDL, LIPO, prostatic fluid, and the canine spermatozoal membrane during chilling. Results indicate that LDL and LIPO interact differently with the biomimetic membrane. The most likely conclusion of these findings is that LDL and liposomes employ different protective mechanisms during the chilling (4°C) of canine spermatozoa.