Cytoskeletal proteins F-actin and β-dystrobrevin are altered by the cryopreservation process in bull sperm

The cryopreservation process has an important impact on sperm structure and physiology. The negative effects have been mainly observed on the plasma membrane, which is directly stabilized by the cytoskeleton. Since cytoskeleton proteins are osmosensitive and thermosensitive, the aim of this study was to evaluate the damage caused to the bull sperm cytoskeleton by cryopreservation (freezing-thawing). Fresh and frozen-thawed bull semen samples were exposed to a treatment with the neutral detergent Brij 36-T. Electron microscopy evidenced important damages at the sperm perinuclear theca after the protein extraction protocol; the perinuclear theca was partially solubilized, the perinuclear theca substructure disappeared in the cryopreserved samples. Furthermore, the sperm head's shape was significantly altered on the cryopreserved samples. Fluorescence analysis showed a decrease of the intensity of actin and dystrobrevin on the frozen-thawed samples. Western blot assays revealed a stronger signal for actin and β-dystrobrevin in the frozen-thawed sperm samples than in the fresh ones. Our results suggest that the cryopreservation process highly alters the sperm cytoskeleton stability, causing its proteins to become more fragile and therefore more susceptible to be extracted.

Cryopreservation of bull spermatozoa alters the perinuclear theca

The perinuclear theca (PT) is involved in several important sperm functions leading to fertilization. The objective of this study was to investigate the effect of cryopreservation of bull spermatozoa on the integrity of the PT and the relationship between PT integrity and semen characteristics. Semen from seven bulls was evaluated before and after cryopreservation, comparing the integrity of the plasma membrane (hypo-osmotic test), percentage of live and dead spermatozoa (triple stain), acrosome integrity (triple stain) and the integrity of the PT (negative stain by electron microscopy). Cryopreservation of bull semen caused substantial damage to the PT; the proportion of spermatozoa with a damaged PT was 15.2% versus 52.5% (P<0.05) in fresh versus frozen-thawed spermatozoa, respectively. Furthermore, on average, 67.4% (range, 64-72%) of fresh spermatozoa were live, compared to 53.1% (range, 49-58%) for frozen-thawed spermatozoa; there was an inverse correlation between the percentage of live spermatozoa and the percentage with damage to the PT. Although 59.1% of frozen-thawed spermatozoa had an intact acrosome, only 43.7% of them still remained alive. In frozen-thawed semen, there was a high correlation (r=0.69) between live spermatozoa with an intact acrosome and spermatozoa that maintained an intact PT. In conclusion, freezing/thawing of bull spermatozoa altered the PT and maintaining PT integrity may be necessary to maintain acrosome integrity.

Alterations of domains in the plasmatic membrane due to damages of the perinuclear theca of pig preserved spermatozoa

Samples of semen from 12 pigs, three from Yorkshire, Landrace, Duroc and Mexican Hairless each where obtained to study cryopreservation methods. Three stages of boar semen cryopreservation were evaluated: none (fresh stage), cooling at 5 degrees C and freezing at -196 degrees C then thawing to 56 degrees C for 12 sec. Perinuclear theca damage and domain alterations were selected as indices of seminal quality, as measured by electronic and fluorescence microcopy, respectively according to two lineal models considering by separately the effect of semen preservation and breed. Integrity and absence of perinuclear theca significantly (p < 0.001) decreased and increased, respectively according to a decrease in temperature of cryopreservation, from 87.4 to 58.8% and from 0.8 to 26.2%, respectively. This same significant (p < 0.001) effect was found for acrosomal and post-acrosomal membrane distribution of domains, from 92.1 to 76.8% and from 3.1 to 13.1% in this same order. Slight but highly significant (p < 0.001) differences were observed when theca integrity was evaluated as affected by breed, with highest and lowest values for Yorkshire and Pel6n Mexicano pigs, respectively. No breed effect was encountered for presence of acrosomal domains. A strong interdependence was found between perinuclear theca damage and domain distribution. In this connection, a highly significant (p < 0.001) positive, interdependence was observed between the theca damage and acrosomal domain (r = 0.87), while this same relationship was although highly significant (p < 0.001), negative in nature for equatorial and post-acrosonal domains (r = -0.77 and -0.85, respectively). This experiment confirmed that cryopreservation methods may severely affect semen quality of pigs and that genotype may further influence these same indices. More research is needed for improving methods of preservation of pig semen quality, from the point of view of perinuclear theca and domain characteristics of spermatozoa.

Cryopreservation, in addition to protein tyrosine phosphorylation, alters the distribution of phosphatidyl inositol bisphosphate and the localization of cytoskeletal and signaling proteins (gelsolin, tyrosine kinase c-SRC and phospholipase C-ζ) in the perinuclear theca of boar sperm

Cryopreservation of boar spermatozoa affects the perinuclear theca (PT) and involves several proteins and molecules that play important roles during capacitation and the acrosomal reaction. The objective of the present study was to evaluate whether the deleterious effects of cryopreservation in addition to protein tyrosine phosphorylation are accompanied by changes in the distribution of phosphatidyl inositol bisphosphate (PIP2) and the localization of cytoskeletal and signaling proteins in the perinuclear theca of cryopreserved boar spermatozoa. For this purpose, by immunocytochemistry (IC) the changes in localization of phosphorylated proteins in tyrosine residues, gelsolin, c-SRC kinase and PLC-ζ, as well as in the distribution of phosphatidyl inositol bisphosphate were analyzed in thawed spermatozoa (T) non capacitated (NC), capacitated (C) and in those with acrosomal reaction (AR) and compared with fresh spermatozoa (F) under the same physiological status. Western blotting (WB) and co-immunoprecipitation were performed to confirm the presence of these proteins in PT and to determine the interaction between these molecules. IC showed that immunostaining for phosphorylated proteins significantly increased in the acrosomal region and flagellum in TNC spermatozoa (p < 0.05). The proportion of cells displaying immunolabeling for gelsolin in the acrosomal region decreased after capacitation in cryopreserved spermatozoa; the same change was found (p < 0.05) in the proportion of spermatozoa immunoreactive to PIP2 in the sperm head. c-SRC was observed in the equatorial segment and acrosomal region, subdomains that coincide with the site where phosphorylated proteins were detected. PLC-ζ immunolocalization in fresh spermatozoa underwent changes after capacitation and acrosomal reaction, with a significant increase in the equatorial segment and post-acrosomal region in cryopreserved spermatozoa (p < 0.05). WB analysis indicated the presence of gelsolin, c-SRC and PLC-ζ in PT; besides, we confirmed that gelsolin co-immunoprecipitated with c-SRC and PLC-ζ, which changes according to the physiological state of spermatozoa. As a conclusion, cryopreservation together with increased immunodetection of tyrosine phosphorylated proteins decreases the detection of PIP2 and alters the immunolocalization patterns of gelsolin, c-SRC and PLC-ζ in the PT in boar spermatozoa.

Disruption of gonocyte development following neonatal exposure to di (2-ethylhexyl) phthalate

Pre- and/or post-natal administrations of di(2-ethylhexyl) phthalate (DEHP) in experimental animals cause alterations in the spermatogenesis. However, the mechanism by which DEHP affects fertility is unknown and could be through alterations in the survival and differentiation of the gonocytes. The aim of the present study was to evaluate the effect of a single administration of DEHP in newborn mice on gonocytic proliferation, differentiation and survival and its long-term effects on seminiferous epithelium and sperm quality. BALB/c mice distributed into Control and DEHP groups were used. Each animal in the DEHP group was given a single dose of 500 mg/Kg at birth. The animals were analyzed at 1, 2, 4, 6, 8, 10 and 70 days postpartum (dpp). Testicular tissues were processed for morphological analysis to determine the different types of gonocytes, differentiation index, seminiferous epithelial alterations, and immunoreactivity to Stra8, Pcna and Vimentin proteins. Long-term evaluation of the seminiferous epithelium and sperm quality were carried out at 70 dpp. The DEHP animal group presented gonocytic degeneration with delayed differentiation, causing a reduction in the population of spermatogonia (Stra8 +) in the cellular proliferation (Pcna+) and disorganization of Vimentin filaments. These events had long-term repercussions on the quality of the seminiferous epithelium and semen. Our study demonstrates that at birth, there is a period that the testes are extremely sensitive to DEHP exposure, which leads to gonocytic degeneration and delay in their differentiation. This situation can have long-term repercussions or permanent effects on the quality of the seminiferous epithelium and sperm parameters.