229 From head to tail: A red wolf sperm project

Abstract

Development of assisted reproductive technologies for the critically endangered red wolf (Canis rufus) is crucial to the maintenance of genetic diversity to support species recovery. Towards this goal, a cryopreservation protocol has previously been developed for red wolf sperm; however, the ability of the gametes to undergo capacitation has not been assessed in this species. Previously, we have shown that oviductal extracellular vesicles (oEVs) improve cat sperm motility and fertilizing ability. The objectives were to (1) compare the effects of culture media on motility and acrosomal integrity of fresh sperm, and select the best medium that can be used in a capacitation protocol; (2) identify potential biomarkers for sperm cryo-tolerance; and (3) determine the influence of canine oEVs on sperm survival and motility post-thaw. In Study 1, sperm were collected by electro-ejaculation from adult red wolves (n = 8) and immediately cryopreserved in TRIS-egg yolk buffer with 8% glycerol or incubated for 18 h in 5% CO₂ and 38.5°C in one of the following media: canine capacitation medium (CCM), FERT-TALP (FERT), NCSU, synthetic oviductal fluid (SOF) and TRIS. At 0, 1, 2, 3, 4, and 18 h, sperm were evaluated for total motility and acrosome integrity (FITC-PNA). In Study 2, sperm with high (>80%, HM, n = 2 wolves) and low (<15%, LM, n = 2 wolves) motility post-incubation at 4°C in the cryopreservation medium for 18 h were subjected to proteomic analysis. In Study 3, oviducts were collected from domestic dogs (1-9 years, n = 12) after elective spaying, and oEVs from various stages of the oestrous cycle [early follicular (EF), late follicular (LF), early luteal (EL), and late luteal (LL)] were isolated using the Total Exosome Isolation kit (Invitrogen). Frozen-thawed red wolf sperm (n = 4 males) were incubated with 30 × 10⁶ oEVs in non-capacitating CCM, and assessed as in study 1 at 0, 0.5, 1, 2, 3, 4, 6, 8, and 10 h. Data were analysed using a paired samples t-test with 95% CI (Prism8, GraphPad Inc.). Sperm incubated in CCM and NCSU had higher motility than those in FERT, SOF, and TRIS after 2 h of incubation and onward (2 h: 65 ± 6, 68 ± 6, 42 ± 10, 57 ± 8, and 43 ± 5; 3 h: 60 ± 9, 63 ± 8, 36 ± 11, 46 ± 9, and 34 ± 6; 4 h: 60 ± 9, 60 ± 10, 30 ± 10, 43 ± 8, and 20 ± 5; 18 h: 12 ± 7, 15 ± 7, 9 ± 5, 3 ± 2, and 0, respectively; P < 0.05). After 1 h of incubation, samples incubated in CCM, NCSU, and SOF had a higher number of sperm with intact acrosomal membranes (P > 0.05) than other treatments. A total of 179 proteins were identified, of which 129, including those regulating energy metabolism and mitochondrial mediated apoptosis, were differentially expressed between HM and LM. Preliminary data from Study 3 suggested that thawing and incubating sperm in the presence of LF, EL, and LL oEVs improved sperm motility. In conclusion, CCM and NCSU sustained sperm survival after in vitro incubation and could be candidates for in vitro fertilization studies in the red wolf. Data generated from sperm proteomic analysis provided insights into cellular pathways regulating sperm cryo-sensitivity. Finally, we demonstrated the potential of oEVs in improving wolf sperm survival post-thawing.