High-throughput proteomic profiling reveals dysregulated serum proteins in low fertility bulls linked to...

Although blood serum proteins play various roles in male reproduction, and imbalances or deficiencies in these proteins can lead to infertility or subfertility, however, the impact of serum proteomics on bull fertility remains underexplored. Using a high-throughput LC-MS/MS approach, the current study examined the proteomic profile of serum from 12 Holstein Friesian crossbred bulls (6 with high fertility, having a conception rate of 62.09 ± 9.64%, and 6 with low fertility, having a conception rate of 15.12 ± 4.94%) with the aim to identify potential proteins associated with bull fertility. A total of 511 proteins were identified in blood serum of bull, with 480 detected in high-fertility bulls and 490 in low-fertility bulls. Of these, 459 proteins were common to both groups, while 21 (4%) were exclusive to high-fertility bulls and 31 (6%) exclusive to low-fertility bulls. Among the shared proteins, 22 were upregulated (log2 fold change > 1) and 25 downregulated (log2 fold change < 1) in low-fertility bulls compared to high-fertility bulls, with 412 proteins exhibiting neutral expression (p < 0.05). The dysregulated proteins identified in low-fertility bulls include C1QTNF3, C-reactive protein, cathepsins, serum amyloid A (SAA1), thrombospondin-4, fructose-bisphosphate aldolase, carbonic anhydrase 2, insulin-like growth factor binding protein 2 (IGFBP2), von Willebrand factor, immunoglobulin J chain, peroxiredoxin-2, CD44, LAMP2, LGMN, SPADH1, KRT17, S100A12, lactotransferrin (LTF), kininogen-1 (KNG1), S100A9, and PLOD1, along with several uncharacterized proteins. Many of these proteins are functionally involved in key biological processes such as lysine metabolism, autophagy, antigen processing and presentation, lysosomal activity, and ECM remodelling. Further, Gene ontology and KEGG pathway analysis revealed dysregulation of proteins associated with the pentose phosphate pathway, estrogen signaling, peroxiredoxin activity, and keratinization in low-fertility bulls. The upregulated proteins were linked to oxidative stress and sperm motility, while the downregulated proteins were associated with antioxidant activity, sperm-egg binding, and hyperactivation. These findings suggest that the proteomic variations in blood serum may underlie the reduced fertility observed in low-fertility bulls. It is concluded that low-fertility bulls exhibit significant dysregulation in several serum proteins associated with the nutrient-autophagy-inflammation-extracellular matrix axis, and the identified proteins may serve as potential biomarkers for selecting high-fertility crossbred bulls for breeding programs.