Proteins associated with critical sperm functions and sperm head shape are differentially expressed in morphologically abnormal bovine sperm induced by scrotal insulation

• Content of proteins differed in pyriform versus morphologically normal bovine sperm.
• Proteomic analysis of pyriform sperm identified several sperm functional proteins.
• Pathways of oxidative stress, apoptosis and metabolism were upregulated.
• Pathways of capacitation and gamete interaction were downregulated.

The objective was to investigate expression patterns of proteins in pyriform sperm, a common morphological abnormality in bull sperm. Ejaculates were collected from sexually mature Holstein bulls (n = 3) twice weekly for 10 weeks (pre-thermal insult samples). Testicular temperature was elevated in all bulls by scrotal insulation for 72 consecutive hours during week 2. Total sperm proteins were extracted from pre- and post-thermal insult sperm samples and subjected to two-dimensional gel electrophoresis. Among the protein spots detected, 131 spots were significantly expressed (False Detection Rate < 0.01) with ≥ 2 fold changes between normal and pyriform sperm. Among them, 25 spots with ≥ 4 fold difference in expression patterns were identified using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). Expression of several proteins involved in sperm capacitation, sperm–egg interaction and sperm cytoskeletal structure was decreased in pyriform sperm, whereas proteins regulating antioxidant activity, apoptosis and metabolic activity were increased. Contents of reactive oxygen species and ubiquitinated proteins were higher in pyriform sperm. In addition to understanding the molecular basis of functional deficiencies in sperm with specific morphological abnormalities, comparing normal versus morphologically abnormal sperm appeared to be a suitable experimental model for identifying important sperm functional proteins.Biological significanceTo our knowledge, this study is the first report on differential expression of proteins in pyriform bovine sperm versus morphologically normal sperm. We report that expression of several proteins involved in sperm capacitation, sperm–egg interaction and sperm cytoskeletal structure was decreased in pyriform sperm, whereas proteins which regulate antioxidant activity, apoptosis and metabolic activity were increased. Contents of reactive oxygen species and ubiquitinated proteins were higher in pyriform sperm. In addition to understanding the molecular basis of functional deficiencies in sperm with specific morphological abnormalities, our results suggest that comparing normal versus morphologically abnormal sperm appeared to be a suitable experimental model for identifying important sperm functional proteins.

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