Molecular Biomarkers of Canine Reproductive Functions

Abstract

The aim of the current study is to review potential molecular biomarker substances selected so far as useful for assessing the quality of dog semen. Proteins, lipids, carbohydrates, and ions can serve as molecular biomarkers of reproductive functions (BRFs) for evaluating male reproductive health and identifying potential risk factors for infertility or reproductive disorders. Evaluation of BRF levels in semen samples or reproductive tissues may provide insights into the underlying causes of infertility, such as impaired sperm function, abnormal sperm-egg interaction, or dysfunction of the male reproductive tract. Molecular biomarker proteins may be divided into two groups: proteins that are well-studied, such as A-kinase anchoring proteins (AKAPs), albumins (ALBs), alkaline phosphatase (ALPL), clusterin (CLU), canine prostate-specific esterase (CPSE), cysteine-rich secretory protein 2 (CRISP2), lactotransferrin (LTF), metalloproteinases (MMPs), and osteopontin (OPN) and proteins that are not well-studied. Non-protein markers include lipid-based substances (fatty acids, phosphatidylcholine), carbohydrates (glycosaminoglycans), and ions (zinc, calcium). Assessing the levels of BRFs in semen samples may provide valuable information for breeding management and reproductive assessments in dogs. This review systematizes current knowledge that could serve as a starting point for developing practical tests with the use of biomarkers of canine reproductive functions and their predictive value for assisted reproductive technique outcomes and semen preservation.

Keywords: biomarkers; canine; carbohydrates; lipids; proteins; semen.

Figure 1

Well-studied/highly abundant molecular biomarker proteins that coat canine sperm and change its surface properties, biochemistry, and metabolism. AKAP4—A-kinase anchoring protein; ALB—albumin; ALPL—alkaline phosphatase; CLU—clusterin; CPSE—canine prostate-specific esterase; CRISP2—cysteine-rich secretory protein 2; LTF—lactotransferrin; MMPs—metalloproteinases; OPN—osteopontin; PTGDS—prostaglandin-H2 D-isomerase; SP—seminal plasma; EF—epididymal fluid; ES—epididymal spermatozoa. Created with BioRender.com.

Figure 2

Poorly studied/newly recognized/low-abundance molecular biomarker proteins in canines that change sperm biochemistry and metabolism. ACBP—Acrosin binding protein; ACTB—Actin binding protein; ASPM—Abnormal spindle-like microcephaly-associated protein homolog; CARD6—Caspase recruitment domain containing protein 6; CEMIP—Hyaluronoglucosaminidase; ELSPBP1—Epididymal sperm-binding protein 1; FAM135—A family with sequence similarity 135 member A; GALNT6—Polypeptide N-acetylgalactosaminyltransferase 6; LCNL1—Lipocalin cytosolic FA-bd domain-containing protein; LOC607874—Cystatin domain-containing protein; NPC2—Niemann-Pick type C2 protein; OLFM4—Olfactomedin 4; PLEKHH1—Pleckstrin homolog, MyTH4, and FERM domain-containing H1; TUBB—Tubulin; EF—epididymal fluid; ES—epididymal spermatozoa. Created with BioRender.com.

Figure 3

Antioxidant enzymes that function as molecular biomarkers and participate in sperm biochemistry and metabolism in canines. SOD—superoxide dismutase; GPX—glutathione peroxidase, CAT—catalase, ROS—reactive oxygen species.

Figure 4

Lipids, carbohydrates, and ions and their binding proteins that are involved in canine sperm functions. ALB—albumin; CPSE—canine prostate-specific esterase; CRISP2—cysteine-rich secretory protein 2; LTF—lactotransferrin; NPC2—Niemann-Pick type C2 protein; OPN—osteopontin; Pch—phosphorylcholine; Zn²⁺—zinc ions. Created with BioRender.com.