Expression of Matrix Metalloproteinases (MMP-2, MMP-9) and their Inhibitors (TIMP-1, TIMP-2) in Canine Testis, Epididymis and Semen

Abstract

This study aims to investigate the role of matrix metalloproteinases (MMPs) in determining semen quality and to evaluate the expression and cellular localization of MMP-2, MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 in the testes, epididymis and ejaculated spermatozoa. Gelatinase activities between normal (n = 21) and abnormal (n = 25) semen samples showed a significant, sixfold increase in proMMP-2 and MMP-2 activity in high than low sperm concentration samples (p < 0.001). ProMMP-9 and MMP-9 levels were significantly elevated in samples with low sperm counts compared to those with high sperm density (p < 0.001). High levels of proMMP-2 and MMP-2 were associated with high sperm motility (≥70%, p < 0.001). Sperm-rich fraction showed significantly (eight-fold) higher proMMP-9 enzymatic activity compared with prostatic fraction. The mRNA expressions of MMP-2, MMP-9, TIMP-1 and TIMP-2 were confirmed in testicular and epididymal tissues. Immunohistochemical staining illustrated the MMP-2-specific strong immunoreactivity in the head of mature spermatids during spermatogenesis, whereas MMP-9, TIMP-1 and TIMP-2 were absent in these cells. Matrix metalloproteinase-9 immunoreactivity was observed in the spermatocyte and round spermatid, whereas TIMP-1 was only exhibited in the residual bodies. Immunolabeling of epididymal and ejaculated sperm demonstrated MMP-2 localization along acrosomal region of sperm, while MMP-9, TIMP-1 and TIMP-2 localization was merely limited to the flagella. In conclusion, spermatozoa initially acquire MMP-2 during their formation at testicular level, and the presence of this protein persists through the epididymal transit and up to ejaculate. The enzymatic activity of MMP-2 and MMP-9 may serve as an alternative biomarker in determining semen quality